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.
Dolphin caught in fishing net (WWW1)
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. Both biological and economic issues arise from the issue of bycatch. From an economic standpoint, bycatch increases costs leaving revenues steady, while for fisheries, bad image is generated thus incurring limitations and further restriction pressures, on an industry that is already under strain. Protected species, such as *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 Habitat 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).
Best estimates of population sizes of harbour and grey seals in Ireland (2003 and 2005) (Cosgrove et al. 2013)
Seals in particular 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, and tangle nets between two vessels, 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. It is not just these static gear types that are a danger for these animals; long lines pose a particular threat to seabirds (Løkkeborg, 1998), while 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).
Anatomy of a bottom trawl (WWW2)
Effects of bottom trawling showing destriction of seabed and resuspension of sediments
Relative size of supertrawlers
Mitigation of this issue has been brought about by the use of selective gear usage. Net mesh sizes are being altered to allow smaller fish to avoid capture, “dolphin gates” 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 fishing industry, many of whom are already under serious pressures from the aforementioned issues.
*Benthic Creatures are organisms that occur in the lowest level of a body of water
**Cetaceans are a widely distributed and diverse clade of aquatic mammals that include whales, dolphins and porpoises.
***Pinniped which means, fin or flipper-footed, refers to the marine mammals that have front and rear flippers which includes seals, sea-lions and walruses.
Althaus, F., Williams, A., Schlacher, T. A., Kloser, R. J., Green, M. A., Barker, B. A.,
Schlacher-Hoenlinger, M. A. (2009). Impacts of bottom trawling on deep-coral
ecosystems of seamounts are long-lasting. Marine Ecology Progress Series,
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Ball, B., Munday, B., Fox, G. 1999. The impact of a Nephrops otter trawl fishery on the benthos of the Irish Sea. Journal of Shellfish Research, 18 (2)708
Brown, J., & Macfadyen, G. (2007). Ghost fishing in European waters: Impacts and management responses. Marine Policy, 31(4), 488–504.
Cosgrove, R., Cronin, M., Reid, D., Gosch, M., Sheridan, M., Chopin, N., & Jessopp, M. (2013). Seal depredation and bycatch in set net fisheries in Irish waters. Fisheries Resource Series, 10.
Evans, D., & Roma, C. (2006).The Habitats of the European Union Habitats Directive, 173(3), 167–173.
Hall, M. A., Alverson, D. L., & Metuzals, K. I. (2000). By-catch: Problems and solutions. Marine Pollution Bulletin, 41(1-6), 204–219.
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bird-scaring streamer line and line shooter on the incidental capture of northern
fulmars Fulmarus glacialis. Biological Conservation, 106(3), 359–364.
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Rogan, E., & Mackey, M. (2007). Megafauna bycatch in drift nets for albacore tuna
(Thunnus alalunga) in the NE Atlantic. Fisheries Research, 86(1), 6–14.
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WWW1 – http://oceana.org/
WWW2 – http://www.archive.xray-mag.com/content/anatomy-bottom-trawl
WWW3 – https://www.fix.com/blog/biggest-threats-to-global-fisheries/