Tying together California’s marine laws

This is the sixth in a yearlong series of stories showcasing the research that the Ocean Protection Council supported in partnership with California Sea Grant, with funding from Proposition 84.

When it comes to protecting marine ecosystems, two pieces of California legislation are key. The Marine Life Management Act, passed in 1999, sets guidelines for how commercial fisheries are to be managed — how the plans for each species will be developed, in essence. The same year, the Marine Life Protection Act led to the implementation of a system of more than a hundred protected areas off California’s coast between 2007 and 2013. Think of these as state parks on the ocean; no fishing is allowed inside the boundaries of many of these areas. Even their names suggest that the two laws are interrelated, but, unfortunately, for the most part, they are functionally separate.

The state’s marine protected areas (MPAs) have been shown to produce positive impacts for commercially harvested species — even outside the protected areas, since larvae and fish can spread from within the MPA to fishable zones. This phenomenon, known as “spillover,” should be reflected in fisheries management plans. 

But for that to happen, researchers needed models that predict the way that implementing an MPA might impact fisheries. That’s what a team of researchers set out to build, using funding from the Ocean Protection Council.

The team consisted of two scientists from the University of California, Davis — conservation biologist Louis Botsford and theoretical ecologist Alan Hastings – and Will White, a fisheries ecologist at Oregon State University. The first thread of their project focused on developing specific timelines for how long it will take before changes in spillover yield are likely to occur.

One key goal within an MPA is that the biomass of species within the protected zone returns to natural levels. The research team had already worked with the California Department of Fish and Wildlife to determine how long that would take for 19 local species, including several species of rockfish. (The answer: between 10 and 45 years.) Now, 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 straightforward mathematical solution, the team 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. The precise results also depend on fishing techniques, which can impact the ages of the fish captured as well as mortality rates.

The second thread of their research focused on resilience — which in this case meant how populations respond to a brief and sudden disturbance, such as the marine heatwave that hit California’s waters in 2014-2016. Using mathematical representations of fish demography, the research team found that mortalities are expected to be lower in MPAs, which in turn should speed up recovery times. They also found that in the face of repeated disturbances over many years, MPAs should help “buffer” fluctuations in the abundance of fish populations, helping sustain steadier populations. Under some conditions, the MPAs might also buffer fluctuations in fishery harvests outside their boundaries.

Together the results of this project will help fishery managers set expectations for the types of benefits MPAs could have for fisheries, and how soon those benefits could be detected.