Monday, 13 June 2011

Scottish salmon getting smaller

Salmon catches on many Scottish rivers were at high, or even record levels during 2010.  Salmon abundances have fallen markedly since the 1970s - perhaps by as much as a third - and in recent years numbers have been consistently at a historical low; so the 2010 catches were a welcome exception to this general pattern.  In collaboration with Scottish government scientists, Professor Chris Todd, of the School of Biology, has been researching changes in size and quality of wild salmon and has found that the size of salmon in Scottish waters is reducing along with their number.  Monitoring on a major Scottish river has seen the weight of the average grilse, a first-year returning adult salmon, reduced from 2.4 kg to 1.7 kg and its average length reduced from 59cm to 54cm over the past 17 years.  Fish returning in the poorest condition are up to one third down in their weight but their fat reserves are reduced by up to 80%.  A concern is that this reduction in salmon size and fat content has a negative effect on egg numbers and quality, implying a worrying future for the species.  Warming ocean temperatures and plankton sources moving further north due to global warming are suspected to be causes, and it may well be many years before this situation improves for salmon at sea.
An 24% underweight fish

An unusual 'normal'-size fish
This funding has been kindly supported by the Association of Salmon Fishery Boards for Scotland (ASFB), the Atlantic Salmon Trust (AST) and the Fishmongers Company.