Many research projects are focused on tracking sharks and rays. The objective of is research is data collection about habitat and migration patterns to support conservation of species, by f.i. restricting allowable catches, protect the habitat itself by restricting access of construction and development. Restricting fishing quota for adult individuals is not sufficient: the protection of breeding areas is crucial as well. Several shark and ray species begin their independent lives in mangrove swamps, estuaries, shallow coastal areas, that are unfortunately frequently destroyed for tourist development projects or polluted by sewage.
Research data can be collected through several types of tags.
The cheapest tags are the so-called spaghetti, dag and anchor tags are markings with a unique number printed on them, along with the contact information of the tagging program. An animal is caught, measured and tagged. The dart-like tip or the bar at the end are inserted into the muscle of the fish’s body to secure the tag. When the animal is recaptured, data about growth rate, migration and age can be collected through comparison.
Acoustic tags issue a sound signal and can be attached to or implanted in the animal. The signal is transmitted to a receiver, that can be read. The simplest version of the acoustic transmitter is the ‘pinger’. The ‘pinger’ produces ultrasonic pings that can be heard using a hydrophone (underwater microphone) and receiver. More sophisticated versions of these tags include onboard sensors (typically pressure and temperature) to provide depth and water temperature information from the fishes track. The depth and temperature information is encoded in the acoustic pings transmitted from the tag. A pinger can be followed by a boat (active listening).
Passive acoustic monitoring uses the same basic transmitter-receiver technology, but is for longer-term (months or years) studies. This system consists of uniquely identifiable ultrasonic transmitters that are surgically implanted into sharks and fishes to ensure longer retention. These transmitters are then detected by underwater receivers stationed at various locations on the sea floor. The receivers are deployed on subsurface moorings and continuously listen for transmitters, 24 hours a day, 365 days of the year. When a tagged shark comes within detection range of a receiver (detection radius is up to 1 km depending on transmitter type), its unique ID code is recorded, together with the date and time. The records from receivers at different locations are combined to create an overview of shark movement patterns.
Smart Position or Temperature Transmitting Tag (SPOT tags) are attached to an animal and detectable over broad geographic areas and remotely relay information to satellite arrays. These tags utilize radio transmissions and have to get in contact with air to send data and must therefore be externally attached. This makes them vulnerable: they can be damaged and lost. They are commonly attached to the dorsal fin, but can also cause damage to the fin if attached over a longer time. SPOT tags transmit a signal to the satellite array whenever the fin breaks the surface of the water.
Another type of tag is the data storage tag (DST), a data logger that uses sensors to record data at predetermined intervals. Data storage tags usually have a large memory size and a long lifetime, batteries can last several years, some tags are solar powered. Archival tags record data on internal body temperature, water temperature, the animal’s swimming depth and light intensity.
Pop-up satellite archival tags (PSATs) are used to track movements of usually larger sharks. A PSAT is an archival tag (or data logger) that is equipped with a means to transmit the data via satellite. Its major advantage is that it does not have to be physically retrieved like an archival tag for the data to be available. Location, depth, and temperature data are used to answer questions about migratory patterns, seasonal feeding movements, daily habits, and survival after catch and release, for example.
When the PSAT releases from the animal on which it was attached, it floats to the surface, and begins to transmit data to one of the manufacturer’s satellites at a frequency of about 400 MHz. Therefore, the PSAT does not have to be physically recovered for the data to be obtained. Depending on the number and coverage of the satellites, it can take 7 to 10 days or longer for the data to be completely transmitted.
The PSAT is battery powered, it relies on light levels to determine latitude and longitude. These tags also record temperature and depth. The tags are attached to the animal in various ways including adhesives, and are released to “pop up” and begin transmitting data via a galvanic release.
Many shark and ray species migrate through international waters. This causes international problems: Protected status in the Netherlands would be ineffective, if catching the shark or ray is still allowed in other countries, to which the species migrates.
There have been thousands of tagging projects. Unfortunately, not all scientists share their data, causing (expensive) duplication of projects and delay in the conservation of elasmobranchs. An excellent development in this field is the Ocean Tracking Network, in which marine species are followed through acoustic tagging. Every participating scientists has to share the info: data are also transmitted to a central network computer. The network covers more and more regions and will be extended continuously.
New Dutch project!
In the summer of 2012, ‘Sharkatag’ was organized in the Netherlands, a collaboration between the Scottish Sea Angling Conservation Network (SSACN),
Sportvisserij Nederland en Sportvisserij Zuidwest Nederland (recreational angling clubs. During this sharkfishing event participants fished for sharks from ten charter boats, leaving from Neeltje Jans. They fished for the sharks that migrate to the ‘Zeeuwse Delta’ in the summer months. In a couple of days, the anglers caught as many sharks are possible, that were all tagged SSACN is the founder of this program, and has extensive experience in the tracking en conservation of sharks. All sharks were caught and released, all anglers were educated in the handling of sharks.
In 2011 Sportvisserij Nederland started tagging starry smooth-hounds. They had a license for 15 skippers and 1,000 sharks of various species. Until the end of 2012 nearly 700 sharks were tagged. Project participants also tagged tope sharks in the Eastern Schelde. They also caught and measures stingrays, but those are not yet tagged.
The Dutch Shark Society will keep visitors informed about research projects worldwide. Visit the links on our website for shark tracking websites and Media / Video’s for videos that show shark tagging.