San Diego, and at Yankee Point near 

 Monterey) supplemented with aerial 

 observations and boat surveys, have 

 fixed the timing and described most 

 aspects of that migration in detail. 



Even so. several interesting gaps 

 still exist in our knowledge of the mi- 

 grating animals. For instance, although 

 Gilmore (1969) has discussed move- 

 ment patterns of yearling whales on 

 the southern migration, there are no 

 reports on the movements of yearlings 

 during the northern migration. Simi- 

 larly, although Hubhs (1959) reported 

 that "cows with calves seem to take a 

 more offshore path." actual data on 



JAN FEB MM APR MAY JUN JUL AUG SEP OCT NOV DEC 



Figure 1. — Flight hours, 1969-72. 



the movements of mothers with calves 

 after they leave the breeding lagoons 

 are so scant that Rice and Wolman 

 (1971) simpl>' report that '"the route 

 taken by females and calves during 

 the spring migration is unknown." 

 Finally, although average rates of 

 movement for the population have 

 been computed from dates of peak 

 passage at two separate shore stations, 

 there are actual numbers for rates of 

 movement of individual animals to 

 test those averages only for the south- 

 ward migration (W\rick. 1954; Cum- 

 mings, Thompson, and Cook. 1968). 

 Since February of 1969. the author 

 has been conducting routine aerial 

 surveys of the cetaceans off southern 

 California, primarily in the area from 

 lat.34°N south to Islas Todos Santos 

 and offshore as far as 280 km. 

 Additional flights have surveyed the 



coast from Point Mugu north to Mon- 

 terey Bay in March and the area 

 from San Diego to Cedros and Guada- 

 lupe Islands in January and February. 



Ill 3^41(UP3 3 1 3^^,„„„ 



^-J 2 1 1 2 5lM 4 1 2 1^^ 



T|?1l 1 1 1 4 911 5 4 2 I'l'jJCEAN 



1J2|1 IJ 2^^5 4 5 5 62" '™^ 



Wlfri 1 !i8 5 4 7 9 9 8 



ijzil'l 1 2 2 3 412 62431*^ 



142 15 3 2 12 3 I02J3221 



1 2 



23322533366 y 

 3!2 2 2 1 1 14 2^ 



1 2 1111 1*1-|32' 



Figure 2. — Survey effort by 10-minute blocks, 

 southern migration, 1 October to 15 February. 

 Each number represents total number of times 

 that area was surveyed during this time period. 



METHODS 



Flights were made in Navy H-3 

 helicopters and S-2 reconnaissance 

 aircraft, and in twin-engine rental air- 

 craft. Survey altitudes ranged from 

 150 to 300 meters depending on 

 weather conditions. Detailed observa- 

 tions were made from as low as 15 

 meters. Although gray whales were 

 not the exclusive target of the survey, 

 for every gra\ whale sighting the 

 number and estimated size of indi\id- 

 uals. their location, swimming direc- 

 tion and speed, and details of behav- 

 ior were recorded. 



Through I July 1972 we made 74 

 flights totaling 279.7 hours of obser- 

 vation time (Figure 1). Sampling ef- 

 fort was accelerated during March. 

 April. May. and June 1972 in support 

 of the radio track of the gray whale 

 Gigi (Evans. 1972. and this publica- 

 tion) and of a common dolphin. Dcl- 

 pliiiui\ ilclphis. subsequently tagged 

 and radio-tracked from aircraft (Evans 

 and l.eatherwood. 1972). In general, 

 surveys were more extensive during 

 the period of the northern migration 

 (approximaieh mid-February through 

 Mav). 



J. S. Leafherwood is a member 

 of the staff of the Bio-Systems 

 Program. Naval Undersea Cen- 

 ter, San Diego, CA 92132. 



To facilitate data analysis, the 

 study area was divided into 10-minute 

 blocks, and tallies were maintained 

 of the number of times each zone was 

 surveyed for cetaceans whether or not 

 animals were sighted. Zones were not 

 recorded as surveyed if cloud cover, 

 fog. or surface water conditions pre- 

 vented adequate observation in the 

 area. 



Figure 3, — Survey effort by 10-mtnute blocks, 

 northern migration, 16 February to 1 June, Each 

 number represents total number of times that 

 area was surveyed during this period. 



Figures 2 and 3 summarize the to- 

 tal number of times each zone was 

 surveved during the periods of the 

 southern migration ( I October to 15 

 February) and northern migration (16 

 Februar> to I June) of gray whales. 

 Effort was concentrated off San Di- 

 ego during both periods because all 

 three airfields used are located there. 

 The substantial increase of effort in 

 the southern San Pedro Channel from 

 the southern to the northern migra- 

 tion is the result oi the aerial radio- 

 tracking mentioned above. 



During the three migratory seasons, 

 gray whale groups were sighted 91 

 times in the stud> area. Of these. 23 

 groups included mothers with calves, 

 19 included yearling whales, and 8 

 sightings represented observations of 

 the same animals on successive davs. 



46 



