View All Projects

Satellite tracking of Broadbill Swordfish

Swordfish (Xiphias gladius) do not breed in New Zealand waters. During the austral spring they move to warmer subtropical spawning grounds. For the first time electronic tags that store and transmit information on the temperature, depth and location have been attached to New Zealand swordfish. These are helping to reveal quite variable spawning migrations and fish subsequently returning to the New Zealand region. Data from other SW Pacific tagging locations is also presented.

Funded by the Ministry of Fisheries
Researchers Blue Water Marine Research

 The aim of this project is to electronically track swordfish (Xiphias gladius) captured within New Zealand waters, and to collect data coinciding with their expected subtropical spawning period and subsequent return to temperate waters. 

Nineteen pop-off satellite archival transmitting tags (PAT) (Wildlife Computers, Redmond, WA, USA) were deployed on swordfish. Tags were programmed to record data between 66 and 246 days, and 10 tags provided 66–236 days of data. The attachment failed on 5 tags which caused them to transmit prematurely, two mortalities occurred soon after tag and release, and two tags didn’t report data back. Two different styles of plastic anchors were used, with the Prince/Musyl nylon anchor providing notably better results.   

 The crepuscular diving behaviour of swordfish makes estimating geolocation using dawn and dusk light level changes problematic. Geolocations have been estimated by using the SST Kalman filter on data transmitted from 10 tags. These tags yielded between 8 and 37 usable light-level geolocations each, plus the tagging and popup coordinates, giving a total of 251 locations from a combined deployment of 1603 days. On average there are 4.7 locations per month from these tags. 

From the small sample size we have at present, it appears to be that fish tagged north of New Zealand came back down the west coast. Fish tagged to the east and northeast returned to those areas or came down the east coast. This may warrant further investigation. There is evidence of foraging site fidelity in New   Zealand waters. All tracks plotted show fish leaving the New Zealand region usually to the north and returning to New Zealand. This includes the smaller fish (56 to 80 kg) which may not be sexually mature if female.


Site by Big Fish Creative