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A new recreational fishery for large Pacific bluefin tuna (Thunnus orientalis) has developed of the west coast of the New Zealand's South Island. We are involved in an international research project to discover how their behaviour fits with other large migratory species in the southwest Pacific and what connection they have to the northwestern Pacific breeding grounds. Electronic tags also provide information of the survival of these fish following tag and release.
Bluefin tuna tagging Hokitika Trench 2006 Karamea Bight 2007Funded by Stanford University, Tag-a-Giant Foundation & Ministry of Fisheries New Zealand Marine Research Foundation
Researchers Blue Water Marine Research
Prof Barbara Block
George Shillinger  For the first time in the southern hemisphere pop-up satellite tags were deployed on large Pacific bluefin tuna in August 2006. Tagging was carried out near the Hokitika Trench as a joint venture between Blue Water Marine Research (NZ) and Stanford University (California), and was greatly assisted by the owners, skippers and their clients fishing out of Greymouth, on the west coast of New Zealand’s South Island.
The high-tech tags are capable of storing months of data and transmitting it back to researchers via satellite, after they have released from the fish. In 2006 7 tags were provided by Professor Barbara Block of Stanford University and brought to New Zealand by George Shillinger, who placed them on tuna from the vessels “Cerveza 2” and “Apollo”. Two additional tags were sourced through the New Zealand Ministry of Fisheries, and implanted by the crew on “Cerveza 2”. Tagging took place between 16 and 26 August 2006.
Four of the tuna were caught on handlines. The remainder were caught on heavy tackle game fishing rods, employing 60 kg mainline. Fish sizes were estimated to range between 190 kg and 250 kg. All fish were tagged in the water alongside the vessel, and some were also tagged with standard gamefish dart tags issued by the NZ Big Game Fishing Council. Fighting times varied from 15 minutes to 145 minutes.
In 2007 Professor Block provided 12 PAT tags and the Ministry of Fisheries provided 3. The hoki fleet was fishing further north and the weather delayed proceedings for quite a while, but the fish were back. In a remarkable effort the anglers and skipper of “Cerveza 2” provided George 7 giant bluefin to tag in one day, including a certain world record size fish estimated at 425 kg (940 lb).
All 15 tags were placed on fish with assistance from the anglers and crew of “Cerveza 2”.
Blue Water Marine Research director Pete Saul was both angler and tagger on one fish, an experience he will not forget. The fish ranged in size from 200 to 425 kg and all but one handlined fish were caught on 60kg test rod and reel.
Results from 2006 deployments
Four tags released and transmitted successfully. Several of the tags did not stay on as long as intended and all tags came off between 13 November 2006 and 11 February 2007, recorded data for 3 to 6 months. There are a number of possible reasons that tags don’t report. The fish may have gone too deep for the tag, they may have died, or growth on the tag may have prevented it from floating properly.
Bluefin tag BFT06-02 This 220 kg fish was caught on a hoki bait and was brought to the boat in 15 minutes using a handline aboard “Cerveza 2” on 15 August. By late August this tuna had moved to a large reef system (the Wanganella Banks) WNW of New Zealand and south of Norfolk Island. It remained close to the banks during much of September and October, moved away to the NW for a time in November but then headed back to the banks, where the tag popped off on 13 November 2006, around 400 km from the top of the North Island This fish spent some time right at the surface every day and much of its time within 50m of the surface, with occasional dives below 100 m. However, this might be partially explained by the fact that it was in the vicinity of a very extensive, shallow reef system for much of the time. It experienced temperatures ranging between 10 and 20 oC, with the lower temperatures mainly during late October, when it at times reached depths of 200 m. Bluefin tag BFT06-05
This was another tuna estimated at 220 kg, handlined using hoki bait from “Apollo” in darkness and moderate seas. It was brought to the boat and tagged in 30 minutes. Data from the tags show that this tuna also moved quite directly to the area of the Wanganella Banks. In September, it moved eastwards across the top of New Zealand. It spent the rest of September and October north-east of the North Island, before working its way down the east coast of the country as far as the southern end of the South Island. It then moved extensively up and down the east coast of both islands before the tag popped off on 11 February 2007. This fish moved through a much greater range of depths than the first one, although it was tracked for a much longer period and covered far more ground than the first tag. BFT06-05 regularly dived to depths in excess of 100 m, commonly exceeded 200 m and on several occasions went as deep as 400 m. During late December and early January it spent a considerable period in water temperatures of less than 10 oC. Its deepest dives occurred in late January and early February, shortly before its tag popped up about 300 km SE of Banks Peninsula.
