Concerns raised over approach to assessing sustainability of stocks

Serious doubts have been raised about the manner in which the sustainability of fish stocks is assessed.

Arbitrary targets for maximum sustainable yield (MSY) are a “political commitment rather than a biological or management necessity”, according to an expert paper produced by the Shetland Fishermen’s Association.

It points out that although setting fishing quotas in line with MSY is an internationally agreed commitment, it is an extremely difficult concept to measure in practice and this can result in counterproductive management decisions.

MSY is based on the concept that there is a maximum amount of fish in any given stock that can be fished without depleting the overall size of the stock from year to year.

However, the paper argues that this does not reflect the “complexity, variability and uncertainty of the real world”.

It says: “The so-called ‘MSY-approach’ to fisheries management is not based on the knowledge of the maximum sustainable yields from fish stocks, but rather on various proxies. Most of these in turn are based in turn on historic levels of abundance.

“The political commitment to MSY takes no account of the difficulties of achieving MSY in practice. Instead, it has resulted in unrealistic targets and unrealistic timescales.”

The paper points out that the swingeing cut to the North Sea cod quota for 2020 was a political requirement to meet an arbitrary target based on what the cod stock was in 1996.

In the real world it is not possible to identify the actual maximum sustainable yield of a fish stock “since we lack a sufficiently detailed understanding of the relationships between the size of fish stocks and their recruitment and growth, as well as density-depending factors such as competition and predation that affect their production”.

“Further, in the real world the production of fish stocks is affected by a multiplicity of varying environmental factors which affect their recruitment, growth and survival.

“Consequently, the production of fish stocks varies from year to year (and over other timescales): what may be sustainable in one year may not be sustainable in another.”