Questions and answers about the new salmon study
University of California, Davis, Dec. 13, 2010
Here are answers to some questions you may have about the new salmon study in Proceedings of the National Academy of Sciences. The answers were written by the
study’s lead author, Gary Marty.
Are sea lice from farm salmon causing wild pink salmon populations to go extinct, as other researchers have said?
No. In fact, because adult wild pink salmon are a source of sea lice for farm salmon, large numbers of sea lice on farm fish seem to be a good indicator of abundant wild pink salmon.
How could you reach a different conclusion from the same data?
The main difference is that we analyzed sea lice information from fish farms, data that had not been available before. Other researchers used only sea lice information from wild juvenile fish. We used the same population data for wild salmon but analyzed the area as a whole rather than as individual streams. The same underlying mathematical model was used to analyze the data.
Can the number of sea lice on farm fish be used to predict pink salmon returns?
No. Farm lice numbers provide no clues about how many juvenile wild pink salmon will eventually return to spawn. However, interestingly, our analysis shows that the number ofwild pink salmon returning to spawn in the fall can be used to predict the number of sealice on farm fish the next spring.
Are the researchers independent scientists?
None of the authors were compensated for this research. Co-author Sonja Saksida has served as a veterinarian and applied researcher to the aquaculture industry in British
Columbia for 15 years. She is now the executive director of a non-profit research facility—the BC Centre for Aquatic Health Sciences—that conducts wild and farm fish research. Since 2004, lead author Gary Marty has analyzed fish-farm samples for the
British Columbia provincial government, which is sometimes paid a fee for those services by the farm companies. In 2000 and 2001, Marty analyzed samples for fish farm companies in California and Virginia. The mathematical analysis was conducted by coauthor Terrance Quinn, a professor of fish population dynamics at University of Alaska Fairbanks, who has not worked for the aquaculture industry. Marty and Quinn have collaborated for more than a decade, investigating the effect of disease on population abundance of a Pacific herring population in Alaska.
Do other scientists have access to your data?
Yes. All data used for our analyses are posted on the Proceedings of the National Academy of Sciences (PNAS) web site as supplementary online reference material.
Why didn’t the farms release the sea lice data before?
Because of many mergers and acquisitions in the aquaculture industry, none of the companies operating fish farms today in the Broughton Archipelago were operating there in 2000. The current aquaculture companies simply did not know the details about what data they inherited from their predecessors. Then, a couple of years ago, Dr. Saksida discovered the old sea lice counts. Many of the old counts were stored in handwritten logbooks filed in cardboard boxes stacked in a warehouse. The discovered data were still incomplete by today’s standards because counts from 2000-2002 were not done on every farm. Only recently—after many years of sea lice counts on all farms—did we realize that counts from only three farms were sufficient to estimate the number of farm sea lice in the entire Broughton Archipelago (about 15 active farms). Interestingly, analysis of multiple years of data has revealed important relationships that would not have been detected with only one or two years of data. Fish farm companies now post online the sea lice counts from all farms (except one) in the Broughton Archipelago.
Do you really think sea lice on farms don’t affect the health of individual wild fish, or wild populations?
Our analysis did not examine effects on individual fish, but controlled laboratory studies by other researchers have indicated that severe infestations of sea lice can kill the smallest pink salmon. Other research found that pink salmon eat sea lice. We found that in nearly all years any negative consequences must have been balanced by positive benefits. The 2003 run is the only one in which sea lice might have contributed to the population decline, but we can’t be sure about even that year because samples were not collected from those fish to rule out other causes of death. We also found that, from 1975 to 1977, the number of pink salmon returning to spawn declined 85 percent in the Broughton Archipelago but increased 72 percent in nearby populations that have no fish farms (“reference populations”). These differences occurred more than a decade before fish farming began in the Broughton Archipelago.
Do you think there is any decline in wild salmon populations today compared with pre-European-settlement times?
Yes, although effects have been lessened in the North Pacific now that billions of salmon are released annually from non-commercial hatcheries (mostly in Alaska, Russia, and Japan). Loss of habitat is probably the biggest threat to wild salmon populations during the freshwater phase of their life. Few comprehensive studies have been done on causes of mortality in the marine environment, so we really don’t know what threatens pink salmon populations during the saltwater phase of their life.
Does your study mean open-net salmon farms are not a threat to wild salmon populations?
Like many human activities, salmon farms are potentially a threat to wild salmon populations. But science-based regulations and changes in aquaculture practices can minimize and even eliminate these threats. My scientific opinion is that our finding of “no significant negative effect” is generally applicable for salmon aquaculture in the eastern Pacific. However, the strain of sea lice in the eastern Pacific is less of a problem.
Link: Gary Marty, D.V.M., Ph.D., Diplomate, A.C.V.P.
