基于鱼类体长结构分析的鄱阳湖禁渔效果评估

研究分析了禁捕前(2017—2019年)和禁捕后(2021—2022年)鄱阳湖25种主要鱼类种群平均体长、体长比例分布(Proportional size distribution, PSD)及性成熟个体占比等3个指标的变化, 从鱼类种群体长结构变化方面评估鄱阳湖禁渔效果。结果显示: 鄱阳湖持续禁渔2年后, 大部分评估鱼类物种个体小型化现象有效缓解, 种群中大个体及性成熟个体占比增加, 种群结构得到优化。具体而言, 在25种评估鱼类中, 24个物种平均体长增加2.3%—115.0% (P<0.05)、种群PSD值增长3—71 (P<0.05); 20个物种种群性成熟个体占比增长23.2%—10712.8%。但不是所有物种都呈现一致性的变化, 其中有1种鱼类(飘鱼)平均体长下降5.0% (P<0.05), 种群PSD值下降21 (P<0.05); 5种鱼类(鲤、鳊、花䱻、飘鱼、大鳍鱊)种群性成熟个体占比下降23.5%—79.8%。在种群稳定状况评估方面, 禁渔前处于不稳定状况(PSD<50及PSD≥80)的鱼类有21种, 仅4种处于稳定状况(50≤PSD<80); 禁渔后种群处于不稳定状况的鱼类减少至15种, 处于稳定状况的增长至10种。总体来说, 禁渔措施促进了鄱阳湖大多数评估物种种群结构的优化, 但也有一部分物种的种群结构呈现出不同的变化趋势。因此, 鄱阳湖应持续执行全面禁渔措施, 同时建立和完善鱼类种群动态的长期监测体系, 通过科学评估与管理, 以实现鄱阳湖渔业资源的可持续恢复及生态系统服务功能的优化提升。     

Length–weight relationships of mesopelagic fishes from the equatorial and tropical Atlantic waters: influence of environment and body shape

Length–weight relationships (LWRs) were estimated for 36 mesopelagic fish species collected from the equatorial and tropical Atlantic encompassing several oceanographic regions: oligotrophic, equatorial, Cape Blanc, Cape Verde and the Canary Islands. The sample was composed of myctophids (25 species), gonostomatids (5), sternoptychids (3), stomiids (2) and phosichthyids (1). The species were clustered according to body shape: “short-deep” (sternoptychids), “elongate” (gonostomatids, stomiids and some phosichthyids) and “fusiform” (myctophids and some phosichthyids). Three types of weight and LWRs were considered: wet weight (WW), eviscerated wet weight (eWW) and eviscerated dry weight (eDW). The study demonstrated that most species present a positive allometric growth, independent of the weight used. However, the allometric value varied in 40–50% of species depending on the type of weight considered. Significant variations linked to fish morphology were found in the relationship between the slope and intercept of the LWR equation. Significant differences were also noted in the water content linked to fish body shape. Based on the distributions of several species we compare their fitness between oceanographic regions using the relative condition factor (K_rel). Except for Diaphus brachycephalus (oligotrophic vs. equatorial waters) and Lampanyctus alatus (equatorial, Cape Blanc, Cape Verde and the Canary Islands), no regional significant differences were observed in the species analysed.     

北大西洋大青鲨种群统计分析

大青鲨是金枪鱼延绳钓渔业中最主要的兼捕鱼种,在海洋食物网中属于顶端物种,在海洋生态系统中处于重要地位.由于数据限制,传统的资源评估方法很难准确描述大青鲨的资源动态.本研究基于大青鲨的生活史参数,应用种群统计分析法评估大青鲨的种群参数和资源状态,并探讨了内禀增长率为0时对应的临界捕捞死亡系数F_c与开捕年龄t_c的关系.结果表明： 未开发状态下,大青鲨存活率为0.719～0.820;大青鲨的内在瞬时增长率(r₀)为0.250～0.381,种群倍增时间(t_x2)为1.819～2.773年,种群的净繁殖力(R₀)为6.600～22.255,世代间期时间(G)为8.498～〖JP2〗10.162年,种群资源状态良好.生活史参数的敏感性检验显示,大青鲨初始年龄的自然死亡系数、种群性成熟年龄及寿命的不确定性对种群统计参数的意义影响不大;临界捕捞死亡系数伴随开捕年龄的增大而增大,当t_c≥5时,F_c值与t_c无显著相关关系.     

