Recovery potential assessment of Northern Brook Lamprey (Ichthyomyzon fossor) - Saskatchewan-Nelson River populations (Designatable Unit 2)

Abstract

The known distribution of Northern Brook Lamprey (Ichthyomyzon fossor) in the Saskatchewan-Nelson River designatable unit (DU) is limited to southeastern Manitoba, including the Whitemouth River (~ 3.4 km2) and its tributary, the Birch River (~ 0.7 km2). The status of Northern Brook Lamprey in the Winnipeg River is unknown. Ichthyomyzon larvae, but no Northern Brook Lamprey adults, have been captured in the Winnipeg River at its confluence with the Whitemouth River. Northern Brook Lamprey cannot be distinguished from Silver Lamprey (I. unicuspis) at this life stage, and consequently the Winnipeg River does not form part of the species’ known distribution. Northern Brook Lamprey are typically found in pools and runs of cool streams. Water depths are typically > 0.1 m with slow or moderate velocities. Larval lamprey are found in substrates dominated by sand and some silt, organic detritus, and small gravel that allows for burrowing. Adults typically burrow in coarser substrates prior to spawning. Spawning occurs in late spring to early summer in shallow riffles on gravel dominated substrate when water temperatures are 13 to 22°C. The most serious threats to Northern Brook Lamprey are inadequate stream flow and excessive water temperature. Future climate change scenarios are anticipated to exacerbate these threats. Additional threats were considered to have a lower impact, including non-native species (and their complex interactions), agricultural and forestry effluents, dams and water management/use, other ecosystem modifications (e.g., shoreline development), and mining and quarrying. Based on a population model, Northern Brook Lamprey were predicted to be highly sensitive to perturbations in vital rates that affect recruitment, and age 1–3 larval survival. The Northern Brook Lamprey minimum viable population (MVP) size for a 1% probability of extinction over 60 years was estimated as 8,752 [95% confidence interval: 3,924, 16,316] adults. The minimum area required to support a recovered population is highly dependent on the density of Northern Brook Lamprey that could be supported in available habitat, both of which are poorly understood for the Whitemouth and Birch rivers. Very little is known about the Northern Brook Lamprey Saskatchewan-Nelson River DU. Key knowledge gaps exist around co-occurrence and biological distinction from Silver Lamprey, population distribution and abundance, availability of suitable habitat, life-history characteristics, and sensitivity to, and frequency of threats.