Impacts of stock enhancement strategies on the effective population size of Murray cod,Maccullochella peelii,a threatened Australian fish

Abstract Murray cod, Maccullochella peelii (Mitchell) is an iconic Australian species endemic to the Murray‐Darling Basin (MDB) of inland south‐eastern Australia. Murray cod has been a valuable food source and supported a large commercial fishery throughout much of the 20th century. Over‐fishing and habitat destruction have resulted in significant declines in Murray cod populations throughout much of its range. Since the early 1980s, large numbers of Murray cod have been stocked into waterways to support both recreational fishing and conservation efforts. In this study, the likely impacts of past and current stocking practices on genetic diversity of Murray cod were modelled and new strategies to maximise genetic diversity in stocked populations are explored. The results suggest that a large, well‐managed breeding and stocking programme could help maintain genetic diversity of Murray cod across the MDB. In catchments within the MDB where the effective population size is very small, a well‐designed stocking programme, following strict guidelines for numbers of families reared and number of individuals maintained per family, could increase genetic diversity in a few generations.     

A Genetic Assessment of a Red Drum,Sciaenops ocellatus,Stock Enhancement Program

The South Carolina Department of Natural Resources began a stock enhancement research program for red drum, Sciaenops ocellatus, as a possible management strategy for augmenting the availability of juveniles for recreational harvest in South Carolina estuaries. Between 1999 and 2011, approximately 6 million juveniles and 260 million larvae were stocked into the Charleston Harbor (CH) estuary, and proportions of stocked fish were found through standardized sampling as high as 49.6% within a subadult year‐class and up to 12% within the spatially separate spawning population. This study evaluated the genetic influences of stocking on the spawning population, using microsatellite loci, and examined any changes in genetic diversity metrics over the course of the stock enhancement program. Percent contribution of stocked fish among subadult and adult collections was compared against measures of genetic diversity. No statistically significant correlations were found among genetic diversity metrics, suggesting that responsible stocking of red drum as small juveniles has not altered the genetic diversity of adults spawning offshore the CH. Life‐history characteristics likely play a large role in mitigating changes in genetic diversity, despite high contributions of stocked fish in some years, because red drum exhibit a long adult life span and benefit from overlapping generations.     

Loss of genetic diversity due to hatchery culture practices in barramundi (Lates calcarifer)

Many aquaculture hatchery practices are detrimental to the long-term viability of restocking and selective improvement programs. Small effective broodstock population sizes, differential broodstock contribution, differential larval/juvenile survival during metamorphosis and size-based grading, all have the potential to drastically reduce the level of genetic variation remaining in hatchery populations. Monitoring levels of genetic variation and maintaining detailed pedigrees on progeny is the key to circumventing these problems. In this study we used microsatellites, coupled with DNA parentage analyses, to track the loss of genetic diversity in two independent commercial barramundi (Lates calcarifer) hatcheries over three mass spawning events, where up to two females and seven males had the opportunity to participate. Initial broodstock contributions were observed to be highly skewed, with significant differences observed in both the level of contribution by females to each mass spawning, as well as in the number of males participating and subsequently contributing to the genetic composition of cohorts. Effective population sizes were around half that of census sizes. We then examined whether differential family survival through metamorphosis (27 days post-hatch) and/or first size grading further influenced the retention of genetic diversity levels initially sampled during spawning. Parentage analyses indicated that some families that had been initially represented in cohorts had been lost, or that the contribution by particular broodstock had changed. In one cohort, as many as 55% of progeny were found to be sired by a single male individual. Size grading was also found to potentially impact on genetic diversity, with data suggesting that family representation in each of the grades was non-uniform and that some families were on average faster or slower growing than others. These results illustrate that hatchery management practices have the potential to significantly impact on the retention of genetic diversity in this species.     

