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Journal articles on the topic 'Juvenile migrants'
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1
Morinville, Geneviève R., and Joseph B. Rasmussen. "Early juvenile bioenergetic differences between anadromous and resident brook trout (Salvelinus fontinalis)." Canadian Journal of Fisheries and Aquatic Sciences 60, no. 4 (April 1, 2003): 401–10. http://dx.doi.org/10.1139/f03-036.
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Many salmonids, including brook trout (Salvelinus fontinalis), contain both anadromous (migrant) and nonanadromous (resident) forms within a population (partial migration). Although partial migration is commonly observed, the mechanisms governing the adoption of migration or residency are poorly understood. We used field estimates of fish growth coupled with in situ estimates of food consumption rates to demonstrate that a trade-off exists between the ability to efficiently exploit local environments (resident approach) and the capacity to capitalize from large-scale environmental heterogeneity (migrant approach). We demonstrate that in the year before migration, migrant brook trout have consumption rates 1.4 times higher than those of resident brook trout. However, migrants have lower growth efficiencies (ratio of growth to consumption) than residents, indicating that migrants have higher metabolic costs. Residents and migrants also differed in their stable carbon isotope signatures (δ13C), a time-integrated measure that has been linked to habitat use. Fish muscle δ13C of migrants was depleted by 1 ± 0.1 compared with that of residents, and this could not be explained by any biases introduced by the time of sampling or the size of fish sampled. Our findings thus agree with the notion that a link exists between metabolic costs (efficiency) and the adopted life-history strategy.
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Morgan, Ian J., and Neil B. Metcalfe. "The influence of energetic requirements on the preferred temperature of overwintering juvenile Atlantic salmon (Salmo salar)." Canadian Journal of Fisheries and Aquatic Sciences 58, no. 4 (April 1, 2001): 762–68. http://dx.doi.org/10.1139/f01-016.
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We used a horizontal temperature gradient to investigate the effect of alternate life history strategies and nutritional state on the preferred temperature of overwintering juvenile Atlantic salmon (Salmo salar L.). Contrary to our prediction, there was no significant difference in final preferred temperature between juvenile Atlantic salmon that will migrate to sea the following spring (early migrants) and those that show reduced growth and delay migration for at least another year (delayed migrants). Both migrant groups preferentially selected relatively low temperatures (<10°C), likely owing to their low appetite and growth rates. Food deprivation resulted in a significant increase, rather than our predicted decrease, in the final preferred temperature of the juvenile Atlantic salmon of approximately 2°C. We suggest that this is due to the need for an increased foraging effort to offset the projected energy deficit later in the winter. The final preferred temperature of delayed migrants increased from winter to spring, as predicted, coincident with increases in natural food availability and endogenous seasonal increases in appetite and growth rates. We conclude that the preferred temperature of overwintering juvenile Atlantic salmon may be influenced by future energetic requirements rather than the current level of energy reserves.
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Rodgers, Jeffrey D., Richard D. Ewing, and James D. Hall. "Physiological Changes during Seaward Migration of Wild Juvenile Coho Salmon (Oncorhynchus kisutch)." Canadian Journal of Fisheries and Aquatic Sciences 44, no. 2 (February 1, 1987): 452–57. http://dx.doi.org/10.1139/f87-053.
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Peaks in migration of wild juvenile coho salmon (Oncorhynchus kisutch) from Knowles Creek (Siuslaw River, Oregon) occurred in November and May. Condition factor of nonmigrant fish was higher than migrants or captives throughout the study. Skin guanine levels of migrant fish rose sharply during the first 2 wk of April and continued to rise through June. Gill (Na + K)-ATPase specific activity of migrants rose gradually from a low in January to a maximum in June. Gill (Na + K)-ATPase activity of migrants and nonmigrants was low and not significantly different during November to mid-March. During April, however, gill ATPase activity of migrants rose to become significantly higher than that of nonmigrants until the first 2 wk of May. Cyclic changes in gill (Na + K)-ATPase activity was not observed in these fish. Gill (Na + K)-ATPase activity of fish reared in a laboratory was similar to that of wild nonmigrants until it peaked during the last 2 wk of April, after which the specific activity was lower than either migrants or nonmigrants.
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Graves, John E., Andrew S. Wozniak, Rebecca M. Dickhut, Michele A. Cochran, Elizabeth H. MacDonald, Elizabeth Bush, Haritz Arrizabalaga, and Nicolas Goñi. "Transatlantic movements of juvenile Atlantic bluefin tuna inferred from analyses of organochlorine tracers." Canadian Journal of Fisheries and Aquatic Sciences 72, no. 4 (April 2015): 625–33. http://dx.doi.org/10.1139/cjfas-2014-0305.
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Ratios of certain organochlorine pollutants in fish tissues are significantly different between the eastern and western North Atlantic and have been used to identify recent (<1 year) transatlantic migrants of Atlantic bluefin tuna (Thunnus thynnus). In this study we observed limited variation of organochlorine pollutant ratios across collections of young-of-the-year (YOY) bluefin tuna from the western North Atlantic (WNA) and eastern North Atlantic (ENA) in different years and highly significant differences between WNA and ENA YOY samples each year and for all years combined. A significant increase in organochlorine ratios was noted between YOY and age-1 ENA bluefin tuna, consistent with the movement of YOY out of the Mediterranean Sea and into the ENA. Using baseline organochlorine ratios from WNA YOY to identify recent eastern migrants, 29% of age-2, 33% of age-3, and 24% of age-4 juvenile bluefin tuna in the WNA were identified as recent migrants from the east during 2011 and 2012. Applying baseline ratios from age-1 ENA bluefin tuna to identify recent migrants from the WNA, 14.3% of age-2, 9.5% of age-3, and 0% of age-4 juvenile bluefin tuna caught in the Bay of Biscay fishery were identified as recent western migrants during 2010 and 2011. These data reveal substantial connectivity of juvenile bluefin tuna across the North Atlantic and demonstrate that WNA juveniles are heavily subsidized by eastern fish.
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Poiesz, SSH, JIJ Witte, and HW van der Veer. "Only a few key prey species fuel a temperate coastal fish food web." Marine Ecology Progress Series 653 (October 29, 2020): 153–66. http://dx.doi.org/10.3354/meps13472.
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The food web structure of a coastal fish community (western Dutch Wadden Sea) was studied based on stomach content data from samples collected between 2010 and 2018. In total, 54 fish species were caught and 72 different prey items were identified. Fish species consumed from only a few up to >30 different prey species, suggesting the presence of both opportunistic and more specialized feeders. We found no significant differences between years or switches in food source with fish size. The trophic positions of the Wadden Sea fish community ranged from 2.0 to 4.7, with most trophic positions above 3.0. In the past, (near)-resident species were the most abundant guild in spring, and juvenile marine migrants in autumn. At present, all guilds are present in similar but low abundances. The (near)-resident community consisted of about 20 species that fed primarily on amphipod crustaceans, brown shrimps and juvenile herring. There was only a slight overlap in diet with the group of juvenile marine migrants (5 species of juvenile flatfishes and clupeids), whose preferred prey were copepods, polychaetes and brown shrimps. About 15 species of marine seasonal visitors showed an overlap in diet with both the (near)-resident and the juvenile marine migrants, especially for brown shrimps and to a lesser extent herring and gobies. Our results illustrate (1) the pivotal position of a few key prey species (amphipod crustaceans, brown shrimps, juvenile herring and gobies) for the coastal Wadden Sea fishes and (2) that the substantial prey overlap in the diet of some predators cannot exclude intra- and inter-specific competition among these predators.
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Zydlewski, J., and S. D. McCormick. "The loss of hyperosmoregulatory ability in migrating juvenile American shad, Alosa sapidissima." Canadian Journal of Fisheries and Aquatic Sciences 54, no. 10 (October 1, 1997): 2377–87. http://dx.doi.org/10.1139/f97-144.
