Space invaders: searching for invasive Smallmouth Bass (Micropterus dolomieu) in a renowned Atlantic Salmon (Salmo salar) river

Humans have the ability to permanently alter aquatic ecosystems and the
introduction of species is often the most serious alteration. 
Non-native Smallmouth Bass (Micropterus dolomieu) were identified in
Miramichi Lake c. 2008, which is a headwater tributary to the Southwest
Miramichi River, a renowned Atlantic Salmon (Salmo salar) river whose
salmon population is dwindling.  A containment programme managed
by the Department of Fisheries and Oceans, Canada (DFO) was implemented in
2009 to confine Smallmouth Bass (SMB) to the lake.  We utilized
environmental DNA (eDNA) as a detection tool to establish the potential
escape of SMB into the Southwest Miramichi River.  We sampled at
26 unique sites within Miramichi Lake, the outlet of Miramichi Lake (Lake
Brook), which flows into the main stem Southwest Miramichi River, and the
main stem Southwest Miramichi River between August and October
2017.  We observed n=6 positive detections located in the lake,
Lake Brook, and the main stem Southwest Miramichi downstream of the
lake.  No detections were observed upstream of the confluence of
Lake Brook and the main stem Southwest Miramichi.  The spatial
pattern of positive eDNA detections downstream of the lake suggests the
presence of individual fish versus lake-sourced DNA in the outlet stream
discharging to the main river.  Smallmouth Bass were later
confirmed by visual observation during a snorkeling campaign, and
angling.  Our results, both eDNA and visual confirmation,
definitively show Smallmouth Bass now occupy the main stem of the
Southwest Miramichi.