首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 343 毫秒
1.
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   

2.
From 1998 to 2003, we observed large fluctuations in the abundance and distribution of four pelagic predatory (piscivorous) fishes off northern Oregon and southern Washington, USA. Fluctuations in predatory fish species composition and abundance were strongly linked to the date of the spring transition and to ocean temperatures. Predatory fishes, forage fishes, and juvenile salmonids had distinct spatial distributions, with predators distributed primarily offshore and forage fish and salmonids onshore, but this varied depending on ocean conditions. We suggest that predatory and forage fish distributions respond to ocean temperatures, predator/prey interactions, and possibly turbidity. A shift in ocean conditions in 1999 decreased overall predator fish abundance in the Columbia River plume, particularly for Pacific hake. Marine survival of juvenile salmon started to increase in 1999, and forage fish densities increased in 2000, lagging by one year.  相似文献   

3.
根据第4次中国北极科学考察在白令海与楚科奇海进行的鱼类拖网调查资料,分析了白令海与楚科奇海鱼类生物的种类组成、优势种、物种多样性和区系特征,探讨了鱼类生物对北极气候快速变化的响应。结果表明,白令海与楚科奇海两个海域共鉴定鱼类生物14科41种;主要优势种类为粗壮拟庸鲽(Hippoglossoides robustus)、北鳕(Boreogadus saida)、短角床杜父鱼(Myoxocephalus scorpius)、斑鳍北鳚(Lumpenus fabricii)、粗糙钩杜父鱼(Artediellus scaber);从适温性来看,冷水性种类最多,有35种,冷温性种类6种;从栖息地生态类型来看,底层鱼类、近底层鱼类和中上层鱼类分别为35、5和1种;Shannon-Wiener多样性指数平均为1.21,呈现南高北低的特点,整体多样性水平不高;气候变化引起部分北极、亚北极海区鱼类出现不同程度的纬向和纵向移动,由此将引起北极渔业资源分布格局的变化。  相似文献   

4.
The diverse pelagic fish assemblage of sub-tropical southern Queensland includes fishes with predominantly temperate distributions, such as tailor Pomatomus saltatrix, sardine Sardinops sagax, round herring Etrumeus teres, and Australian anchovy Engraulis australis. The peak spawning seasons of P. saltatrix, S. sagax and E. teres occur during late winter and early spring (June–October). Eggs and larvae of these three species are widely distributed in shelf waters and comprise >50% of the ichthyoplankton assemblage during this period. Mean monthly sea surface temperatures (SSTs) during late winter and early spring range from 21 to 23 °C, and are thus similar to those recorded in southern Australia during summer and autumn, which is the spawning season of these three species in those temperate waters. E. australis eggs occur mainly in inshore waters, and comprise >50% of fish eggs collected during summer and autumn when mean monthly SSTs in southern Queensland exceed 27 °C. E. australis also spawns mainly during summer and autumn in temperate Australia. Hence, water temperature may be less important as a determinant of the spawning season of E. australis than it is for the other three species. The suitability of southern Queensland for spawning by predominantly temperate species during late winter and early spring may contribute to the high diversity of the region's pelagic fish assemblage. Adult P. saltatrix, S. sagax and E. teres appear to migrate northwards into southern Queensland during early winter to spawn, and larvae may be transported southwards into temperate waters by the East Australian Current. This dispersal-migration pattern is similar to those observed for several species, including P. saltatrix, in the western boundary current systems off the east coasts of North America and Africa. Hence, pelagic fishes in ecosystems off the east coast of three continents migrate into sub-tropical waters to spawn, and larvae are transported back into temperate nursery areas by the prevailing current.  相似文献   

