共查询到20条相似文献，搜索用时 625 毫秒
1.
Influences of gear type and analytical methodology on fish assemblage characterisations in temperate lakes 
下载免费PDF全文
下载免费PDF全文 C. J. Sullivan D. P. Coulter Z. S. Feiner S. B. Donabauer T. O. Hk 《Fisheries Management and Ecology》2015,22(5):388-399
A variety of gears and analytical methods can be used to characterise lentic fish assemblages; however, the combined influence of gear type and analysis can affect conclusions about assemblage patterns. Fish assemblages sampled with night electric fishing, gillnets and trapnets from 153 lakes were evaluated using summary indices of species composition, pairwise community similarity comparisons and multivariate ordination. For a given amount of effort, electric fishing had the highest species richness, while gillnets had higher diversity and evenness. Pairwise comparisons between gears revealed that (1) richness was positively correlated among all gears, (2) diversity and evenness were generally not correlated across gears and (3) electric fishing and trapnets captured more similar species than all other pairwise comparisons. Gear‐specific multivariate correlation and ordination revealed that gillnet and electric fishing samples more similarly characterised variation in assemblages among lakes, while trapnets characterised assemblages along different gradients of species composition. These results indicate that either electric fishing or trapnetting can be used when assessing shallow‐water assemblages for diversity or evenness, gillnets and either electric fishing or trapnets should be used for whole‐lake assessments, and either gillnets or electric fishing should be used when evaluating regionwide variation in lake assemblages. 相似文献
2.
Abstract Length, life history and ecological characteristics of landed fish communities were studied over a 10‐year period to test theories of fishing disturbance during a time of increased gear and closure management in heavily utilised fisheries. It was predicted that with greater management restrictions: (1) the earliest and fastest responses in the fishery will be seen in those species with faster turnovers, or relatively lower vulnerabilities to fishing; (2) the fishery would transition to a landed catch with higher mean trophic levels, and greater mean body lengths. In addition, the removal of a non‐selective, small‐mesh seine nets should benefit the catch of gears that previously had the greatest species selectivity overlap with the seine net. Many predictions were supported, although maximum lengths and lengths at maturity responded more rapidly than anticipated. The response to eliminating the non‐selective seine net was a more rapid increase in sizes caught by gears with a larger overlap in size (hook and lines) than species selectivity (gill nets). The simultaneous comparison of management systems over time indicates that open‐access fishing grounds can benefit from restrictions imposed in adjacent fishing grounds. The study indicated that multi‐species coral reef fisheries management objectives of maximising yields, as well as maintaining the fish community’s life‐history diversity, require management trade‐offs that balance local socio‐economic and biodiversity needs. 相似文献
3.
Influences of twine diameter and mesh area on the efficiency and durability of baited hoop nets targeting portunids 下载免费PDF全文
下载免费PDF全文 M. K. Broadhurst P. A. Butcher B. R. Cullis D. J. Tolhurst 《Fisheries Management and Ecology》2015,22(6):488-500
The utility of varying twine diameter (0.5–0.8 mm Ø) and/or mesh area (0.5:1) in south‐eastern Australian recreational hoop nets was assessed in response to concerns over (1) impacts to discarded, undersize Scylla serrata L. and Portunus pelagicus Forskål and (2) marine debris (lost meshes). There was a negative relationship between Ø and breakage, with more in the narrowest (16.16–18.42 meshes deployment?1) than thickest (8.79–4.68) twines. Mesh damage was also affected by interactions between netting area and (1) soak time (only S. serrata) and (2) catches, with all nets similarly damaged during <3.5‐h soaks, or when only one crab was caught, beyond which the large‐area nets incurred more. Irrespective of net, there were consistent positive relationships between mesh damage and water temperature, and more damage overnight. Large crabs took longer to remove, but more so from thicker‐twined and large‐area nets, and some also sustained the most damage. Twine diameter did not affect S. serrata catches, but was negatively associated with catches of P. pelagicus, while the small‐area nets caught proportionally (to area) fewer portunids. The results reflect species‐ and size‐specific behavioural variability, but support using thick twine and limiting deployment durations for hoop nets. Alternatively, other less controversial traps might offer a more holistic solution to the stated concerns. 相似文献
4.
