School and gummy shark tagging by CSIRO in southern Australia: 1997 - 1998

46 school shark were tagged with archival tags during 1997-98, in South Australian and Tasmanian waters. 19 tags were recovered. The tags yielded 15.3 years of data on light level, depth and temperature collected at 4 minute intervals. The basic release-recapture data has been entered into the CSIRO pelagic tag data base but not the actual electronic data. The electronic data for the Lotek tags is in a different format to that of the Wildlife Computer tags, and may require dedicated geolocation software to process. Wildlife Computers provides geolocation software for their tags free of charge. While longitudinal movements have been described, there was no analysis of corresponding latitudes, as light-based latitude estimation was unreliable. There is scope for additional research into latitudinal movements based on the depth data. The depth pattern shown by the sharks can be used to examine if the fish was close to the bottom, and combined with a longitude estimate for a particular day, latitude can be estimated as across much of southern Australia where depth increases with latitude. However, there is a software development challenge associated with this, as there may be more than one depth fit for a particular longitude, especially towards eastern Australia. In this eastern region the restricted depth of Bass Strait can provide additional information on the latitude, as fish data at >86m indicates that it was too deep for Bass Strait. An additional factor that was not examined was the temperature data from the tags. In pelagic species surface water temperature is used to estimate latitude and at times school shark do come close to the surface. Some of the tags were set up to record internal as well as external temperatures but this data was not examined. There have been 2 recaptures of Wildlife Computers tags since West & Stevens (1996) published the results. There have also been two Lotek tags returned since this publication but the data for these tags was corrupted.