Skipper Meggs Amidships
Too much fun on and off the water

Shooting Black Jewfish in a Barrel

Posted by Meggs | Fish Life Cycle Posts | Posted on February 29th, 2008

A freshly caught black jewfish with the line in its mouth indicating it was gut hooked

Most fishermen have a fascination with all manner of jewfish and to be honest I must admit I am the same.

I’m not quite sure whether it’s just the thrill of the chase or the size of the prize but one thing is for sure if you’re heading to places like the Northern Territory or Cape York, as we are in May, Black Jewfish (Protonibea diacanthus) are always on the agenda.

The Territory Government in conjunction with the Fisheries Research and Development Corporation have recently conducted a major study into Black Jewfish and quite frankly I was shocked with the results. In fact it made me very despondent to the point where I am not sure that I wish to target them directly.

Black Jewfish inhabit the tropical areas of Northern Australia, across to Asia, China and India.

In 1995 Asia, China and India actively fished for this species accounting for 400,000 tonnes in that year alone. Ten years later the catch was zero as the populations were wiped out.

Local aggregations still exist in the Northern Territory and northern Queensland and today little is known about their life cycle although the recent study referred to certainly has uncovered some interesting facts.

With regard to spawning, it appears that the NT Black Jewfish tend to spawn in December whilst their Cape York counterparts spawn in May. Black Jewfish are sometimes called “croakers” as when they are caught they sometimes make a croaking sound on the deck. It is thought that this sound may be related to the fish’s mating behaviour as is the case with other species.

There also appears to be stunning differences between populations of Black Jewfish.


For instance in NT the average size of a 1 year old fish is 65cm, a 2 year old fish 90cm, a 3 year old fish 100cm and a 4 year old fish 110cm. In Queensland the corresponding lengths for 1 to 4 year old fish would be 40cm, 60cm, 80cm and 85cm respectively perhaps due to overfishing and the removal of larger breeding fish stock.

The Black Jewfish can grow to 45kg but also has a short life span – 12 years. This compares poorly with the southern mulloway that can live to 45 years of age.

Although it is said that the fish like to inhabit reefs, wrecks and holes to a depth of 100m, the NT tests have shown that the areas the fish inhabit don’t necessarily fit this logical pattern as aggregations studied appeared to be located in a trench and a relatively flat and featureless ocean area.

One interesting fact about the Black Jewfish is that they have a tendancy to school up or, more correctly, “aggregate” in large numbers – sometimes in their thousands. This makes them susceptible to overfishing.

Their problem is that, unlike the southern jewfish, they are not elusive and respond to live bait, strip baits and lures and are relatively easy to locate. A little knowledge of deep holes or jewie spots, some strong line and brute strength and an angler with little experience is able to extricate these fish from the depths.

Over fishing these aggregations can cause serious problems for the Black Jewfish – size/age balance and reproductive issues for the populations. Results of the NT study show that there doesn’t appear to be any blending of aggregations and fish lost to populations are not replaced with members of other schools.

Tests also show that the Black Jewfish remain in the same location which also makes them easy targets. Tagged fish were found in the same spot after 500 days of release.

It seems that catching Black Jew is akin to shooting fish in a barrel – you catch one, you should catch more.

Apparently 30% of Black Jewfish caught by recreational fisherman are released which is good news. However the NT study also looked into the survival rates of released fish.

Barotrauma caused by changes in pressure on the fish whilst raising it from the depths is a serious issue for those fishermen keen to release after capture.

In summary, fish pulled in from depths of water greater than 15m had little chance of survival as the impact of barotrama caused “pop-eye”, swim bladder perforation and extended stomachs through their mouths.

Between depths of 10-15m 46% of fish sustained life threatening injuries whilst those caught in depths less than 10m had 100% survival rates.

Another consideration for safely releasing Black Jewfish is the use of circle hooks as these were found to set inside the lip or the mouth of the fish every time unlike the traditional “j” hooks that set in the gut of the fish 40% of the time thus inducing life threatening injuries to the fish.

Ok, so what should you do to make sure the remaining Black Jewfish stocks flourish rather than vanish?

1) Fish in waters less than 10m and use circle hooks, not “j” hooks

2) If you catch one or two, use smaller hooks to avoid Black Jewfish or better still move on to another spot

3) Never release fish with extended stomachs through their mouths and never vent the fish’s swim bladder by bursting it with a needle – it will take a good five minutes to reduce and may never recover. Use barbless weighted hooks to release the fish quickly to the bottom. I will write about this method in upcoming weeks.

For me, the discovery of the plight of the Black Jewfish was rather sad - it seems the odds are stacked against them.

I’m not so sure that I would particularly like to target them knowing what I know now.

Thoughts?

Sea you later,

Skipper Meggs