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Incorporating known sources of uncertainty to determine precautionary harvests of saltwater crocodiles

机译：结合不确定性的已知来源来确定咸水鳄的预防性收获

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It has been demonstrated repeatedly that the degree to which regulation operates and the magnitude of environmental variation in an exploited population will together dictate the type of sustainable harvest achievable. Yet typically, harvest models fail to incorporate uncertainty in the underlying dynamics of the target population by assuming a particular (unknown) form of endogenous control. We use a novel approach to estimate the sustainable yield of saltwater crocodile (Crocodylus porosus) populations from major river systems in the Northern Territory, Australia, as an example of a system with high uncertainty. We used multimodel inference to incorporate three levels of uncertainty in yield estimation: (1) uncertainty in the choice of the underlying model(s) used to describe population dynamics, (2) the error associated with the precision and bias of model parameter estimation, and (3) environmental fluctuation (process error). We demonstrate varying strength of evidence for density regulation (1.3-96.7%) for crocodiles among 19 river systems by applying a continuum of five dynamical models (density-independent with and without drift and three alternative density-dependent models) to time series of density estimates. Evidence for density dependence increased with the number of yearly transitions over which each river system was monitored. Deterministic proportional maximum sustainable yield (PMSY) models varied widely among river systems (0.042-0.611), and there was strong evidence for an increasing PMSY as support for density dependence rose. However, there was also a large discrepancy between PMSY values and those produced by the full stochastic simulation projection incorporating all forms of uncertainty, which can be explained by the contribution of process error to estimates of sustainable harvest. We also determined that a fixed-quota harvest strategy (up to 0.2K, where K is the carrying capacity) reduces population size much more rapidly than proportional harvest (the latter strategy requiring temporal monitoring of population size to adjust harvest quotas) and greatly inflates the risk of resource depletion. Using an iconic species recovering from recent extreme overexploitation to examine the potential for renewed sustainable harvest, we have demonstrated that incorporating major forms of uncertainty into a single quantitative framework provides a robust approach to modeling the dynamics of exploited populations.
机译：反复证明，监管的有效程度和被剥削人口中环境变化的严重程度共同决定了可实现的可持续收获的类型。然而，通常，收获模型无法通过假设特定（未知）形式的内源控制，将不确定性纳入目标种群的潜在动态中。我们使用一种新颖的方法来估算来自澳大利亚北领地主要河流系统的咸水鳄（Crocodylus porosus）种群的可持续产量，这是一个不确定性很高的系统的例子。我们使用多模型推论在收益估算中纳入了三个不确定性级别：（1）用于描述种群动态的基础模型选择中的不确定性;（2）与模型参数估算的精度和偏差相关的误差; （3）环境波动（过程误差）。我们通过对密度的时间序列应用五个动力学模型（与密度无关的有无漂移和三个与密度有关的替代模型）的连续统，证明了19个河流系统中鳄鱼密度调节的证据强度（1.3-96.7％）各不相同。估计。密度依赖性的证据随着对每个河流系统进行监测的年度过渡次数而增加。确定性比例最大可持续产量（PMSY）模型在河流系统之间差异很大（0.042-0.611），并且有强有力的证据表明随着对密度依赖性的支持增加，PMSY会增加。但是，PMSY值与包含所有形式不确定性的完全随机模拟预测所产生的值之间也存在很大差异，这可以用过程误差对可持续收成估算的贡献来解释。我们还确定，固定配额的采伐策略（最大为0.2K，其中K为承载力）比比例采伐（人口采伐需要临时监控人口规模以调整采伐配额）减少人口规模的速度要快得多，资源枯竭的风险。通过使用从最近的极端过度开发中恢复过来的标志性物种来检查新的可持续收获的潜力，我们证明了将主要形式的不确定性纳入单个定量框架中提供了一种强大的方法来模拟被开发种群的动态。

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