1. Standardizing Biological Modelling of Sea Lice Dispersal
Alexander G Murray1, Tom Adams2, Lars Asplin3 and Sam Shephard4
Marine Scotland Science, Aberdeen
Scottish Association for Marine Science, Oban
Institute of Marine Research, Bergen
Inland Fisheries Ireland, Dublin

2. Importance of sea lice
Key limitation to sustainable increase in marine salmonid farming
Treatments and controls are expensive and have problems
Transmit to (and from) wild salmonids
Number are up
Treatment rate is up

3. Planktonic larvae
One of the issues that makes sea lice difficult to control are their free living larvae
These are transported with ocean currents
Potentially over long distances
Although activity is relatively limited they are not passive particles
Links farms and between farm and wild populations

4. Coupled modelling of coupled processes
Larval transport depends on movement of water and biological properties of the sea lice
Therefore coupled hydrodynamic-particle modelling is used
Model 1. derives current velocities through simulation of physical processes in response to drivers such as wind and tides
Model 2. describes the biological processes such as mortality or swimming behaviours of sea lice

5. Applications
Scotland: Loch Torridon, Loch Linnhe, Loch Fyne, west coast, Scottish shelf
Norway: Hardanger Fjord, entire Norwegian coast
Canada: Broughton Archipelago BC
Faeroes
Ireland Killary Harbour

6. Multiple applications (nearly) same problem
The models used have been developed by different institutions in different countries
There are different issues in different territories and applications, but generally similar problems addressed
So there are shared problems with potential for collaboration
Collaboration has in fact occurred for some time (particularly between Norway, Scotland and Canada)
However this can be taken further and models standardised

7. Why standardise models?
Not to force round pegs into square holes
Sometimes different models are required for different purposes
However, a flexible standard model (e.g. with temperature dependence) can cover a range of conditions
Standardised models allow an accepted ‘off the peg’ model to be used in new areas
Cheaper and easier
Modelling assumptions already accepted
Standardised models allow simulations of different systems to be compared
different outputs are differences in the system not in the model

8. MASTS funded workshop
MASTS funded workshop held in Aberdeen in February
Meeting of delegates from the institutions on this presentation
Discussed modelling approaches to identify similarities and differences
Outputs relating to biological processes discussed here

9. Biological standardization
Physical models need standards too, and these were discussed, but time limits what is presented here
Biological processes are divided into two topics:
(a) processes such as production and mortality which are relatively simple rates
(b) processes related to lice swimming which is more complex issue of behaviour
These introduce a range of different issues

10. The basic rate processes
Egg production
Survival of larvae
Maturation of larvae
Modelling rates requires empirical data
Much of this data already exists from existing studies
Some refinements needed through future research

11. Egg production
It is possible to model relative lice production without explicit egg production model
Needs relative size of production sources
Egg production to estimate absolute lice production
Need estimate of numbers of ovigerous females
Clutch size varies with
Age of female
Farmed or wild fish
Environment
Egg survival high but varies with environment
Still not standardised

12. Survival Very sensitive to environment
Mortality increases rapidly as salinity drops below 29ppt
Biological mortality, e.g. grazing by plankton or mussels
For full strength sea water mortality of about 1% h-1 is a reasonable standard
Also finite life-span

13. Maturation Sea lice go through non-infectious stages
Time required is highly dependent on temperature
Use a single value based on average temperature for any particular scenarios e.g. 3.6 days for 10 c
Early Brooks
Boxaspen & Naess low temp
Standard by Stien

14. Effects of rate sensitivities
Shorter cycles with faster maturation as temperature warms
Problem populations can build up faster
Dispersal distances less so smaller management areas may be effective
Populations inhibited if salinity drops

15. Swimming behaviour Lice are not passive particles
Phototactic tend to be found near surface
This is standard used in Scottish models lice particles are held in surface layer
In Norway more complexity may be required e.g. to avoid haloclines
More sophisticated models therefore being developed

16. Vertical swimming Sea lice swim towards surface
In downwellings this means rising particles become concentrated
Can be trapped by onshore winds forming concentrations

17. Effect of swimming behaviour
Lice are not scattered through water column
Subject to surface currents which are often stronger and more sensitive to winds, so lice may move greater distances than passive particles
Lice can form concentrations at downwelling locations and shorelines with onshore wind, sometimes distant from the source
Lice can avoid dangerous low salinities (this is not yet standardised)
This is an area in greater need for new data than the rates

18. Also Standardisation of hydrodynamic modelling approaches
Standardisation of field sampling
Standardisation of outputs

19. Application of standardisation
Modelling for European standard that will take lessons learned from previous models
Partners from organisation involved in this model
Application to Killary Harbour, Ireland