LAST month we looked at pearl perch and part of that article reviewed recent research from Queensland on survival of pearlies after release from deep water.
Snapper (Pagrus auratus) are another species commonly captured from the same deep water grounds as pearl perch, and this month we’ll look at the results of newly published research that has been done to examine how snapper respond to depressurisation damage (barotrauma) after being captured from depth.
Readers will know that snapper are a very popular target species throughout Australia, certainly along the eastern seaboard and particularly in SE Queensland.
Here there is evidence that the snapper stock has been overfished, and in August 2011 this was reflected in fisheries management changes that were covered in Fisho at the time http://www.fishingworld.com.au/news/snapper-ban-winds-up-limits-reduced.
The minimum size limit of 35 cm remained unchanged, but the possession limit was reduced from five to four fish, including only one fish over 70 cm. Research has shown these regulations contribute to the fact that between 57 and 76 per cent of all snapper caught in SE QLD are released. Of course, as for pearl perch, these management measures will help protect and restore snapper stocks only if the undersized, oversized and excess fish survive release, which may not necessarily be the case when they are taken from deep water offshore.
Because of the need to know whether their management methods were effective, fisheries researchers in QLD conducted a study of barotrauma in snapper, but with a twist. The most recent study compared survival of fish for which the swimbladder was vented laterally through the side of the fish with a hypodermic needle, vs that of fish which were vented by piercing the swimbladder through the everted stomach. “Control” fish, which were not vented, were also studied. The snapper in the study were taken from waters between 37 and 180 metres deep from off Double island Point and Cape Moreton and they were monitored for short term (3 day) initial mortality rates.
The results showed that the overall survival rate of all fish taken during the experiment was a surprisingly high 88 per cent, especially given the depths being fished. The fish that were vented by piercing the swimbladder through the everted stomach had the highest survival rate (95 per cent), compared to control fish that were not vented (87 per cent) while those fish vented through the body had a slightly lower survival rate of 83 per cent.
Like for pearl perch, depth of capture only had a very slight effect on mortality rate of snapper, with overall survival of fish caught from “shallow” water (37-50 metres) being 90 per cent, reducing to 86 per cent for those caught from “moderate” depths (51-100 metres), and 85 per cent for fish caught from deep water (101-180 metres). Over all depths, larger legal sized fish had slightly reduced survival chances (82 per cent) compared to sublegal fish (91 per cent).
Another interesting finding from this study was the researchers recorded rapid healing of perforations in both the swimbladder and stomach of the fish they sampled. Indeed, 64 per cent of stomachs and 45-55 per cent of the swimbladders of the fish examined had healed within three days of capture. This makes sense when you consider the evolutionary benefits of selecting for ability to rapidly repair wounds in the stomach area of fish that eat a wide variety of very sharp objects like broken shells, crabs, prawn heads and the like.
Given that capture depth had less influence on survival than venting method, astute readers might ask the question, what was the most important factor influencing survival of snapper? The answer (as it usually is for most studies of the mortality of released fish), was the anatomical hooking location. This was evidenced by the fact that survival was only 20 per cent in gut hooked fish, and indirectly by the fact that bleeding was a significant indicator of reduced survival chances, with only 60 per cent of bleeding fish surviving, compared to 91 per cent of the non bleeders.
So, as for pearl perch, the researchers found that around 9 of 10 snapper taken and released from deep offshore reefs in QLD are likely to survive, and that hooking location was the main predictor of mortality. Because of this, the upshot from the snapper study is identical to the recommendations arising from the pearl perch research – circle hooks are recommended when using bait to reduce damage to undersized fish due to deep hooking, while using lures instead of bait can also generate the same effect.
Even so, dragging undersized snapper from depths of 80 to 100 metres is still not ideal for their survival. Consequently, like for pearl perch, this species should not be considered a catch and release sportfishing target when taken from deep waters, and the usual mantra of taking only what you need is recommended, as is moving to a new spot when large numbers of undersized snapper are encountered.
