Biological and life history characteristics for a previously unstudied population of sailfish, Istiophorus platypterus, in the Arabian Gulf were investigated. Notable findings include temporal-spatial migration patterns for a genetically isolated population that is threatened by overexploitation. Conventional tagging resulted in 2053 releases and 114 recaptures (5.55%) inside the Gulf. Linear displacement ranged from 2.5 to 697 km, while days at liberty ranged from 17 to 818 days. Dead recoveries in Iranian gillnets account for 88.6% of recaptures. Modeling analyses produced a best estimate of annual survival probability (S) at 0.375 (slope = -0.101, SE = 0.324). Fifteen pop-up satellite archival tags were deployed on sailfish during 2001 - 2002 to track temporal and spatial movements. Extensive data from four tags showed 83.7% of time-at-depth was spent above 10 m with no significant difference (P &lt 0.05) in diel preference. Depth ranged from 0.0 m to 61.0 m, while temperature ranged from 19.7 °C to 30.1 °C. Small-scale movements of eight sailfish were measured using ultrasonic tracking for periods ranging from 3:33 to 53:06 hours. Track distances ranged from 5.5 to 78.5 km, while linear displacement ranged from 4.6 to 37.0 km. Average speed ranged from 0.29 to 0.75 m s-1. Vertical distributions showed 84.3% of time was spent above 10 m depth, even though water temperature showed negligible variation with depth. Mitochondrial DNA comparison of 147 sailfish produced 39 composite haplotypes using eight restriction enzymes. Significant differences occurred in the frequency between population groups inside and outside the Gulf (amova 34.8%, P &lt 0.01; FST = 0.356), along with evidence of restricted migration between them (average number of migrants, Nm = 0.903). Nine year classes (0-8) were determined from aging analysis of fin spines. Females (n = 50) ranged from 0 to 8 years, while males (n = 34) ranged from 0 to 6 years. Von Bertalanffy growth function indicated rapid growth during the first two years, after which males stabilized and females continued growing to a greater maximum mean length and weight. A comparison of allometric growth between sexes indicated no significant difference between length and other morphometric characters (P ranged 0.135 0.980).