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1.
Tropical tuna purse‐seine fisheries spatially co‐occur with various megafauna species, such as whale sharks, dolphins and baleen whales in all oceans of the world. Here, we analyzed a 10‐year (2002–2011) dataset from logbooks of European tropical tuna purse‐seine vessels operating in the tropical Eastern Atlantic and Western Indian Oceans, with the aim of identifying the principle environmental variables under which such co‐occurrence appear. We applied a Delta‐model approach using Generalized Additive Models (GAM) and Boosted Regression Trees (BRT) models, accounting for spatial autocorrelation using a contiguity matrix based on a residuals autocovariate (RAC) approach. The variables that contributed most in the models were chlorophyll‐a concentration in the Atlantic Ocean, as well as depth and monsoon in the Indian Ocean. High co‐occurrence between whale sharks, baleen whales and tuna purse‐seine fisheries were mostly observed in productive areas during particular seasons. In light of the lack of a full coverage scientific observer on board program, the large, long‐term dataset obtained from logbooks of tuna purse‐seine vessels is highly important for identifying seasonal and spatial co‐occurrence between the distribution of fisheries and megafauna, and the underlying environmental variables. This study can help to design conservation management measures for megafauna species within the framework of spatial fishery management strategies.  相似文献   

2.
运用生产力-易捕率指数对10种热带太平洋鲨鱼种群的研究   总被引：2，自引：0，他引：2  
热带太平洋是全球产量最高的金枪鱼渔场,大洋性鲨鱼种群遭受金枪鱼渔业的影响受到国际社会的高度关注。由于缺少渔业统计资料,一般难以运用标准的资源评估方法对这些兼捕的种类进行评估。笔者运用种群生产力-易捕率分析（productivity-susceptibility analysis,PSA）方法,对热带太平洋10种鲨鱼遭受金枪鱼延绳钓渔业影响的风险程度进行比较分析,并计算风险指数（vulnerability）。风险指数从低到高的种类依次为锤头双髻鲨（Sphyrna zygaena）、路氏双髻鲨（S.lewini）、无沟双髻鲨（S.mokarran）、尖吻鲭鲨（Isurus oxyrinchus）、狐形长尾鲨（Alopias vulpinus）、长鳍真鲨（Carcharhinus longimanus）、大青鲨（Prionace glauca）、镰状真鲨（C.falciformis）、浅海长尾鲨（A.pelagicus）、大眼长尾鲨（A.superciliosus）,表明大眼长尾鲨种群受延绳钓渔业影响而遭受过度捕捞的潜在风险最高,垂头双髻鲨的风险最低。该研究结果可以为热带太平洋金枪鱼延绳钓渔业的管理和生态系统保护提供科学参考。  相似文献   

3.
大西洋中上层鲨鱼资源状况的初步探讨   总被引：2，自引：1，他引：2       下载免费PDF全文
戴小杰 《水产学报》2003,27(4):328-333
据1994—2001年4个航次在金枪鱼延绳钓渔船对热带大洋性中上层鲨鱼资源进行调查，并分析国际大西洋金枪鱼资源保护委员会提供的关于中上层鲨鱼的渔业数据。结果表明：延绳钓渔业共兼捕13种鲨鱼，其中，尖吻鲭鲨和大青鲨是优势种类。尖吻鲭鲨在第1、第2和第4航次的CPUE分别为每千钩0．3502、0．1754和0．0642尾，呈下降趋势。大青鲨在第1～3航次的的CPUE达到每千钩5～7尾，而在第4航次下降为每千钩0．8尾。研究报告了中国金枪鱼船队自1993年开始在大西洋兼捕尖吻鲭鲨和大青鲨的渔获量，并根据捕捞死亡系数和大西洋总渔获量数据，初步探讨了尖吻鲭鲨和大青鲨年平均资源量，影响CPUE的因素和大西洋中上层资源状况。  相似文献   

4.
大青鲨(Prionace glauca)广泛分布于南、北温带和热带的三大洋区,是延绳钓渔业和刺网渔业的主要兼捕对象,对维持海洋生态系统的稳定性和多样性起着重要的作用。随着捕捞强度的加大,大青鲨的资源出现衰退的现象。但由于基础数据的不确定性,大青鲨资源评估的结果并未能得到很好的应用。本文以文献计量统计分析为基础,对大青鲨渔业生物学的研究历程进行阐述,了解了不同时期大青鲨渔业生物学的研究重点。综合诸多文献资料,对大青鲨的年龄与生长、基础繁殖生物学、种群结构的鉴定、资源丰度指数和资源评估等方面的研究方法进行综述和分析。最后根据上述的综合和分析结果,提出了今后相关研究的注意事项以及相关的方法,以进一步提高大青鲨的资源评估的可信度,提高对大青鲨资源现状的了解,以期为大青鲨的资源养护提供科学依据。  相似文献   

