Sea lice are considered one of the main problems in the salmon industry in almost all farming areas in the world. This ectoparasitic copepod is a limiting factor to achieving maximum sustainable production.
There are a number of species of sea lice that affect the salmon industry throughout the world, in Europe Lepeophtheirus salmonis is of concern, in the North Atlantic the sea lice Caligus elongatus; for its part, C. clemensi is the main parasite of salmon in the Pacific of Canada and C. rogercresseyi in Chile; these parasites cause significant infestations on salmon farms.
Control of sea lice is complicated by planktonic larval stages lasting several days, which allows transmission over considerable distances with the help of currents.
In this way, researchers from Marine Scotland Science, Inland Fisheries Ireland, the Institute of Marine Research, the Scottish Association of Marine Science, the National University of Ireland, and Fisheries and Oceans Canada propose a generic standardized model of sea lice components for application in conjunction with particle hydrodynamics models.
The purpose of the study is to provide guidance for a generic sea lice model framework, where the parasite, simulated as particles with associated biological and behavioral characteristics, can be affected by the results of available hydrodynamic models.
Why a standardized model?
Different research institutions in various countries have developed the models that are being used. However, there are many common challenges, particularly in northwestern Europe.
The issues that promote sea lice spread, and the modeling methods used, are therefore similar in different salmon farming areas.
Even though there may be differences in modeling approaches for valid reasons. Standardization makes sense unless there are strong reasons to use area- or topic-specific models.
Standards can be flexible, explicitly simulating the local environment, for example, it is important to take local water temperatures into account.
Reasons for standardization include:
to. The results of the model run by different organizations can be directly compared and ensure that any differences are due to differences in the system, not the modeling approach.
b. An accepted standard model means that parties seeking to model sea lice in a specific area do not have to justify their individual decisions on how to approach sea lice biology.
c. Field validation of models is necessary, but it is expensive and time-consuming. An accepted standard means there is less need for specific validation in each individual case of application.
Standards for the hydrodynamic model
Hydrodynamic models must resolve sea lice-carrying currents in three dimensions to a resolution in time and space appropriate to the question being addressed.
Also, time-scale models need to be fine enough to generate results with at least hourly resolution, simulate particle transport and include ocean currents and changing winds. The resolution also depends on the purpose.
The hydrodynamic model will require forcing the appropriate scales to predict behavior at the scales of interest.
Standards for the particle model
The hydrodynamic model drives the motions of the particles. The biological model of sea lice particles has two classes of properties:
to. The models describe rates (egg production, maturation, mortality), which are relatively simple to implement and have no interaction with the transport model.
b. The model of properties related to the movement of the sea lice, particularly the vertical movement, but also the manipulation of the boundaries.
Conclusion
“Standard models based on a genetic framework can be used to compare the pressure distributions of sea lice infection in different systems with different environments, different production levels, and different farm layouts,” the researchers conclude.
The proposed models can be used to assess the impacts of new farms or the closure of existing farms, or changes in production levels on salmon farms.
Finally, the researchers conclude that the proposed generic model framework will contribute to developing best management practices for sea lice control and have the potential to define a range of production strategies on salmon farms, in order to reduce the presence of sea lice and their negative impacts.
Reference (open access):
Murray, A., et al., A standardised generic framework of sea lice model components for application in coupled hydrodynamic-particle models, in Sea Lice Biology and Control, edited by Jim Treasurer, Ian Bricknell and James Bron, 5m Books, 2022.
