DAILY PATTERNS IN THE ACTIVITIES OF SWORDFISH, 

 XIPHIAS GLADIUS, OBSERVED BY ACOUSTIC TELEMETRY 



Francis G. Carey' and Bruce H. Robison^ 



ABSTRACT 



Horizontal and \ertical movements ofswoidfish were studied using acoustic telemetry. Five swordfish 

 in the Pacific and one in the Atlantic were tagged with transmitters which provided information on 

 location, depth, and surrounding water temperature. Two of the Pacific fish showed a clear daily cycle 

 of movement between an inshore bank during the day and deep water offshore at night. All of the 

 swordfish responded to light, sv\imming deep during the day and coming near the surface at night. In 

 the Pacific depth during daylight appeared to be limited to about 100 m by the oxygen-minimum layer, 

 but in well-oxygenated waters of the Atlantic, a midday depth of greater than 600 m was recorded and 

 the fish appeared to follow an isolume. Depth of the Atlantic fish in daylight was related to changes in 

 light caused by variation in water transparency. The vertical movements were associated with 

 temperature changes of as much as 19° C within 2 hours. The implications of rapid vertical movements 

 on buoyancv and swim bladder volume are discussed. 



Despite their high commercial value and their 

 significance as one of the large predators of the 

 open ocean, relatively little is known about the 

 habits and behavior of the swordfish, Xiphias 

 gladius. The information which is available comes 

 chiefly from observations made at the sea surface 

 by commercial fishermen and from a few scientific 

 studies based on commercial captures. Swordfish 

 are large, fast-swimming fish that offer little 

 opportunity for direct observation; however, some 

 aspects of their behavior can be readily examined 

 by telemetry from attached sensors. 



Xiphias gladius is found throughout tropical 

 and temperate waters. Its appearance in higher 

 latitudes usually occurs in warm-season aggre- 

 gations along the edge of the continental shelf and 

 on offshore banks (Rich 1947; Wise and Davis 

 1973). The seasonal appearance of swordfish in 

 both the western North Atlantic and Hawaiian 

 fisheries (Uchiyama and Shomura 1974; Caddy ) 

 coupled with the known distribution of their 

 larvae and of adults with ripe gonads indicate a 

 spawning migration to waters warmer than 23°- 

 24° C (Arata 1954; Taning 1955; Gorbunova 1969; 

 Markle 1974; Nishikawa and Ueyanagi 1974), 



'Woods Hole Oceanographic Institution, Woods Hole, MA 

 02543. 



^Marine Science Institute, University of California, Santa 

 Barbara, CA 93106. 



'^Caddy, J. F. 1976. A review of some factors relevant 

 to management of swordfish fi.sheries in the northwest Atlan- 

 tic. Environ. Can., Fish. Mar. Serv., Tech. Rep. 633, 42 p. 



while nonspawning fish appear to move between 

 coastal and oceanic waters. Tagging studies show 

 that some swordfish undertake long-distance 

 movements. For example, a 12 kg swordfish 

 tagged near the Mississippi Delta in March 1974 

 was recovered from Georges Bank at a weight of 

 86 kg in August 1977 (Casey^). The recovery of 

 tagged swordfish near the point of release, even 

 after several years at large (Beckett 1974), implies 

 homing behavior if we assume that these fishes 

 are regular migrators. 



Longline fishery captures of swordfish occur 

 primarily at night on hooks set at depths of 5-50 m. 

 Deeper vertical excursions have been documented 

 by DSV Alvin when the submersible was attacked 

 by a swordfish at 610 m (Zarudski and Haedrich 

 1974) and by observation from Deepstar at 654 m 

 (Church 1968). The harpoon fishery relies on the 

 occurrence of swordfish near the surface during 

 the day where they are commonly found resting in 

 the warmer surface waters, often with their dorsal 

 and upper caudal fins exposed. In this situation 

 they can be approached and harpooned. This 

 "basking" behavior may warm the fish and aid in 

 the digestion of prey caught while foraging at 

 greater depths. Spotter pilots for the harpoon 

 fishery report that basking swordfish often defe- 

 cate before sounding or breaching. 



Manuscript accepted December 1980. 

 FISHERY BULLETIN: VOL. 79, NO. 2, 1981. 



■'John G. Casey, .^pex Predator Program. Northeast Fisheries 

 Center Narragansett Laboratory, National Marine Fisheries 

 Service, NOAA, Narragansett, RI 02882, pers. commun. 1978. 



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