Diel movement patterns and habitat preferences of the common thresher shark (Alopias vulpinus) in the Southern California Bight

Abstract

The common thresher shark, Alopias vulpinus, is the basis of the largest commercial shark fishery in California waters. We used acoustic telemetry to determine the diel movement patterns and habitat preferences of this species in the Southern California Bight (SCB), where commercial fishing for the common thresher shark is concentrated. Eight common threshers (fork length: 122–203 cm) were tagged with temperature and depth-sensing acoustic transmitters and tracked for periods ranging from 22 to 49 h. Tracked sharks preferentially utilized deep offshore waters, and avoided shallower waters over the continental shelf. Mean rate of movement (ROM ± s.d.) was 2.15 ± 0.46 km h−1. ROM and angular concentration (r, a measure of relative linearity) both showed a strong daytime pattern, with highest values at dawn that decreased throughout the day, whereas nocturnal ROM and r were less variable. Daytime vertical movements consisted of either vertical excursions below the thermocline or relatively level swimming within the upper portion of the thermocline. Nocturnally, all sharks remained within the mixed layer. These findings suggest that the common thresher shark is primarily a daytime predator, and have relevance for estimating how the alteration of the set depth of fishing-gear could affect catch rates of this species in the SCB.

Post release survival and movement patterns of roosterfish (Nematistius pectoralis) off the Central American coastline

“…Upon release, roosterfish moved away from the capture site, sounded to the seafloor and displayed reduced vertical activity for 2 to 3 h after release, all responses consistent with short-term capture stress (Cartamil et al, 2010). Similar recovery periods have been reported in other tracking studies of pelagic fishes and sharks (Carey & Scharold, 1990;Holland et al, 1990a;Holts & Bedford, 1993;Pepperell & Davis, 1999).…”

“…Although this observation does not assure longer-term survival, postrelease feeding is a critical step that must occur in order to facilitate recovery (Aalbers et al, 2004;Cooke & Schramm, 2007;Meka & Margraf, 2007). We also observed repeated periods of increased vertical movements (oscillations) during the track sessions, behaviors that have been shown to be associated with foraging activity in several pelagic species (Carey & Lawson, 1973;Pepperell & Davis, 1999;Sepulveda et al, 2004;Cartamil et al, 2010;Nakamura et al, 2011). These behaviors also contrast the unidirectional movements commonly associated with moribund behavior (Moyes et al, 2006;Heberer et al, 2010).…”

“…The effect of fish size and fight time on the mean depth and horizontal rate of movement (ROM) were evaluated using regression analyses. ROM values were calculated as described by Cartamil et al (2010), while assuming straight-line distances between position recordings at 5 min intervals. Hourly ROMs were plotted against time of day and data were analyzed for diurnal differences using a paired t-test.…”

Development and Trial of Deep-set Buoy Gear for Swordfish, Xiphias gladius, in the Southern California Bight

“…Additional information from consultations with active California DGN participants as well as depth distribution statistics for swordfi sh and other species that coinhabit the SCB (previous studies and concurrent short-term PSAT deployments) were also used to tailor DSBG confi guration (Holts and Bedford, 1990;Sepulveda et al, 2004;Sepulveda et al, 2010;Cartamil et al, 2010;Dewar et al, 2011).…”

Abundance, habitat use and movement patterns of the shovelnose guitarfish (Rhinobatos productus) in a restored southern California estuary

“…Shovelnose are the most commonly landed batoid in Baja California (Márquez-Farias 2005), where fishers catch them exclusively during the summer in shallow bays (Salazar-Hermoso and Villavicencio-Garayzar 1999). The artisanal elasmobranch fishery in Baja has been economically and culturally important for decades with catch rates over 30 000 tonnes year -1 (Cartamil 2009). The longevity and intensity of the shovelnose fishery in Baja California and results from our study suggest that shovelnose in the FTB are not philopatric, as a highly philopatric population in Baja would certainly have been extirpated by now considering the high degree of fishing pressure on this species.…”