Invading brown bullhead catfish (Ameiurus nebulosus) show thermal niche rigidity and benthic niche plasticity: implications for management

Species invasions remain a key contributing factor to the global rise in extinction rates of native fishes in freshwater ecosystems. While efforts to remove non-native species from newly invaded water bodies often target well-established ecological characteristics and habitat associations, invasive species may exhibit different behaviour to conspecifics in their native range. Brown bullhead catfish ( Ameiurus nebulosus ) is a widespread invader characterized in their native range as a thermophilic nocturnal littoral-benthic predator with high site fidelity. We used acoustic telemetry to examine seasonal movement patterns and habitat use of catfish in Lake Rotoiti, a recently invaded lake in Aotearoa-New Zealand. Invasive catfish demonstrated strong habitat niche plasticity and thermal niche rigidity. Only in spring and summer were catfish regularly found in nearshore areas (between shore and < 7 m bottom depth). Instead, catfish were highly mobile, especially in autumn when catfish routinely occupied offshore regions (≥ 7 m bottom depth; 80% of positions), where they rarely associated with the lake bottom. Invasive catfish sought the warmest water temperatures available in the lake and their movement to offshore areas in autumn, along with marked increases in movement rates and nightly areas of use at this time, coincided with warmer waters in the offshore region. Informed by best practice, much of the catfish control effort in Lake Rotoiti relies on nearshore benthic netting. Our findings suggest that while this strategy may be effective in spring and summer, characterising and targeting thermal optimal habitat is a promising avenue.