南海北部张网主要技术参数的变化分析 总被引：1，自引：0，他引：1
根据2000～2005年和1983～1985年渔具渔法调查资料，对南海北部张网主要技术参数进行了比较分析。结果表明，与1983～1985年相比，现阶段张网网口纲长、网口网目尺寸和网身末段网目尺寸等稍有增大，网衣拉直长、网囊长和网囊网目尺寸等略有减小，网身长与网囊长之比、网身大头宽与小头宽之比等明显增大，其平均值分别由原来的5．8：1、19．8：1增至现在的13．8：1和26．2：1。张网主要技术参数的变化反映了张网渔具结构已经随着渔业资源的衰退发生了变化，但这种变化并不是积极的、革命性的改革。为合理利用渔业资源和促进张网渔业可持续发展，应根据南海北部渔业资源的特点研究相适应的选择性张网捕捞技术或装置，减少对幼鱼、幼虾资源的损害。 相似文献
5.
Blue sucker Cycleptus elongatus (L.) in the upper Yazoo River basin, Mississippi, USA was studied using overnight hoop net sets (n = 4093) during 1988 and 1990–1998 to determine the influence of channel dredging. There were 264 blue suckers captured, ranging from 3 to 11 years of age. Length ranged from 265 to 700 mm and weight from 120 to 4700 g. Concurrent studies with smaller mesh hoop nets failed to capture any juvenile blue suckers. Catch‐per‐unit‐effort (CPUE: fish net?1) declined throughout the study in the Yalobusha River, a river subjected to channel dredging during 1988 and 1994. With the exception of limited hydraulic dredging in the Tallahatchie River, there was no dredging in the other Yazoo River tributaries, nor were there declines in blue sucker catch rates in these rivers. Throughout the upper Yazoo River basin, blue sucker stocks were dominated by adult fish, and there was little evidence of reproduction or recruitment. Conservation of the blue sucker in the upper Yazoo River basin should include actions that ensure the functional integrity of this floodplain river ecosystem and elimination of channel dredging throughout the basin. 相似文献
6.
7.
Estimating abundance is fundamental to effective fishery management but can be challenging in a river where spatial and temporal heterogeneity may preclude the consistent use of a single sampling gear and different gears have differing size selectivity and capture probabilities of fish. In this study, the number of smallmouth bass, Micropterus dolomieu Lacepède, was estimated based on mark–recapture data from angling and boat electric fishing in a 4.2‐km regulated section (mean width = 115 m) of the Broad River, South Carolina, USA. Closed‐population capture–mark–recapture models were fit in the Bayesian hierarchical modelling framework with an estimated number of 2,380 fish (95% credible interval: 1,578–3,693) over 200 mm TL, although simulations indicated that abundance would be slightly overestimated (<20%) when two gears selected for different individuals. Integrating two gear types into a mark–recapture study can provide a method for assessing abundance in spatially or temporally heterogeneous habitats. 相似文献
8.
Giulia Cambiè 《水产资源保护:海洋与淡水生态系统》2011,21(1):28-36
- 1. Trammel nets are one important cause of sea turtle mortality resulting from incidental capture. This study presents findings over a 10‐year period during which loggerhead turtle by‐catch in trammel nets, set off the central west coast of Sardinia (Italy) in the summer months, was recorded by 17 fishing vessels.
- 2. Since the by‐catch registered represented counts of a rare event, data from the 17 vessels were used in the zero‐inflated Poisson (ZIP) model to determine the abundance of turtle by‐catch in trammel nets of the entire fleet, while a binomial generalized linear model was used to assess the probability of immediate survival for sea turtles incidentally caught in this gear.
- 3. The ZIP model quantified in about 45% the probability that 0.6 turtles have been caught by each vessel using trammel nets during summer over the 10‐year period. In addition, the model estimated a total of 916 by‐catch if the entire small‐scale fleet was to use trammel nets in the study area in the summers between 1992 and 2001, with a direct mortality rate of 69%.
- 4. The probability of immediate survival for sea turtles caught in trammel nets seems to be directly related to the size of the specimens caught; however, this relationship is plausible only when incidental capture in the net occurs shortly before gear retrieval.
