Gregory S. Silver

Occupancy and Detection of Larval Pacific Lampreys and Lampetra spp. in a Large River: the Lower Willamette River

Abstract Pacific lampreys Entosphenus tridentatus (formerly Lampetra tridentata) are declining in the Columbia River basin, and the use of large, main-stem river habitats by larvae of this species is unknown. We used a deepwater electrofisher to explore occupancy, detection, and habitat use of larval Pacific lampreys and larval Lampetra spp. in the lower Willamette River, Oregon. We used a generalized random tessellation stratified approach to select sampling quadrats (30 × 30 m) in a random, spatially balanced order. Pacific lampreys, Lampetra spp., and unidentified lampreys were found in the Willamette River; larvae were detected in all areas except the Multnomah Channel. We calculated reach- and quadrat-specific detection probabilities and the amount of sampling effort required for 80% confidence that larval lampreys were in fact absent when they were not detected. Lampreys were detected in a variety of areas (although relatively low numbers were collected), including shallow, nearshore areas; midchann...

Detection and Longevity of Uncured and Cured Visible Implant Elastomer Tags in Larval Pacific Lampreys

Abstract Studies of the biology, ecology, and status of the Pacific lamprey Lampetra tridentata may require effective means of tagging larval Pacific lampreys. However, few assessments of the methods suitable for tagging larval Pacific lampreys have been conducted. We evaluated the performance of visible implant elastomer (VIE) tags in larval Pacific lampreys, specifically testing the effects of elastomer treatment (uncured versus cured VIE) and inspection light source (ambient light versus blue light-emitting diode [LED] flashlight) on tag detection in 40 larvae. Through day 251 after tagging, tag detection was 100% for both uncured and cured VIE tags observed under ambient light and blue LED light. Longevity of uncured VIE tags was assessed in a second cohort of 32 VIE-tagged larval Pacific lampreys over a 2-year captive rearing period. Percent VIE tag detection was 91% for red tags, 90% for orange tags, and 64% for green tags through day 699 after tagging. This study affirms that both uncured and cured...

Simple Genetic Assay Distinguishes Lamprey Genera Entosphenus and Lampetra: Comparison with Existing Genetic and Morphological Identification Methods

AbstractSeveral species of lamprey belonging to the genera Entosphenus and Lampetra, including the widely distributed Pacific Lamprey E. tridentatus and Western Brook Lamprey L. richardsoni, co-occur along the West Coast of North America. These genera can be difficult to distinguish morphologically during their first few years of larval life in freshwater, thus hampering research and conservation efforts. However, existing genetic identification methods are time consuming or expensive. Here, we describe a simpler genetic assay using the Pacific Lamprey microsatellite locus Etr-1; the assay was found to be 100% reliable in distinguishing Entosphenus from Lampetra, even in genetically divergent Lampetra populations. Using a sample of 244 larvae (18–136 mm TL) from the Columbia River basin, we tested the accuracy with which previously described differences in caudal fin pigmentation can distinguish these genera. Attempts at morphological identification were abandoned for 50-mm and smaller larvae because diff...

An Experimental Evaluation of Electrofishing Catchability and Catch Depletion Abundance Estimates of Larval Lampreys in a Wadeable Stream: Use of a Hierarchical Approach

AbstractSome lamprey species are in decline, and assessments of local abundance could benefit research and conservation. In wadeable streams, larval lampreys are collected by using specialized backpack electrofishing techniques, although catchability has not been sufficiently evaluated. We assessed removal models for estimating the local abundance of larval lampreys in experimental net-pen enclosures within a wadeable stream. Known numbers of larvae were seeded at densities of 4–130 larvae/m2 into 1-m2 enclosures that were lined with fine sand and placed into Cedar Creek, Washington (Columbia River basin). Depletion sampling in each enclosure (n = 69) was conducted by three to five electrofishing passes, and abundance was estimated by six removal models that assumed different catchability functions. Catchability averaged 0.28. For the standard removal model, which assumed that catchability varied independently by enclosure but not by pass, the 95% highest posterior density credible intervals (95% HPD-CIs)...

Evaluation of Methods to Measure Condition in Pacific Northwest Larval Lampreys

Abstract Pacific lamprey (Entosphenus tridentatus) populations are declining and western brook lamprey (Lampetra richardsoni) status is unknown in the Pacific Northwest. Accurate measures of fish condition are a basic requirement to monitor health and status of fish populations. Fultons condition factor has traditionally been used to assess condition of larval lamprey but alternative field-based and laboratory-based measures have not been assessed. We compared condition factor, body density, and lipid content of sympatric larval Pacific lamprey and western brook lamprey in 2010 and 2011 from two rivers of the Pacific Northwest. Condition factor was higher for Pacific lamprey than it was for western brook lamprey. All measures were variable and correlations among condition indices were weak. Body density and lipid content were higher in western brook lamprey in one year suggesting the possibility of increased energy requirements of metamorphosis to a nontrophic adult stage. The body density technique was onerous and likely has little field-based practicality. Body density and lipid content had a negative relationship as increased lipids leads to a more buoyant and less dense fish. Condition factor did not appear to be a good predictor of lipid content in our study and a suite of complex factors, including lipid dynamics prior to metamorphosis and nutritional resources, may underlie these results. This study provides one of the few empirical datasets on sympatric lampreys with different life history strategies.