Australian bass

Taxobox
name = Australian bass
regnum = Animalia
phylum = Chordata
classis = Actinopterygii
ordo = Perciformes
familia = Percichthyidae
genus = "Macquaria"
species = "M. novemaculeata"
binomial = "Macquaria novemaculeata"
binomial_authority = (Steindachner, 1866)

Australian bass ("Macquaria novemaculeata") are a small to medium sized, primarily freshwater native fish found in coastal rivers and streams along the east coast of Australia. They are a member of the Percichthyidae family and, currently, the "Macquaria" genus. Australian bass are an iconic, highly predatory native fish. They are an important member of the native fish faunas found in east coast river systems and an extremely popular angling species.

Taxonomy

Australian bass ("Macquaria novemaculeata") are closely related and very similar in appearance to estuary perch ("Macquaria colonorum"). Estuary perch however tend to remain in the estuarine reaches or (occasionally) the extreme lower freshwater reaches.

As their scientific names indicate, Australian bass and estuary perch are currently placed in the "Macquaria" genus — one of a number of Australian genera in the Percichthyidae family — along with two species of native perch from the Murray-Darling Basin, golden perch ("Macquaria ambigua") and Macquarie perch ("Macquaria australasica"). This revision to their taxonomy occurred in the late 1970s. Prior to that, Australian bass and estuary perch were placed in a separate genus, "Percalates". Results from recent research using MtDNA analysis indicate Australian bass and estuary perch do belong in a separate genus to golden perch and Macquarie perch, and this may result in them being put back into a resurrected "Percalates" genus. A rather surprising and unexpected finding of this research is that the putative "Percalates" genus (i.e. Australian bass and estuary perch) appears to be genetically closer to the "Maccullochella" genus (i.e. Murray cod and other cod species) than the remnant "Macquaria" genus is (i.e. golden perch and Macquarie perch) (Jerry "et al.", 2001).

Description and Size

Australian bass have a moderately deep, elongated body that is laterally compressed. They have a forked caudal ("tail") fin and angular anal and soft dorsal fins. Their spiny dorsal fin is of medium height, strong and sharp. They have a medium sized mouth and relatively large eyes than can appear dark in low light or red in bright light. The opercula or gill covers on Australian bass carry extremely sharp flat spines that can cut fishermens' fingers deeply.

Australian bass vary in colour from gold in clear sandy streams to the more usual bronze or bronze-green colouration in streams with darker substrates and/or some tannin staining to the water.

Australian bass are, overall, a smallish-sized species, averaging in most waters around 0.5 kg and 20–30 cm. A fish of 1 kg or larger is a good specimen. Maximum size appears to be around 2.5 kg and 55 cm in southern waters, and around 3.0 kg and 60–65 cm in northern waters.

Typically, Australian bass stocked in man-made impoundments (where they cannot breed) show greater average and maximum sizes than wild river fish.

Range

Australian bass are found in coastal rivers and streams from Wilson's Promontory in Victoria east and north along the eastern seaboard to the rivers and creeks of the Bundaberg region in central Queensland.

Australian bass are not found in the Murray-Darling system because although the system is extensive, it has only one variable entrance to the Southern Ocean, a feature that appears to be incompatible with the estuarine breeding habits of Australian bass and other aspects of their life cycle.

Migratory Patterns

Australian bass are primarily a freshwater riverine species, but must breed in estuarine waters. Consequently, Australian bass reside in the freshwater reaches of coastal rivers for the warmer half of the year or slightly more and the estuarine reaches in winter, and are highly migratory in general.

A general description of the migratory pattern for adult Australian bass would be:

*September: re-enter lower freshwater reaches after spawning
*October–November: movement through middle freshwater reaches
*December–February: maximum penetration into upper freshwater reaches
*March–April: slow movement back down through freshwater reaches in anticipation of spawning run
*May: strong spawning run to estuarine reaches
*June–July–August: aggregation and spawning in estuarine reaches

Obviously the timing of these migratory movements varies slightly from the south to the north of their range. The timing of these migratory movements are also dependent on river flows, particularly freshes and floods that drown out and make larger rapids and cascades passable.

