Fiordland blue cod: “Smile – you’re on baited-underwater-video”

NIWA marine scientists will use baited-underwater-video (BUV) to assess blue cod stocks in Fiordland this week. It's the first time this unique way of monitoring fish stocks has been used in the fiords.

Blue cod are one of the most sought-after recreational fish in the south of New Zealand. Whether the abundance of blue cod within the fiords is influenced by environmental factors or has been affected by fishing is not known.

In 2005, the Minister of Fisheries, on the recommendation of the Fiordland Marine Guardians, closed the two most popular recreational blue cod fishing areas (Milford and Doubtful Sounds). Initially the closure was for two years. The ban was extended for another two years in 2007 and has subsequently been extended further.

The ban allowed the Ministry of Fisheries and Fiordland Marine Guardians to establish an ongoing research project in 2006 to monitor blue cod abundance in the fiords. Most of this monitoring has been done by hook-and-line angling catches and tagging fish.

This year, for the first time, digital cameras housed in a waterproof casing and baited with paua guts will be remotely deployed to depths up to 80 metres to video the numbers of blue cod in the fiords. The numbers of fish caught on camera can then be used to estimate relative blue cod stock abundance. Lengths of the blue cod will also be measured, using specialised image analysis software that can accurately pinpoint the size of the fish to within 20 millimetres.

NIWA scientist Dr Trevor Willis says nearby marine reserves will also be surveyed using the BUV to see how blue cod populations that have been totally protected from fishing since 1993 compare with those where the fishing ban has been in place for only five years.

"This will provide a critical baseline to estimate the impacts of fishing. This assessment hasn't been done before so we can't be sure whether improvements in fish numbers seen in the protected areas were actually a result of not being fished or reflect larger population-scale trends."

Malcolm Lawson, Chair of the Fiordland Marine Guardians, says that it has always been the intention of the Guardians to establish a management plan for blue cod fishing in these areas but to do so good information is required.

"Fishing has been one of the main activities in Fiordland ever since people have been here. The research that has been carried out while the areas have been closed has given us some information and the BUV monitoring will provide even more. We are currently in the process of consulting the public on the rules relating to the Fiordland Marine Area, including future blue cod fishing in Doubtful and Milford Sounds, and seeking comments on any rules such as catch limits and fishing method restrictions that need to be applied."

The survey will also assess the movement of blue cod within the fiords by recapturing previously tagged fish using cod pots.

A local charter boat, the Pembroke, will be used in the survey which starts on Wednesday and runs for 10 days.

For comment, contact:

Dr Trevor Willis
Scientist, Marine Ecology and Fisheries

Malcolm Lawson
Chair, Fiordland Marine Guardians