Science Advisory Report 2011/004
Recovery Potential Assessment for Lake Utopia Rainbow Smelt (Osmerus mordax) Designatable Units
- Lake Utopia is part of the Magaguadavic River watershed in southwestern New Brunswick.
- Lake Utopia Rainbow Smelt (LURS) represent one of the only three confirmed occurrences in Canada where genetically divergent smelt populations co-exist.
- Two populations of smelt co-exist in Lake Utopia, a small-bodied form and a large-bodied form. These populations differ in physical characteristics, life history, and are reproductively isolated.
- The two populations were assessed as separate Designatable Units (DUs) by COSEWIC in 2008 and both were designated as Threatened in part because of their natural small areas of occurrence and occupancy and in part because this small area is sensitive to the effects of human activities.
- Spawning of the small-bodied form has been confirmed in only three small, vulnerable brooks (about 1 m in width and estimated to provide ≤ 500 m of accessible linear spawning habitat) at the northern end of Lake Utopia: Smelt Brook, Unnamed Brook, and Second Brook.
- The large-bodied form spawns in the two larger tributaries at the northeastern end of Lake Utopia: Mill Lake Stream and Trout Lake Stream (which outflows from Trout Lake and has Spear Brook as a tributary and which is recognized as a spawning site).
- Adult body size is recommended as the most useful, and practical criteria for the general description and operational definition of the two body forms. Small-bodied smelt would be those less than 170 mm fork length (FL) whereas the large-bodied smelt would be those ≥ 170 mm FL. A length of 170 mm FL is equivalent to 187 mm Total Length.
- 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.
- There were fewer recorded occurrences of small-bodied smelt in Scout Brook during the 2009 and 2010 spawning seasons, and when they were present they were in low numbers (<100 fish) and few egg mats were observed. There is no known natural factor as to why this occurred.
- The abundance of large-bodied Lake Utopia Rainbow Smelt (LURS) population can not be assessed with the current data.
- The presence of large-bodied spawners in Mill Lake Stream was observed to be low (few eggs and less than 20 fish) in 2010. A stream blockage resulting from the presence of a beaver dam was evident at that time.
- Recovery targets for both body forms of the Lake Utopia Rainbow Smelt can be defined on the basis of abundance and distribution.
- An interim (5 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 2 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 LURS 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.
This Science Advisory Report is from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, Regional Advisory Meeting of October 26-27, 2010 on Recovery Potential Assessment (RPA) for Lake Utopia Rainbow Smelt (Osmerus mordax). Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule at http://www.dfo-mpo.gc.ca/csas-sccs/index-eng.htm.
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