Bluefin tags BFT06-08 and BFT06-09
The detailed analysis of data from these tags is not yet available. However, both were caught from “Cerveza 2” on August 26, using heavy tackle game fishing rods and hoki bait. The first fish was caught by Glenn Baker in 24 minutes. When the tag popped on 20 December 2006 the tuna was some 600 km northwest of the Hokitika Trench. The second fish that trip was caught by Peter Begovich and tagged after 35 minutes on the line. This tag popped up on 7 January 2007 around 500 km southeast of Banks Peninsula (Figure 1). 
Figure 1. Pacific bluefin tagging location on the Hokitika trench off Greymouth and tag pop-up locations and dates. Pacific bluefin tagged in August 2007
The tagging team had to endure a frustrating ten day wait in Greymouth in 2007 due to bad weather and poor fishing. Few of the large commercial trawlers were operating, and very little activity was taking place near the Hokitika Trench, where the fishing had been hot in 2006. However, reports began to filter in of good fishing further north, in the Karamea Bight. Most charter vessels relocated to Westport, much closer to the action, after August 17 and the fishing success was immediate as the weather also improved.
On 18 August, 7 tags were successfully deployed, with a further 5 placed on tuna the next day all from “Cerveza 2”. Two more were deployed on September 5, and the last tag was deployed on September 7. The tuna were generally larger in 2007 than in 2006. The estimated weights ranged between 200kg and 425kg. This latter fish was well in excess of the existing All-Tackle world record for the species, standing at 300kg. In fact, seven of the tuna released were estimated to equal or exceed the current record, while only three tuna were estimated at less than 250kg. All but one fish were caught on rod and reel using hoki or squid bait. Fight times ranged between 30 minutes and 3 hours.
PAT tags have intelligent software that ensures that if the fish lies dead on the bottom for a specified time (in this case, 72 hours) the tag will automatically release and report the information it has recorded. This year some tags were also fitted with a device that would release the tag if the fish went deeper than 1800 m. There was a possibility that some of the 2006 tags that never reported may have been on tuna that died and sank into deep water. Generally if fish die from capture stress or damage it is within a few days of release. None of the tags on the 15 fish tagged reported in the first 4 weeks as a result of the tuna dying and sinking.
One tag was programmed to release from the fish after 30 days and it came up on schedule, over 200 miles north east of North Cape. This tuna appeared to have followed a similar course to two of the bluefin tagged in 2006. During October the attachment failed and a tag reported early near the Kermadec Ridge. It was from the largest tuna tagged, the one estimated at 425kg. This was a significant event, since the fish was played for 148 minutes before release, and appeared to be tired when it was set free. The fact that this particular tuna clearly survived the catch and release process is extremely encouraging, because some anglers and skippers still believe that tuna are unable to withstand the rigours involved in being brought to the boat on rod and reel over a prolonged time. Clearly this fish recovered and survived.
Particular thanks are due to the following people, whose whole-hearted assistance made the tagging operation possible:
Dave Woof, owner of “Cerveza 2” and skipper Larry Johnston.
Super deckies Adrian, Rads and Josh
Craig Watson
Warren Bunn and Steve Potter
Carey McIvor and Haley Nelson of “Apollo”.
Glenn Baker and Peter Begovich
Paul Copestake, Dennis Bree, John McCall
Professor Barbara Block of Hopkins Marine Station, Stanford University
George Shillinger, Stanford University
Tag-A-Giant Foundation
Ministry of Fisheries |
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