Status of freshwater catfish (Tandanus tandanus) populations in Gunbower Creek 2009

"December 2009".

Project Number: Status of freshwater catfish (Tandanus tandanus) populations in Gunbower Creek - M/BUS/321.

MDFRC item.

In May 2009 The North Central Catchment Management Authority (CMA) engaged The Murray-Darling Freshwater Research Centre (MDFRC) to establish the status of freshwater catfish Tandanus tandanus (T. tandanus) populations within selected lagoons associated with the Gunbower Creek. Seven sites were examined: Turner, Cockatoo, Phyland, Longmore, Gum, and Upper Gunbower Lagoons, as well as the 4km reach of the Gunbower Creek between Turner and Phyland Lagoons. Habitat character of each lagoon was established following AUSRIVAS habitat assessment protocols and the fish assemblage from each lagoon was surveyed utilising large and small fyke nets during July and August 2009. Patterns in fish assemblage structure (species present and species abundance) and habitat characteristics among wetlands were related to the presence/absence of T. tandanus, to determine if fish assemblage structure, habitat character or a combination of fish assemblage/habitat characteristics influenced the structure of T. tandanus populations within sites surveyed during this investigation. A total of 24 T. tandanus were captured from the seven wetland sites sampled; Turner Lagoon (n = 21), Phyland Lagoon (n = 2) and Cockatoo Lagoon (n = 1). T. tandanus was not recorded in Upper Gunbower, Longmore or Gum Lagoons, or at Gunbower Creek survey sites. An additional 28,920 fish were captured from 8 native and 5 exotic species from the seven wetlands sampled. The fish assemblages and habitat characteristics from wetlands where T. tandanus were encountered were more than 75% and 80% similar (respectively), with exception of Phyland Lagoon which exhibited a markedly different suite of habitat characteristics to other wetlands. As such, habitat character was not considered to significantly influence the distribution of T. tandanus at those sites examined: however, the structure of fish assemblages, particularly the relative abundance of redfin and carp, may have been of significant influence.

The status of the T. tandanus population in Turner Lagoon may be considered robust, as individuals from young of the year (0+) and a variety of year classes through to mature adults (based upon size-at age information) were represented within the population. Furthermore, the timing (winter) of sampling conducted here was considered to result in significantly fewer individual T. tandanus being encountered as might be expected from spring or summer sampling: As such, the status of the Turner Lagoon population may reflect other robust T. tandanus populations elsewhere in the Murray River system. Conversely, the status of T. tandanus populations within Cockatoo and Phyland Lagoons were not considered robust, even when considering the effects of sampling season. As T. tandanus is listed as threatened under Victoria's Flora and Fauna Guarantee Act (1988), are patchily distributed throughout Victoria, and a robust population was detected within Turner Lagoon, we recommend that the recent (past decades) hydrological regime of Turner Lagoon be determined and then a similar hydrological regime be maintained in order to sustain the T. tandanus population there. Consideration of this recommendation is especially important in regard to the proposed changes to the delivery of water throughout the Gunbower anabranch system via NVIRP. Furthermore, rehabilitation of fish passage (conducive to the requirements of small and large T. tandanus) between Turner Lagoon and the Gunbower Creek may stimulate the re-colonisation of adjacent wetlands within the Gunbower system by T. tandanus.