Key words: Datasets, native fish, Native Fish Strategy
Broad aim and specific objectives: This project aimed to collate all fish survey information from around the MDB and to provide a Basin scale overview of the status of native fish in the MDB and trends in their abundance and distribution. A key objective of this project was to assess historical trends in native fish abundance across the Basin.
Method: Datasets were sourced from a range of custodians, quality checked and either integrated into analysis or rejected if it did not meet the criteria for use. The applicability of a range of statistical techniques for assessing trends in fish abundance were explored and the potential techniques were presented at the two scientific workshops. However, the following substantial limitations to existing data were found:
- data were of variable quality, often with missing fields and obvious errors.
- there were insufficient data to enable standardised assessment of trends in abundance over historical time scales.
- when stratified for method there is a limited time scale over which trends can be assessed (only the last 10-15 years).
- trends in relative abundance can be assessed over recent years for some specific locations, but the majority of historical declines in native fish populations has likely occurred before suitable survey methods commenced.
As a result of these limitations the approach taken was to document historical trends based on available literature and anecdotal information and where possible augment this qualitative assessment with specific examples where some quantitative data are available, although such examples are limited to only a few locations over the entire Basin
Findings. From the records of early explorers in the early to mid 1800s, native fish, namely Murray Cod (Maccullochella peelii), Silver Perch (Bidyanus bidyanus) and Freshwater Catfish (Tandanus tandanus) appeared widely distributed and abundant. Evidence regarding the distribution and abundance of native fish around the time of European exploration and settlement is limited to descriptions of large bodied fish, presumably because of their food value. But it is understood that Aboriginal people were adept at catching fish using a variety of techniques, and at times fish were so plentiful that sufficient fish were available to feed hundreds or even thousands of people during seasonal gatherings along the Darling River, and presumably elsewhere in the Basin.
Commercial fishing targeting Murray Cod commenced in the mid 1800s, predominantly along the lower Murray, Murrumbidgee and Darling Rivers. Within a few decades concerns regarding the state of the fishery and declines in fish stocks were being voiced, although occasional good harvest years, probably related to wet years, still occurred into the mid and later 1900s.
In general, native fish communities within the Murray-Darling Basin have declined in abundance and distribution. Many populations of native fish, which were considered to be widespread throughout the Basin prior to European settlement, are now fragmented and reproductively isolated. In general, fish communities tend to show differences between highly regulated systems (predominantly in the south of the Basin, those in the northern Basin and arid zone areas that retain a more natural flow.
- Even though the data collected were of limited value for assessing abundance it provides a significant volume of data on fish location and collection date.
- Historic data around European settlement is limited to large-bodied species.
- From the mid 1800s, commercial fishing was established in the larger waterways of the Basin, with the fishery declining within a few decades.
- The majority of decline in native fish abundance occurred in the late 19th and early to mid 20th centuries.
- Increases in fish abundance in some regions observed over the last 10-15 years are likely to represent relatively small changes in abundance compared to the longer term historical decline
- It is extremely difficult to rigorously assess change in fish abundance without standardised sampling techniques.
Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy and undertaken by consultants at Sinclair Knight Merz, 590 Orrong Road, Armadale 3143. Tel:+61 3 9248 3100
Contacts: Sinclair Knight Merz, 590 Orrong Road, Armadale 3143. Tel:+61 3 9248 3100