Marlins have the ability to thermo regulate, that is, they can control the temperature of their body at a certain limit. Thus, unlike most fish which are cold-blooded, marlins do not have to migrate to warmer waters in deep sea when winter sets in. Still, significant migration can still be seen in many marlin species – largely attributed to their taking advantage of feeding opportunities in the temperate zones during spring and summer.
Marlin spawning happens in tropical waters. Thus, fish living or foraging in temperate waters have to migrate to the warmer tropical waters during spawning season. Studies have indicated that a significant population of marlin stays in these tropical waters, though; many also migrate to colder regions.