The Coastal Dolphin Project examines the population ecology of bottlenose dolphins (Tursiops truncatus gilli) in California inshore waters with particular emphasis on Monterey Bay.

During the present century, coastal bottlenose dolphins have been absent from the sighting record for the central California coast and northward. Based on strandings and natural history studies, the normal range for coastal bottlenose dolphins in California was considered to be from Point Conception southward, and sightings between Point Conception and Point Dume were considered rare before 1982-83. Historical records depict a rather different picture. A bottlenose dolphin skull was collected in Monterey Bay in 1871, another, estimated to be 50-100 years old, was recovered in San Francisco Bay in 1958, and a third skull was dredged in Richmond, Contra Costa County, in 1980, indicating the presence of this species in central California waters in the past. Records unfortunately do not indicate whether this presence was due to a temporary shift in range or if it was indicative of long-term residency.

The reappearance of coastal bottlenose dolphins along the central California coast, as far north as Monterey Bay, was attributed to the 1982-83 El Nino Southern Oscillation (ENSO) event, which caused massive movements of traditionally warmer water prey to northern latitudes and may have affected the dolphins foraging efficiency, causing them to move further north. Maldini-Feinholz determined that bottlenose dolphins found in Monterey Bay were part of a larger population inhabiting coastal California waters from Ensenada, Mexico, to at least as far north as San Francisco; this is among the widest known ranges occupied by the same population of bottlenose dolphins. Transit times between San Diego and Monterey Bay, an 837-kilometer one way trip, ranged from 66 to 74 days, but no data is currently available on the periodicity with which individuals travel within this range. This information would greatly enhance the possibility of understanding the ecological significance of these movements and their relationship to food availability or temperature changes.

The current best estimate of the number of coastal bottlenose dolphins between San Diego and San Francisco is only 206 individuals, although the overall population size may be up to about 450-500 animals. Clearly, due to the small size of this population and its coastal habitat, there is cause for concern about its conservation status (currently classified as “data deficient” NOAA 2007). In order to ensure proper management in the long-term, studies need to be conducted to monitor population trends and status, as well as to clarify threats.

Coastal bottlenose dolphins spend their lives within two kilometers of shore and can be seen easily from the beach. Since these dolphins live so close to shore, they are likely to be impacted by human activities, such as by-catch in fisheries, prey depletion, recreational boating, coastal pollution, and loss or degradation of habitat due to coastal development. Previous analysis of the tissues of a handful of stranded animals found alarmingly-high concentrations of organochlorines, such as PCBs and DDTs, in blubber, which could have devastating effects on dolphin reproduction, health, and survival. However, strandings are rare events, making such information difficult to come by. As stated by Lowther, “Diligent monitoring of health and water quality for the coastal population should begin as they are a small population susceptible to harmful anthropogenic and land run-off influences due to their narrow ‘coastal corridor’ habitat.

Okeanis and the Coastal Dolphin Project

The Coastal Dolphin Project has been in operation since 1990 and is led by Dr. Daniela Maldini. The long-term goal of the study is to understand all aspects of the ecology of coastal bottlenose dolphins and their role as top predators in the coastal strip. Studies have been underway to determine population size, social structure, long range movements and distribution patterns. The population in Monterey Bay is now well known and was found to be composed of individuals that use Monterey Bay as a core area, but also move either seasonally or periodically to other areas of the coastline such as the Southern California Bight. El Nino may play a significant role in determining the frequency and extent of bottlenose dolphin overall movement along the California coastline. However, gender specific movements appear to occur. We have identified several male alliances which exhibit strong pair bonding and a tendency to roam more widely than the rest of the population. This has been observed in other bottlenose dolphin populations. Through collaborative studies with Dr. Maddalena Bearzi at the Ocean Conservation Society in Santa Monica Bay, we seek to understand the movement patterns and long-term habitat use along the entire California coast. To do this we are exchanging photo-identification information for known individuals seen in both Monterey Bay and Santa Monica Bay over time.

In collaboration with Dr. Thomas Jefferson at the National Marine Fisheries Service/Southwest Fisheries Science Center in La Jolla, we are currently conducting targeted biopsy sampling (to determine gender (using skin samples), and contaminant, stress, and reproductive hormone levels (using blubber). In addition, in collaboration with Dr. Alessandro Ponzo, a veterinarian, we are looking at the incidence and severity of skin conditions in animals with known sighting histories to hopefully understand the linkages of these conditions to the environment.