Editor's Choice: The impact of small-scale fisheries on non-target marine organisms

December 2011 (Issue 48:6)

Alfaro-Shigueto, J., Mangel, J. C., Bernedo, F., Dutton, P. H., Seminoff, J. A. & Godley, B. J. (2011) Small-scale fisheries of Peru: a major sink for marine turtles in the Pacific Journal of Applied Ecology, 48, 1432-1440.

Turtle

The bycatch of non-target marine organisms by commercial fisheries vessels has received a huge amount of attention in recent years, as a major threat to marine biodiversity. Particular concern has been expressed about cetaceans, turtles and sharks and rays, but no taxonomic group is immune; bottom trawl bycatch includes a wide range of invertebrates for example. This concern has led to legislative changes at the international level and to the development of a number of effective mitigation measures, such as the Turtle Excluder Devices used in many longline fisheries. Observer programmes in commercial fisheries now routinely record bycatch levels on a vessel-by-vessel basis, with this data forming the basis for measures implemented as part of international agreements such as the International Commission on the Conservation of Atlantic Tunas.

Although large-scale commercial fisheries are a clear target for bycatch reduction, the vast majority of fishing worldwide is carried out by small-scale artisanal fleets in coastal waters. Very few studies have robustly quantified the levels of bycatch in these fisheries, which is of concern because even if individual vessels have a relatively minor impact, their sheer numbers could lead to substantial levels of bycatch mortality. It is also much harder to quantify bycatch in these fisheries because of the many small boats involved, from many ports, so that collecting reliable data is difficult. Short-term observations or interviews asking fishers to recall their bycatch are of limited value because of the very low rates of bycatch by individual vessels, while interviewees may be reluctant to reveal information, particularly regarding protected species.

Turtle

This issue's Editor's Choice is a major step forward in providing a robust estimate for the levels of turtle bycatch in Peruvian coastal waters, based on the combination of an observer programme on vessels and port surveys to obtain an estimate of the total number of vessels of each type in the fisheries concerned. This study represents the most comprehensive bycatch dataset for small-scale fisheries in existence. Joanna Alfaro-Shigueto and her co-authors at the University of Exeter and Peruvian NGO Pro-Delphinus carried out the study with collaboration and funding from the USA's National Marine Fisheries Service. In their study of four fisheries (two longline, two bottom-set nets) at three ports from 2000 to 2007, they recorded 807 bycatch turtles in 264 observed trips. The majority of these turtles were released alive, but 149 were caught dead and 246 were retained alive for future consumption. The bycatch rates were heterogeneous, but some were very high. For example 56% of all nets set in one location caught green turtles, with an average of 2.78 turtles in each set. It is very hard to extrapolate up, but given that the study sampled about 1% of the fishing effort by Peru's artisanal fleet, it is likely that tens of thousands of turtles are killed by artisanal fishers in Peru each year. Similar levels of bycatch may well be operating in other countries in the region.

One of the interesting findings of the study is that more than a quarter of bycatch turtles were retained for food. The majority were released, however, giving a basis upon which to build engagement with local fishers; clearly an understanding of why people do or do not retain particular turtles is needed. The use of turtles for food points to the importance of understanding the socio-economic context of bycatch, and of planning mitigation measures with the consent and involvement of local fishers. Given the scale and the dispersed nature of the bycatch problem, a top-down rules-based approach that ignores local priorities is very unlikely to yield significant reductions in mortality.

Turtle

This paper has been chosen as Editor's Choice because of the remarkable, long-term dataset which the authors have collected, based on many years of hard work and an excellent study design. The outcome of this research effort is of clear relevance to the management of Peruvian fisheries, but also has general lessons for bycatch monitoring worldwide. Strong and well analysed datasets such as these are vital for guiding policy-makers as to the need for intervention, and for highlighting the considerations that need to be taken into account when implementing change. The authors are careful not to over-interpret their data while still making clear how serious an issue bycatch in small-scale fisheries is likely to be worldwide. Studies such as these are the necessary foundation for conservation action.

E.J. Milner-Gulland

e.j.milner-gulland@imperial.ac.uk

Reference

Alfaro-Shigueto, J., Mangel, J. C., Bernedo, F., Dutton, P. H., Seminoff, J. A. & Godley, B. J. (2011) Small-scale fisheries of Peru: a major sink for marine turtles in the Pacific. Journal of Applied Ecology, 48, 1432-1440.
 

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