Scripps Institution study explains collapse of kelp, sand bass numbers
Press ReleaseOverfishing and changes in ocean conditions have contributed to the collapse of barred sand bass and kelp bass off the Southern California coast, according to a new study led by a researcher from Scripps Institution of Oceanography at UCSD.
Scripps postdoctoral researcher Brad Erisman and his colleagues examined the health of regional populations of the two fish — staple catches of Southern California’s recreational fishing fleet — by combining information from fishing records and other data on regional fish populations.
In a report in the Canadian Journal of Fisheries and Aquatic Sciences, the researchers say the total amount, or biomass, of each bass species has decreased 90 percent since 1980. Yet fisheries catch rates have remained stable for a number of years, even as overall population sizes dropped drastically.
This is due, the authors say, to a phenomenon known as “hyperstability” in which fishing targets spawning areas at which large numbers of fish congregate, leading to a misleading high catch rate and masking a decline in the overall population.
“The problem is when fish are aggregating in these huge masses, fishermen can still catch a lot each trip, so everything looks fine — but in reality the true population is declining,” said Erisman, a member of the Scripps Center for Marine Biodiversity and Conservation. “So as the true abundance is declining, the fisheries data used to assess the health of the fisheries are not showing that and give no indication of a collapse — this is referred to as ‘the illusion of plenty.’”
Erisman says the cod fishery that collapsed in the North Atlantic Ocean is the world’s most famous example of fisheries data masking an impending collapse, but other fish stocks in regions where fish congregate to spawn are declining as well.
In order to grasp a clear picture of the true health of the barred sand bass and kelp bass in Southern California, Erisman and his colleagues looked outside fisheries data. They tapped into fish population numbers tracked by power plant generating stations, which are required to log fish entrapments as part of their water cooling systems, and underwater visual censuses conducted by Occidental College since 1974.
“The combined evidence from this study indicates that persistent overfishing of seasonal spawning aggregations by recreational fisheries brought about the collapse of barred sand bass and kelp bass stocks in Southern California,” the authors wrote.
Larry Allen of California State University Northridge; Jeremy Claisse and Daniel Pondella II of Occidental College; Eric Miller of MBC Applied Environmental Sciences; and Jason Murray of the University of South Carolina coauthored the study.