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Investigations on juvenile American shad (Alosa sapidissima) revealed several physiological changes associated with downstream migration. Plasma chloride decreased 20% in wild juvenile shad during the autumn migration. Migrants had lower condition factor and hematocrit than non-migrant shad captured by beach seining. Gill Na + ,K + -ATPase activity of migrant shad was higher than non-migrant; a 2.5-fold increase was observed in 1993, while a 57% increase was observed in 1994. Similar changes were observed in laboratory studies of shad maintained in fresh water under simulated natural temperature and photoperiod. Plasma chloride dropped 68% and gill Na + ,K + -ATPase activity increased 3-fold over a 3-month period. Decreased plasma chloride was associated with increased mortality. Increases in gill Na + ,K + -ATPase activity decreases in plasma chloride and osmolality, and incidence of mortality were delayed and moderated, but not eliminated, in shad maintained at constant temperature (24°C). Shad did not survive in fresh water past December regardless of temperature regime. In seawater, all shad survived and showed no perturbation of plasma chloride at 24°C or simulated natural temperature (above 4°C). The decline in hyperosmoregulatory ability, as influenced by declining temperatures, may serve as a proximate cue for autumnal migration.
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Lovvorn, James R., and Jeb A. Barzen. "Molt in the Annual Cycle of Canvasbacks." Auk 105, no. 3 (July 1, 1988): 543–52. http://dx.doi.org/10.1093/auk/105.3.543.
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Abstract We studied the intensity of molt of capital, down, and contour plumages of male and female Canvasbacks (Aythya valisineria) from late fall through winter, spring migration, and nesting. Molt intensities in both juvenile and adult males were highest among arriving fall migrants and during prewinter fat deposition, and molt in juvenile males increased during early spring migration. Among females, capital molt was high among arriving migrants in fall, and molt of all plumage types increased during spring migration and courtship. Paired females tended to molt more heavily than unpaired females during spring migration, but many females initiated intensive prebasic molt before pairing. Molt in females peaked in spring migration and early breeding, concurrently with accelerated fat storage and ovarian growth. Capital and contour molt in females decreased during laying and essentially ceased during incubation, perhaps to mitigate energetic constraints during these periods. Prewinter nutrient storage appeared independent of molt intensity, except for body protein among juveniles. During spring migration, molt intensities were greater in adult females with higher levels of body fat and protein, indicating that molt did not necessarily precede or interfere with nutrient storage. We suggest that outside the laying, incubation, and wing molt periods, the energetic costs of molt in Canvasbacks are not sufficient to mandate temporal separation of molt from nutrient storage, migration, courtship, or early stages of rapid ovarian growth.
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Vansteelant, W. M. G., J. Kekkonen, and P. Byholm. "Wind conditions and geography shape the first outbound migration of juvenile honey buzzards and their distribution across sub-Saharan Africa." Proceedings of the Royal Society B: Biological Sciences 284, no. 1855 (May 24, 2017): 20170387. http://dx.doi.org/10.1098/rspb.2017.0387.
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Contemporary tracking studies reveal that low migratory connectivity between breeding and non-breeding ranges is common in migrant landbirds. It is unclear, however, how internal factors and early-life experiences of individual migrants shape the development of their migration routes and concomitant population-level non-breeding distributions. Stochastic wind conditions and geography may determine whether and where migrants end up by the end of their journey. We tested this hypothesis by satellite-tagging 31 fledgling honey buzzards Pernis apivorus from southern Finland and used a global atmospheric reanalysis model to estimate the wind conditions they encountered on their first outbound migration. Migration routes diverged rapidly upon departure and the birds eventually spread out across 3340 km of longitude. Using linear regression models, we show that the birds' longitudinal speeds were strongly affected by zonal wind speed, and negatively affected by latitudinal wind, with significant but minor differences between individuals. Eventually, 49% of variability in the birds' total longitudinal displacements was accounted for by wind conditions on migration. Some birds circumvented the Baltic Sea via Scandinavia or engaged in unusual downwind movements over the Mediterranean, which also affected the longitude at which these individuals arrived in sub-Saharan Africa. To understand why adult migrants use the migration routes and non-breeding sites they use, we must take into account the way in which wind conditions moulded their very first journeys. Our results present some of the first evidence into the mechanisms through which low migratory connectivity emerges.
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Godbout, L., C. C. Wood, R. E. Withler, S. Latham, R. J. Nelson, L. Wetzel, R. Barnett-Johnson, M. J. Grove, A. K. Schmitt, and K. D. McKeegan. "Sockeye salmon (Oncorhynchus nerka) return after an absence of nearly 90 years: a case of reversion to anadromy." Canadian Journal of Fisheries and Aquatic Sciences 68, no. 9 (September 2011): 1590–602. http://dx.doi.org/10.1139/f2011-089.
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We document the recent reappearance of anadromous sockeye salmon ( Oncorhynchus nerka ) that were thought to have been extirpated by the construction of hydroelectric dams on the Coquitlam and Alouette rivers in British Columbia, Canada, in 1914 and 1927, respectively. Unexpected downstream migrations of juveniles during experimental water releases into both rivers in 2005 and 2006 preceded upstream return migrations of adults in 2007 and 2008. Genetic (microsatellite and mitochondrial DNA) markers and stable isotope (δ34S and 87Sr/86Sr) patterns in otoliths confirm that both the juvenile downstream migrants and adult upstream migrants were progeny of nonanadromous sockeye salmon (kokanee) that inhabit Coquitlam and Alouette reservoirs. Low genetic diversity and evidence of genetic bottlenecks suggest that the kokanee populations in both reservoirs originated from relatively few anadromous individuals that residualized after downstream migration was largely prevented by the construction of dams. Once given an opportunity for upstream and downstream migration, both populations appear capable of reverting to a successful anadromous form, even after 25 generations.
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Butler, Luke K., Michael G. Donahue, and Sievert Rohwer. "Molt-Migration in Western Tanagers (Piranga Ludoviciana): Age Effects, Aerodynamics, and Conservation Implications." Auk 119, no. 4 (October 1, 2002): 1010–23. http://dx.doi.org/10.1093/auk/119.4.1010.
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AbstractWe describe timing and location of the prebasic molt in Western Tanagers (Piranga ludoviciana), focusing on age class differences in premolt movements. Most adults migrate south to the American Southwest where they stop to molt before moving on to their wintering grounds. Molting adults are found in southern mountain regions (Sierra Madres and southern Rockies) and in the Mexican monsoon region, where late summer rains cause a substantial increase in productivity. In contrast, juvenile Western Tanagers move to nearby montane habitats to molt before migrating, a previously undocumented strategy in western passerines that show molt-related movements. By molting in nearby montane habitats, juveniles avoid the aerodynamic cost of migrating in their “fluffy”, aerodynamically inefficient juvenal plumage. Western Tanagers are the fifth species known to use the Mexican monsoon region during the prebasic molt, further affirming the importance of that area to the conservation of Neotropical migrants that breed in western North America.
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Voronova, E. S., T. N. Travina, and A. M. Biryukov. "Characterization of feeding and downstream migration of juvenile chum salmon in the Kichiga river (north-eastern kamchatka)." Researches of the aquatic biological resources of Kamchatka and the North-West Part of the Pacific Ocean, no. 59 (September 18, 2021): 39–50. http://dx.doi.org/10.15853/2072-8212.2020.59.39-50.
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Analysis of the data of fish biology spring-summer researches in the Kichiga river basin in the period 2017–2019 for the first time brought results as next: characterized dynamics of chum salmon juvenile downstrean migration, including daily dynamics, revealed qualitative characteristics of the underyearlings, described diet of the juvenile migrants, demonstrated effects of the spring-summer hydrological regime on the intensity of the underyearling feeding. Also noted, that the conditions for the downstream migration of chum salmon in 2018 were maximum favouravle, and most likely that could enhance later juvenile survival.
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RILEY, W. D., A. T. IBBOTSON, N. LOWER, A. C. COOK, A. MOORE, S. MIZUNO, A. C. PINDER, W. R. C. BEAUMONT, and L. PRIVITERA. "Physiological seawater adaptation in juvenile Atlantic salmon (Salmo salar) autumn migrants." Freshwater Biology 53, no. 4 (April 2008): 745–55. http://dx.doi.org/10.1111/j.1365-2427.2007.01933.x.
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Lenormand, Sophie, Julian J. Dodson, and Annie Ménard. "Seasonal and ontogenetic patterns in the migration of anadromous brook charr (Salvelinus fontinalis)." Canadian Journal of Fisheries and Aquatic Sciences 61, no. 1 (January 1, 2004): 54–67. http://dx.doi.org/10.1139/f03-137.
