Population genetic structure of Atlantic salmon,Salmo salar L., in the River Tamar,southwest England

Abstract Population genetic studies can be useful for informing conservation and management. In Atlantic salmon, Salmo salar L., population structuring frequently occurs between river systems, but contrasting patterns occur within rivers, highlighting the need for catchment‐specific studies to inform management. Here, population structure of Atlantic salmon was examined in the River Tamar, United Kingdom, using 12 microsatellite loci. Gene diversity and allelic richness ranged from 0.80 to 0.84 and from 8.96 to 10.24, respectively. Some evidence of genetic structure was found, including significant genetic differentiation between samples in different subcatchments (pairwise θ and tests of genic differentiation), results from assignment tests and a pattern of isolation by distance. Conversely, structure revealed only one population cluster, and an analysis of molecular variance showed no significant variation between subcatchments. Evidence of population bottlenecks depended on the mutation model assumed and is discussed with reference to catchment‐specific studies of stock abundance. Implications for implementing management actions are considered.     

Low allozyme variation in snapper, Pagrus auratus, in Victoria, Australia

The population genetic structure of snapper, Pagrus auratus (Bloch and Schneider), in Victoria was investigated using six polymorphic allozyme loci. Fish were sampled from four sites in Victoria and single locations in South Australia, Western Australia and New Zealand. Although there were distinct genetic differences between the snapper populations from each of the Australian states and New Zealand, only minor and largely insignificant differences were detected among Victorian populations. The results are consistent with previous genetic and tagging studies that indicate no mixing between snapper stocks in Victoria and Spencer Gulf in South Australia. This justifies separate management of the snapper fisheries in these regions. The low levels of polymorphism and heterozygosity in Victorian snapper suggest an isolation by distance model of population structure rather than one of discrete subpopulations.     

Assessing the long-term genetic impact of historical stocking events on contemporary populations of Atlantic salmon, Salmo salar

Abstract  Supplementation of wild fish with non-native or domesticated fish is common practice. However, these stocked and native fish differ both ecologically and genetically and, in the wild, they interact in a multitude of ways, often with negative repercussions for the native population. This study assessed the long-term genetic impact of historical stocking activities on a contemporary population of Atlantic salmon, Salmo salar L. During the 1960s salmon from hatcheries in Scotland and Iceland were transplanted to the River Dart, England. Microsatellite loci were used to assess the current level of population admixture between samples taken from the source location of the stocked fish during the 1960s and contemporary Dart populations. After allowances were made for natural genetic relationships between donor and recipient populations, the long-term impact of the historical stocking events on a catchment scale appears minimal. However, one tributary consistently reflected closer genetic relationships with the donor populations, indicating a possible long-term impact on a localised scale.     

Evolution of marine fisheries management in China from 1949 to 2019: How did China get here and where does China go next?

China is the world’s biggest fishing nation and a major player in the global seafood trade. Its fisheries development can decisively influence the global seafood trade, food security and marine conservation. In recent years, significant changes have taken place in China’s fisheries management priorities, policies and regulations. In this paper, we review the evolving fisheries management practices in China to delineate changes in the management policies, methods and their performances from 1949 to 2019. We determined that the following issues impede the development, implementation and enforcement of fisheries policies and regulations, namely the large size of the fishing fleet, large and poorly organized fisheries population, the “hidden” fishing capacity, uniform management approaches that sometimes fail to account for local conditions, lack of clearly defined and allocated fishing rights, limited data quality and availability, insufficient fisheries monitoring programmes, absence of a robust scientific input framework and insufficient stakeholder involvement. Combining those problems with China’s current management initiatives, we propose recommendations for China’s future fisheries reforms. We hope this paper can inform China’s marine fisheries policies and provide valuable references for further researches related to China’s sustainable fisheries management.     

Varying the timing of oyster transplant: implications for management from simulation studies

The transplanting of oysters from one ground to another is a common practice in the oyster industry. In Delaware Bay, for instance, oysters are typically transplanted from upper-bay low-salinity seed beds onto lower-bay leased grounds for growth and conditioning before market. The higher salinity on the leased grounds, however, also favours higher losses to predation and disease. A coupled oyster–Perkinsus marinus–predator model was used to investigate how varying the timing of transplant affects the ultimate yield of Eastern oysters, Crassostrea virginica, in Delaware Bay. Simulations were run in which oysters were moved from seed beds to leased grounds in November, January, March, April and May. The number of market-size (≥ 76 mm) adults available for harvest in the following July to November was compared for populations undergoing mortality from predation (crabs, oyster drills) and/or disease (Perkinsus marinus). In all simulations, the abundance of market-size oysters declined between July and November. However, transplanting oysters in November resulted in the largest yield of market-size oysters for all harvest times; transplanting in May resulted in the smallest yield. The autumn transplant allows oysters to benefit from the larger spring phytoplankton bloom over the leased grounds in the lower estuary. The effect of varying the season of transplant was most noticeable if oysters were harvested early (July or August). In all simulations, transplanting resulted in a higher abundance of market-size oysters than direct harvest from the seed beds. Direct harvest would rarely be advantageous if the cost of transplant were insignificant and the relative rates of mortality were as stipulated. However, a May transplant is only moderately better than a direct harvest and the economic benefits of either option are likely to be determined by the cost of transplanting and the mortality associated with the process. In the same vein, the decision as to when to harvest relies on balancing the increased price obtained for oysters in the autumn with the increased loss owing to predation and disease. Awaiting an autumn harvest is clearly much riskier if the principal source of mortality is disease rather than predation, because disease mortality is concentrated on the market-size oysters and is greatest in the autumn.     

