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71.
72.
《African Journal of Marine Science》2013,35(3):613-624
This study describes the Thukela Banks crustacean and linefish fisheries and investigates the potential impacts of reduced flow from the Thukela River on the value of these fisheries. Data were obtained from published and unpublished material, key informants and government records. The crustacean fishery employs about 300 people, and comprises an inshore and offshore fishery. Inshore catches and effort are strongly seasonal, peaking in April to June. The probability of fishing in any particular month is positively correlated with catch per unit effort. Average overall annual catch (inshore and offshore) was estimated to be in the region of 700 tonnes for 1992–2002 with a gross output of about R36.7 million per annum, and a gross value added (net output) of R13.8 million (1 US$ = R6.40; 2003). Inshore prawns were estimated to contribute R8.5 million of the gross output. The Thukela Banks was estimated to contribute R4.5 million and R35 million (rand value in 2003) to the gross output of the commercial linefishery and boat-based recreational angling fishery respectively. Freshwater reduction scenarios yielded 0.7–11% reductions in prawn catches, which translated into only a 1–2% drop in the annual value of the fishery. The latter was attributed to the fishery's diversity (predominantly the buffering effect of bycatch) and the fact that the stocks of the species targeted by the offshore component are largely independent of flow. Catches and value of the recreational boat-based linefishery were predicted to remain fairly constant irrespective of any changes in flow. The commercial linefishery was the most responsive, with a 20% decline in total catch and 17% value predicted for the most extreme flow reduction scenario. 相似文献
73.
Fishery benefits from exploiting spawning aggregations not solely dependent on enhanced fish density
The vulnerability of spawning aggregations to exploitation varies among fisheries as a result of differences in the population-density changes associated with this behaviour. However, vulnerability to fishing is also influenced by technology, environmental factors, and fish and fisher behaviours. Focusing on a fishery for the rabbitfish Siganus sutor at Praslin Island, Seychelles, we examined how catch rate varied across spawning and non-spawning habitats in relation to in situ population-density changes and other factors known to influence catchability. Catch rates in spawning habitat were disproportionate to density changes, being only fourfold greater than catch rates in non-spawning habitat, despite the fact that spawning-aggregation formation involved nine- to thirteen-fold increases in population density. Catch rates in spawning habitat were also highly variable across the spawning season (0–23.4 fish trap-hour?1). Current strength was of similar importance to density as a catch-rate predictor, with the highest catch rates in spawning habitats confined to months with the strongest currents. Therefore, in addition to density-dependent catchability, other factors that influence catch rates must be examined to avoid overestimation of the vulnerability of populations to aggregation fishing. The dynamics of catchability at spawning sites can limit the ability of fishers to predict and maximise returns based on increases in fish density. 相似文献
74.
《Marine Policy》2015
There is a demand for a management mechanism that can reduce the discarding problems of EU fisheries. Catch quota management (CQM) seems to be a promising candidate for such a mechanism. Drawing on a principal–agent model, the objective of this study is to develop and test a method for investigating if the CQM mechanism is efficient in providing fishers with incentives for participating in CQM and complying with the rules. The study uses the 2011 Danish CQM trial project as its empirical basis. The results indicate that CQM fishers have a higher average gross income compared to fishers harvesting according to the conventional rules. Hence, there is an incentive for fishers to participate in the trial. However, with the possibility to cheat, CQM fishers may achieve even higher gross income. It is not obvious that the CQM mechanism׳s payoff structure (incentives) is attractive enough to ensure that the fishers comply with the rules. The empirical data illustrate that without discarding the CQM fishers achieve a lower average price for their catches. Therefore, to make the CQM mechanism sufficiently attractive to fishers, the participating fishers must be compensated. 相似文献
75.
WANG Yingbin LIU Qun* and WANG Yanjun College of Fisheries Ocean University of China Qingdao P. R. China 《中国海洋大学学报(英文版)》2007,6(1):53-59
1 Introduction Natural mortality coefficient (M) is one of the key population parameters common to most analyses in fish stock assessment. Many mathematical models of fish stock dynamics include M directly or indirectly. However, until now M is the least known among the four factors affecting fish stock variation: recruitment, growth, natural death and fishing death (Quinn and Deriso, 1999). There is an extensive literature concerning the impact of errors in M on stock assessment (Mertz and… 相似文献
76.
