Fraser Sockeye Collapse: Did sea lice play a role?

UW sockeye (c)There has been much media attention about the factors responsible for the Fraser sockeye collapse, and whether sea lice from fish farms were a contributor. As an organization on the front lines of this issue, our research plays a pivotal role in finding an answer.

In the spring of 2007, Raincoast’s field crew searched the waters for juvenile sockeye among the Discovery Islands (at the northern end of Georgia Strait). This region hosts BC’s largest concentration of salmon farms, and there is growing concern that sea lice from farms may be infecting migrating juvenile sockeye from the Fraser River; hence, our study.

The now missing Fraser sockeye were on course to migrate through this region in the late spring of 2007. Roughly 60% of the sockeye smolts we sampled that spring were of Fraser River origin. Chilko and Quesnel Lake stocks were the only Fraser populations we identified, which suggests that they were the most abundant populations leaving the Fraser that year, and that they had travelled at least as far as the Discovery Islands. Ironically, Chilko and Quesnel Lake fry were the 2 most abundant populations to leave the Fraser River in 2007, with Chilko alone producing over 78 million fry.

Even at a low survival rate, the return from Chilko Lake fish alone should have been 1 million sockeye. Because ocean conditions were considered favourable for marine survival during the 2007 out-migration, DFO predicted high spawner returns to the Fraser of over 10 million sockeye. These fish failed to return.

Incidental surveys by DFO during 2007 suggested that very low numbers of sockeye juveniles were in the Georgia Strait that spring. However, these surveys occurred in late July, a time when the majority of Fraser sockeye smolts have already left Georgia Strait.

Could parasitism of smolts by sea lice be the reason so many Fraser sockeye failed to return, just as pink salmon populations have shown declines from fish farms in the northern end of Vancouver Island? It is highly possible, especially if sea lice act as vectors for the transmission of disease. A disease event is the most likely explanation for the massive die-off of Fraser smolts. If a salmon farm in the Discovery Islands region hosted a disease outbreak, sockeye transiting past that farm may also have become infected. And research from Europe has shown that sea lice can effectively transfer disease between hosts, jumping from an infected farm fish to a wild fish.

Poor early marine survival is the likely cause for the missing Fraser sockeye – the question is, are salmon farms the culprit. At Raincoast, we hope our Discovery Islands sea lice research will shed some light on the Fraser sockeye issue; we’ll be out there sampling again in the spring of 2010.

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