A multi-scale approach for understanding factors limiting invasive carp distribution in the Ohio River Basin

The spread of aquatic invasive species (AIS) poses a major threat to freshwater biodiversity. Understanding the mechanisms regulating spread in invaded systems requires a multi-scale approach, as regional dispersal can facilitate arrival while local processes ultimately determine establishment and persistence. We used a dynamic multi-scale occupancy model to test hypothesized factors limiting the spread of invasive bigheaded carps (bighead carp Hypophthalmichthys nobilis and silver carp H. molitrix ) in the Ohio River, USA. Across the basin, invasion has slowed, with limited upstream colonization of either species between years. However, once present, invasive carp populations tended to persist even in apparently low numbers. Bighead carp models were relatively uninformative, due to the low number of detections. On the local scale, silver carp exhibit clear habitat and flow preferences, where populations persisted in low velocity tributary locations especially when flows are too high in the main channel. We found evidence for decreasing detection of both species of invasive carp in mid-reach and upstream pools, potentially because of lower abundance in these reaches. Our results indicated that while invasive carp were able to disperse throughout a large range of the Ohio River, upstream populations are likely sustained by immigration from established reaches and spread is likely stalled because of limited population growth rates. Our results highlight the need to focus management efforts on controlling source populations to reduce upstream dispersal. Understanding multi-scale dynamics is critical for developing effective strategies to contain invasive carp in the Ohio River and other systems.