548 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Family DELPHINIDAE. Porpoises and Dolphins 



These are small to medium-sized toothed whales 

 with numerous uniform teeth in both jaA^s. Some 

 enter fresh water, and some species in South 

 America, India, and China live there entirely. 



The dolphins of the ancients were mammals. 

 During the time of heraldry the word was con- 

 fusedly applied to both the mammals and a fish. 

 Today, the double usage still exists, and in popu- 

 lar usage the term is more often applied by lay- 

 men, at least in the United States, to the fish, 

 Coryphaena. The true dolphin is a delphinid with 

 a beak-like snout. The porpoises have a rounded 

 snout, more or less flush with the mouth. The 

 difference is not recognized by laymen, who usu- 

 ally refer to all members of this group as porpoises. 



Stenella plagiodon (Cope). Long-snouted Dolphin 



The approximate size limit of this dolphin is 7 

 feet in length. It is found on the South Atlantic 

 coast of the United States and most of the Gulf 

 of Mexico. It was only recorded from the western 

 Gulf a few years ago (Gunter 1941). Moore (1953) 

 has given many records for Florida, some of which 

 indicate that the animal leaves northern Florida 

 waters in winter. Lowery (1943) records it from 

 Louisiana. It is common in offshore waters and 

 is quite often seen in schools of 50 or more. The 

 habitat is oceanic, and it is seldom seen within 12 

 miles of the beach. The base color is purplish 

 gray, and the back is thickly studded with white 

 spots. Calves are uniformly gray. This dolphin 

 often swims just ahead of ships and plays about 

 them for long distances. It feeds on fish (Kellogg 

 1940). The southward extension of its range and 

 most points concerning its natural history are 

 unknown. 



Stetio bredanensis (Lesson), 1817. Rough-toothed 

 Dolphin 



Miller (1924) reported one specimen from 

 Tampa in 1902. The skeleton is in the U. S. 

 National Museum. This dolphin is known from 

 the warmer Atlantic and Indian Oceans. Moore 

 (1953) questioned the record on the ground that 

 the specimen might have been brought in aboard 

 ship. 



Tursiops truncatus (Montague). Bottlenose Dolphin 



This is the common "porpoise" of the Atlantic 

 coast of the United States and the Gulf of Mexico. 

 It also lives on the European coasts. The largest 



males reach a length of 12 feet. The color is 

 almost uniformly purplish gray on the back shad- 

 ing to lighter beneath. A dorsal fin is present. 



This dolphin inhabits shallow coastal waters 

 and is often found in low salinity bays and very 

 shallow water. Occasionally, it is seen 4 or 5 

 miles out to sea. More is known of its habits and 

 life history than of any other cetacean. True 

 (1891) observed the animals taken in a commercial 

 fishery for them in North Carolina and recorded 

 many facts. Wislocki and Enders (1941) were 

 able to study placentation and fetal membranes 

 more completely than has been done for any other 

 cetacean. Gunter (1942) made some contribu- 

 tions to natural history, especially concerning food 

 habits in Texas bays. There have been several 

 observations of this animal in captivity beginning 

 with Townsend (1914). McBride and his asso- 

 ciates have made particular studies of behavior, 

 intelligence, birth and postnatal care as exhibited 

 by these dolphins at Marineland, Florida. The 

 most recent paper is that of McBride and Kritzler 

 (1951). 



In the Texas bays they oft«n venture out on 

 to the flats near shore in pursuit of mullet, Mugil 

 cephalus Linnaeus, which forms a very high 

 percentage of their diet. In deeper waters they 

 subsist mainly on the sand trout, Cynoscion 

 arenarius Ginsburg, the spot, Leiostomus xan- 

 thurus Lacepede, and the croaker, Micropogon 

 undtUatus (Linnaeus). Nevertheless, they will 

 feed upon almost any species of fish and have 

 been reported to eat the hardhead catfish, Galeich- 

 thys felis Linnaeus, first chopping them in two 

 just back of the dorsal spine. Sports fishermen 

 complain because they chop tarpon and saUfish 

 off of lines after they are hooked. They are 

 also known to eat sting rays. They will even 

 ingest very small specimens of needle gar (Strongy- 

 lura) and puffers {Sphoeroides) . They apparently 

 feel an enmity toward sharks and sometimes en- 

 gage in vicious battles with them. Their stomachs 

 have been found containing large hunks of shark 

 flesh. Although they have from 22 to 24 peg- 

 shaped teeth in each jaw, dolphins prefer to 

 swallow their prey whole, and if fishes are removed 

 from their stomachs after being recently swal- 

 lowed, they are found to have not a scale dis- 

 turbed. One shrimp, Penaeus setijerus (Linnaeus) , 

 was found among some 500 fishes taken from dol- 

 phin stomachs in Texas. The late E. A. Mcll- 