Australian bass are found at their highest altitude in the freshwater reaches of rivers during the months of December, January and February. Research indicates there is sexual segregation in this non-spawning season for resource partitioning purposes (Harris, 1988). Males inhabit the lower freshwater reaches of rivers while females travel far into the middle and upper freshwater (upland) reaches, up to an altitudinal limit of around 600 metres (if there are no natural or man-made obstructions). For instance, Australian bass originally migrated up to the Dalgety region in the Snowy River, Oallen Crossing on the Shoalhaven River and far up the Warragamba River and Cox's River before these rivers were dammed.

Habitat

In the freshwater reaches of coastal rivers in the warmer months, Australian bass require reasonable quality, unsilted habitats with adequate native riparian vegetation and in-stream cover/habitat. Australian bass generally sit in cover during the day. However, they are fairly flexible about the type of cover used. Sunken timber (“snags”), undercut banks, boulders, shade under trees and bushes overhanging the water and thick weedbeds are all used as cover. Such cover does not need to be in deep water to be used; Australian bass are happy to use cover in water as shallow as 1 metre in depth.

Australian bass are strong swimmers at all sizes and can easily traverse rapids and fast-flowing water. However, they generally avoid sitting directly in currents to conserve energy.

At night Australian bass display pelagic (“near-surface”) behaviour and actively hunt prey in shallow water and at the water's surface.

When aggregated for spawning in the broad reaches of estuaries in winter, Australian bass are less cover oriented, and generally sit in deeper water.

Diet

The common items in the diet of Australian bass are:

* terrestrial insects, particularly cicadas
* aquatic macroinvertebrates, particularly Trichoptera larvae
* crustaceans in the forms of freshwater shrimps and estuarine prawns
* small fish, particularly flathead gudgeon ("Philhypnodon grandiceps"), which are common in their freshwater habitats.

However, Australian bass are fierce predators and any small creature that swims across a bass pool such as (introduced) mice and native lizards or frogs are at risk of being taken by a large Australian bass, and are regularly taken.

Growth and Age

For reasons that are not clear, Australian bass are extremely slow growing. Australian bass continue the trend present in the larger native fish species of SE Australia of being very long-lived. Longevity is a survival strategy to ensure that most adults participate in at least one exceptional spawning and recruitment event, which are often linked to unusually wet 'La Niña' years and may only occur every one or two decades. Maximum age recorded so far is 22 years.

As with other "Macquaria" species, there is sexual dimorphism in Australian bass. Males tend to have an absolute maximum size of 1.0 kg or less, while females regularly exceed 1.0 kg and sometimes reach the maximum size of 2.5–3.0 kg. Males reach sexual maturity at around 3–4 years of age, females at 5–6 years of age.

Reproduction

Australian bass spawn in estuaries in winter, generally in the months of July or August.

The salinity range in which Australian bass spawn is still not clear. Estuaries are dynamic habitats with daily fluxes in salinity due to tides, and are also affected by droughts, floods and freshes, making measurements of preferred spawning salinities for wild Australian bass difficult.

Harris (1986) concluded Australian bass spawned in salinities of 8–12 parts per thousand (salt water is approximately 36 ppt), based on capture of recently-spawned larval and juvenile Australian bass in estuaries. Harris (1986) also found Australian bass sperm had no viability at or below 6 ppt, but was most viable at 12 ppt, the latter probably being the most relevant fact. However, Harris (in McDowall (ed.), 1996) stated Australian bass spawned in salinities of 12–18 ppt, with this statement based on fishermens' reports of observing wild Australian bass spawnings and some unpublished data gathered by the NSW Fisheries Department.

Artificial breeding of Australian bass is carried out at much higher salinities than natural.

Australian bass are highly fecund, with Harris (1986) reporting a mean fecundity ("fertility") of 440,000 eggs from the mature wild female specimens examined, and one very large specimen yielding 1,400,000 eggs. The eggs are reported as being demersal ("sinking") in natural spawning salinities, in which case estuarine vegetation such as sea grass almost certainly play an important in "trapping" and protecting eggs. Larvae hatch in 2–3 days. Juvenile Australian bass migrate into the freshwater reaches after spending several months in estuarine waters.

