双船变水层拖网试验初见成效

为捕捞离底较高的鱼群，和开发外海渔场；上海市海洋渔业公司在水产总局领导下，1978年起进行双船变水层拖网试验。     

海洋捕捞强度盲目增长势头要坚决煞住

我国近海渔业资源自七十年代始日渐衰退。特别是进入九十年代后，海洋捕捞强度与海洋渔业资源间的矛盾更日益加剧。固然造成海洋渔业资源衰退的原因是多方面的，但海洋捕捞强度盲目增长，却不能不说是重要原因之一。目前，我国海洋渔业资源仍在继续衰退。特别是底层或近底层鱼类资源已严重过度利用；一些传统捕捞品种或渔场已形不成渔汛；一些主要渔获对象的小型化，低龄化和性成熟期提前的现象也更加明显。控制捕捞强度，限定捕捞渔船数量、马力．是对渔业资源具有一定主动性的、直接的管理方式，它代表了现代渔l资源管理的趋势，是资源管…     

严格控制捕捞强度 保证海洋渔业持续发展

我国海洋捕捞业在我国海洋渔业中具有举足轻重的地位。1995年全国海洋捕捞产量1026万吨，占当年全国水产品总产量的45％，比1985年的348万吨增长了2．95倍，年递增率达11．4％。当前，我国海洋捕捞业面临严峻形势，主要表现在海洋捕捞强度与海洋渔业资源的矛盾进一步加剧，海洋捕捞作业结构与海洋渔业资源状况不相适应，沿岸和近海海域环境恶化的趋势仍在继续，渔业资源继续衰退，特别是底层和近底层鱼类资源利用严重过度；一些传统的捕捞鱼种或渔场已形不成渔汛，渔获对象小型化、低龄化和性成熟提前的状况日趋明显；一些沿岸产卵场或水域…     

嵊山渔场冬季带鱼汛喜获大丰收——许多大城市和边远地区都吃到来自嵊山的新鲜带鱼

全国海洋渔业规模最大、渔船最集中、产量最高的冬季嵊山带鱼汛生产,获得历史上空前未有的大丰收.去年入冬以后,东海嵊山渔场上云集了浙江、江苏、福建、上海等三省一市一万六千多艘渔船,十万多渔民,投入冬季捕捞.十一月十五日,随着北方冷空气南下,水温、气温下降,由北向南洄游的带鱼群,比往年早十天进入嵊山渔场,渔汛提前     

遥感探鱼技术

渔场预报和鱼群侦察是海洋捕捞的重要环节。遥感技术能在大面积范围内、长期地、及时的取得多种信息，它在海洋捕捞渔业中的应用将能提高渔场预报和鱼群侦察的范围和质量。目前国外的遥感探鱼虽处在发展初期，离推广使用还有一定距离；但从已取得的一些研究结果和分析来看，它是未来科学探鱼的有力手段，是实现海洋捕捞渔业现代化的重要一环。     

气候对我国海洋渔业的影响

海洋渔业与气候密切相关 ,因为渔业捕捞不管是在近海还是在大洋中 ,都要受到天气变化的影响 :浓雾的产生容易使渔船迷航导致触礁 ;大风的突袭 ,会造成生命财产重大损失。而且天气的变化对鱼群洄游路线、鱼群的集散分布、渔汛的迟早、渔场位置的迁移 ,都有直接或间接的影响。本文分析了气候各要素 (气温、风、气压、降水、光照等 )的变化对渔场、渔汛以及海洋捕捞作业的影响 ,为科学捕捞和安全生产提供一些借鉴。     

舟山渔场冬汛寻找带鱼群的经验(上)

海洋渔业生产对象,主要是捕捞洄游集群的鱼类。能否找到好渔场,决定着产量的高低。舟山渔场的冬季带鱼讯是一个全国性的大渔汛。近年来每届汛期,自福建以北沿海各省、市的渔民大都云集此地生产。由于渔场广阔,鱼群洄游集散变动性大,外地渔民对渔场情况尚多不够熟悉,特将当地渔民寻找鱼群的经验介绍如下:(一)找鱼群的船队组织和采用的渔具:“分散探索,集中捕捞”这是渔民在组织起来后得出的一条找鱼群经验。渔船队出海后,先分散     

200马力对钓渔船设计与试验

当前，我省海洋渔业的捕捞强度不断增加，渔政管理上存在着问题与困难，致使近海主要经济鱼类产量下降，大、小黄鱼已形不成渔汛，目鱼生产日趋恶化，带鱼资源的捕捞压力极大，为此，保护近海水产资源，减轻沿岸近海渔场的捕捞强度，合理利用水产资源是我省渔业生产上必须解决的重大问题。鉴于东海中南部的上层鱼类和浙江中南部外海以及钓鱼岛渔场的马面鱼等鱼类资源，尚有生产潜力。因此，1983年浙江省科委、省水产厅为了尽快打开我省海洋渔业新局面和扶植恢复钓业生产，     

