Laboratório de Dinâmica de Populações Aquáticas (DAQUA), Universidade Federal Rural de Pernambuco (UFRPE), Unidade Acadêmica de Serra Talhada (UAST), Serra Talhada, PE, Brazil.
Laboratório de Dinâmica de Populações Marinhas (DIMAR), Universidade Federal Rural de Pernambuco (UFRPE), Departamento de Pesca e Aqüicultura (DEPAq), Recife, PE, Brazil.
PLoS One. 2020 Aug 6;15(8):e0236146. doi: 10.1371/journal.pone.0236146. eCollection 2020.
The smalltail shark, Carcharhinus porosus, was the most abundant elasmobranch species in fisheries off Brazil's northern coast (BNC) in the 1980s, but its population has been declining since the 1990s. For this reason, a demographic analysis is necessary to determine the extent of this decline and the fishing effect on the BNC's population. Therefore, we performed a stochastic demographic analysis of the population in the BNC, and considered its global center of abundance. Smalltail shark specimens (n = 937) were collected with gillnets in Maranhão state, eastern BNC, in the 1980s with sizes ranging between 29.6 and 120.0 cm total length. Most of the individuals (90.6%) caught were juveniles (< 6 years-old), and the mortality and exploitation rates showed that the species was overexploited (92.3% above the fishing mortality corresponding to the population equilibrium threshold). The smalltail shark's biological characteristics, such as slow growth and low fecundity, demonstrate that it is one of the least resilient species among similar sized coastal sharks in the region. All these factors yielded an annual decrease of 28% in the intrinsic population growth rate, resulting in a population decline of more than 90% in only 10 years, and much higher for the current period. This set of features comprising fishing recruitment occurring upon juveniles, overfishing, and intrinsically low resilience make the population unable to sustain fishing pressure and severely hamper biological recruitment, thus causing this drastic population decline. Furthermore, several local extinctions for this species in the northeastern and southeastern regions of Brazil highlight its concerning conservation scenario. Therefore, since similar fisheries characteristics occur throughout its distribution range, C. porosus fits the criteria E of the IUCN Red List for a critically endangered species and urgent conservation measures are needed to prevent its extinction in the near future.
小尾真鲨（Carcharhinus porosus）是 20 世纪 80 年代巴西北部海域（BNC）渔业中最丰富的鲨鱼物种，但自 20 世纪 90 年代以来，其数量一直在下降。因此，有必要进行人口统计分析，以确定这种下降的程度以及渔业对 BNC 种群的影响。因此，我们对 BNC 的小尾真鲨种群进行了随机人口统计分析，并考虑了其全球丰富度中心。20 世纪 80 年代，在马腊尼昂州（Maranhão state）的 BNC 东部，使用刺网采集了 937 个小尾真鲨标本，体长范围在 29.6 至 120.0 厘米之间。被捕捞的个体中，大部分为幼鱼（<6 岁），死亡率和捕捞率表明该物种已过度捕捞（超过种群平衡阈值对应的捕捞死亡率 92.3%）。小尾真鲨的生长缓慢和低繁殖力等生物学特征表明，它是该地区类似体型沿海鲨鱼中最缺乏弹性的物种之一。所有这些因素导致其内在种群增长率每年下降 28%，仅在 10 年内种群数量就下降了 90%以上，而目前的情况则更高。这种由捕捞幼鱼、过度捕捞和内在低弹性引起的捕捞压力，使得种群无法维持，严重阻碍了生物补充，从而导致这种急剧的种群下降。此外，该物种在巴西东北部和东南部的局部灭绝突显了其令人担忧的保护状况。因此，由于其分布范围内存在类似的渔业特征，小尾真鲨符合 IUCN 红色名录极度濒危物种 E 类标准，需要采取紧急保护措施，以防止其在不久的将来灭绝。
