Diel movement patterns and habitat preferences of the common thresher shark ( Alopias vulpinus ) in the Southern California Bight (original) (raw)
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Marine Biology, 2011
The common thresher shark (Alopias vulpinus) is a secondary target species of the California drift gillnet fishery (CA-DGN) and supports a growing recreational fishery in California waters. This study used archival tags to examine the movement patterns and habitat preferences of common threshers of the size range captured in the CA-DGN (>120 cm fork length). Depth and temperature-logging archival tags were deployed on 57 subadult and adult common threshers in the Southern California Bight. Tags from five individuals (8.8%) were recovered, and 154 days of data were successfully obtained from four of these. By night, shark movements were primarily limited to waters above the thermocline, which ranged in depth from 15 to 20 m. Sharks were significantly deeper by day, and daytime vertical distribution consisted of two distinct modes: a ‘shallow mode’ (wherein sharks occupied only the upper 20 m of the water column) and a ‘deep mode’ (characterized by frequent vertical excursions below the thermocline). This modal switch is interpreted as relating to regional differences in abundance of surface-oriented prey and prey in deeper water. Maximum dive depth was 320 m, greatest dive duration was 712 min, minimum temperature experienced during a dive was 9.1°C, and dive descent rate was significantly greater than ascent rate. Sharks inhabited waters corresponding to a sea surface temperature range of 16 to 21°C. The nocturnal depth distribution of common threshers has implications for management of drift gillnet deployment depths in the CA-DGN.
Frontiers in Marine Science, 2023
We used acoustic telemetry to investigate the roles of depth and temperature in the daytime foraging behaviours of 13 tagged pelagic thresher sharks by monitoring their fine scale vertical movements in the Philippines. Cumulatively, pelagic thresher shark dives traversed the entire water column where they encountered temperatures that ranged from 33°C at the surface to 12°C at 250 m depths throughout the day, but the movements of individuals varied in the extent of both their deep and shallow water limits. Dives were not synchronized to diurnal cycles, and periodicity reflected cycles of similar dives, the dives themselves, deviations, cruising, and individuality. Pelagic thresher shark movements between the warm surface layer and cooler waters below the thermocline (155-175 m) may reflect a common Alopiid strategy that balances maintaining tolerable ambient water temperatures with opportunities to search for and forage on spatially patchy distributions of prey.
2010
This document examines movement pattern and environmental preference data collected from dusky sharks in the northern Gulf of Mexico (GOM) using pop-up satellite archival tag technology. Prior to this study, few data existed on essential fish habitat (EFH) of dusky sharks in the GOM. During summer 2008-2009, pop-up satellite archival tags (PSAT) were attached to 10 (8 adult, 2 sub-adult) dusky sharks in the northern GOM. All tags reported data, with deployment durations ranging from 7 to 124 days. A total of 426 total days of movement and habitat preference data were acquired. Dusky sharks traveled distances >200 km, primarily utilizing GOM waters along the continental shelf edge from the Desoto Canyon to the Texas/Mexican border. They spent 75% of their time between 10 125m, and 70% of their time between 23 – 30C. One dusky shark moved into the southern GOM (Mexican waters), which demonstrates the need for shared stock management of this species. This study represents the first ...
Marine Biology, 2014
southwest of the Mississippi river Delta to examine their movement patterns and habitat utilization. all tags successfully transmitted data with deployment durations ranging from 6 to 124 days. Tag data revealed shark movements in excess of 200 km from initial tagging locations, with sharks primarily utilizing offshore waters associated with the continental shelf edge from Desoto Canyon to the Texas/Mexican border. While most sharks remained in US waters, one individual moved from the northern gulf of Mexico into the Bay of Campeche off the coast of Mexico. Sharks spent 87 % of their time between 20 and 125 m and 83 % of their time in waters between 23 and 30 °C. Since dusky sharks are among the most vulnerable shark species to fishing mortality, there is a recovery plan in place for US waters; however, since they have been shown to make long-distance migrations, a multi-national management plan within the Wna may be needed to ensure the successful recovery of this population.
Tidal movements of female leopard sharks (Triakis semifasciata) in Elkhorn Slough, California
Environmental Biology of Fishes, 2010
The leopard shark (Triakis semifasciata) is one of the most common species of elasmobranch in California, and uses the shallow bays and estuaries of California extensively throughout its life history. To examine the role that tides and time of day play on the distribution and movements of leopard sharks in an estuarine environment, a total of 22 female leopard sharks (78-140 cm TL) were tagged with acoustic transmitters in Elkhorn Slough, California, USA. Eight sharks were manually tracked for 20-71.5 h, and 13 sharks were monitored for 4-280 days using an array of acoustic receivers. Overall, the distribution and movements of sharks were strongly influenced by the tides and to a lesser extent by period of day, although general patterns of movement differed depending on what region of Elkhorn Slough the sharks were using. In the main channel of Elkhorn Slough, sharks generally moved with the tide, maximizing the area over which they could forage on a more dispersed prey field. Conversely, leopard sharks within the Elkhorn Slough National Estuarine Research Reserve regularly swam against strong currents to remain in proximity to the intertidal mudflats. This high degree of fidelity to a specific region was probably due to an abundance of important prey in the area. These results indicate that movements, and thus the foraging ecology, of leopard sharks show a high degree of plasticity and are influenced by tidal stage, tidal current, availability of suitable habitat, and availability and distribution of important prey items.