- 5. The study area represents a region where the abundance of sea turtle by‐catch per vessel in trammel nets was much higher in July and August than in June and could represent a potential hot spot for the presence of juvenile loggerhead turtles, with high levels of interactions between the species and this fishing gear. Further research should better characterize the incidents of by‐catch and assess potential innovative solutions that allow small‐scale fisheries to coexist alongside sea turtles. Copyright © 2010 John Wiley & Sons, Ltd.
9.
10.
Hidekatsu Yamazaki Wataru Aoyama Eiji Masunaga Mamoru Tanaka 《Aquaculture Research》2019,50(4):1107-1116
A field campaign was conducted around salmon cages, using a combination of a towed ADCP and a free‐fall multi‐parameter profiler, in order to investigate flow structures and the possible distribution of effluent materials. Two transect observations showed that hydrographic conditions changed dramatically within 5 days, from highly stratified open water conditions to weak stratification. Three‐dimensional observation revealed that flow was blocked behind the cages and that the blockage was reduced as the distance from the cages increased. The flow speed was positively correlated with the intensity of the backscattering signal. The R2 value was high immediately behind the cages and decreased with distance from the cages. The flow time series behind the cages exhibited a k–2 power law spectrum that was consistent with a typical internal wave spectrum. This suggests that eddies shed from the cages were highly influenced by stratification. We estimated the rate of kinetic energy dissipation, , from YODA Profiler data based on the Thorpe scale approach. We also estimated the eddy diffusivity coefficient, . Both and followed a lognormal probability density function. The mean was consistent with a one‐dimensional diffusion model assessed from the R2 values of flow speed and backscatter intensity. 相似文献
11.
为了提高近海渔业资源养护型捕捞与管理技术,促进《全国海洋捕捞渔具目录》的实施,2014年10-11月在辽东湾进行了网目尺寸为40 mm、50 mm、60 mm的单片刺网、双重刺网和三重刺网以及生产对照网的选择性对比实验.结果显示,各种实验网的渔获种类数均在6-9种之间,优势种口虾蛄(Oratosquilla oratoria)的优势度随网目尺寸的增大而减小,但花鲈(Lateolabrax japonicas)的优势度随网目尺寸的增大而增大.同型试验网在不同网目尺寸条件下的渔获量有显著性差异,其中,60 mm试验网与40 mm同型试验网的单位捕捞努力量渔获量(CPUE)比较,单片刺网为800％,双重刺网为650％,三重刺网为500％;而异型试验网在网目尺寸相同条件下对渔获量的影响相对较小.试验网的组内渔获组成平均相似度分别为单片刺网59.24％,双重刺网62.63％,三重刺网66.51％;组间分别为71.44％、67.50％和70.58％;对组内和组间平均相似度贡献最高的种类均为口虾蛄和花鲈.随着网目尺寸的增大,各型试验网的渔获物幼鱼比例呈下降趋势. 相似文献
12.
Cannibalism is frequently observed in larviculture of orange‐spotted grouper Epinephelus coioides. Previously, based on measurements of morphometric characters, a linear equation of total length (TL) of prey to cannibals was proposed: TLprey = 0.80 TLcannibal – 1.50. To verify the reliability of the equation, experiments were performed with pairs of fish with different TLs. Cannibalism occurred only when the cannibal‐prey size ratios were equal to or larger than that predicted by the equation. To predict the probability of cannibalism among the grouper of known TLs, a logistic regression model was proposed. The logistic regression model is: The logistic regression model showed the following: when either TLprey or TLcannibal is constant, the probability of cannibalism increases with increase in the cannibal‐prey size ratios; if given a constant cannibal‐prey size ratio, probability of cannibalism is lower in early stages than in later stages. The prediction contrasts with that calculated from the linear equation where the minimum cannibal‐prey size ratios decrease with size of the cannibal. However, the prediction matches observed rearing experiences: cannibals prefer smaller prey to larger ones and the cannibalism rate declines as fry age. 相似文献
13.
- 1. Artisanal fishing on coral reefs in Papua New Guinea is an important livelihood activity that is managed primarily at the level of local communities. Pockets of overexploitation exist and are expected to increase with plans for increased commercialization.
- 2. This paper provides a current assessment of the artisanal multi‐species coral reef fishery by examining selectivity of the dominant gear, namely line fishing, spearguns, and gill nets. Each gear has its own strengths and weaknesses in terms of use and conservation of resources, with no clear problem gear.
