Fish Facts

Fish Facts: Redbait & more

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Redbait. Image: PIRSA

REDBAIT (Emmelichthys nitidus), also known as bonnetmouths or rovers, are torpedo shaped baitfish that resemble a cross between a pilchard and a jack mackerel in appearance, being grey to dark blue above with reddish pink sides and bellies.

Like pilchards and jack mackerel, red bait feed on planktonic crustaceans, particularly small copepods, but also krill. They occur in large midwater schools in cooler temperate waters near continental shelf dropoffs, seamounts, upwellings and other such oceanic features at depths of 20 to 500 m.

In Australia they are found offshore from around Sydney, NSW, south and west to southern WA, including both the east and west coasts of Tasmania. Further afield, some scientists recognise two sub-species of redbait throughout the temperate southern hemisphere, Emmelichthys nitidus nitidus from the eastern Atlantic around South Africa to east of New Zealand (including Australia), and Emmelichthys nitidus cyanescens from the waters around South America.

Redbait can reach nearly 50 cm long and live for over 15 years, but compared to other baitfish they are relatively slow growing and long lived, growing to around 15, 24 and 27 cm in their first one, three and five years, respectively. Sexes are separate throughout their lives and length at maturity is around 1-2 cm longer for females compared to male fish. Actual size at maturity varies by region, with populations on Tasmania’s east coast maturing at between 14 and 16 cm long, while in the cooler waters of Tasmania’s south west maturity is reached between 24 and 26 cm long. This suggests that there may be discrete redbait populations in different parts of the country, and therefore a chance of localised depletion if they were to be heavily fished by commercial interests in any one part of their distribution.

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In recent times a lot of research has examined the warming trend in the western Tasman Sea (east of Tasmania), particularly its impacts on fisheries there. The warming of the waters off eastern Tasmania results from what the climate scientists call “a multi-decadal southward penetration of the East Australian Current due to the decadal-scale ‘spin-up’ of the South Pacific Gyre”.

In other words, global warming has resulted in more warm water coming down each summer from up Queensland way, and this has resulted in reduced recruitment of temperate species like rock lobsters, and other such things. But it’s not all bad news, because the increased southward influence of the East Australian Current also favours production of small warm-water copepods, which are a key part of the diet of redbait. Indeed, scientists consider that the changing climate is the main factor responsible for an increase in the relative abundance of redbait in mid water trawl fisheries east of Tasmania.

Any fisheries scientist who passed “Fisheries 101” will know that the tendency of small pelagic species like redbait to aggregate in schools makes them vulnerable to overfishing in poorly managed fisheries. Fish that eat zooplankton also tend to be more heavily influenced by environmental variables, and if they are heavily fished commercially, and the boom and bust nature of their populations is not taken into account by fishery managers, this can result in stock collapses. However, is this to say that a fishery cannot be developed when long term environmental changes become more favourable and fish numbers are increasing? Redbait in Australia’s Small Pelagic Fishery are a case in point.

The recent supertrawler issues have thrust redbait into the spotlight as they form an integral part of the federally managed Small Pelagic Fishery (SPF). Australia’s SPF is no doubt one of the best managed fisheries in the world, but for the reasons outlined above (and many more that are not), expanding any fishery in today’s world is something that cannot be considered lightly.

Certainly when the original “supertrawler idea” surfaced a few years ago, there were a few unanswered questions about localised depletion and overall ecosystem impacts that needed more research. But more science was done and it’s much harder to say the same situation occurs today, yet controversy remains.

Indeed, when you read all of the scientific reports underpinning the management of Australia’s SPF, it’s becoming so voluminous, it seems even a supertrawler could float on the amount of paperwork the fishery managers and scientists have generated in recent years. The piles of paper are getting so high the managers risk drowning in it. For those who can’t be bothered to read it all, the upshot is, the management of the fishery amounts to world’s best practice. This is what any independent assessment would conclude, considering that vessels operating in the fishery would be managed to a very conservative total allowable catch (TAC) quota of around 7.5 per cent of the estimated stock size. The low fishing effort takes into consideration ecosystem effects, with coverage by observers, GPS tracking, compulsory exclusion devices and other regulations to minimise direct impacts on non target species such as birds and marine mammals, and so on.

And this is, I think, the crux of the whole supertrawler debate.

When some interest groups are simply against use of trawlers of a certain size in an otherwise well researched and TAC managed fishery, despite these midwater trawlers not even touching the bottom with their nets (and thus avoiding many of the usual environmental issues with trawling), this shows some groups are ready to throw science out the door in opposition to certain forms of fishing.

In such a climate of public debate, the obvious question then becomes “what type of best practice, sustainable fishing could be banned next?”. Scientists might then point out (and rightly so), that if recreational fishing groups choose to heed the science only when it suits them, it’s quite likely they will be right in the firing line, with nowhere to turn, next time the anti-fishing brigade decides to go to Canberra.

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