Assessment of the distribution and population viability of the Pearl Cichlid in the Swan River catchment, Western Australia
Beatty, S., Morgan, D., Sarre, G., Cottingham, A. and Buckland, A. (2010) Assessment of the distribution and population viability of the Pearl Cichlid in the Swan River catchment, Western Australia. Murdoch University. Centre for Fish & Fisheries Research, Western Australia.
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The Pearl Cichlid Geophagus brasiliensis (which is native to eastern South America) was first reported in Bennett Brook in February 2006 by Ben de Haan (North Metro Catchment Group Inc.) who visually observed what he believed to be a cichlid species. The senior authors were notified and subsequently initially captured and identified the species in the system on 15th of February 2006. Subsequent monitoring programs have been periodically undertaken and confirmed that the species was self‐maintaining and is able to tolerate high salinities. There is thus the potential for the species to invade many tributaries and the main channel of the region’s largest river basin, the Swan River. However, little information existed on the biology and ecology of the species within Bennett Brook and this information is crucial in understanding its pattern of recruitment, ecological impact, and potential for control or eradication. The current study involved monthly sampling of fishes within Bennett Brook and Lanius Drain (a major storm water drain that flows into Bennett Brook) between January and June 2010. Numerous other sites within the Swan River catchment were also sampled to determine whether the species had spread to other sections of the river. The report provides information on the distribution, biology and ecology of the Pearl Cichlid.
Despite widespread sampling, the Pearl Cichlid was not recorded within the Swan River or any of the major tributaries near the established population within Bennett Brook. Within Bennett Brook and Lanius Drain the species was shown to be sympatric with three native freshwater fishes, one other introduced species, and two native and one introduced freshwater crayfish species. The population of Pearl Cichlid within the Bennett Brook system was found to have traits typical of an invasive, r‐strategist species, and key findings included:
•The monthly presence of gravid, spawning and spent mature fish and consistent presence of new recruits (20‐40 mm Total Length TL) suggested the species underwent a protracted breeding period (January to June 2010).
•However, no very small juveniles (<20 mm TL) were recorded from Lanius Drain or Bennett Brook, nor was there evidence of nesting and, as a downstream re‐colonisation of breeding adults and larger new recruits was recorded monthly, this suggests successful breeding almost certainly only occurred within the Altone Park wetlands.
•The majority of the population matured at the end of their first year of life at an average size of ~91 and 82 mm TL for females and males, respectively, determined via logistic regression for the length at which 50% of males and females were found to be mature.
•A relatively high growth rate was recorded up to a maximum size of ~250 mm TL. Pearl Cichlids attained sizes larger than native freshwater fishes in the system by the end of their second year of life.
•The largest fish recorded were found to be in their fourth year of life, and these represented the oldest fish recorded during the study.
•Although previous limited data suggested considerable piscivory in larger individuals (n=2), stomach content analysis in the present study revealed their diet to be omnivorous; dominated by benthic food items including vegetation, invertebrates (adults and larvae) such as insects and decapods.
Together, the above traits would have allowed the species to rapidly establish in the Bennett Brook environment and would similarly allow it to colonise a number of other systems within this region should it be introduced or migrate to them.
A key finding of the current study is that the overwhelming evidence suggests that the smallest juveniles (new recruits) appear to be entering Bennett Brook via the Lanius Drain and that the wetlands in Altone Park that drain into Lanius Drain are the key spawning habitat for the species. It is unclear why this is the case but is probably due to the higher temperature regime in the lentic wetland compared to lotic downstream habitats. If this is the sole spawning habitat for the species in the system, the control or eradication of the species would be more feasible than if the species was reproducing within Bennett Brook. It is also noteworthy that a wide size range of fish moved downstream each month.
|Murdoch Affiliation:||Centre for Fish and Fisheries Research|
|Series Name:||Murdoch University Report to the Swan River Trust|
|Publisher:||Murdoch University. Centre for Fish & Fisheries Research|
|Copyright:||2010 Murdoch University. Centre for Fish & Fisheries Research|
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