Presentation: State-of-Knowledge Initiative for the Special Committee on Sustainable Aquaculture of the British Columbia Legislature

Delivered November, 2006.

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Managing Risk and Sustaining Wild Pacific Salmon Populations

[A full pdf copy for printing may be downloaded from the WAVES database.]

Concern about sea lice and juvenile Pacific salmon in the BA is ultimately related to the sustainability of wild salmon populations and their ecosystems. 

The DFO Strategic Plan for 2006-2010 (released Oct. 31, 2006)[1] and the Wild Salmon Policy[2] are strong commitments to the conservation of these values. The Strategic Plan also sets an objective to “undertake comprehensive action to ensure the safety and sustainability of the aquaculture industry, and respond to public interest in this area.”

Within this context, risks associated with the salmon farming will be treated equally to other users or impacts on wild Pacific salmon.

For example, given the uncertainties and difficulty of attributing causes to changes in salmon returns; a risk adverse approach to managing concerns about sea lice and salmon farms would be to minimize the potential source from farms during periods of juvenile salmon emigration in an area. This strategy may be the only action possible to directly address the perceived risk associated with open-net pen salmon aquaculture in areas of wild Pacific salmon production. While we must ensure that real, as opposed to perceived, causes are identified; this approach could be extremely useful in isolating and explaining causes.

The scientific components of this strategy would be to determine the most efficient and effective means to minimize sea lice production in the farms, assess the effectiveness of actions and determine safe levels of lice production, and evaluate ecosystem effects of associated treatments.

As background, it should be noted that salmon farming developed in the BA in 1987 but the observations that triggered the sea lice concern did not occur until June 2001.

The patterns of variation in pink salmon production (by even and odd-year lines) from the Area 12 Mainland Inlet rivers and streams are presented in Figure B. These data include DFO estimates of catch from BA streams and the aggregate estimate of spawning adults returning annually.

Poorer returns since 2002 are certainly evident but in considering the annual changes before 2002, there are several factors that could have contributed, including: the development of artificial spawning channels in the Glendale and Kakweiken Rivers (1988 and 1989 respectively), logging impacts in the watersheds, climate variation and effects on stream flows, variation in fishing pressure, etc.

To-date, management steps taken in the BA have involved fallowing along a prescribed “migration corridor” for juvenile salmon in 2003, and Provincial sea lice management plans[3]. DFO has also more intensively surveyed pink and chum returns since implementation of the Sea Lice Action Plan in 2003[4].

Assessment of the 2003 fallowing and migration corridor continues to be debated.

The prevalence of sea lice declined in 2003 relative to 2002 and 2001 and the adult return in 2004 improved substantially relative to the spawning population size in 2002. Morton et al.⁴ argue that the 2003 action was therefore effective, but Beamish et al.1 report that fallowing in 2003 did not reduce the production volume on BA salmon farms. The Provincial website (footnote C) supports the production values stated in Beamish et al.
Beamish et al. suggest that the significant increase in pink returns to the BA in 2004 was the result of exceptional survival during their marine rearing.

Also, the utility of specific migration corridors to protect juvenile salmon is not generally supported by DFO or Provincial staff. Corridors must, however, be of some value to specific populations since they can only access off-shore areas via certain channels or inlets.

The present treatment method to control sea lice uses emamectin benzoate or Slice® (Schering-Plough Animal Health Corp). This product may be used in Canada when requested by a veterinarian under an “Emergency Drug Use” basis for controlling sea lice at coastal finfish aquaculture operations. Slice® is applied in feed and causes paralysis and death in parasites on the hosts.

Treatment is effective for feeding salmon and protection of the salmon may last a few months depending on temperatures^{5, 6, 7} (see Technical Monographs, Schering-Plough[5]). However, the ecological effect of Slice® on the environment near a treated farm remains to be further investigated.

The information available on the environmental fate and effects of Slice® was recently reviewed for Environment Canada by Bright and Dionne².

The review notes a limited knowledge base for assessment of the environmental effects, particularly for sub-lethal effects and for species of interest in British Columbia (only one poster cited, Dungeness crab and Spot prawns).

