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Home > Resources & Publications > Newsletters & Magazines > Fact Sheets > Dolphin

Resources & Publications: Fact Sheets

by Jerald Horst

If ever a motto could be used to describe a fish, this one describes the dolphin (Coryphaena hippurus). This brilliantly-colored open-ocean fish is found worldwide wherever waters are above 68ºF. In the Gulf of Mexico, dolphin support a substantial fishery, primarily in the summer months.

Dolphin have an explosively fast growth rate. It may be the only fish for which scientists can measure their growth rate per day. In the Gulf of Mexico, dolphin grow at the rate of five inches per month, toping out at a maximum size of four and one-half to five feet in length in two years. Then they die! Scientists estimate that 100 percent of Gulf of Mexico dolphin die before they are two years old. Live fast-die young!

Dolphin begin spawning when they are almost 21 inches long during their first year of life. In the Gulf, spawning occurs in the summer in high-salinity offshore waters at water temperatures of 75ºF or higher. Particularly high numbers of larval (baby) dolphins have been found near the Mississippi River delta. They spawn repeatedly during the season, laying 85,000 to 1.5 million eggs per spawn, with larger fish producing more eggs.

Dolphin are eating machines. In the Gulf of Mexico and south Atlantic, they eat more triggerfish than anything else, followed by decapods (shrimp relatives), squid, jacks and flying fish.

Dolphin are pursued by both recreational and commercial fishermen, with recreational landings being six times higher than commercial landings in the Gulf of Mexico. More females than males are caught in the fishery. It seems that small fish of both sexes, and females of all sizes, spend more time around floating objects and seaweed rips, and are therefore easier to locate. Large males spend more time in open water traveling between female dominated schools near floating cover. This makes females (and small dolphins) easier for fishermen to find and therefore catch. Females resemble males in color, but have a more rounded forehead profile compared to the blunt vertical profile of male fish. The biology of this fish — short life span, fast growth rate, and early maturity — suggests that dolphin are a fish that is not easily overfished.

The dolphin may be difficult to separate from its smaller relative, the pompano dolphin, (Coryphaena equisetis). The only sure way is to inspect the shape of the tooth patch on the tongue. In dolphin it is round; in pompano dolphin it is noticeably squarish in shape. Pompano dolphin are often found offshore mixed with dolphin. It is likely that a high percentage of the small dolphin caught in the Gulf of Mexico are pompano dolphin. The maximum size of pompano dolphin is about five pounds, but they usually average much smaller.

Download: dolphin.pdf (495KB)


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