5.
Eye migration, asymmetrical pigmentation, and a 90° rotation in posture are developmental changes that unify all flatfishes and facilitate a transition from a pelagic to a benthic existence. Settlement places the fish in new environmental conditions which may require different types and levels of performance for survival compared to those needed in the water column. Since structure and performance vary as a consequence of ontogeny, it is likely that natural selection has acted on the ontogeny of flatfishes differently from fishes that do not settle (pelagic fishes) to provide different survival skills by the time flatfishes settle. This paper provides examples of quantitative methods for comparing fish ontogenies in the context of three predictions: (1) different flatfish species undergo settlement at a common ontogenetic state; (2) they have a common set of skills at settlement that differ from those of pelagic species of the same ontogenetic state; and (3) skills or features that appear earlier in the ontogenetic program of flatfishes than in pelagic fishes suggest attributes that are important to survival in a benthic habitat. Preliminary comparisons suggest that flatfishes may have accelerated development of their mechanosensory system relative to pelagic species. Firm conclusions about ecologically important differences between the pelagic and benthic habitats derived from analyses of ontogenetic events will require more kinds of data from a broader selection of species.  相似文献   

6.
秋季黄海中南部鱼类群落对饵料生物的摄食量   总被引：8，自引：0，他引：8  
研究鱼类与饵料生物之间食物定量关系进而为多鱼种资源评估提供依据,2000~2002年秋季(10~11月)在黄海中南部海域进行了定点底拖网调查,应用Eggers模型,计算了带鱼(Trichiurus lepturus)、小黄鱼(Pseudosciaena polyactis)、黄(Lophius litulon)、细纹狮子鱼(Liparis tanakae)等23种鱼类在秋季对饵料生物的摄食量。结果表明:黄海中南部23种鱼类在秋季对饵料生物的总摄食量约为309万t,其中,鱼(Engraulis japonicus)的摄食量最高(在250万t以上),占总摄食量的80.9%。中上层和底层鱼类对饵料生物的摄食量分别为262万t和47万t左右,占总摄食量的84.7%和15.3%,鱼和细纹狮子鱼分别是中上层和底层鱼类中最主要的捕食者。磷虾类是中上层鱼类最主要的食物来源,其次是桡足类、端足类和毛颚类;虾类和鱼类是底层鱼类最主要的食物来源,其次是磷虾类。太平洋磷虾(Euphausia pacifica)、中华哲水蚤(Calanus sinicus)、细长脚虫戎(Themisto gracilipes)、脊腹褐虾(Crangon affinis)和鱼同时是黄海中南部被摄食量最高的5种饵料生物,它们被摄食的生物量之和约为233万t,占总摄食量的75.5%。  相似文献   

7.
Based on trawl surveys in the Bering Sea and Chukchi Sea during the 2010 Chinese National Arctic Research Expedition, fish biodiversity characteristics, such as fish composition, dominant species, biodiversity, and faunal characteristics were conducted. We also discussed the responses of fishes to the quick changes in Arctic climate. The results showed that a total of 41 species in 14 families were recorded in these waters. The dominant species were Hippoglossoides robustus, Boreogadus saida, Myoxocephalus scorpius, Lumpenus fabricii, and Artediellus scaber. There were 35 coldwater species, accounting for 85.37%, and six cold temperate species, occupying 14.63%. The habitat types of fish could be grouped as follows: 35 species of demersal fishes, five benthopelagic fishes, and one pelagic fish. The Shannon–Wiener diversity index(H)(range between 0 and 2.18, 1.21 on average) was not high, and descended from south to north. Climate change has caused some fishes to shift along their latitudinal and longitudinal distribution around the Arctic and Subarctic areas, and this could lead to the decline of Arctic fishery resources.  相似文献   

8.
闽南及闽中近海常见鲨鳐类肝油的脂肪酸组成   总被引：5，自引：0，他引：5  
刘晓春  丘书院 《海洋学报》2001,23(2):100-108
闽南及闽中近海鲨鳐类肝油的脂肪酸组成相似,主要的脂肪酸包括16:0(14.9%～23.7%),18:0(5.3%～10.4%),18:1ω9(8.6%～16.9%),16:1(3.4%～7.5%),20:4ω6(3.8%～14.7%)和22:6ω3(10.7%～36.9%).22:6ω3在分析的所有种类(基齿鲨Hypoprion sp除外)均是含量最高的脂肪酸成分.可见,闽南及闽中近海鲨鳐类肝油是22:6ω3良好的来源.底层生活习性种类肝油ω6PUFA的含量高于中上层种类,而中上层生活习性种类肝油22:6ω3的含量以及ω3PUFA与ω6PUFA的比值则相对地高于底层种类,这种现象可能与它们各自的摄食习性有关.  相似文献   

