Marine

Satellite Tagging

December 19, 2013 by Paul Stainer No Comments | Category Marine Directorate Science, Marine Renewables

© Miramichi Salmon Association

In early summer 2013 a team from MSS Freshwater Laboratory set off for the north coast to fit the first satellite tags ever deployed on maiden salmon in Europe. To ensure protection of this iconic species Scottish Government urgently needs information about the degree of spatial overlap between salmon and potential MRE developments. No-one knows what depths returning salmon swim at or what routes they take when they migrate round Scotland’s coasts: we were going to try to find out.

The tags were programmed to detach from the fish after a period of 1-10 days, and pop-up to the surface, having recorded depth and temperature every minute during deployment. Unless the tags reach the surface they cannot communicate their stored data to the satellite system.

There were many potential technical pitfalls, and complete failure could occur at any stage. Even if all the technical stuff worked as planned there was still the risk that the salmon themselves wouldn’t co-operate. They might swim into their home rivers before the tags detached and never be heard again (release systems require salt water to activate), or they might sink rather than swim, or even refuse to be caught at all.

However, with the help of James Mackay of Armadale Fisheries, 50 salmon were caught in bag nets, fitted with tags and released. The tags weigh only 50g in air, and are slightly buoyant in water, but we felt the full weight of their £2000 price tag. The team agreed that if as many as 20 of the 50 tags reported some useable depth data by the end of the project we would consider it a great success.

In the event, far beyond expectation, we heard back from 47 of the tags and obtained useful data from 43 of them – this despite one tag being swallowed by a shark and another probably by a dolphin or whale. After awarding ourselves a brief pat on the back we have been busy analysing the data and are about to submit a manuscript for peer review. If accepted, our data will provide the first published account of depth-use by salmon on their first return migration in an area of open sea.

Article by Jason Godfrey

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