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1.
Density,biomass and community structure of demersal fishes off the Pacific coast of northeastern Japan 总被引：8，自引：0，他引：8
Demersal fish communities were studied on the lower continental shelf and the upper continental slope along the Pacific coast of northeastern Japan. Species composition, number and weight of each species were examined based on otter trawl samples at 45 stations. Mean density and biomass of demersal fishes were 131 ha–1 and 21 kg ha–1, respectively. The ten most abundant species comprised of about 95% of total number and weight of overall catch indicating simple species composition. Gadiform fishesTheragra chalcogramma, Gadus macrocephalus andPhysiculus maximowiczi were the most important species by number, weight and frequency of occurrences, and three main community types represented by the three key species were recognized.Theragra-dominant community showed higher density and biomass, and lower diversity thanPhysiculus-dominant community did. Species diversity of demersal fish community was negatively correlated to density and biomass. Density and biomass of demersal fish community were high on the uppermost slope, and the high abundance resulted from low-diversity communities dominated byT. chalcogramma andG. macrocephalus. 相似文献
2.
为了研究春季长江口外海底层鱼类群聚特征及其与环境因子的关系,我们根据2015年5月长江口外海底层鱼类的调查资料,使用聚类分析(Cluster)、非参数多维标度排序(NMDS)、相似性分析(ANOSIM)、相似性百分比分析(SIMPER)以及典型对应分析(CCA)等方法对资料进行分析。本研究共记录底层鱼类58种,其中鲈形目种类数最多(21种),鲽形目次之。六丝钝尾虾虎鱼(Amblychaeturichthys hexanema)是优势种。底层鱼类可以划分为3个群组—近海组、南部中间组和南部远海组,不同群组的物种组成差异显著。南部中间组和南部远海组的物种多为东海外海种类,这可能是近岸黑潮底层分支影响的结果。物种数、Margalef丰富度、Shannon-Wiener多样性和Pielou均匀度从近海到与远海呈逐渐增加的趋势。CCA分析表明深度是显著影响底层鱼类的环境因子。短鳄齿鱼(Champsodon snyderi)、丝鳍(Repomucenus virgis)、多棘腔吻鳕(Coelorinchus multispinulosus)等东海外海种类与深度呈正相关,而优势种六丝钝尾虾虎鱼受环境因子影响较小。 相似文献
3.
Twice monthly sampling over two 16 month periods at a shallow site on Newfoundland's east coast showed the fish assemblage to be dominated by four taxa (Gasterosteus aculeatus, G. wheatlandi, Osmerus mordax, Gadus spp.) that accounted for 96% of the individuals collected. Of the 16 479 fish measured, 65% were adults based on the estimated size of first spawning. The fish assemblage was dominated (86%) by species with demersal eggs, several of which spawn at the same shallow sites used by juveniles as nursery sites. Coastal spawning and demersal eggs maintain offspring in coastal nursery areas where survival is thought to be increased. Number of species and number of fish were both correlated with water temperature being highest from mid-summer to early autumn and lowest in winter. Temperature, time of spawning, and movements of juveniles and adults facilitated grouping species into five assemblages based on seasonal abundance: seasonal periodic species (summer and winter), regular species, regular species collected in all seasons except winter, and occasional (rare) species. At the diel scale, two consistent species groupings were observed: species that showed no significant difference between day and night and species caught primarily at night. Number of night species exceeded day species by a factor of two. No seine-caught species in shallow water exhibited significantly higher catches during the day. Observations by SCUBA divers indicated some species were more abundant during day time at slightly deeper depths. This observation in conjunction with day and night seining in shallower water, suggests these species aggregate in deeper water during day and move to shallow waters at night. 相似文献
4.
