No abstract

Common coral trout, Plectropomus leopardus Lacepe`de, crimson snapper, Lutjanus erythropterus Bloch, saddletail snapper, Lutjanus malabaricus (Bloch & Schneider), red emperor, Lutjanus sebae (Cuvier), redthroat emperor, Lethrinus miniatus (Schneider) and grass emperor, Lethrinus laticaudis Alleyne & Macleay, were tagged to determine the effects of barotrauma relief procedures (weighted shot-line release and venting using a hollow needle) and other factors on survival. Release condition was the most significant factor affecting the subsequent recapture rate of all species. Capture depth was significant in all species apart from L. malabaricus and L. miniatus, the general trend being reduced recapture probability with increasing capture depth. Recapture rates of fish hooked in either the lip or mouth were generally significantly higher than for those hooked in the throat or gut. Statistically significant benefit from treating fish for barotrauma was found in only L. malabaricus, but the Correspondence: Wayne Sumpton,

Promotion of better procedures for releasing undersize fish, advocacy of catch-and-release angling, and changing minimum legal sizes are increasingly being used as tools for sustainable management of fish stocks. However without knowing the proportion of released fish that survive, the conservation value of any of these measures is uncertain. We developed a floating vertical enclosure to estimate short-term survival of released line-caught tropical and subtropical reef-associated species, and used it to compare the effectiveness of two barotrauma-relief procedures (venting and shotline releasing) on red emperor (Lutjanus sebae). Barotrauma signs varied with capture depth, but not with the size of the fish. Fish from the greatest depths (40-52 m) exhibited extreme signs less frequently than did those from intermediate depths (30-40 m), possibly as a result of swim bladder gas being vented externally through a rupture in the body wall. All but two fish survived the experiment, and as neither release technique significantly improved short-term survival of the red emperor over non-treatment we see little benefit in promoting either venting or shotline releasing for this comparatively resilient species. Floating vertical enclosures can improve short-term post-release mortality estimates as they overcome many problems encountered when constraining fish in submerged cages.

The present study indicated significant post mortem decreases in length for four Australian teleost species from temperate to tropical habitats: black bream Acanthopagrus butcheri, King George whiting Sillaginodes punctata, summer whiting Sillago ciliata and redthroat emperor Lethrinus miniatus. Shrinkage averaged 5·0 mm after 24 h (range 0–10 mm) for A. butcheri, 4 mm (0–8 mm) for S. punctata, 2·2 mm (0·7–3·7 mm) for S. ciliata and 5·4 mm (−2·5–15·0 mm) for L. miniatus. For A. butcheri held under three different post mortem treatments, the mean length of fish in all treatments decreased but there was no significant effect of treatment type on the extent of shrinkage. The rate of shrinkage of S. ciliata varied with treatment, but the ultimate extent did not. For A. butcheri shrinkage was most rapid (2·5 mm h−1) between 1 and 2 h postcapture. The results from these studies confirm that a post mortem decrease in length is a common phenomenon, even in fishes that are not frozen or preserved. Such shrinkage has implications for the enforcement of minimum legal length legislation, and may cause bias in biological investigations, including growth estimates from tag and recapture studies.

This study examined post-release survival in sand flathead (Platycephalus bassensis) and whether there were survival benefits from the use of circle hooks over conventional hook patterns. Anatomical hooking location was the major factor contributing to mortality, with an almost 100% survival rate for fish hooked in the lip, mouth or eye (shallow-hooked) compared with around 64% for fish hooked in the throat or gut (deep-hooked). Mortality in deep-hooked fish was generally associated with injuries to vital organs (gills, heart, liver) and survival was significantly lower if bleeding was associated with injury (54% compared with 85% for non-bleeders). Circle hooks resulted in significantly lower deep-hooking rates (1%) compared with conventional hook types (4–9%) and, based on catch rates, were at least as effective as conventional hook patterns. Estimated survival rates for line-caught sand flathead were high, over 99% for circle hooks and between 94 and 97% for conventional hooks. These findings support the efficacy of management strategies based on size and bag limits and the practice of catch-and-release fishing for sand flathead, as well as a potential conservation benefit from the use of circle hooks.