California Cooperative Oceanic …, 2001
The diet of common thresher shark (Alopius vulpinus) from US. Pacific Coast waters was investigated by means of frequency of occurrence, gravimetric and numerical methods, and calculating the geometric index of importance (GII) of prey taxa taken from stoniachs collected by fishery observers from the California-based drift gill net fishery. Sampling was done from 16 August 1998 to 24 January 1999, a time when the California Current was undergoing rapid change from El Niiio to La Niiia conhtions. Of the 165 stomachs examined, 107 contained food representing a total of 20 taxa, revealing a broader trophic spectrum than previously reported for this species. Of the identifiable items, northern anchovy (Engraulis mordax) was the most important in the diet (GI1 = 48.2), followed by Pacific hake (Merluccius productus; GI1 = 31.2), Pacific mackerel (Scomber japonicus; GI1 = 24.8), and Pacific sardine (Savdinops sagax; GI1 = 9.2). Of the invertebrates, squid (Teuthoidea, including Loligo opalescenr; GI1 = 6.3), and pelagic red crab (Pleuroncodes planipes; GI1 = 6.6), were also important, especially numerically. For sharks collected north of 34% latitude, hake was the most important identifiable species in the diet; northern anchovy was most important in the south, but was not identified in stomachs collected north of Point Conception.
To fill data gaps on movements, behaviors and habitat use, both near-and offshore, two programs were initiated to deploy satellite tags on basking sharks off the coast of California. Basking sharks are large filter-feeding sharks that are second in size only to whale sharks. Similar to many megafauna populations, available data suggest that populations are below historic levels. In the eastern North Pacific (ENP) Ocean, the limited information on basking sharks comes from nearshore habitats where they forage. From 2010 to 2011, four sharks were tagged with pop-off satellite archival tags with deployments ranging from 9 to 240 days. The tags provided both transmitted and archived data on habitat use and geographic movement patterns. Nearshore, sharks tended to move north in the summer and prefer shelf and slope habitat around San Diego, Point Conception and Monterey Bay. The two sharks with 180 and 240 days deployments left the coast in the summer and fall. Offshore their paths diverged and by January one shark had moved to near the tip of the Baja Peninsula, Mexico and the other to the waters near Hawaii, USA. Vertical habitat use was variable both within and among individuals and changed as sharks moved offshore. Nearshore, most time was spent in the mixed layer but sharks did spend hours in cold waters below the mixed layer. Offshore vertical movements depended on location. The shark that went to Hawaii had a distinct diel pattern, with days spent at ∼450–470 m and nights at ∼250–300 m and almost no time in surface waters, corresponding with the diel migration of a specific portion of the deep scattering layer. The shark that moved south along the Baja Peninsula spent progressively more time in deep water but came to the surface daily. Movement patterns and shifts in vertical habitat and use are likely linked to shifts in prey availability and oceanography. Data collected indicate the potential for large-scale movements and the need for international dialogue in any recovery efforts.
Marine Ecology Progress Series, 2007
Understanding of juvenile life stages of large pelagic predators such as the white shark Carcharodon carcharias remains limited. We tracked 6 juvenile white sharks (147 to 250 cm total length) in the eastern Pacific using pop-up satellite archival tags for a total of 534 d, demonstrating that the nursery region of white sharks includes waters of southern California, USA, and Baja California, Mexico. Young-of-the-year sharks remained south of Point Conception whereas one 3 yr old shark moved north to Point Reyes. All juvenile white sharks displayed a diel change in behavior, with deeper mean positions during dawn, day and dusk (26 ± 15 m) than during night (6 ± 3 m). Sharks occasionally displayed deeper nocturnal movements during full moon nights. On average, vertical excursions were deeper and cooler for 3 yr olds (226 ± 81 m; 9.2 ± 0.9°C) than young-of-the-year animals (100 ± 59 m; 11.2 ± 1.4°C). Juvenile white sharks are captured as bycatch in both US and Mexican waters, suggesting that management of fishing mortality should be of increased concern.
2000
We used ultrasonic telemetry to determine the movement directions and movement rates of leopard sharks, Triakis semifasciata, in Tomales Bay, California. To analyze tide and time of day effects, we surgically implanted transmitters in the peritoneal cavities of one male and five female leopard sharks, which we located during summer for three to five sampling sessions lasting 12 to 24 h each. All leopard sharks showed strong movement direction patterns with tide. During incoming tides, sharks moved significantly (p < 0.0001) towards the inner bay, apparently to exploit the extensive inner bay muddy littoral zones' food resources. On outgoing tides, sharks showed significant (p < 0.0001) movements towards the outer bay. During high tide, there was no discernible pattern to their movements (p = 0.092). Shark movement rates were significantly (p < 0.0001) greater during dark periods (mean ± SE: 10.5 ± 1.0 m min −1 ), compared with fully lighted ones (6.7 ± 0.5 m min −1 ). Movement rates of longer sharks tended to be greater than those of shorter ones (range means ± SE: 5.8 ± 0.6 m min −1 for the 91 cm shark, to 12.8 ± 1.6 m min −1 for the 119 cm shark), but the leopard sharks' overall mean movement rate (8.1 ± 0.5 m min −1 ) was slower than other (more pelagic) sharks.