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Migration patterns of brook charr (Salvelinus fontinalis) from the Sainte-Marguerite River, Québec, Canada, were investigated to explore the hypothesis that migratory behaviour changes according to size during the critical period of first downstream migration, when survival is likely to be related to size, and during subsequent seasonal movements. We hypothesized that as fish grow, they should adopt more conservative behaviours to protect the reproductive assets that they have accumulated. First downstream migration occurred over a month in spring. Larger juvenile charr migrated early, whereas smaller charr seemed to delay offshore migration. As predicted, migratory patterns of charr changed through ontogeny. Sea age 0 juveniles stayed in estuarine areas until October and overwintered outside their natal river. Sea age 1 juveniles returned to their natal river earlier in the fall and some of them overwintered there. Adults (some sea age 1 migrants and older migrants) undertook their upstream migration to spawning areas from July to September, larger ones migrating earlier than smaller ones. Postspawners migrated downstream after reproduction or overwintered in the river. Environmental differences related to geographical location may be responsible for the variation of migration patterns and other life-history traits observed among brook charr populations, emphasizing the co-evolution of anadromy and life history.
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Perry, Diana, Thomas A. B. Staveley, Linus Hammar, Alyssa Meyers, Regina Lindborg, and Martin Gullström. "Temperate fish community variation over seasons in relation to large-scale geographic seascape variables." Canadian Journal of Fisheries and Aquatic Sciences 75, no. 10 (October 2018): 1723–32. http://dx.doi.org/10.1139/cjfas-2017-0032.
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In shallow-water marine environments, ecosystem functioning is a complex interworking of fine-scale characteristics and region-wide factors, and the importance of these variables can vary on multiple temporal and spatial scales. This underwater video study targeted seasonal changes in the fish community of seagrass habitats along the Swedish west coast and the influence of offshore seascape variables (latitudinal position, wave exposure, open ocean, and deep water). Results showed that fish assemblage structure exhibited seasonal changes between summer and autumn and strong spatiotemporal variations in the importance of offshore factors affecting shallow-water fish communities. In summer, abundance from the Gobiidae family responded to wave exposure, whereas the Gadidae family and juvenile migrant habitat preference guild responded to latitudinal position and proximity to deep water. In autumn, deep water was related to abundance of Gadidae and juvenile migrants, whereas latitudinal position influenced Gasterosteidae. These findings underscore the importance of understanding the influence of offshore factors on facets of coastal fish assemblages to address large-scale geographic connectivity along nearshore–offshore gradients.
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Guglielmo, Christopher G., Theunis Piersma, and Tony D. Williams. "A sport-physiological perspective on bird migration: evidence for flight-induced muscle damage." Journal of Experimental Biology 204, no. 15 (August 1, 2001): 2683–90. http://dx.doi.org/10.1242/jeb.204.15.2683.
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SUMMARY Exercise-induced muscle damage is a well-described consequence of strenuous exercise, but its potential importance in the evolution of animal activity patterns is unknown. We used plasma creatine kinase (CK) activity as an indicator of muscle damage to investigate whether the high intensity, long-duration flights of two migratory shorebird species cause muscle damage that must be repaired during stopover. In two years of study, plasma CK activity was significantly higher in migrating western sandpipers (a non-synchronous, short-hop migrant), than in non-migrants. Similarly, in the bar-tailed godwit (a synchronous, long-jump migrant), plasma CK activity was highest immediately after arrival from a 4000–5000km flight from West Africa to The Netherlands, and declined before departure for the arctic breeding areas. Late-arriving godwits had higher plasma CK activity than birds that had been at the stopover site longer. Juvenile western sandpipers making their first southward migration had higher plasma CK activity than adults. These results indicate that muscle damage occurs during migration, and that it is exacerbated in young, relatively untrained birds. However, the magnitude of the increases in plasma CK activity associated with migratory flight were relatively small, suggesting that the level of muscle damage is moderate. Migrants may avoid damage behaviourally, or have efficient biochemical and physiological defences against muscle injury.
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Lo, Celia C., Tyrone C. Cheng, Maggie Bohm, and Hua Zhong. "Rural-to-Urban Migration, Strain, and Juvenile Delinquency: A Study of Eighth-Grade Students in Guangzhou, China." International Journal of Offender Therapy and Comparative Criminology 62, no. 2 (May 26, 2016): 334–59. http://dx.doi.org/10.1177/0306624x16650236.
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This examination of minor and serious delinquency among eighth graders in a large southern Chinese city, Guangzhou, also compared groups of these students, observing differences between the delinquency of migrants and that of urban natives. Data used were originally collected for the study “Stuck in the City: Migration and Delinquency Among Migrant Adolescents in Guangzhou.” The present study asked whether and how various sources of strain and social control factors explained students’ delinquency, questioning how meaningfully migration status moderated several of the observed delinquency relationships. Of students in the sample, 741 reported being natives of Guangzhou, and 497 reported migrating to Guangzhou from a rural area. The study conceptualized internal migration as a strain factor leading to delinquency, but the analyses did not suggest direct association between internal migration and delinquency. Results generally supported Agnew’s theory, and, what’s more, they tended to confirm that migration status moderated juvenile delinquency.
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Tiyawattanaroj, Warakorn, Stefan Witte, Michael Fehr, and Marko Legler. "Monitoring of Organochlorine Pesticide and Polychlorinated Biphenyl Residues in Common Swifts (Apus apus) in the Region of Hannover, Lower Saxony, Germany." Veterinary Sciences 8, no. 5 (May 16, 2021): 87. http://dx.doi.org/10.3390/vetsci8050087.
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The use of pesticides is associated with the decline of several avian species. In this study, we monitored the organochlorine contaminants in common swifts (Apus apus) in the years 2016 to 2018. These long-distance migrants breed in Europe and winter in Africa. Their only feeding source is aerial plankton. Pooled organ samples of 42 adult and 40 juvenile swifts were tested with the multi-residue method by gas chromatography-mass spectrometry (GC-TOF/MS). Predominantly, 4,4′-DDE, dieldrin, hexachlorobenzene (HCB), lindane and polychlorinated biphenyls (PCBs) were found in most of these common swifts. Only 4,4′-DDE (adult: 83 ± 70 μg/kg, juvenile: 17 ± 39 μg/kg) and dieldrin (adult: 2 ± 3 μg/kg, juvenile: 0.3 ± 1 μg/kg) concentrations were significantly different between adult and juvenile birds. All detected concentrations in our study were far lower than the previously recorded pesticide concentrations of common swifts in Italy and those which are known to cause toxicity and death in birds.
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Sabal, Megan C., Michelle L. Workman, Joseph E. Merz, and Eric P. Palkovacs. "Shade affects magnitude and tactics of juvenile Chinook salmon antipredator behavior in the migration corridor." Oecologia 197, no. 1 (August 5, 2021): 89–100. http://dx.doi.org/10.1007/s00442-021-05008-4.
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AbstractEnvironmental conditions strongly affect antipredator behaviors; however, it is less known how migrating prey adjust antipredator behavior in migration corridors, in part, because active migrants are difficult to observe and study. Migrants are vulnerable and encounter many predators in the corridor, and their propensity to travel towards their destination ties antipredator behavior with movement. We evaluated how environmental risk cues in the migration corridor including in-water habitat structure (present, absent) and overhead shade (sun, shade), and salmon origin (hatchery, wild) affected how juvenile Chinook salmon (Oncorhynchus tshawytscha) reacted to a live predator. We measured how salmon react to predation risk as the difference in time to swim downstream through a 9.1-m long field enclosure with or without a live predatory largemouth bass (Micropterus salmoides). Shade significantly modified the reaction to the predator, and it did so in two ways. First, the magnitude of antipredator behavior was larger in shade compared to direct sun, which suggests salmon perceived shade to be a riskier environment than sun. Second, the escape tactic also varied; salmon slowed down to be cautious in shade and sped up in sun. Structure did not significantly affect behavior and hatchery and wild salmon behaved similarly. Our study suggests that environmental risk cues can shape the magnitude and tactics of how migrants react to predation risk and illustrates how these responses relate to movement with potential to scale up and affect migration patterns.
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Bennett, Todd R., Phil Roni, Keith Denton, Michael McHenry, and Raymond Moses. "Nomads no more: early juvenile coho salmon migrants contribute to the adult return." Ecology of Freshwater Fish 24, no. 2 (April 26, 2014): 264–75. http://dx.doi.org/10.1111/eff.12144.
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Sabo, Ann M., Natasha D. G. Hagemeyer, Ally S. Lahey, and Eric L. Walters. "Local avian density influences risk of mortality from window strikes." PeerJ 4 (June 23, 2016): e2170. http://dx.doi.org/10.7717/peerj.2170.
