Portal de Periódicos da CAPES

Seabird mortality and trawl fisheries

2008; Wiley; Volume: 11; Issue: 4 Linguagem: Inglês

10.1111/j.1469-1795.2008.00196.x

1469-1795

John P. Croxall,

Avian ecology and behavior

Over the last decade or so, we have come to recognize that where commercial longline fisheries overlap with susceptible species like albatrosses and petrels, the ensuing 'incidental' mortality of these species is a major factor contributing to the population declines of many such species (Weimerskirch, Brothers & Jouventin, 1997; Nel, Ryan & Watkins, 2002; Lewison & Crowder, 2003). Although the typical progression of response by relevant management authorities – from denial through data collection to practical action – has usually been slow, nevertheless there are now widespread attempts to implement solutions, both in coastal and high seas fisheries (Agnew et al., 2000; Løkkeborg, 2003; Robertson et al., 2006). While we cannot afford to be complacent, it is just possible that, in a decade or so, we might be able to start to observe the beginning of a restoration of some of the seabird populations most affected. It is, therefore, especially serious to receive such a clear indication of the nature and potential scale of seabird mortality associated with a trawl fishery as that provided by Watkins, Petersen & Ryan (2008) for the hake fishery in the Benguela Current off South Africa. The main concern is that this study [which develops similar work in the Falkland Islands (Sullivan, Reid & Bugoni, 2006a; Sullivan et al., 2006b)] might be just the tip of an iceberg, identifying a problem hitherto largely unrecognized, and that the global total mortality in all relevant and analogous trawl fisheries might be many times the 18 000 seabirds estimated killed annually in this fishery. In this commentary, I would like to (1) address certain potential difficulties suggested by the study; (2) briefly evaluate its main implications for seabirds; (3) indicate some important wider implications and priority actions, both in terms of policy and practice. The study is based on 190 h of observations, whereby 30 birds (80% albatrosses, 10% petrels, 7% gannets) were observed killed, 80% due to collisions with warps, the rest entangled in the net, most mortality coinciding with dumping of fishery waste. Extrapolation from the observed mortality rates produced an estimated annual mortality of 18 000 (range 8000–31 000) birds. This may seem a slender factual basis on which to assert such a substantial mortality. However, at least three considerations can mitigate this (1) observers operated on 14 different vessels at all seasons of the year and observed a total of 331 trawls; (2) fatal collisions are relatively rare events, making it especially difficult to obtain really accurate estimates; (3) placing independent observers on commercial fishing vessels is a difficult – even challenging – task and this study represents the best example currently available. Furthermore, such data should be readily available as the responsibility for collecting information on the impacts of a fishery on non-target species is an obligation, under the United Nations Fish Stocks Agreement and the Code of Conduct for Responsible Fishing, on the managers and practitioners of a fishery. One would hope that further data on this will now become available through appropriate collaborations involving fishery managers and that this will be able to monitor improvements in levels and rates of bycatch due to the application of appropriate mitigation and measures. It should also be recollected that the initial data on incidental mortality in longline fisheries rested on an even more slender basis (see Croxall, Rivera & Moreno, 2007). There are two particularly worrying aspects. The first reflects the importance of the Benguela Current system to Southern Hemisphere seabirds. It is one of the main hotspots and the birds killed in this study reflect this. Thus the victims include local breeding species (cape gannet), breeding commuters from the Indian Ocean (e.g. white-chinned petrel) and wintering species from as far afield as South Georgia and Australasia (black-browed and shy albatrosses, respectively). The impact of this one local fishery therefore has very widespread geographical repercussions. Second, all the main species killed are already Globally Threatened according to the IUCN criteria (BirdLife International, 2008) and, as the authors emphasize, certainly for the albatrosses, mortality at this scale in this one fishery alone is unsustainable for the populations concerned. There is increasing concern at the levels of incidental mortality of seabirds associated with trawl fisheries. This paper itself notes some of the other examples and studies worldwide contributing to this diagnosis. It also emphasizes that potential solutions – or measures to reduce incidental mortality – exist, particularly with respect to improved waste management and to the use of devices protecting the warp cables from bird strikes. To address the problems in a more concerted and coordinated fashion will require a combination of implementing now best-practice mitigation measures, conducting research to improve these and introducing the requirement to use such measures in the management regulations for appropriate fisheries. Important elements in the approaches to delivering this will include: New international best-practice standards for measures to eliminate or reduce seabird bycatch in trawl fisheries. In September 2008, the United Nations Food and Agriculture Organisation will hold an Expert Consultation to develop Best Practice Guidelines for National Plans of Action Seabirds (NPOA Seabirds), which will address seabird mortality in longline, trawl and gill-net fisheries. To date, NPOA-Seabirds have only been required to address longline fisheries. So, the new guidelines are a critical step in providing an international framework for reducing seabird mortality in trawl fisheries. Actions at appropriate Regional Fisheries Management Organisations (RFMOs) with responsibilities for trawl fisheries. These are likely to include the South East Atlantic Fisheries Organisation, the Southern Indian Ocean Fisheries Agreement (currently awaiting ratification) and the South Pacific RFMO that is currently under negotiation. Under the UN Fish Stocks Agreement, RFMOs have been given a central responsibility in working to reduce and minimize bycatch within their fisheries, and to minimize the impact of fisheries on associated ecosystems. Improving practical implementation of appropriate measures. There may be an enhanced role here for BirdLife International's Albatross Task Force (BirdLife International Global Seabird Programme, 2008), which has developed the world's first international team of mitigation instructors working with fishermen and government agencies in global bycatch 'hotspots' (Argentina, Brazil, Chile, Namibia, South Africa and Uruguay) to demonstrate the adoption of mitigation measures that are both operationally and economically effective.