Literatura académica sobre el tema "Marine animals – Juvenile fiction"

Abstract Many animals live in colonies, groups of organisms of the same species, living together in a single location. In many cases, the colonies are permanent organizations of sessile animals. In other cases, they are temporary and functional, as in breeding colonies. In clonal colonies, all individuals or zooids are genetically identical descendants of a founder zooid. The zooids of a colony can be morphologically similar or can be specialized, with a greater or lesser level of division of labor among the zooids. Colonial animas often have complex life cycles, but this is not unique to them. Complex life cycles include a separation between juvenile stages and adult stages. In complex life cycles, the juvenile stage or larva is usually morphologically and ecologically different from the adult. In marine animals, the larva is often planktonic. The transition from larva to adult is usually accompanied by a dramatic change in form known as metamorphosis.

<em>Abstract.</em> —The spatial and seasonal distribution of humpback whales in the Great Barrier Reef Marine Park (GBRMP) was defined using data from a systematic aerial surveillance program. The data comprised 414 pod sightings (812 individuals) recorded from July 1982 to March 1996. These sightings were supposedly of humpbacks from the east Australian Group V substock that migrates during the austral autumn from Antarctic feeding grounds to winter breeding grounds in GBR waters. Humpbacks were sighted in all months and throughout the GBRMP. However, most pods (75%) were sighted in southern GBR waters (below 19°S) and mainly during winter and spring ( July to September). Occasional sightings of humpbacks in northern GBR waters (above 16°S) in summer supports previous claims of a substock resident year-round in northern Australian tropical waters. Mother–calf sightings were rare with most recorded below 21°S and mainly in August and September. These limited sightings suggest that the main calving grounds for the east Australian Group V substock occur in the extensive southern GBR lagoonal waters defined northward by the Whitsunday Group of islands and reefs and eastward by the Pompey/Swains reef complex. An estimate of the crude birth rate was 0.072 (95% confidence interval [CI]: 0.06–0.11) with Monte Carlo estimates of the median calving rate at 0.3 calves per mature female per year (95% CI: 0.22–0.43) and the median interbirth interval at 3.4 years (95% CI: 2.3–4.5) indicating low and variable juvenile recruitment. Nonparametric time series analysis (seasonal and trend decomposition using loess, STL) of monthly humpback sightings showed that the long-term trend in sightings was increasing but that there was significant inter-annual variability in the seasonal abundance of humpbacks in the GBRMP. The STL analysis also suggested that the frequency of sightings increased earlier in winter (June) and later in the season during spring/summer (October to December). Time series regression analysis of the STL-derived trend in sightings suggested that the east Australian Group V substock increased slowly in abundance over the 14 years from 1982 to 1996 at about 3.9% per year (95% CI: 1.9% to 5.7%)—a finding consistent with an estimate of low and variable juvenile recruitment.

<em>Abstract.</em> —Effective fisheries management requires considerable information on life history characteristics, recruitment dynamics, habitat requirements, and fishery interactions for the managed species. It is clear that we have little of this information for any of the myriad temperate reef fishes managed in the South Atlantic or Gulf of Mexico regions, not only from our reliance on size limits, controlled effort, or limited harvest but from the repeated failures of all but complete closures of fisheries to allow recovery from overexploitation. Several of the life history features that reef fish share render them particularly vulnerable to both fishing pressure and habitat degradation, including their longevity, their slow maturation, their spatially and temporally predictable spawning aggregations, and the reliance of juveniles on estuarine nursery grounds. In addition, traditional hindcasting methods like virtual population analysis and the use of spawningpotential ratio to diagnose overfishing have not proved reliable means of assessing population status. Virtually unexplored in the United States to date are (1) use of marine fishery reserves to protect demographics and reproductive potential of exploited species, habitat and community structure of all species, and biodiversity and (2) use of forecasting methods of stock assessment based on juvenile abundances. We discuss the ability of these methods to provide insurance against management error and to predict fishery abundances for future year classes, respectively.

