1. The small population paradigm assumes that populations with low numbers of individuals intrinsically have a high probability of extinction. The small population of Lahille’s bottlenose dolphins Tursiops truncatus gephyreus that specializes in foraging with artisanal fishers in Laguna, southern Brazil, faces human pressures including bycatch in fishing gear. The viability of this population was modelled over 30 and 100 years under different levels of bycatch, including the current scenario of two bycatches every year, two scenarios with higher incidence of bycatches and three management scenarios. The sensitivity of predicted growth rates to fixed-proportion and observed-variation changes in life history parameters was explored.
2. The current scenario predicted a declining population (r = −0.014; λ = 0.986) with a high probability of extinction in the long term (PE = 0.71). A small increase in bycatches would result in a marked increase in the probability of extinction. Management scenarios seem promising, but only the zero-bycatch management scenario would make the difference between a declining and an increasing population.
3. As expected for slow-growing species, population growth rate was most sensitive to proportional changes in adult female and juvenile survival. However, considering observed variation in vital rates, population dynamics were most influenced by variation in reproductive rates.
4. To determine the highest priority for management action, another simulation was made of how additional threat scenarios of recognized human activities (i.e. bycatch influencing adult survival and increased underwater noise or pollution influencing calf survival) would affect population dynamics. Population growth rate was very sensitive to changes in adult bycatch (especially females), as expected, and only subtly sensitive to a reduction in calf survival.
5. The current level of bycatch is unsustainable. Bycatch needs to be eliminated to maximize the probability of long-term persistence of this dolphin population. However, this population’s persistence could be threatened by natural variation in reproductive rates.

中文翻译：

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专门与手工渔民一起觅食的海豚种群需要零兼捕管理才能持续

1. 小种群范式假设个体数量少的种群本质上具有很高的灭绝概率。Lahille 的宽吻海豚Tursiops truncatus gephyreus的小种群在巴西南部拉古纳专门与手工渔民一起觅食，面临着人类压力，包括渔具中的兼捕。该种群的生存能力在 30 年和 100 年的不同兼捕水平下建模，包括目前每年两次兼捕的情况、兼捕发生率较高的两种情况和三种管理情况。探讨了预测增长率对固定比例和观察到的生活史参数变化的敏感性。
2. 目前的情景预测人口下降（r  = -0.014；λ  = 0.986），长期灭绝的可能性很高（PE = 0.71）。兼捕量的小幅增加将导致灭绝概率的显着增加。管理方案似乎很有希望，但只有零兼捕管理方案才能在人口减少和增加之间产生差异。
3. 正如对生长缓慢的物种所预期的那样，种群增长率对成年雌性和幼鱼存活率的比例变化最为敏感。然而，考虑到观察到的生命率变化，人口动态受生殖率变化的影响最大。
4. 为确定管理行动的最高优先级，对已确认的人类活动的其他威胁情景（即影响成鱼生存的兼捕和影响小牛生存的水下噪音或污染增加）如何影响种群动态进行了另一次模拟。正如预期的那样，种群增长率对成年兼捕物（尤其是雌性）的变化非常敏感，并且对小牛存活率的降低只有微妙的敏感度。
5. 目前的兼捕水平是不可持续的。需要消除兼捕，以最大限度地提高这种海豚种群长期存在的可能性。然而，这一种群的持久性可能会受到繁殖率自然变化的威胁。