Despite spawning in estuaries, Australian bass rely on floods coming down river systems into the estuaries throughout the winter period, both to stimulate migration and spawning in adult Australian bass and for strong survival and recruitment of Australian bass larvae.

Australian bass adults and larvae may also enter the sea (the latter perhaps involuntarily) during winter spawning in times of flood. Trnski "et al." (2005) state:

"The presence of field-caught larvae of both species on incoming tides in Swansea Channel indicates that the larvae have spent some time in the ocean... "Macquaria novemaculeata" adults move downstream into estuaries to spawn in water of suitable salinity. In low rainfall years, the spawning location is further upstream than in wet years, when spawning can occur in shallow coastal waters adjacent to estuaries (Searle, pers. comm.). Mature "M. novemaculeata" adults can be found outside of estuaries in wet years (Williams, 1970). This is verified by the collection of mature adults by trawl in July 1995 in 11–17 m of water off Newcastle, NSW (AMS I.37358-001)."

This kind of movement leads to some genetic interchange between river systems and is important in maintaining a high degree of genetic homogeneity ("sameness") in Australian bass stocks (Chenowith & Hughes, 1997) and preventing speciation. However, this movement has not prevented distinct genetic profiles and subtle morphological ("body") differences developing in different river systems (Jerry, 1997; Jerry & Baverstock, 1998; Jerry & Cairns, 1998). These findings indicate it is important to use the appropriate regional Australian bass stocks for artificial breeding and stocking projects.

Conservation

Wild Australian bass stocks have declined seriously since European settlement.

Dams and weirs blocking migration of Australian bass both to estuaries and to the upper freshwater reaches of coastal rivers is the most potent cause of decline. Most coastal rivers now have dams and weirs on them. If Australian bass are prevented from migrating to estuaries for breeding by an impassable dam or weir, then they will die out above that dam or weir. Some dams or weirs exclude Australian bass from the vast majority of their habitat. It is estimated for example that Tallowa Dam on the Shoalhaven River, once an Australian bass stronghold, currently excludes wild Australian bass from more than 80% of their former habitat. Dams and weirs also diminish or completely remove flood events required for effective breeding of adult bass and effective recruitment of juvenile Australian bass. A related issue is the myriad of other structures on coastal rivers such as poorly-designed road crossings that (often needlessly) block migration of Australian bass.

Another potent cause of decline is habitat degradation. Unfortunately poor land management practices have been the norm historically in Australia. Complete clearing of riparian (river bank) vegetation, stock trampling river banks, and massive siltation from these poor practices as well as poor practices in catchment, can severely degrade and silt coastal rivers to the point of being uninhabitable for Australian bass. The Bega River in southern NSW is a particularly salutory example of a coastal river so stripped of riparian vegetation and so silted with coarse granitic sands from poor land management practices, that the majority of it is now completely uninhabitable by Australian bass and other native fish.

As a slow-growing fish, Australian bass are vulnerable to overfishing, and overfishing has been a driver of decline in Australian bass stocks in past decades. However, the situation has improved markedly now the majority of fishermen are practicing catch and release with Australian bass.

Hatchery breeding and stocking of Australian bass is used to create fisheries above dams and weirs but these are causing concern over genetic diversity issues, use of bass broodfish from different genetic strains, and introduction/translocation of unwanted pest fish species in stockings.

Fishing

Fishing for Australian bass is a summertime affair, undertaken during the warmer months in the freshwater reaches of the rivers they inhabitat. Australian bass are keenly fished for as they are an outstanding sportsfish, extraordinarily fast and powerful for their size. Their extraordinary speed and power is probably due to their significant, strenuous annual migrations for spawning and a life-style that is migratory in general. Australian bass in their natural river habitats are not to be underestimated; they head straight for the nearest snags (sunken timber) when hooked and light but powerful tackle and stiff drag settings are needed to stop them.

As mentioned above, during the day Australian bass generally remain close to or in cover (e.g. snags, overhanging trees), and small plug lures and flies cast close to such cover are used. In recent years fly fishing for Australian bass using large surface flies imitating cicadas has proven to be extremely effective. At night Australian bass are a roaming pelagic feeder and surface lures (which waddle or fizz across the surface of the water) are used. The large and sudden explosion a good Australian bass makes when taking a surface lure is guaranteed to the give the fisherman a fright!

