Regional Population Connectivity, Oceanic Habitat, and Return Migration Revealed by Satellite Tagging of White Sharks, Carcharodon carcharias, at New Zealand Aggregation Sites.
A joint NIWA/Department of Conservation (DOC) tagging programme was launched in 2005. Hi-tech electronic tags are being used to gather information on where the sharks are and when, and to record their depth and the temperature of the surrounding water. Three tag types have been used: popup archival tags, acoustic tags, and dorsal fin tags.
Popup tags are implanted in the muscle under the dorsal fin with a tagging pole, and record depth, temperature and location, storing the data for up to a year. They then release themselves from the shark, float to the surface, and transmit summaries of the data to a satellite. If the tags are physically recovered, the high resolution data collected at one minute intervals can be downloaded. Popup tags provide only approximate location data, so they are most useful for tracking long-distance migrations.
Acoustic tags send out coded, individually identifiable sound ‘pings’ that can be detected up to a kilometre away by acoustic data loggers. The tag batteries last long enough to monitor the presence of white sharks in the region in the vicinity of a data logger for two years. Acoustic tags provide accurate fine-scale information on sharks at specific locations.
Dorsal fin tags bridge the gap between popup and acoustic tags. They provide accurate location information by transmitting to orbiting satellites every time the shark is at the surface and the dorsal fin and the tag’s aerial are exposed to air. Their batteries can last for more than one year, so both fine scale and large scale movement patterns can be recorded. However, dorsal fin tags are more difficult to deploy: the shark has to be caught and restrained while the tag is attached to the dorsal fin. So far, only a few of these tags have been deployed in New Zealand.
Since 2005, 44 white sharks have been tagged with popup tags, mainly at the Chatham Islands and Stewart Island. These islands support large colonies of fur seals, which are a major food source for white sharks. Our research has focussed on Stewart Island since 2009. The population there is dominated by males (about 2.2 males for every female). Nearly all of the females are immature, being shorter than the female length at maturity of 4.5 to 5 m. Only about one-third of the males are longer than the male length at maturity of about 3.6 m. This indicates that the white shark aggregations at Stewart Island are not related to mating, and are most likely driven by the abundance of seals for food. Large, mature females are rarely seen anywhere in New Zealand and their distribution, habitat and behaviour are almost completely unknown.
Tagging results show that most New Zealand white sharks make annual migrations to tropical waters in winter, travelling as far as 3,300 km away. Sharks have migrated to the Great Barrier Reef in Australia, the Coral Sea, New Caledonia, Vanuatu, Norfolk Island, Fiji and Tonga. They don't cross the equator.
Most of the sharks from Stewart Island headed northwest of New Zealand, whereas most Chatham Islands sharks headed north. However, some sharks from the two tagging locations overlap in the tropics. Surprisingly, we have not detected any direct movement between Stewart and Chatham islands.
Some popup tags have remained on the sharks for long enough (up to one year) to reveal that the sharks returned to their tagging locations after their tropical holiday. This has been confirmed by photo-identification work at Stewart Island. Each shark has a unique colour pattern, particularly around the gills and on the tail. Some individuals have been seen at Stewart Island each year for multiple years. This indicates that white sharks have a sophisticated navigation mechanism that enables them to make major direct oceanic migrations, and then return to precisely the spot they left from. We do not know how they achieve this.
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Duffy, C.A.J.; Francis, M.P.; Manning, M.; Bonfil, R. (2012). Data from: Regional population connectivity, oceanic habitat, and return migration revealed by satellite tagging of white sharks, Carcharodon carcharias, at New Zealand aggregation sites. Southwestern OBIS, National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand, 2014 records, Online http://nzobisipt.niwa.co.nz/resource.do?r=mbis_whiteshark released on May 26, 2014.
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South western Pacific Ocean and Tasman Sea
|Bounding Coordinates||South West [-51, -156.9], North East [-15.3, 149.2]|
|Species||Carcharodon carcharias (White shark)|
|Start Date / End Date||2005-04-01 / 2010-02-01|
No Description available
|Title||White shark tagging off New Zealand|
|Funding||This project was funded by the New Zealand Department of Conservation, National Institute of Water and Atmospheric Research Ltd., the Foundation for Research Science and Technology, Wildlife Conservation Society NY, National Geographic Society, and NABU/SharkTracker|
|Study Area Description||White sharks were tagged off Stewart Island and the Chatham Islands, New Zealand|
|Design Description||Twenty-five White Sharks (Carcharodon carcharias) were tagged with pop-up archival transmitting tags at Chatham Islands, Stewart Island, and one coastal location in New Zealand between April 2005 and September 2009.|
The personnel involved in the project:
All but one shark were tagged free-swimming. White Sharks were attracted with chum (minced Albacore) and lured close enough with fish baits to tag. Tags were deployed using a hand-held tagging pole that inserted a nylon umbrella-style dart (Domeier et al., 2005) into the dorsal musculature of the shark. Three sharks were tagged with Microwave Telemetry (MT) PTT100, and twenty-two were tagged with Wildlife Computers (WC) PAT4 and MK10 pop-up archival transmitting (PAT) tags. These were attached to the dart by a 23–25-cm leader of 2-mm diameter (181.4-kg test) monofilament nylon. One shark (64035), a 330 cm total length (TL) immature male, was caught using a baited line and secured in a cradle. This shark was double tagged with a MT PAT tag and a WC smart position and temperature (SPOT) satellite tag. The latter was bolted to the shark’s first dorsal fin.
|Study Extent||Twenty-five White Sharks (Carcharodon carcharias) were tagged with pop-up archival transmitting tags at Chatham Islands, Stewart Island, and one coastal location in New Zealand between April 2005 and September 2009.|
Method step description:
- Daily positions were estimated from ambient light data stored on WC PAT4 and Mk10 tags using WC-GPE: Global Position Estimator Program Suite software (www.wildlifecomputers.com). Dawn/dusk light-level data were extracted using WC-AMP, and daily longitudes and latitudes were estimated using WC-GPE. Daily records with poor dawn/dusk light level curves were excluded from the analyses. Microwave Telemetry provided estimated latitudes and longitudes for data from PTT 100 tags. The most probable tracks were fitted by matching tag-measured SST with remotely sensed SST data using unscented Kalman filtering (UKFSST) (Nielsen et al., 2006; Lam et al., 2008). Preliminary fits indicated that models incorporating longitude bias and SST bias always produced implausible tracks, so we omitted these parameters. For sharks whose tags popped up on the programmed date (n = 8), the UKFSST models incorporated parameters for latitude bias and solstice error variance (which accounts for greater error around the equinoxes), and the measurement error for the last position was set to zero. For sharks whose tags popped up prematurely or reported their first accurate location some time after pop-up (N = 11), the pop-up locations were not known accurately, so measurement error was estimated for the last position. For nine of these sharks, the UKFSST models incorporated parameters for latitude bias and solstice error variance; the remaining two sharks did not provide enough data to estimate the solstice error parameter, so uniform error was assumed.
- Duffy, C.A.J.; Francis, M.P.; Manning, M.; Bonfil, R. (2012). Regional population connectivity, oceanic habitat, and return migration revealed by satellite tagging of white sharks, Carcharodon carcharias, at New Zealand aggregation sites. In: Domeier, M.L. (ed.). Global perspectives on the biology and life history of the white shark, pp. 301-318. CRC Press, Boca Raton, USA. ISBN 9781439848401
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