Sunfish, a giant mysterious animal in our oceans
Fisheries management is a touchy question all around the world. The many species exploited require quotas, seasonal or regional limitations on fishing in order to maintain stocks at renewable levels. Argos satellite telemetry enables better understanding of the behavior of underwater species, and thus makes it possible to decide on fishing regulations or bans.
Exploring the unknown
Pelagic fish like tuna, billfish and sunfish are highly mobile species with seasonal and also vertical (daily) movements. Do they show seasonal movement patterns? Do they change their diving depths due to variations in ambient temperature and/or light? To better understand their behavior while swimming, reproducing or feeding, Argos pop-up satellite archival tag are used.
Among those species, sunfish (Molidae) are the largest bony fish inhabiting the epipelagic to mesopelagic realms (surface to 1000-m depths) in tropical through temperate ocean regions. They are giant species with an exotic shape, and a short, rounded rudder, or clavus. They swim elegantly in the ocean, spending some of their time basking near the surface – they stay at shallow depths during nights and dive deeper during the day. As the main target species in Eastern Taiwan, sunfish are caught abundantly.
Unveiling mysteries of wildlife
There’s still a lot we don’t know about this marine species. The Tuna and Billfish Tagging Project in Taiwan tracks them using X-Tag from Microwave Telemetry to understand their movement patterns. Several of them were thus tagged off Eastern Taiwan in 2017 and 2018 to study their horizontal and vertical movements. One tag popped-up after remaining attached for 150 days and another tag popped-up after remaining attached for 18 days. The latter tag was recovered by Argos Goniometer on the shore of Qixingtan in Eastern Taiwan since the tag was washed to the shore instead of drifting with the Northward Kuroshio Current under the strong North-East monsoon winds.
Data results indicated that sunfishes inhabit a wide range of water temperature from 10 to 35 °C. They spent less time in surface waters and they present a clear diel, or diurnal, pattern.
Retrieving tags with the Argos goniometer
The Tuna and Billfish Tagging Project in Taiwan also uses Argos satellite telemetry pop-up tags to track other pelagic species. A total of five tags were recently retrieved using Argos Goniometer, including three tags on amberjacks, one on a big-eye tuna and one on a sunfish. Two of them were found on the shore and three were found off the coast of eastern Taiwan. The Argos Goniometer got the first signal at about 12 km from the tag and the signal updated in 2 to 3 minutes. Signal strength became stronger at about 2 km from the tag and the signal updated in 30 to 60 seconds. Signal reflections from buildings and mountains can make it a little difficult to determine the direction of the tags on shore – but not offshore.
The goniometer is a key tool for wildlife protection because retrieving the tag gives scientists access to additional data that were not transferred by satellite. In addition, the tag can be redeployed on another fish.
Potential for fisheries management
The project still has many tags attached to fish of the three migratory species and waiting to be recovered soon. The behavioral data thus obtained is fishery-independent and can provide higher quality information such as migration paths and spawning grounds. The data could help governments and regional fisheries management organizations to manage the population dynamics and decide policies relative to pelagic species in order to conserve wildlife.
Featured photo: Sunfish tagged with an X-Tag at Eastern Taiwan. Credits Tuna and Billfish Tagging Project in Taiwan
NTOU (http://www.fd.ntou.edu.tw/index_en.php): Shian-Jhong Lin firstname.lastname@example.org/ Sheng-Ping Wang: email@example.com/ Nan-Jay Su firstname.lastname@example.org, Yuan-Shing Ho email@example.com , Sheng-Ping Wang: firstname.lastname@example.org
On Argos web site: Billfish movement patterns revealed with Argos pop-up satellite tags ( https://www.argos-system.org/billfish-movements-satellite-tags/ )