The concept of essential fish habitats (EFHs) is widely accepted for conservational and management purposes. EFHs are often considered as high quality habitats for fisheries species and subsequently of high values for society. In this study, fish and Substrate-Associated Prey (SAP) were sampled during the productive summer season 1998 (fish) and 2003 and 2004 (SAP) in shallow coastal rocky- and soft-bottom habitats on the Swedish west coast. The aim was to study the spatial and monthly variation of SAP as well as abundance and biomass of fish, and to examine if food items found in the diet of the fish assemblage were derived from SAP. We also examined if the diet of Ctenolabrus rupestris, a resident and abundant fish species in the shallow coastal habitats, and the diet of four seasonally abundant and commercially important fish species (Gadus morhua, Pleuronectes platessa, Salmo trutta and Scomber scombrus) were derived from SAP. There were significantly higher mean species number and abundance of the SAP assemblage on rocky compared to soft bottoms and the highest values were found on the rocky bottoms in August and in the shallowest (0–3 m) depth strata. There were no significant differences in number of fish species caught in the two habitats, although mean number of fish and mean biomass were significantly higher on rocky bottoms. Both habitats showed the same seasonal variation and the highest values of number of fish species, abundance and biomass were observed in June. On rocky bottoms, gastropods and amphipods were the most frequent food items in the diet of the entire fish assemblage and these items were also the most abundant SAP in this habitat. The dominant food items of the soft-bottom fish assemblage were decapods and fish, which were not common SAP. However, except for S. scombrus, the diet of the selected fish species showed a strong association to the SAP availability. Gadus morhua displayed the strongest association to SAP on rocky bottoms and P. platessa and C. rupestris to SAP on soft bottoms. Further, for C. rupestris, multivariate statistical analysis showed a significant association to the SAP assemblage on both rocky and soft bottoms. These results provide vital new information for the management and conservation of Essential Fish Habitats on the Swedish west coast. 相似文献
5.
《Estuarine, Coastal and Shelf Science》2003,56(3-4):503-515
The degree of relationship between trawl catch and environmental variables was assessed in a bay-estuarine system of Goa, west coast of India using multivariate techniques. The demersal fish assemblage was dominated by the families, Leiognathidae, Sciaenidae, Clupeidae, Cynoglossidae and Stromateidae and were considered to be typical for the Indo-Pacific. Patterns in community-structure were analyzed by principal component analysis (PCA) which identified five major species-groups that explained 66% of the variation in absolute fish biomass. PCA was also performed using 13 environmental variables to reduce data set variability to four components which accounted for 75% of environmental variation. The model that best explained variation in absolute biomass based on maximum R2 (adjusted) and minimum Mallows' Cp statistic was 71% and included six variables such as dissolved oxygen, macrobenthic density, sediment pH, photosynthetic pigment (Chl a), particulate organic carbon (POC) and seston. The regression coefficients were significant (P<0.05) and small values of Cp indicated the preciseness of the developed model. Path analysis was used to construct a hypothetical causal path diagram to depict the interaction between fish biomass and environmental variables. The study demonstrated the most important variables with regard to environmental–biotic interactions, although the measured variables did not account for all the variation in trawl catches. Further studies elucidating ecologically meaningful relationships should be helpful in bay-estuarine fisheries management. 相似文献
6.
《African Journal of Marine Science》2013,35(1):635-649
Demersal fish communities off southern Namibia were analysed on the basis of seven winter and five summer stratified random sampling cruises between 1983 and 1990. The 37 most abundant species selected for analysis represented 78-&ndash96 per cent of the total estimated biomass. The biomass of most of them decreased over the period of study. However, the decreases were only substantial for winter cruises; the fluctuations recorded on the summer cruises appeared to be more closely related to hydrographic conditions. In relatively cool summers the estimated biomasses of seven species (including Merluccius capensis and Lophius vomerinus) were quite similar to, or lower than, the biomasses estimated six months earlier. In contrast, the estimated biomasses of the same seven species during relatively warm summers were distinctly higher than the estimates made the previous winter. In all, 10 species, including the commercially important Austroglossus microlepis, Lophius vomerinus and Merluccius capensis, were more available to bottom trawls in summer than in winter. Multivariate analysis revealed several distinct assemblages separated by latitude and depth, but with seasonal variation. Similarity indices between cruises were high (mean Schoener index around 0,7), indicating that changes in biomass do not affect the structure of the demersal fish community. It is suggested that, although the high levels of fishing effort deployed in the region lowered the total fish biomass, community stability, expressed as absence of change in species assemblages, was significantly high. 相似文献
7.
