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Publications (8)8.28 Total impact

  • Steven D. Feldkamp, Robert L. DeLong, George A. Antonelis
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    ABSTRACT: The diving patterns of 10 adult female California sea lions (Zalophus californianus) were examined during the summer breeding season on San Miguel Island, California, in 1982 and 1983 using time–depth recorders. During 17 feeding trips, representing 40.6 days at sea, animals made over 8900 dives, the deepest of which was estimated at 274 m, while the longest was 9.9 min. The majority of dives, however, were less than 3 min in duration and 80 m in depth. From estimates of body oxygen stores, we predict that dives up to 5.8 min can be supported aerobically. Therefore, cost–benefit considerations based on prey availability and encounter rate may be more important than physiological limits in shaping the foraging patterns of Zalophus. Sea lions were active virtually throughout their time at sea, resting on the surface for only 3% of the average trip. Peak diving frequency occurred during the twilight hours near sunrise and sunset. Dives were frequent, however, during all hours of the day and were typically clustered into bouts that lasted a mean (±SD) of 3.3 ± 1.5 h. We suggest that these bouts represent active feeding on discrete prey patches. During short bouts (<3 h), dive depth was less variable than for dives occurring between bouts. During longer bouts, dive depth changed in a manner consistent with pursuit of vertically migrating prey. During the 1983 El Niño, sea lions compensated for a reduction in food availability by lengthening dive bouts. These seasonal and diel variations in diving patterns suggest that the rate of prey encounter strongly influences the depth and duration of individual dives.
    Canadian Journal of Zoology 02/2011; 67(4):872-883. · 1.50 Impact Factor
  • Steven D. Feldkamp
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    ABSTRACT: The family Otariidae comprises the only group of marine mammals that habitually use their pectoral appendages to generate propulsive forces during swimming. This method of propulsion was examined in the California sea lion (Zalophus californianus), a representative member of the family. High-speed films were taken as a sea lion swam against a water current generated inside a large flow channel. Thrust production was determined by examining the body's movement at various stages of the propulsive cycle. Sea lions generate thrust continuously throughout the stroke. Over its initial three-quarters, foreflippers act as hydrofoils creating forward thrust and lift as they move vertically through the water. Thrust production is greatest, however, near the end of the stroke, when flippers are used as paddles and are oriented broad side to the oncoming flow. The force generated by this three-phased system of propulsion is likely to be greater than that attainable by either an exclusively lift-based hydrofoil or drag-based paddling style of swimming.The kinematic changes that enable sea lions to change speed were also investigated. Film records revealed that stroke amplitude became greater with speed, although total stroke duration remained essentially constant. Sea lions increase stroke frequency with velocity but large variations in the measured values suggest that changes in amplitude and flipper angle of attack are also important parameters for modulating swimming speed.
    Journal of Zoology 05/2009; 212(1):43 - 57. · 2.04 Impact Factor
  • S. D. Feldkamp, D. P. Costa, G. K. Dekrey
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    ABSTRACT: The energetic costs and behavioral changes associated with net entanglement were studied in three captive juvenile male northern fur seals, Callorhinus ursinus. Rates of energy expenditure were highly dependent upon swim velocity and size of the net fragment. At a speed of 1.1m/s, northern fur seals expended a mean (.plus-minus.SD) of 6.5 (.plus-minus.0.7) W/kg before entanglement, 9.7 (.plus-minus.3.8) W/kg when entangled in 100 g nets, and 13.8 W/kg with 200 g nets. These results showed that a free-ranging animal entangled in a net fragment of 200 g or larger will experience considerable difficulty swimming. The northern fur seals' average daily metabolic rates (ADMR) were measured with doubly labeled water over 6 day periods before and during entanglement in 225 g net fragments. Concurrent behavioral observations revealed a 75% reduction in time spent swimming and a 138% increase in time spent resting due to entanglement. Nevertheless, the northern fur seals' mean ADMR rose from 8.0 (.plus-minus.0.4) W/kg to 9.3 (.plus-minus.1.9) W/kg. While this increase was primarily due to one animal's performance, it suggests that entanglement may also elevate the costs of resting and grooming. At 17 months of age, the northern fur seals had averaged head diameters (.plus-minus.SD) of 14.7 (.plus-minus.0.2) cm, making them most susceptible to entanglement in nets with stretched mesh sizes of 23 cm or more. Observations showed that these juvenile fur seals were naturally inquisitive and rapidly became entangled upon their first encounter with a floating net. Subsequent entanglements depended more upon each animal's behavior than upon net fragment size. Captive aniamls were unable to free themselves from the entangling fragments.
