SARF023:  A review of the sea lice bath treatment dispersion model used for discharge consenting in Scotland

Start Date: 12/5/06 
End Date: 11/5/07
Main Contractor(s): Institute of Aquaculture, University of Stirling
Other Sponsor(s): Novartis Animal Health, Marine Harvest

Objectives

The objective of this study is to generate data which may allow SEPA to review the models used to guide the consenting of sea lice bath treatments and, taken with the conclusions of the PAMP report and SEPA`s own data (The occurrence of the active ingredients of sea lice treatments in sediments adjacent to marine fish farms 2001-2004), to allow farmers more flexibility in sea lice management. 

The project will examine three areas: 

1. A review of the meta-data on environmental distribution of active ingredient.. 

2. An examination of the data on actual values of cypermethrin at the point of release and short term distribution.

3. A theoretical appraisal of the potential implications of using skirts for treatment in terms of initial dilution of active ingredient and effect of treatment regime.

Summary

In Scotland only three therapeutants against marine ectoparasite infestation are commonly used with salmon farms, two are bath treatments (EXCIS and hydrogen peroxide) and one is an “infeed” (SLICE). Hydrogen peroxide has minimal environmental impact but can stress or even harm fish if the dose is not carefully managed, and thus is unpopular with fish farmers. SLICE is an “infeed” treatment which is preferentially used by the salmon farming industry as it is highly effective against sea lice and treatment is convenient through inclusion in fish feeds. EXCIS (active ingredient cypermethrin) is a bath treatment and is though used as a primary sea lice treatment is more often used as an alternative to SLICE to prevent overdependency. For anti-sea lice treatments to be used a discharge consent (as total amount of treatment in a specified time) must be granted by SEPA. This is granted in light of the ability of the environment to dilute the active ingredients to levels specified by environmental quality standards (EQSs), and done through modelling the dispersion of the treatment after release into the environment based on local environmental conditions. The amount of therapeutant consented is very sensitive to these models, making the accuracy of the model and assumptions incorporated within the model vital for effective treatment of these parasites. Some concern has been expressed from both environmental regulators and the aquaculture industry that these treatments are not being used as effectively as they can be. Some of this can be attributed to the models used. The purpose of this research project is to review the dispersion model used for bath treatments, in light of the findings of the Post Authorisation Monitoring Programme (PAMP; SAMS et al, 2005). In addition this research will undertake experiments to investigate the input concentrations of the active ingredient. This data may enable the model to be reformulated to give more realistic and environmentally relevant treatment methods for sea lice using EXCIS