Over the past several decades, California has implemented two major pieces of legislation to improve management of our local marine ecosystem: the Marine Life Management Act (MLMA) to improve fishery management, and the Marine Life Protection Act (MLPA) to implement a network of marine protected areas (MPAs). In spite of various meetings and efforts to manage these as a unified whole, they continue to be regarded as functionally different entities, often working at cross purposes as far as management goes.
Adaptive management, called for by both MLMA and MLPA, involves making predictions about the expected outcomes of a management action, monitoring the system to determine if expectations are met, and then adjusting management (or the predictive model) if expectations are not met.
One way to better integrate the MLMA and MLPA would be to take advantage of existing data that could help quantify the benefits of MPAs to fisheries and be used into adaptive management. In this project, the researchers aimed to develop new life history models to address adaptive management of the contribution of MPAs to fisheries yield outside the MPAs.
One thread of the research focused on resilience, which in this case meant how populations respond to a brief and sudden disturbance. Using complex math, Botsford, White, and their team found that the decreased mortality rates expected in MPAs increase resilience. Another thread of this project focused on developing specific timelines for how long it will take before changes in spillover yield are likely to occur.
One key outcome of an MPA is the return of the biomass of species within the protected zone to its natural level. Botsford and White had already worked with the California Department of Fish and Wildlife to determine how long that would take for 19 local species, including a number of rockfish. Next, they used that data to determine when the larvae produced by those bigger fish would begin spreading out beyond the MPA — thereby increasing the spillover yield.
That question has a “general solution,” as the researchers noted in a paper that was published in ICES Journal of Marine Science in 2021. Using a model that included data about how fish of different ages respond to environmental variations, they calculated that timeline for the species in question. This extended the time range to between 15 and 60 years, though the precise results also depend on fishing techniques, which can impact the ages of the fish captured as well as mortality rates.