- 3. The three gears utilize different resources but there was moderate overlap in the species caught, particularly between gill nets and line fishing and marginally between lines and spearguns. Gill nets have the disadvantage of being destructive to coral and the advantage of catching commercial species. Line fishing catches an intermediate number of species but mostly large‐bodied and predatory species that could potentially reduce predation and the mean trophic level of the fishery. Spearguns catch the highest numbers of species, including many non‐commercial and herbivorous fish and could reduce the diversity of fish and encourage algal growth.
- 4. This information could be used in combination with scientific monitoring and traditional ecological knowledge to develop an adaptive management framework that uses local restrictions on the various gears to restore or balance the fishery and ecosystem. Restrictions could be selectively imposed: on gill nets when coral cover is low, line fishing when large‐bodied predators are depleted, and spearguns when biodiversity is reduced and algal abundance high.
14.
利用几何相似原理将传统的过滤性渔具选择性曲线转化为选择性曲面。运用选择性方程，并假设不同网目大小的渔具对相同尺寸渔获个体的渔获服从多项分布后，对过滤性渔具的网目选择性建立模型。使用极大似然估计法对模型进行拟合，同时，通过假设检验对模型进行简化。使用平行作业法试验条件下的张网渔具的黄鲫(Setipinrm taty)渔获数据进行模型拟合。结果显示，所建模型可以在没有对照网的情况下估算出各不同网目大小网囊的选择率，并同样适用于套网法试验条件下的选择性分析。模型的建立为今后进行过滤性渔具网目选择性试验方法改革提供了理论参考。通过与SELECT模型比较，认为模型使用选择性方程并区分渔获能力和捕捞努力量使得模型更具普遍性。 相似文献
15.
Chronic exposure to nitrate significantly reduces growth and affects the health status of juvenile Nile tilapia (Oreochromis niloticus L.) in recirculating aquaculture systems 下载免费PDF全文
下载免费PDF全文 Studies on chronic or acute toxicity of nitrogen species on fish in recirculating aquaculture systems (RAS) usually focused on adverse effects of total ammonia nitrogen (TAN: sum of NH3 + NH4+) and nitrite (), while underestimating the potential effects of high nitrate accumulation on growth and health status of fish. In our study, Nile tilapia (Oreochromis niloticus) were exposed to five different nitrate concentrations (0, 10, 100, 500 and 1000 mg L?1 ‐N) over 30 days. Growth parameters (feed conversion ratio (FCR), specific growth rate (SGR), hepatosomatic index (HSI)), blood samples (concentrations of haemoglobin, methaemoglobin, plasma /) and the histology of the gills were studied to evaluate growth and health status of the fish. At the highest nitrate concentration, the fish showed significantly reduced growth and impaired health status (SGR, FCR, plasma /, haemoglobin and methaemoglobin concentration), demonstrating that too high nitrate concentrations can negatively influence tilapia production in RAS. Here, we recommend not exceeding concentrations of 500 mg L?1 ‐N in juvenile tilapia culture to ensure an optimal health and growth status of the fish, as below that concentration no effects on the tilapia have been observed. 相似文献
16.
近年来,张网渔具渔获中幼鱼比重大的问题突出,而使用放大网目等传统手段在一些场合下并不适用。本研究设计制作了一种新型刚性幼鱼释放装置,该装置由3个框架组合构成、框架使用铰链连接、外型呈Y型,并通过2014年冬季海上测试,分析这一装置对幼鱼的释放效果。海上对比试验结果显示,安装于张网囊头网部、不锈钢材料、栅栏间距2 cm、分隔框架与来流方向呈60°的装置能释放90%的幼鱼并同时保留大部分大个体渔获。该Y型幼鱼释放装置角度可调等特点使其功能得以扩展、适用性增大,可为今后开展过滤性渔具幼鱼释放研究提供参考。 相似文献
17.