9.
中街山列岛岩礁海域鱼类群落多样性研究   总被引：2，自引：0，他引：2  
汪洋  吴常文 《海洋与湖沼》2015,46(4):776-785
加快包括岛礁海域鱼类资源在内的渔业资源调查研究,可以进一步完善该区域鱼类群落生态学内容,探究岩礁海域生境生态学功能,为该海域鱼类资源的养护修复、可持续利用和有效管理提供科学依据。本文基于2013年11月—2014年10月的中街山列岛岩礁海域鱼类资源调查数据,对研究区域鱼类组成及群落多样性分析,结果如下:全年渔获鱼类49种隶属9目28科42属,暖水种和暖温种分别为25和24种,底层、近底层和中上层鱼类各为12、26和11种,定居种、季节性洄游种和偶见种各为28、19和2种;褐菖鲉为全年的绝对优势种,黄姑鱼年IRI值最大,为37.23;迁移指数分析显示群落7月份稳定性最高;ABC曲线分析显示6月受到的干扰最小,2月受到的干扰最大;流刺网年渔获率和CPUE分别为44.03尾/km、13.43 kg/km,延绳钓作业分别为4.91尾/100钓、1.67kg/100钓;群落多样性指数分析结果显示,Margalef种类丰富度指数2月最低,为2.35,7月最大,为4.93;Shannon-Wiener多样性指数7—8月均值最大,为2.80左右;均匀度指数最大和最小值分别是0.97、0.74;三种多样性指数均呈现随气温升高而增大的趋势,但均匀度指数变化没有前2个指数明显,12月和5月3种指数均有波动现象发生。  相似文献   

10.
南澎列岛近海海域底拖网鱼类组成的季节性变化   总被引：1，自引：0，他引：1  
1991年逐月对南澎列岛近海海域作底拖网调查,共捕获鱼类132种,其中软骨鱼类7种（4目6科6属）,硬骨鱼类125种（10目58科95属）,后 者以鲈形目居多（69种）。全年渔获优质种类为条尾鲱鲤、黑天竺鱼、二长棘鲷、大头狗母鱼、多齿蛇鲻、三线矶鲈、绿布氏筋鱼、多鳞Xi和乔氏台雅鱼等9种,其渔获尾数之和是渔获总数的71．1％。季节性优势种类除全年优势种类外,尚有粗纹Fu、半线天竺鲷、印白姑鱼、静Fu和翼红娘鱼等5种;各种类全的渔获尾数及出现月份数相关,各月份的渔获尾数和渔获种数不相关;渔获物中仅有少量的中上层鱼类（13种）。就适温性而言,该海区鱼类以亚热带性为主并兼有热带性特征,以Shannon、Brillouin、Simpson和McIn-tosh等多样性指标及相应的Hurlbert均匀度指标对逐月样本做估计,这8种指标之间高度显著相关;该海域鱼类的Shannon多样性指标及相应的均匀度指标皆以秋冬季为高,春夏季较低。  相似文献   

11.
Analyses of six years of bottom trawl data collected from Northumberland Strait, southern Gulf of St. Lawrence revealed four major fish assemblages, two of which occurred in the same two geographic areas each year. One of the two persistent assemblages occurred in deeper water off northwestern Prince Edward Island and consisted mostly of demersal fishes. The other persistent assemblage contained a mixture of demersal and pelagic fishes and occurred primarily in shallow water of central Northumberland Strait. Analyses of abiotic (depth, bottom temperature, substratum type) and biotic (presence of American lobster Homarus americanus, northern lady crab Ovalipes ocellatus) factors revealed bottom temperature and catches of lady crab correlate best with the fish assemblage structure each year, but correlation values were low (ρw ≤ 0.48). Combinations of all abiotic and biotic variables only marginally improved the strength of the correlations in four of six years (2002, 2003, 2005, 2006). Changes observed in the Northumberland Strait ecosystem over the six years included an increase in the ratio of pelagic to demersal fishes, disappearance of one of the four assemblages, and increased spatial overlap between the two persistent assemblages, which coincided with an increase in bottom temperature. The increasing importance of pelagic fishes, relative to demersal fishes, suggests a shift in food web structure may be occurring in Northumberland Strait.  相似文献   

