Title: Distribution and relative abundance of billfishes (Istiophoridae) of the Indian Ocean
Description: "The family Istiophoridae is represented by the same five species in both the Indian and Pacific oceans. Recommended common and scientific names for these species are Indo-Pacific sailfish (Istiophorus gladius), shortbill spearfish (Tetraputrus angustirostris), striped marlin (T. audax), blue marlin (Makaira nigricans), and black marlin (M. indica). The only important commercial fishery for these fish in the Indian Ocean is the Japanese longline fishery. Longlining in the Indian Ocean began at least as early as 1926 but did not really become important until the early 1950's. Sportfishing for Istiophoridae in the Indian Ocean did not develop until the 1950's and is important at only a few locations along the east coast of Africa south of the equator. Striped marlin are distributed throughout the area from 30°S to 20°N latitude.^

Seasonal concentrations appear in the Bay of Bengal, off northwestern Australia, and along the East African coast from 0° to 10°S and in the western Arabian Sea. Sizes of longline-caught fish range from less than 100 cm in body length from orbit to fork of tail to 240 cm. The mode in most areas is around 171 to 180 cm. Limited data indicate that spawning occurs in spring in both hemispheres. Only a limited number of striped marlin are taken in the Indian Ocean by sportfishing. Blue marlin occur from 20°N to between 40°S and 45°S, with highest catch-rates between 15°N and 25°S. Seasonal concentrations occur in the general area of the Laccadive Islands, east of Mauritius, and off northwestern Java. Greatest latitudinal distribution occurs in summer in the south and in spring in the north. Lengths of longline-caught fish ranged from 121 to about 260 cm. Modes fall between 161 and 190 cm except off western Australia where fish of 201 to 231 cm predominate.^

Postlarval blue marlin have been taken during all months of the year except April in low latitudinal areas of the Indian Ocean. Very few blue marlin have been taken by sportfishing in the Indian Ocean. Catches of black marlin by longline occur at a low rate over much of the Indian Ocean from 10°N to 30°S. The only important concentration occurs between northwestern Australia and Java. Size ranges of catches is largely between 121 and 260 cm. Modal sizes are between 181 and 210 cm in all areas but the one off western Australia, where limited data indicated a mode at between 221 and 230 cm. Eleven postlarval black marlin and other data indicate spawning activity is greatest around October, and the area between northwestern Australia and Java is probably an important spawning ground. Black marlin are important sport fish along the East African coast and especially at Bazaruto Bay, Mozambique, where sportfishing for this species is centered. Catch data for sailfish is limited.^

Most catches are between 20°N and 20°S. The Bay of Bengal and the area west of the Maldive Islands show indications of some seasonal concentration in winter and spring. Weights of sportfishing catches at Malindi, Kenya, range from 20 to 110 pounds with a mode between 60 and 79 pounds. Collections of postlarvae come from off the Indonesian Islands, near the Laccadive Islands, and off Madagascar. Sailfish are important sport fish chiefly at Malindi, Kenya, where several hundred are caught each year. Shortbill spearfish are the least abundant billfish in the Indian Ocean. Catches are very scattered between 12°N and 29°S. Highest recorded catchrates occur in the Mozambique Channel and between Madagascar and Mauritius"--Page 26.
Subjects: Billfishes, Marine fishes
Places: Indian Ocean