Bowlby Heather D, Gibson A Jamie F
Population Ecology Division Science Branch, Fisheries and Oceans Canada Dartmouth NS Canada.
Ecol Evol. 2020 Apr 28;10(11):4990-5000. doi: 10.1002/ece3.6252. eCollection 2020 Jun.
To effectively protect at-risk sharks, resource managers and conservation practitioners must have a good understanding of how fisheries removals contribute to changes in abundance and how regulatory restrictions may impact a population trajectory. This means they need to know the number of animals being removed from a population and whether a given number of removals will lead to population increases or declines. For white shark (), theoretical quantities like the intrinsic rate of population increase or rebound potential (ability to increase in size following decline) are difficult to conceptualize in terms of real-world abundance changes, which limits our ability to answer practical management questions. To address this shortfall, we designed a simulation model to evaluate how our understanding of longevity and life history variability of white shark affects our understanding of population trends in the Northwest Atlantic. Then, we quantified the magnitude of removals that could have caused historical population declines, compared these to biologically based reference points, and explored the removal scenarios which would result in population increase. Our results suggest that removals on the order of 100s of juveniles per year could have resulted in population-level declines in excess of 60% during the 1970s and 1980s. Conservation actions implemented since the 1990s would have needed to be nearly 100% effective at preventing fishing mortality in order for the population to double in abundance over the last 30 years. Total removals from all fleets needed to be exceptionally small to keep them below biological reference points for white shark in the Northwest Atlantic. The population's inherent vulnerability to fishing pressure reaffirms the need for restrictive national and international conservation measures, even under a situation of abundance increase.
为了有效保护濒危鲨鱼，资源管理者和保护从业者必须充分了解渔业捕捞如何导致种群数量变化，以及监管限制可能如何影响种群发展轨迹。这意味着他们需要知道从种群中捕捞的动物数量，以及特定数量的捕捞是否会导致种群数量增加或减少。对于大白鲨（ ）来说，诸如种群内在增长率或恢复潜力（数量下降后增加的能力）等理论数量，很难根据现实世界中的数量变化来概念化，这限制了我们回答实际管理问题的能力。为了解决这一不足，我们设计了一个模拟模型，以评估我们对大白鲨寿命和生活史变异性的了解如何影响我们对西北大西洋种群趋势的理解。然后，我们量化了可能导致历史种群数量下降的捕捞量，将其与基于生物学的参考点进行比较，并探讨了会导致种群数量增加的捕捞情景。我们的结果表明，在20世纪70年代和80年代，每年捕捞数百条幼鲨可能导致种群数量下降超过60%。自20世纪90年代以来实施的保护行动需要几乎100%有效地防止捕捞死亡，才能使种群数量在过去30年中翻倍。为了使西北大西洋大白鲨的总捕捞量保持在生物学参考点以下，所有船队的总捕捞量必须极小。即使在种群数量增加的情况下，该种群对捕捞压力的固有脆弱性再次凸显了采取严格的国家和国际保护措施的必要性。
