Deep-sea organisms are increasingly subject to bycatch interactions worldwide. Recent studies have shown that discard mortality
can lead to significant declines in deep sea fish stocks, and highlight the inherent vulnerability of deep sea organisms to
overexploitation due to their shared suite of conservative life history characteristics. Estimating the post-release mortality (PRM) rates
of these deep-sea organisms is a necessary step towards responsible fisheries management, particularly as PRM represents a substantial
source of uncertainty when estimating total fishery mortality. The deep-sea giant isopod Bathynomus giganteus and its relatives are
captured as bycatch in numerous fisheries, although knowledge is limited regarding their population trends or response to capture and
release. In order to assess and predict PRM in B. giganteus, we used reflex action mortality predictors (RAMP) whereby the presence or
absence of target reflexes was used to create a delayed mortality model, and considered factors affecting mortality. Mortality rates five
days post-capture ranged from 50-100% and both RAMP scores and time at the surface were significant predictors of mortality, although our
conclusions regarding the effect of surface time are limited. In-cage video documented little movement within the 24 h monitoring period
following cage deployment, and it appeared that surviving individuals often fed within the holding period after cage deployment. Our
results suggest that PRM in B. giganteus is common and that this unaccounted source of mortality should be quantified and investigated for
other deep-sea crustaceans as well. Similarly, bycatch interactions with deep-sea elasmobranchs can lead to dramatic declines in abundance
over short time scales. Sharks hooked in the deep sea could face a higher likelihood of severe physiological disturbance, at-vessel
mortality, and PRM than their shallower counterparts. Unfortunately, robust PRM rates have not yet been estimated for deep-sea
elasmobranchs and as such are not currently incorporated into total fishery mortality estimates or bycatch assessments, limiting the
effectiveness of conservation or management initiatives. We empirically estimated PRM for two focal species of deep-sea shark, the Cuban
dogfish Squalus cubensis and the gulper shark Centrophorus sp. using post-release cages deployed at-depth. We calculated 24 h PRM rates of
49.7% (± 8.5 SE) for S. cubensis and 83% (± 16 SE) for Centrophorus sp. and identified shark size (total length), blood lactate, blood pH,
and vitality scores as predictors of PRM in Squalus cubensis. We also observed all PRM within 11 h post-capture and demonstrated the
effects of capture and recovery depth on stress and behavior. Our results suggest that PRM rates of deep-sea sharks are higher than
previously assumed, and highlight the need for filling in this gap in fishery mortality estimates for other common deep-sea discards in
the future. / A Thesis submitted to the Department of Biological Science in partial fulfillment of the Master of
Science. / Spring Semester 2016. / March 31, 2016. / bycatch, deep-sea, giant isopod, mortality, post-release, shark / Includes bibliographical references. / Brendan Suneel Talwar defended this Thesis on March 31, 2016, Professor Directing Thesis; Edward
J. Brooks, Committee Member; Don Levitan, Committee Member; Joseph Travis, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_360456 |
| Contributors | Talwar, Brendan Suneel (authoraut), Grubbs, R. Dean (Ralph Dean) (professor directing thesis), Brooks, Edward J. (committee member), Levitan, Don R. (committee member), Travis, Joseph (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Biological Science (degree granting department) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource (78 pages), computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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