Improving the collection of data and samples from bycaught basking sharks

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Summary

Sampling protocols were designed to collect information and samples that will be useful for understanding more about the biology, population structure and behaviour of basking sharks in New Zealand waters. The key parameters are date, location, size, sex, maturity (males only), in combination with photos and a fin clip for genetic analysis. A sampling kit was supplied to each vessel involved in the programme. In the first year, 10 sampling kits were deployed with fishing companies that operate on the Stewart Island – Snares Shelf and the Auckland Islands Shelf (where most basking sharks have historically been caught). At the end of the first year of the project, only one sampling kit was used. For the second year of the project, additional sampling kits were made up to increase sampling capacity and cover the full extent of observed vessels in the arrow squid fishery, for a total of 20 available sampling kits. Four additional kits were made available to deploy on non-observer vessels.

Kits were deployed on approximately 50 trips across 22 vessels. These vessels targeted arrow squid (Nototodarus sloanii), barracouta (Thyrsites atun), and hoki (Macruronus novaezelandiae) in areas Southland/Southeast Coast/Southeast (SOU/SEC/SOE) and Sub-Antarctic/Sub-Antarctic Islands (SUB/SOI) across Fisheries Management Areas (FMAs) 3, 4, 5, and 6. It was estimated that from December 2020, all trips targeting arrow squid had a sampling kit onboard and kits have remained on vessels where observer coverage was continuous. As of 30 April 2021, one sampling kit had been returned to NIWA.

From 01 September 2019 to 30 April 2021, there were 16 reported basking shark interactions (for a total of 17 sharks). Fifteen interactions occurred during commercial fishing operations and one occurred during a research trawl survey. Most commercial interactions occurred when an observer was onboard (80%) and most occurred during December (60%) and in FMA 5 (60%). Most interactions were reported by vessels targeting arrow squid (53%) at depths from 145–350 m and all interactions were reported by trawl fishing. One vessel reported 30% of the basking shark interactions.

Efforts should be made to continue sampling bycaught basking sharks with the available sampling kits. Alternative means of sampling sharks (e.g. biopsy poles) will be necessary to ensure health and safety regulations are met with regards to observers approaching sharks. Genetic samples are needed for understanding stock structure, aggregation structure and dynamics, and with sufficient sampling, could be used to estimate population size. It is also recommended to continue the collection of basking shark biological measurements, including length and sex, to understand spatial differences in catch composition and commercial vessels are also encouraged to collect this information. Sampling efforts should be targeted to where interactions are most likely to occur – in the arrow squid target trawl fishery operating on the southern edge of the Stewart-Snares Shelf during December. Preference could also be given to these vessels to deploy popup satellite tags to released basking sharks to provide insight into post-release survival and movement patterns.

Publication details

Finucci, B. 2021. Improving the collection of data and samples from bycaught basking sharks. INT2018-04 final report prepared by NIWA for the Conservation Services Programme, Department of Conservation. 19 p.