FISHERY BULLETIN: VOL. 75, NO. 1 



and other features were made. Observations of 

 aerial behavior, sound, respiration, and the re- 

 lationship between mother-calf pairs were made. 

 The sound recording system consisted of an At- 

 lantic Research Corporation LC 32 hydrophone, 

 with a response of ±4.0 dB over 0.1-100 kHz, a 

 Hewlett-Packard 466A amplifier, and a Uher 4400 

 Report Stereo tape recorder with an upper flat 

 frequency response of approximately 20 kHz at 7.5 

 ips. Signals recorded above 20 kHz are, at best, 

 nonquantitative indications of energy at these 

 levels and may also be instrumental in nature 

 (i.e., the result of ringing in one or more parts of 

 the system). 



Counts of whales and their distribution were 

 made both from shipboard and from aircraft. 



RESULTS 



Tracking Studies 



Tracking experiments were designed for a 

 maximum of 6 days and were intended primarily 

 to test logistic systems and instrumentation for 

 longer tracks. Nonetheless, examination of the 

 data provides some insights into behavior in and 

 out of the calving lagoons. Two animals were 

 equipped with radio packs and the depth/ 

 temperature tape recorder units in the 1974 test 

 series. (Details of the data system are in prep- 

 aration and will be reported elsewhere.) The first 

 whale calf (a 5.6-m total length male) was caught 

 in Bahia Grande south of Lopez Mateos on 31 

 January 1974. During capture, its mother re- 

 peatedly rose beneath the captive which slid to 

 either side off the rising body of the larger animal. 

 The adult made no attempt to entangle the re- 

 straining line, nor was there any aggression noted 

 toward the collecting vessel, which sometimes 

 approached within approximately 15 m of the 

 struggling pair. The animal, restrained by a single 

 head noose that had cinched tight anterior to the 

 pectoral fins, proved to be extremely strong and 

 required 25 min of concerted effort by eight men to 

 beach it. The harness was attached and the animal 

 was quickly returned to the mother who patrolled 

 in the nearby channel. This pair stayed in the 

 lagoon for approximately 4 days. They first moved 

 northward toward Lopez Mateos and then turned 

 and swam southward through Bahia Grande, past 

 Colina Coyote, and into the narrowing channel 

 area north of Devil's Bend. They, however, did not 

 enter this narrow (approximately 50 m wide) 



channel. Aboard the tracking vessel, we noted 

 that the animals were effectively in a cul-de-sac, 

 and that they would probably have to move 

 northward to leave the lagoon via Boca Soledad. 

 The vessel was therefore moved northward and 

 moored near the fishing village of Lopez Mateos. 

 During the night, the whale pair swam from Dev- 

 il's Bend to Lopez Mateos (22 km) and passed the 

 anchored vessel, stopping at a moderate-sized bay 

 just inside Boca Soledad. The next day the animals 

 returned downchannel past the vessel disap- 

 pearing into the region of Bahia Grande where 

 radio contact was lost. It was correctly assumed 

 that they would not pass through Devil's Bend, but 

 instead would remain in these southern channels. 

 The collecting crew then caught a young female 

 whale and instrumented it. This calf and its 

 mother immediately moved northward out of the 

 lagoon, through Boca Soledad, and began an ocean 

 traverse southward just offshore of the barrier 

 dunes. The crew was able to follow the pair by 

 shipboard direction finder over the intervening 

 dunes of Isla Magdalena for approximately 33 km 

 south of Boca Soledad when contact was finally 

 lost. That night the first cow and calf again came 

 upchannel and passed the anchored vessel at 

 Lopez Mateos moving toward the entrance at Boca 

 Soledad. It is surmised that somewhere in this 

 region the calfs harness cast loose, since a con- 

 tinuous signal was intermittently received. Only 

 when the vessel moved into the Boca itself, clear of 

 intervening sand hills, was the signal reacquired 

 fully. Directional signals indicated that it was 

 located approximately in the middle of the Boca, 

 and probably washing back and forth with each 

 tide change. It was later recovered on the beach 3 

 km north of the Boca, its instruments intact and 

 operating. 



For the 1975 tracking study a 5.3-m male calf 

 was captured directly in front of Puerto San Carlos 

 in upper Magdalena Bay, stranded on the beach 

 south of the main pier, harnessed and released 

 there. When released at 1105 h on 5 February, 

 mother and calf reunited quickly and began mov- 

 ing rapidly toward the main part of Magdalena 

 Bay. The pair skirted along the 20-m contour of 

 the main bay until deeper water at the bay en- 

 trance (along Punta Redondo at the north tip of 

 Santa Margarita Island) was reached at 0200 h, 6 

 February. The pair went directly into deep water 

 past the point, out at least to the 100-m contour 

 before curving back toward shore again at 0600 h. 

 The depth recorder on the calf later showed that 



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