Does selectivity reduce sustainability?

Published on March 16, 2012

A recent study published in the journal Science has challenged the concept of selective fishing as an efficient way to maximise the harvest of fish stocks in a sustainable way. It may be questioned, however, to what degree these results are valid and applicable for modern large-scale fisheries.

In the study “Reconsidering the Consequences of Selective Fisheries”, Garcia et al. present models which show by catching fish of all sizes and species, as opposed to selectively targeting larger specimens for example, a larger fraction of the total biomass can be harvested without risking fish stock collapse. The theory behind this is that by catching proportions of all non-larval fish, which reflect their natural abundance, the composition of fish species and sizes is maintained.

The report argues that fishing non-selectively recognises that different fishes and sizes of the same fish species have different ecological functions (differences in food choice, preferred habitat etc.). In contrast to this, they state that in selective fisheries, which only target some species or sizes (mainly larger individuals), there is a risk that some of these functions are lost, which thereby weakens the state of stocks.

This study contradicts calls for more selective fishing, as proposed by many NGOs and fisheries scientists who commonly advocate the avoidance of fishing on small and juvenile individuals. However, the study could be criticised for relying mostly on modelling (although datasets from a large number of different ecosystems has been used) and not being properly validated by results found in non-selective or mixed fisheries; the examples referenced are African small-scale inland fisheries.

As most (if not all) fishing techniques used in modern fisheries are more or less size selective, it is difficult to see how the conclusions from the report could be practised in reality – especially within the large-scale fleet. Neither the catches from passive (gillnets) or towed gears (trawls) that are most commonly used in marine fisheries today comprise species or size compositions which reflect these natural variations. Today, only specific parts of fish populations are caught using these techniques.

That said, the study could provide support for the view that sustainable fishing should make use of a variety of gears and techniques, as too large conformity would skew fish populations by only exploiting specific sizes and species. Behavioural differences among species, as well as among sizes of the same species, alter their susceptibility to being caught, which further highlights difficulties in catches that reflect the natural assemblies.

When implementing policy that aims to alter catch compositions and selectivity measures, the state of the stocks must be taken into account. Currently, this approach would be especially problematic in Europe as most stocks are overfished and large parts of the spawning stocks are caught. Therefore, practising selective fishing and avoiding juvenile individuals, acts as a buffer to secure the survival of these overfished stocks.

If a broader and more unselective fishing were practiced, smaller sized fish and a wider range of species that today are classified as non-commercial would enter the market, which most consumers today perhaps are not prepared to adjust to. This would also entail negative economic consequences for fishermen, as smaller sized and non-commercial species generally are considered to be of poorer quality and generate less income.

Even considering these obstacles, the study opens up the discussion of whether more selective fishing is always appropriate for achieving sustainable fisheries.