Movement of tagged rig and school shark among QMAs, and implications for stock management boundaries. New Zealand Fisheries Assessment Report 2010/3, January 2010. 

Francis, M P. 

2010 

Ministry of Fisheries 

 

Report 

In the 23 years since rig and school shark Quota Management Area (QMA) boundaries were established, a significant amount of new, pertinent information has been accumulated. Fishery managers are currently making decisions that may have important sustainability and cost implications if QMA boundaries are inappropriate because they either encompass multiple biological stocks, or cover only part of a biological stock. It is therefore timely to review the existing QMA boundaries in order to determine whether they are appropriate. A fundamental principle is that QMAs should be matched to biological stock boundaries as closely as possible, unless other overriding considerations exist. This report re-analyses d tagging datasets to assess the degree of inter-QMA movement of rig and school shark. Companion studies have examined a range of other measures or indicators that might provide information on stock range and boundaries. All these sources of information are reviewed in order to assess the match between the current QMA boundaries and biological stock boundaries. Despite many caveats about using tagging data from inappropriate experimental designs to infer movement rates, it is possible to draw several robust conclusions from the tagging results. · Male rig rarely moved outside the release QMA, even after more than 5 years at liberty. · Female rig were more mobile than male rig, with about 30% moving beyond the release QMA boundaries within 2–5 years of release. The proportion moving beyond the release QMA increased steadily with time. However, few females moved more than one QMA away from the release point. · Female school shark were slightly more mobile than males, with higher proportions of the former moving to non-adjacent QMAs and to Australia. · About 30% of school sharks moved outside the release QMA within a year of release, and this was maintained in the second year after release. After 2–5 years at liberty about 60% of school sharks (both sexes) had moved outside the release QMA. After more than 5 years at liberty, 8% of males and 19% of females had moved to Australia. Male rig move shorter distances than female rig, so a conservative management approach would be to set rig QMAs at a size appropriate for males. Tagging data indicate that male rig do not often move outside current QMA boundaries. A large proportion of tagged school sharks moved outside the QMA of release within 5 years, and a significant proportion eventually moved to Australia. From the tagging evidence, there is probably a single biological stock in the New Zealand EEZ. Companion studies reviewed genetic, biological, and fishery information for evidence of separate stocks of rig and school shark in New Zealand. Little genetic variation was found that might indicate different stocks of either species. Some differences were found in CPUE trends at a small spatial scale, but stock separation at these small scales seems unlikely. The only persuasive evidence for a mismatch between existing QMA boundaries and biological stocks in these studies was the apparent lack of juvenile school shark nursery areas in SCH 4 and SCH 5, suggesting that these Fishstocks are not distinct, but are instead maintained by recruitment from other QMAs. The existing QMAs are probably appropriate for rig stocks, although the boundaries between biological stocks are not clearly defined. School shark QMAs are much smaller than the ranges inhabited by the sharks. However, management of school shark in the current small QMAs is probably not having a detrimental effect on the stock. The relative importance of various breeding grounds around New Zealand (e.g., aggregations of breeding females in Kaipara Harbour) and whether females return to the area in which they were born are unknown. Therefore, the current stock management units may be a wise precautionary measure to spread fishing effort; amalgamation of all QMAs into one QMA for the whole country could create unacceptable risks to stock sustainability. 

Biodiversity, Fisheries 

Fisheries, quota management areas, school shark, rig, Kaipara Harbour, fish stock, sustainability issues, fish biology, fish genetics