Ask Dr Dazza | Sea Mullet

Published 5:05pm 19 May 2021

Ask Dr Dazza | Sea Mullet
Words by Dr Dazza

The sea mullet is the most important species for commercial fisheries in Moreton Bay. It was the most important species for Indigenous people prior to European arrival and remains culturally important. The sea mullet occurs in all the world’s major oceans and is important for fisheries throughout most of its range.

Sea mullet are one of several species of mullet found locally.

On the Australian east coast, sea mullet migrate from estuaries and inshore areas during late autumn and early winter for spawning. This is the time of the year you will see large shoals of sea mullet. Often the shoals congregate at the mouth of estuaries, with the migration out of the estuary and on to beaches triggered by strong offshore winds. Reducing day-length during autumn may also be an important cue for fish to roe up and get ready for migration and spawning. Around the Redcliffe peninsula, the shoals of fish generally leave the Pine River and Hays Inlet and move north along Redcliffe beaches.

Results from tagging suggest that, while sea mullet can undertake large movements (more than 300km), the majority of fish recaptured were in the locality (eg. the same river or embayment) where they were tagged and released. While earlier work suggested that sea mullet on the east coast were a single stock, new molecular techniques have raised the possibility of regional scale population differentiation. It is not the case that large numbers of fish move from waters south of Moreton Bay to a location such as Redcliffe.

The age at first spawning for sea mullet is three years and 50 per cent of male sea mullet mature at about 27cm fork length. The minimum legal size of sea mullet is 30cm total length. You cannot keep sea mullet below this size, even for bait. If you are keeping small mullet for bait you need to make sure that they are flat tail or “flicker” mullet which have no minimum legal size.

Sea mullet larvae hatch at sea and use tidal currents to enter estuaries approximately one month after hatching. The majority of juvenile mullet will then remain within one river system until maturity. Sea mullet can occur in freshwater. In the absence of instream barriers, such as dams or weirs, sea mullet will move upstream into brackish or freshwater habitats for feeding.

Early juvenile mullet feed on plankton and very small animals that live in the seabed. Larger juvenile and adult sea mullet principally feed on algae and detritus (and associated bacteria and protozoa) that is either sucked up from the surface layer of the mud or grazed from rocks or seagrass blades. They also typically ingest sand and mud while feeding. This sand and mud is thought to be used in the thick muscled gizzard (the anterior portion of the stomach of the fish to grind the ingested food particles. The gizzard is the “onion” in mullet gut which is used by recreational fishers to principally target yellowfin bream.

Many an observer has seen a mullet jump lazily out of the water with nothing apparently chasing them. Why do they do it? There is circumstantial that they use part of their pharynx for aerial respiration, the air obtained by jumping or rolling at the surface. This may help them feed in estuarine mud where oxygen content is very low.

Although often maligned as a table fish, sea mullet this time of the year are extremely tasty and nutritious. Smoked mullet is a delicacy. Sea mullet are very high in “good oils” and the oil content is high this time of the year during their spawning period. They are best consumed fresh and not frozen. Buy local from your Moreton Bay fishmongers.


Related Stories

Popular Stories