全国海水养鱼业—现状,存在问题和可持续发展对策（上）

前言二十一世纪将迎来“兰色革命”，向海洋要蛋白质，是各国的共识。其手段以前主要靠捕捞，捕捞渔业依赖资源和环境，由于传统渔场的过度捕捞，生态环境受污染日益恶化，周边国家先后扩大渔业专管区，致使我国捕捞渔业的产量、质量、经济效益普遍下降。农业部审时度势，要求各省实行海洋捕捞产量“零”增长。全国海洋渔业增产的希望寄托在海水养殖上。建国以来，我国海水养殖业确实做出了较大业绩。有人把海水养殖发展史，描绘成三次浪潮。第一次浪潮是从五十年代藻类养殖大发展开始的，育苗技术、养殖面积、产量均在世界领先，成为世界藻…     

在创新中打造海洋渔业发展优势

中日、中韩、中越渔业协定签订生效之后,我国渔民传统的作业渔场大大缩小。随着海洋渔业资源特别是近海渔业资源的日益衰退和渔用柴油价格高涨,以捕捞为主的海洋渔业效益每况愈下。为了保护海洋渔业资源,降低捕捞强度,国家实行了捕捞量"零增长"和促进渔民转产转业等政策。许多祖辈以海为生的渔     

The consequences of density-dependent individual growth for sustainable harvesting and management of fish stocks

Density dependence is likely to act as a regulatory mechanism in fish stocks that are recovering from overfishing. In general, density dependence in fish stocks is assumed to only occur in reproduction and early life stages and is therefore usually modelled as a stock-recruitment relationship. Recent research shows that density dependence can also reduce individual growth in body size later in life. In this study, we show how optimal fishing effort changes with the strength of density dependence in individual growth for four stocks of North Sea flatfish species. Using size-structured population models we show that density dependence arises due to a mechanistic link between the resource availability and life history processes at the individual level. We furthermore show that the stock response to harvesting is either driven by changes in individual reproduction when density dependence in individual growth is weak or by changes in individual growth rate when individual growth is strongly affected by density dependence. These two types or regimes are separated by a sudden shift in dynamics. It is therefore of great importance to account for density dependence in growth when managing fish stocks.     

Selectivity matters: Rules of thumb for management of plate‐sized,sex‐changing fish in the live reef food fish trade

Effective management of fisheries depends on the selectivity of different fishing methods, control of fishing effort and the life history and mating system of the target species. For sex‐changing species, it is unclear how the truncation of age‐structure or selection of specific size or age classes (by fishing for specific markets) affects population dynamics. We specifically address the consequences of plate‐sized selectivity, whereby submature, “plate‐sized” fish are preferred in the live reef food fish trade. We use an age‐structured model to investigate the decline and recovery of populations fished with three different selectivity scenarios (asymptotic, dome‐shaped and plate‐sized) applied to two sexual systems (female‐first hermaphroditism and gonochorism). We parameterized our model with life‐history data from Brown‐marbled grouper (Epinephelus fuscoguttatus) and Napoleon fish (Cheilinus undulatus). “Plate‐sized” selectivity had the greatest negative effect on population trajectories, assuming accumulated fishing effort across ages was equal, while the relative effect of fishing on biomass was greatest with low natural mortality. Fishing such sex‐changing species before maturation decreased egg production (and the spawning potential ratio) in two ways: average individual size decreased and, assuming plasticity, females became males at a smaller size. Somatic growth rate affected biomass if selectivity was based on size at age because in slow growers, a smaller proportion of total biomass was vulnerable to fishing. We recommend fisheries avoid taking individuals near their maturation age, regardless of mating system, unless catch is tightly controlled. We also discuss the implications of fishing post‐settlement individuals on population dynamics and offer practical management recommendations.     

