Fishing: Unlocking secrets of the striped marlin

By PETER JESSUP

Researchers hope their work tagging and tracking marlin will provide information about the fish and the health of the oceans generally, while debunking myths that billfish that are captured and released are doomed to die.

After four years in preparation, a project to tag marlin with archival recorders that detach and pop to the surface then transmit their data via satellite has come to fruition.

Five of the US$3500 ($6250) tags, the size and shape of a cigar, have been anchored into striped marlin during recent months. A sixth is to be attached this week. Three have already been recovered.

The aim is to determine where marlin travel, how quickly, what feeding and breeding patterns they display, the water depth and temperature preferences they have. Little is known about the species biologically but, as top of the oceanic food chain, it is thought that marlin are a good indicator of the health of other marine life - if they are struggling then other food species must be too.

But that's not the case, it appears. The fishery looks to be in healthy condition, continuing the recovery it underwent after longliners were banned from taking any marlin from New Zealand's exclusive economic zone in the early 1980s.

Marlin grow to 90kg, are big enough to breed in three years and have a life expectancy of seven or eight. They feed on almost anything but follow squid, albacore and skipjack tuna into New Zealand waters each summer when temperatures rise before returning to the Coral Sea and waters off Tahiti to spawn.

The tags recovered so far were set to pop off the fish after 30-60 days. The marlin were tagged off the east coast of Northland and the data maps sent via the tags show they moved mainly within that area during that time. But one travelled 850 nautical miles northeast into the mid-Pacific. All the fish stayed near the surface most of the time, within the top 5m, but one dived to 200m once.

Another tag, due to pop off on July 10, will give evidence of wider travel.

Each year more than 1000 stripeys are tagged in New Zealand waters but returns number less than 0.05 per cent and the information they offer is confined to growth estimates and raw A-to-B travel.

This project, co-ordinated by Massey University in collaboration with Stanford in California, financed by the NZ Marine Research Foundation with backing from gamefish clubs, and involving Pete Saul and John Holdsworth of Blue Water Marine Research as taggers, intends to broaden global knowledge of the species.

There are also commercial applications. New Zealand striped marlin are the biggest in the world and provide a healthy return in charter fishing.

It may not aid anglers in their technique or timing but should tell where marlin are most likely to be found, which in turn offers suggestions of where the food is at what times and why.



Holdsworth said evidence from the returned tags proved fish do survive the catch-and-release process. Stressed fish - those over-heated, bleeding from the gills or otherwise damaged - would die within two days.

Fishing continues to be hot in all areas, the cooler conditions bringing them on the bite. Big snapper are still in close around the Hauraki Gulf and Manukau anglers report this summer as being their best for snapper catches in many years.