Reported New Zealand sea lion (Phocarctos hookeri) captures in commercial trawl fisheries, 1991–92 to 2012–13

Citation

Thompson, F. N., Berkenbusch, K., & Beritzhoff-Law, M. (2015). Reported New Zealand sea lion (Phocarctos hookeri) captures in commercial trawl fisheries, 1991–92 to 2012–13. New Zealand Aquatic Environment and Biodiversity Report No. 145. 43 p. Retrieved from https://www.mpi.govt.nz/document-vault/7974

Summary

This report presents an authoritative data set of documented captures of New Zealand sea lion (Phocarctos hookeri) in New Zealand's commercial trawl fisheries.

Data were sourced from the Ministry for Primary Industries (MPI) observer programme, fisher-reported captures, necropsy records, and records of the Deepwater Group. Sea lion captures are usually recorded in multiple data sources. Duplicate records were reconciled by collating all data from the different sources into a single database, and then linking the records using a set of matching rules.

The resulting data set included 388 sea lion captures, reported in the 22-year period between October 1991 and September 2013 from trawlers operating near New Zealand's subantarctic islands. In the data set, 337 (86.9%) sea lion captures were reported by MPI observers compared with 289 (74.5%) sea lion captures reported by fishers or the Deepwater Group. Of the fisher-reported captures, 43 (11.1%) were not also reported by MPI observers. Of the 169 (43.6%) captured animals returned for necropsy, 8 records could not be linked to any other records.

Capture events were linked to fisher-reported catch effort where possible. The majority of reported sea lion captures over the entire reporting period was from squid trawlers operating near Auckland Islands, and there were 239 (61.6%) sea lion captures in this target fishery. Trawlers targeting southern blue whiting had the second largest number of reported sea lion captures, with 55 (14.2%) capture records. Comparing these target fisheries over time, since 2008, there were more reported sea lion captures in southern blue whiting fisheries than in the Auckland Islands squid target fishery each year. Trawlers targeting other species accounted for 94 (24.2%) sea lion captures.

Records by MPI observers and recent fisher-reported captures include additional information, such as the gender of captured animals and the life status of animals after release. Not all data sources recorded the status of animals following their release. Included in the data set were 29 (7.5%) records of sea lions that were released alive.

Only the captured animals have information regarding their gender. These captures were recorded with a gender code when they were reported by MPI observers, returned for necropsy, or reported on the old nonfish bycatch form. Of the 365 captures that had gender information available, 180 (46.4%) were reported as being female.