Gulf mangrove jack decline
  |  First Published: December 2003

RECREATIONAL anglers and charter operators around Weipa, along with the mother ship operators working between Mapoon and Bamaga, have reported a marked decline in mangrove jack numbers in recent years. Here, in Weipa, my log books show catches during my seven seasons here have gone downhill, particularly during the past three.

Interestingly, in the same period, juvenile Queensland groper have gone from being an incidental catch to a regular occurrence. Lure casting clients this year landed nine groper in one days fishing, seven of those coming off a single snag! In years past, seven groper in an entire season would have been a more realistic figure. It would seem that the decline in mangrove jack and the increase in groper could be in some way related.

Scientists have the breeding cycle of mangrove jack well established – immature fish leave the rivers and congregate offshore, where they mature and spawn. Mangrove jack breeding stocks on the east coast are largely protected from exploitation because they aggregate on reef areas, in particular, the Great Barrier Reef. In the Gulf, given a marked lack of offshore reef structure, breeding fish are believed to aggregate over a relatively flat bottom.

In the mid-90s a purportedly Commonwealth-licensed fish trawler started working in the Gulf, mainly off the north-western Queensland coast. Since 1999, following the issuing of developmental fish trawling permits, another trawler has been periodically working the waters off Weipa because of the proximity of its port facilities.

I was a member of the ‘expert’ consultative committee, Tropical Finfish MAC, when the developmental fish trawling proposal was discussed, and the MAC unanimously agreed that the practice not be allowed to proceed because the scientific information available was not conclusive. The Queensland Joint Authority, a combined Commonwealth/State body that administered the permits, opted to ignore the MAC’s recommendations and hand out permits.

It has since been established that the trawler has been catching large numbers of mangrove jacks, the exact figures of which are unavailable, but it is thought to be in tonnes rather than tens. A couple of tag returns some years ago established that jacks being caught over 100km offshore had come from the Weipa rivers.

So why are mangrove jacks on the western Cape getting scarce? Many recreational fishers and charter operators are reaching the conclusion that the exposed spawning stocks are being severely overfished by the fish trawling and this is leading to the estuarine decline.

Speculation also revolves around whether mangrove jacks normally predate heavily on juvenile groper and the subsequent reduction in jacks has let the groper proliferate. I can attest to the fact that some of the productive jack snags of five years ago in the Weipa rivers are now more likely to yield a groper!

All this is further complicated by reports that undersized mangrove jacks were being sold in Cairns, and you’d never guess where they supposedly came from! The conditions placed on the Commonwealth permit are so vague that the QFS (at time of writing) are still trying to work out whether Queensland regulations could be applied to the fish trawlers’ catch.

Imagine the scenario – two rec. fishers arrive at the Weipa boat ramp and a check by Fisheries officers finds 17 mangrove jacks in their possession, two of which are undersized. They can therefore be booked for having seven more jacks than the regulated ‘in possession’ limit (10), as well as having two undersized fish.

Similarly, a Queensland-licensed commercial fisher with one crew member arrives in port and is found to have a similar catch. He, too, can be booked for the two offences as mangrove jack are one of the few species in our state to be classified as a non-commercial species.

Yet down at the nearby wharf, a Commonwealth-licensed vessel is unloading dozens of mangrove jacks on to Queensland soil and is able to sell these fish with impunity. If the QFS has deemed the mangrove jack needs across-the-board regulations to protect its integrity, how can it allow a vessel, of which it is a joint regulator through the Queensland Joint Authority, to openly flout these rules that apply to all other members of the community? Because the Gulf fish trawling permits are for a ‘developmental’ fishery rather than an established one, they must be constantly subject to review, particularly when detrimental effects can be established. Recreational fishers have an excellent case to request that the Gulf fish trawl fishery permits be suspended pending a scientific investigation into its effects on the area’s mangrove jack population.

I know many of you feel passionate about mangrove jacks – they have a mystique all their own – so why don’t you let those concerned know just what you think? Send an email to State Primary Industries Minister Henry Palaszczuk --e-mail address hidden-- and to Commonwealth Fisheries Minister Ian McDonald --e-mail address hidden-- asking for this matter to be investigated immediately.

1) Is fish trawling causing northern Cape York mangrove jack stocks to plummet? It certainly seems so.

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