October 16, 2024 — Two weeks ago I published an op-ed in the Santa Barbara Independent critiquing the proposals for expansion of California’s Marine Life Protection Act (MLPA) that established 124 MPAs across California. Follow this link to read the full op-ed, but essentially, I argued that in the last decade since the MPA network was established, there have been no benefits to the marine ecosystems of California. Thus, what are the proposed benefits to even more MPAs?
Carl Safina took particular exception to the op-ed and sent a note to his email list criticizing it. His note was flawed and sloppy and I feel compelled to respond on our own email list:
The MLPA 10-year review does not show that there are more fish in California because of the MLPA. It only shows that there are more fish inside some of the closed areas. The question of MPA effectiveness (in relation to fish) is how MPAs affect fish populations as a whole, not just in a closed area. There is no science that shows an increase in fish across California. Ovando et al., A 2021 paper evaluating the MPAs in the Channel Islands found no regional increase. In other words, the increase in fish inside the MPA was counterbalanced by less fish outside the MPA.
The fishing effort that was in the closed areas simply moved somewhere else and caught the fish there (often with more fuel burnt moving farther). During the planning process, many of us suggested there would be no overall benefit unless the stocks were overfished, and there was no evidence that overfishing was taking place. Everyone, even Safina, seems to accept that the amount of response you see inside the MPA depends on how much fishing pressure there was before the closure.
But the basis of Safina’s response to me was copy and pasting passages from the California Department of Fish and Wildlife decadal review. What he failed to grasp is that most of the review and the science in the report was looking at fish abundance inside the MPAs versus so called “reference sites” outside the MPAs. In theory, a reference site has similar habitat to the MPA so the abundance in the reference site is potentially what would have happened to the MPA without closure. You can think of it as what scientists would call a “control” site. What Safina (and many other MPA advocates) don’t understand about MPA science is the fallacy of comparing reference sites outside a protected area to fish abundance inside after the MPA is established.
Reference sites cannot be used as a scientific control because they are a “treatment.” After an MPA is established, the reference sites would have been fished harder after areas were closed because some of the fishing effort would have moved there. It is not a true control group as the establishment of the MPA essentially “treats” the reference site to more fishing. This fallacy permeates all of the quotes from the 10-year review Safina used to argue for positive benefits.
If the MPAs show more stability because fishing effort was removed, would we not expect the reference sites to show less stability because fishing effort increased there?
In the below figure from Ziegler et al. 2024, the catch per hour fished in different California MPAs is compared to nearby “reference sites” (arranged from north to south). The red is the MPA, the blue is the reference site. There is little difference in the areas where population density is low and MPAs are far from harbors (i.e. Cape Mendocino), while in Southern California, where there are far more people and MPAs are closer to harbors, the number of fish inside the MPAs went up. The differences are presumably influenced not only by how heavily the area was fished before the closure (leading to an increase inside the MPA), but also how much effort was then pushed out, leading to a decline in the reference areas.
Safina suggests that having some areas with more fish means the MLPA was a success. But if there are more fish in closed areas, and fewer fish outside, is this a success? I frankly doubt that the California legislature, or the people of California, would have supported the MLPA if it had been put to them that there would be no increase in fish abundance because of the MPAs but instead there would be more fish in some closed areas, but everywhere people wanted to go fishing would have fewer fish.
There are certainly advantages in having some closed areas as special sites for diving tourism and scientific study, but as the 10-year review said regarding tourism, “MPAs that allow some level of take and have nearby infrastructure, such as easily accessible parking lots, attract more human uses.” So does California need even more no-take areas?
Finally, I go back to a key point of my critique of the 10-year review. If the MLPA was a biological success, why are only 4 pages out of a 120 page report devoted to changes in species abundance?
Ray Hilborn
“Skepticism is the highest duty, blind faith the one unpardonable sin.” Thomas Huxley