<em>Abstract.</em> —The wreckfish <em>Polyprion americanus </em> is a long-lived, globally distributed species that supports fisheries on both sides of the Atlantic Ocean, in the Mediterranean, and in the western South Pacific. Wreckfish in the western North Atlantic have a life history that includes an extended (perhaps for two years) pelagic juvenile stage that drifts in the North Atlantic gyre; slow growth rates after assuming demersal existence; recruitment to the American fishery resulting from migration to the grounds at an advanced age (four years); and a long life (31 years at 1460 mm total length and 47 kg total weight). Experience with wreckfish in isolated geographic habitats such as Bermuda indicates that wreckfish can be quickly overfished as fishing technology develops to target the species. Because of its life history and evidence for a single stock of wreckfish for the northern hemisphere, recruitment to local fisheries may depend on management imposed by agencies that regulate distant fisheries. In the United States, the fishery is managed with an individual transferable quota (ITQ), which has sustained a small fishery (annual total allowable catch [TAC] = 907 metric tons) similar in magnitude to that in the Azores and mainland Portugal. There is no management in other portions of the northern hemisphere range. With the exception of Bermuda and perhaps the Mediterranean, northern hemisphere wreckfish stocks do not appear to be in decline; however, landings in the Azores and Madeira have decreased since 1994, after initial increases resulting from introduction of longlines. Current exploratory fishing on the Mid-Atlantic Ridge and probable expansion of landings of deepwater species in the North Atlantic islands may result in expansion of the fishery and may necessitate international management plans.

Abstract Data from a long-term study of individually identified humpback whales, Megaptera novaeangliae, were used to describe patterns of association and grouping of this species on one of its principal North Atlantic feeding grounds in the southern Gulf of Maine. Most groups were small and unstable, and individual whales of both sexes and all age classes associated with many conspecifics. Only six instances of stable associations were recorded. Analysis of the class composition of singles and pairs showed that: (1) among singles, juveniles of both sexes were significantly over represented and mature females significantly under-represented; (2) male-female adult pairs were over-represented; (3) adult-juvenile pairs of any gender combination were under-represented; and (4) pairings between adult males were under represented except during feeding. Only 12 of 2690 pairs consisted of animals that were known to be related. It is suggested that the fission-fusion sociality that characterized the study population represents a response to two ecological factors. Firstly, absence of predation nullifies the need for large groups for predator detection or communal defence. Secondly, the spatial characteristics of piscine prey favour a foraging strategy involving frequent changes in group size. In this system, kinship and dominance probably play reduced roles, while the apparent lack of territoriality is typical of taxa confronted by heterogeneously distributed and mobile resources. The apparent preference by mature males for associations with mature females may represent an attempt to establish bonds with potential future mates.

<em>Abstract.</em>—During 1984–1992, 97,483 shortnose sturgeon <em>Acipenser brevirostrum</em> were stocked in the Savannah River as part of a state/federal program to develop techniques and evaluate issues related to stock enhancement of sturgeons. Based on recovery of marked fish after a mean time out of 7.2 ± 1.9 years (range 5.9–10.4) and results from double-tagging studies, it is estimated that stocked juveniles provide at least 38.7% of the current adult population. Population estimates and catch/effort data suggest that the adult population is larger than 10 years ago, but juveniles are still scarce, suggesting a recruitment bottleneck during the early life stages. Based on field sampling, water quality degradation in the nursery habitat is believed to be at least partially responsible. The program identified issues associated with long term marking of stocked fish and showed that marking of small juvenile sturgeon for later recapture as adults was especially problematic. Improvement in tagging technologies including use of genetic markers should help resolve this issue. Stocking protocols approximated current recommendations developed by the Atlantic States Marine Fisheries Commission for Atlantic sturgeon <em>A. oxyrinchus</em>. However, stocking similar numbers of progeny per mating was not well controlled. This coupled with assumed differential survival of different groups of stocked animals appears to have resulted in lower genetic diversity of the adult population relative to other river systems. Future stocking efforts need to strive for balanced numbers of progeny per broodstock matings over time and similar survival rates. Straying of some stocked fish into nontarget rivers was noted and new enhancement or restoration programs should address the issue of imprinting of sturgeon.