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Re-Creating Missing Population Baselines for Pacific Reef Sharks

机译：重新创建太平洋鲨鱼的缺失人口基线

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Sharks and other large predators are scarce on most coral reefs, but studies of their historical ecology provide qualitative evidence that predators were once numerous in these ecosystems. Quantifying density of sharks in the absence of humans (baseline) is, however, hindered by a paucity of pertinent time-series data. Recently researchers have used underwater visual surveys, primarily of limited spatial extent or nonstandard design, to infer negative associations between reef shark abundance and human populations. We analyzed data from 1607 towed-diver surveys (>1 ha transects surveyed by observers towed behind a boat) conducted at 46 reefs in the central-western Pacific Ocean, reefs that included some of the world's most pristine coral reefs. Estimates of shark density from towed-diver surveys were substantially lower (<10%) than published estimates from surveys along small transects (<0.02 ha), which is not consistent with inverted biomass pyramids (predator biomass greater than prey biomass) reported by other researchers for pristine reefs. We examined the relation between the density of reef sharks observed in towed-diver surveys and human population in models that accounted for the influence of oceanic primary productivity, sea surface temperature, reef area, and reef physical complexity. We used these models to estimate the density of sharks in the absence of humans. Densities of gray reef sharks (Carcharhinus amblyrhynchos), whitetip reef sharks (Triaenodon obesus), and the group "all reef sharks" increased substantially as human population decreased and as primary productivity and minimum sea surface temperature (or reef area, which was highly correlated with temperature) increased. Simulated baseline densities of reef sharks under the absence of humans were 1.1-2.4/ha for the main Hawaiian Islands, 1.2-2.4/ha for inhabited islands of American Samoa, and 0.9-2.1/ha for inhabited islands in the Mariana Archipelago, which suggests that density of reef sharks has declined to 3-10% of baseline levels in these areas.
机译：鲨鱼和其他大型捕食者在大多数珊瑚礁上都很稀少，但是对其历史生态学的研究提供了定性证据，表明这些生态系统中捕食者曾经很多。但是，由于缺乏相关的时间序列数据，无法在没有人类的情况下（基准）量化鲨鱼的密度。最近，研究人员已使用水下视觉调查（主要是有限的空间范围或非标准设计）来推断珊瑚礁鲨鱼数量和人口之间的负相关关系。我们分析了在中西部太平洋46个礁石上进行的1607个拖曳潜水员调查（观察员将其拖到小船后大于1公顷的横断面）的数据，这些礁石包括一些世界上最原始的珊瑚礁。拖曳潜水员调查的鲨鱼密度估计值大大低于（<10％），低于沿小样条线的调查报告的鲨鱼密度估计值（<0.02公顷），这与其他人报告的倒置生物金字塔（捕食者生物量大于猎物生物量）不一致原始珊瑚礁的研究人员。我们在模型中检查了拖曳潜水员调查中观察到的礁鲨密度与人口之间的关系，该模型解释了海洋初级生产力，海面温度，礁石面积和礁石物理复杂性的影响。我们使用这些模型来估计没有人类时鲨鱼的密度。随着人口的减少，初级生产力和最低海面温度（或礁石面积的高度相关），灰礁鲨（Carcharhinus amblyrhynchos），白鳍礁鲨（Triaenodon obesus）和“所有礁鲨”的密度显着增加。随着温度）增加。在没有人类的情况下，模拟的礁鲨基线密度在主要夏威夷群岛为1.1-2.4 /公顷，在美属萨摩亚有人居住的岛屿为1.2-2.4 /公顷，在马里亚纳群岛有人居住的岛屿为0.9-2.1 /公顷。这表明这些地区的礁鲨密度已降至基线水平的3-10％。

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