5.
运用数据缺乏方法估算印度洋大青鲨可持续渔获量   总被引：2，自引：1，他引：1  
运用数据缺乏方法,即基于资源衰减的可持续渔获量估算模型(DCAC),结合Monte Carol模拟,对印度洋大青鲨(Prionace glauca)的可持续渔获量进行估计。结果表明,若大青鲨资源衰减比率(Δ)为正值,当自然死亡系数M增大或最大可持续产量对应的捕捞死亡系数(F_(MSY))与M的比值c增大时,可持续渔获量估算值(Y_(sust))增大;若Δ接近零甚至为负值,当M或c增大时,Y_(sust)呈减小趋势。资源丰度指数的选择对DCAC结果有较大影响,基于日本延绳钓渔业1998—2014年和2001—2014年两个时间序列的丰度指数得到的Y_(sust)结果可靠,且与其他模型估算的MSY值接近。2014年印度洋大青鲨的年渔获量正好处在或略高于最大可持续产量(MSY)水平,但该结果仍具有一定的不确定性。本研究表明运用DCAC方法估算印度洋大青鲨可持续渔获量是可行的,但对其他鲨鱼种类的适用性仍需进一步研究,该结果可为数据缺乏方法在大洋和中国近海渔业中的应用提供参考。  相似文献   

6.
  1. The sand tiger shark (Carcharias taurus) is a coastal species distributed in temperate and sub‐tropical waters, classified as ‘Vulnerable’ at global level and ‘Critically endangered’ in eastern Australia, south‐western Atlantic Ocean, and Mediterranean Sea. Six populations (north‐western Atlantic, Brazil, South Africa, Japan, eastern Australia, and western Australia) with low genetic diversity and limited gene flow were identified worldwide, but genetic information for many other geographic areas are still missing. Specifically, this species is listed in several reports as part of the Mediterranean fauna, even if there has been a lack of catches and sightings in recent years in this basin. To clarify the origin of C. taurus individuals caught in the past in the Mediterranean Sea, historical samples were genetically analysed.
  2. Nine samples with certain Mediterranean origin were collected from different European museums. DNA was extracted and ~600 bp of the mitochondrial DNA control region were amplified using eight overlapping species‐specific primer pairs. Sequences obtained were aligned with all the haplotypes globally known so far.
  3. Genetic analysis revealed the misidentification of one museum specimen. Among the remaining Mediterranean historical samples, three different haplotypes were recovered. Two of them previously observed only in South Africa and one described in both South African and Brazilian populations.
  4. Results suggest a genetic relationship between Mediterranean sand tiger sharks and those from the western Indian Ocean. According to previous studies, we hypothesized that, during the Pleistocene, the cold Benguela upwelling barrier was temporarily reduced allowing the passage of C. taurus individuals from the Indian to Atlantic Ocean. After the restoration of this phylogeographic barrier some individuals were trapped in the Atlantic Ocean and probably migrated northward colonizing the western African coasts and the Mediterranean Sea.
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7.
根据2007年12月~2008年3月采集的热带大西洋(05°37′~12°01′N、29°00′~36°51′W)金枪鱼延绳钓渔获物数据,分析了金枪鱼延绳钓兼捕鲨鱼的种类组成、渔获量、渔获率及其与表温的关系。本次调查共捕获鲨鱼8种,隶属3目7科7属,总渔获尾数为633 ind,总渔获量达26 837.4 kg,其中大青鲨为主要兼捕种类。各种鲨鱼渔获率平均值在0.003~1.524 ind/1 000 hooks之间,其中大青鲨最高,其值为1.524 ind/1 000 hooks,大眼砂锥齿鲨最低,其值为0.003 ind/1 000 hooks。各种鲨鱼渔获率月变化不明显(ANOVA,P=0.901)。鲨鱼总渔获率和大青鲨渔获率与表温都呈显著性负相关。大青鲨主要出现渔场的表温范围为24.6~25.8℃。  相似文献   

