The Effects of Fishing on Chondrichthyans
Global fishing activity is major threat to chondrichthyan (sharks, rays and chimaeras) populations. The effects of fishing are predominantly estimated by quantifying immediate and post-capture mortality rates. However, the true effect of fishing is likely to be underestimated, because measuring the...
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| Format: | Thesis |
| Language: | unknown |
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2016
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| Online Access: | https://doi.org/10.4225/03/5850b8e4186e4 https://figshare.com/articles/thesis/The_Effects_of_Fishing_on_Chondrichthyans/4315226 |
| Summary: | Global fishing activity is major threat to chondrichthyan (sharks, rays and chimaeras) populations. The effects of fishing are predominantly estimated by quantifying immediate and post-capture mortality rates. However, the true effect of fishing is likely to be underestimated, because measuring the mortality rates of released animals is logistically challenging and little is known about the sub-lethal effects of capture on life-processes such as reproduction. The physiological stress response to capture driving lethal and sub-lethal outcomes in chondrichthyans is not fully understood. The overall aim of this study is to better understand the post-capture fate of chondrichthyans for the purpose of developing and improving sustainable fishing practices. This aim is addressed by investigating how the behaviour during capture influences the stress response; improving the estimation of mortality risk by developing an additional physiological stress indicator; and investigating the sub-lethal effects of capture by examining reproductive consequences. To determine how behaviour during longline capture influenced the stress response of the gummy shark ( Mustelus antarcticus ), haematologically derived stress indicators were correlated with animal movement and water temperature data obtained from time-depth recorders (TDR) attached to individual hooks. In water temperatures ranging 12–20°C, higher temperatures increased metabolic rate but variable capture duration (32–241 min) did not change the stress response. Animal movement occurred for an average of 10% of the time spent captured. Limited movement of M. antarcticus for the majority of capture and the ability to respire whilst stationary probably mitigated the influence of increased temperature and capture duration on the stress response. TDRs were also evaluated for their ability to measure capture behaviour in eight species caught in either surface or demersal longline configurations. Three analytical methods were developed to interpret TDR data; the Visual ... |
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