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Bycatch is defined as “the incidental take of undesirable size or age classes of the target species (e.g. juveniles or large females), or to the incidental take of other non-target species. Individuals caught as bycatch can be unharmed, released with injuries, or killed” (Lewison et al., 2004). This applies not only to non-target, commercially worthless fish species, but also to marine mammals, turtles, sharks, invertebrates, and sea birds.
Issues Arising from Bycatch
Both biological and economic problems arise from the issue of bycatch. From an economic standpoint, bycatch increases costs leaving revenues steady, while for fisheries, a bad image is generated, which incurs limitations and further restriction pressures on an industry that is already under strain.
Protected species, such as various cetaceans and pinnipeds, raise further issues, as these animals have been placed under the Habitats Directive of the EU (Hall et al., 2000). Adopted in 1992, the Habitats Directive seeks to “contribute towards ensuring bio-diversity through the conservation of natural habitats and of wild fauna and flora in the European territory of the Member States” (Article 2(1)). As such, their habitats and resources are kept under a strict legislative protection and any accidental mortality must be reported to the authorities (Evans and Roma, 2006).
Seals for example, have been shown to be particularly vulnerable to becoming entangled in nets. A study carried out in the South West of Ireland (Cosgrove et al., 2013) observed 68 individual seals (from 2 species) bycaught in gill, trammel, over the course of a single year. This same study found 2 dolphin and 1 whale species as bycatch, with tangle nets having the highest affinity for accidental mortality. In addition, longlines pose a particular threat to seabirds (Løkkeborg, 1998).
It is not just these particular static gear types that are a danger for these animals, bottom trawling can cause extensive damage to benthic creatures, such as corals, sea pens, and crustaceans, through direct physical damage or smothering due to resuspension of sediments (Althaus et al., 2009).
Mitigating Bycatch
Mitigation of this issue has been brought about by selective gear usage. Net mesh sizes are being altered to allow smaller fish to avoid capture, “dolphin gates” and “turtle excluder devices”are left in nets for larger animals to escape, the use of streamers on long lines have greatly reduced the number of sea bird bycatch incidents, and the banning of bottom trawling in particular areas, have all been shown to have positive effects in the reduction of accidental catch of non-target species (Ball et al., 1999; Løkkeborg et al., 2002; Rogan and Mackey, 2007). These further limitations can, again, be costly to the fishermen, many of whom are already under serious pressures from the aforementioned issues.
The Role of Fisheries Observers in Monitoring Bycatch
In most countries, including Ireland, fisheries observers have a dual role in that of monitoring adherence to regulations, but also in scientific data gathering (Furlong and Martin, 2000). Although not directly enforcing the law aboard vessels, it has been proven that the maintenance of an on-ship log book can deter under-reporting of landings by fishermen, while maintaining the personal safety of these non-crew members (Warner, 2004; Van Atten, 2007). As part of their duties, observers will also report on any bycatch species landed by the vessel.