Marlin Reseacch Programme - Satellite Tagging

The NZ Marine Research Foundation is a Trust formed by the NZBGFC. It has had a very successful year carrying out striped marlin research utilizing two types of tags that report via satellite. This year’s project is stage three of on going work so we can better understand the habits and travel patterns of marlin that visit our waters.

The program for the season gone builds on concept development work carried out in the previous seasons where it was proved that a Smart Position or Temperature (SPOT) tag could be attached to a striped marlin and then report the position of the fish every time it tailed on the surface. The tricky part to solve was the requirement for the aerial to be out of the water to work and in the upright position.

The science team from Blue Water Marine Research developed a special sleeve that was fitted onto the upper tail of the marlin and anchored with stainless staples and a bolt. A trial of five marlin tested this last year proved the concept worked which was a world first for marlin.

The benefit of the trial enabled further improvements to the tag sleeve, minor improvements to the aerial to increase time before failure, improved security of the tag and better technique of fish handling while the tag was applied. All marlin in stage 2 & 3 were also fitted with a more conventional Pop-up Satellite

Archival Tag (PSAT) which records depth, water temp and light levels so position could be established. The useful time of the SPOT tag averaged 30 days on the fish with the maximum time being 43 days. The PSAT tags were set from 1 month to 12 months to pop off.

Data gained from the first five fish is a useful addition to the 15 fish that were tagged for stage three. Release points varied from the Bay of Plenty, East Northland Coast, Three Kings and 7 at the Wanganella Banks. Most of the fish were caught and released from the vessel Ultimate Lady which proved to be a very capable platform. It is also the only recreational boat in NZ that visits the Wanganella Banks each season as a planned destination.

The purpose of including the Wanganella in the program was to see if the high concentration of striped marlin there travel to NZ. Given the confidence we now have using the PSAT tags following the first two stages, the Foundation was now keen to try four units set for 12 months attached to the fish so we could get a full years activity and migration with a good chance of getting the data back via satellite.

So what have we learned so far? Early indications from the SPOT tags which have now all expired and those PSAT that have popped off have already given us some vital information not previously noted. By using the frequent position information that SPOT tags gave us and over laying the migration of fish over the geographic relief chart showed something very interesting.

First of all without exception all tagged fish got out of Dodge very quickly once they had undergone the capture and release experience. This was not expected and needs more investigation. While the odd one did later return back to NZ waters most kept heading away from NZ or Wanganella Banks. It appears the fish use underwater ridgelines as migration corridors. The fish released in the Bay of Plenty all made their way north via either the Colville Ridge or Kermadec Ridge. Those that were release at other locations showed a similar affinity to follow ridge lines or high spots under the water. There also appears to be a relationship with upwellings, surface current convergence, prey concentrations and geomagnetic fields.

There were two very unusual events that were similar but remarkable. It appears that two marlin were killed by either a white pointer or mako shark after release, one at 12 hours the other 53 days later. The scientist received data from the PSAT tags that was consistent with the tag being inside the sharks stomach.

The data from the tags recorded no light and there should have been, a constant temperature of 25-27° C when the tag was taken to depths greater than 700m, a depth not known as marlin behavior. These are facts consistence with endothermic fish but not mammals. It is believed the sharks regurgitated the tag after a period of several days since consuming their marlin.

The swim behavior determined from the tags showed a 1-3 km/hr speed with frequent bursts to 10km/hr and a maximum of 38km/hr, the last figure does have a margin of error of ± 9km/hr.  None of the fish tagged at Wanganella proceeded to NZ, this may have been due to the time they were tagged – March.

Two of 20 SPOT tags failed to report which could be either tag attachment failure or mortality. Confirmation of this was expected when PSAT tags were due to report but nothing was heard. The Foundation has five sets of tags remaining and is investigating how we may attach these to free swimming marlin to see if the capture and tagging process is altering the fish behavior.

We are currently looking at techniques on how this may be achieved. We still await the detail from the remaining PSAT tags to report the last of which is not expected until March 2007. The full report is not expected until 2008 when the program is complete but will keep updates coming.

NZBGFC - Jeff Romeril - President