12.
Estimates of consumption of fish by breeding seabirds in the southern Benguela region converge on 50–60 × 103 tons of food per year. Total annual avian consumption of food is approximately 15,5 × 104 tons, 74 per cent being taken by species which feed on pelagic prey and most of the rest by species which frequently feed on offal at demersal trawlers. Avian consumption is similar in magnitude to that of Cape fur seals and to the catch of the commercial fishery in the southern Benguela region, but far less than consumption by snoek, squid, and, probably, sharks and jellyfish.  相似文献   

13.
中国近海渔业资源结构特点及演替的研究   总被引：1，自引：0，他引：1  
渔业资源是一种不断变化和更新的生物资源,如能合理地开发和利用可望取得良好的经济、社会和生态效益及永续利用的目的。然而由于人类的过度的开发和利用,加之生态环境的日趋恶化,使得许多渔业资源遭到破坏而严重衰退。近十多年来我国渔业与世界渔业发展的总趋势相似,随着捕捞强度的盲目增加,使得许多传统渔业资源遭到不同程度的破坏,主要捕捞对象替代频繁,其结构发生了显著的变化,总趋势是:经济价值高的、个体大的、年龄结构复杂的和在生态系统中营养层次高的类群逐渐被经济价值低的、个体小的、年龄结构简单的和营养层次低的类群所替代;底层鱼类所占比例日益减少,中、上层鱼类及虾、蟹类比例逐年增加。 对渔业资源结构特点和演替规律的研究一直受到国内外学者的重视,许多国家为了保护其近海渔业资源和本国的渔业权益,纷纷宣布建立渔业保护区和专属经济区,并采取了一系列的保护措施,因此近年特别着重研究建立保护区后的渔业资源结构的变化( Gunnar,1989; Megrey and Wespestaa,1990; Pinhorn and Halliday,1990)。我国学者也有许多渔业资源方面的研究报告(中国海洋渔业资源编写组,1990;邓景耀等,1991；孙宗烨等,1987;宋海棠等,1990;罗秉征等,1992;1993)。本文探讨了近40年来我国近海渔业资源结构的特点及其演变规律及趋势,并对我国不同海区渔业资源的演变进行了比较,进而分析了我国海洋渔业资源变化的原因,旨在为更加合理地利用我国的海洋渔业资源,并为其持续发展提供科学依据。  相似文献   

14.
张跃平  洪一川 《台湾海峡》2009,28(3):379-385
本文根据2007年3月至2008年2月期间在泉州地区3个海湾的调查资料，对其浮性鱼卵和仔稚鱼的种类组成与数量分布特点进行初步研究和探讨．结果表明，本调查海域共出现鱼卵和仔稚鱼51种（含未定种），隶属于21科，主要是近岸底层鱼类、近海中上层鱼类和港湾河口型鱼类三个生态类型．各站鱼卵总平均丰度是81．2彬网，仔稚鱼总平均丰度31．0个／网．数量平面分布呈现优势种明显，占总量比例大，不同季节不同海湾差别较大，规律性不强等特点．整体数量上与往年比有下降趋势．  相似文献   

15.
The northern Mid-Atlantic Ridge, from Iceland to the Azores (MAR), is the largest topographical feature in the Atlantic Ocean. Despite its size, few studies have described dietary patterns of pelagic fishes along the MAR. MAR-ECO, a Census of Marine Life field project, aimed to describe the food web structure of abundant fish species along the ridge through a series of research expeditions to the MAR. Among the midwater fishes sampled during the MAR-ECO project, Bathylagus euryops (Osmeriformes: Bathylagidae) was the biomass-dominant pelagic species and ranked third in total abundance. In this paper, we describe the dietary composition of B. euryops along the MAR. Overall, copepods represented the dominant prey group consumed by B. euryops. Multivariate analyses, including a cluster analysis and a canonical correspondence analysis, revealed that fish size significantly influenced the diet of B. euryops with ostracods representing the most important prey group at small sizes (<95 mm) and decapod shrimp and calanoid copepods becoming more important with increasing fish size. Due to the high abundance and biomass observed along the MAR combined with its role as a link for energy transfer between zooplankton and higher trophic level predators, B. euryops appears to be an ecologically important species in the oceanic food web of the North Atlantic Ocean.  相似文献   