Forecasting the genetic influences of red drum stock enhancement in South Carolina

The South Carolina Department of Natural Resources (SCDNR) began stocking red drum, Sciaenops ocellatus (Linnaeus), in 1989 to augment the abundance of juveniles available for recreational harvest in South Carolina estuaries. While stock enhancement can help supplement wild populations under high fishing pressure, releasing hatchery‐raised fish into the wild also presents the risk of decreased genetic diversity. An individual‐based model (IBM) was developed to forecast the genetic influences of stocking on the wild spawning population to inform responsible stocking strategies. Model results indicated the SCDNR red drum stock enhancement programme should maintain mean contributions of stocked fish no greater than 30% per year class over a 45‐year stocking period, coupled with at least 10 effective breeders in the hatchery replaced annually, to maintain current levels of genetic diversity estimated in the wild population. The IBM is a useful tool for hatchery managers to guide responsible stock enhancement.     

Conservation of spawning time between years in lumpfish Cyclopterus lumpus and potential impacts from the temporal distribution of fishing effort

Lumpfish, Cyclopterus lumpus L., has an extended ovary development period and a relatively long spawning season. It therefore seems unlikely that individuals spawning later in the season would be able to recover from spawning and develop their gonads in time to spawn during the early part of the season the following year. The hypothesis that individuals spawning early or late in a spawning season would spawn early or late the following year was tested using fish tagged in Iceland between 2008 and 2017. The tagging date and recapture date the following year were positively correlated with an average of 356 days at large (DAL). Fish sampled from the fishery indicate that tagging/recapture date gives an indication of spawning time. From this, it was concluded that spawning time in the current year can be used to predict spawning time the following year. As fishing effort was greatest at the end of April/beginning of May, it seems likely that fish that come to spawn at this time will be subject to a higher fishing mortality. Therefore, they will be less likely to spawn successfully than fish spawning earlier or later in the year. If spawning time is under genetic control, then this could have consequences for the spawning phenology of lumpfish.     

我国近海星康吉鳗群体的形态学、遗传学比较研究

结合形态学、遗传学的方法,分别对青岛近海(黄海)、舟山近海(东海)的星康吉鳗群体做了相关系统的研究。通过单因素方差分析、判别分析、主成分分析方法对两个星康吉鳗地理群体的9个可量性状进行形态学比较研究;基于线粒体DNA (mtDNA)序列进行遗传学分析研究。形态学研究结果显示,舟山海域的星康吉鳗肌肉中含有"I"形硬肌间骨,青岛海域星康吉鳗的肌肉中无硬肌间骨;单因素方差分析结果显示,两个群体的7个可量指标:肛长、头宽、吻长、口裂长、眼径长、背鳍前长和胸鳍长存在显著差异;在主成分分析中,基于前两个主成分绘制的散点图基本能够将两个星康吉鳗群体区分开来;判别分析结果显示,青岛、舟山两群体的判别准确率分别为100%和94.7%。3种多元统计分析结果均表明青岛、舟山两个星康吉鳗群体在外部形态上存在一定程度差异,但根据75%识别与划分规则,认为两组群体的形态学差异尚未达到亚种水平。遗传学研究表明,在所检测的mtDNA水平上两个星康吉鳗群体遗传多样性无明显差异,邻接系统发育树未呈现明显的谱系关系,遗传分化指数FST也显示两群体遗传差异小,遗传分化不显著,属同一种群。     

约氏笛鲷自然群体遗传多样性的RAPD分析

约氏笛鲷 (Lutjanusjohni)样品 10尾 ,取自湛江近海自然种群。从 12 0个随机引物中筛选出 16个引物 ,采用RAPD技术对其进行分析。结果表明 ,16个引物共检测到 2 15个位点 ,其中多态位点比例 (P)为 78.6 0 % ,遗传相似系数 (S)为 0 .72 70 ,遗传距离 (D)为 0 .2 730 ,遗传多样性指数 (H)为 0 .2 0 85。目前湛江近海约氏笛鲷自然群体种质资源仍然维持在良好水平 ,捕捞尚未对其造成明显影响     

Decreased genetic diversity and a reduced effective population size in cultured silver-lipped pearl oysters (Pinctada maxima)

