Barotrauma

[Jamie Crawford] When the need arises to release a fish, we’re all responsible for ensuring it is released in a way that provides the greatest chance of survival.

Snapper, like many other bottom dwelling species, are susceptible to barotrauma when caught from depths greater than 10 metres.

[Courtney Cheesman] Barotrauma is a pressure related injury that fish experience when reeled up from depth. These injuries are caused by the expansion of gases within the fish’s body, as a result, of the rapid change in pressure when brought to the surface.

There are a number of injuries caused by barotrauma including hyperextension of the swimbladder that results in a swollen abdomen, and eversion of the stomach into the throat or out of the mouth.

[Jamie Crawford] The expansion of gas in the swimbladder can result in excessive buoyancy, which prevents the fish from returning to depth on its own, and can lead to sun damage and increased risk from predators.

[Troy Rogers] A recent study led by SARDI and funded by the Fisheries Research and Development Corporation monitored the survival rates of released Snapper caught in South Australia’s gulfs using electronic tags.

The fish were captured at various depths up to 35 metres and released either at the surface or returned to their depth of capture using a release weight.

[Jamie Crawford] The study found that the severity of barotrauma increased with depth, which resulted in a rapid decline in the survival rates of released fish. Despite initially appearing healthy when released, some fish succumbed to their injuries up to 10 hours after they were returned to the water.

The study also showed that fish returned to the water using a release weight had a higher probability of survival than those released at the surface.

[Courtney Cheesman] Recreational fishers in South Australia are strongly encouraged to carry a release weight when releasing in deeper water, especially to assist with the release of unintentionally caught or undersized Snapper.

A release weight returns the fish to its depth of capture, which recompresses the gasses in the fish’s body and allows it to regain correct buoyancy.

[Troy Rogers] The most common form of release weight is a large sinker attached to an inverted barbless hook, which is fitted to a separate fishing rod or a heavy retrieval line.

These can be purchased from fishing and tackle stores around South Australia or made at home using a large sinker and a barbless hook.

[Jamie Crawford] There are a number of things that fishers can do to optimise the survival of released Snapper.

Firstly, fishing for Snapper in shallow water is the best option to reduce barotrauma and improve survival, given the strong relationship between barotrauma and depth.

Deep hooking, where the fish is hooked in the gills or stomach, can significantly impact post-release survival. This can be reduced by using circle hooks rather than traditional J hooks when bait fishing, or by lure fishing instead.

[Courtney Cheesman] When landing and handling a fish intended for release, it is considered best practice to be prepared before the fish is hooked by having the necessary tools and equipment readily available, such as a landing net, wet towel and pliers.

Reducing handling time and air exposure will optimise the probability of survival.

It is also recommended to use a knotless or silicon landing net to support the weight of the fish when bringing it to the vessel and placing the fish onto a cool, wet surface and handling with wet hands or gloves to minimise the removal of protective mucus.

You should also remove the hook from the fish’s mouth or cut the line close to the mouth if the fish is ‘deep hooked’.

[Troy Rogers] The release weight is most easily used by two people, where one person supports the fish and the other attaches the weight.

However, it can also be used individually.

The recommended approach is to support the fish and attach the release weight through the upper jaw.

Where possible, use the existing hole from where the fish was hooked.

Place the fish in the water and then let it go, allowing the release weight to take the fish back to depth.

[Courtney Cheesman] Let the retrieval line run free as the fish is released and then detach the release weight from the fish by stopping the retrieval line and briefly pulling on it.

The barbless hook will slide out of the fish’s mouth and the release weight can be retrieved.

[Jamie Crawford] By making small changes to the way that we handle and release Snapper, we can all optimise their probability of survival when released and contribute to the recovery of this iconic fish species.