西北太平洋鲐的资源养护和管理研究

鲐(Scomberjaponicus)是西北太平洋海域重要的渔业种类,该渔业涉及多个国家的多种作业方式,渔业形势较复杂,但目前西北太平洋海域尚无基于资源评估的、完善的鲐养护管理措施。本研究使用传统渔业管理方法(资源预测)和较新颖的方法[数据有限的渔业管理规程评价(managementstrategyevaluation,MSE)]对鲐的渔业管理进行了研究。在资源预测方法中,通过JABBA和JABBA-Select两个资源评估模型对种群未来的资源动态进行模拟,探讨不同捕捞控制规则(harvest control rules, HCR)下种群的变化。本研究设置了4个HCR,分别以2020年渔获量的0.8～1.4倍,最大可持续产量MSY、B×FMSY和SB×HMSY (分别用于JABBA和JABBA-Select)、历史最高渔获量为总可捕量(totalallowablecatch,TAC),预测2023—2032年间的鲐种群变化。结果显示基于亲体资源量进行研究的JABBA-Select模型,其预测结果相比于JABBA模型略悲观,但都是基于生物学参考点设定的HCR养护和管理效果最好(TAC分别为50～80万t和50～66万t)。MSE则根据设定筛选出12种养护管理效果较好的策略,其中DAAC(消耗率修正后的平均捕获量)与SBT2 (基于资源量和渔获量水平的总可捕量递增矫正法)养护管理效果最好。SBT2求得的TAC (520387 t),与近些年产量及上述HCR的结果较为接近。此外,敏感性分析表明,可捕系数,自然死亡系数和渔获量相关的参数(平均渔获量、渔获量、渔获量参考点)对于养护管理效果的影响最为明显,需要额外关注两者的准确性和精确性。现阶段为确保西北太平洋鲐资源的养护和最佳利用,建议根据B×FMSY或SB×HMSY设定年可捕量,同时基于资源量和渔获量水平进行调整,综合制定管理措施。     

褐菖鲉渔业生物学初步研究

褐菖鲉为肉食性、暧水性底栖鱼类,体长范围10～28.7cm,优势组15.0～19.0cm,体重范围46～500g,优势组120～200g,体长与体重关系为W=0.2857L~(29163);褐菖鲉为多次产仔型卵胎生鱼类,体重300～400g亲鱼可产仔3～5万尾;褐菖鲉资源呈季节性分布,不同季节出现密度有明显差异。     

Marine fish life history strategies: applications to fishery management

The life history traits of 42 marine fish species were grouped according to the theoretical classifications of life history strategies. This provides a conceptual framework of management options, because life history strategies are the underlying determinants for population responses to climate and ocean changes, they can be used to classify typical population responses. When faced with providing management advice for species for which there is no information on absolute or relative biomass, such as newly exploited species, life history traits can be used to classify the species into a strategist grouping and the appropriate management options can be selected from the conceptual framework.     

Genetic diversity and population history of the migratory catfishes Pangasianodon hypophthalmus and Pangasius bocourti in the Cambodian Mekong River

ABSTRACT:   Polymerase chain reaction (PCR) restriction fragment length polymorphism analysis of mitochondrial DNA was applied to the genetic structure and evolutionary history of the more ancestral Pangasianodon hypophthalmus ( n  = 82), and the recently speciated catfish Pangasius bocourti ( n  = 90) from the Cambodian Mekong River. Both pangasiids were characterized by a lack of genetic population structure that may result from high levels of contemporary gene flow. Genetic diversity was lower in P. hypophthalmus than in P. bocourti . However, a different evolutionary history was inferred for both species based on genealogical and demographic analyses (mismatch analysis, Tajima's D- and Fu's F _S-tests). The genetic profile of the more ancestral P. hypophthalmus shows indications of a recent population bottleneck, whereas the recently speciated P. bocourti shows signatures of historical population expansion. This study stresses the importance of preserving the migration routes in the Cambodian Mekong basin in order to maintain the genetic diversity and long-term integrity of both species.