Robust Management Strategies for a Commercial Marine Eel Conger Myriaster with Respect to Uncertain and Nonstationary Recruitment

Abstract

The stock recruitment relationship (SRR) is one of the key components in fish population dynamics. It can be easily affected by uncertainty from various sources, which are often overlooked in stock assessment especially for fisheries with limited data. Additionally, numbers of evidence indicate that the process of recruitment may exhibit nonstationarity with the intensification of global climate change. These factors can negatively impact the performance of fisheries management, however, the influences of uncertain and nonstationary recruitment have been rarely evaluated with respect to the robustness of fisheries management. In this study, a typical marine eel with complex life history and variable recruitment, whitespotted conger Conger myriaster, was used as an example to evaluate the impacts of process errors and steepness on the robustness of data-limited management procedures (MPs). The combined effect of variability and autocorrelation in recruitment was considered as process errors. As for steepness, we investigated the effects of estimated steepness from different methods and time-varying steepness, before we conducted the sensitivity analysis on the uncertain parameters, and designed six scenarios of time-varying steepness under the assumption of nonstationary recruitment, to assess their impact on the performance of tested MPs. We demonstrated that some simple, responsive MPs that can adjust catch (or effort) as abundance changes could be beneficial for fisheries management, although some were still sensitive to recruitment variability especially in terms of maintaining long-term yield. In addition, steepness from different estimation methods had little impact on their performance, while sensitivity analysis revealed that the overestimate of steepness may lead to higher risks in management. Finally, regarding the situation of time-varying steepness, all the MPs became substantially less robust. We highlight that for fish with complex recruitment processes and limited data, it is critical to identify the risks induced by uncertain recruitment for developing robust management strategies to achieve sustainable stock utilization.

Keywords: stock recruitment relationship, steepness, uncertainty, nonstationary, management strategy evaluation, robust management