Effects of the presence of subadult longfinned eels (Anguilla dieffenbachii) on cover preferences of juvenile eels (Anguilla spp.) in replicate channels

Abstract

The effects of the presence of subadult (420–875 mm total length (TL)) longfinned eels (Anguilla dieffenbachii Gray) on day‐time cover preferences of three juvenile size groups (small = <100; medium = 100–199; large = 200–299 mm TL) of shortfinned eels (A. australis Richardson) and longfinned eels were tested in replicate channels provided with natural (macrophytes, cobbles, woody debris) and artificial (shade, plastic pipes) cover. Macrophytes, cobbles, and woody debris were the most frequently occupied cover by both species of juvenile eel, whereas overhead shade and plastic pipes were rarely used. In most instances, the subadult longfinned eels occupied the macrophytes, the cover type preferred by juvenile eels when tested in the absence of subadult eels. The small juvenile eels used the three natural cover types similarly between species, whereas the cover preferences of medium and large juvenile eels differed between species—whether tested in species unmixed or mixed situations, shortfinned eels preferred macrophytes and longfinned eels preferred cobbles. It is concluded that as juvenile eels increase in size in the wild, their cover preferences will be more restricted because of greater interaction with that of predatory subadult eels in the population.