The composition of the demersal nekton assemblage inhabiting the Mediterranean shelf-break of west-central Italy was examined to investigate the diel variation in species composition and abundance. Fish were obtained during four 24-h sampling periods that represented the four annual seasons. Thirty-two hauls (eight in each season) were conducted in a shelf-break area at 140–160 m depth. The density of fish, crustaceans, and decapods exhibited differences on short- and long-term time scales: multidimensional scaling suggested that season and light intensity may be important factors influencing fish assemblage composition.At the diel scale two main assemblages separating nocturnal and diurnal hauls were identified. The typical assemblage structure of shelf-break bottoms was represented during daylight by species such as Merluccius merluccius, Capros aper, Serranus hepatus, Macroramphosus scolopax and Trisopterus minutus capelanus. At night, the assemblage showed a drastic change due to the increase of small nektobenthic species, Argentina sphyraena and Glossanodon leioglossus, together with cave-dwelling fish (Gnathophis mystax, Chlopsis bicolor, Nettastoma melanurum) and nektobenthic crustaceans (i.e., Parapenaeus longirostris and Solenocera membranacea).The above-mentioned differences in species composition may be related to changes in vertical distribution for trophic needs (M. merluccius) and/or in the shoal structure (A. sphyraena and G. leioglossus). The lack of data on the pattern of trawl catchability of Mediterranean species during the day may lead to an inaccurate estimation of species abundance when only diurnal trawl survey data are used. 相似文献
8.
根据2019年1月、4月、7月和10月四个季度10个站位定置张网调查资料, 对福建三沙湾游泳动物的种类组成及季节变化进行分析研究。结果表明: 调查共获得游泳动物209种, 隶属于3门4纲19目73科144属, 其中鱼类154种, 甲壳类48种, 头足类7种。游泳动物种类数以秋季出现最多, 四个季节共同出现的种类有42种。鲈形目种类最多, 其次是十足目。鱼类适温性以暖水性种类居多, 占71.43%, 暖温性种类次之(27.92%); 生态类型以底层、近底层鱼类居多, 两者合占75.97%。鹰爪虾(Trachypenaeus curvirostris)、大黄鱼(Larimichthys crocea)、棘头梅童鱼(Collichthys lucidus)、红星梭子蟹(Portunus sanguinolentus)和日本蟳(Charybdis japonica)等14个种类是三沙湾游泳动物的优势种类, 季节性优势种居多。三沙湾定置张网调查渔业资源质量密度为111.09 kg/km2, 尾数密度为13.72×103 ind./km2, 均以夏季最高, 春季最低。应该进一步加强对三沙湾渔业资源的合理利用和有效保护, 同时重视对外来物种的监测。 相似文献
9.
《Oceanologica Acta》1999,22(3):353-364
The Bay of Guaratuba, whose area is approximately 45 km2, is a basin, situated to the south of Brazil (25° 52′ S; 48° 39′ W) and connected to the Atlantic ocean. In its northern part, a region of mangrove is found, under the influence of seasonal fluvial contributions, dominated by Laguncularia racemosa. The depth exceeds 6 m in some places. According to the period of the year, salinity varies between 3 and 37, and temperature between 15 and 28 °C. Several of the present fish species are exploited by commercial and recreational fisheries. This work describes characteristics of the fish populations occupying this mangrove, and temporal and spatial evolution of populations of the main species from available data on their biology. Between September 1993 and August 1996, fish samplings have been undertaken monthly by trawl, according to the same fishing effort (20 min), in channels of this ecosystem. Size, numerical abundance and weight of each individual of species were measured, as well as surface and bottom temperatures and bottom salinity. Species richness, Shannon-Weaver's diversity index were calculated and abundances were processed by the multivaried analysis. The global species richness is 61 species, distributed in 28 families; the better represented species are Sciaenidae (10), Gerreidae (5), Carangidae (5), Ariidae (4), Haemulidae (3), Serranidae (3), Bothidae (3). Each year, the number of species varies between 41 and 44, and a group of eight species represents between 80 to 90 % of the density and 75 % of the biomass. The constancy of this dominance is the main characteristic of this fish assemblage. The most represented species in abundance is Pomadasys corvinaeformis is the first two years, then Stellifer rastrifer. The group of eight main species is shared by 15 species in total, of which 13 for the density and 14 for the biomass. The most important monthly catches take place in winter season, during which one observes a decrease of water temperature and an increase of salinity. These species, however, being likely to be replaced by others according to the year or the season; one never finds the same composition in the assemblage which preserves always the same structures. Seasonal differences between seasons under marine (winter) and continental (summer) influences play a major role on the dynamics of fish in the Guaratuba mangrove. This ecosystem plays a functional role in the achievement of the life cycle of many permanent or temporary species. Those having succeeded to reach high levels of abundance are not represented in a uniform way in the course of the year, even when they reside permanently in the ecosystem. Periodic displacement strategies for self regulation of stocks abundance, are necessary mechanisms for these populations, which thus success to coexist in occupying the mangrove. 相似文献
10.