Rapid microsatellite marker development in the endangered neotropical freshwater turtle Podocnemis lewyana (Testudines: Podocnemididae) using 454 sequencing

Using high throughput sequencing we obtained a large number of microsatellites from Podocnemis lewyana, an endemic turtle from northwestern South America. We used 454 Genome Sequence FLX platform of sheared genomic DNA from randomly sampling approximately 17% of the haploid genome. We identified 86,501 reads (8.1% of all reads) that contained our definition of microsatellite loci. AC and TC were the most abundant motifs in the P. lewyana genome. TGC and AAAC were most abundant tri and tetra-nucleotide motifs respectively. 72.7% of microsatellite reads had flanking sequence regions suitable for primer design and PCR amplification. We validated the identified potentially amplifiable loci (PAL) and tested for polymorphism by selecting 15 loci corresponding to tetranucleotides. Twelve loci showed polymorphism in eight individuals. These findings demonstrates that microsatellite detection using next-generation sequencing is an efficient way of getting a lot of loci for listed taxa and in turn will have a large impact on future genetic studies aiming to understand and implement conservation plans for this highly threatened freshwater turtle.     

长江流域的主要人类活动干扰、水生态系统健康与水生态保护

为评估赤水河禁渔效果, 研究分析了禁渔前5年(2012—2016年)与禁渔后5年(2017—2021年) 20种主要鱼类种群的平均体长、种群体长比例分布(Proportional size distribution, PSD)及种群中性成熟个体占比变化。结果显示: 在禁渔持续5年后, 主要物种个体小型化初步缓解, 大个体及性成熟个体占比增加, 种群结构得到优化。其中, 16种鱼类种群平均体长增长1.7%—104.5% (P<0.05); 种群PSD值增长1—57 (P<0.05); 13种鱼类种群中性成熟个体占比增加1.0%—81.4%。但是, 并非所有物种都呈现一致性的表现, 有2种鱼类种群平均体长及PSD值无显著变化; 2种鱼类种群平均体长下降2.4%—6.2% (P<0.05), 种群PSD值下降3—15 (P<0.05)。7种鱼类种群中性成熟个体占比下降0.8%—18.1%。在禁渔后, 20种主要鱼类的种群体长结构变化存在差异, 这表明尽管大部分的优势鱼类种群结构得到有效改善, 赤水河鱼类的全面恢复却尚未实现。禁渔措施在促进部分鱼类资源恢复的同时, 也改变了鱼类群落结构, 并推动了整个水域生态系统的动态调整。因此文章建议, 赤水河禁渔应当持续, 并应在此基础上开展全面、长期、连续的监测和研究, 以期实现赤水河鱼类资源的有效恢复和生态系统服务功能的提升, 并为长江十年禁渔效果的评估及未来资源管理和生态保护提供可靠的理论和技术支撑。

     

Diversity of isopods (Crustacea): new data from the Arctic and Atlantic Oceans

New data on the diversity pattern of isopods (Crustacea) from the northern most part of the North Atlantic and the Arctic Oceans is presented. The pattern of diversity with depth is similar at depths <1000m, but differs considerably below about 1000m. In the Arctic the diversity of isopods (expressed both as numbers of species per sled and expected number of species) increased with increased depth to a maximum at depths of about 320 to 1100m, but then declined towards deeper waters. There was a significant increase in numbers per sled and in the expected number of species with increased depth in the northernmost part of the North Atlantic Ocean. Additionally, changes occurred in the relative composition of the shallow and deep water fauna, with asellote isopods being relatively larger part of the isopod fauna in the Arctic than in the northern most part of the North Atlantic. This indicates major faunistic changes occurring at the Greenland-Iceland-Faeroe Ridge, possibly caused by rapid changes in the temperature. Furthermore, that the low diversity of the Arctic deep-sea is a regional phenomenon, and not a part of a large scale latitudinal pattern in the North Atlantic.     