8.
Spatio‐temporal modeling estimates a species distribution function that represents variation in population density over space and time. Recent studies show that the approach may precisely identify spatial hotspots in species distribution, but have not addressed whether seasonal hotspots are identifiable using commonly available fishery data. In this study, we analyzed the seasonal spatio‐temporal distribution of pelagic sharks in the western and central North Pacific using fishery catch rates and a generalized linear mixed model with spatio‐temporal effects. Different spatial distribution patterns were observed between two shark species. The hotspots of shortfin mako (SFM) appeared in the vicinity of the coastal and offshore waters of Japan and the Kuroshio‐Oyashio transition zone (TZ), whereas the hotspots of blue shark (BSH) were widely distributed in the areas from the TZ to the waters of the Emperor Seamount Chain. Shortfin mako distribution changes seasonally with clear north‐south movement, which follows higher sea surface temperatures (SST). However, preferred spring and summer water temperature was still colder than those in fall and winter, but not as cold as for BSH, which did not show seasonal north‐south movement. BSH exhibits seasonal east‐west movement apparently unrelated to temperature. The spatial fishing effort by season generally follows the seasonal movement of temperature possibly making SFM more vulnerable to the fishery than BSH. These findings could be used to reduce the capture risk of bycatch sharks and to better manage the spatial distribution of fishing for targeted sharks.  相似文献   

9.
Management and conservation of marine predator species relies on a fundamental knowledge of their movements and behaviour. Pop‐up satellite archival tags were used to investigate the vertical movement patterns of five blue sharks (Prionace glauca) and one thresher shark (Alopias vulpinus) within the southeastern Indian Ocean. Sections of similar depth distribution, identified using a split moving window analysis, were investigated in relation to the thermal structure of the water column and activity rates. Minimum horizontal displacement of between 66 and 5,187 km for blue sharks and 16 km for the thresher shark were recorded over 863 tracking days. Maximum depths ranged from 540 to 807 m for blue sharks and 144 m for the thresher shark. All sharks displayed plasticity in their depth distribution, with diel vertical movements and surface‐oriented movements the two most common patterns. Diel movement of prey is the most likely explanation for diel vertical movements of thresher and blue sharks. This study has improved our understanding of the vertical movement patterns of these pelagic predators and the relationship between their depth distribution, temperature, and activity.  相似文献   

10.
1. Whale shark, the world's largest fish, is believed to be particularly vulnerable owing to its biological characteristics (slow growth, late maturation, great longevity) and is listed as Vulnerable by IUCN and included in Appendix II of CITES. 2. Whale sharks are occasionally encircled in tropical tuna purse‐seine nets, throughout this global fishery. Although apparent immediate survival rates following encirclement and release have recently been assessed through scientific onboard observer programmes, a more rigorous methodology is still required for studying post‐released survival. 3. This work provides a method for applying pop‐up satellite tags and reports an enhanced release procedure for whale sharks. The first assessment of survival after release from purse‐seine nets involved six whale sharks tagged between May and September 2014 in the eastern tropical Atlantic Ocean. Five tags transmitted data: three popped up as programmed (after 30 days), while two surfaced prematurely (one after 21 and the other after 71 days (programmed to pop off after 30 and 90 days, respectively)) but showed no sign of unusual behaviour. 4. Overall, whale sharks survived at least 21 days (one at least 71 days) after release from purse‐seine nets. These observations based on five large individuals (total length > 8 m), suggest that whale sharks have a good chance of survival when released with the proposed method. 5. Additional tagging in this and other oceans, especially of juveniles which may be more sensitive to encirclement and release operations, is essential to further assess whale shark post‐release survival rates in tuna purse‐seine fisheries. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

11.
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12.
Blue marlin is distributed throughout tropical and temperate waters in the Pacific Ocean. However, the preference of this species for particular habitats may impact its vulnerability to being caught. The relationship between spatio‐temporal patterns of blue marlin abundance and environmental factors is examined using generalized additive models fitted to catch and effort data from longline fisheries. The presence of blue marlin, and the catch rate given presence, are modeled separately. Latitude, longitude, and sea‐surface temperature explain the greatest proportion of the deviance. Spatial distributions of relative density of blue marlin, based on combining the probability of presence and relative density given presence, indicate that there is seasonal variation in the distribution of blue marlin, and that the highest densities occur in the tropics. Seasonal patterns in the relative density of blue marlin appear to be related to shifts in SST. The distribution and relative abundance of blue marlin are sufficiently heterogeneous in space and time that the results of analyses of catch and effort data to identify ‘hotspots’ could be used as the basis for time‐area management to reduce the amount of blue marlin bycaught in longline fisheries.  相似文献   

