Studies on the Age and Growth of the Atlantic Sailfish, Istiophorus Americanus (Cuvier), Using Length-Frequency Curves

Length frequencies of 8630 young to adult Atlantic sailfish, Istiophorus americanus, from southern Florida, the western Bahamas and the Gulf of Mexico were plotted by month for a three-year period. Growth is rapid during the apparently short life span, and fish hatched in June appear to reach a modal value of about 56 inches total length by November, at which time they weigh about seven pounds. At one year they have increased to 72 inches and an average weight of 21 pounds. By their second summer they are about 85 inches long and weigh about 43 pounds. The length increment drops off rapidly, and by their third year sailfish are about 92 inches long, with an average weight of 63 pounds. Interpretation beyond this point is difficult, but apparently few fish reach four years of age. There is great variation in weight for a given unit of length, particularly in the longer specimens. A 92-inch fish may weigh from 42 to 109 pounds, with an average weight of 63 pounds. An apparently high natural mortality in this species is reflected in the occurrence of only two major year classes in the sport fishery during any one month. During the winter months nearly half of the sport fishery is composed of six-month old fish. The conservation value of a Florida law that now prohibits the possession of more than two sailfish is questioned. It is suggested that tagging experiments now in progress be intensified during the winter months and that these be confined largely to the smaller specimens.