Before selection programmes for aquaculture species can commence, a fundamental knowledge of how the culture process affects genetic diversity is requisite. “South Sea” pearl production, through the culture of the silver-lipped pearl oyster, Pinctada maxima, stands to gain substantially from genetic selection. Aquaculture techniques for P. maxima have progressed vastly, to a point where the majority of current operations are based on hatchery-propagated stock; however, there has been no investigation on how the culture process is affecting the genetic diversity of this species. To address this deficiency, we investigated the genetic diversity and effective population sizes (N_e) in three wild and five hatchery-produced P. maxima populations. Using six microsatellite DNA markers, cultured populations exhibited low N_e (3.5–9.2) and reduced allelic richness (29–44%) compared with their wild progenitors. Observed heterozygosities were not affected greatly, however, an increased mean pairwise genetic relatedness was observed in all cultured populations. The practice of mass spawning was identified as a major factor in the reduction of diversity, although diversity was not necessarily maintained when a more controlled spawning approach was utilised. Pedigree reconstructions revealed genetic diversity and N_e is affected by large skews in full-sib family representations (up to 40% from a single family, in a cohort using 28 broodstock), and could be due to differential survival rates amongst communally reared families. In order to maximise future selective breeding efforts, further research should be directed towards identifying critical stages of the culture process in which genetic diversity is lost.     

Do estuaries with different fishing activity have different fish assemblages and populations?

Commercial and recreational fishing have impacts on fish assemblages and populations, but does their combined fishing pressure result in different fish assemblages in estuaries with only one type of fishing activity? This pilot study tested the model that estuaries with only one type of fishing activity have fewer impacts on fish assemblages and populations than estuaries with more than one type because the fishing pressure in the latter will be greater and results in different fish assemblages and taxa. Fish assemblages and populations, including diversity, abundance and size, did not significantly differ despite exposure to different fishing activities. Detecting differences in fish assemblages in estuaries associated with different fishing activities is difficult as smaller scale spatial and temporal factors have a significant influence on the patterns observed. This highlights the importance of paying close attention to the design of sampling programmes. The nested design of this study enabled identification of where greater effort is required to increase the capacity to detect differences. Recommendations for future studies are provided.     

福建莆田近海鲻鱼渔业现状及秋冬季产卵群体特点

本文主要根据2010年11月—2011年2月福建莆田近海流刺网作业鲻鱼生产调查资料,分析秋冬季渔获鲻鱼产卵群体组成、性腺成熟度分布等生物学特点及鲻鱼生产基本情况。结果表明:秋冬季(11月至翌年1月)是鲻鱼产卵盛期,也是鲻鱼渔业生产旺季;鲻鱼产卵群体主要为流刺网作业所利用,渔获群体优势叉长450～550 mm;近岸众多的流刺网作业过度捕捞亲鱼是造成鲻鱼资源量不断减少的主要原因之一。为更好地保护和利用莆田近海鲻鱼资源,建议进一步开展流刺网及张网作业对鲻鱼资源合理开发利用的专项调查研究。     

Essential Fish Habitat and the Effective Design of Marine Reserves: Application for Marine Ornamental Fishes

Extensive and unregulated harvest of marine ornamental fishes can lead to localized depletion of target species and habitat degradation from inappropriate collecting techniques. One potential solution to these problems is the creation of marine reserves where fishing is prohibited. Marine reserves have been shown to increase fish abundance and protect ecosystems from habitat destruction associated with fishing. If protective areas are to be effective, they must include the diversity of habitats necessary to accommodate the wide range of fish species that are of interest to the marine ornamental fish trade.Fish assemblages with high diversity and abundance are often associated with habitats of high structural complexity. A relationship between fish size and reef complexity suggests the importance of shelter as a refuge for certain fishes in avoiding predation. Many species tend to aggregate to spawn in structurally complex habitats to reduce their risk of predation. Closing of spawning areas during aggregation periods has been shown to be a highly effective management strategy for these species. The limited home ranges and high degree of habitat specificity associated with many marine ornamental fishes should make marine reserves a highly effective strategy for managing these resources.     

