Immediate fate of angled-and-released Australian bass Macquaria novemaculeata

Abstract

The prevalence of catch-and-release factors known to adversely affect the mortality or physical condition of Australian bass Macquaria novemaculeata were surveyed across a range of anglers throughout impoundments and rivers in New South Wales. Subsamples of tournament-caught fish were also monitored in tanks for 1 h after being weighed to quantify immediate mortalities and sublethal physical damage. Most fish were caught on actively fished artificial baits, and were mouth hooked (96%), which resulted in no immediate mortality amongst monitored fish and a low frequency of mortality-causing factors in surveys. However, fish that were weighed-in during tournaments often had fin damage (52% of fish) and/or barotrauma (25% of fish, in impoundments only), and were held in live wells with poor water-quality. The prevalence of these sublethal effects varied considerably according to the specific seasons, locations, rules and procedures of each tournament; but could not be reliably attributed to any of the recorded catchand-release variables (except for dissolved oxygen, which was significantly influenced by live-well volume). While these results validate the current release of angled Australian bass as a means of conserving their stocks, the potential for adverse effects could nevertheless be minimised via simple changes to conventional handling.

Effects of barotrauma and mitigation methods on released Australian bass Macquaria novemaculeata

“…As for previously assessed M. novemaculeata that were angled and released from shallow water ( i.e. without barotrauma; Hall et al , 2009 a ; Dowling et al , 2010), there was considerable variability in the measurable effects among barotrauma fish monitored during the two tournaments. While these effects clearly resulted in proportionally greater fatalities among the barotrauma fish ( e.g.…”

“…The only deaths were four vented females that had injured vital organs. While tournament anglers might be expected to be reasonably proficient at minimizing harm to released fishes (Dowling et al , 2010), some may have inadvertently caused damage during venting, and so contributed towards the mortality of mouth‐hooked individuals at Lake Glenbawn.…”

“…The fish deployed to 5 m (controls) were also retrieved diagonally for 20 m. It was hypothesized that these fish would control for the effects of hauling, but without incurring barotrauma. The deployment depth of the controls was based on negligible barotrauma among >800 M. novemaculeata angled from <5 m during nine tournaments (Hall et al , 2009 b ; Dowling et al , 2010).…”

“…The assumption of minimal post‐release mortality of M. novemaculeata has been validated for many angling scenarios, with total estimates <6% (Hall et al , 2009 a ; Dowling et al , 2010). This research has suggested that the species is quite robust, with most deaths attributed to fairly extreme treatments including the ingestion of hooks (Hall et al , 2009 a , b ).…”

Ecology and welfare of aquatic animals in wild capture fisheries

“…Several studies have shown that improperly used live wells can expose fish to suboptimal water quality that can result in significant reductions in the physiological fitness of teleosts held in them for extended periods of time (Suski et al 2006(Suski et al , 2007White et al 2008), while live weighins expose the fish to additional handling, prolonged air exposure and fin and scale damage (Dowling et al 2010). Water quality in display/ recovery tanks used after live weighins in some tournaments can also be suboptimal, and the tanks themselves can be used in multiple tournaments in quick succession in different catchments, presenting an unquantitated biosecurity risk (B Diggles, unpublished observations).…”