Karina C. Hall

Effects of angling on post-release mortality, gonadal development and somatic condition of Australian bass Macquaria novemaculeata

This study assessed the protracted effects of two angling treatments (mild and harsh) on the post-release mortality, gonadal development and somatic condition of Australian bass Macquaria novemaculeata in a pond-based experiment. Angled fish were destructively sampled (along with controls) three times: immediately before, and 1 or 4 weeks after release into cages. Compared with the other groups, harshly angled fish had similar, low immediate and short-term mortalities (< or =5%), but significant delayed mortality (25%) and fed only minimally. None of these fish ejected ingested hooks. Forty-six per cent of captive fish (across all groups) and 20% of wild fish had non-ripening gonads (stage I) prior to, or during, the experiment. In females with ripening ovaries (stages II or III), neither angling treatment significantly reduced standardized gonadal mass. The mean per cent of atretic oocytes increased among females in all groups, but was significantly greater in those that were harshly angled. The results demonstrated that the gonadal development of M. novemaculeata could be suppressed or impaired (by angling, handling and confinement), and that further research is warranted. In particular, the timing and severity of angling in relation to the stage of gonadal development could have important implications for the introduction of temporal restrictions to angling.

Resilience of inshore, juvenile snapper Pagrus auratus to angling and release

This study assessed the mortality of 157 snapper Pagrus auratus (9-29 cm, total length, L(T) ) after being conventionally angled and then released into cages (along with 48 controls) for 4 days off south-eastern Australia. Fatalities were restricted to 12 angled fish (7·6%) and mostly attributed to the ingestion of hooks and especially their subsequent removal, which caused substantial blood loss and immediate death. Hook ingestion was significantly biased towards smaller fish (<21 cm L(T)) and attributed to a lower chance of anglers initially detecting these individuals on the line (allowing them to consume more of the baits). While mortalities might be reduced in future via (1) choosing terminal rigs that promote mouth hooking and (2) cutting the line on any-hook ingested fish, the results nevertheless validate releasing unwanted angled inshore juvenile P. auratus as a means for managing their exploitation.

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

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 1xa0h 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 catch-and-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.

Clinical signs of barotrauma in golden perch, Macquaria ambigua (Richardson), and associated effects on post-release mortality and health

This study assessed the effects of different retrieval depths (2, 10 or 20 m), surface intervals (none or 15 min) and release methods (untreated, vented or recompressed) on the incidence of external and internal clinical signs of barotrauma (ECSB and ICSB) and post-release mortality in golden perch, Macquaria ambigua (Richardson). Fish were assessed for ECSB before and after surface intervals and either monitored for mortality over 3 days in two deep cages or killed for internal examination. When all fish were left untreated, short-term mortality increased with retrieval depth from 0% and 4.2% among 2 and 10-m fish, respectively, to 19.2% among 20-m fish; while surface interval only affected the incidence of two ECSB (excess buoyancy and a prolapsed cloaca). Mortality was also greater among 20-m fish that were subjected to a 15-min surface interval and left untreated (22.2%) or vented (22.2%) than those that were recompressed (5.6%). Of the ECSB, only exophthalmia was associated with increased mortality, with half of the affected fish dying. However, many fish retrieved from 10 and 20 m also sustained numerous ICSB, including compressed gonads or vital organs and ruptured or collapsed, haemorrhaging swimbladders that remained deflated for up to 3 days after release.

Deep Hooking and Postrelease Mortality of Two Australian Native Freshwater Fishes Angled from Rivers by using Natural Baits

AbstractDeep hooking is one of the key causes of mortality among angled-and-released teleosts worldwide. We assessed the effects of natural baits and other variables on the frequency of deep hooking and postrelease mortality in two Australian native freshwater fishes that are classified as vulnerable or endangered: Golden Perch Macquaria ambigua and Freshwater Catfish Tandanus tandanus. Sixty-one angled Golden Perch were released and monitored in individual submersible cages at their capture location or were held in shore-based group tanks; of these fish, 97% were hooked with natural baits, 41% were deep hooked and had their lines cut, and 44% died. Of the Golden Perch that died, 70% were deep hooked, and hook location and two associated factors (hook removal and ease of handling) were identified as significant predictors of mortality. Mortality of Golden Perch was also significantly greater during the afternoon session on the first day of angling than during other sessions and days. In contrast, of the 9...

Sublethal effects of angling and release on golden perch Macquaria ambigua : implications for reproduction and fish health

The present study tested the hypothesis of no delayed sublethal effects of mild angling and release on the feeding, growth, somatic condition and gonadal development of golden perch Macquaria ambigua during gametogenesis. Subsamples of adult M. ambigua (n = 17-21 of 207), originally captured from the wild and stocked into ten 0·1 ha earthen ponds, were angled and released during early and late gametogenesis. Wild samples that were concurrently collected throughout the experiment underwent rapid and synchronous gonadal development and many spawned. While no spawning occurred in the ponds, most M. ambigua underwent normal gonadal development to maturity, including the angled fish. Angled fish also fed, maintained condition and actually grew faster than non-angled captive controls. Although females that were angled during late gametogenesis more readily ingested and retained baited hooks, neither their subsequent condition nor gonadal development was significantly affected. The predominance of null results was attributed to the combined effects of the flexible reproductive strategy of M. ambigua, the benignness of mouth hooking and immediate release, and possible methodological issues arising from differential hooking success of more aggressive and resilient individuals. The findings support earlier catch-and-release research, but contrast with reports of acute reproductive effects following capture and handling for aquaculture broodstock. This discrepancy highlights the need for research to specifically address welfare questions relevant to recreational fisheries across various species and angling scenarios.