Stream spawning of Arctic charr in Scotland

Abstract –  Scotland is a stronghold for Arctic charr, with about 200 freshwater, wholly loch-resident populations, most of which have yet to be studied. To date, no anadromous populations or individual sea-run charr, have been reported. In Scotland, most Arctic charr spawn in stillwater, during autumn and early winter (September to January), with only one population spawning in spring. Spawning in running water does occur, but has been regarded as rare. This paper examines the status of stream spawning of charr in Scotland, describing instances from 10 populations, although two of these are now extinct. Most stream-spawning charr migrate relatively short distances to running water and construct redds in gently flowing water. The longest recorded migration occurs in Loch Insh, Speyside, with fish travelling 15 km within the River Spey. Information on the extent of stream spawning is essential to help conserve the rich phenotypic and genetic diversity of our remaining charr populations.     

Genetic differentiation between and within ecotypes of pike (Esox lucius) in the Baltic Sea

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Baltic Sea genetic biodiversity: Current knowledge relating to conservation management

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Gillnet fishing drives lake‐migrating brown trout to near extinction in the Lake Päijänne region,Finland

Abstract Wild stocks of brown trout, Salmo trutta L., collapsed in Finnish inland waters during the 20th Century because dams prevented upstream migration, and low water quality and stream dredging weakened reproduction. The demise in migratory stocks was coupled with overfishing, mainly by gillnetting on lakes. Consequently, the migratory spawning stocks have diminished to negligible levels. The remaining stocks exhibit restricted immigration and emigration, are supplemented by continuous stocking, and their natural genetic diversity is affected by human activities. In recent years, various recovery actions have been implemented including stream channel restorations, fish passage facilities constructed and stocking of eggs and smolts. Gillnetting has also been regulated by banning certain mesh sizes, and catch‐and‐release of wild trout is spreading amongst sport fishers. However, these measures seem to be inadequate and almost no recovery of migratory populations has been reported. The problem of by‐catch in intensive gillnetting continues to threaten stocks and creates disputes between stakeholders.     

Current status of the brown trout (Salmo trutta) populations within eastern Pyrenees genetic refuges

Since the end of the 20th century, some headwaters of rivers in the eastern Pyrenees have been designated as genetic refuges to protect remaining native brown trout (Salmo trutta) diversity. The declaration was based on limited or no evidence of genetic impact from released non‐native Atlantic hatchery fish. Hatchery releases were completely banned into the genetic refuges, but pre‐existing fishing activities were maintained. Specific locations in each refuge have been monitored every 2–3 trout generations to update genetic information to accurately assess the contribution of these reservoirs to the preservation of native brown trout gene pools. This work updates genetic information to year 2014 in three of these locations (in Ter, Freser and Flamisell rivers). Previous studies identified hatchery introgressed populations within refuges and suggested discrepancies between the underlying intention of the genetic refuges and the gene pools detected. Therefore, we also examined genetic divergences among locations inside refuge river segments. Combined information at five microsatellite and the lactate dehydrogenase C (LDH‐C*) loci showed reduced but significant temporal native allele frequency fluctuations in some of the above specific locations that did not modify overall levels of local diversity and river divergences. Bayesian clustering analyses confirmed the presence of differentiated native units within each genetic refuge. Some locations of the Freser River within the genetic refuge area showed high hatchery impact of non‐native fish (over 20%). We discuss additional local actions (releases of native fish, selective removals and fishery reinforcement with sterile individuals) to improve the conservation objective of genetic refuges.     