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Up to a billion birds die per year in North America as a result of striking windows. Both transparent and reflective glass panes are a cause for concern, misleading birds by either acting as invisible, impenetrable barriers to desired resources, or reflecting those resources over a large surface area. A high number of window strikes occur during migration, but little is known about the factors of susceptibility, or whether particular avian taxa are more vulnerable than others. We report on a study of window strikes and mist-netting data at the Virginia Zoological Park (Norfolk, Virginia, USA), conducted in the autumn of 2013 and 2014. We focused on three factors likely to contribute to an individual’s predisposition to collide with windows: (i) taxonomic classification, (ii) age, and (iii) migrant vs. resident status. Thrushes, dominated by the partial migrant American Robin (Turdus migratorius), were significantly less likely to strike glass than be sampled in mist nets (χ2= 9.21, p = 0.002), while wood-warblers (Parulidae) were more likely to strike than expected (χ2= 13.55, p < 0.001). The proportion of juveniles striking windows (45.4%) was not significantly different (χ2= 0.05, p = 0.827) than the population of juvenile birds naturally occurring at the zoo (48.8%). Migrants, however, were significantly more susceptible to window strikes than residents (χ2= 6.35, p = 0.012). Our results suggest that resident birds are able to learn to avoid and thus reduce their likelihood of striking windows; this intrinsic risk factor may help explain the apparent susceptibility of certain taxa to window strikes.
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Whitaker, D. J. "A parasite survey of juvenile chum salmon (Oncorhynchus keta) from the Nanaimo River." Canadian Journal of Zoology 63, no. 12 (December 1, 1985): 2875–77. http://dx.doi.org/10.1139/z85-428.
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The sequence of parasite acquisition in a cohort of juvenile chum salmon, Oncorhynchus keta (Walbaum), during their first few months of life is presented. Although no parasites were found in fish collected as downstream migrants, six of the species found in fish collected from other locations were of freshwater origin. Marine species were acquired shortly after entrance into the sea and prevalence and intensity increased with time. Ecological factors influencing the acquisition of the different species found are discussed.
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Swartz, Rebecca. "Children In Between: Child Migrants from England to the Cape in the 1830s." History Workshop Journal 91, no. 1 (March 24, 2021): 71–90. http://dx.doi.org/10.1093/hwj/dbaa034.
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Abstract Between 1833 and 1841 the Children’s Friend Society, a London-based philanthropic organization, sent some eight hundred children from England to the Cape, where they were apprenticed to local settlers. This article focuses on two of them: Alfred Brooks, aged thirteen or fourteen, and twelve-year-old Elizabeth Foulger. Both of these children appear in archival traces because they transgressed and were subsequently disciplined by their masters. The article argues that a series of binaries shaped these young migrants’ lives: between infant and adult, black and white, and colonizer and colonized. The in-between status of the CFS apprentices had the potential to disrupt increasingly rigid hierarchies at the colonial Cape, during a time of significant social and political turmoil. The context of slave emancipation, as well as concerns over juvenile delinquency in London, affected these children’s experiences. Concerns over their categorization illustrate the complicated range of positions that migrant workers in the British empire could hold beyond simply ‘free’ and ‘unfree’. Thinking through the position of these young white emigrant workers in the post-emancipation Cape sheds light on the fragility of classed, gendered, racialized, adult and free identities in that context.
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Munro, Ursula, John A. Munro, John B. Phillips, and Wolfgang Wiltschko. "Effect of Wavelength of Light and Pulse Magnetisation on Different Magnetoreception Systems in a Migratory Bird." Australian Journal of Zoology 45, no. 2 (1997): 189. http://dx.doi.org/10.1071/zo96066.
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Two hypotheses on magnetoreception in animals are currently discussed. The first hypothesis is based on light-dependent processes associated with the visual system, while the second hypothesis suggests that magnetoreception is based on biogenic magnetite. Both mechanisms are supported by experimental evidence, but whether the information they provide involves the magnetic compass or the ‘map’ is still open. In order to identify the relevance of light-dependent or magnetite-transduced processes in magnetoreception, juvenile migratory birds were tested for their orientation behaviour in the natural geomagnetic field as the only directional cue available to them. The test birds were juvenile Tasmanian silvereyes (Zosterops l. lateralis), which were caught on their native island soon after fledging, before they had an opportunity to establish a navigational ‘map’. (1) Under ‘white’ (full spectrum) and green light (571 nm), they were well oriented in their appropriate migratory direction, while they were disoriented under red light (633 nm). This coincides with previous findings on adult silvereyes and suggests that light-dependent processes are involved in an orientation mechanism used by both juvenile and adult migrants, namely the magnetic compass. (2) A short, high-intensity magnetic pulse, a treatment designed to alter the magnetisation of magnetite, did not affect the young birds´ orientation. They continued to select their seasonally appropriate migratory direction. In contrast, adult silvereyes from the same population had responded in a previous study with a 90° clockwise deflection from their normal migratory course. These results suggest that (a) magnetite is involved in an orientation mechanism used exclusively by adult migrants; and (b) a magnetite-based receptor is associated with the navigational ‘map’, which provides information on geographic position.
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Bradford, Michael J., Jeff A. Grout, and Sue Moodie. "Ecology of juvenile chinook salmon in a small non-natal stream of the Yukon River drainage and the role of ice conditions on their distribution and survival." Canadian Journal of Zoology 79, no. 11 (November 1, 2001): 2043–54. http://dx.doi.org/10.1139/z01-165.
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We investigated the ecology of juvenile stream-type chinook salmon (Oncorhynchus tshawytscha) in Croucher Creek, a small non-natal tributary of the upper Yukon River, in 1998 and 1999. Underyearling (age 0+) salmon enter Croucher Creek from the Yukon River in June, and by midsummer reached an average density of >0.5/m2. Fish were most commonly found in small pools. Their mean size increased until the end of August, but growth virtually ceased after that, when water temperatures fell. Juveniles remained in the stream through winter, and their distribution and survival were strongly influenced by aufeis, a thick layer of ice that develops from the freezing of groundwater. Over-winter survival was not dependent on fish size. Those fish that survived the winter grew rapidly and doubled in body mass in the spring. About 900 yearling fish emigrated from Croucher Creek in late June and early July at a mean length of 89 mm and mass of 7.2 g. Most of the migrants overwintered in a 700 m long reach of the creek that was downstream from groundwater sources and did not experience severe icing conditions. We suggest that small streams may be important habitats for juvenile salmon in the Yukon drainage, especially if there is a year-round source of groundwater flow that creates conditions suitable for overwintering.
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Visty, Hannah, Scott Wilson, Ryan Germain, Jessica Krippel, and Peter Arcese. "Demography of Sooty Fox Sparrows (Passerella unalaschcensis) following a shift from a migratory to resident life history." Canadian Journal of Zoology 96, no. 5 (May 2018): 436–40. http://dx.doi.org/10.1139/cjz-2017-0102.
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Identifying causes and consequences of variation in species life history has the potential to improve predictions about how climate and land-use change may affect the demography and distribution of species in future. Sooty Fox Sparrows (Passerella unalaschcensis (J.F. Gmelin, 1789); or commonly grouped within the Fox Sparrow, Passerella iliaca (Merrem, 1786)) were migrants that rarely bred in the Georgia Basin of British Columbia prior to ∼1950 but have since established resident populations. Data on 270 color-banded birds and 54 nests on Mandarte Island, British Columbia, allowed us to estimate demographic vital rates and population growth in one recently established population. Annual fecundity (F), estimated as the product of the number of broods initiated (1.5 ± 0.01; mean ± SD), clutch size (2.82 ± 0.44), and probability of survival to fledging (0.68 ± 0.02), exceeded values reported for migrants, supporting the hypothesis that residents invest more in reproduction, on average, than migrants within species. Estimating juvenile and adult overwinter survival (Sj = 0.32 ± 0.06 and Sa = 0.69 ± 0.05) next allowed us to simulate an expected distribution of population growth rates as λexp = Sa + (Sj × F), given parameter error. Our estimate of λexp (1.61 ± 0.57) implies expeditious population growth, consistent with the species’ recent colonization of the region.
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Murphy, Michael L., K. V. Koski, J. Mitchel Lorenz, and John F. Thedinga. "Downstream migrations of juvenile Pacific salmon (Oncorhynchus spp.) in a glacial transboundary river." Canadian Journal of Fisheries and Aquatic Sciences 54, no. 12 (December 1, 1997): 2837–46. http://dx.doi.org/10.1139/f97-178.
