Skate tagging in the Heard Island and McDonald Island (Division 58.5.2) toothfish fishery up to 2013

The fisheries targeting Patagonian toothfish (Dissostichus eleginoides) and mackerel icefish (Champsocephalus gunnari) in the Australian Fishing Zone surrounding Heard Island and McDonald take three species of skates, Bathyraja eatonii, B. irrasa and B. murrayi, as their most common bycatches. A tagging program has operated in these fisheries since 2001 to learn more about the movement and biology of these species. In the 13 years, over 12,000 skates have been tagged, with 112 recaptures, a recapture rate of less than one percent. The average distance between release and recapture for each of the three species was 4 nm, and the longest distance travelled was 23 nm. The skates appear to move equally in all directions. Most recaptures occurred within the first three years, with the maximum time at liberty of nearly eight years for one B. irrasa. Range of movement in depth was between -266 m and 280 m from release to recapture, with B. irrasa tending to move in depth more than the other two species. Growth increments for tagged and recaptured B. eatonii indicated growth of ~20mm/year for both sexes between 600 and 1000mm total length, indicating maximum ages of several decades. In combination with biological and catch and effort data, the ongoing program of skate tagging will continue to contribute data which will be used for better informed risk assessments in the future.