Patterns of population variability in marine fish stocks

Exploited marine fish and invertebrate stocks fluctuate in a myriad of complex patterns, exhibiting variability on interannual, decadal, and longer time scales. To characterize various patterns of variation, time series of catch, catch per unit effort, or biomass from 30 stocks were examined with a variety of statistical methods including autocorrelation analysis and Lowess smoothing. A hierarchical cluster analysis classified the stocks into six identifiable groups: steady-state; low-variation, low-frequency; cyclic; irregular; high-variation, high-frequency; and spasmodic. The observed patterns are consistent with life history traits; for example, stocks with high variability are generally small, pelagic species whereas low-variability stocks are generally slow-growing, demersal fish. Each of the six general patterns of variability can be produced from a simple multiple-equilibrium population model by varying the intrinsic rate of population growth, and the time scale and amplitude of environmental variability. Suitable management policies depend on the type of variation observed, and the vast majority of stocks examined do not correspond to the steady-state assumptions of classical fisheries models. For example, management of spasmodic stocks may alternate between periods of active exploitation and periods of rebuilding, a process enhanced by the existence of alternative fisheries.     

Population dynamics and management of culture-based fisheries

Abstract The population dynamics of culture-based fisheries are studied by means of a mathematical model, which incorporates explicit sub-models for density-dependent individual growth and size-dependent mortality. The model applies to populations of carps, i.e. common carp, Chinese carps, and Indian major carps, and coregonids.
The effects on production of stocking density and size of seed fish, fishing mortality, and size at harvesting are studied in a model population of carp. Management implications of the modelling results are emphasized. An adaptive approach to management, involving judicious experimentation with stocking and harvesting regimes, is proposed to gain information on the dynamics of actual fisheries, and to optimize their production.     

Ecologically and evolutionarily sustainable fishing of the pikeperch Sander lucioperca: Lake Oulujärvi as an example

Due to the multitude of participants and a diverse range of fishing gear used freshwater fisheries are often managed using minimum size limits (MSL) rather than regulations of total fishing effort. However, a concern has arisen whether attempts to improve ecological sustainability of fisheries by increasing MSLs would induce undesired adaptations to selective fishing. We examined the ecological and evolutionary impacts of varying fishing mortality rates under varying MSLs, with and without stockings, in an age-, size-, and maturity-structured evolutionary model which was parameterized for the Lake Oulujärvi pikeperch, Sander lucioperca. We found that at the current level of harvesting (fishing mortality rate, F = 0.7) and stockings (430 000 year⁻¹), and under the assumption of strongly density-dependent growth, the nation-wide MSL of 370 mm maximizes theoretical biomass yield in a deterministic model but does not prevent severe recruitment overfishing under further increased fishing pressures or stochasticity in recruitment success. The recently imposed, local MSL of 450 mm better ensures stable yields, and even increases them if individual growth is density-independent, but further increase of MSL to 500 mm would already reduce yield especially if there was discard mortality for undersized fish. Given density-dependent growth, equal survival between wild and stocked fish, and sustainable fishing mortality rate, stockings do not increase yield or significantly improve the stability of yields. Evolutionarily stable size at maturation decreases under strong fishing mortality, but increased MSLs reduce the magnitude of this undesired effect. Negatively size-dependent natural mortality was found to have a positive effect on the otherwise negative selection for length-at-age. Increased MSLs also reduce the total selection for decreased length-at-age. Our results support the intentions to increase MSLs in order to improve both ecological and evolutionary sustainability of recreational fisheries.     

Broadbill swordfish: status of established fisheries and lessons for developing fisheries

Guidelines for the assessment and management of developing swordfish fisheries are derived through an examination of five swordfish fisheries. As they develop, swordfish fisheries may be inclined to local depletion around underwater features, such as seamounts and banks. Few nations have applied the precautionary approach in managing their developing swordfish fisheries. Without controls, swordfish fisheries expand geographically and fishing effort increases, often overshooting optimum levels. However, it is difficult to distinguish clear evidence of fishery collapse; modern longliners harvest widely distributed tuna and swordfish and they are able to relocate to distant areas or switch between target species in response to fluctuations in species abundance and price. Furthermore, the wide distribution of swordfish combined with year‐round spawning and high growth rates amongst juveniles probably contribute to the apparent resilience of swordfish stocks to intensive harvesting. Over half the world’s swordfish catch is taken as an incidental catch of longliners fishing for tuna. In several areas, such as the North Atlantic, catch quotas have sometimes caused tuna longline fishers to discard swordfish. Minimum size limits have also resulted in discarding of swordfish in tuna fisheries and in dedicated swordfish fisheries. In addition to weakening the effectiveness of those management measures, bycatch and discarding add to the complexities of managing swordfish fisheries and to uncertainties in assessing the stocks. Longliners that target swordfish often fish at high latitudes where interactions with marine wildlife, such as seabird, are generally more frequent than at low latitudes. Concern over incidental catches of marine wildlife and other species is becoming a driving force in the management of several swordfish fisheries. Fishery management organisations will need to implement management measures to protect non‐target species and gather reliable data and information on the situation by placing observers on boats fishing for swordfish.     

