Direct and indirect effects of barriers to migration: Pacific lamprey at McNary and Ice Harbour dams in the Columbia River basin

Barriers to migration, such as dams, roads, and areas of deforestation, can have bothdirect (mortality and migration delay) and indirect (increase in disease susceptibility, decrease ingenetic variability, and increase in predation) effects on anadromous fish. This study focused onpassage performance for adult Pacific lamprey (Lampetra tridentata) at McNary and Ice Harbordams. During the 2005 and 2006 migration season (summer and early fall), 120 adult lampreywere collected at McNary Dam on the Columbia River and equipped with a half-duplex passiveintegrated transducer (HD PIT) tag and a coded radio transmitter, and an additional 70 fishreceived only a HD PIT tag to assess passage success and behaviour at this stage of theirmigration. Of the radio-tagged fish released 1 km below McNary and Ice Harbor dams, 48.8%(39/80) and 55.0% (22/40), respectively, returned to the dam and were detected outside of afishway entrance. At McNary Dam, 61.5% (24/39) of the fish that approached an entrance eventually passed the dam and at Ice Harbor Dam, 59.1% (13/22) passed. Median dampassage times for the radio-tagged lamprey were 2.1 and 2.3 days at McNary and Ice Harbordams, respectively. Individual lamprey movements through the fish ladders showed thatpotential problem areas for adult lamprey at McNary and Ice Harbor dams included fishwayentrances, the top of transition pools, and areas associated with diffuser grating.During the 2006 season, 29 adult Pacific lamprey were collected at Bonneville and McNarydams and were assayed for the presence of known fish pathogens and then processed forproximate analysis. In the disease analysis, Aeromonas hydrophila was the only pathogenidentified, found in 6 of the 29 lamprey inspected. Proximate analysis of the crude fat contentshowed that adult Pacific lamprey collected at Bonneville Dam had a mean lipid content of 91 gversus 59 g at McNary Dam, representing a 35% decline in lipid reserves over a distance of 235km