DIEL BEHAVIOR OF THE BLUE SHARK, PRIONACE GLAUCA, 

 NEAR SANTA CATALINA ISLAND, CALIFORNIA 1 



Terry C. Sciarrotta 2 and Donald R. Nelson 3 



ABSTRACT 



The diel activity levels and movements of the blue shark, Prionace glauca, were studied in the natural 

 environment using ultrasonic telemetry. Two initial sharks were tagged with single-channel trans- 

 mitters equipped with depth sensors. Twelve sharks were tagged with multichannel transmitters with 

 various combinations of sensors to measure depth, swimming speed, swimming direction, and temper- 

 ature. From March to early June, the sharks made an evening-twilight migration from their 

 epipelagic daytime habitat to the shallower waters bordering the island. From late June to October, the 

 sharks remained offshore throughout the day and night. This change in movement pattern is suggested 

 to be in response to a seasonal shift in location of prey. The telemetry data indicated that the blue shark 

 is basically nocturnal, showing highest activity in the early evening and lowest activity in the early 

 daylight morning. Measured parameters increasing at night included 1) rate of horizontal movement, 

 2) swimming speed, 3) variability in depth, and 4) variability in swimming direction. The sharks 

 usually remained within a relatively narrow range of water temperatures. 



This paper describes a study in which the diel 

 activities of an epipelagic shark were monitored 

 remotely in the natural environment. Multichan- 

 nel ultrasonic transmitters were used to telemeter 

 certain behavioral and environmental parameters 

 of free-ranging blue sharks, Prionace glauca (Lin- 

 naeus). The primary objective was to track the 

 sharks continuously throughout the day-night 

 cycle to determine diel patterns of activity and 

 movement. 



Prior to the initiation of this study, surprisingly 

 little had been published on the behavior of the 

 blue shark, one of the most abundant large pred- 

 ators in warm temperate seas. Bigelow and 

 Schroeder (1948) summarized what was then 

 known about the biology of the species. Suda 

 (1953) studied embryonic development, size re- 

 lationsips, and sex ratios as related to distribution 

 in the north tropical and subtropical Pacific. 

 Strasburg (1958) investigated the distribution, 

 abundance, capture depths, reproduction, and food 

 habits of pelagic sharks, including the blue shark, 

 in the central Pacific. Miscellaneous data on blue 



'Adapted in part from the Masters Thesis of the senior author, 

 Sciarrotta. 



department of Biology, California State University, Long 

 Beach, Calif.; present address: Southern California Edison, 

 Water Quality Biology Group, 2244 Walnut Grove Ave., Rose- 

 mead, CA 91770. 



department of Biology, California State University, Long 

 Beach, CA 90840. 



Manuscript accepted February 1977. 

 FISHERY BULLETIN: VOL. 75, NO 3, 1977. 



sharks have been reported from the Atlantic 

 ( Aasen 1966), the Canadian Atlantic (Templeman 

 1963), and the Gulf of Alaska (LeBrasseur 1964). 

 A study of the blue shark off southern California, 

 still largely unpublished, was conducted by Bane 

 (1968). 



More recently, the blue sharks off southwest 

 England have received investigation in regard to 

 age determination, reproduction, diet, and migra- 

 tion (Stevens 1973, 1974, 1975, 1976; Clarke and 

 Stevens 1974). Casey, Stillwell, and Pratt at Nar- 

 ragansett, R.I. have gathered considerable infor- 

 mation on the biology of sharks of that area, in- 

 cluding data on migrations, food habits, and 

 reproduction of blue sharks (Weeks 1974; Casey 

 1976; Stevens 1976). Tag returns from these 

 studies have documented some long-range, long- 

 term movements by blue sharks in the Atlantic. 

 Several similar movements have also occurred in 

 the Pacific (Bane 1968; D. R. Nelson, unpubl. 

 data — see Discussion). Short-term movements, 

 however, such as related to the diel cycle, have not 

 been described for the blue shark. 



Observations relating to the diel patterns of 

 sharks have been mentioned by several authors 

 (Springer 1963; Limbaugh 1963; Randall 1967; 

 Hobson 1968), but specific quantitative studies 

 have been few. Nelson and Johnson (1970) found 

 that the horn shark, Heterodontus francisci, and 

 the swell shark, Cephaloscyllium ventriosum, 

 exhibited distinctly nocturnal activity patterns 



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