Research Document - 2012/124
Lake Utopia Rainbow Smelt (Osmerus mordax) Status, Trends, Habitat Considerations and Threats
By R.G. Bradford, P. Bentzen, and I. Bradbury
Abstract
The native rainbow smelt (Osmerus mordax) inhabiting Lake Utopia, New Brunswick, consists of two co-existing (sympatric) morphologically, ecologically, and genetically differentiated populations: a small-bodied form and a large-bodied form. Each population was assessed in November 2008 by the Committee on the Status of Endangered Wildlife in Canada as meeting their criteria for a Designatable Unit (DU), and each DU was designated Threatened. This Recovery Potential Assessment was undertaken to provide information and advice, for both small-bodied smelt and large-bodied smelt, on current status, trends, their potential for recovery and to propose population abundance and distribution targets for recovery. Information on habitat requirements, as well as the impact of human activities on both the species and their habitat, including possible alternatives and management measures to mitigate these impacts, are also included. Spawning of the small-bodied (<170 mm fork length) form has been confirmed in only three small, vulnerable brooks at the northern end of Lake Utopia. The large-bodied (≥170 mm fork length) form spawns in the two larger tributaries at the northeastern end of Lake Utopia. Individual within-stream daily estimates of spawner abundance for small-bodied smelt have varied between 3,000 and 150,000 fish during the years that estimates have been acquired, with estimates on the order of 104 fish being the most frequent. Among-stream daily abundance estimates are typically in excess of 100,000 spawning small-bodied smelt. The abundance of the large-bodied Lake Utopia Rainbow Smelt (LURS) population cannot be assessed with the current data. Recovery targets for both body forms of LURS can be defined on the basis of abundance and distribution. An interim (five years) daily abundance target for small-bodied LURS of 100,000 spawning fish distributed among the three brooks during peak spawning period is recommended to demonstrate their continued high productivity. The recommended annual distribution target for small-bodied LURS is the synchronous occupation under natural conditions of the three spawning brooks, with no individual brook to be unoccupied for two consecutive years. An interim (until a population estimate is available) abundance target for the large-bodied LURS, derived from the estimated minimum population size needed to maintain genetic diversity, is recommended at 2,000 spawners. An interim (until more is learned about spawning in Trout Lake Stream and Spear Brook) distribution target for large-bodied LURS is the annual occupancy of Mill Lake Stream. Human activities have the potential to affect the smelt populations in the attributes of water quality, water quantity, direct mortality, and habitat impacts. Present mitigative measures, options to reduce affect, and research and monitoring proposals have been identified for all known threats under each attribute. Risks of potential effects under current management measures were ranked low, medium, or high for the individuals of both DUs of the LURS. The location of the effect (either lake or spawning streams) is also included. The recovery of both small-bodied and large-bodied rainbow smelt DUs in Lake Utopia is considered to be both biologically and technically feasible. Recovery requires maintaining self-sustaining populations for both DUs and mitigating the threats through existing regulations, education and stewardship efforts.
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