Updated Lake Chubsucker RPA 2011-2020

This Recovery Potential Assessment provides updates to knowledge of Lake Chubsucker (Erimyzon sucetta) in Canada from 2011–2020. Information contained herein replaces previous advice. The current distribution of Lake Chubsucker is limited to 11 distinct areas in the Great Lakes basin: Old Ausable Channel, L Lake, Lake St. Clair, dyked marshes within the Lake St. Clair drainage, St. Clair National Wildlife Area (NWA), Point Pelee National Park, Rondeau Bay, Long Point Bay, Long Point NWA, Big Creek NWA (dyked marshes), and Lyons Creek. The species is thought to be extirpated from three historical areas: Jeannette’s Creek, the upper tributaries of Big Creek, and Tea Creek. Adult Lake Chubsucker are generally found in clear, shallow, still, well-vegetated waters. Substrate in these systems is generally composed of organic matter, silt, sand, and, to a lesser extent, clay and gravel. Juvenile and young-of-year (YOY) captures from L Lake were found over substrate composed mainly of organic debris, and vegetative cover (combination of submerged, floating, and emergent) was greater than 70%. Recent sampling of the St. Clair NWA East cell found all life stages associated with dense mixed stands of submerged aquatic vegetation. To achieve ~99% probability of persistence, given a 15% per generation chance of catastrophic population decline (50% or higher), requires ~33,600 age-1 and older Lake Chubsucker and at least 0.41 km2 of lacustrine or 0.12 km2 of riverine habitat. Minimum viable population (MVP) values increase as an exponential function of the annual catastrophe probability. In the absence of additional harm, recovery efforts, or habitat limitations, a population at 10% of MVP (3,360 age-1 and older) will have a median time-to-recovery of 15 years and a 95% chance of recovering within 39 years (if probability of catastrophe is 15% per generation). The greatest threats to the survival and recovery of Lake Chubsucker in Canada are related to natural system modifications associated with habitat-related effects of aquatic invasive species, dredging, drawdown of dyked wetlands, increased sediment loading from agricultural land use, and climate change. Cumulative threat effects likely impact Lake Chubsucker across its Canadian range. Population density and growth of Lake Chubsucker are most sensitive to changes in adult survival across all scenarios examined. As population growth rate increases, the population becomes more sensitive to changes in fecundity, YOY and juvenile survival while sensitivity to adult survival decreases. There remain numerous sources of uncertainty related to Lake Chubsucker: population distribution, abundance, and trajectory; recent life-history parameters for Canadian populations; habitat preferences for early life stages and over wintering; and, the threat mechanisms and extent of threat impacts.

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