Review of Lobo, A.S., Balmford, A., Arthur, R., & Mannica, A. (2010). Commercializing bycatch can push a fishery beyond economic extinction. Conservation Letters 3:277-285

Trawling boats and emerging markets spell trouble for Coromandel fisheries.

If you enjoy eating meat, but choose farmed over wild-caught meat out of concern for wild species and the environment, then this might leave you with a bad taste in the mouth. Industries such as chicken farming contribute significantly to reducing the sustainability of marine fisheries off India's east coast, a recent paper by scientists at the University of Cambridge and Nature Conservation Foundation, Mysore has revealed.

The authors worked along south-east India's Coromandel coast to document trends in fish catches and the dynamics in associated markets over the last thirty years. This is a period when commercial mechanized trawl fishing has come to replace traditional artisan fisheries across much of this coast. From a sustainability viewpoint, trawl fishing has several undesirable impacts on fisheries and the marine ecosystem, perhaps none are more damaging than the indiscriminate manner in which this technique decimates marine populations. Globally, the target fish of a trawling expedition (termed 'catch') and the unintended catch (termed 'bycatch') occur in a highly skewed ratio of 1:10 on the average trawling expedition.

The authors interviewed a variety of stakeholders involved in the marine fishery industry across three major fish-landing centres in the region. They document that the numbers of fish caught and incomes initially increased soon after the 1970s (presumably as the mechanized technology opened up previously unexploited fisheries), but then declined over more recent years till present. Simultaneously, the reward in terms of catch per fishing effort too increased in the early period, before declining. In contrast, the costs of fishing (corrected for inflation) have steadily increased till the present day. Interestingly,the value of bycatch has invariably increased over the last thirty years. The authors note that this is potentially dangerous for the health of the marine ecosystem as well as the sustainability of the fishery. They argue that as the value of bycatch increases, thereby making it a more important part of the fisheries economy, fishers would continue to trawl an area toa point of decimation when most species would have been wiped out. In this particular fishery along India's east coast, the authors discover that the chicken farming industry creates the main demand for bycatch, which gets used as a part of chicken feed. While most of the results presented are along expected lines, and mirror the trajectories of fisheries across the tropics, the paper still does put across a powerful message about the urgent need for better management of the east Indian fisheries.

 An unavoidable limitation of this work is the complete dependence on interview surveys for data in the absence of primary data sources on bycatch. One can only speculate on how accurately these surveys represent reality. The authors make some efforts to cross-validate their data with other shorter term datasets. In addition, lead author Aaron Lobo notes “Private trawler owners maintain some records, and although these are not entirely reliable as quantitative datasets, they do show general agreement with our interview-based results”. To their credit, the authors largely focus on the general directions in overall trends in their dataset, and not on the magnitudes of these changes.

On the whole, the discussion on the ecosystem impacts of bycatch economics makes for compelling reading, and the implications would certainly give a lot of us some food for thought. Lobo adds “This is a complex problem because almost any intervention is likely to impose high socio-economic costs. For starters, what can certainly change is the monitoring system. A more wholesome ecosystem-level monitoring needs to be practised, instead of the current system which merely focuses on a few species.”

-          M.O. Anand

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MOA is a PhD student at National Centre for Biological Sciences, Bangalore. His broad area of research is ecosystem ecology, with specific focus on vegetation dynamics in tropical forests.