A fish marking practice commonly used in Washington and Oregon could significantly increase wild salmon populations in California, while allowing continued harvest of abundant hatchery populations, according to a recent study published in Marine and Coastal Fisheries.
The article, first published June 18, is authored by Brian J. Pyper of Cramer Fish Sciences and Fish Metrics, Steven P. Cramer of Cramer Fish Sciences and Randoph P. Ericksen of Cramer Fish Sciences and the Wild Salmon Center.
California wild chinook salmon populations, including several populations that are protected under the Endangered Species Act, have declined over the past decades. This has led to increased management restrictions on commercial and recreational fisheries, as well as increased reliance on hatchery-raised fish to support those fisheries.
In Oregon and Washington, nearly all hatchery salmon produced for harvest receive a visible mark, while wild salmon remain unmarked and are therefore easily identified in ocean and river fisheries. When adult salmon are caught, marked hatchery salmon are kept, while unmarked wild salmon in most cases must be released back to the ocean or river.
This practice of “mark-selective fishing” has enabled many salmon fisheries in Oregon and Washington to continue despite serious concerns for the abundance of wild salmon, according to the recently published study. As an example naturally produced fish from a total of 13 salmon and steelhead stocks originating in the Columbia River basin are protected from non-tribal harvest.
Although California has not adopted this practice, the new study suggests that mark-selective fishing could result in substantial increases in wild salmon populations while maintaining important harvest opportunities, the research paper says.
“A harvest strategy that targets hatchery salmon over wild salmon makes sense when hatchery salmon are plentiful but are mixed with depleted wild populations” said Steve Cramer, founding scientist of the consulting firm Cramer Fish Sciences, and co-author of the publication. “If wild salmon populations in California continue to struggle and we do not find a solution that enables targeted capture of hatchery fish while allowing wild fish to escape, then it is likely that salmon fishing in California will be increasingly constrained to low levels.”
The study used data on the actual abundance and harvest of chinook salmon in northern California’s Central Valley and the ocean off California over two decades (1988-2007) to examine how mark-selective fishing regulations would have affected harvest and spawner abundance.
The study showed that selective fishing could have, if applied to past fishing seasons, doubled the number of wild salmon in California rivers. At the same time, it would have allowed substantial harvests of hatchery fish, depending on the proportion of salmon that were of hatchery origin.
The key results of the study applied to recent years (2001-2007) in which ocean fisheries were constrained to protect weak wild populations.
“We examined a range of plausible scenarios of fishing effort and hatchery salmon abundance,” Cramer explained. “When 60 percent or more of the salmon are from hatcheries, the mark-selective scenarios generally allowed for higher total harvests of salmon and modest increases in wild populations compared to the traditional regulations that were in place to constrain harvest and protect wild fish.”
The study cited other research that estimated hatchery fish have composed as high as 90 percent of chinook off California in recent years.
About 35 million juvenile chinook are released each year from Central Valley hatcheries, but most of these fish are unmarked.
“The high cost of marking all hatchery fish, and the challenge of working out new methods to estimate catch-and-release mortality of wild salmon has hindered fisheries agencies in California from implementing mark-selective fisheries,” Cramer said. “Despite these challenges, the results of our study suggest that serious consideration and evaluation of mark-selective fisheries for California salmon are warranted.”
The full study, “Implications of Mark-Selective Fishing for Ocean Harvests and Escapements of Sacramento River Fall Chinook Salmon Populations,” can be found here: http://www.tandfonline.com/doi/pdf/10.1080/19425120.2012.679575