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《Marine Policy》2017
The catch of non-target species or discarding of target species (bycatch) in commercial fisheries can result in negative species level and ecosystem wide impacts as well as adverse social and economic effects. Bycatch has become one of the foremost, global issues of fishery managers and conservationists, especially when the non-target species is from a protected or threatened population. However, the impact and spatial distribution of bycatch is frequently unknown making it difficult to develop effective, justifiable mitigation regulations. This challenge is exemplified by the bycatch of river herring (alewife, Alosa pseudoharengus, and blueback herring, A. aestivalis) and American shad (A. sapidissima) in the northwest Atlantic mid-water trawl fishery targeting Atlantic herring (Clupea harengus) and Atlantic mackerel (Scomber scombrus). As an alternative to immediate management action, a voluntary bycatch avoidance program was established through an industry, state government, and university partnership. Here the program is described and its impact is evaluated by comparing fleet behavior and bycatch prior to and during the program. The combined results suggest that consistent communication, facilitated by the avoidance program, positively influenced fishing habits and played a role in the approximately 60% decrease in total bycatch and 20% decrease in the bycatch ratio observed during the program. However, the success of small scale move-along strategies to reduce bycatch ratios varied greatly in different areas of the fishery and years. This suggests the program is best viewed as an intermediate or complimentary solution. Overall, this project exemplifies of how collaborative programs can help alleviate difficult management scenarios. 相似文献
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Pier Giorgio Bianco 《Marine Ecology》2002,23(S1):51-64
Abstract. The twaite shad, Alosa agone , is still quite common in Italy and the western Balkans, but locally is endangered or extinct. Two eco-phenotypes are recognized: the migratory'Cheppia'or'Laccia'and the landlocked'Agone'. The two forms have never been in contact, at least in Italy. The migratory form is more endangered since barriers and dams prevent it from reaching upstream spawning grounds. A few reproductive communities are documented, e. g. in the Po River in Italy and Neretva River in Croatia. Resident stocks have increased to substantial populations in the large lakes of Italy, especially in the last ten years, probably as a result of improved water quality. The landlocked form from northern Italy was successfully introduced into lakes of central Italy about 75 years ago. In Sardinia a population derived from the migratory form was established about 80 years ago in the artificial Lake Omodeo. In Croatia the'Cheppia'seems to live only in the lower course of the Neretva River. In Montenegro,'Cheppia'and'Agone'live in sympatry in Lake Skadar, but a dam built in 1960 caused a strong decline of both forms. The twaite shad is a very variable species, able to modify its morphology and biology according to its adaptation to freshwater or marine biotopes. In the Mediterranean area, only one taxon should be then recognized, Alosa agone (Scopoli, 1786). This will replace Alosa fallax (Lacépède, 1803), a taxon described from the Atlantic drainage area which seems to be distinct from Mediterranean populations. A survey of the distribution of reproductive communities of the migrating form in the Mediterranean area must be carried out. 相似文献
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Automated egg counting and sizing from scanned images: Rapid sample processing and large data volumes for fecundity estimates 总被引：1，自引：0，他引：1
K.D. Friedland D. Ama-Abasi M. Manning L. Clarke G. Kligys R.C. Chambers 《Journal of Sea Research》2005,54(4):307-316
The production of eggs in a fish population is a fundamental parameter in fisheries management and ecology. Management decisions are based largely on the abundance and composition of the spawning stock; hence it is essential to estimate the contribution of viable eggs by females of various ages, which may depend on the size and maturation schedules in females of younger ages, and the size and reproductive senescence of older ones. The level of recruitment may also be influenced by the size and quality of eggs. Egg quality can be characterised in a number of ways; however, the most useful methods are those that are efficient and widely available. Estimating potential fecundity and egg size in fish and invertebrate populations has been hindered by the processing time, toxicity, and resources required by traditional methods. We have developed an imaging-based technique that counts and measures oocytes from a gravimetric gonadal sub-sample in relatively little time and at low cost. Sub-samples were preserved in a non-toxic formulation of Gilson's solution, which offers an alternative to other preservatives commonly used in fecundity studies. The technique uses high-resolution optical scans of plated oocytes, imaging software, and user-defined object classifications to separate oocyte from ancillary material likely to be present in a processed sample. Estimates of misclassification are as low as 1% (false-negatives) in automated counts. 相似文献
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There is a growing need to incorporate biotic interactions, particularly those between predators and their prey, when predicting climate-driven shifts in marine fishes. Predators dependent on a narrow range of prey species should respond rapidly to shifts in the distribution of their prey, whereas those with broad trophic adaptability may respond to shifts in their prey by altering their diet. Small pelagic fishes are an extremely important component of the diet of many marine predators. However, their populations are expected to shift in distribution and fluctuate in abundance as the climate changes. We conducted a comparative study of the seasonal diet of adult Pomatomus saltatrix over two periods (June–December 2006 and 2012) and examined the available data on small pelagic fishes biomass in a global hotspot (the coastal region of southern Angola, southern Africa) to gain an understanding of the tropic adaptability of the species. Despite a drop (630 000 t to 353 000 t) in the abundance of their dominant prey (Sardinella aurita) in the region, it remained the most important prey item during both study periods (Period 1 = 99.3% RI, Period 2 = 85.3% RI, where %RI is a ranking index of relative importance). However, the diet during Period 2 was supplemented with prey typically associated with the nearshore zone. The seasonal data showed that P. saltatrix were capable not only of switching their diet from S. aurita to other prey items, but also of switching their trophic habitat from the pelagic to the nearshore zone. These findings suggest that P. saltatrix will not necessarily co-migrate if there is a climate-driven shift in the distribution of small pelagic fishes (their dominant prey). Accordingly, understanding the trophic adaptability of predators is critical for understanding their response to the impacts of climate change. 相似文献
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《African Journal of Marine Science》2013,35(3):401-410
Elf Pomatomus saltatrix account for between 28% and 80% of the annually recorded recreational shore-angling catch in KwaZulu-Natal, South Africa, and have been subjected to various management regimes over the past 33 years. Management of the elf fishery was amended in 2005 to reduce fishing mortality and enhance egg production, following an assessment in 1997, which considered the elf stock to be overexploited and in need of rebuilding. A compromise was reached whereby the bag limit was reduced from five to four elf per angler per day, but the closed season was shortened, allowing an extra month of fishing for elf. A total of 33 years of recreational elf catches recorded on the National Marine Linefish System was investigated for any long-term trends and how they related to management of this species. Over 3 million angler-outings from the recreational shore-fishery in KZN were analysed, including more than 1.5 million elf in the catch. Despite the fast growth of elf and the latest management intervention seven years ago, which was based on a rigorous investigation of life-history parameters, the present study showed no evidence of an improvement in catch rate. It could not be determined whether this was due to a reduction in the bag limit, which would naturally reduce catch rates or whether other factors, including the shortened closed season, had been detrimental to elf stocks. Some shortfalls in the management of elf are discussed and possible reasons for the great variability in catches, which complicated the assessment of trends, are explored. 相似文献
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