Tweed Grilse Run

Screen Shot 2014-10-09 at 15.45.44Whilst Summer fishing has produced some good numbers of salmon on Tweed, the Tweed Foundation’s senior Biologist, Dr Ronald Campbell has said “the river has seen fewer grilse this season.”

Fisheries Management Scotland have just issued an advice note on grilse.

Advice note – September 2017

Introduction
Fisheries Management Scotland has been alerted to a much-reduced grilse run again in 2017. This appears to be following a pattern observed in recent years, and there is some consistency, based on anecdotal reports, that a number of rivers across Scotland appear to be showing this trend. This also seems to be borne out by the experience at the Armadale net fishery tagging/tracking project on the North coast, where there was a marked absence of fish caught for tagging during the time when grilse, if present, would expect to be caught. Likewise, the North Esk net and coble fishery has reportedly caught very few grilse. We have also received reports that some rivers have had good catches of grilse, and we are engaging with our members to explore this further.
Coupled with this observation there are suggestions of an increase in larger summer fish, and less fish running in the autumn period. Whilst many rivers will not have long term catch data, where these do exist for some of the larger rivers including the Tweed, some long-term trends have been researched on historical catch and meteorological data. This suggests that there are likely to have been long term episodic changes in the past, and a characteristic of these changes are variations in the size and composition of the overall salmon stock. This has included major reductions in grilse abundance lasting several decades at least.

Cause?
Whilst it is difficult to attribute the current reduction in grilse numbers to any one factor, one theory which may explain the changes we are seeing is related to large scale changes in the marine environment. In recent decades, there has been an increase in surface temperatures in the NE Atlantic and there have been widespread changes in the abundance and distribution of other marine species consistent with this. There is some evidence to suggest that warmer conditions in the sub- Arctic may mean more salmon than grilse. If they have to migrate further to feed they may not obtain sufficient resources to mature in their first year. They may therefore delay maturation for a further year and return as salmon having reached productive feeding grounds, or they may simply die. As there is also a genetic element to the maturation of salmon a compensatory increase in salmon numbers may develop over a number of years, assuming the underlying driving force continues in the same direction for some time.

What next?
Fisheries Management Scotland will be monitoring the situation to determine how widespread this problem is and we would welcome feedback and input from members with a view to considering what management action might be appropriate and feasible in response to these reports. We will also be raising this issue with Scottish Government and associated agencies to ensure that they are aware of the situation, and whether there should be any response or action at this level.

Source: Fisheries Management Scotland

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