Stealthier than we thought

In Freycinet Marine Park off the Tasmanian coast, a school of jackass morwong (Nemadactylus macropterus) hovers behind a Melbourne skate (Spiniraja whitleyi) attempting to feed on a baited remote underwater stereo video system (stereo-BRUV), which works by attracting fish into the camera's field of view using bait in a container on the end of a pole – a method that has become an internationally endorsed best practice (Methods Ecol Evol 2020; doi.org/10.1111/2041-210X.13470) for monitoring the diversity and size of marine fishes. The Melbourne skate – the largest of Australian skates – feeds on or just beneath the ocean floor, preying on mobile invertebrates and small benthic fishes. Skates are known to excavate buried prey by “wing flapping”, to stir up bottom sediment; by hydraulic mining, whereby repeated jaw opening and closing generates water flow in and out of the buccal (oral) cavity and resuspends food and sand; and lastly, by suction. The jaws of skates are only loosely connected to the cranium, an anatomical development that allows these cartilaginous fish to protrude their jaws a short distance from their heads when feeding. This action, in turn, creates suction for picking or pulling prey off the sea bottom, accompanied by sediment. The latter is ejected out of the skate's mouth, spiracles, or gill slits once the food is separated from the sediment within the mouth.