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Migrations of juvenile Pacific salmon (Oncorhynchus spp.) in the glacial Taku River (seventh order) were studied to assess movement from upriver spawning areas (in British Columbia) into lower-river rearing areas (in Alaska). Differences between fyke-net catches in the river and seine catches in the river's estuary indicated that many downstream migrants remained in the lower river instead of migrating to sea. In particular, age-0 coho salmon (O. kisutch) and chinook salmon (O. tshawytscha) moved downriver from May to November but were not caught in the estuary. Age-0 sockeye salmon (O. nerka), coho presmolts, and other groups delayed entry into the estuary after moving downriver. We tagged groups of juvenile coho (ages 0-2) from the fyke net with coded-wire to determine when they left the river. One-third of all tags recovered from sport and commercial fisheries occurred 2-3 years later, showing that many coho remained in fresh water for 1-2 years after moving to the lower river. Lower-river areas of large glacial rivers like the Taku River can provide essential rearing habitat for juvenile salmon spawned upriver and are important to consider in integrated whole-river management of transboundary rivers.
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Dutil, J. D., M. Michaud, and A. Giroux. "Seasonal and diel patterns of stream invasion by American eels (Anguilla rostrata) in the northern Gulf of St. Lawrence." Canadian Journal of Zoology 67, no. 1 (January 1, 1989): 182–88. http://dx.doi.org/10.1139/z89-024.
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Seasonal and diel patterns of stream invasion by American eels (Anguilla rostrata) were monitored in a small stream located on the north shore of the Gulf of St. Lawrence from 1981 to 1985. Glass eels and elvers migrated from the sea in late June and July. Glass eels made up only a small percentage of the migrants. Pigmentation progressed quickly in the estuary, but elvers grew very slowly. Migration from the estuary and through the lower reaches of the stream was slow; no glass eels or elvers occurred at a station located only 4 km from saltwater. Juvenile eels reached that station in their second summer of stream residence. Juvenile eels migrated in July and August. They ranged from 70 to 250 mm in length and included more than one age-class. Those less than 100 mm in length were most numerous. Relative abundance of glass eels and elvers decreased in the estuary from 1981 to 1985. This coincided with a decrease in the proportion of smaller sized eels in the stream migration over the same period. Juvenile eels migrated progressively later in summer as the proportion of smaller sized eels decreased. Stream migration was nocturnal. Movements mainly occurred between 21:00 and 23:00. The relationship between glass eel and elver abundance in the estuary and juvenile eel abundance in the stream 1 and 2 years later was not clear.
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Ungruhe, Christian. "Symbols of success: Youth, peer pressure and the role of adulthood among juvenile male return migrants in Ghana." Childhood 17, no. 2 (May 2010): 259–71. http://dx.doi.org/10.1177/0907568210365753.
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Independent youth migration is socially embedded in many African societies. While it is often exclusively perceived of as a process of intergenerational negotiation which leads to higher social positions after returning home, this article points out that peer influences play a major role in the process of decision-making of leaving and returning among young northern Ghanaian males. Juvenile migrants make little effort to generate means to enter into adulthood but struggle to return with modern goods. Rather than being a means of achieving adulthood, enjoying youth and gaining recognition among friends are the prevailing motives for going and returning.
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Gibbs, Timothy. "Inkatha's young militants: reconsidering political violence in South Africa." Africa 87, no. 2 (April 11, 2017): 362–86. http://dx.doi.org/10.1017/s0001972016001005.
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AbstractSouth Africa's township revolts have generated much excellent research on the central role played by rebellious, urban youth. This article explores a parallel set of intergenerational conflicts that opened up in the marginal rural districts of the Natal Midlands, which were exacerbated by apartheid's forced removals of labour tenants from commercial farming districts to crowded ‘Native Reserves’ in the 1970s. At this time of deepening poverty, elders worried about the rising incidence of juvenile petty crime, particularly amongst the teenagers who increasingly took itinerant, seasonal labour on the commercial farms. Some of these young migrants, unable to find steady factory work at a time of mounting unemployment, also played a leading role in the illicit, sometimes criminal networks of South Africa's growing popular economy. Finally, I show how some of these youths were mobilized by Inkatha during the war against the African National Congress in Johannesburg – often to the revulsion of older men who abhorred their socially harmful, thuggish violence, which spiralled uncontrollably along migrant routes. Thus the political violence was often known as theudlame: a brutal savagery that destroys households, communities and society.
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Bugaev, A. V., A. I. Chistyakova, and S. Urava. "Long-term trends in distribution and regional composition of the catches of hatchery pink and chum salmon during autumn migrations in the basin of the Sea of Okhotsk." Researches of the aquatic biological resources of Kamchatka and the North-West Part of the Pacific Ocean 57, no. 57 (February 15, 2021): 67–98. http://dx.doi.org/10.15853/2072-8212.2020.57.67-98.
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Long-term trends in distribution and regional composition of the catches of hatchery pink and chum salmon during autumn post-catadromous migrations in the basin of the Sea of Okhotsk in 2011–2017 were evaluated based on the otolith marking data. Qualitative and intraspecific structure of the hatchery fish aggregations was analyzed in connection to the interannual variety in forming abundant and not abundant generations of pink salmon. The analyze is carried out allowed to find out that the aggregation density of Russian and Japan hatchery juvenile chum salmon in the eastern part of the Sea of Okhotsk is higher in the even years of observation. Along that the distribution of the active migrants of the Sakhalin-Kurile and Hokkaido stock complexes in the north-east direction withing the Okhotsk Sea basin is better expressed. We think, that the main reason is low abundance of pink salmon generations (odd years of spawning) on West Kamchatka during autumn migration in the even years.In general the results obtained indicate that the cyclic migration of juvenile pink and chum salmon in the basin of the Sea of Okhotsk during post-catadromous migrations is of a systemic and mass character. Hatchery and wild fish have been engaged. The scheme of the juvenile distribution is similar in even and odd years.
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Sayono, Joko, Indah Wahyu, and Lutfiah Ayundasari. "Migrant workers and socio-economic changes." Masyarakat, Kebudayaan dan Politik 31, no. 2 (June 30, 2018): 176. http://dx.doi.org/10.20473/mkp.v31i22018.176-189.
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This study was conducted based on the socio-economic changes among South Malang’s residents due to the recognition of a new job opportunity, namely the role of migrant worker. The objective of this study is to describe the socio-economic changes in South Malang from a historical standpoint from the 1980s to 2015. In the 1980s, being a migrant worker as a job opportunity was popular, but in 2015, the number of migrant workers started to decrease drastically due to the changing of the economic direction. This study was conducted in eleven sub-districts in South Malang, which is known as the origin place of migrants, and where many of the residents have worked as migrant workers. The data used in this study was collected by interviewing and tracking the archives of the social economic development of the Malang District by way of various institutions. The results of this study indicate that the South Malang residents chose to work as migrant workers based on three main factors. First, are the internal factors that consist of the economic and infrastructure limitations. The external factor consist of the Oil Boom and Asian Miracle’s impact. Second, are the unproductive and costly environmental conditions which forced the residents to move out and find better life prospects. Third, is the socio-cultural context, where the society has only known about monetisation since the colonial era. Thecombination of these factors motivates the rural community of South Malang to work as migrant workers and this changed the socio-economic landscape of the region from plantations and subsistence agriculture to having a capitalist focus in the period 1980 to 2015. The positive impacts brought about by the presence of migrant workers in South Malang include economic progress, socio-economic welfare, and area improvement. On the other hand, the negative impacts include the increasing number of divorce cases, the cases of child abandonment, and the increase in the number of juvenile delinquency cases.
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Fraile, Igaratza, Haritz Arrizabalaga, and Jay R. Rooker. "Origin of Atlantic bluefin tuna (Thunnus thynnus) in the Bay of Biscay." ICES Journal of Marine Science 72, no. 2 (July 2, 2014): 625–34. http://dx.doi.org/10.1093/icesjms/fsu156.