F. Martinho M. Dolbeth I. Viegas C.M. Teixeira H.N. Cabral M.A. Pardal 《Estuarine, Coastal and Shelf Science》2009,83(4):460-468
The recruitment variability of the marine fish species Dicentrarchus labrax, Platichthys flesus and Solea solea was evaluated in the Mondego estuary (Portugal) from 2003 to 2007. The relationships between sea surface temperature, NAO index, coastal wind speed and direction, precipitation and river runoff prior to the estuarine colonization and the abundance of 0-group fish were evaluated using gamma-based Generalized Linear Models. Dicentrarchus labrax and P. flesus 0-group decreased in abundance towards the end of the study period, while S. solea, despite low abundance in 2004, increased in abundance in 2007. For D. labrax, river runoff, precipitation and east–west wind were significant; for P. flesus, precipitation, river runoff and both north–south and east–west wind components were significant parameters, while for S. solea only river runoff was important. Results were compared with recent projections for climate change scenarios, to evaluate their effects on future recruitment levels. 相似文献
11.
杜建国 王彦国 PERISTIWADY Teguh 廖建基 MAKATIPU Petrus Christianus HUWAE Ricardo 鞠培龙 LOH Kar Hoe 陈彬 《海洋学报(英文版)》2018,37(12):63-72
本文以印尼北苏拉威西东部的潟湖为对象，研究了热带海草床鱼类群落的种类组成和时空变化。研究发现当地鱼类的香农-威纳指数在1.57-3.69之间多样性相对较高。在科水平，天竺鲷科的丰度（8.27 ind./（100 m2））和生物量（28.49 g/（100 m2））最高。在物种水平，侧带天竺鲷（Apogon lateralis）的丰度最高，环纹圆天竺鲷（Sphaeramia orbicularis）的生物量最大。对于物种的空间变化，潟湖湖顶、湖中和湖口首先聚类在一起，这可能是由于基质类型引起的。干季和湿季的鱼类种类、丰度和生物量均比转换季高，这可能是由较强的季风造成的，强季风为鱼类提供了更适宜的环境和食物。93.1%的鱼类的最大体长小于它们的性成熟体长，暗示了海草床是很多鱼类的育幼场。因此，保护海草床对渔业和资源的可持续利用至关重要。 相似文献
12.
