Why is the Arabian Sea a hotspot for myctophids?

Myctophids are the dominant mesopelagic fishes in most of the world’s oceans. They play a key ecological roleand also have a potential for harvest. We here synthesize general traits of myctophid biology and address thesuccess and life history strategy of the dominant myctophid species in the mesopelagic hotspot of the ArabianSea. In this ocean, the biomass of myctophids is particularly high, but dominated by only a few species. With lowabundance of competing small pelagic fish, much of the high production is channeled via zooplankton to thestocks of mesopelagic fishes.

The ability of the successful species to tolerate low oxygen levels facilitatesexploitation of these productive waters and reduces competition for prey. Simultaneously, the hypoxic watersprovide refuge from predators. The myctophids in the Arabian Sea feed in warm waters at night and inhabitcooler, yet relatively warm waters during daytime. We hypothesize that this temperature regime combined witha high abundance of prey provides a favorable combination of foraging and digestion.

To this adds that thelocation near the Equator provides a year-long favorable regular shift between length of day and night forforaging in upper waters and digestion in deep waters, though digestion may be constrained by low oxygenconcentrations. Myctophid species from tropical habitats have shorter life spans than species from colder regions.We suggest that in tropical habitats, such as the Arabian Sea, extended spawning seasons are common formyctophids whereas restricted spawning seasons are more common in cold-water habitats.

The Gulf of Oman,which is the upwelling region with the highest primary production in Indian Ocean, is recognized to have thegreatest potential for any commercial exploitation of mesopelagic fish.