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Abstract We used carbon and oxygen isotope ratios (δ13C and δ18O) in otoliths as a tool for identifying the nursery origin of Atlantic bluefin tuna (Thunnus thynnus) caught in the eastern North Atlantic Ocean (Bay of Biscay). Juvenile and adult bluefin tuna were collected over three consecutive years (2009—2011) using the regional bait boat fleet. Otolith δ13C and δ18O values of bluefin tuna were measured by mass spectrometry, and values were compared with a reference sample of yearling bluefin tuna from eastern (Mediterranean Sea) and western (Gulf of Mexico) nurseries to determine nursery origin. Maximum likelihood estimates based on otolith δ13C and δ18O values indicated that the overall contribution of western migrants to the Bay of Biscay fishery was <1% and varied over the years assessed. A small number of potential western migrants (2.7%) was detected in 2009, and most of these fish appear members of the abundant 2002 and 2003 year classes. In contrast, the Bay of Biscay fishery was composed exclusively (100%) of eastern origin bluefin tuna in 2010 and 2011, suggesting that this fishery is supported almost exclusively by the eastern spawning area but transatlantic western population may contribute to this fishery in a few years.
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Mendoza Pérez, Karmele, and Marta Morgade Salgado. "Mobility and the mobile: A study of adolescent migrants and their use of the mobile phone." Mobile Media & Communication 8, no. 1 (April 3, 2019): 104–23. http://dx.doi.org/10.1177/2050157918824626.
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In this article, we explore the day-to-day importance of digital media, specifically the use of mobile phones in the lives of migrant minors—also known as unaccompanied foreign minors—in juvenile residential centres. For this study, we employed a general ethnographic methodology and, in particular, a workshop based on different artistic techniques that encouraged the young people involved to become active participants, committed from the start in the generation of the material to be used for the analysis of their daily practices. This approach emerged from the recognition of the importance for these young people to feel included and connected. Migrant adolescents take refuge in their mobile devices to participate in the youth microculture, both locally and globally. In addition, they are able to access different social networks that allow them to play out the personas they wish to adopt. Finally, we recognise the importance of digital media in allowing them to maintain close and affective relationships with their relatives, fellow citizens, and communities in their country of origin.
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Burke, Brian J., Martin C. Liermann, David J. Teel, and James J. Anderson. "Environmental and geospatial factors drive juvenile Chinook salmon distribution during early ocean migration." Canadian Journal of Fisheries and Aquatic Sciences 70, no. 8 (August 2013): 1167–77. http://dx.doi.org/10.1139/cjfas-2012-0505.
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Migrating animals rely on a variety of cues to guide them, but the relative importance of those signals may vary with size, life stage, or location. During their initial ocean migration, yearling Chinook salmon (Oncorhynchus tshawytcha) from the Columbia River have stock-specific spatial distributions that shift through time. We used a two-process mixture model to examine how the distribution of yearling migrants from three Chinook salmon stocks varies as a function of geospatial (e.g., latitude and distance from shore) and environmental (e.g., chlorophyll a and temperature) covariates. In this framework, one process described the probability of being inside the spatial, temporal, and environmental boundaries of the migration route, and one process described the patchy distribution of salmon abundance within that route. We found that both environmental and geospatial covariates explained substantial portions of observed spatial patterns in abundance, suggesting that these stocks responded to multiple cues during migration. However, model selection criteria indicated that fish distributions were more affected by geospatial than by environmental covariates. We conclude that during migration, behavioral responses to environmental variation are secondary to responses to geospatial variation, sometimes resulting in suboptimal environmental conditions. This may have sublethal effects on growth and could ultimately influence stock-specific responses to broad-scale climate changes.
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Hinam, Heather L., Spencer G. Sealy, and Todd J. Underwood. "Ruby-throated Hummingbird, Archilochus colubris, Entanglements in Burdock, Arctium spp., at Delta Marsh, Manitoba." Canadian Field-Naturalist 118, no. 1 (January 1, 2004): 85. http://dx.doi.org/10.22621/cfn.v118i1.887.
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Exotic burdock (Arctium spp.) pose a risk of mortality for small native birds, such as the Ruby-throated Hummingbird (Archilochus colubris), which may become entangled in its burrs. At Delta Marsh, Manitoba, we found 11 hummingbirds and five individuals of four species of songbirds entangled on burdock in the dune-ridge forest over a 20-year period. Entangled birds were mostly migrants. Most hummingbirds caught were juvenile males, whereas the few songbirds were mostly adult males. We suspect that hummingbird entanglements resulted from an attraction to the purple flowers of burdock, but aggressive interactions with conspecifics and other factors may have been involved. Birds may be at a higher risk of entanglement at important migratory stopover sites, such as Delta Marsh, where both burdock and large numbers of birds are concentrated in a small area.
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Scanlan, Michelle M., Nathan F. Putman, Amanda M. Pollock, and David L. G. Noakes. "Magnetic map in nonanadromous Atlantic salmon." Proceedings of the National Academy of Sciences 115, no. 43 (October 8, 2018): 10995–99. http://dx.doi.org/10.1073/pnas.1807705115.
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Long-distance migrants, including Pacific salmon (Oncorhynchus spp), can use geomagnetic information to navigate. We tested the hypothesis that a “magnetic map” (i.e., an ability to extract positional information from Earth’s magnetic field) also exists in a population of salmon that do not undertake oceanic migrations. This study examined juvenile Atlantic salmon (Salmo salar) originally from a nonanadromous population in Maine transferred ∼60 years ago to a lake in central Oregon. We exposed juveniles to magnetic displacements representative of locations at the latitudinal boundaries of the Pacific salmon oceanic range in the North Pacific and at the periphery of their ancestral oceanic range in the North Atlantic. Orientation differed among the magnetic treatments, indicating that Atlantic salmon detect map information from the geomagnetic field. Despite no recent history of ocean migration, these fish displayed adaptive orientation responses similar to those observed in native Pacific salmonids. These findings indicate that use of map information from the geomagnetic field is a shared ancestral character in the family Salmonidae and is not restricted to populations with anadromous life histories. Lastly, given that Atlantic salmon are transported throughout the world for capture fisheries and aquaculture, such a robust navigational system is of some concern. Escaped individuals may have greater potential to successfully navigate, and thus invade, introduced habitats than previously suspected.
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Burla, Michela, António M. Baptista, Edmundo Casillas, John G. Williams, and Douglas M. Marsh. "The influence of the Columbia River plume on the survival of steelhead (Oncorhynchus mykiss) and Chinook salmon (Oncorhynchus tshawytscha): a numerical exploration." Canadian Journal of Fisheries and Aquatic Sciences 67, no. 10 (October 2010): 1671–84. http://dx.doi.org/10.1139/f10-083.
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Are smolt-to-adult return rates (SARs) for wild steelhead (i.e., sea-run rainbow trout, Oncorhynchus mykiss ) and wild Snake River spring–summer Chinook salmon ( Oncorhynchus tshawytscha ) related to changes in the Columbia River plume at the time that juvenile migrants enter the ocean? We used three-dimensional (3D) numerical models of the baroclinic circulation in the Columbia River estuary–plume–shelf system to simulate within-season variation in plume size and location, comparing the results with SARs for each day that juvenile salmon entered the ocean for 1999–2003. We found that steelhead benefited from the plume environment at a narrow window of time around their ocean entry. However, when large-scale ocean conditions turned unfavorable, the contribution of local plume conditions to the overall variability in steelhead survival became not significant. A similar evaluation revealed that the plume did not affect survival of Chinook salmon, at least at the fine scale of variability considered. The differential response between the two species is consistent with observed and previously reported behavioral characteristics they exhibit. We speculate that steelhead mainly use the plume to move quickly away from coastal habitats and the predation pressures associated with this environment, for a more direct migration than Chinook salmon to ocean habitats in the Gulf of Alaska.
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Polak, Marcin. "Biometry of young White Wagtails (Motacilla alba) and Yellow Wagtails (Motacilla flava) caught in the Gulf of Gdańsk region during autumn migration." Ring 27, no. 1 (January 1, 2005): 69–78. http://dx.doi.org/10.2478/v10050-008-0010-5.
Full textAbstract:
Biometry of young White Wagtails (Motacilla alba) and Yellow Wagtails (Motacilla flava) caught in the Gulf of Gdańsk region during autumn migration Biometrics of juvenile 760 White Wagtails and 714 Yellow Wagtails migrating through the Gulf of Gdańsk region in autumn were studied between 1990 and 2000. In both species distributions of wing length, body mass and indices of wing shape were unimodal, with only one exception - in the White Wagtail the wing length distribution showed two peaks caused by sexual dimorphism. The mean body mass and reserves of fat in both species were low in comparison to other stopover sites. There were significant differences in mean weight between birds caught in the morning and in the evening. The majority of birds behave as energy minimising migrants and migrate with low fat reserves in small steps.
