Risk Analysis of Plausible Incidental Exploitation Rates for the Pacific Sleeper Shark, a Data-Poor Species in the Gulf of Alaska

Monte Carlo simulation was used to investigate the sustainability of incidental exploitation rates (<i>U</i>) for Pacific Sleeper Sharks <i>Somniosus pacificus</i> in the Gulf of Alaska (GOA) under status quo management. Monte Carlo simulations were implemented with a standard, length-based, age-structured model that was evaluated with forward projection. Given the paucity of relevant data, we investigated the sensitivity of simulation results to a range of assumptions about key model parameters by using 24 alternative model configurations, each simulated 1,000 times. The risk analysis results were most sensitive to Pacific Sleeper Shark <i>U</i>-values. The aggregate fraction of simulations ending in an overfished condition increased from 0% under the low-<i>U</i> scenario to 59% under the high-<i>U</i> scenario. Risk analysis results were also sensitive to the assumed shape of the length-based selectivity curve (asymptotic or dome shaped) but were less sensitive to the range of assumptions about other key model parameters, including maximum age and stock productivity. These results indicate that a priority for Pacific Sleeper Shark management is to reduce the uncertainty in <i>U</i>. This major uncertainty will be decreased by an observer program that is now in place to monitor the historically unobserved GOA Pacific Halibut <i>Hippoglossus stenolepis</i> fishery, which incidentally catches Pacific Sleeper Sharks. Received March 19, 2015; accepted December 7, 2015 Published online May 16, 2016

蒙特卡洛模拟（Monte Carlo simulation）被用于探究阿拉斯加湾（Gulf of Alaska, 缩写GOA）内太平洋睡鲨（Somniosus pacificus）在现状管理模式下的兼捕利用率（U）的可持续性。本次研究采用标准的基于体长的年龄结构模型，并通过正向投影对模型进行验证。鉴于相关数据匮乏，研究通过设置24种不同的模型配置（每种配置均模拟1000次），探究了模拟结果对关键模型参数的各类假设的敏感性。风险分析结果对太平洋睡鲨的U值最为敏感。最终处于过度捕捞状态的模拟结果占比从低U情景下的0%上升至高U情景下的59%。风险分析结果同样对基于体长的选择性曲线的假设形状（渐近型或穹顶型）较为敏感，但对包括最大年龄与种群生产力在内的其他关键模型参数的各类假设敏感性较低。上述结果表明，太平洋睡鲨管理工作的首要任务是降低U值的不确定性。目前已启动一项渔业观察员计划，对长期未被监测的阿拉斯加湾太平洋庸鲽（Hippoglossus stenolepis）渔业进行监管——该渔业同时兼捕太平洋睡鲨，这一计划将降低上述主要不确定性。收稿日期：2015年3月19日；录用日期：2015年12月7日；在线发表日期：2016年5月16日。