Center for Marine Biodiversity and Conservation

The health of fish stocks greatly depends on the largest individuals within a population due to their high fecundity and genetic value, which contribute to the overall resilience and adaptability of the population. However, large fish are a common oversight in data-limited management decisions. Because of this, size truncation, the removal of large fish from an exploited population, poses significant ecological and management implications. This research presents a comprehensive analysis of size truncation in three rockfish species in Southern California – grass rockfish (Sebastes rastrelliger), squarespot rockfish (S. hopkinsi), and speckled rockfish (S. ovalis). This study applied Convergent Cross Mapping (CCM), which is a powerful statistical methodology often used for detecting causality in complex, non-linear ecosystems. I used CCM to identify the non-linear factors driving the size of both large and small fish, and the relative strengths of each factor, for three commonly caught species in California. Using an extensive dataset spanning 2004-2022 from the California Recreational Fisheries Survey (CRFS), alongside environmental variables including Scripps Pier ocean bottom temperature and Biologically Effective Upwelling Transport Index (BEUTI), this research identifies key patterns and relationships affecting fish size. The results reveal the complexities between fishing pressure and environmental variables, revealing that these factors exert distinct influences across different species. Most notably, fishing effort emerged as a stronger driver of big fish size than small fish size, while the opposite was true for temperature. These findings can provide valuable insights into the intricate dynamics contributing to size truncation and fishery recruitment, with implications for sustainable fisheries management.