16.
The spatial and temporal characteristics of trophic structure of fish communities in the southern Huanghai Sea were examined based on the data sampled from bottom trawl surveys conducted during the autumn of 2000 and the spring of 2001. Hierarchical agglomerative cluster method and bootstrap randomization were used to identify significant trophic groups for each fish assemblage in the southern Huanghai Sea. A total of six major trophic groups were identified within this system, which classified predators based upon location in the water column or prey size （ i. e. , benthic to pelagic predators or fish to small invertebrate prey predators）. The similarity level used to identify significant trophic groups in each assemblage ranged from 24% to 34%. Although planktivores were the dominant trophic group in each assemblage （60% - 79% ）, there were spatial and temporal variations in the trophic structure, which reflected the differences in the abundance and availability of dominant preys. Simplified food webs were constructed to evaluate the most important trophic relationships between the dominant prey taxa and the fishes in each assemblage within this system. Although there were some differences in the key prey species among different food webs, pelagic prey items （mainly euphausiids and copepods） represent the most important energetic link between primary producers and higher trophic level predators. The trophic level for most fishes was between 3 and d, and the weighted mean trophic level for each assemblage ranged from 3.3 to 3.4. Compared with previous study in the mid-1980s, there was an obvious downward trend in the trophic level for most fish species, which resulted mainly from the fluctuation in key prey species in the Huanghai Sea. The decrease in the importance of Japanese anchovy seems to be offset by other abundant prey species such as Euphausia pacifica and copepods （ mainly Calanus sinicus ） .  相似文献   

17.
The Wadden Sea (North Sea, Europe) is a shallow coastal sea with high benthic and pelagic primary production rates. To date, no studies have been carried out in the Wadden Sea that were specifically designed to study the relation between pelagic respiration and production by comparable methods. Because previous studies have suggested that the import of primary-produced pelagic organic matter is important for benthic Wadden Sea carbon budgets, we hypothesised that on an annual average the northern Wadden Sea water column is autotrophic. To test this hypothesis, we studied annual dynamics of primary production and respiration at a pelagic station in a shallow tidal basin (List Tidal Basin, northern Wadden Sea). Since water depth strongly influences production estimates, we calculated primary production rates per unit area in two ways: on the basis of the mean water depth (2.7 m) and on the basis of 1 m depth intervals and their respective spatial extent in the List Tidal Basin. The latter more precise estimate yielded an annual primary production of 146 g C m− 2 y− 1. Estimates based on the mean water depth resulted in a 40% higher annual rate of 204 g C m− 2 y− 1. The total annual pelagic respiration was 50 g C m− 2 y− 1. The P/R ratio varied between seasons: from February to October the water column was autotrophic, with the highest P/R ratio of 4–5 during the diatom spring bloom in April/May. In autumn and winter the water column was heterotrophic. On an annual average, the water column of the List Tidal Basin was autotrophic (P/R 3). We suggest that a large fraction of the pelagic produced organic matter was respired locally in the sediment.  相似文献   

18.
Biomass distribution and trophodynamics in the oceanic ecosystem in the Oyashio region are presented and analyzed, combining the seasonal data for plankton and micronekton collected at Site H since 1996 with data for nekton and other animals at higher trophic levels from various sources. The total biomass of biological components including bacteria, phytoplankton, microzooplankton, mesozooplankton, micronekton, fishes/squids and marine birds/mammals was 23 g C m−2, among which the most dominant component was mesozooplankton (34% of the total), followed by phytoplankton (28%), bacteria (15%) and microzooplankton (protozoans) (14%). The remainder (9%) was largely composed of micronekton and fish/squid. Marine mammals/birds are only a small fraction (0.14%) of the total biomass. Large/medium grazing copepods (Neocalaus spp., Eucalanus bungii and Metridia spp.) accounted for 77% of the mesozooplankton biomass. Based on information about diet composition, predators were assigned broadly into mean trophic level 3–4, and carbon flow through the grazing food chain was established based on the estimated annual production/food consumption balance of each trophic level. From the food chain scheme, ecological efficiencies as high as 24% were calculated for the primary/secondary production and 21% for the secondary/tertiary production. Biomass and production of bacteria were estimated as 1/10 of the respective values for phytoplankton at Site H, but the role of the microbial food chain remains unresolved in the present analysis. As keystone species in the oceanic Oyashio region, Neocalanus spp. are suggested as a vital link between primary production and production of pelagic fishes, mammals and birds.  相似文献   

