What Is Biotelemetry? How Can It Be Used In Marine Biology Today?

Biotelemetry can be described as the tracking of biological organisms by using electronic or satellite tags that send the data via radio waves in the atmosphere. There are a wide range of devices used in biotelemetry. These include devices that can record environmental conditions such a temperature, depth and salinity which are either attached to the animal or implanted into the animal. They also record the animal’s position on earth (Berrow and Connor 2013). Biotelemetry has a huge range of uses such as studying the ecology of an animal, its foraging, migration and behaviour. It can be used to examine an animal’s physiology in terms of its diving capacity. Tagging marine animals can give scientists information in marine habitats that are inaccessible. Biotelemetry can be a key tool in conservation and management as it can give information on survival rates and hotspots of certain species. There are several different types of tags including (Global Positioning System) GPS tags, archival tags, and time-temperature-depth recorders. GPS tagging has become increasingly popular in animals that take on large scale movement in the ocean (Witt et al. 2010). GPS tags are usually attached to the animal and then released after a period of time.

The Argos System is a satellite system which receives the data from the GPS tags and the data can then be downloaded. The system works using the Doppler Effect. The tags usually have to be recovered by recapturing the animal or by self-release. Archival tags are used to record environmental conditions in relation to the animal tagged. These tags can record data for prolonged periods of time from months to years (Welsh and Eveson 1999). These tags can record temperature, light and depth. Archival tags are a very effective tool in gaining large amounts of information on an animal’s ecology. They are also known as pop off tags as they can be set to self-release to the surface of the water. Time-temperature-depth recorders (TDR’s) are mainly used to examine the diving habits of marine animals. They can also record how fast an animal swims, the temperature of the environment and the temperature of the stomach of the animal. These tags do not send the data to a satellite it is stored in an internal memory. This has its advantages and disadvantages when compared to the satellite tags.

Biotelemetry is paramount in the study of migration and navigation of marine animals such as the Atlantic Bluefin Tuna (Thunnus thynnus) (Block et al. 2005). 772 fish were tagged and the results showed that there was extensive migrations of these fish. From the data it could be seen that some fish made transatlantic migrations to spawning areas in the Mediterranean Sea. There were hotspots identified in the north of the Gulf of Mexico. After this study there was restrictions put in place where longline fishing occurs. This was to reduce the number of mortalities from bycatch. This study resulted in procedures put into place in order to conserve T. thynnus, showing that biotelemetry is vital in the conservation of endangered species. The long distance migrations of sea turtle is one of the most remarkable in the animal kingdom. Adult turtles migrate several thousands of kilometres of seas to nest and lay their eggs. These beaches can be on remote and isolated islands (Lohmann and Lohmann 1996). It is widely thought that turtles use magnetic cues in order to navigate the seas but there is little known about this. Luschi et al. (2007) tagged 20 Green Turtles (Chenonia mydas) and released them away from their nesting beached in Mozambique. They also attached magnets to 13 turtles. The study showed all but one returned to the nesting site. The turtles with magnets showed a longer navigation. This was the first study to show that turtles used magnetic cues in their navigation. The use of biotelemetry in this study was hugely important in understanding how turtles navigate across oceans. Biotelemetry is key in marine biology today in terms of conservation and management of marine animals. Whale sharks (Rhincodon typus) are the largest fish in the world, they can reach up to 18 meters.

They are listed as endangered now and are in the conservation lists in ICUN (International Union for Conservation of Nature) and CITES (Convention of International Trade in Endangered Species of Wild Fauna and Flora) (Hsu et al. 2008). R. typus were tagged in the greater Sulu Sea region off the coast of the Philippines. Two sharks travelled distances of 4567km and 8025km. The sharks migrated through many political jurisdictions (Eckert et al. 2002). This study proved that this population needed to be managed on a regional level. The use of biotelemetry in marine biology can also be used to study the behaviour of animals which can be linked to foraging behaviour. A study done by Doyle at el. (2015) examined the behaviour known as knifing in Blue Sharks (Prionace glauca). It is when the shark swims at the surface of the water and the dorsal fin breaks the water. This behaviour was observed when studying the sharks but the reason behind it was unknown. Five sharks were tagged off the coast of Cork, Ireland and it was noted that knifing behaviour was seen in all sharks. The frequency of the behaviour increased at dawn and it was concluded that the sharks were optimizing foraging opportunities at twilight due to the prey being more visible. Biotelemetry is important in the study of marine biology today as it can be used to study the behaviour and mortality rates of certain animals after they have been released from being caught in fishing line. P. glauca are the most common discarded fish in commercial longlining (Campana et al. 2009). In a study by Campana et al. (2009) examined the effects of discarding on P. glauca. Forty sharks were tagged in Canada while swordfish longlining was taking place. It was seen that mortality was estimated at 35% and 95% of mortality occurred within eleven days after release. This was more than likely due to trauma and not starvation.

This study showed that discarding has an effect on the shark’s behaviour and can lead to death. Biotelemetry can be used to study foraging and migration but it can also be used to study the diving capacity of marine animals. Most marine animals make short shallow dives there are only a few that can make long deep dives. Biotelemetry studies on Leatherback sea turtles (Dermochelys coriacea) have revealed that they can up to 1000 meters (Eckert et al. 1989). Some mammals can hold their breath and dive for up to forty minutes like the Elephant Seal (Miroung) (Boeuf et al. 1998). Studies done by Kooyman and Ponganis (1998) examined the dive depths of Weddal seals. They examined lactic acid levels in the seal before and after dives and it was seen that the dives were aerobic. It was seen that the animals had an Aerobic Dive Limit of twenty minutes and lactic acid would increase after this. The Aerobic Dive Limit is the amount of time the animal could stay under the water without using its anaerobic metabolism. It was noted that on regular dives they rarely surpass their Aerobic Dive Limit. If they do surpass it they have increased surface intervals so as to allow the lactate in the muscles decrease.

Although biotelemetry and biologging are crucial in marine biology research today there are some disadvantages associated with them. They can be expensive, if tags are fitted with depth, pressure and time sensors each tag can be expensive. If an animal need to be captured to be tagged there is a risk of causing trauma and stress to the animal. In some cases t it can be fatal (Mech and Barber, 2002). There can also be issues with retrieving tags as they may get lost, batteries running out and inaccuracies in statistical data. There are new advances in technology now that are overcoming these difficulties such as stronger batteries and mathematical packages to solve any inaccuracies in the data. Even though there are some disadvantages over all biotelemetry and biologging are hugely advantageous in marine biology today. They allow scientists to gain an insight into the behaviour, migration and navigation, of animals. This research can then be used in the conservation and management of species that are endangered such as T. thynnus and R. typus. It is a powerful tool in science that has allowed marine biologists an insight to environments that can be hostile and inaccessible to humans. It can give information about the environment around the animal which can lead to a more in-depth about climate change and the effect it is having on the oceans.