13.
  1. In the south‐eastern Pacific Ocean, few studies of whale sharks (Rhincodon typus) exist. In Peru, the northern coast has been identified as the area with the highest presence of whale sharks, yet their ecology in this area is poorly defined.
  2. This study predicts the spatial distribution of whale sharks off coastal northern Peru (03°00′S–04°30′S) during La Niña and El Niño seasonal conditions, utilizing maximum entropy modelling. Between 2009 and 2018 (except for 2011), 347 whale sharks were geo‐referenced in northern Peru with greatest data recordings in the austral summer and spring during La Niña events.
  3. Depth was the most important predictive variable for spatial distribution of whale sharks, followed by chlorophyll‐a. Sharks were predicted in shallower coastal waters in which chlorophyll‐a values are higher.
  4. Habitat suitability was higher in the northern coastal part of the study area. Spring presents the most suitable environmental conditions for whale sharks, both during La Niña and El Niño conditions. The probability of whale shark presence in the north of Peru increases at higher chlorophyll‐a and sea surface temperature values. Therefore, whale sharks appear to aggregate seasonally in northern Peru, potentially exploiting rich foraging grounds.
  5. In these areas of high suitability, whale sharks are susceptible to fisheries, bycatch, ship collisions, unmanaged tourism, and pollution; thus, management actions should focus in these areas.
  6. This study represents a first step to understand the distribution and habitat suitability of whale shark in Peruvian waters. Further studies should identify suitable habitat for whale sharks in offshore areas. Also, these should focus on the connectivity of these aggregations with other localities in the south‐eastern Pacific in order to contribute to regional strategies for the conservation of this iconic species in this particular region.
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14.
热带东太平洋海域拟锥齿鲨的繁殖生物学特性   总被引：1，自引：0，他引：1  
刘维  戴小杰 《南方水产》2008,4(2):21-25
研究根据科学观察员在热带东太平洋海域2次调查,调查时间和海域分别为2003年7～11月的03°S～17°S,96°W～146°W范围,2006年2～11月的05°N～10°S,134°W～173°W范围。调查共测定了202尾拟锥齿鲨（Pseudocarcharias kamoharai）的样本,并对其进行分析。结果表明,拟锥齿鲨全长（TL）与全重（W）的关系,雌性是W=9×10^-5TL^2.3116,雄性是W=9×10^-6TL^2.9007。其雌雄性比接近1：1。雌性拟锥齿鲨的总性腺重量随体长增加而增加,增加幅度较大;雌性拟锥齿鲨性成熟的最小TL约为89cm,雄性大约在85～100cm。雌体怀仔数量平均为3.85尾。出生时的TL约为40cm左右。  相似文献   

15.
A variety of changes are occurring in the ecosystems of the North Pacific Ocean and Bering Sea, but information about the mechanisms of change has been relatively limited, due in part to the region’s remoteness and subarctic conditions. Any number of ecosystem components or indicators could be used to exemplify this dilemma, but here we point to the salmon shark (Lamna ditropis, Lamnidae) as an example of a species that can potentially mediate considerable ecosystem change due to its high trophic level, but for which some basic information is lacking despite attracting some interesting research and widespread rumours and anecdotal evidence of increased abundance. Increases in the abundance of sharks such as salmon sharks in this region during the 1990s, if true, may help explain other observed changes such as declines in ocean survival rates of Pacific salmon (Oncorhynchus spp., Salmonidae) in the region and declines in some wild salmon stocks. Mechanisms that could cause salmon shark increases in Alaskan coastal waters include: (i) increases in sea temperature since the 1970s allowing distributional shifts of this species and changes in the abundance or distribution of their prey; (ii) the 1992 banning of high seas drift gillnets; and (iii) indirect fisheries effects such as competitive release of salmon sharks in the North Pacific transition region and towards the more southern geographic extent of their annual migration as the result of fishery‐related reductions in blue sharks (Prionace glauca, Carcharhinidae) and other pelagic predators. The relative plausibility of these alternative explanations can be evaluated using combinations of existing ecosystem models and empirical research and monitoring programmes including local and indigenous observations.  相似文献   