    U S National Marine Fisheries Service Fishery Bulletin. 01/1989; 87(1):85-94.
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    ABSTRACT: The free-ranging dive pattern of seven adult female northern elephant seals (Mirounga angustirostris) was obtained with time-depth recorders during the first 14-27 days at sea following lactation. The instruments were recovered and mass gain at sea determined when the animals returned to the rookery at Ano Nuevo, California [USA] to molt. The seals gained a mean of 76.5 .plus-minus. 13.9 kg during a mean of 72.6 .plus-minus. 5.0 days at sea. The mean dive rate was 2.7 .plus-minus. 0.2 dives/h and diving was virtually continuous during the entire period at sea. Mean dive duration was 19.2 .plus-minus. 4.3 min with the longest submersion lasting 48 min. Mean surface interval between dives was 2.8 .plus-minus. 0.5 min, so that only 14.4% of the recorded time at sea was spent on the surface. Surface intervals did not vary with the duration of preceding or succeeding dives. Modal dive depth for each female was between 350 and 650 m. The maximum dive depth was estimated at 894 m, a depth record for pinnipeds and appears to serve in foraging, energy conservation, and predator avoidance.
    Canadian Journal of Zoology 01/1988; 66(2):446-458. · 1.50 Impact Factor
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    S D Feldkamp
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    ABSTRACT: During swimming, the California sea lion, Zalophus californianus (Lesson), generates thrust forces solely by means of its pectoral flippers. This study examines the drag, energetic cost and efficiency associated with this method of locomotion. Sea lions are highly streamlined, with a fineness ratio of 5.5 and maximum girth at 40% of body length. This profile leads to reduced drag and swimming power requirements. Films of gliding animals showed the drag coefficient (based on wetted surface area) to be 0.0042 at a Reynolds number of 2.0 X 10(6). This value is comparable to that found for other aquatic vertebrates and suggests that the sea lion's morphology helps to delay turbulent separation and maintain laminar flow over the forward portion of its body. Swimming metabolism was measured in a water flume at velocities up to 1.3 ms-1. Effective swimming speeds up to 2.7 ms-1 were attained by increasing each animal's drag. Oxygen consumption rose exponentially with velocity and for two animals was best described as VO2 = 6.27e0.48U, where VO2 is in mlO2 min-1 kg-1 and U is in ms-1. Minimum cost of transport for these animals was 0.12 ml O2 kg-1 m-1 at a relative speed of 1.4 body lengths s-1. This is 2.5 times that predicted for a fish of similar size. Swimming efficiencies were determined from these results using power output values calculated from the measured drag coefficient and standard hydrodynamic equations. At the highest velocity, aerobic efficiency reached a maximum of 15% while mechanical efficiency of the foreflippers was 80%. The results demonstrate that foreflipper propulsion is a highly efficient and comparatively inexpensive method of locomotion in aquatic mammals.
    Journal of Experimental Biology 10/1987; 131:117-35. · 3.24 Impact Factor
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    pages 247-270;
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    Pinnipeds and El Nino, eds. Fritz Trillmich et al. (Ecological studies ; 88), Berlin [u.a.]: Springer, pp. 247-270, ISBN: 3-540-53634-5.
  • Federation Proceedings. 44(4).