A new insight into lice
The talk was given by Dr Nabeil Salama who, alongside colleagues at Marine Scotland Science (MSS), has been gathering and collating hydrographic data from Loch Linnhe – winds, tidal flow, fresh water input and currents – for the last 15 years. The water body is positively peppered with data loggers of one kind or another.
Loch Linnhe is the largest fjordic loch system in Scotland, which contributes just over 10% of the total farmed Atlantic salmon production in Scotland, but where there are salmon, there are lice.
On the screen above Dr Salama’s head swarms of tiny black dots rushed about – looking much like an autumnal flock of starlings mustering at dusk – representing the planktonic dispersal phases of sea lice, drifting in accelerated time lapse from farm to farm: settling, growing, breeding and dispersing.
Bringing biological, hydrographical and mathematical/simulation approaches together, Dr Salama has developed a sophisticated model for sea louse dispersal. Dr Salama is not the first to model sea lice movements. The hydrographic model he employs he modestly refers to as “off-the-shelf”, but in many ways, Dr Salama’s approach is really unique.
Most importantly, he has taken steps to robustly validate his simulations with hard empirical data. Well over 500 plankton trawls have been conducted to identify the microscopic nauplii dispersal phase and test the model prediction. Sentinel fish – young adult salmon in sunken cages – have been strategically placed for passing lice larva to attach to. To recreate real-life scenarios, SDr Salama has even taken to towing cages of sentinel fish slowly through the loch. All these efforts serve to check whether the lice really are turning up where the model predicts they will.
Secondly, the long-term relationship Dr Salama and his team have built with the salmon producers in the loch means that his models are likely to have real impact on salmon production. Farmers are signing up on a voluntary basis to establish control and exclusion zones using recommendations from the model data. Careful planning of farm siting in this way could drastically reduce farm-to-farm transmission, improving yields and fish welfare.
Dr Salama’s models provide some hope for understanding local interactions between farms and targeting louse control measures. However, the general applicability of such models outside Loch Linnhe has yet to be tested. Similarly, patterns of long range transmission of lice between farms and regions is poorly understood, as is the role of wild fish and escapees in spreading infections. Dr Salama’s work is an important step in the right direction, but an integrated louse control strategy is still a long way off.
