FISHERY BULLETIN: VOL. 75, NO. 1 



(1962) and Eberhardt and Norris (1964). Studies 

 by White and Mathews (1956) and Spencer (1973) 

 have given some information about physiological 

 functions of the whales. 



Henderson (1972) has reviewed historical data 

 on the eastern Pacific gray whale fishery and 

 speculated about previous distributions of num- 

 bers in the breeding population. 



The capture of the suckling gray whale calf, 

 Gigi, and her subsequent captivity and release 

 revealed several new aspects of young gray whale 

 behavioral and physiological biology. The various 

 studies performed on Gigi were collated and edited 

 by Evans (1974a). 



Rice and Wolman ( 197 1 ) have summarized data 

 from all parts of the migratory path and their 

 studies of 316 whales captured off San Francisco 

 provide the best information on reproductive cy- 

 cles and what might be called the migrant 

 procession. They described the sequence occupied 

 by various age and sex classes in the migratory 

 column (see also Sund et al. 1974 and Leather- 

 wood 1974). 



The study reported here will draw from these 

 works and add further information on feeding on 

 southern grounds, mating, aggression, mother- 

 calf relations, aerial behavior, respiration, and 

 tidally related movement. 



MATERIALS AND METHODS 



During 1974, capture and tracking exercises 

 were carried out using the 45-foot swordfish boat 

 Louson under the direction of Captain Tim 

 Houshar. In 1975, captures were performed from 

 the Orion (Captain Peter Zimmerman) and 

 tracking performed on the Scripps Institution RV 

 Dolphin, a 95-foot motor vessel. 



Tracks were performed using Ocean Applied 

 Research (OAR) tracking radios, model PT-219, 

 equipped with lithium batteries that generate a 

 pulsed 50-ms/s signal each time the antenna rose 

 above the surface. 4 Because the whip antenna had 

 been broken on one radio when a young whale 

 rubbed against the capture vessel during 1973 

 work, a flexible antenna equipped with a spring 

 base was substituted in 1974. This minimized such 

 antenna damage. Signals were processed with an 

 OAR automatic radio direction finder and plotted 

 on a strip chart recorder. In 1974, a multichannel 



••Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



sensing and digital recorder system developed by 

 the Biotechnology Laboratory of the Franklin 

 Institute, Philadelphia, Pa., was used to record 

 water depth (pressure) and water temperature. 



In 1975 a pressure recorder (TSK depth recor- 

 der, 0-1,000 m model) was used to record 

 maximum dive depth. 



Harnesses used in both years consisted of a 

 stretchable nylon fabric harness, reinforced at 

 appropriate points with heavy nylon straps. This 

 material was fastened to a curved aluminum back 

 plate which was protected beneath with neoprene 

 sheeting to minimize abrasion to the animal (see 

 fig. 3, Norris and Gentry 1974). Instruments and 

 the tracking radio were mounted on the plate. A 

 syntactic polyurethane foam float was molded to 

 fit over these and painted bright yellow to aid 

 visual sighting. This float provided about 0.5 kg of 

 positive buoyancy to float the harness after jet- 

 tisoning. 



Release was achieved by two means. First, 

 soluble machined magnesium bolts were used to 

 give timed release of up to 6 days duration. One 

 release during the 1975 expedition used a crystal 

 timed explosive bolt system backed up by a soluble 

 magnesium nut. The timing circuitry, which used 

 a serially charged capacitor bank, released early 

 because of a faulty magnetic switch. 



The 25-m sand hill of Colina Coyote provides a 

 fine site for observation of undisturbed whales. 

 From it an observer can see a stretch of channel 

 approximately 5 km long. Often animals within 

 the area could be identified individually by scars 

 and marks. Details of behavior such as spying out, 

 respiration, and other features were observed 

 (Figure 1). 



This dune appears to be just north of the south- 

 ern limit of most whale movement in the Boca 

 Soledad area. A moderate number of animals 

 passed the dune and swam a kilometer or so south 

 toward the north end of Devil's Bend, a narrow 

 winding channel flanked by tidal flats that ul- 

 timately connects to upper Magdalena Bay. Dur- 

 ing our observation period, we sighted no whales 

 swimming into the narrow channel itself. 



The channel in front of Colina Coyote is ap- 

 proximately 1,200 m wide, is bordered on both 

 sides by tidal flats of variable width, and has a 

 central channel of rather uniform depth, varying 

 from about 8 to 10 m. Various landmarks were 

 named by our observation team to permit easy 

 notation and reference and are noted in the inset of 

 Figure 1. A camp was established behind a small 



160 



