New wave

Model chooses best sites in Scot­land for salmon farm­ing

Fish Farmer - - – Offshore Aquacultur­e Europe 2019 -

THE Scot­tish salmon farm­ing in­dus­try’s ex­pan­sion has been lim­ited by con­cerns over its po­ten­tial en­vi­ron­men­tal im­pact – on wild fish stocks and on the seabed.

The other lim­it­ing fac­tor is that many of the eas­i­est to op­er­ate, shel­tered lo­ca­tions are rea­son­ably well filled, said Thomas Adams of SAMS (Scot­tish As­so­ci­a­tion for Ma­rine Sci­ence).

He has been eval­u­at­ing the en­vi­ron­men­tal con­di­tions re­quired for the de­vel­op­ment of off­shore aqua­cul­ture, as part of the Off-Aqua project.

A par­tic­u­lar en­vi­ron­men­tal chal­lenge in salmon aqua­cul­ture is posed by sea lice, he said. En­hanced avail­abil­ity of host fish at farms can al­low lice to reach much greater num­bers than they would nat­u­rally.

Dis­per­sive en­vi­ron­ments in an off­shore set­ting will re­duce the pres­sure of sea lice from salmon farms, with re­duced in­ter­ac­tion with wild fish as well as in­creased dis­per­sal.

The hope, too, is that more ex­posed en­vi­ron­ments will be more dis­per­sive of waste and chem­i­cal treat­ments so they don’t have so much of an im­pact on the seabed.

And thirdly, the hope is that th­ese en­vi­ron­ments will be less im­pacted by harm­ful al­gal blooms (HABs) which tend to pro­lif­er­ate in en­closed sea lochs.

There are a range of is­sues as­so­ci­ated with mov­ing salmon pro­duc­tion sites to more ex­posed lo­ca­tions in Scot­tish wa­ters, in­clud­ing phys­i­cal, eco­log­i­cal, eco­nomic and fish wel­fare is­sues, and the Off-Aqua project in­cludes four work pack­ages:

• Phys­i­cal oceanog­ra­phy – de­tailed phys­i­cal ob­ser­va­tions at three con­trast­ing sites, rep­re­sent­ing a spec­trum of con­di­tions and po­ten­tial sites for de­vel­op­ment;

• Wave mod­el­ling and risk anal­y­sis – a long term (25-year) high res­o­lu­tion hind­cast wave model will sim­u­late con­di­tions on the west coast with spe­cific fo­cus on sites of in­ter­est;

• Hy­dro­dy­namic and bio­phys­i­cal mod­el­ling (which is Adams’s work) – to eval­u­ate sea lice con­nec­tiv­ity and HAB de­vel­op­ment in con­trast­ing en­vi­ron­ments;

• Fish health and wel­fare – open wa­ter aqua­cul­ture of­fers a less pre­dictable en­vi­ron­ment than fjordic sys­tems, but the im­pact on farmed an­i­mals has been lit­tle stud­ied.

The re­search team has been phys­i­cally mod­el­ling the west coast con­sis­tently for six and a half years with a me­te­o­ro­log­i­cal-hy­dro­dy­namic model, with in­for­ma­tion on cur­rents,

tem­per­a­ture, and salin­ity.

In 2019, the do­main was ex­panded to in­cor­po­rate more ex­posed en­vi­ron­ments. The aim is to show how out­puts can be used by in­dus­try, reg­u­la­tors and other stake­hold­ers to help guide man­age­ment of new and ex­ist­ing sites.

A bi­o­log­i­cal par­ti­cle track­ing model was used to sim­u­late the spread of ‘sea lice’ lar­vae from three dif­fer­ent farm sites Rum ex­ist­ing ex­posed farm ; Gorsten shel­tered farm ; and a more in­ter­me­di­ate site.

The sites also dif­fer in the num­ber of neigh­bours they have; the Rum site has very few neigh­bours, for in­stance, which in uences the spread of lice and re­ten­tion whether they are able to re in­fect the site .

While the Rum site be­haves rel­a­tively in­de­pen­dently, shel­tered sites are typ­i­cally more con­nected to other sites and have higher ‘self in­fec­tion’ rates, said Adams.

n the re­la­tion­ship of farms with their lo­cal en­vi­ron­ment, whether farms are net re­ceivers of lice or dis­persers of lice, and whether they suffer from large amounts of self in­fec­tion, af­fects how they are best man­aged.

The next steps in the project will look to de­velop fore­cast­ing ca­pa­bil­ity with the hy­dro­dy­namic model.

ore ex­posed sites of­fer an op­por­tu­nity to re­duce en­vi­ron­men­tal im­pacts in terms of sea lice con­nec­tiv­ity, with an as­so­ci­ated re­duc­tion in out­break fre­quency and risk to wild fish, said Adams.

They may also of­fer in­creased dis­per­sion of ex­cess or­ganic ma­te­rial. But while phys­i­cal con­di­tions at more ex­posed sites gen­er­ally lie within the range suit­able for fish, they can pose op­er­a­tional di cul­ties for site man­agers.

A range of fac­tors must be taken into ac­count when se­lect­ing the most sus­tain­able ap­proach to in­dus­try ex­pan­sion, and choos­ing sites upon which to fo­cus.

Above left: Thomas Adams of SAMS Above: Cooke Aqua­cul­ture’s off­shore farm at East Skel­wick, Orkney

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