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Kowalczyk, Nicole D., André Chiaradia, Tiana J. Preston, and Richard D. Reina. "Fine-scale dietary changes between the breeding and non-breeding diet of a resident seabird." Royal Society Open Science 2, no. 4 (April 2015): 140291. http://dx.doi.org/10.1098/rsos.140291.
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Unlike migratory seabirds with wide foraging ranges, resident seabirds forage in a relatively small range year-round and are thus particularly vulnerable to local shifts in prey availability. In order to manage their populations effectively, it is necessary to identify their key prey across and within years. Here, stomach content and stable isotope analyses were used to reconstruct the diet and isotopic niche of the little penguin ( Eudyptula minor ). Across years, the diet of penguins was dominated by anchovy ( Engraulis australis ). Within years, during winter, penguins were consistently enriched in δ 15 N and δ 13 C levels relative to pre-moult penguins. This was probably due to their increased reliance on juvenile anchovies, which dominate prey biomass in winter months. Following winter and during breeding, the δ 13 C values of penguins declined. We suggest this subtle shift was in response to the increased consumption of prey that enter the bay from offshore regions to spawn. Our findings highlight that penguins have access to both juvenile fish communities and spawning migrants across the year, enabling these seabirds to remain in close proximity to their colony. However, annual fluctuations in penguin isotopic niche suggest that the recruitment success and abundance of fish communities fluctuate dramatically between years. As such, the continued monitoring of penguin diet will be central to their ongoing management.
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Flack, Andrea, Wolfgang Fiedler, Julio Blas, Ivan Pokrovsky, Michael Kaatz, Maxim Mitropolsky, Karen Aghababyan, et al. "Costs of migratory decisions: A comparison across eight white stork populations." Science Advances 2, no. 1 (January 2016): e1500931. http://dx.doi.org/10.1126/sciadv.1500931.
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Annual migratory movements can range from a few tens to thousands of kilometers, creating unique energetic requirements for each specific species and journey. Even within the same species, migration costs can vary largely because of flexible, opportunistic life history strategies. We uncover the large extent of variation in the lifetime migratory decisions of young white storks originating from eight populations. Not only did juvenile storks differ in their geographically distinct wintering locations, their diverse migration patterns also affected the amount of energy individuals invested for locomotion during the first months of their life. Overwintering in areas with higher human population reduced the stork’s overall energy expenditure because of shorter daily foraging trips, closer wintering grounds, or a complete suppression of migration. Because migrants can change ecological processes in several distinct communities simultaneously, understanding their life history decisions helps not only to protect migratory species but also to conserve stable ecosystems.
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Morgan, I. J., I. D. McCarthy, and N. B. Metcalfe. "Life‐history strategies and protein metabolism in overwintering juvenile Atlantic salmon: growth is enhanced in early migrants through lower protein turnover." Journal of Fish Biology 56, no. 3 (March 2000): 637–47. http://dx.doi.org/10.1111/j.1095-8649.2000.tb00761.x.
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Maia, Bruno Pereira, Sandra Maria Franco Ribeiro, Paula Maciel Bizzotto, Volney Vono, and Hugo Pereira Godinho. "Reproductive activity and recruitment of the yellow-mandi Pimelodus maculatus (Teleostei: Pimelodidae) in the Igarapava Reservoir, Grande River, Southeast Brazil." Neotropical Ichthyology 5, no. 2 (2007): 147–52. http://dx.doi.org/10.1590/s1679-62252007000200008.
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The catfish yellow-mandi, Pimelodus maculatus, is a valuable sporting and commercial fish of inland waters of Southeast Brazil including Igarapava Reservoir. It is a short-distance migrant that needs shorter stretches of free-flowing river to spawn compared to other Neotropical migrants. Igarapava Reservoir is one the 13 hydroelectric reservoirs, arranged in a cascade fashion, impounding the 1,300 km-long Grande River, SE Brazil. In this paper, we examined reproductive features and recruitment of the yellow-mandi in Igarapava Reservoir. We also evaluated the role of the Igarapava Fish Ladder (IFL) built around Igarapava Dam on the sustainability of its fisheries. Female adult yellow-mandis that were gill netted (nets of 8-20 cm stretch-mesh) during the reproductive season of 2002/2003, showed adequate ovarian development, indicated by the gonadosomatic index (12.9 ± 2.1, at mature stage) and absolute fecundity (413,794 ± 206,259; range = 125,601-742,026), which were higher than those found in the literature. Postovulatory follicles present in ovarian tissue of 32% of the females examined showed that they possibly could have spawned in the reservoir area. Gill nets of 3-5 cm stretch-mesh aimed at capturing juvenile yellow-mandi were unproductive. These results indicated that Igarapava Reservoir and its reduced catchment area did not provide adequate conditions for recruitment of the yellow-mandi. This fish, the most abundant in the IFL, and those reaching the reservoir tended to remain there since no upstream passage mechanism is present. Thus, the IFL apparently was responsible for maintaining the Igarapava Reservoir stock of yellow-mandi.
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Plessia, Vasiliki. "“Fallen Angels” under European Union’s migration gesture." HAPSc Policy Briefs Series 1, no. 1 (June 30, 2020): 219. http://dx.doi.org/10.12681/hapscpbs.24969.
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According to the European Commission, from January 2020 till now, there have been new 8636 asylum requests to Greece. In the meanwhile, the living conditions of refugees and migrants in the overcrowded camps and hotspots, have attracted the attention of the press once again, amid the COVID-19 pandemic.After her visit at the Greek, and thus European, borders, the President of the European Commission, Ursula von der Leyen was alarmed by the current situation of thousands unaccompanied minors and asked Commissioner Ylva Johansson to ensure their protection. (European Commission, 2020).This policy brief outlines the parameters of all International and European judiciary background, which protects children under refugee or migrant status. Moreover, referring to recent quantitative data, it analyses the current state of affairs, as well as the problems children face as residents in current camps and hotspots in Greece. Thus, taking all these into account it suggests briefly the following possible measures:The creation of a minors’ allocation platform for all EU countries.Public awareness-raising, through media campaigning at a European level.The adoption of the Proposal for a new Asylum Procedures Regulation 2013/32/EU.The facilitation of mutual trust and cooperation between national authorities, in order to proceed quickly with the relocation of unaccompanied minors and the raising of funds for that purpose.The increase of juvenile prosecutors per child.The application of safety measures in camps and hotspots, in order to tackle the COVID-19 pandemic.The establishment of external consultancy methods for NGOs in order to monitor the use of EU funds in accordance with childrens’ needs.
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Runge, Jan-Niklas, and Anna K. Lindholm. "Carrying a selfish genetic element predicts increased migration propensity in free-living wild house mice." Proceedings of the Royal Society B: Biological Sciences 285, no. 1888 (October 3, 2018): 20181333. http://dx.doi.org/10.1098/rspb.2018.1333.
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Life is built on cooperation between genes, which makes it vulnerable to parasitism. Selfish genetic elements that exploit this cooperation can achieve large fitness gains by increasing their transmission relative to the rest of the genome. This leads to counter-adaptations that generate unique selection pressures on the selfish genetic element. This arms race is similar to host–parasite coevolution, as some multi-host parasites alter the host’s behaviour to increase the chance of transmission to the next host. Here, we ask if, similarly to these parasites, a selfish genetic element in house mice, the t haplotype, also manipulates host behaviour, specifically the host’s migration propensity. Variants of the t that manipulate migration propensity could increase in fitness in a meta-population. We show that juvenile mice carrying the t haplotype were more likely to emigrate from and were more often found as migrants within a long-term free-living house mouse population. This result may have applied relevance as the t has been proposed as a basis for artificial gene drive systems for use in population control.
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Gardali, Thomas, Daniel C. Barton, Jennifer D. White, and Geoffrey R. Geupel. "Juvenile and Adult Survival of Swainson's Thrush (Catharus Ustulatus) in Coastal California: Annual Estimates Using Capture-Recapture Analyses." Auk 120, no. 4 (October 1, 2003): 1188–94. http://dx.doi.org/10.1093/auk/120.4.1188.