Environmental factors structuring fish composition and assemblages in a small macrotidal estuary (eastern English Channel) 总被引：4，自引：1，他引：3
The fish assemblage structure was analyzed along an estuarine gradient of a small macrotidal estuary (the Canche, France). Fishes were collected every two months between May 2006 and July 2007 from 12 sampling stations using a 1.5-m beam trawl with a 5 mm mesh size in the cod end. To complement this information, sampling was also performed using 15-m fyke nets (8 mm mesh size in the cod end). For each sample, abiotic (temperature, salinity, pH, oxygen, turbidity, river flow, wind speed and depth) and biotic (macro crustacean species abundances) were recorded. Throughout the study, 28 fish species belonging to 20 families were collected. Fish catches were dominated by juveniles, especially Young-Of-the-Year (YOY) for the majority of the species. According to the Index of Relative Importance (IRI), common goby Pomatoschistus microps, flounder Platichtys flesus, sprat Sprattus sprattus, sea-bass Dicentrarchus labrax and plaice Pleuronectes platessa were the most abundant species, together accounting for 99.2% of the total IRI. Estuarine residents (ER = 66.2%) and marine juvenile migrants species (MJ = 31.4%) were the most important ecological guilds. The structure of the fish assemblage and its relationship to environmental variables was examined using multivariate techniques. Cluster and non-metric multidimensional scaling (nMDS) analysis defined six distinct groups in the Canche estuary, which are discriminated by specific species (SIMPER). Spatio-temporal variations in fish assemblage structure reflect the density peaks of the most abundant species. Spearman rank correlations and canonical correspondence analysis (CCA) showed that among the ten environmental variables examined, temperature, salinity and Crangon crangon (a potential predator for YOY fish or prey for older ones) are the three most important factors influencing fish species richness and abundances. Our observations reinforce the idea that certain fish species may have different life history styles in different geographic areas. The present study highlights the necessity of a better knowledge of the connectivity between estuaries and adjacent marine areas. The Canche constitutes an important ecosystem for fishes and as it is subject to little anthropogenic disturbance; its ichthyofauna can be viewed as a reference or normal assemblage for small temperate macrotidal estuaries. 相似文献
13.
《Marine environmental research》2009,67(5):536-547
Marine protected areas (MPAs) could be useful as fisheries management tools for the exportation of pelagic eggs, larvae and adult fish. A decreasing gradient of fish biomass across MPAs boundary may indicate export. We determine whether gradients of decreasing biomass of fish assemblage occurred in Tabarca Marine Reserve over two habitats with different continuity across the boundaries, to test if the patchy nature of the marine environment might act as a barrier for the fish export. In general, significant decreasing gradients in total fish biomass and biomass of some species were observed on P. oceanica and rocky substrates, independently of their different continuity through the reserve boundaries. Changes in the multivariate structure of the fish assemblage were correlated with the distance from integral reserve. All of these results support the hypothesis that the exportation of adult fish from Tabarca Marine Reserve occurs, and this process may influence the surrounding fished areas. 相似文献
14.
Spatial distribution of surgeonfish and parrotfish in the north sector of the Mesoamerican Barrier Reef System 
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下载免费PDF全文 Roberto C. Hernández‐Landa Gilberto Acosta‐González Enrique Núñez‐Lara Jesús E Arias‐González 《Marine Ecology》2015,36(3):432-446
Surgeonfish and parrotfish play an important role in structuring the benthic communities of coral reefs. However, despite their importance, little is known about their distribution patterns in the north sector of the Mesoamerican Reef System. This study evaluated the distribution of these fish in 34 sites in four habitats (lagoon, front, slopes and terrace) along a depth gradient (c 0.5–20 m). These herbivorous fish were assessed by visual censuses. Species dominance was evaluated for each habitat using SIMPER analysis. Habitat characteristics data were collected to determine the relationship between habitat conditions and spatial variations in herbivorous fish (using abundance and biomass as a proxy) via redundancy analysis. The herbivorous fish assemblage had a low density (fish per 100 m2) and biomass (g·100 m?2) in comparison with assemblages in similar studies. In contrast, species richness was high compared with other studies in the Caribbean. Spatial variation of the abundance, biomass and size of herbivorous fish was strongly related to coral and seagrass cover, as well as to depth and rugosity. These four variables were critical in controlling the distribution patterns of the herbivorous fish assemblages. No associations were found between fish and macroalgae or any other benthic group. The present study indicates that the species richness of surgeonfish and parrotfish was not regionally affected by the dominance of macroalgae in the habitats studied. Seagrass beds and the coral reef matrix need to be preserved for the herbivorous fish assemblages to remain healthy and capable of controlling excess macroalgae growth. 相似文献
15.
