UC San Diego

The common thresher shark Alopias vulpinus) is a pelagic species that constitutes the largest commercial shark fishery in California waters. Despite its commercial value, little is known of thresher shark biology, nor is there adequate data on which to base fishery management decisions. This dissertation entails four studies dealing with the biology and fisheries interactions of common thresher shark in the Southern California Bight (SCB). Chapter 1 examines the movement patterns of adult and subadult thresher sharks using acoustic telemetry. These larger threshers preferentially inhabit waters offshore of the continental shelf, inhabit shallow waters nocturnally, and may make extensive vertical excursions by day that are suggestive of foraging. In Chapter 2, movement patterns of larger threshers are further examined over extended time periods through the use of archival tagging. Archival data show that in addition to exhibiting diel periodicity in movement patterns, threshers undergo distinct modes of daytime depth distribution for extended periods that are interpreted as relating to regional difference in abundance of surface oriented prey and prey in deeper water. Chapter 3 investigates the habitat utilized by juvenile threshers and shows that they preferentially inhabit waters over the SCB continental shelf as a nursery area. Chapter 4 describes the artisanal fishery for threshers and other elasmobranchs along the Pacific coast of Baja California Norte, Mexico. It was found that 44 artisanal fishing camps are located in the region, of which at least 26 target elasmobranchs. In addition, the detailed species, size, and sex composition of elasmobranchs captured at the Laguna Manuela fishing camp is reported. Finally, Chapter 5 provides a synoptic view of the contributions made by this dissertation towards the current status of knowledge regarding thresher shark life history, ecology, and fisheries biology