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Abstract We estimated annual rates of survival for juvenile and adult Swainson's Thrushes (Catharus ustulatus) using capture-recapture analyses from 22 years of mist-neting data in coastal California (n= 2,651 individual captures). Our apparent survival estimate was 56% for adults and 25% for juveniles. We are the first to estimate an annual juvenile survival rate for a Neotropical migrant using capture-recapture probability estimates. Like most estimates of annual survival, we could not distinguish between dispersal away from our study area (which is likely high for juveniles) and mortality. Hence, survival is underestimated. However, our juvenile survival estimate did not include the period from fledging to independence, a time when mortality can be high. Many researchers have assumed juvenile survival to be half that of adult survival in population models (e.g. source-sink). Our juvenile to adult survival ratio was 45% (95% CI = 27 to 65%). We caution researchers from simply assuming that juvenile survival approximates half of adult survival when modeling populations and suggest using a range of values. Using a range of values is prudent because of the potential for annual variation, site-specific variation, and especially because estimates are imprecise or completely lacking.
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Peterman, David J., Ryan Shell, Charles N. Ciampaglio, and Margaret M. Yacobucci. "Stable hooks: biomechanics of heteromorph ammonoids with U-shaped body chambers." Journal of Molluscan Studies 86, no. 4 (August 20, 2020): 267–79. http://dx.doi.org/10.1093/mollus/eyaa018.
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ABSTRACT The biomechanics of uncoiled heteromorph ammonoids with body chambers that terminate in U-shaped hooks (ancylocones) were investigated with virtual and physical models of Audouliceras renauxianum. Virtual models were used to compute the hydrostatic properties of this morphotype. Audouliceras has the capacity for neutral buoyancy and this suggests that other taxa with similar proportions had this ability as well. Hydrostatic stability gradually increases during ontogeny, coincident with the larger degree of uncoiling. The juvenile planispiral stage has a similar stability and apertural orientation to the extant Nautilus. The adult stage, however, undergoes an increase in stability by a factor of over 3, while assuming an upward-facing posture. Counterintuitively, the stage during the formation of the shaft (before the growth of the U-shaped hook) is oriented horizontally. This intermediate stage would have had poor horizontal mobility due to the positioning of the hyponome below the centre of mass. The juvenile planispiral stage and mature stage, however, would have been well suited to horizontal backward movement with minimal rocking. Ancylocones are generally thought of as quasiplanktic vertical migrants. Thus, their relative horizontal swimming ability has been largely disregarded. Experiments on 3D printed, neutrally buoyant physical models reveal that hydrodynamic drag is indeed larger compared to Nautilus. However, Audouliceras could reach similar maximum horizontal velocities depending on the available thrust. Sepia-like thrusts yield velocities similar to equivalently sized Nautilus (c. 15 cm/s), while Nautilus-like thrusts yield velocities not much lower (c. 11 cm/s). Due to the hydrostatic properties of the ancylocone, the adult model undergoes less rocking (±4.5°) during movement than Nautilus (±10°). The minimal hydrodynamic consequences for ancylocones suggest that stability, orientation and directional efficiency are key selective pressures for some heteromorph shells, which may have primarily served as hydrostatic devices.
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Massé, Gérard, Pierre Dumont, and Réjean Fortin. "Survie oeufs–juvéniles et force des classes d'âge des grands brochets (Esox lucius) de la rivière aux Pins, près de Montréal, Québec." Canadian Journal of Zoology 71, no. 2 (February 1, 1993): 368–75. http://dx.doi.org/10.1139/z93-051.
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Exhaustive counts of northern pike that use the Rivière aux Pins and of 0+ juvenile pike produced in this river, based on trap net and seine catches, coupled with potential fecundity estimates, allowed survival rates of pike eggs to migrant 0+ juveniles to be evaluated in a natural situation, in 1975, and in a controlled water level situation, in 1976. In 1975, 3393 juveniles aged 0+ were produced from 9 210 900 eggs potentially deposited by 404 females, yielding a 0.037% survival rate. In 1976, 34 062 juveniles aged 0+ were produced from 8 536 800 eggs potentially deposited by 310 females, yielding a 0.399% survival rate. The higher survival rate in 1976 could have resulted from the water level control and (or) from the higher spring waters in 1976. However, 1975 and 1976 both produced strong year classes, suggesting that potential fecundity and 0+ juvenile production on the spawning grounds are not the only factors influencing recruitment in this species.
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Hayes, Michael C., Stephen P. Rubin, Reginald R. Reisenbichler, and Lisa A. Wetzel. "Migratory Behavior of Chinook Salmon Microjacks Reared in Artificial and Natural Environments." Journal of Fish and Wildlife Management 6, no. 1 (October 1, 2014): 176–86. http://dx.doi.org/10.3996/022014-jfwm-013.
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Abstract Emigration was evaluated for hatchery Chinook salmon (Oncorhynchus tshawytscha) microjacks (age-1 mature males) and immature parr (age-1 juveniles, both sexes) released from both a hatchery and a natural stream (fish released as fry). In the hatchery, volitional releases (∼14 to 15 months post-fertilization) to an adjacent river occurred during October–November. The hatchery release was monitored by using an experimental volitional release that diverted fish to a neighboring raceway. Fish captured during the experimental release (range 361–4,321 volitional migrants) were made up of microjacks and immature parr. Microjacks were found only in the migrant samples, averaged 18% (range 0–52%) of all migrants, and were rarely found in non-migrant samples. In comparison, immature parr were common in both the migrant and non-migrant samples. Microjacks were significantly longer (9%), heavier (36%), and had a greater condition factor (16%) than migrant immature parr (P < 0.01). In addition, they differed significantly (P < 0.01) from non-migrant immature parr; 10% longer, 44% heavier and 14% greater condition factor. In natural streams, microjacks were captured significantly earlier (P < 0.01) than immature parr during the late-summer/fall migration and comprised 9–89% of all fish captured. Microjacks have the potential to contribute to natural spawning populations but can also represent a loss of productivity to hatchery programs or create negative effects by introducing non-native genes to wild populations and should be monitored by fishery managers.
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Gorbatenko, K. M., I. V. Melnikov, and S. I. Kiyashko. "Seasonal dynamics in fish and squid trophic status in the pelagic Sea of Okhotsk, based on d13C and d15N stable isotope data analysis." Trudy VNIRO 181 (2020): 52–68. http://dx.doi.org/10.36038/2307-3497-2020-181-52-68.
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Seasonal trophic dynamics was analyzed based on d13C and d15N stable isotope mass content in the Sea of Okhotsk 35 nekton species (fish and squid (Teuthida)). It was shown that considerable differences between species in stable isotope mass contents were associated with diet type. The d15N average values of the Sea of Okhotsk species were 4.5 ‰ in spring, 7.5 ‰ in summer, and 5.4 ‰ in autumn. The summer increase was caused by the appearance of juvenile fish and squid with low trophic status and minimal d15N values, and the autumn decline was due increased trophic status of growing up young individuals. Variability range in d15N values was 11.5 ‰ for all nekton species in summer including migrants into the Sea of Okhotsk from the Pacific Ocean. Relatively narrow variability range in d13C for nekton species, of 2.2–3.3 ‰, reflects seasonal homogeneity in the trophic web basement in the pelagic Sea of Okhotsk. The structure of the food web of the pelagic nekton, presented according to the d15N and d13C data, provides useful information on the pathways of organic matter transfer to the pelagic zone at the upper trophic levels and can be further used to construct trophodynamic models of the Sea of Okhotsk.
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Bond, Morgan H., Sean A. Hayes, Chad V. Hanson, and R. Bruce MacFarlane. "Marine survival of steelhead (Oncorhynchus mykiss) enhanced by a seasonally closed estuary." Canadian Journal of Fisheries and Aquatic Sciences 65, no. 10 (October 2008): 2242–52. http://dx.doi.org/10.1139/f08-131.
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To investigate the role that estuaries play in the survival of steelhead, Oncorhynchus mykiss , we compared juvenile size at ocean entry with back-calculated measures of size at ocean entry for returning adults in Scott Creek, a representative California coastal stream. During the annual spring emigration, the largest smolts (>150 mm fork length (FL)) move directly to sea, while some smaller smolts remain in the estuary until sandbar formation creates a closed freshwater lagoon. High growth rates in the estuary throughout the summer result in a near doubling of fork length from the time of estuary entry (mean FL of spring migrants = 102.2 mm; mean FL of fall lagoon resident = 195.9 mm). Analysis of the scale morphology of returning adult steelhead indicates that there is strong size-dependent mortality at sea, with estuary-reared steelhead showing a large survival advantage, comprising between 87% and 95.5% (based on tag returns and scale analysis, respectively) of the returning adult population despite being between 8% and 48% of the annual downstream migrating population. Although the estuary forms less than 5% of the watershed area, it is critical nursery habitat, and steelhead population persistence in southern margin ecosystems may well depend upon healthy estuaries.