Connectivity among White Shark Coastal Aggregation Areas

Connectivity among White Shark Coastal Aggregation Areas in the Northeastern Pacific

Salvador Jorgensen, Taylor Chapple, Scot Anderson, Mauricio Hoyos, Carol Reeb & Barbara A. Block

In book: Global Perspectives on the Biology and Life History of the Great White Shark,

Ed. Michael L. Domeier, CRC Press: 159-168.

DOI: https://doi.org/10.1201/b11532-16

Abstract 

White Sharks (Carcharodon carcharias) in the northeastern Pacific comprise a genetically distinct population, demographically isolated from other populations in Australia/New Zealand and South Africa. Within the northeastern Pacific, mature and subadult White Sharks show strong fidelity to aggregation sites in Central California and Guadalupe Island, Mexico, respectively. Individuals tagged at both sites migrate offshore to common pelagic habitats but routinely return to the coastal site where they were tagged. To date, evidence for the connectivity of these coastal sites has been lacking, raising the question whether they comprise one continuous or two distinct populations. A third coastal area, comprising the near-shore waters from Point Conception, California, and extending southward through the Southern California Bight to Sebastian Vizcaino Bay, Mexico, has been recognized as a White Shark nursery area. Although incidental catches in the Southern California Bight comprise mostly neonates and large females, little evidence exists demonstrating the movement of mature females to this purported pupping area, leaving open the possibility that parturition might occur elsewhere followed by immigration of neonates into the nursery area. We illustrate how rare events in a large tagging data set provide important information about the connectivity of aggregation areas within the northeastern Pacific. Acoustic tagging revealed the rare movement of one single female out of 140 deployments, from Central California to Guadalupe Island; the first result to demonstrate movement connecting these aggregation sites. Of 97 pop-up archival transmitting (PAT) tags deployed in Central California, only one deployment was on a large female with healing mating scars indicative of prior mating activity. This female was tracked offshore and eventually into the Southern California Bight where the tag popped up 362 d later off Santa Catalina Island. The movement of this female into the Southern California Bight coincided with the peak period for neonates in the area.