Temperature tolerance of plaice and its effects on survival

Master Thesis subject (30 ECTS)
Under the “high survival” exemption of the European landing obligation or discard ban, monitoring vitality and survival of flatfish such as European plaice (Pleuronectes platessa) becomes relevant to a discard-intensive beam trawl fishery. In commercial trawl fisheries, multiple stressors such as technical gear configurations (i.e., gear deployment duration, fishing speed, gear type), biological (i.e., catch composition, sediment type) and environmental conditions (i.e., water and air temperature, air exposure) may affect fish survival probability (Broadhurst et al., 2006; Uhlmann and Broadhurst, 2015). For Belgian fisheries, previous research addressed the impact of gear deployment duration, and air exposure on vitality and mortality of plaice and also indicated the relevance of temperature changes to fish when being trawled through the water column, exposed to air on deck, and being re-submerged under water (Uhlmann et al., 2016). Although in Uhlmann’s et al. (2016) analysis an interaction between temperature change (between seawater and air) with air exposure on deck was not significant, at least seawater temperature seemed to be an important contributor to mortality. Similarly to van Beek et al. (1990), Uhlmann et al. (2016) repeatedly observed higher survival at cooler days in winter compared with trips in summer onboard the Eurocutter vessels. It is unclear, however, whether higher temperature per se or thermoclines during the hauling process cumulatively stressed captured fish. Elevated temperature do exacerbate physiological responses towards commercial fishing capture stress (Davis, 2002; Broadhurst et al., 2006; Gale et al., 2013). With warmer water, a fish’s metabolic rate increases, resulting in a rapid depletion of energy reserves (Gale et al., 2013). The objective of this proposed study is to address temperature tolerance of trawl-caught plaice and determine the effect of temperature changes (either within the water column or between water and air) on survival probability. References: Broadhurst, M. K., Suuronen, P., and Hulme, A. 2006. Estimating collateral mortality from towed fishing gear. Fish and Fisheries, 7: 180–218. Davis, M. W. 2002. Key principles for understanding fish bycatch discard mortality. Canadian Journal of Fisheries and Aquatic Sciences, 59: 1834–1843. Gale, M. K., Hinch, S. G., and Donaldson, M. R. 2013. The role of temperature in the capture and release of fish. Fish and Fisheries, 14: 1–33. Uhlmann, S. S., Theunynck, R., Ampe, B., Desender, M., Soetaert, M., and Depestele, J. 2016. Injury, reflex impairment, and survival of beam-trawled flatfish. ICES Journal of Marine Science, 73 : 1244–1254. Uhlmann, S. S., and Broadhurst, M. K. 2015. Mitigating unaccounted fishing mortality from gillnets and traps. Fish and Fisheries, 16: 183–229. van Beek, F. A. van, Leeuwen, P. I. van, and Rijnsdorp, A. D. 1990. On the survival of plaice and sole discards in the otter-trawl and beam-trawl fisheries in the North Sea. Netherlands Journal of Sea Research, 26(1): 151–160.
fluent English in spoken and written word
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Christian Vandenberghe (fisheries technician)
Reference Number: RP-47301