First direct documentation of associations of Ceratolithus cristatus ceratoliths, hoop-coccoliths and Neosphaera coccolithomorpha planoliths

Study of plankton sample from the northeast Atlantic has revealed an exceptional specimen of Ceratolithus cristatus. This consists of a rostratus-type ceratolith surrounded by a collapsed coccosphere of delicate hoop-coccoliths and a partial outer collapsed coccosphere of nishidae-type planoliths. This provides the final direct evidence needed to support the earlier hypothesis that these three calcareous structures are all provided by the single species Ceratolithus cristatus. It appears likely that this species has a complex life-cycle.     

What can metazoan parasites reveal about the taxonomy of Scomber japonicus Houttuyn in the coast of South America and Madeira Islands?

The metazoan parasites of four populations of the chub mackerel Scomber japonicus were analysed from two localities in the Atlantic Ocean (Madeira Islands, Portugal, and Rio de Janeiro, Brazil) and two localities in the Pacific Ocean (Callao, Peru, and Antofagasta, Chile), collected during 2002 and 2003. A total of 373 fish specimens were studied and 34 metazoan parasite species were obtained. Parasites identified from the populations of chub mackerel studied could be separated into three categories: parasites with a wide distribution, present in the Pacific and Atlantic, parasites proper of the Pacific Ocean and parasites proper of the Atlantic Ocean. The analyses of some highly specific parasites of the genus Scomber ( i.e. monogeneans of the genus Kuhnia and didymozoid digeneans) strongly suggest the need for a revision of the taxonomic status of chub mackerels from the Atlantic and Pacific coast of America. The results demonstrated the usefulness of parasites as adequate tools to clarify the taxonomic status of their hosts.     

Long-term declining trend of zooplankton biomass in the Tropical Atlantic

We report evidences that the zooplankton biomass in the tropical Atlantic has declined with an almost 10-fold drop from the 1950s to 2000. The results of the multiple regression analysis showed that the decline in zooplankton biomass was positively related to the NAO-index and to phosphate concentration. We also found that the depth of the thermocline has decreased over the period of our investigation. Thus, the decline we report in zooplankton biomass may be related to the combined effect of two phenomena driven by global temperature increase: (1) the widening of the distributional range of tropical species due to the expansion of the ‘tropical belt’ and (2) a decrease in primary production resulting from the thinning of the thermocline. The decline of zooplankton biomass we report suggests that global warming of the ocean may be altering tropical food webs, and through them, it may also indirectly impact tropical oceans biogeochemical cycles. Handling editor: S. I. Dodson     

Distribution of the twenty seven dominant species of shelf benthic foraminifers on the continental shelf, north of Dakar (Senegal)

One hundred and thirty-one samples were collected on the shelf and on the uppermost slope (down to 180 m) off Northern Senegal, between 14 °50′ and 16 °20′ N latitude.Two hundred and three species of benthic foraminifers were recognized. Most of them were reported in previous works, along the coast of Africa. Twenty seven species are selected for detailed analysis and distribution maps are given for each of them. Q mode and R mode statistical analyses were performed on these selected species. The distribution is mainly related to depth; the second factor of distribution is the nature of the sediments: about 30% of the study area is covered by the muddy sediments of the pro-delta of the Senegal river. Hierarchical analysis shows that the main limit in the pattern of change of these 27 species with depth is about 60–65 m.A depth index Di, calculated on the basis of twelve selected species, gives a depth indication with a precision of about 40 m over the shelf. It is possible to envisage a possible use of this index for the investigation of Quaternary sea-level changes.