Shark tagging is a specialized research technique marine biologists use to gather information about these ocean inhabitants. This method involves attaching a small device to an individual shark, which transmits or stores data about its movements and environment. The process requires precision, specialized technology, and a commitment to animal welfare.
The Scientific Rationale for Tagging Sharks
Researchers tag sharks primarily to uncover the hidden aspects of their lives. Tracking movement allows scientists to map out precise migration routes that span hundreds or thousands of miles. This mapping helps identify the seasonal ocean highways sharks use, which is information applied directly to conservation strategies.
Identifying critical habitats is another major goal, as tagging data reveals where sharks congregate to feed, breed, and give birth in nursery areas. Knowing these specific locations allows for the establishment of protected zones to safeguard vulnerable life stages. Monitoring movements also provides insights into the overall health and structure of populations, informing management decisions regarding species protection and sustainable fishing practices.
Technology Used in Shark Tracking
The choice of technology depends on the scientific question being asked, necessitating a range of specialized tags. Conventional tags are simple numbered darts that rely on the chance recapture of the shark by a fisherman or diver. This mark-recapture method provides basic information on the minimum distance traveled and growth between sightings.
For fine-scale, localized studies, researchers use acoustic tags, which are small transmitters emitting a unique ultrasonic ping. These tags require a network of stationary acoustic receivers deployed on the seafloor to log the presence of a tagged shark. This system is effective for determining residency patterns and movements within a defined area, such as a reef or bay.
For tracking movements across entire ocean basins, satellite tags are the preferred technology.
Satellite Tag Types
- Pop-up Satellite Archival Tags (PAT tags) record data like depth and temperature over several months. They automatically detach on a pre-programmed date, float to the surface, and transmit a summary of stored data to an orbiting satellite.
- Smart Position or Temperature Transmitting (SPOT) tags are attached externally to the dorsal fin. They transmit a location signal every time the shark’s fin breaks the water surface, allowing for near real-time tracking.
Procedures for Attaching Tags Safely
Attaching a tag must prioritize the safety and well-being of the shark and the research team. Researchers must follow strict ethical guidelines to minimize stress and injury to the animal. For smaller, free-swimming sharks, a basic dart tag can be deployed remotely using a specialized pole. The tag is inserted into the muscle near the dorsal fin, with the dart head anchoring beneath the skin.
For larger sharks or for deploying sophisticated internal tags, the animal is often brought alongside the vessel and safely restrained. Researchers may induce tonic immobility by gently inverting the shark, which temporarily calms it for the procedure. Sensitive tags, such as acoustic transmitters, require surgical implantation into the coelomic cavity. This involves a small incision on the shark’s underside, inserting the sterilized tag, and closing the wound with surgical sutures.
Interpreting the Data Collected from Tags
Once deployed, tags collect data that researchers analyze to gain scientific insights. Satellite tag data provides horizontal movement patterns, allowing scientists to construct maps of a shark’s journey. This data is often combined with environmental factors, such as water temperature or current, to understand influences on the shark’s route.
Acoustic and archival tags provide a detailed look into the shark’s vertical habitat use through depth and temperature profiles. Analyzing these profiles can reveal specific behaviors, such as deep-diving for foraging. Researchers use computational models to process the data, combining geolocation estimates with environmental factors to refine the shark’s probable location. The analysis confirms migratory patterns, identifies preferred water conditions, and helps predict how sharks may respond to changes in their marine environment.