Sea lice are getting local sockeye down

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Sockeye with higher levels of sea lice eat 20 per cent less than others. - Momo Lin
Sockeye with higher levels of sea lice eat 20 per cent less than others. - Momo Lin
Sockeye with higher levels of sea lice eat 20 per cent less than others. – Momo Lin

A study led by SFU researchers has found that sea lice infections are more common among juvenile sockeye salmon than previously thought, and infections caused by the parasites are negatively impacting the survival of the fish.

Sean Godwin, a PhD student in SFU’s department of biological sciences, explained: “Juvenile sockeye salmon that are migrating from the Fraser river, that are highly infected with sea lice, are less able to compete for food.”

Godwin explained, “sea lice are a type of parasite that attach to the outside of fish and feed on the surface tissue.” Although the species found on the sockeye during the study are native to BC, there has been rising concern over the past couple decades since the amount of lice on juvenile salmon is much higher than expected.

The study was based at the Salmon Coast Field Station in Port McNeill, and researchers collected the fish from the Johnstone Strait — a corridor along the east side of Vancouver Island used by migrating juvenile salmon to reach their winter feeding grounds as they travel from the Fraser River to the open ocean.

After collecting the juvenile sockeye, Godwin originally planned on separating the uninfected fish from the highly infected fish, but they were hard pressed to find uninfected fish. “Almost every single fish that we caught had sea lice on them,” he said.

Instead, the study focused on comparing the competitive abilities of lightly infected fish versus highly infected fish. Their results found that the highly infected fish were 20 per cent less successful at consuming food compared to the lightly infected fish. Each group was fed the same limited amount of food and contained fish of the same sizes.

Fish farms found along migratory routes seem to have played a role in the increase of sea lice found on salmon. These fish farms are “high-density environments for young Atlantic salmon in net pens, and the net pens do not have any barriers,” according to Godwin. Because of this, they serve as reservoirs for sea lice to grow and spread to wild salmon populations.

Godwin hopes that his research will help inform parasite management on fish farms, because the majority of sea lice species found on the juvenile sockeye he studied were different from the species that fish farmers treat for.

The next step is working towards forming a fuller understanding of the impact that sea-lice infection levels have on the young fish as they continue on their migratory route and age into adults.

“I hope other people can build on my results, we really need to do more research to figure out how and whether the sea lice levels will affect adult return stock,” said Godwin.