Coastal Research and Education Society of Long Island
Coastal Research and Education Society of Long Island

Bottlenose dolphins

By: A. H. Kopelman


Bottlenose dolphins

Bottlenose Dolphin (Tursiops truncatus)

The common bottlenose dolphin (Tursiops truncatus) is one of the best known of the cetaceans (whales, dolphins, and porpoises); a cosmopolitan species found in the coastal and offshore waters of the world’s temperate to tropical seas. As in most other dolphin species, T. truncatus are social animals. While the typical social group consists of 10-20 individuals, larger aggregations can be found.

In the North Atlantic, during the summer T. truncatus can typically be found offshore as far north as Nova Scotia; and inshore, typically from Long Island southward.

In the waters of the Western North Atlantic two distinct types, the Northern Migratory Coastal Stock and the offshore stock have been identified. These types differ not only in their distribution (coastal morphotypes, in warmer, shallower near shore waters less than 7.5 km from shore; offshore morphotypes, in deeper, cooler waters greater than 35 km from shore); they also differ morphologically, differ in their diet, differ in their typical parasite loads, and they differ genetically (different mitochondrial DNA haplotypes).

It is thought that the coastal morphotype is distributed continuously along the Atlantic coast, from south of Long Island, around the Florida peninsula, and along the coast of the Gulf of Mexico. Coastal T. truncatus from the Gulf of Mexico and the Western North Atlantic are known to belong to two different stocks, based on mitochondrial DNA differences. It wasn’t until recently that an accurate delineation of the stock structure of the Western North Atlantic coastal morphotype had been developed. According to the NOAA Fisheries 2015, Stock Assessment Report (SAR), the Western North Atlantic Northern Migratory Coastal Stock is now considered to be composed of “a complex mosaic of coastal bottlenose dolphin stocks.” NOAA Fisheries now recognizes 5 coastal stocks: the Northern Migratory Coastal stock, the Southern Migratory Coastal stock, the South Carolina/Georgia Coastal stock, and the Northern Florida Coastal and Central Florida Coastal stocks. The coastal bottlenose dolphins of NY and New England are members of the Northern Migratory Coastal Stock.

While the coastal morphotype had occasionally been seen north of New Jersey,  sightings of large groups were rare. In late June 2009, a large group of bottlenose dolphins was sighted near Glenn Cove, NY, and through July 2009, a group of 200 coastal morphotype bottlenose dolphins was sighted in elsewhere in Western Long Island Sound (Cold Spring, Huntington, Northport, Hempstead, Oyster Bay, Smithtown and Rye). Over the next few weeks the group (or others like it) were seen further east in the Sound, and ultimately were sighted and photographed near Montauk Point in early August 2009 and  again in early September 2009.

In 2011 and 2012, the summer sea surface temperatures around Long Island were the warmest, on average, ever recorded.  Those two years saw a tremendous increase in the abundance and distribution of the inshore morphotype bottlenose dolphin, essentially found in larger aggregations along the entire south shore of LI.  During the summer of 2013, sea surface temperatures were much cooler, and the inshore bottlenose dolphins were once again more limited in their distribution. Since 2014, coastal bottlenose dolphins have become a regular compenent of the cetacean fauna in the waters of NY

RELATED SITES

2015 NOAA Fisheries Stock Assessment Report -Western North Atlantic Northern Migratory Coastal Stock
2016 NOAA Fisheries Stock Assessment Report for Offshore Stock of Bottlenose dolphins