BOTTLENOSE DOLPHIN 

 Turswps iruncatus (Montagu, 1821) 



In all areas where bottlenose dolphin systematics have been studied 

 there appear to be two ecotypes, a coastal form and an offshore form. 

 Such is the case in the SCB and in and near the CINMS. In the 

 northeastern Pacific, specimens of the two forms can be distinguished 

 by differences m size at sexual maturity, tooth diameter, parasite loads 

 and feeding habits. The living animals are, at present, impossible to 

 differentiate to form, except perhaps inferentially by distribution. The 

 coastal form, distributed along shore of Central America, Mexico - 

 including the mainland and both Baja coasts - and Southern Califor- 

 nia, IS found primarily within 1 km of shore and often enters the surt 

 zone, bays, inlets, lagoons and river mouths. The offshore form is 

 abundant and widely distributed in southern temperate and tropical 

 waters, over the coastal shelf slope and pelagic zones and around such 

 oceanic islands as the Revillagigedos, Cocos, Clipperton and Hawaii. 

 The former dolphins take a varied diet. The latter are found frec|uentlv 

 in association with pilot whales, with which thev share a diet predomi- 

 nantly of squid. 



Both coastal and offshore bottlenose dolphins are known from the 

 SCB, including waters in or near the CINMS. In a 1982 summary of 

 modern records we found the coastal ecotype documented only south 

 of southern Los Angeles County, the offshore ecotype only south of 

 Point Conception. Their populations in United States waters of the 

 eastern North Pacific were estimated to contain about 250 and 500-600 

 individuals, respectively. Within the SCB the vast majority of records 

 had been from alon^ the coast from Point Loma to about San Pedro or 

 near the southern Channel Islands (Catalina, San Clemente and Santa 

 Barbara). 



In the first half of this decade, however, significant changes have been 

 noted in the tendency of bottlenose dolphins to venture north of these 

 formerly held limits. An anonymous publication in 1978 alleged that 

 bottlenose dolphins occurred "infrequently ... in offshore currents, 

 perhaps as far north as southern Oregon" but presented no evidence. In 

 1982 a single animal stranded dead near Eureka, California fFrom 

 available evidence this specimen was thought to be of the offshore 

 type). One must be cautious in interpreting such strandings as evidence 

 of range extension as the specimen(s) may have died elsewhere and 

 simply drifted ashore. The type specimen of Tursiops gilli is a specimen 

 from "Monterey" and there is a single skull dredged from inside San 

 Francisco Bay. These two records are similarly weak bases for extending 

 the species' range north of Point Conception. But a recent series of 

 sightings of live bottlenose dolphins deserves more serious considera- 

 tion in deliberations about geographical range. 



In November 1982, bottlenose dolphins were seen and pho- 

 tographed 25 km north of San Pedro. Among them were individuals 

 photo-identified in a study farther south, off La Jolla, by Larry 

 Hansen, of NMFS. Between January 1985 and December 1985 we 

 recorded or received reports of i 1 sightings of bottlenose dolphins 

 between Bass Rock and Carpenteria Beach, all along the north shore of 

 the Santa Barbara Channel. During the same period the Santa Barbara 

 Museum of Natural History noted seeing a bottlenose dolphins near 

 Santa Barbara and U. S. Fish and Wildlife Service personel observed 



Figure 42. Bottlenose dolphins, like many other cetaceans, can be identified 

 by unique pigmentation and scarring patterns. These individuals were 

 catalogued and monitored in a study of movement patterns between Ocean- 

 side and San Diego. In the early 1980s some of them moved north with the El 

 Nino, reaching Santa Cruz and spending protracted periods along the 

 mainland coast of the Santa Barbara Channel, i Photo courtes)' of Larry 

 Hansen NMFS/SWFC. ) 



some near Piedras Blancas. In igSj, staff of the California Marine 

 Mammal Center observed bottlenose dolphins, with Pacific white- 

 sided dolphins, off the Farallon Islands. Of greatest interest, however, is 

 the occurrence between October 1985 and January 1984 of some ten 

 sightings near Santa Cruz, California. Involved were some 25-50 

 indivuduals, including animals known by photographs from much 

 farther south. At least four of these "photo-tagged" animals have been 

 seen subsequently off La Jolla. two in January and two in March 1984. 

 Reasons for the movements have not been quantitatively demonstrated 

 but are thought to be related to recent warming of California coastal 

 waters, associated with a protracted "El Niiio" current and resulting 

 shifts in prey of bottlenose dolphins. 



Bottlenose dolphins can be expected within the CINMS at anytime, 

 thouirh their use of the area and the number of animals involved may 

 fluctuate within and among years as a function of varying environmen- 

 tal features. In any case, populations using the SCB and CINMS 

 appear relatively small and, therefore, likely vulnerable to disturbance. 

 Elsewhere, for example, bottlenose dolphins are often caught and 

 killed accidentally or incidentally in fishing nets. Growing use of gill 

 nets and continuing use of seine nets in the SCB is, therefore, a cause 

 for concern as they might affect this species. Further, bottlenose 

 dolphins from the SCB have been found to have the highest polutant 

 levels yet measured among mammals. Though the effects of such 

 pollutants on marine mammals are not clear, they are not likely to be 

 beneficial to the dolphins. The high levels occurring in this species in 

 the SCB are cause for special vigilance. 



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