福建近海蓝圆鲹种群遗传多样性的AFLP分析

以往研究表明,福建近海的蓝圆鲹分属2个地理种群,即东海西部种群和闽南—粤东近海地方种群。为研究这两个群系的遗传结构,对蓝圆鲹闽东(30尾)和闽南(32尾)种群进行了AFLP分析,8对选择性引物在2个种群62个个体中,共扩增出563个位点,其中多态位点364个。闽东和闽南种群的多态位点比例、Nei遗传多样性指数和Shannon遗传多样性指数分别为62.70%、58.97%,0.1875、0.1809和0.2878、0.2763。与其他鱼类对比显示,福建近海蓝圆鲹种群的遗传多样性水平高,说明种群遗传结构尚未遭到明显破坏;基因分化系数GST、Shannon遗传多样性指数和AMOVA分析均显示蓝圆鲹的遗传变异主要来源于种群内,而种群间无明显的遗传分化。Nm显示2个种群间基因交流频繁。种群的显性基因型频率分布和位点差异数分布显示2个种群有基本相同的群体遗传结构。结果表明,蓝圆鲹闽东和闽南种群间无明显的遗传差异,因此可将福建海域的蓝圆鲹划归同一个管理保护单元。较强的扩散能力及海洋环流可能是造成福建近海蓝圆鲹种群间遗传同质性较高的原因。     

基于《物权法》的中国捕捞权保护制度的探索

《物权法》明确了捕捞权和养殖权的用益物权属性,并规定其受法律保护。但依据我国现有渔业法律制度,实施《物权法》有关保护捕捞权的法律规定还存在一定困难。通过比较分析《物权法》和《渔业法》及相关法规对捕捞权的规定,考察造成捕捞权损害的主要原因,提出了我国捕捞权保护制度的路径选择:(1) 将近岸海洋渔场和内陆水域渔场按县级或县级以下基层行政区域进行划分,确定给所属区域内的传统捕捞渔民专属使用,从而明确捕捞权主体和客体,为建立捕捞权保护制度提供基础。(2) 建立捕捞权损害评估体系,制定捕捞权损害赔偿、补偿标准,规范捕捞权损害赔偿、补偿程序,健全和完善捕捞权损害赔偿、补偿制度。     

Japanese chum salmon stock enhancement: current perspective and future challenges

This study reviews the present status of the Japanese chum salmon Oncorhynchus keta stock enhancement program and considers the ecological sustainability of wild populations while providing fishery production, exemplified by the hatchery-based Kitami region set net fishery. The return rate and the number of returns have been historically high in the Sea of Okhotsk, but have decreased in other regions since 2005. Natural spawning of chum salmon occurred in at least 160 rivers in Hokkaido. The genetic diversity of Japanese chum salmon was similar to or higher than that of other Pacific Rim populations. Numbers of alleles were high at microsatellite loci, but the loss of rare haplotypes was observed in all populations. The estimated N _e /N ratio for the Kitami region was >0.15 % including hatchery and wild fish under the present high fishing pressure. Four regional populations were inferred in Hokkaido, however, genetic differentiation was weak and some river-populations were nested. Substantial changes in run timing were observed, but it has recovered gradually owing to the recent practice of escapement. Our analyses highlight the importance of juvenile quality and the vital roles of escapements in enhanced and non-enhanced rivers. New research is needed to minimize the genetic risks associated with hatchery programs.     

Optimising recreational harvests of blue cod: The effects of catch-and-release mortality and size selectivity

A yield-per-recruit model is developed for the recreational fishery on blue cod (Parapercis colias: Pinguipedidae) in the Marlborough Sounds, New Zealand. The model incorporates sex differences in growth rates, protogyny, minimum size limits, catch-and-release mortality and size-selective fishing. Mortality of released fish due to hooking damage and post-release predation is a potentially significant factor for blue cod management. High levels of catch-and-release mortality favour small minimum size limits and reduced fishing intensity. Even in the absence of size limits, hook and line fishing for blue cod is highly selective on larger fish and this greatly reduces the potential impact of catch-and-release mortality on yields and management choices. Catch-and-release mortality will also lower the spawning stock biomass-per-recruit and therefore has the potential to impact on stock sustainability as well as yields. In protogynous species the effects of fishing on spawning stock biomass will be different for males and females and it is important to model these separately, as well as understanding the cues for, or timing and extent of, sex change. Catch-and-release mortality can also slow the recovery of stocks when no-take rules still allow fishing for other species and therefore by-catch of the species targeted for protection. It is suggested that a small reduction in size limit and a small increase in daily bag limit relative to present regulations, would result in optimal yields from this fishery. Predation on fish released by recreational anglers is less widely reported than mortality due to hooking damage but both have the potential to negate the benefits of minimum size limits.