| Australian bass | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Perciformes |
| Family: | Percichthyidae |
| Genus: | Macquaria |
| Species: | M. novemaculeata |
| Binomial name | |
| Macquaria novemaculeata (Steindachner, 1866) |
|
Australian bass (Macquaria novemaculeata) are a small to medium sized, primarily freshwater (but estuarine spawning) 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.
Contents |
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.[1] Prior to that, Australian bass and estuary perch were placed in a separate genus, Percalates. Results from recent research using genetic 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).[2]
The specific name for Australian bass — novemaculeata — coined by Steindachner when he scientifically described and named the species, translates literally from the Latin as "new" (novem) and "spotted" (maculeata), and refers to the distinct black blotches juvenile bass are marked with when very small (i.e. <6–7 cm).
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 0.4–0.5 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.
Australian bass are found in coastal rivers and streams from Wilsons 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.
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:
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.[3] 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, well above Oallen Crossing on the Shoalhaven River and far up the Warragamba River and Coxs River before these rivers were dammed.
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.
Common items in the diet of Australian bass are:[4]
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.
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.
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 (minor, temporary rises in flow), making measurements of preferred spawning salinities for wild Australian bass difficult.
Australian bass spawn 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.[5] Australian bass sperm have no viability at or below 6 ppt, but are most viable at 12 ppt, the latter probably being the most relevant fact.[5] However, it has been reported that 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.[6]
Artificial breeding of Australian bass is carried out at much higher salinities than natural.
Australian bass are highly fecund, with a reported mean fecundity ("fertility") of 440,000 eggs from the mature wild female specimens examined, and one very large specimen yielding 1,400,000 eggs.[5] 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 role 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. It has been reported:[7]
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[8] and preventing speciation. However, this movement has not prevented distinct genetic profiles and subtle morphological ("body shape") differences developing in different river systems.[9][10][11] These findings indicate it is important to use the appropriate regional Australian bass stocks for artificial breeding and stocking projects.
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 (in early 2010 however a "fish lift" was fitted to the dam). 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 the catchment, can severely degrade and silt coastal rivers to the point of being uninhabitable for Australian bass. The Bega River in southern New South Wales 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. Stockings can also mask and divert attention away from serious habitat degradation and decline of wild stocks in catchments.
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 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!
Some of the best Australian bass fishing is coastal rivers and tributaries where access is difficult. Fishing these more remote locations can be extremely rewarding both for the fishing and the scenery. Fishing the more remote bass water is therefore usually the domain of the hardened backpacking fisherman or the dedicated kayak fisherman willing to drag his kayak over numerous logs and other obstacles.
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 1 June to 31 August.