It pays for fishermen to remember that wild Australian bass are still a highly migratory when in the freshwater reaches of rivers, and can also be an extremely wary fish in these habitats, much more so than exotic trout species.

Australian bass fishermen almost exclusively practice catch and release, which is necessary for the preservation of wild Australian bass stocks. The use of barbless hooks (which can be created by crushing the barbs flat with a pair of needle-nosed pliers) is essential as Australian bass hit lures with great ferocity and are consequently almost impossible to unhook on barbed hooks. Conversely, Australian bass are swiftly and easily released if barbless hooks are used.

Responsible fishermen now avoid fishing for wild Australian bass in estuaries in winter, so that this increasingly pressured native fish can spawn in peace. In late July 2007 the NSW Fisheries Department announced a new closed season for Australian bass and estuary perch, from June 1 to August 31, for this purpose.

References

* Chenoweth, S.F. & Hughes, J.M. (1997) Genetic population structure of the catadromous Perciform: "Macquaria novemaculeata" (Percichthyidae). "Journal of Fish Biology" 50: 721–733.

* Harris, J.H. (1985) Diet of Australian bass, "Macquaria novemaculeata" (Perciformes: Percichthyidae) in the Sydney Basin. "Australian Journal of Marine and Freshwater Research" 36: 219–34.

* Harris, J.H. (1985) Age of Australian bass, "Macquaria novemaculeata" (Perciformes: Percichthyidae) in the Sydney Basin. "Australian Journal of Marine and Freshwater Research" 36: 235–46.

* Harris, J.H. (1986) Reproduction of the Australian bass, "Macquaria novemaculeata" (Perciformes: Percichthyidae) in the Sydney Basin. "Australian Journal of Marine and Freshwater Research" 37: 209–35.

* Harris, J.H. (1987) Growth of Australian bass, "Macquaria novemaculeata" (Perciformes: Percichthyidae) in the Sydney Basin. "Australian Journal of Marine and Freshwater Research" 38: 351–61.

* Harris, J.H. (1988) Demography of Australian bass, "Macquaria novemaculeata" (Perciformes: Percichthyidae), in the Sydney Basin. "Australian Journal of Marine and Freshwater Research" 39: 355–69.

* Jerry, D.R. (1998) Population genetic structure of the catadromous Australian bass from throughout its range. "Journal of Fish Biology" 51: 909–920.

* Jerry, D.R. & Cairns, S.C. (1998) Morphological variation in the catadromous Australian bass, from seven geographically distinct riverine drainages. "Journal of Fish Biology" 52: 829–843.

* Jerry, D.R. & Baverstock, P.R. (1998) Consequences of a catadromous life-strategy for levels of mitochondrial DNA differentiation among populations of the Australian bass, Macquaria novemaculeata. "Molecular Ecology" 7: 1003–1013.

* Jerry, D.R., Elphinstone, M.S. and Baverstock, P.R. (2001) Phylogenetic Relationships of Australian Members of the Family Percichthyidae Inferred from Mitochondrial 12S rRNA Sequence Data. "Molecular Phylogenetics and Evolution" 18: 335–347

* Mallen-Cooper, M. (1992) Swimming ability of juvenile Australian bass, "Macquaria novemaculeata" (Steindachner), and juvenile barramundi, "Lates calcarifer" (Bloch), in an experimental vertical-slot fishway. "Australian Journal of Marine and Freshwater Research" 43: 823–833.

* McDowall, R.M. (1996) (ed.) "Freshwater Fishes of South-Eastern Australia." Reed Books, Sydney.

* Trnski, T., Hay, A.C. and Fielder, D.S. (2005) Larval development of estuary perch ("Macquaria colonorum") and Australian bass ("M.novemaculeata") (Perciformes: Percichthyidae), and comments on their life history. "Fisheries Bulletin" 103: 183–194.

External links

* [http://www.nativefish.asn.au/bass.html Native Fish Australia — Australian bass page] .

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