A GOOD sized golden snapper or fingermark (Lutjanus johnii), is a welcome sight for any hungry angler fishing in our tropical waters.
This hard fighting, great tasting lutjanid is found in estuaries and near shore reefs throughout Top End Australia, particularly in the NT, Gulf of Carpentaria and Kimberley regions.
In recent years, size and bag limits have been introduced for golden snapper in all these areas, in response to increasing fishing pressure originating from improved access to the top end and increasing human populations in our northern regions. Bag and size limits can protect fish stocks, but the underlying assumption is that the released fish should have a high chance of survival.
While high survival rates have been documented for many tropical species, recent research conducted by NT Fisheries has found that golden snapper caught and then released from water deeper than around 10 meters are particularly susceptible to pressure damage (barotrauma). To illustrate the point, they released this video of fish recompressed to the depth of capture:
http://www.youtube.com/watch?v=C-1n4YZNaSY
Like many other lutjanids, golden snapper spend their juvenile years living in shallow estuaries, and then move to coastal and offshore reefs as they mature. Because of their schooling habits, immature and undersized golden snapper (they mature at around 45-60 cm long) are often encountered by anglers. Indeed around 50 per cent of those caught in NT waters are released, but if the water depth at the site of capture is over 10 metres, how many of these survive? No doubt they can be tough fish – I have caught golden snapper which are missing whole gill arches – but what about barotrauma damage?
My observations suggest that golden snapper taken in depths over 10 metres may still be able to survive their injuries, as perforated swim bladders can and do heal over several days, as can the other internal damage. However, when you factor in the Top End’s healthy shark populations, it becomes clear that when released fish (of all species, not just golden snapper) need time to recover, shark predation can be a problem with fish suffering from barotrauma.
The take home message is this: Release weights won’t work in this instance. Golden snapper are not suitable for catch and release in water deeper than 10 metres, due to the effects of barotrauma. In waters deeper than that, catch what you need for a feed and move on. Recent proposals by NT Fisheries to address the issue include reducing the possession limit to three golden snapper, and instigating five specific area closures for a period of five years to protect barotrauma prone species like golden snapper and black jew. See here for more details.
Because of the specific and temporary nature of the proposed area closures, it seems they have been accepted as necessary by NT angling groups: http://afant.com.au/wp-content/uploads/2013/11/AFANT-Protecting-our-reef-fish-submission-2013.pdf An interesting contrast to the usual permanent MPA closure issues.
One final interesting fish fact about this species is the origin of the name fingermark. It stems from the single brownish spot found on each side of the rear flanks of these fish. Similar spots are a distinctive feature of many lutjanid species, with another good example being those of the moses perch (L. russelli).
Names such as fingermark and moses perch have biblical connotations. The spots are said to have originated from the fingers of biblical characters who picked up their fishy ancestors a long time ago, or so the story goes. In reality, it’s more likely these spots have evolved as a form of camouflage which confuses predators. When predators approach a school of lutjanids, the spots can be mistaken as eyes, reducing the effectiveness of those predators which orient their attacks towards the heads of their prey. A spit second of confusion over why that fingermark left the scene backwards can mean the difference between life and death in the kill-or-be-killed fishy realm.
