Over the past 10 years anglers have been noticing more instances of bream with fins missing and indentations on the top of the head. The reason is a mystery at present but a recent project has been funded to look at the cause and possible solutions to remedy the problem.
To do this it is important to understand to biology of bream and their movements. It also helps to catch them if you know where to look. Dr Barry Pollock has been involved for many years studying and the following has been supplied by him.
The Yellowfin Bream Acanthopagrus australis is native to the Australian east coast. It can live in a wide variety of shallow-water coastal habitats – brackish limits of rivers and creeks, estuaries, embayments where seagrass and mangroves occur, sandy ocean beaches, surf bars, and rocky headlands.
Yellowfin Bream consume a wide variety of different foods mostly of animal origin, but also some plant material. It is a highly adaptable species in terms of its habitat and food requirements.
Reproduction
Yellowfin bream aggregate at surf bars, river mouths, and associated coastal waters where salinity is high and turbidity low during the winter months for spawning. Yellowfin Bream in common with many other species in the Sparid family can change sex. In the case of Yellowfin Bream the internal reproductive organs contain both male (testes) and female (ovaries) organs. During the breeding period, one of the sex organs develops whilst the other remains dormant. Research has shown that most young Yellowfin Bream mature as males in their first years, and subsequently change sex to function as females as they get older. However a proportion of males remain as functional males throughout their life. Also a small proportion of young fish mature first as females. In short, sex determination is highly variable in Yellowfin Bream.
Another interesting feature of the reproductive cycle of Yellowfin Bream is that only about half of the adult population migrate/aggregate at the spawning grounds each year. The remainder of the adult population remain in the western feeding grounds, developing their sex organs, but then reabsorbing all the reproductive material. The only fish that successfully release eggs or sperm are those which aggregate in the open/oceanic waters.
Fishers know that early in the breeding season the fish are in good condition, with lots of stored fat. At the completion of the breeding season the fish have used their fat reserves and are in poor condition. It is interesting that food is limited in the spawning aggregation areas even though Yellowfin Bream readily take any available food there.
Growth and minimum size
Research has shown that Yellowfin Bream on average reach 14.5cm Fork Length in their first year, 20.5cm FL at two, and 24cm FL at three. Due to the sex-change phenomenon in Yellowfin Bream most male fish mature by 23cm Total Length. However only half of the female population reach maturity by 25cm Total Length. There are very few mature females in the population at or below 23cm Total Length.
This has implications for the choice of the legal minimum size based on the criterion that at least half of the population should be able to spawn before they can be kept. In this instance the size of 25cm Total Length is preferable.
Larval ecology
Yellowfin Bream reproduce by the females and males shedding eggs and sperm into the water where fertilisation occurs. The fertile eggs are planktonic. The eggs undergo development and hatching within the water column. At about 4-6 weeks the larvae are 10mm in length and can swim in the water currents, but they are still planktonic.
Vast numbers of planktonic Yellowfin Bream larvae have been taken in research surveys at Jumpinpin and Caloundra bar areas in late winter. These larvae soon settle out of the plankton and take up life as small fish on the bottom, especially in the rich feeding areas (eg. seagrass and mangrove creeks).
The Yellowfin Bream Fishery
Yellowfin Bream are highly sought by recreational fishers. They are in fact one of the most important species for recreational fishing in Queensland.
Strict size and bag limits now apply to recreational fishing to ensure the sustainability of this important resource.
The Yellowfin Bream is a highly adaptable species in terms of its food and habitat requirements. It is highly fecund with females able to produce around half a million eggs annually. Abundance of the larval stages is extremely high following the breeding season. There is no reason why a healthy and productive recreational fishery for Yellowfin Bream cannot be maintained for future generations.
