Research Document - 2013/015
Recovery potential modelling of Silver Chub (Macrhybopsis storeriana) in Ontario
By J.A.M. Young and M.A. Koops
Abstract
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has assessed the Great Lakes - Upper St. Lawrence population of Silver Chub (Macrhybopsis storeriana) as Endangered, due to a substantial decline in abundance (COSEWIC 2012). Here we present population modelling to assess population sensitivity, and determine population-based recovery targets and allowable harm in support of a recovery potential assessment (RPA) for Silver Chub. Our analyses demonstrated that the dynamics of a growing Silver Chub population would be very sensitive to perturbations that affect fecundity, or the survival of young-of-the-year. A stable or declining population, however, will be more sensitive to changes in adult survival. Based on an objective of demographic sustainability (i.e., a self-sustaining population over the long term), and a 15% probability of catastrophic decline per generation, we propose a population abundance recovery targets of ~444,000 adult Silver Chub (ages 1+). This abundance requires, at minimum, 84 km² of suitable habitat. The current abundance of Silver Chub in this DU (Western Basin of Lake Erie only) is estimated at approximately 660,000 adults, but has been as low as 251,000 within the last five years (Ohio Division of Wildlife 2013, OMNR 2013). The potential habitat (surface area) in the Western Basin is estimated to be in excess of 3000 km². If the Silver Chub population is stable, the risk of extirpation from Ontario for a population of 251,000 (the lowest measured abundance) is 1% within the next 100 years. Since 2000, however, Silver Chub has been declining, on average, at a rate of 20% annually. At this rate, Silver Chub would become extirpated from Ontario within 36-95 years. The rate of decline has decreased since 2000, and the Silver Chub population may be stabilizing. If so, some harm may be allowed. Transient harm should not exceed a 15% reduction in adult abundance, or a 23% reduction in young-of-the-year (YOY) abundance, or an 8% reduction in total abundance within a 7 year period (approximately three generations).
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