《African Journal of Marine Science》2013,35(1):823-834
Six species of skates were trawled commonly on the continental shelf off the Southern Cape during routine surveys of demersal fish between 1986 and 1990. Raja miraletus is a small skate found principally in shallow (<50 m) water that feeds mainly on small crustaceans, such as mysids and macrurans. The large Raja alba occurs over most of the continental shelf, is a piscivore throughout its life and preys heavily on flatfish, especially Cynoglossus zanzibarensis. R. cf. clavata is ubiquitous on the shelf but most abundant between 50 and 150 m deep. Feeding predominantly on crustaceans, this skate switches from carids, penaeids and mysids when small to brachyurans and small benthic fish when larger. R. pullopunctata is found over a similar depth range but attains a much larger size. It eats small mysids and macrurans when small, but brachyurans and fish become more important in the diet with increasing size of the predator. R. wallacei is most commonly taken at depths of 80–>200 m, feeds initially on small crustaceans, but switches to fish, including eels, as it grows. The small Cruriraja parcomaculata is found at the edge of the continental shelf and over the upper slope; it preys on small crustaceans, including mysids, isopods and macrurans. The distribution pattern of the skates and their prey suggest overlap in prey taken, the overlap being greatest in those species which feed on crustaceans. The large biomass of skates in the area suggests that they are an important component of the demersal faunal assemblage of the continental shelf there, and also that they may have a significant impact on the benthic fauna. 相似文献
16.
捕捞和气候变化在南海北部湾口鱼类长期种类演替和种群动态的作用 总被引：2，自引：0，他引：2
捕捞压力在改变南海鱼类种类演替和生物量波动方面所起的作用大于气候和环境因素是一个普遍的、有争议的假设。根据1959~2010年南海北部北部湾口底拖网的调查数据，报告了该海域鱼类种类组成、优势类群的丰度比例、生物量的季节和年际变化。建立了鱼类生物量与捕捞压力和气候变化外部因素之间的广义加性模型。结果表明，捕捞压力驱动底层渔业资源急剧下降的主要因素，并随着时间的推移，高值鱼类被低值鱼类所取代。1993年和1998年期间鱼类生物量的突然减少与同期厄尔尼诺事件相对应，气候变化可能是渔业拖网捕捞中中上层鱼类比例变化的主要驱动因素。为了更好地了解鱼类群落动态，需要区分捕捞压力和环境驱动因素对不同生活史策略鱼类物种的影响。 相似文献
17.
Augustine W. Mwandya Martin Gullström Marcus C. Öhman Mathias H. Andersson Yunus D. Mgaya 《Estuarine, Coastal and Shelf Science》2009
Deforestation of mangrove forests is common occurrence worldwide. We examined fish assemblage composition in three mangrove creek systems in Tanzania (East Africa), including two creeks where the upper parts were partly clear-cut of mangrove forest due to the construction of solar salt farms, and one creek with undisturbed mangrove forest. Fish were caught monthly for one year using a seine net (each haul covering 170 m2) within three locations in each creek, i.e. at the upper, intermediate and lower reaches. Density, biomass and species number of fish were lower in the upper deforested sites compared to the mangrove-fringed sites at the intermediate and lower parts in the two creeks affected by deforestation, whereas there were no differences among the three sites in the undisturbed mangrove creek system. In addition, multivariate analyses showed that the structure of fish assemblages varied between forested and clear-cut sites within the two disturbed creeks, but not within the undisturbed creek. Across the season, we found no significant differences except for a tendency of a minor increase in fish densities during the rainy season. At least 75% of the fishes were juveniles and of commercial interest for coastal fisheries and/or aquaculture. Mugil cephalus, Gerres oyena and Chanos chanos were the most abundant species in the forested sites. The dominant species in the clear-cut areas were M. cephalus and Elops machnata, which were both found in relatively low abundances compared to the undisturbed areas. The conversion of mangrove forests into solar salt farms not only altered fish assemblage composition, but also water and sediment conditions. In comparison with undisturbed areas, the clear-cut sites showed higher salinity, water temperature as well as organic matter and chlorophyll a in the sediments. Our results suggest that mangrove habitat loss and changes in environmental conditions caused by salt farm developments will decrease fish densities, biomass and species numbers as well as alter the overall fish assemblage composition in the salt farm area but not downstream in the creek. 相似文献
18.
