Loch Duart’s Sea Lice Numbers

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As was written a while ago in our blog about “mistakes we have made and things we could do better”, we mentioned that sea lice numbers on some of our sites are high. There will be a continuing pressure raised in the media about this and no doubt the activists will be calling for action. Our numbers in Sutherland have been higher than we would have wished this year but it is important to understand that we are doing things about this and we expect to see results.

Firstly, and most importantly, our sea lice numbers are coming down sharply as of now. Just so it is on record, we report gravid (that is with eggs) and adult female lice per fish in our reporting area in Sutherland. The figures are as follows: July: 1.5, August: 3.7 and September 9.4. During this period we worked hard to try and keep the numbers down but the population grew despite our efforts.  As a result of the situation we decided to harvest all the fish in the affected sites as soon as possible. Because of this, by December, the whole of Sutherland will be below 1 adult female per fish. Clearly we can’t predict exactly where that number will fall but at the point of putting this up on our website our numbers have already fallen considerably.

It seems like a good idea to put out some background to what these numbers mean in the context of farming. As each generation of salmon involves two years at sea, it takes two years to get on top of a problem. Once a generation is over we fallow for long periods and the areas where lice were have no lice for this period.

Our sites and their fallow periods:          Guaranteed to have no sea lice
Laxford                                                          7-9 months in every 24 months
Oldany                                                          6 months in every 12 months
Droigniche                                                    12 months in every 24 months
Drumbeg                                                      12 months in every 24 months
Nedd                                                             12 months in every 24 months
Badcall                                                         14 months in every 24 months
Calbha                                                          14 months in every 24 months
Reintraid                                                       7-9 months in every 24 months
Torgawn                                                       7-9 months in every 24 months

From this you can see that for a considerable proportion of the time there are no fish and thus no sea lice in our sites. So now we need to look at how sea lice develop on our sites.

It is important to note that sea lice do not come with the salmon when they go to sea. When we put our smolt to sea they have no lice on them as sea lice cannot occur in freshwater. They can only get these sea lice from wild salmon or sea trout. The salmon louse will only occur on salmonids and thus if there were no wild salmon and sea trout, there would be no problem. Luckily there are wild stocks in our area and so after a while a salmon or sea trout passes our pens and transfers a juvenile louse or the gravid sea lice on it releasing its eggs and so our journey begins.

We rarely see any lice on our first year fish before the late autumn and then very low numbers. This period is very easy to manage and lice numbers usually stay low till early spring. It is from here that it becomes more difficult to predict and lately we have found periods when lice are hard to control. It is important that we state that we do treat our fish for sea lice infestations. We use the treatment thresholds in the Code of Good Practice as our trigger, which is why these figures were set.

In the past we were trying to live with an old farming system designed by an old farmer (the Managing Director) and this system was based on understandings from another time. As we realised that we were not achieving the level of control that we wanted, we decided to review the whole stocking strategy in Sutherland. We believe that this review has significantly changed things for us. It will take several years for it to achieve the level of control that we want but there are some very encouraging signs already.

What is actually important to point out is that sea lice levels, even in cases like just now where we have less control than we want, are only high for a few months. As we fallow for such long periods the combined effect is that, at worst, lice levels are elevated for 4 or 5 months in every two year period, usually at the back end of the year.

It is important to stress that we do not think that this is the way we want to farm but sometimes in a relatively young industry it takes a while to get on top of a particular problem. As explained before, our cycle is long so, changes take a while to show their promise.

So at the time of writing our sea lice levels are falling rapidly in Sutherland. By December we will have considerably less than 1 gravid or female louse per fish and we expect that to be maintained for some time.

Finally, as I am sure that we will see the usual criticism of what we do, it is important to look at what is happening wild stock numbers locally. Though the picture is mixed, to an outsider the overall position looks not too bad. Below is a graph from the West Sutherland Fisheries Trust annual review. It is important to note that salmon farming has been in the area since 1976.