16.
Understanding large‐scale migratory behaviours, local movement patterns and population connectivity are critical to determining the natural processes and anthropogenic stressors that influence population dynamics and for developing effective conservation plans. Atlantic tarpon occur over a broad geographic range in the Atlantic Ocean where they support valuable subsistence, commercial and recreational fisheries. From 2001 through 2018, we deployed 292 satellite telemetry tags on Atlantic tarpon in coastal waters off three continents to document: (a) seasonal migrations and regional population connectivity; (b) freshwater and estuarine habitat utilization; (c) spawning locations; and (d) shark predation across the south‐eastern United States, Gulf of Mexico and northern Caribbean Sea. These results showed that some mature tarpon make long seasonal migrations over thousands of kilometres crossing state and national jurisdictional borders. Others showed more local movements and habitat use. The tag data also revealed potential spawning locations consistent with those inferred in other studies from observations of early life stage tarpon leptocephalus larvae. Our analyses indicated that shark predation mortality on released tarpon is higher than previously estimated, especially at ocean passes, river mouths and inlets to bays. To date, there has been no formal stock assessment of Atlantic tarpon, and regional fishery management plans do not exist. Our findings will provide critical input to these important efforts and assist the multinational community in the development of a stock‐wide management information system to support informed decision‐making for sustaining Atlantic tarpon fisheries.  相似文献   

17.
Striped marlin (Kajikia audax) is an epipelagic species distributed in tropical and temperate waters of the Pacific Ocean. In the central and eastern Pacific Ocean, it is captured principally in commercial longline fisheries, and in small artisanal fisheries, however, it is also taken throughout its range in this region as an incidental catch of the tuna purse‐seine fishery. Previous studies suggest that overexploitation and climate change may reduce abundance and cause changes in spatial distributions of marine species. The main objective of this study was to describe the habitat preferences of striped marlin and the changes in its distribution in response to environmental factors. Habitat modeling was conducted using a maximum entropy model. Operational level data for 2003–2014, collected by scientific observers aboard large purse seine vessels, were compiled by the Inter‐American Tropical Tuna Commission and were matched with detailed (4 km) oceanographic data from satellites and general circulation models. Results showed that the spatial distribution of habitat was dynamic, with seasonal shifts between coastal (winter) and oceanic (summer) waters. We found that the preferred habitat is mainly in coastal waters with warm sea surface temperatures and a high chlorophyll‐a concentration.  相似文献   

18.
The distribution of egg and larvae of mackerel, horse mackerel, sardine, hake, megrim, blue whiting and anchovy along the European Atlantic waters (south Portugal to Scotland) during 1998 is described. Time of the year, sea surface temperature and bottom depth are used to define the spawning habitat of the different species. Mackerel, horse mackerel, and sardine eggs and larvae presented the widest distribution, whereas megrim and anchovy showed a limited distribution, restricted to the Celtic Sea and the Bay of Biscay respectively. Correspondingly mackerel, horse mackerel and sardine showed the highest aggregation indices. Blue whiting larvae were found at the lowest temperatures, whereas anchovy eggs and larvae were found in the warmest waters. The analysis is a basis for evaluation of ongoing changes in the pelagic ecosystem of the north‐east Atlantic.  相似文献   

19.
  • 1. Fishing spans all oceans and the impact on ocean predators such as sharks and rays is largely unknown. A lack of data and complicated jurisdictional issues present particular challenges for assessing and conserving high seas biodiversity. It is clear, however, that pelagic sharks and rays of the open ocean are subject to high and often unrestricted levels of mortality from bycatch and targeted fisheries for their meat and valuable fins.
  • 2. These species exhibit a wide range of life‐history characteristics, but many have relatively low productivity and consequently relatively high intrinsic vulnerability to over‐exploitation. The IUCN — World Conservation Union Red List criteria were used to assess the global status of 21 oceanic pelagic shark and ray species.
  • 3. Three‐quarters (16) of these species are classified as Threatened or Near Threatened. Eleven species are globally threatened with higher risk of extinction: the giant devilray is Endangered, ten sharks are Vulnerable and a further five species are Near Threatened. Threat status depends on the interaction between the demographic resilience of the species and intensity of fisheries exploitation.
  • 4. 4. Most threatened species, like the shortfin mako shark, have low population increase rates and suffer high fishing mortality throughout their range. Species with a lower risk of extinction have either fast, resilient life histories (e.g. pelagic stingray) or are species with slow, less resilient life histories but subject to fisheries management (e.g. salmon shark).
  • 5. 5. Recommendations, including implementing and enforcing finning bans and catch limits, are made to guide effective conservation and management of these sharks and rays.
Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

20.
大青鲨(Prionace glauca)是一种分布广泛的大型中上层远洋性鲨鱼,在以金枪鱼等经济鱼种为目标的延绳钓渔业中渔获率较高.根据中国远洋延绳钓渔船2015—2018年在中西太平洋(Western Central Pacific Ocean,WCPO)海域共51个航次采集的兼捕大青鲨数据,分析了该海域兼捕到的大青鲨...  相似文献   

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