Figure 40. Common dolphins are present vear-round m and near the 

 CINMS, though their numbers peak in Spring and Autumn. The long, slim 

 snout and vivid white side are unmistakable clues to their identity. (Photos 

 off Anacapa Island by C. Pillsbury.) 



As the name implies, common dolphms .ire, indeed, verv widely 

 distributed, occuring in all oceans to the limits ot tropical and warm 

 temperate waters. There are several distinctive forms that probably 

 deserve racial or subspecific status; some scientists recognize more than 

 one species. In the northeastern Pacific there are at least two forms: a 

 smaller, short-beaked form which occurs in three apparently separate 

 populations, north ol 52 N, between 25 N and jo N off Baja and 

 south of 1 5 N and a long beaked form found inside loo fathoms north 

 of 20 N. Where both forms are found together thev do not mi.v. 

 Common dolphins have been reported stranded as far north as 

 Victoria. British Columbia and alive to at least latitude 56 N. The 

 northernmost strandings can best be regarded as extra-limital and the 

 few confirmed sightings north of Point Conception have generally 

 occurred in spring and summer when fingers of warm water extend 

 northward. Most previous records were from tar offshore and usually 

 have been presumed associated with outer margins of the California 

 Current. In recent (1980-8;) extensive aerial surveys ot the coastal 

 waters of Central and Northern California, to 100 nm oft shore, there 

 were no observations of common dolphins at all. 



Within the SCB overall, common dolphins are the most abundant 

 small cetacean .it all seasons. Bv the most conservative estimates, 

 populations m the SCB and adjacent waters ott Baja California may 

 number in excess of 25,000 and as many as 15,000 may invade 

 productive portions ot the SCB in peak seasons. One research team 

 estimates no more than "125,000 animals in peak seasons" in the entire 

 SCB. 



In aerial and vessel searches ot the SCB, 1968-1978 (NOSC") and 

 1975-78 (BLM/UCSC), more common dolphins were seen in summer 

 and autumn than at other times of vear but at no time were these 

 animals sparse. Though some common dolphins are likelv to be seen in 

 the area ot the northern Channel Islands at any season observations in 

 those areas have been most common m spring and summer and along 

 the outer (southern and western) coasts of the islands. From surveys 

 and radiotelemetric studies, herds of common dolphins in the SCB 

 were tound to (al distribute most commonly in regions of high 

 topographic relief and avoid plains and flat areas (b) follow predictable 

 daily patterns of assembly and dispersal (cj feed nightly on organisms 

 of the vertically migrating deep scattering layer (DSL) (d) select for a 

 narrow temperature range in waters less than 28 C and (e ) calve in 

 spring and autumn. 



These are among the most visible and important top predators in 

 the SCB and in and near CINMS waters. They are listed in this 

 treatment behind white-sided and right-whale dolphins only because 

 the former two maybe more common in waters ot the CINMS, 

 themsleves. 



Figure 41. The sight of common dolphins riding the how wave can enliven 

 the seagoing part of anv visitor's experience of the Channel Islands. (Photo 

 from the Santa Barbara Channel by P. C. Howorth.) 



29 



