Bradshaw Corey J A, Fukuda Yusuke, Letnic Mike, Brook Barry W
School for Environmental Research, Institute of Advanced Studies, Charles Darwin University, Northern Territory, Australia.
Ecol Appl. 2006 Aug;16(4):1436-48. doi: 10.1890/1051-0761(2006)016[1436:iksout]2.0.co;2.
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.
反复的研究表明，在一个被开发利用的种群中，调控机制的作用程度和环境变化的幅度共同决定了可实现的可持续捕捞类型。然而，通常情况下，捕捞模型通过假定一种特定的（未知的）内生控制形式，未能将目标种群潜在动态中的不确定性纳入其中。我们采用一种新颖的方法，以澳大利亚北领地主要河流系统中的咸水鳄（湾鳄）种群为例，该系统具有高度不确定性，来估计其可持续产量。我们使用多模型推断在产量估计中纳入三个层次的不确定性：（1）用于描述种群动态的基础模型选择的不确定性，（2）与模型参数估计的精度和偏差相关的误差，以及（3）环境波动（过程误差）。通过将五个连续的动态模型（有和没有漂移的密度无关模型以及三个替代的密度依赖模型）应用于密度估计的时间序列，我们证明了19个河流系统中鳄鱼密度调控的证据强度各不相同（1.3 - 96.7%）。随着每个河流系统监测的年度变化数量增加，密度依赖的证据也增加。确定性比例最大可持续产量（PMSY）模型在不同河流系统中差异很大（0.042 - 0.611），并且随着对密度依赖支持的增加，有强有力的证据表明PMSY在增加。然而，PMSY值与纳入所有形式不确定性的全随机模拟预测所产生的值之间也存在很大差异，这可以通过过程误差对可持续捕捞估计的贡献来解释。我们还确定，固定配额捕捞策略（高达0.2K，其中K是承载能力）比比例捕捞更快地减少种群规模（后一种策略需要对种群规模进行时间监测以调整捕捞配额），并极大地增加了资源枯竭的风险。通过利用一个从近期极端过度开发中恢复的标志性物种来研究重新实现可持续捕捞的潜力，我们证明将主要形式的不确定性纳入一个单一的定量框架为模拟被开发利用种群的动态提供了一种稳健的方法。
