EMPIRICAL LENGTH AND WEIGHT CONVERSION EQUATIONS FOR BLUE MARLIN, WHITE MARLIN, AND SAILFISH FROM THE NORTH-ATLANTIC OCEAN

Because commercially caught billfishes are usually processed at sea. a nd because size measurements are usually taken after the fish have bee n dressed, there is a need for conversion among different measures of size (length or weight) for assessment and management purposes. Here, we present empirical equations for converting among measures of size f or blue marlin, Makaira nigricans; white marlin, Tetrapturus albidus; and sailfish, Istiophorus platypterus, from the North Atlantic Ocean. A series of length-length equations allows conversion from any of six length measures to lower jaw-fork length; and a series of length-weigh t and weight-length equations allow conversion between lower jaw-fork length and round weight. To estimate the equations, we used large data sets that have recently become available. We incorporated bias correc tions into the length-weight and weight-length equations and used robu st regressions for the length conversions. Equations for each species are given by sex and also for combined sexes, so that conversions can be made whether the sex of the specimen is known or not.