Ingestion and ejection of hooks: effects on long-term health and mortality of angler-caught yellowfin bream Acanthopagrus australis

Abstract

Ninety juvenile yellowfin bream Acanthopagrus australis were angled from holding tanks, allowed to ingest nickel-plated, carbon-steel J-hooks and released (with their lines cut) into individual experimental tanks during 2 experiments in order to assess their (1) long-term (up to 105 d) health, mortality and rate of hook ejection and (2) short-and medium-term (< 42 d) temporal changes in health during hook ingestion. Equal numbers of control fish were scooped from holding tanks and similarly monitored in experimental tanks. Of 20 hook-ingested fish released during Expt 1, 3 died within 8 d, providing a non-significant mortality of 15%. Between Day 6 and Day 56 post-release, 13 of the surviving individuals ejected their hooks, which were typically oxidized to about 94% of their original weight and often broken into 2 pieces. At Day 105, there were no significant differences between the 20 control and 17 hook-ingested/-ejected fish in terms of their ability to digest and assimilate food (measured as changes in apparent digestibility coefficients), stress (measured as concentrations of plasma cortisol and glucose) or of morphological parameters that included weight (Wt) and maximum height (MH), maximum width (MW) and maximum girth (MG). During Expt 2, 3 individuals that still contained ingested hooks and 3 controls were sampled on each of 9 occasions between Day 3 and Day 42 post-release. All fish were sampled for blood cortisol and glucose and were then euthanized before being weighed and measured for total length (TL), MH, MW and MG. Hook-ingested individuals were also X-rayed to determine the position and orientation of hooks. There were no significant differences in plasma glucose between hook-ingested and control fish. Irrespective of the treatment of fish, concentrations of cortisol were elevated on some sampling occasions, indicating variable, acute stress. The MH and MG of fish were not significantly different between groups. Significant differences were detected for MG and Wt, with hook-ingested fish having weights similar to those of the control fish but a relatively greater MW (owing to stomach distension from ingested hooks) until 2 wk post-release, after which both morphological parameters generally declined. There was no significant temporal progression of hooks in the stomach of treatment fish; however, some hooks reorientated to positions that may have precluded passage along the digestive tract. We conclude that, for the J-hooks examined, cutting the line is an appropriate strategy that results in the greater majority of released hook-ingested yellowfin bream surviving with minimal negative long-term effects. KEY WORDS: Acanthopagrus australis · Catch-and-release · Hook mortality · Hook ingestionResale or republication not permitted without written consent of the publisher

Mortality of discards from southeastern Australian beach seines and gillnets

“…Compared with their larger conspecifics, smaller A. australis may have been less able to avoid tactile stressors during their capture in the beach seines. However, unlike Gerres subfasciatus, A. australis have hard scales, are physically robust and apparently quite resilient to a range of impacts with different fishing gears (Broadhurst et al 2005, 2007b, Uhlmann & Broadhurst 2007. While there were no concomitant, significant effects of TL on the mortality of Sillago ciliata, this may reflect their smaller sample size (i.e.…”

“…seined-or gilled-and-discarded vs. controls) on the numbers surviving at the end of each experiment. The blood samples collected from confined and angled Acanthopagrus australis and Neoarius graeffei at the end of the monitoring periods were analysed for concentrations of plasma glucose (mmol l -1 ) to provide an index of acute stress (Mazeaud et al 1977, Grutter & Pankhurst 2000, Broadhurst et al 2007b. Glucose concentrations were derived by means of colorimetric clinical kits (Roche Diagnostics) using an enzymatic spectrophotometric assay done according to the manufacturer's instructions.…”

Fate of three Australian teleosts after ingesting conventional and modified stainless- and carbon-steel hooks

“…The long-term utility of this approach for minimizing negative impacts has been validated for yellowfin bream Butcher et al, 2010). In particular, Broadhurst et al (2007) observed a non-significant mortality of 15% for line-cut, hook-ingested fish over more than three months, with 76% of survivors ejecting their hooks after an average of 20 d while maintaining their overall condition. No similar data are available for snapper or mulloway, but during 3 d of monitoring, Grixti et al (2010) recorded 13% hook ejection by similarly treated snapper (n ¼ 59).…”

“…For some species, their morphology and feeding strategies are probably important (Aalbers et al, 2004;Broadhurst et al, 2007;McGrath et al, 2009). However, irrespective of biological traits, it is likely that both the mortality of fish and their hook ejection are strongly influenced by hook decay, mainly because this dictates how long the point and barb remain sharp (and the potential for associated internal damage), and overall structural integrity is maintained (Aalbers et al, 2004;Broadhurst et al, 2007). Recognition of the importance of hook decay precipitated a recent study by McGrath et al (in press) to isolate some of the key contributory technical factors.…”

Short-term survival of discarded pearl perch (Glaucosoma scapulare Ramsay, 1881) caught by hook-and-line in Queensland, Australia

“…The survival of these regulatory discards is unquantified but current management measures would only be effective in conserving stocks if released fish survive capture and subsequent release (Broadhurst et al, 2005a;Butcher et al, 2007Butcher et al, , 2008. The survival of discarded individuals represents a large source of uncertainty in estimates of total fishing mortality (Davis, 2002).…”