Events & Media

A New Take on Southern California’s Red Abalone
Selective fishing in diseased populations can help the species rebound

By Laura Lea Rubino

March 21, 2016

A new study released earlier this month finds that reopening Southern California’s disease-impacted red abalone fishery to limited fishing could be more beneficial to the health and survival of the highly prized species than continuing the current closure. The finding challenges the historical fisheries-management response to outbreaks of “withering syndrome” by suggesting that selective fishing of infected individuals can enhance the sustainability of the impacted populations.

A diver swabs a red abalone as part of a simple diagnostic test to determine whether it has withering foot disease.

The paper, titled “Fishing Diseased Abalone to Promote Yield and Conservation,” was lead-authored by Bren alumnus Tal Ben-Horin (MESM 2007, PhD 2013) and published in Philosophical Transactions of the Royal Society B. Ben-Horin’s PhD advisor, Bren professor Hunter Lenihan, is a co-author on the paper.

Withering foot first devastated Southern California’s red abalone fishery in the 1980s, and in 1997, the California Fish and Game Commission closed the fishery to save it from collapse. Though the disease has persisted in California populations for decades, red abalone stock densities have remained high in some places, including San Miguel Island. Abalone that have the disease are perfectly edible.

Because of red abalone's high market value and demonstrated resilience in certain locations, some managers are asking if the time has come to reopen San Miguel's red abalone fishery to limited fishing. In an effort to answer that important question, Ben-Horin, now a post-doctoral researcher at the University of Rhode Island, and his colleagues modeled the effects of three different management strategies — fishery closure, selective harvesting of infected individuals, and non-selective harvesting — on the presence of withering foot, productivity of the fishery, and abundance of abalone at San Miguel.

Using population models that predict the effects of different harvesting techniques on stock densities through time, the researchers found that when infected individuals are targeted, fishing can actually enhance stock abundance and sustainable yield. While non-selective fishing is expected to put disease-impacted populations at greater risk of collapse, selective fishing can decrease the prevalence of withering syndrome and improve the sustainability of the stock, making it harvestable again.

Selective fishing of red abalone is possible thanks to low-cost diagnostic tools that make it easy for managers to identify and remove infected individuals from the larger population. The authors of this study suggest that the technique could be used in other disease-impacted fisheries where managers can identify infected individuals in a non-destructive way, and where the diagnostic cost is small relative to the species’ economic value.

The study underscores the importance of understanding the relationship between infectious diseases and species population densities. By suggesting that the presence of a disease and fishing do not need to be mutually exclusive, Ben-Horin and his colleagues are changing the scientific conversation about how to optimally manage disease-impacted fisheries. When done the right way, fishing can in fact benefit conservation, the authors find, creating a win-win for marine ecosystems and the humans who depend on them.