Migratory Behavior of Adult Sea Lamprey and Cumulative Passage Performance through Four Fishways

We describe a study of PIT-tagged lamprey ascending 4 fishways comprising 3 designs at two dams on the Connecticut River, USA.  Migration between dams was rapid (median migration rate = 23 km d^-1). Movement through the fishways was much slower, however (median = 0.02 - 0.33 km d^-1). Overall delay at dams was substantial (median =13.6 - 14.6 d); many fish failed to pass (percent passage: 29% - 55%), and repeated passage attempts compounded delay for both passers and failers. Cox regression revealed that fishway entry rates were influenced by flow, temperature, and diel cycle, with most lampreys entering at night and at elevated flows, but with no apparent effect of sex or length.  Overall delay was influenced by slow movement through the fishway, but repeated failures were the primary factor determining delay. These data suggest that although some lamprey were able to pass fishways they did so with difficulty, and delays incurred as they attempted to pass may act to limit their range.