Using a length-based stock assessment model to evaluate population structure hypotheses of nylon shrimp Heterocarpus reedi (Decapoda, Caridea) exploited off central Chile

Spatial processes are rarely considered explicitly in the evaluation and management of marine invertebrate populations. This is particularly true when larval drift acts as one of the main mechanisms of population expansion. The ecological concept metapopulation is widely used and accepted for understanding low-mobility marine populations. This study uses a length-based dynamic analysis model for nylon shrimp (Heterocarpus reedi) exploited off central Chile (25°-37°S) to contrast various hypotheses of population structure and spatial connectivity. The two subpopulations studied are located to the north and south of 32°S. The model is fitted to the historical fishery data (from the mid-1940s to the present), the results of monitoring of fishing activities (1970s-present), and research surveys (1990s-present). Statistically, several hypotheses can explain the data. The most likely hypothesis is that of a metapopulation in which the south zone acts as a source population (reproductive refuge) and determines, partially or totally, the recruits in the north zone, thereby explaining the population increase over the last decade. Empirical evidence will strengthen the hypothesis of spatial connectivity and special attention should be paid to the biological-fishery conditions recorded south of 32°S given the implications for managing the fishery for this resource.