SHARK TRACK

Tracking Porirua's rig sharks

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Do the same rig sharks use Porirua Harbour each year?

23rd May, 2015

Uniquely numbered fisheries tags I removed from two previously caught and tagged rig sharks

Rig sharks spend most of their year outside Porirua Harbour, with the largest numbers found inside the harbour during December and January (Jones and Hadfield 1985). I attach numbered fisheries tags (in photo) to all the rig sharks I catch, with the hope that recatching them at a latter date will help me understand how many and how often they use Porirua Harbour.

This week I caught, tagged (with fisheries tags) and then released 11 adult rig sharks during a 3 hour fishing session in Pauatahanui inlet. This was unusual because such large catches were meant to only occur during December and January at the peak of the shark season.

What made this catch extra-exciting was that I had caught two of the rig sharks before, one just before Christmas and another during February 2014 (over a year ago). This may indicate that some of the rig sharks come to the estuary and stay for several months (#2356 December to May) rather than only for the 2 month peak of the season.

Because I caught a shark that I had also caught the previous season (#2312 February 2014) this may indicate that rig sharks find their way back to Porirua Harbour each year, rather than using different  spawning sites along the coast, or only coming to Porirua Harbour every 2nd or 3rd year.

The more recaptures of rig sharks I’ve previously caught and tagged will tell me more and more about how the Harbour is being used by rig sharks.

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