Curves and complexity of riverine fish invasions

Non-native aquatic species are of global conservation concern, in which potential impacts on native biodiversity are often assessed at watershed scales. The Potomac River watershed, a tributary of the Chesapeake Bay in the eastern United States, represents a model example of this concern, as it contains a high proportion of non-native fishes. We examined distribution ranges of 46 non-native and 30 native fishes in West Virginia waters of the upper Potomac River watershed based on temporal changes in the area of occupied 12-digit hydrological units (HUC-12s). In terms of native fishes, we assessed the percent change in the number of occupied HUC-12s between two time periods (1871–1979 and 1980–2023). Conversely, we assessed lag, exponential growth, and asymptotic phases of range expansion for each non-native fish. Reductions and expansions of ranges exceeded 10% change for 10 and 5 native fishes, respectively. Invasion curve models were fit to occurrence data from 21 of 46 non-native fishes, whose expansions ranged from 1015 to 8310 km 2 . Native fishes more frequently experienced range reductions while almost half of all introduced non-native fishes increased their ranges, a finding that broadly aligns with observations worldwide on anthropogenic alterations and associated reshaping of aquatic faunas.