Low Mortality of Larval Lampreys from Electrofishing, Suction-pumping, Anesthesia, and Handling

Abstract

Native lamprey populations are declining worldwide. In the Pacific Northwest focus on conservation and management of these ecologically and culturally important species has increased. Concern has emerged regarding the effects of sampling and handling of lamprey, with little to no attention given to the larval lifestage. We monitored the survival of larval Pacific Lamprey Entosphenus tridentatus and Lampetra spp. after backpack electrofishing, deepwater electrofishing and suction-pumping, anesthesia, and handling. We performed survival trials on wild-caught lamprey (n = 15 larvae in each trial) collected from the Clackamas River drainage in Oregon, USA, coupled with control group trials from lamprey sourced from a hatchery (n = 10 larvae). Short-term (96 h) survival was >98% with only one observed mortality. Delayed mortality (1 wk) was observed for four individuals that had fungus; two of those were positive for the bacteria Aeromonas hyrdrophila. We recorded blood hematocrit as a secondary measure of stress. The baseline, nonstressed larvae hematocrit levels did not differ from those of fish that had undergone stress through electrofishing, suction-pumping, and handling without anesthesia. Electrofishing, suction-pumping, and anesthesia showed no short-term negative effects on larval lamprey although potential long-term effects remain unstudied. These techniques appear to provide efficient and relatively safe methods for collecting and surveying larval lamprey.

Pathogens of Pacific Lamprey Detected Through Routine Fish Health Screenings

“…of lamprey species is uncertain as current knowledge on this topic is greatly lagging compared with that for other fish species. The detection of A. hydrophila in larvae and A. salmonicida in adults is consistent with previous studies that have detected A. hydrophila and A. salmonicida in adult and larval Pacific Lamprey (Cummings et al 2008;Clemens et al 2009;Jolley et al 2017). The ecology of Aeromonas spp.…”

“…We used the Clackamas River subbasin as the source of larval Pacific Lamprey for captive-rearing research conducted at Eagle Creek National Fish Hatchery (Jolley et al 2015(Jolley et al , 2017. Eagle Creek National Fish Hatchery is located along Eagle Creek and is within the Clackamas River subbasin ( Figure 2).…”

“…We collected the larvae with an AbP-2 backpack electrofisher (ETS Electrofishing, Verona, Wisconsin). This electrofisher was specifically designed to collect larval Sea Lamprey (Weisser and Klar 1990) and is widely used to target the larvae of other lamprey species including the Pacific Lamprey (Torgersen and Close 2004;Stone and Barndt 2005;Reid and Goodman 2015;Jolley et al 2017). We concurrently collected samples of larval Pacific Lamprey (n ¼ 30) as part of routine fish health screenings for wild fish at this time.…”

Effects of dewatering on behavior, distribution, and abundance of larval lampreys

“…We followed a 60‐second pulse delivery by 60 s of pumping to allow displaced larvae to pass into the basket. This deepwater electrofishing method can sample larval lampreys in depths of 0.25–18 m, has an estimated capture probability (i.e., probability of collecting a larvae in the enclosure) of 0.7 (Harris & Jolley, 2017), and has caused no documented mortality or sub‐lethal effects to larval lampreys, although only short‐term (≤96 hrs) effects have been evaluated (Jolley, Uh, Silver, & Whitesel, 2017).…”

“…Capture probability ( p ) was estimated using data from an experimental tank study described in Harris & Jolley et al (2017). Capture probability ( p ) was a function of the number of larvae captured by the electrofisher's enclosure ( c i ) and the total number of larvae in the enclosure area that were thus available for capture ( A i ): …”