Evaluating relative abundance, fish length, and marine protected area effectiveness for four key rocky reef species along the Northern Californian coast

Marine protected areas (MPAs) were created with the purpose of helping conserve and restore diminished populations of marine organisms. Measuring the effectiveness of MPAs requires long-term monitoring, investigating the abundance and size distributions of the species that utilize the conservation areas, and comparing the results to neighboring reference sites that are not currently protected. In this study, observations from long-term MPA monitoring in northern California (2010-2019) were modeled with substrate, oceanographic, spatial, temporal, and body size variables to describe the variability in abundance and size of three fish groups: Black rockfish (Sebastes melanops), the Blue rockfish group (comprised of Blue rockfish (Sebastes mystinus) and Deacon rockfish (Sebastes diaconus)), and Lingcod (Ophiodon elongatus). Models were also used to explain the differences in the abundance and size associated with protection status (MPA vs. reference). The data consisted of two MPAs and their paired reference sites (accessed from the ports of Eureka and Fort Bragg, CA), and another set of two auxiliary reference sites north of Trinidad, CA that were not paired with an MPA. Lagged oceanographic covariates had strong relationships with relative abundance of Black rockfish and illustrated the importance of upwelling as a long-lasting driver of adult relative abundance. Lagged oceanographic effects could be products of the long-term effects that upwelling has on recruitment. Substrate covariates and distance to port played an important role in describing the variability in relative abundance and length of the species, while substantiating previous studies. Weak, but detectable, effects of protection status on abundances of lingcod and lengths of all species were also found. The presence of detectable signals indicates that the MPAs within this study are beginning to positively influence abundances and lengths of the fish that reside within them, further supporting their utility and functionality as tools of conservation that can be used by fisheries managers. This study adds general information and critical insight into the population dynamics, environmental drivers, and management effectiveness of the species studied, along the California North Coast