New Zealand Journal of Marine and Freshwater Research abstracts
Exploitation rates of rig (Mustelus lenticulatus) around the South Island of New Zealand
MALCOLM P. FRANCIS
Fisheries Research Centre
Ministry of Agriculture and Fisheries
P.O. Box 297, Wellington, New Zealand
Abstract Two-thousand-and-ten rig were tagged around southern New Zealand during the 1982/83 and 1983/84 fishing seasons to estimate exploitation rates. 520 were double-tagged to estimate tag shedding rates. Tags placed in front of the first dorsal fin were shed more often than those placed between the 2 dorsal fins, possibly because of entanglement in the meshes of set nets during recapture. The estimated front tag shedding rate was used to correct ■■ recapture numbers. Reported recapture rates increased with total length, reflecting increasing exploitation by the predominantly set-net commercial fishery. Reportedrecapture rates of trawl-tagged rig wereless than those of set-net tagged rig, suggesting that initial mortality was significant for the former method. Annual exploitation rates probably exceeded 10% year
1 for 75-89 cm rig off both east and west coasts of southern New Zealand. Exploitation rates of rig > 90 cm probably exceeded 20% year
1 for males and may have exceeded 30% year
1 for females. These high rates are thought to explain the steady declines in catch-per-unit-effort observed in several set-net fisheries.
Keywords Triakidae; Mustelus lenticulatus; rig; exploitation rates; tagging; tag shedding; mortality
New Zealand Journal of Marine and Freshwater Research, 1989, Vol. 23: 239-245 0028-8330/89/2302-0239$2.50/0 © Crown copyright 1989 Received 10 March 1988; accepted 5 October 1988
PDF file of entire paper: medium quality (596K); (scanned from paper original: notes about this process)
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