Impact of satellite linked radio transmitting (SLRT) tags on the dorsal fin of subadult and adult white sharks (Carcharodon carcharias)

Abstract

Satellite linked radio transmitting (SLRT) tags provide long-term, high accuracy, near real-time tracking data for marine wildlife. Adult white sharks (Carcharodon carcharias Linnaeus, 1758) in the northeastern Pacific at both Guadalupe Island, Mexico and Southeast Farallon Island, USA were tagged with SLRT oval and inline finmout tags. These tags provided up to 7.4 yrs of tracking data. A previous study showed structural dorsal fin damage for SLRT tagged juvenile and subadult white sharks off South Africa. Sharks tagged in the northeastern Pacific were resighted between 1 and 11 yrs post tagging and included 10 adults and 2 subadults. Sharks that were resighted did not exhibit significant fin deformation, although in one case the oval finmount tag did cause bending of the dorsal fin due to tag shape, weight, and placement of the tag on the dorsal fin. Four inline tags came off after deployments of at least 2.2 to 3.7 yrs (based on date of last message received), and two of these caused a tear to the trailing edge of the dorsal fin upon release. Overall, SLRT tags provided long-term tracking data and there was no apparent impact on the behavior or migration cycles of the sharks. Serious dorsal fin deformation seems to occur in the case of juvenile and subadult white sharks where the fin is rapidly growing and thus for tracking juvenile white sharks, alternate methods should be considered.