Clearly, more research is required to address ecological toxicity issues in the B.C. environment. However, a recent publication on the effect of Slice® on zooplankton communities indicates no adverse effect of treatment on this important part of the marine food chain⁸.

In addition to treatment of single farms, other jurisdictions (Norway, Scotland, and Ireland) have proceeded to develop regional management plans for the management of sea lice on multiple farms within a geographic area.

These regional plans may involve use of single age-class stocking of salmon farms and coordinated treatments amongst farms to minimize the risk of between farm transfers. Heuch at al.³ recently reviewed the Norwegian Action Plan implemented in 1997. The Norwegian Action Plan was a consensus tool developed by their Animal Health Authority and the salmon farming industry.

Related to treatment of multiple farms, however, Bright and Dionne2 note a concern for the expanded use of Slice® under regional management plans, since previous environmental assessments have involved one-time applications as opposed to multiple, simultaneous treatments.

[1] http://www.dfo-mpo.gc.ca/dfo-mpo/plan_e.htm
[2] http://www-comm.pac.dfo-mpo.gc.ca/publications/wsp/default_e.htm
[3] http://www.agf.gov.bc.ca/ahc/fish_health/sealice_MS.htm
[4] http://www-sci.pac.dfo-mpo.gc.ca/aquaculture/sealice/default_e.htm
[5] http://www.schering-plough.com/schering_plough/pc/animal_health.jsp

Figure B. Historical returns of Pink salmon to Area 12 Mainland Inlet streams, 1953-2006
Source: DFO records, Stock Assessment Program, Science Branch. (2006 data is preliminary)

 Click on the image to enlarge

Click on the image to enlarge

References

1. Beamish, R.J., S. Jones, C. Neville, R. Sweeting, G. Karreman, S. Saksida, and E. Gordon. 2006. Exceptional
    marine survival of pink salmon that entered the marine environment in 2003 suggests that farmed Atlantic
    salmon and Pacific salmon can coexist successfully in a marine ecosystem on the Pacific coast of Canada.
    ICES J. Mar. Sci. 63: 1326-1337.

2. Bright, D.A. and S. Dionne. 2004. Use of emamectin benzoate in the Canadian finfish aquaculture industry: A
    review of environmental fate and effects. Contract report prepared for Environment Canada, Environ. Prot.
    Branch.

3. Heuch, P.A., P.A. Bjorn, B. Finstad, J.C. Holst, L. Asplin, and F. Nilsen. 2005. A review of the Norwegian
    ‘National Action Plan Against Salmon Lice on Salmonids’: The effect on wild salmonids. Aquaculture 246: 79
    92.

4. Morton, A., R.D. Routledge, and R. Williams. 2005. Temporal patterns of sea louse infestations on wild
    Pacific salmon in relation to the fallowing of Atlantic salmon farms. N. Am. J. Fish. Manage. 25: 811-821.

5. Ramstad, A., D.J. Colquhoun, R. Nordmo, I.H. Sutherland, and R. Simmons. 2002. Field trials in Norway with
    Slice® (0.2% emamectin benzoate) for the oral treatment of sea lice infestation in farmed Atlantic salmon
    Salmo salar. Dis. Aquat.Org. 50:29-33.

6. Stone, J., I.H. Sutherland, C. Sommerville, R.H. Richards, and K.J. Varma. 2000a. Commercial trials using
    emamectin benzoate to control sea lice Lepeophtheirus salmonis infestations in Atlantic salmon Salmo salar.
    Dis. Aquat. Org. 41: 141-149.

7. Stone, J. I.H. Sutherland, C. Sommerville, R.H. Richards, and R.G. Endris. 2000b. The duration of efficacy
    following oral treatment with emamectin benzoate against infestations of sea lice, Lepeophtheirus salmonis
    (Kroyer), in Atlantic salmon Salmo salar L. J. Fish Dis. 23: 185-192.

8. Willis, K.J., P.A. Gillibrand, C.J. Cromey, and K.D. Black. 2005. Sea lice treatments on salmon farms have no
    adverse effects on zooplankton communities: a case study. Aquaculture 50: 806-816.