ASFB Home > 2003 > Biological Invasions: Consequences for Parasites, Pathogens, Emerging Diseases, and Fisheries in the Marine Environment.

What do tag returns tell us?

Jason Lieschke¹, Charles Todd¹, Richard Barker² and Simon Nicol¹

¹ Department of Sustainability and Environment, Arthur Rylah Institute, 123 Brown Street, Heidelberg, Victoria, 3084
² Department of Mathematics and Statistics, University Of Otago, Dunedin, New Zealand
Email: Jason.Lieschke@nre.vic.gov.au

Large Woody Debris (Snags) are the main form of structural habitat in lowland rivers such as the Murray River and have been demonstrated to be critical habitat for native fish. Snags were removed in the early 1900's from the Murray River to improve boat passage for paddle steamers as well as 'facilitating hydraulic capacity' and 'river improvement'. The removal of this structural habitat has led to depleted fish and macroinvertebrate populations.

Snags were placed into the Murray River at fourteen locations between Yarrawonga and Tocumwal in June 2000 to identify optimal locations as habitat for the endangered trout cod and Murray cod. The 14 resnagging sites and 130 control sites were surveyed prior to resnagging using a boat electrofisher with 1340 fish of 5 species tagged. Post resnagging surveys over the following two years have tagged another 3810 fish.

Post resnagging surveys have allowed us to identify the role woody debris plays as structural habitat for fish as well as the success of resnagging, by monitoring fish response to resnagging. During the surveys, over 300 native fish were recaptured, with 400+ additional tag returns recorded by anglers, allowing individual movement patterns and growth rates to be determined. A preliminary mark-recapture model is also being developed to determine survivorship.

Room 1 Friday 11.50 am