Fishing efficiency of competitive largemouth bass tournament anglers has increased since early 21st century

Tournament fishing has risen in popularity over the last half a century. As such, social and financial incentives combined with technological advancements are expected to drive changes in angler's capacity to exploit tournament‐eligible fish stocks, as has been observed in commercial fisheries. The aim of this study was to quantify temporal trends in angler efficiency and their ability to exploit a given fish stock relative to effort in largemouth bass fishing tournaments. A collective analysis across seven Illinois reservoirs comparing change through time in angler catch rates and relative population abundances indicated that angler efficiency has generally improved through time. For the decade from 2005 to 2015, a greater than threefold increase in the efficiency of anglers to exploit a static population of largemouth bass was estimated. Anglers have become more efficient at exploiting populations, which is likely to influence management decisions in the future, particularly in harvest‐orientated fisheries and those reliant upon fishery‐dependent surveys.     

Discriminating alternative stock–recruitment models and evaluating uncertainty in model structure

Fish stock–recruitment (S–R) assessment is one of the most essential keystones for fisheries management. Yet the analysis involves a variety of uncertainties. Amidst these difficulties, uncertainty in model structure is perhaps the most problematical to investigate because no rigorous statistical techniques can be used to explore the fundamental biological processes in S–R relationships. In this paper, I used computer simulations to investigate: (1) the differences between the estimated parameters of alternative S–R models as a function of stock characteristics: population growth rate, data range, fishing mortality, and process noise; and (2) the probability of selecting a correct model using information criteria. Two popular S–R functions, the Ricker and the Beverton–Holt models, were used as examples. Time series data were generated from a known S–R model and fitted by alternative models. The results show that when the two models fit the data similarly well, significant differences in parameters existed between the alternative models. The Ricker model tended to underestimate the population growth rate (initial slope) and the carrying capacity parameter, whereas the Beverton–Holt model overestimated these parameters. The management quantities (e.g., optimal virgin stock size) produced by one model were more conservative (i.e., larger optimal stock size or lower optimal harvest rate) under some conditions but became less conservative under other conditions. The differences between the alternative models were functions of the population growth rate, long-term fishing mortality, and data range of the stock size. The correct and incorrect models were statistically indistinguishable. For typical fishery data the probability of selecting the correct model based on information criteria was approximately 0.70 for the Ricker model and 0.61 for the Beverton–Holt model.     

First implementation of a Gadget model for the analysis of hake in the Mediterranean

An age-length structured model was built for European hake Merluccius merluccius in the central Mediterranean Sea using Gadget. This analytical framework allowed to integrate multiple sources of information, including fisheries-dependent and fisheries-independent data, collected at different scales and aggregation levels. The model includes the two main fisheries targeting hake in the area, the trawl and the gillnet fisheries, and account for differences in their selectivity and effort. Alternative models were used for testing different assumptions on recruitment and growth. The model is then used to predict the main trajectory of the stock during the next years and to evaluate the potential effects of implementing closed areas management scenarios in the hake nurseries as a specific tool to reduce fishing mortality on recruits. The modelling framework presented performed successfully also in a commercial landing data limited context, common for the Mediterranean. Our results provide statistical support for fast growth and multiple recruitment events assumptions. Including both these key features represent an unprecedented improvement of modelling hake population dynamics in the Mediterranean. We found that the reduction in the fishing effort that characterized the fisheries in the study area during the last few years, coupled with fast recovery abilities of the hake stock, has the potentiality to allow a moderate increase of the stock during the next years. Interestingly, our simulations show that the positive effects which might be expected from protecting hake nursery grounds are only marginally related to a reduction in hake recruits fishing mortality. Although our model relies on assumptions and surely represents an over-simplification of the real world, it still contributed to improve our understanding of the temporal dynamics of one of the most valuable fish stocks in the central Mediterranean.     

基于分期的实际种群分析法研究

实际种群分析法(virtual population analysis,VPA)是开展渔业资源评估最有效的技术之一,一般以世代为基础开展评估.基于实际渔业存在渔汛期、休渔期等特点,本研究运用分期评估的概念对传统实际种群分析进行了扩展,即分期种群分析法,并根据不同时期的捕捞死亡特征,评估与分析了4种不同分期情景对评估结果的影响.模拟研究表明,由于分期不当造成评估结果的误差为6％～33％.文中一并给出了开展分期实际种群分析法对资料收集和参数评估的要求.该方法克服了传统实际种群分析法中没有全面分期产生的误差,使其扩展至适合于评估全年捕捞死亡率不稳定或非连续性渔业种群,评估结果也更接近于评估种群的真实值.