Changes in Fish Communities Before and After Establishment of Northern Snakehead in an Estuarine Marsh of the Chesapeake Bay Watershed

Abstract Northern Snakehead Channa argus an invasive freshwater piscivore discovered in the Potomac River in 2004, has spread throughout the Chesapeake Bay (Maryland, USA). The first incidental reports of Northern Snakehead in Blackwater National Wildlife Refuge (Chesapeake Bay) occurred during 2012. Since that time, Northern Snakehead have become established and has formed the basis for a popular harvest fishery in the Blackwater River drainage. This increase in abundance has caused concern about competition and predation on other species. To determine whether the fish community has changed in composition or relative abundance in Blackwater River drainage (Blackwater River and Little Blackwater River) since the introduction of Northern Snakehead, we replicated fish community surveys from 2006 and 2007 (pre-snakehead) and compared those fish community composition with data collected from 2018 to 2019 (post-snakehead). Subsequent seasonal surveys of fishes between 2021 and 2023 helped to substantiate our findings. Including pre-snakehead and post-snakehead survey periods, we caught 35 species (32 fish species and three invertebrate species) totaling 51,781 individuals. With few exceptions, species richness was similar between periods, with 27 fishes caught pre-snakehead and 26 species caught post-snakehead. However, of 22 species that we captured during both pre-snakehead and post-snakehead survey periods, 19 declined in relative abundance, which was supported during subsequent seasonal surveys. These changes led to four of six sites having significantly different fish communities between survey periods. Fish communities experienced declines in relative abundances of popular prey species for Northern Snakehead: White Perch Morone americana, sunfish Lepomis, and killifishes Fundulus. Our study is among the first to document long-term fish community changes following establishment of Northern Snakehead in its introduced range.