UBC Theses and Dissertations
Effects of acute salinity and temperature change on Pacific hagfish, Eptatretus stoutii; implications for bycatch post release survival Hastey, John Pinkerton
Hagfish captured as bycatch in a commercial fishery may be exposed to a range of elevated temperatures and reduced salinities when brought to the surface but it is not known how this will affect post-release survival. In this study, hagfish were exposed to all combinations of four salinities (33, 28, 23, and 18 g/l) and three temperatures (7, 16 and 25˚C) and sampled following 1, 3 or 6 h exposure to investigate sub-lethal affects on plasma osmolality, [Na⁺], [Cl⁻], [Mg²⁺], and glucose, hematocrit, mean cell haemoglobin concentration , muscle water content, as well as behavioural responses and survival. An additional group of hagfish were sampled after 48 h of recovery (33 g/l at 7˚C) following 3 h exposure to all salinity/temperature combinations to investigate latent effects of exposures. In general, during exposure to salinity and temperature combinations, plasma osmolality, [Na⁺] and [Cl⁻] decreased as: i) the salinity of exposure was reduced, ii) the duration of exposure was increased or iii) the temperature to which hagfish were exposed was increased. Plasma osmolality did not equilibrate with environmental osmolality within 6 h and appeared to approach an asymptote at 60% equilibration. Behavioural effects were observed during exposure to reduced salinity conditions at all temperatures and included full body contractions, reduced slime production, reduced swimming ability, extended body posture. During exposure to 25˚C, hagfish were often unresponsive to touch. Following 48 h of recovery from 3 h exposure to all salinity/temperature combinations most of the parameters measured were restored, with the exception of plasma glucose levels which remained elevated indicating latent stress. Following recovery from exposure to 23 and 18 g/l at 25˚C, morbidity levels of 14 and 100% were observed. Thus, hagfish captured and immediately brought to the surface and released, without exposure to extreme salinity or temperatures, may not physiologically be negatively affected by a catch and release fishery however, diminished survival should be expected if exposure salinity approaches 18 g/l or water temperature approaches 25˚C. Future research should address the implications of observed behaviours on release survival of hagfish in a natural setting.
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