LEATHERWOOD ET AL-: DISTRIBUTION AND MOVEMENTS OF GRAMPUS GRISEUS 



data. The following information on effort, from 

 which we feel reliable trends may be determined, 

 exists for the survey programs in the study area. 



From San Diego to Equator — National Marine 

 Fisheries Service (NMFS) observers, aboard 

 tunaboats working primarily out of San Diego, 

 Calif, surveyed the area from San Diego south to 

 the Equator from 1966 through 1975. The major- 

 ity of effort was concentrated in January and Feb- 

 ruary, declining rapidly through April to no effort 

 in the Commission Yellowfin Regulatory Area 

 (CYRA) of the Inter-American Tropical Tuna 

 Commission by the third quarter (Figure 2). It is 

 evident that there has been very little effort in the 

 nearshore portion of the tropical CYRA during the 

 third and fourth quarters, although there were six 

 chartered cruises between September and De- 

 cember. Far-offshore fishing and research activity 

 continued throughout the year. Because the ves- 

 sels return north to San Diego, running anywhere 

 from 12 mi offshore to beyond the continental shelf 

 off Baja California, effort appears to have been 

 adequate throughout that area to detect major 



seasonal changes in composition of marine mam- 

 mal fauna. This is the only program for the area 

 for which extensive and quantified data on effort 

 and sightings were available. 



Since 1968, cruises of the Naval Ocean Systems 

 Center, San Diego (NOSC, formerly Naval Under- 

 sea Center), have examined the continental shelf 

 area off northwestern Baja California during 

 winter and spring (October-December and 

 February -April I. Vessels of the Scripps Institu- 

 tion of Oceanography with marine mammal ob- 

 servers aboard have cruised extensively among 

 the San Diego-Guadalupe Island-Cedros Island 

 triangle for over 30 yr. 



Southern California Continental Border- 

 land — Survey effort has been extremely heavy 

 over the continental shelf from Ensenada north to 

 Point Conception. Norris and Prescott (1961) re- 

 ported on activities of Marineland of the Pacific, 

 primarily between Catalina and Santa Barbara 

 Islands and the mainland shore near Los Angeles. 

 Leatherwood (1974), Evans (1975), and Leather- 

 wood and Walker ( 1979) summarized NOSC aerial 



40° N 



FIGURE 2.— Relative numbers of hours io"n 



of observation by NMFS/SWFC obser- 

 vers aboard tunaboats in the eastern 

 tropical Pacific by quarter of year, 

 1974-75. 



