TOOLS OF THE TRADE
We use a combination of tag types to answer questions related to shark habitat use and movement behaviors that make them vulnerable to fishing. In this study we are placing satellite linked pop-off archival tags (PAT) on several key* shark species such as; blue, mako, thresher, silky, oceanic whitetip and hammerheads. Satellite archival tags such as the miniPAT shown below (Wildlife Computers. Redmound, WA, USA) gather environmental data such as depth, temperature, and light levels during their deployments. Using light levels to get sunrise and sunset times, combined with environmental data, and user inputted data (tag location, species average swim speed), a computer model generates a series of likelihood positions. These data allow us to examine horizontal (across latitude and longitude) and vertical (across depth) habitat use of pelagic sharks and are essential addressing key issues such as: 1) the overlap of horizontal and vertical habitat use with commercial fishing and 2) how changes in ocean temperatures across latitude and depth will shift or alter the movement and distribution of these species.
We also use acoustic or 'pinger' tags (V16s, Vemco, Nova Scotia Canada). Each tag emits a unique series of sonic pings at 69 kHz at randomized intervals between 2 and 3 minutes. When the shark swims within the hearing range of an acoustic receiver, a timestamp is logged for the individual animal at that location. Our team maintains an array of acoustic receivers on the state operated Fish Aggregating Device (FAD) buoys off the windward coast of Oahu coast and off the Kona coast of Big Island. With these tags we are trying to understand FAD associative behavior, residency and are looking for any patterns in arrival or departure times that may help inform fishers on ways to avoid interactions.
Identification (ID) or spaghetti tags each have a unique 4-digit identification number and contact information. Fishers can place these tags on sharks when they are hooked incidentally. Information recorded from the fishers for each tagged shark will help us gather details about which species are interacting with which fisheries, estimations of depredation rates and costs to fishers, and provide details on when sharks are present. It will also help us understand whether certain individuals are responsible for a large proportion of depredation events, or if the whole population has learned the behavior. Additionally, we can acquire valuable biological information from the recapture of tagged sharks such as, growth rates and residency.
*Key shark species are the species that all nations must report fishery interaction data to regional fishery management organizations.