Common bottlenose dolphin

Species Description

Common bottlenose dolphins (Tursiops truncatus) are generally gray, tending to be darker on their back and lighter on their belly. They grow between two to four meters in length and can live up to sixty years. Although rare in the Salish Sea, they are among the best-studied marine mammals in the world. One population in Sarasota Bay, Florida, has been the focus of a photo-identification project for more than fifty years. 

Behavior and Ecology

Bottlenose dolphins are highly social and tend to travel in groups. They eat a variety of prey, from fish and squid to crustaceans. Like other cetaceans they can hunt using active echolocation, or they might simply listen passively for their prey. 

Range and Population Status

Bottlenose dolphins are one of the most common and widespread cetaceans. They occur all over the world in tropical and warm temperate marine habitats. Although they are protected in the United States under the Marine Mammal Protection Act, as a species they are considered neither endangered nor threatened. In the U.S., the population is divided into 81 stocks. Per the most recent estimate, bottlenose dolphins in the California-Oregon-Washington Offshore stock number about 3,500. The stock shows no apparent trend.

Threats

Because bottlenose dolphins often inhabit coastal and estuarine waters, they are exposed to a variety of human-based threats. These include fisheries bycatch, toxins and disease, chemical and noise pollution in key habitats, oil spills, and illegal feeding by humans. 

In the Salish Sea

Although bottlenose dolphins typically prefer warmer waters, and are not often found north of California, there are signs they may be expanding their range northward. Since their first record in Washington 1989 (Ferrero and Tsunoda 1989), sightings of live and stranded bottlenose dolphins have been increasing in the Salish Sea for the past two decades (Shuster et al. 2018). Individuals or small groups have been seen in 1998, and every year from 2008 through 2011, typically in the spring (Gaydos and Pearson 2011). In September 2017, a group of five or six individuals—eventually determined to belong to the California coastal stock—was regularly sighted in inland waters around Washington and British Columbia (Shuster et al. 2018). Captive bottlenose dolphins have also been used by the U.S. Navy in Hood Canal as part of a formerly top-secret program to monitor the waters around Naval Submarine Base Bangor. 

Works Cited

Ferrero RC, Tsunoda LM. 1989. First record of a bottlenose dolphin (Tursiops truncatus) in Washington State. Marine Mammal Science 5:302–305.

Gaydos JK and Pearson SF. 2011. Birds and mammals that depend on the Salish Sea: a compilation. Northwestern Naturalist 92(2):79-94.

Shuster L, Anderson D, Huggins JL, Douglas AB, Harrison N, Calambokidis J, and Berta S. 2018. "Dolphins in the Salish Sea: Are warmer water species expanding into our region?" Salish Sea Ecosystem Conference. 590.