Identifying threatened populations and quantifying their vulnerability is crucial for establishing priorities for conservation and providing robust information for decision-making. Lahille’s bottlenose dolphins have been long subjected to by-catch mortality in gillnet fisheries in coastal waters of southern Brazil, particularly in the Patos Lagoon estuary (PLE) and adjacent coastal waters, where dolphins from three populations (or Management Units) show overlapping home ranges. In this study we used a stage-classified matrix population model to conduct a demographic analysis of the PLE’s population with life-history data estimated through an 8 years mark-recapture study. A population viability analysis (PVA) was used to run a series of simulations where the risk was assessed under different by-catch scenarios, taking into account the effects of parameter uncertainty and stochasticity in the projections. In the absence of by-catch, we estimated that this dolphin population would growth at a rate of about 3% annually (95% CI: 1.2–5.8%). Under current by-catch rates, prognoses indicated high probabilities of viability over the next 60 years. These optimistic prognoses appear to be associated with the high survival of adult females. However, the eventual removal of very few mature females (one every year or two) would result in a prominent likelihood of decline from its current abundance at all pre-specified levels. The viability of the population would be substantially improved if the survival of juveniles/sub-adults could be increased. This may be achieved through the recently implemented dolphin protection area, which prohibits gillnet fisheries in the core area of this population. If the protection area reduces the entanglement rates of the most impacted life-stages (i.e., juvenile/sub-adult dolphins), there would be a substantial chance of the PLE’s dolphin population increasing above 20% of its current size, which is here proposed as conservation goal. If met, this goal has the potential to promote habitat quality, increase genetic diversity and connectivity with adjacent populations, enhancing the ability of bottlenose dolphins in southern Brazil to cope with environmental change and potential disease outbreaks.

中文翻译：

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巴西南部拉希尔宽吻海豚的小型河口居民种群的动态和生存能力

识别受威胁种群并量化其脆弱性对于确定保护优先事项和为决策提供可靠信息至关重要。拉希尔宽吻海豚长期以来一直在巴西南部沿海水域的刺网渔业中遭受副渔获物死亡率，特别是在帕托斯泻湖河口 (PLE) 和邻近的沿海水域，来自三个种群（或管理单位）的海豚显示出重叠的栖息地. 在这项研究中，我们使用阶段分类矩阵人口模型对 PLE 的人口进行人口统计分析，并通过 8 年的标记重新捕获研究估计的生活史数据。种群生存力分析 (PVA) 用于运行一系列模拟，其中在不同的副渔获物情况下评估风险，考虑到预测中参数不确定性和随机性的影响。在没有副渔获物的情况下，我们估计这种海豚种群将以每年约 3% 的速度增长（95% CI：1.2-5.8%）。在当前的副渔获物率下，预测表明未来 60 年的生存概率很高。这些乐观的预测似乎与成年女性的高存活率有关。然而，最终移除很少的成熟雌性（每年或每两年一个）将导致其当前所有预定水平的丰度下降的显着可能性。如果可以增加幼鱼/亚成鱼的存活率，种群的生存能力将得到显着提高。这可以通过最近实施的海豚保护区来实现，禁止在该种群的核心区域进行刺网渔业。如果保护区降低了受影响最大的生命阶段（即幼年/亚成年海豚）的纠缠率，PLE 的海豚种群将有很大可能增加到其当前规模的 20% 以上，这里建议作为保护目标。如果实现，这一目标有可能提高栖息地质量，增加遗传多样性和与邻近种群的连通性，增强巴西南部宽吻海豚应对环境变化和潜在疾病爆发的能力。PLE 的海豚种群很有可能会增加到其当前规模的 20% 以上，这是这里提出的保护目标。如果实现，这一目标有可能提高栖息地质量，增加遗传多样性和与邻近种群的连通性，增强巴西南部宽吻海豚应对环境变化和潜在疾病爆发的能力。PLE 的海豚种群很有可能会增加到其当前规模的 20% 以上，这是这里提出的保护目标。如果实现，这一目标有可能提高栖息地质量，增加遗传多样性和与邻近种群的连通性，增强巴西南部宽吻海豚应对环境变化和潜在疾病爆发的能力。