|Study Reviews Larval Sea Lice Biology; Models Spread, Infection From Aquaculture Facilities
Posted on Friday, May 04, 2018 (PST) http://www.cbbulletin.com/440646.aspx
|A natural parasite that can infect salmon, it has been thought that sea lice can be transferred from farmed salmon in net pens along Canada’s east and west coasts, but knowledge of whether and how that occurs is thin, according to a recent study.
The study is intended for scientists who attempt to model the spread of sea lice from fish farms to inform best management practices for fish farmers, according to co-author Adam Brooker, postdoctoral researcher at the Institute of Aquaculture, Faculty of Natural Sciences, at the University of Sterling in the United Kingdom.
The paper is a review of past research about the larval stages of sea lice, he said. As such, no new data is presented, and the paper is intended to describe current knowledge of larval sea lice biology and highlight areas where data is lacking.
“While the focus of the paper is on sea lice in the North Atlantic, we also present data from North Pacific studies – the lice from these two areas are separate sub-species with subtle differences in their biology,” Brooker said.
According to the study results, a key problem identified by the review is that current understanding of larval sea lice populations and spread originates from a number of sources and have been determined using a variety of experimental approaches.
Several major gaps in the knowledge of sea lice production, survival and infectivity (how successfully they can infect salmon) are identified by the study’s review, Brooker said. These are barriers to accurately modelling sea lice population dynamics in coastal regions, both in farmed and wild salmon.
A recent audit of Canadian salmon aquaculture operations on both east and west coasts found, among other things, that Fisheries and Oceans Canada and the Canadian Food Inspection Agency have not adequately managed the risks of salmon aquaculture consistent with a mandate to protect wild fish. That includes the spread of infectious diseases and parasites from net pens to wild salmon.
(See CBB, April 27, 2018, “Canadian Audit Finds Salmon Farms Not Being Managed Adequately To Protect Wild Fish,” http://www.cbbulletin.com/440604.aspx)
This study by Brooker et al surveys previous work on the state of the science as to how larval sea lice spread from net-penned salmon to wild salmon and how to predict that spread.
“Predictions of sea lice levels using sea lice models are only as good as the data that is inputted into the models,” Brooker said. “There are many gaps in our knowledge of the basic biology of sea lice, and more research is required to fill these gaps to create more accurate predictions of sea lice levels in coastal areas.”
He went on to say that it is incorrect to assume that all larval sea lice that hatch will survive to infect other fish, either farmed or wild.
“Many of these larvae will not survive, but we do not always know why, and in particular, predation of sea lice larvae by zooplankton is unquantified but is likely to cause significant deaths of sea lice,” Brooker said.
“Production, mortality, and infectivity of planktonic larval sea lice, Lepeophtheirus salmonis (Krøyer, 1837): current knowledge and implications for epidemiological modelling,” was published online February 19, 2018 in the ICES Journal of Marine Science (https://academic.oup.com/icesjms/advance-article-abstract/doi/10.1093/icesjms/fsy015/4877008?redirectedFrom=fulltext).
Brooker’s co-authors are J.E. Bron, also of the Institute of Aquaculture at the University of Sterling, and R. Skern-Mauritzen of the Department of Aquatic Pathogens and Diseases, Institute of Marine Research, Bergen, Norway.
Sea lice are a part of the natural ocean ecosystem, Brooker said. While sea lice can cause significant damage and death in individual salmon in certain circumstances (for example, small fish or lots of sea lice on one fish), both species have lived together in a natural balance for a very long time.
Still, sea lice do take an economic toll on aquaculture operations. In Norway, the economic impact of sea lice is estimated at 3.4 billion Norwegian kroner (nearly $560 million) in 2014 with a loss of 1,272,358 tonnes (about 2.85 billion pounds) of fish production, according to the study.
Salmon farms are required by law to maintain their levels of sea lice below a very low threshold, and on the whole they have succeeded through significant investment in sea lice management strategies, Brooker said.
“Sea lice on both wild and farmed salmon produce eggs, although the relative contribution of each source of eggs to the sea lice population in coastal regions is unknown,” he said. “They are part of a complex and constantly changing ecological system, and it is very difficult to make a ‘one size fits all’ conclusion regarding the role of salmon farms in sea lice production.”
Some of those sea lice management strategies practiced by salmon farms, according to the study, are pesticides, few of which are effective at all stages of the parasite’s lifecycle, combined with husbandry management tools. Those include single-cohort stocking, optimized stocking densities, the use of cleaner fish in polyculture, and fallow periods. Physical techniques to exclude lice, such as the use of barrier nets and snorkel cages, coupled with mechanical tools, including thermal and turbulent de-licers and laser removal, also constitute an increasing component of current integrated pest management strategies.
“Many wild salmon populations have declined in recent decades, and this is likely to be caused by many different factors,” Brooker concluded. “It is easy to blame salmon farms for this decline as we can see them, as opposed to, for example, climate change resulting in changes in the abundance and distribution of the salmon’s prey in the open ocean, which we cannot see. We should consider all potential factors that may influence wild salmon populations and not just those that are visible.”
Study Reviews Larval Sea Lice Biology; Models Spread, Infection From Aquaculture Facilities
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