Using eDNA and Electrofishing to Detect Larval Pacific Lamprey in Sediments

Hart Crowser for Port of Portland

Lorraine Brown, Exa’s statistician, was asked to support Hart Crowser and the Port of Portland to fulfill the requirements of the Port’s maintenance dredging permit. The dredging permit required a study to measure presence/absence and, if possible, density of larval Pacific Lamprey (Entosphenus tridentatus) in berthing areas prior to dredging. Hart Crowser conducted several surveys using the Larval Lamprey Electrofishing System (LLES) method across multiple sites in the lower Willamette and Columbia rivers including several Port of Portland shipping terminals and nearby control areas. Sediments from a subset of the LLES sampling locations were collected and tested for Pacific Lamprey environmental DNA (eDNA). Controlled laboratory studies using both detection methods were also conducted to test the viability of using eDNA for estimating presence and density.

Exa was contracted to estimate occupancy rates and density from these lamprey datasets. Presence within an area was confirmed when lamprey ammocoetes were observed with the LLES survey. The absence of observed lamprey ammocoetes, however, does not guarantee they were truly absent. Exa used results from the LLES lab studies and the field surveys to estimate the probability of occupancy using Bayesian analyses. The field eDNA results were evaluated as an alternative predictor of occupancy. Ms. Brown found that concordance between LLES and sediment eDNA field surveys was positive, and Receiver Operator Characteristic (ROC) curves could be used to identify optimal eDNA thresholds associated with LLES-confirmed lamprey presence. Ms. Brown’s results showed that sediment eDNA samples are a promising method for detecting the presence of larval Pacific Lamprey in sediments.