基于北斗船位数据的渔业信息解译与应用研究——以中国毛虾限额捕捞管理为例 总被引:1,自引:0,他引:1
2020年6月15日—7月15日,我国首次中国毛虾(Acetes chinensis)限额捕捞试点于江苏连云港实施。本研究提取62艘毛虾网船在限额捕捞期间的421700条北斗船位数据经纬度、航速、航向等信息,运用缓冲区叠加分析法、DBSCAN密度聚类算法、平均中心算法、核密度估计以及数据库查询对捕捞努力量等管控要素进行分析研究。结果显示,所有毛虾网船累计作业239个航次、1942个网次,捕捞过程分为航行、抛锚布网、等待渔获、收渔获、停航等5个状态,中国毛虾捕捞状态船位点呈直线分布,总捕捞时长为4413.73h,82.4%的单网次捕捞时长为1.5—3.5h,各网次捕捞产量呈现多核心空间分布模式,总捕捞努力量为108106343 m2·h,计算62艘的捕捞总产量值约为2328 t,比上报产量高12.6%;本文通过北斗船位数据解译和提取捕捞努力量以计算中国毛虾捕捞产量及资源空间分布情况,有效应用于中国毛虾限额捕捞,为解决我国单品种限额捕捞难点积累了宝贵经验。 相似文献
77.
Sea turtle bycatch to fish catch ratios for differentiating Hawaii longline-caught seafood products 总被引:1,自引:0,他引:1
Sea turtles can be incidentally caught in pelagic longline fishing gear targeting tuna and swordfish. Bycatch to fish catch (B/C) ratios can differentiate seafood based on sea turtle impacts. This study demonstrates the use of B/C ratios indexed to the weight of fish catch: (1) to report on the significant progress in reducing sea turtle bycatch in Hawaii's swordfish longline sector and (2) to compare Hawaii and other Pacific longline fisheries by number of sea turtle interactions per weight of catch. Hawaii's longline tuna fishery sets the benchmark of 1 sea turtle interaction per 190,000 kg of tuna caught. 相似文献
78.
This paper compares the management of recreational fisheries for pink snapper (Pagrus auratus) in the inner gulfs of Shark Bay (Australia) and the closely related red sea bream (Pagrus major) in Sagami Bay (Japan). Fishing and other factors have resulted in population declines of these species in both regions. In response, fishery managers have employed contrasting management, more conventional catch controls in Shark Bay and stock enhancement in Sagami Bay. Although recreational harvest levels were higher than commercial levels in both fisheries, the driving mechanisms are comparatively different due to historical, social, economic and political issues in the respective locations. 相似文献
79.
《African Journal of Marine Science》2013,35(2):383-397
Shark catches in the protective nets set off the beaches of KwaZulu-Natal (KZN), South Africa, are strongly influenced by the sardine run, the winter influx of shoals of Sardinops sagax from the south-west. The effect of the sardine run, which is highly variable from year to year, is greatest in June and July at beaches south of Durban. Total annual shark catch and effort are presented for the period 1952–2005, and total monthly shark catch on the KZN south coast for the period May–August, 1965–2005. Measures to reduce catches of sharks associated with the sardine run have been introduced and have been increasingly successful. Reliable species-specific catch data are available for the period 1978–2005 only. For this period, the spatio-temporal distribution of each of 14 species of shark and the frequency of occurrence of sardine in their diets is documented. Occurrence varies according to species, as does the apparent influence of the sardine run on shark distribution. During June and July on the KZN south coast, sardine were found in the diet of all but two species and frequency of occurrence was 40% or greater in eight species. The presence of copper or bronze whaler sharks Carcharhinus brachyurus in KZN waters appears to be strongly associated with the sardine run, as does that of certain life-history stages of dusky sharks C. obscurus. Spinner sharks C. brevipinna and smooth hammerhead sharks Sphyrna lewini are caught in greater numbers in summer than in winter, but appear to shift their spatial distribution seasonally to feed on sardine. 相似文献
80.
总可捕量制度不同实施方式的比较分析 总被引:3,自引:0,他引:3
本文简单介绍了总可捕量制度(Total Allowable Catch,TAC制度)的概念及其实施所需的条件,对TAC制度的不同施式即“奥林区克自由捕捞式”(“free fishing like Olympic competiton”),个体配额制度(Individual Quota,IQ制度)或个体可转让配额制度(Individual Transferable Ouota,ITQ制度)进行了比较分析,并就我国如何实施TAC制度作了探讨。 相似文献