Kun Zhao Xiangli Tian Haidong Li Shuanglin Dong Wenwen Jiang 《Aquaculture Research》2019,50(7):1770-1781
A novel marine origin Bacillus subtilis strain H1 isolated from a shrimp culture pond effectively removed NH4+‐N, ‐N and ‐N, with a maximum ammonium, nitrite and nitrate removal rate of 2.35 mg NH4+‐N L?1 hr?1 per OD, 9.64 mg ‐N L?1 hr?1 per OD and 0.75 mg ‐N L?1 hr?1 respectively. The gas chromatography–isotope ratio mass spectrometry results indicated that N2O was emitted when 15NH4Cl, Na15NO2 or Na15NO3 was used. Additionally, N2 was also produced when Na15NO2 was used. Single‐factor experiments suggested that the optimal conditions for NH4+‐N and ‐N removal were glucose as a carbon source, C/N 15, initial pH 7.5, 30 g/L NaCl, 28°C and a shaking speed of 160 rpm. Orthogonal tests showed that the optimal conditions for NH4+‐N removal were C/N 15, pH 9, 10 g/L NaCl and shaking speed 160 rpm when ammonium chloride was used as the substrate. The optimal conditions for ‐N removal were C/N 10, pH 6, 10 g/L NaCl and a shaking speed of 160 rpm when sodium nitrite was used as the substrate. In summary, B. subtilis strain H1 had highly efficient aerobic nitrifying–denitrifying ability and high adaptability, suggesting that it is potentially valuable to marine aquaculture. 相似文献
18.
Ian G. Baird 《水产资源保护:海洋与淡水生态系统》2006,16(5):517-532
- 1. Probarbus jullieni and Probarbus labeamajor are two of the largest carps in the Mekong River Basin, each reaching a maximum weight of about 70 kg. P. jullieni is listed in Appendix 1 of the Convention on the International Trade in Endangered Species, and both are listed on the IUCN Red List of Threatened Species, the first as ‘endangered’ and the second as ‘data deficient’.
- 2. Six years of quantitative monitoring of a large‐meshed gill net fishery for Probarbus just below the Khone Falls in Khong district, Champasak province, in southern Laos shows that 78% of the overall catch is comprised of Probarbus, with P. jullieni making up 65% of landings.
- 3. Over the 6‐year period catches of Probarbus declined significantly. However, catch‐per‐unit effort statistics do not indicate that the fishery is in decline, although fishers are convinced that real stock reductions are a large part of the reason for catch declines and decreases in fishing effort.
- 4. A number of ecological and social factors are affecting the number and quality of gill nets in use, the length of fishing seasons, and gill net efficiency, making it difficult to compare catch‐per‐unit effort between years.
- 5. There has been a shift from using large‐meshed gill nets for catching Probarbus to targeting smaller species using gill nets with smaller mesh‐sizes. This is an example of the ‘fishing down’ of a Mekong fish community, in which large long‐lived species are the first to be affected by heavy fishing pressure.
19.
Characterizing environmental and spatial variables associated with the incidental catch of olive ridley (Lepidochelys olivacea) in the Eastern Tropical Pacific purse‐seine fishery 下载免费PDF全文
下载免费PDF全文 Jose T. Montero Raul O. Martinez‐Rincon Selina S. Heppell Martin Hall Michael Ewal 《Fisheries Oceanography》2016,25(1):1-14
In the Eastern Tropical Pacific (ETP), a region of high fishing activity, olive ridley (Lepidochelis olivacea) and other sea turtles are accidentally caught in fishing nets with tuna and other animals. To date, the interaction between fishing activity, ocean conditions and sea turtle incidental catch in the ETP has been described and quantified, but the factors leading to the interaction of olive ridleys and fishing activity are not well understood. This information is essential for the development of future management strategies that avoid bycatch and incidental captures of sea turtles. We used Generalized additive models (GAM) to analyze the relationship between olive ridley incidental catch per unit effort (iCPUE) in the ETP purse‐seine fisheries and environmental conditions, geographic extent and fishing set type (associated with dolphins, floating objects or in free‐swimming tuna schools). Our results suggest that water temperature, set type and geographic location (latitude, longitude and distance to nesting beaches) are the most important predictor variables to describe the probability of a capture event, with the highest iCPUE observed in sets made over floating objects. With the environmental predictors used, sea surface temperatures (SST) of 26–30°C and chlorophyll‐a (chl‐a) concentrations <0.36 mg m?3 were associated with the highest probability of an incidental catch. Temporally, the highest probability of an incidental catch was observed in the second half of the year (June to December). Four regions were observed as high incidental catch hotspots: North and south of the equator between 0–10°N; 0–10°S and from 120 to 140°W; and along the Colombian coast and surrounding regions. 相似文献