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NW Fishletter #242, February 7, 2008

[4] Northwest Fish Experts Debunk Controversial Sea Lice Study

A group of Northwest fisheries experts say that wild Canadian pink salmon runs are not in danger of extinction from sea lice infections picked up at British Columbia salmon farms during their juvenile migration, contrary to findings in a recent article (Krkošek et al.) published last December in the weekly journal Science.

The popular media took the original article at face value and ran with it--NPR said wild runs were being "ravaged" by the sea lice and the AP story characterized it as "the most direct evidence yet" that young pink salmon were dying from sea lice infections, while the Washington Post headline ran "Salmon Farming May Doom Wild Populations."

It's a hot-button issue in British Columbia, where salmon farms raise enough Atlantic salmon and chinook to make their products the province's top agricultural export. In 2006, export sales topped $450 million.

Any suspicion that these farms may have adverse effects on wild populations is sure to create a stir. For years, one of the study's authors, ex-whale researcher Alexandra Morton, has been blaming salmon farms in the Broughton Archipelago for infesting wild fish with sea lice.

But Port-Townsend, Wash-based fisheries consultant Kenneth Brooks and Canadian federal fisheries biologist Simon Jones, said when all the watersheds in the Broughton Archipelago were examined, pink salmon returns have "steadily increased" since 2003, "with no indication that they are threatened with extinction."

Their response is in press at the peer-reviewed journal Reviews in Fisheries Science, and should be posted on their website by next week. It has been endorsed by 18 other senior scientists working in this field in both academia and government agencies, including several researchers at NOAA Fisheries.

Brooks and Jones said the Krkošek paper also failed to acknowledge lab studies that show pink salmon can mount an effective resistance to sea lice, a trait not included in the paper's population model that predicted extinction.

They also took issue with the paper's assertion that the salmon farms are the source of larval sea lice--since research reported in 2006 found plenty of lice on sticklebacks in the region, and other work found that pinks that stayed in coastal waters in the Eastern Bering Sea showed about a 25 percent infection rate, which led other researchers to conclude that the overwintering salmon contributed to infestations of migrating smolts in the spring through release of lice larvae.

Brooks and Jones said it is "misleading" to conclude that sea lice infections are mostly associated with releases of larvae from salmon farms. "What is clear is that sea lice are found on juvenile salmon wherever we look in the Northeast Pacific and that there are numerous wild sources of these lice in addition to those contributed by salmon farms."

The critics also say Krkošek's model does not consider that fact that it is very unlikely that sea lice larvae can develop to an infective stage in the few days they are in the vicinity of the farms before being dispersed by wind and current.

Perhaps the most damning criticism Brooks and Jones leveled at the Science paper is their assertion that an analysis of the entire pink salmon database leads to the opposite conclusion reached by Krkošek et al. When all the numbers are examined, they say it's pretty obvious that the huge pink return to the Broughton region in 2000 (3.6 million) led to the population crash in 2002. They produced a graph of fish numbers that went back to 1953 to show "periodic declines, that, when analyzed over short periods of time, could be used to predict the extinction of pink salmon stocks."

With the marine survival of Fraser River pinks averaging little more than 1 percent, and coastwide around 2 percent to 3 percent, Brooks and Jones said pink survival in the Broughton Archipelago has been equal to or better than observed survival along the B.C. coast for the last four years.

The critics said the purpose of their own paper "is not to deny that salmon farms may contribute sea lice to the marine environment. The fact is that at this time research has not determined the relative contribution from wild and farmed sources of lice. Rather, this discussion is intended to provide additional information giving readers a broader perspective of these issues."

Brooks told NW Fishletter that Science refused to publish their letter rebutting the sea lice paper. He said the journal told him that it wasn't printing their response because it contained essentially the same information that was in their "in press" paper.

But Brooks disagrees. He said several other scientists have sent letters to Science that have taken the journal to task for publishing to the sea lice paper. But it remains to be seen whether Science's editorial board will publish any criticism of the Krkošek article.

A group called the Pacific Salmon Forum took issue with Krkošek's finding and went public with their concerns a few days after the Science article was published. The Forum bills itself as "a group of well-informed citizens, chaired by Hon. John Fraser, appointed by the BC Government in 2005 to commission research into salmon issues, fill knowledge gaps, and make recommendations in 2008 aimed at ensuring sustainable wild and farmed salmon industries."

They found similar results to Brooks and Jones. "However, interim findings from this research, to be released in early January 2008, do not support the Krkošek prediction of rapidly declining pink and chum salmon stocks in the Broughton. The marine survival of pink salmon to the Glendale River, the region's major producing river for pinks has been equal or better than the survival rates for pinks in other coastal watersheds where there are no salmon farms. Pink salmon returns in the other Broughton watersheds were as good as or better than those that occurred in 2005. All the field researchers noted that over 80 percent of the wild salmon smolts migrating out of the Broughton in the spring of 2007 had no lice whatsoever."

But in an interim report, the Forum recommended no net increase in farmed salmon production in the Broughton Archipelago until its research results are completed later this year.

The Forum has also invited Krkošek, who is a Ph.D candidate at the Centre for Mathematical Biology at the University of Alberta, to meet with their scientific committee to discuss his study. -B. R.

The following links were mentioned in this story:

Declining Wild Salmon Populations in Relation to Parasites from Farm Salmon, Science, Dec. 14, 2007

Perspectives on pink salmon and sea lice: scientific evidence fails to support the extinction hypothesis, In Press

BC Pacific Salmon Forum, Interim Report

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