Giant Trevally - Biology and Ecology

Biology and Ecology

The giant trevally is a solitary fish once it reaches sexual maturity, only schooling for the purposes of reproduction and more rarely for feeding. Juveniles and subadults commonly school, both in marine and estuarine environments. Observations from South African estuaries indicate the schools of smaller juveniles tend not to intermingle with schools of other species, but larger subadults are known to form mixed-species schools with the brassy trevally. Research has been conducted on the movements of larger fish around their habitats, as well as the movement between habitats as the species grows, to understand how marine reserves impact on the species. Adult giant trevally are known to range back and forth up to 9 km along a home range, with some evidence of diel and seasonal shifts in habitat use. In the Hawaiian Islands, giant trevally do not normally move between atolls, but have specific core areas where they spend most their time. Within these core areas, habitat shifts during different times of the day have been recorded, with the fish being most active at dawn and dusk, and usually shifting location near sunrise or sunset. Furthermore, large seasonal migrations appear to occur for the purpose of aggregating for spawning, with this also known from the Solomon Islands. Despite not moving between atolls, they do make periodic atoll-wide journeys of up to 29 km. Long-term studies show juveniles can move up to 70 km away from their protected habitats to outer reefs and atolls. The giant trevally is one of the most important apex predators in its habitats, both as adults on reefs and as juveniles in estuaries. Observations in relatively untouched waters of the northwestern Hawaiian Islands showed the giant trevally was of high ecological importance, constituting 71% of the apex predator biomass, and was the dominant apex predator. This number is considerably less in heavily fished Hawaiian waters. At smaller sizes, the species is prey to sharks, and large individuals have been recorded as a host of the sharksucker, Echeneis naucrates, a fish which is normally seen attached to the undersides of sharks.