19.
The proximate chemistry of the white muscle and liver of 18 species of demersal fish from the eastern North Pacific was studied to determine trends with depth, locomotory mode and buoyancy mechanism, foraging strategy and to elucidate energetic strategies. Data for 24 species from shallow water were taken from the literature and included for analysis of muscle water content. Benthopelagic species, primarily gadiforms, have significantly larger lipid-rich livers than benthic species. The benthopelagic species may use this lipid to add buoyancy, but it is also used as energy storage. Buoyancy mechanism was directly related to proximate composition. Fishes using gasbladders had normal muscle composition. The two species of benthopelagic fishes without gasbladders have either very high muscle lipid content (Anoplopoma fimbria) or gelatinous muscle (Alepocephalus tenobrosus) to aid in achieving neutral buoyancy. The macrourid, Albatrossia pectoralis, has a very small gasbladder and also has gelatinous muscle. Both of these benthopelagic fishes with gelatinous muscle feed on pelagic organisms. Gelatinous muscle was also found in two flatfishes that inhabit the oxygen minimum zone. For these fishes, high water content may serve to lower metabolic costs while maintaining large body size. Scavengers such as Coryphaenoides armatus and Coryphaenoides acrolepis have lipid rich livers and others such as A. fimbria and Pachycara sp. have high and variable muscle lipid content. Thus foraging mode also acts to influence proximate composition. Several depth-related trends in proximate composition were found. White muscle water content increased significantly with depth, and all four gelatinous species occurred at bathyal depths. This adds evidence in support of the hypothesis that decreasing light levels shorten reactive distances and relax the selective pressure for high locomotory capacity. In addition significant declines in liver protein content were observed, suggesting that the rates of metabolism in this organ also decline with depth. There was little evidence for food availability affecting proximate composition. There were no significant changes in either muscle or liver lipid or caloric density with depth. Total lipid stores actually increased significantly, but they were driven primarily by the abyssal scavenger C. armatus suggesting that foraging strategy rather than depth may be the most important factor determining total lipid stores.  相似文献   

20.
A particle-size spectrum model is used to estimate standing stocks of some pelagic fish from measurements of phytoplankton chlorophyll in two exploited regions in southern Africa (southern Benguela and off South West Africa/Namibia) and in two unexploited regions (the Agulhas Bank and off the eastern Cape Province). The model is based on the assumption that equal biomasses occur in logarithmically equal size classes in the pelagic marine environment. Phytoplankton, with an equivalent spherical diameter ranging from 1 to 128 μm, occupy 21 size classes on the logarithmic scale. Two different size ranges are assumed for some commercial, pelagic fish species, equivalent to exploitation with two different purse-seine mesh sizes. A mesh of 12,7 mm would catch 8 size classes of pilchard, horse mackerel and anchovy whereas a mesh of 32 mm would catch only 3,3 size classes of pilchard and horse mackerel. From the model, the potential biomass of these commercial pelagic fish is estimated, after allowing for the presence of other commercial and non-commercial fish and other taxa in the exploited size range. Total pelagic fish production is estimated by assuming constant turnover rates of 1·y?1 and 1,5·y?1 when exploited with 32 and 12,7 mm mesh nets respectively. Consideration of the maximum and mean reported catches in the exploited areas indicates that only some 25 per cent of pelagic fish production is exploitable by man. On this basis, the unexploited Agulhas Bank region may yield some 400 000 metric tons (wet) of pelagic fish of the species considered, and the East Coast region some 90 000 tons. Exploitation in these regions cannot be recommended, because the Agulhas Bank is an important spawning ground for many pelagic species, and the fish in both regions probably act as a reserve buffer for the heavily exploited pelagic resource of the Western Cape.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号