Twenty-Five Years of Monitoring Anadromous Sea Lamprey Spawning in the Fort River, MA: Abundance and Spawning Timing

Life history of anadromous Sea Lamprey (Petromyzon marinus), hereafter SL, on the Atlantic coast is poorly understood although it is a keystone species, particularly important in nutrient poor streams of New England, USA. In the Connecticut River, some SL are passed upstream in a fish lift and counted at Holyoke Dam, MA (river km 140). Autocorrelation analysis found a regular abundance cycle of Holyoke SL during the past 20 years with a peak every 5−6 years. We annually monitored SL spawning timing and redd abundance for 25 years (1986−2008) in an upstream and a downstream reach in the Fort River, a small undammed tributary to the Connecticut River upstream of Holyoke. During the study, 15,000−97,000 SL were passed at Holyoke and the corresponding redd numbers were 39−179 (mean, 88), with an average of 0.6% of the Holyoke SL spawning in the two Fort River study reaches. The downstream reach had an annual average of 1.3X more redds than the upstream reach (range, 3.5−0.8X). Patterns for number of redds and number of SL passed at Holyoke were similar for some years, but other years differed greatly (r² = 0.27). Redd building usually began about 5 weeks after the first SL passed Holyoke or 10 days after 50% of the SL run passed Holyoke. Spawning began in June (mean, 7 June; range, 1−22 June) and usually ended in June (mean, 23 June; range, 13 June−1 July) with a mean duration of redd building of 14.5 days (range, 6−24 days). Maximum mean daily water temperature during spawning follows: begin —18ºC (range, 14−23ºC) and end —20.5ºC (range, 17.5−23.8ºC). Mean daily discharge when redd building began was 1.81 m³ s^-1 (range, 0.51−7.45 m³ s^-1) and when spawning ended discharge was 0.60 m³ s^-1 (range, 0.28−1.56 m³ s^-1).