Fishes in the forest:High biodiversity and endemism

September 2001

Visitors to the Wet Tropics region areoften captivated by the amazingdiversity of plant and animal life to beseen. It is more difficult however, tosee and appreciate the diversity of lifethat can be found under the surface ofthe region’s abundant aquatic habitats.Unless you don’t mind getting wet ofcourse!

Getting wet in streams of the WetTropics area is what Dr Brad Pusey,Rainforest CRC Senior ResearchFellow, has been doing since 1990 aspart of his research which documentsthe biodiversity, distribution and ecol-ogy of the region’s freshwater fishfauna. His work has revealed that theWet Tropics region sustains a very highdiversity of fishes, parallel to that seenamong the birds, mammals or insectsof the terrestrial environment. Inaddition, the Wet Tropics regioncontains many species not found any-where else in the world.

BiodiversityOver 70 species of fish have beenrecorded from freshwaters of theregion and that number continues toincrease as more research is under-taken. The Wet Tropics region is hometo approximately 45% of Australia’sfreshwater fish species, 70% of generaand 70% of families.

EndemismMore impressive still is the number ofendemic species, in other words, thosespecies that occur only in the WetTropics region and nowhere else in theworld. To date, nine endemic specieshave been identified, and recentgenetic research by a Rainforest CRCstudent, Dugald McGlashan, stronglysuggests the presence of anotherundescribed endemic species (ahardyhead). Comparable levels ofendemism are seen only in the south-west of Western Australia whichsupports 12 known endemic species.

The endemic species of the regioncover a wide range of taxa including:rainbowfishes (C. rhombosomoides,Melanotaenia eachamensis), Utchee Ckcatfishes (Tandanus sp.), grunters(Hephaestus tulliensis), cod (Guyuwujalwujalensis), and gobies (Stiphodonallen, Glossogobius sp. B. andSchismatogobius sp.). Many species areyet to be formally described.

Links to the pastFour features of this endemic group offishes are of interest:

• Two species, G. wujalwujalensisand C. rhombosomoides arepaleoendemics – species that havevery old origins. In the case ofG. wujalwujalensis, this speciesmay have been around whendinosaurs roamed through theforests of the Wet Tropics region.

• With the exception of G.wujalwujalensis, all of the endemicspecies are found in either or boththe Johnstone and Russell/Mulgrave rivers. These riversform the core of freshwater fishbiodiversity and endemism in theWet Tropics region.

Cairns Rainbowfish

(Cairnsichthys rhombosomoides)

Khaki Bream

(Hephaestus tulliensis)

Scaleless Goby

(Schismatogobius sp)Mulgrave Goby

(Glossogobius sp B.)

When this comparison is restricted toonly those groups normally found innorthern Australia, the proportions in-crease to 55%, 80% and 90%, respec-tively. This is exceptional diversity fora small strip of land less than 100 kilo-metres wide that passes through only5 degrees of latitude!

All drawings: Brad Pusey

• Most of the endemics are foundpredominantly in tributarystreams and not the main channel.

• Most occur predominantly inriffle and rapid habitats, whereaselsewhere in Australia, speciesfound in riffles and rapids are avery minor component of thefreshwater fish fauna.

Endemic species persist through timeWhy are these features of interest?Because they indicate that the endemicspecies have persisted in the region fora very long time during periods ofextreme climate changes.

A large body of research, much of itundertaken by Rainforest CRCresearchers, indicates that historicalclimate change has repeatedly causeddrastic contractions and expansions inthe amount of rainforest cover as wellas fragmentation and extinction ofmany terrestrial vertebrate group. Thisapplies particularly to the glacialperiods of the Pleistocene. The distri-bution, persistence and habitat re-quirements of the region’s endemicfish fauna suggest that historicalclimate change did not impact asstrongly on the aquatic environmentas it did on the terrestrial environment.

Some of the region’s rivers functionedmuch as they do today, with perma-nent tributary streams a feature of thelandscape, although total dischargewould have been reduced in keepingwith a reduced rainfall. It is in thesestreams that the endemic freshwaterfishes persisted while extinctions ofterrestrial fauna were occurring

around them. It is notable that theJohnstone and Russell/Mulgraverivers contain Queensland’s highestmountains, Mt Bellenden Kerr and MtBartle Frere, within their catchments.These mountains are likely to haveexerted a powerful influence on thedistribution of rainfall in the areathroughout the Pleistocene.

The current challenge facing theregion’s freshwater fish fauna is notnatural climate change, but the imme-diate human pressures of habitatdegradation (ie, wetland drainage,riparian destruction, invasive grasses),the translocation of native fishes andincreased water resource use. In thelonger term, global climate changecaused by human activities does pose

a threat to the maintenance of overallfish biodiversity if rising sea levelsflood important lowland riverinehabitat. However the endemic fishes,because of their upland distribution,should not be impacted so strongly byrising sea levels. Whilst not currentlyimperilled, it would be a great pity notto ensure the future survival of theamazing endemic fishes of the WetTropics region.

For further information contact:Dr Brad PuseyFaculty of Environmental ScienceGriffith UniversityNATHAN, QLD 4870Phone and Fax: (08)9751 2265Email: bpusey@westnet.com.au

Map showing the Russell/Mulgrave and Johnstone River catchments which form

the core of freshwater fish biodiversity and endemism in the Wet Tropics region