Freshwater inflow has a strong impact on the biological, chemical and physical characteristics of estuaries, which in turn affect the distribution and abundance of estuarine organisms. Increased climatic variability associated with climate change is predicated to modify precipitation patterns, which will likely intensify floods in estuaries. The demersal fish assemblage of the freshwater-dominated Great Fish Estuary, South Africa, was sampled using beam trawls, monthly, from December 2013 to November 2014. The first six months of the study were characterised by river flooding and high flow, with estuarine conditions found only in the mouth region; this was followed by six months of intermediate flow, with estuarine conditions recorded up to 10 km from the mouth. River flooding and subsequent reduced salinity resulted in a decrease in species richness and abundances of fishes in the estuary, with only two estuarine species (Glossogobius callidus and Psammogobius knysnaensis) and one marine migrant (Solea turbynei) recorded following river flooding (201 m3 s?1), in January 2014. The greatest species richness and abundances among both marine and estuarine fishes were recorded during intermediate flow conditions. We conclude that although freshwater inflow into estuaries is important for the nursery function of these systems, flooding—especially in freshwater-dominated estuaries—may cause a temporary decline in the abundance of most marine and estuarine fish species, including important bentho-pelagic marine migrant fishery species, such as Argyrosomus japonicus and Pomadasys commersonnii. 相似文献
19.
S Swart JJ Zietsman JC Coetzee DG Goslett A Hoek D Needham 《African Journal of Marine Science》2016,38(4):525-538
South Africa’s small-pelagic fishery is a socio-economically important component of the country’s commercial fisheries sector, second in value only to the demersal trawl fishery. Management of this sector relies on infrequent hydro-acoustic surveys, which provide measures of anchovy Engraulis encrasicolus and sardine Sardinops sagax biomass used in the assessments of stock status and in the development of management plans for the sustainable utilisation of these resources. We demonstrate how technological capabilities in ocean robotics at the Council for Scientific and Industrial Research (CSIR) could augment the current resource-intensive hydro-acoustic ship-based survey programme and create opportunities for expanding its spatial and temporal resolution. We successfully implement and demonstrate an autonomous wave glider, fitted with a hydro-acoustic sensor and compare the data to a collocated ‘traditional’ ship-based acoustics survey. In the future these autonomous systems approaches could be seen as a means to lessen the cost burden of the ship-based survey, while at the same time with the added advantage of continuous collection over much wider spatial and temporal domains. This could enable a more reflexive stock management approach taking into account the seasonal characteristics of the fishery and its ecosystem. Gliders thus have potential to increase dramatically the quantity of information available to fisheries managers, thereby reducing uncertainty and contributing to improved management of valuable fish resources. They are likely to contribute to improved knowledge of the ecology of small pelagic fish species off the coast of South Africa in a changing climate and should potentially also permit the collection of biomass data for other marine resources currently not routinely monitored. 相似文献
20.
《African Journal of Marine Science》2013,35(3):491-499
This study provides one of the first quantitative assessments of a fish community within a pre-operational deep-water port system. Between September 2006 and September 2007 a total of 4 559 fish, representing 47 species and 27 different families, were caught within the Port of Ngqura, Africa's deepest port, in 1 713 h of shore-angling (2.3 fish angler?1 h?1) and 239 h of boat-based angling (2.8 fish angler?1 h?1). Catches included species representative of both estuarine and shore fisheries. The majority (83.0%) of species caught were marine and most were less than size-at-50% maturity (71.4%). The most abundantly caught species were dusky kob Argyrosomus japonicus (25.5%), elf Pomatomus saltatrix (24.9%), garrick Lichia amia (17.7%) and dusky sharks Carcharhinus obscurus (10.7%). Fish assemblages differed significantly (p < 0.05) between three habitats within the port: Dolosse, Quay Wall and Sandy Shore. The Dolosse habitat supported the greatest abundance (3.1 fish angler?1 h?1) and diversity (43) of fish species. The Port of Ngqura is thus functioning as an important habitat for both juvenile and adult fish. The diversity and abundance of fish suggests the potential use of ports and other artificial structures for enhancing local fisheries in South Africa. 相似文献