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Biology of Sea Lice
Sea lice are small, salt-water copepods or crustaceans with soft bodies and are ordinarily enclosed within a hard, protective outer shell. Sea lice have a rounded body shaped like a cylinder and have many legs for swimming and collecting food. The term sea lice actually refer to several species of copepods that infect fish. Sea lice attach to the outside of fish, either on skin, fins, or gills where they live and feed on the mucous layer secreted by the fish’s skin.
The life cycle of a sea louse begins when a mature female, attached to a fish, sheds thousands of microscopic eggs into the sea. The eggs float near the surface at the whim of tides and currents until they hatch six to eight days later. Only then are they able to attach themselves to a fish.
The life cycle for L. salmonis (source: University of Prince Edward Island)
Sea lice are very common on all Pacific salmon adults during their return migration in coastal waters of BC. Commercial harvesters and First Nations people, both accustomed with handling salmon, have for generations reported seeing sea lice on wild adult salmon. Sea lice usually fall off the fish during processing.
Sea lice are naturally-occurring parasites found in all oceans and on many species of fish around the world. Wild Pacific salmon species have lived with consistent background levels of sea lice for centuries and have developed a natural tolerance to this parasite. Sea lice infections originate with wild salmon and are transferred to farmed salmon. Farmed salmon could then transfer sea lice infection back into the marine environment, infecting wild stocks. However, farm fish carry lower levels of sea lice than wild adult salmon, due to the ability for salmon farmers to control levels on their farm.
DFO is looking at all causes of sea lice levels . Sea lice populations are affected by environmental conditions and thrive in warm water temperatures and high salinity levels. Ocean temperatures and lower levels of freshwater runoff from reduced annual rainfall along the BC coast may be contributing to higher levels of sea lice.
Oceanographic studies, which DFO is conducting this year in the Broughton Archipelago, will help us determine what the impact of these factors may have in sea lice populations.
Two species of sea lice have been observed in the Broughton Archipelago since DFO began monitoring sea lice levels in the Broughton since 2001. Lepeophtheirus salmonis is commonly found on wild and farmed salmon and has been reported throughout the Pacific in areas including the high seas and coastal areas of Russia, Alaska and Canada. Caligus clemensi is found on several species of fish and occasionally on farmed salmon.
Map of the Broughton Archipelago
Source: Living Oceans Society
Stock Status of Wild Pink Salmon Populations in the Broughton Archipelago
DFO began monitoring Pink salmon populations in 1953. Pink salmon populations are known for large fluctuations in year-to-year returns as seen in the last fifty years.
[ Click on graphic to enlarge ]
*Historic average of adult pink salmon returns is 900,000.
Low returns of adult pink salmon in the Broughton Archipelago in the Fall of 2002 raised concern that sea lice levels in the Spring of 2001 – when juvenile salmon migrate from freshwater out to the ocean – were directly related to this decline. DFO, also concerned with the low numbers of adult pink salmon returning to this area, launched the
Pink Salmon Action Plan in 2003. Since 2003, departmental scientists have monitored levels of sea lice on juvenile pink and chum salmon to assess whether there is any correlation.
Pink salmon returns to the Broughton Archipelago and Knight Inlet returned to average levels in 2004 – approximately one million – consistent with what had been observed during the last 50 years. This is noteworthy because many opponents to salmon farms predicted poor returns given the presence of sea lice on wild salmon in 2003.
DFO conducts a thorough survey program including aerial surveys and on-site counts with well-trained technicians to attain the most consistent data possible. The salmon returning to spawn this year are still coming in and it is premature to draw any final conclusions on Pink and Chum spawning numbers. However, early results on adult Pink returns to the Broughton are promising, already exceeding the number that returned in 2003. This is an off-year cycle for Pink stocks in the Broughton Archipelago – meaning that odd-year returns are typically smaller than returns in even-numbered years.
Since 1987 – the introduction of salmon farms to the area – average returns of Pink salmon have been higher than the 50 year average. The chart above, and our research to date, does not support allegations there are collapses in pink salmon populations in this area.
Scientific Research and Assessment
DFO invests and supports collaborative research in this complex area in order to ensure that the best science possible underpins management decisions on salmon farming.
Salmon farms are jointly managed by the provincial and federal governments. DFO is responsible for the management of sustainable fisheries and aquaculture. The province is responsible for the day-to-day management of the industry.
In 2001, DFO examined the incidence of sea lice on juvenile salmon in the Queen Charlotte Strait. Samples were collected in a trawl survey conducted in Queen Charlotte Strait and a purse seine survey conducted in the Broughton Islands areas. Despite the appearance of some sea lice, the report showed that, in general, the juvenile pink salmon, as well as the other species collected in the two surveys appeared to be in very good condition. Here is a link to the report entitled,
Studies of early marine survival of Pacific Salmon and sea lice occurrence in Queen Charlotte Strait in 2001.
Unusually low returns of adult pink salmon to the Broughton Archipelago that fall prompted DFO to
explore potential causes for these low returns with the Pacific Fisheries Research Conservation Council. In 2003, DFO announced the
Pink Salmon Action Plan. We monitor sea lice and the possible effect on wild salmon in the Broughton Archipelago. We are looking at all possible sources of sea lice infections, distribution of juvenile pink and chum salmon, and environmental factors that influence sea lice abundance, like water temperatures and salinity. Our scientists are investigating the impact, if any, sea lice have on the health and productivity of wild salmon.
Please visit these links for detailed summaries of the sampling and findings:
Comparison of juvenile pink and chum salmon infected and non-infected with sea lice in 2003 and 2004 did not indicate any significant differences in condition or size of the sampled fish. See the backgrounder entitled, "2003 - 2005 Results" that compares sea lice levels on pink and chum salmon in the Broughton Archipelago and Knight Inlet during this time period.
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