BREAM are arguably Australia’s most popular estuarine “bread and butter” target species for anglers in the southern and south-eastern parts of the country.
The black bream (Acanthopagrus butcheri) is the main target species throughout most of our southern states, though in the more northern parts of its range (southern NSW and Victoria), this species is known to hybridise with the yellowfin bream (A.australis) under certain conditions. Under normal circumstances, yellowfin bream live most of the time in estuaries and coastal areas and migrate down rivers to spawn near the surf zone around coastal bars in autumn and winter. Black bream live in estuaries too, but in contrast they tend to migrate up rivers to spawn in brackish water in spring and early summer. The hybridisation between the two usually occurs when both species are trapped together in landlocked coastal lakes during the winter/spring spawning season.
Because black bream are such a popular target species, study of their movements is a popular research subject. One study of particular interest to bream anglers was one done by TAFI researchers in Tasmania, who used surgically implanted electronic “pinger” tags to examine the movements of black bream throughout little Swanport estuary on the east coast of Tasmania. The electronic tag technology used acoustic telemetry with the fishes’ position being detected by an array of 10 listening devices which were placed throughout the estuary. This listening device detects the tagged fish if they swim within 200 metres of the device, allowing researchers to track the fine scale movements of black bream in real time.
Thirty-four adult black bream were tagged with pinger tags, which were inserted into the body cavity (the tag incisions healed completely within a month). The fish were tracked for periods of up to 187 days, with 31 of the 35 fish being tracked for over 120 days, suggesting their survival rates were very high. The fish spent most of the time within the upper and middle regions of the estuary, where brackish conditions dominated. Tagged bream exhibited extensive movements with the tide, with upstream movements during incoming tides and downstream movements during out going tides. The extent of these tidal movements was related to the tidal height difference, ie the fish moved further on bigger tides, and it appeared that the fish moved further during daylight hours compared to at night.
Freshwater inflows which changed the estuary’s salinity also changed the behaviour of tagged bream. Tagged fish moved downstream during a flood period after heavy rainfall, concentrating in the middle estuary for around 10 days. They then returned upstream as salinities increased to around 1/3 strength seawater. During the peak of spawning period (November to December) fish moved into the upper region of the estuary, where they aggregated to spawn. However, occasional rainfall events resulted in the bream temporarily leaving the spawning grounds and moving downstream.
Another interesting study looking at electronically tagged bream was conducted by researchers in Victoria DPI, who used acoustic telemetry to determine how black bream behaved around snags (termed by the scientists as termed “large woody debris”) in the Mitchell and Tambo Rivers. This study showed that tagged bream stayed near snags during the day, but exhibited wider movements at night or during the day in areas where snags were absent. Its interesting to see scientists using this cutting edge tagging technology to prove many bream behaviours that anglers have known, or suspected, all along.
