An expert paper produced by the Shetland Fishermen’s Association has cast serious doubts about the method used to assess the sustainability of fish stocks.

According to the paper, arbitrary targets for maximum sustainable yield (MSY) are a “political commitment rather than a biological or management necessity.

”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.

The MSY is theoretically the largest catch that can be taken from a fish stock over an indefinite period without reducing the size of the stock or causing long-term damage to that stock.

The paper says “Theoretically, there is a MSY at the stock size where the surplus production is greatest. This represents the maximum sustainable harvest that can be taken from the stock in the long term. Most modern models suggest that MSY occurs where a fish stock is just under one-third (30%) of it’s exploited size.

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.

A full copy of the paper is available via the link below:

Source: Shetland Fishermen’s Association

Expert Paper from Shetland Fishermen’s Association questions MSY

by editor time to read: 7 min