Single pass electrofishing method for assessment and monitoring of larval lamprey populations

Abstract

Single pass electrofishing method for assessment and monitoring of larval lamprey populationsOur work aims at calibrating and standardizing the single pass protocol of electrofishing to assess and monitor larval lamprey populations, mainly for European populations of sea lamprey (Petromyzon marinus). The method is considered cost-effective and appropriate for use both on the scale of management decisions (from river or watershed to a regional or national scale) and as a routine assessment tool as required by the European Union Habitats Directive. Additionally, the larval surveys may be reconciled with routine electrofishing surveys for fish species, to further reduce costs. In our case, the escapement of larvae from the sampling area when using electrofishing corresponded to 18 % of larvae and 17 % of larval biomass. The general effectiveness of the protocol to determine the density and biomass of age-1 and older larvae in the prospected area was 68 % and 70 %, respectively. Finally, reference categories for density and biomass of larval populations of P. marinus in NW of the Iberian Peninsula are provided.

Salvage using electrofishing methods caused minimal mortality of burrowed and emerged larval lampreys in dewatered habitats

“…Although controls for our salvage evaluations were intended to allow us to adjust for mortality associated with transport and laboratory holding (which was nonexistent within 24 h), these results could also elucidate mortality for larval lampreys salvaged before dewatering, since during a predrawdown salvage, larval lampreys would ideally be collected by lamprey‐specific electrofishing, transported, and released into a nearby watered area. Salvaging all larval lampreys before dewatering would be optimal but is often impractical or impossible because the dewatered habitat area could be large and capture probability of electrofishing is variable and consistently less than 100% (Christie and Goddard 2003; Steeves et al 2003; Silva et al 2014; Harris et al 2016). Results for our salvage treatments in the fall suggest that mortality of salvaged larval lampreys was minimal and excavated enclosures revealed that larval lampreys that remained burrowed throughout the salvage treatment were alive and appeared unharmed, suggesting minimal mortality associated with the salvage protocols examined.…”

Sampling Methods and Survey Designs for Larval Lampreys

“…Third, monitoring data should fill specific information gaps and inform important management decisions (Nichols and Williams 2006). Fourth, we emphasize that “[t]here is no sampling method that can be used or is optimal for all cases” (Silva et al 2014). Finally, the use of standardized survey protocols can facilitate comparisons with other larval lamprey surveys.…”

“…Estimates of abundance (number of larval lampreys) and density (number of larval lampreys per unit area) SAMPLING AND SURVEYING LARVAL LAMPREYS have been used to evaluate trends over space and time (Table 3). If the goal is relative abundance across survey sites or times, then a standardized protocol for all survey sites may be a more logistically achievable method (e.g., Harvey and Cowx 2003;Slade et al 2003;Silva et al 2014Silva et al , 2016. If the goal is absolute abundance of larval lampreys, then rigorous mark-recapture (MR) or depletion studies are essential.…”

“…Capture probability is necessary to consider for larval lampreys since many may not emerge from the substrate, in part because exposure to electrofishing can result in the immobilization of larvae in their burrows (Pajos and Weise 1994; Bowen et al 2003). Capture probability from electrofishing is highly variable for larval lampreys (range = 0.13–0.82; Christie and Goddard 2003; Steeves et al 2003; Silva et al 2014; Harris et al 2016). In general, the capture probability of larval lampreys with backpack electrofishing increases in shallower water, with fewer larvae, and with greater larval length (Steeves et al 2003; see Figure 2).…”