Science Response 2016/024

Estimating Lake Utopia Rainbow Smelt (Osmerus mordax) Spawner Abundance and Allowable Harm

Context

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 as sympatric pairs. Two populations of smelt co-exist in Lake Utopia, a small-bodied (SbP) form and a large-bodied (LbP) form. The LURS-LbP was designated ‘Threatened’ by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in November 2008.  The reason for the designation is as follows:

“This population is part of a genetically divergent sympatric pair of Osmerus that is endemic to a single lake in Canada with an extremely small index of area of occupancy (6 sq. km). It spawns in only three (3) small streams in the watershed and could quickly become extinct through degradation of spawning streams from increasing development around the lake shore and impacts of the dip-net fishery. This population is threatened by introduction of exotic species and by increasing eutrophication.” (COSEWIC 2008).

DFO conducted a Recovery Potential Assessment (RPA) in October 2010 (DFO 2011, Bradford et al. 2012).  At that time, it was not possible to estimate spawner abundance.  An interim (until a population estimate was available) abundance target for LURS-LbP, derived from the estimated minimum population size needed to maintain genetic diversity, was recommended at 2,000 spawners on nights of peak spawning.  Pursuant to the Species at Risk Act (SARA), a regional listing recommendation was subsequently completed in 2013 and a final listing decision is pending. 

In the past, a recreational smelt dip-net fishery occurred on the tributary streams of Lake Utopia between April 1^st and May 31^st. Much of the dip-netting occurred on Mill Lake Stream and Trout Lake Stream (Figure 1), owing in part to ease of access. Therefore, there was a high potential for much of the annual spawning run to be susceptible to fishing. Catch and effort data have never been gathered for this fishery; however, the historical fishing effort is considered to be low (Bradford et al. 2012). The fishery has been closed by Variation Order since spring 2011; however, there is anecdotal information to suggest illegal fishing occurs.

There is one communal Food, Social, and Ceremonial (FSC) license that allows dip-netting and angling for all smelt in Southwest New Brunswick, including the large and small-bodied forms in Lake Utopia. The bag limit for this communal licence was set at 60 fish per person per day, with the season running from April 15^th to May 31^st. Since 2013, the FSC licence holder has agreed to licence conditions that included a spawning season dip-netting closure within Smelt, Unnamed, and Second brooks. 

If LURS-LbP is listed under SARA, activities that result in mortality of LURS-LbP, such as fishing, would not be in compliance with SARA. SARA permits cannot be issued for fisheries targeting (directed at) listed species; however, such fisheries can be exempted in a Recovery Strategy if the activity does not jeopardize the survival or recovery of the species.  Without abundance data for LURS-LbP, it is unknown whether a harvest could occur without jeopardizing survival or recovery of the species.  To inform the provision of exemptions, a population abundance estimate, and a resulting updated recovery abundance objective are needed, as well as an understanding of current levels of mortality and maximum levels of allowable harm.  Such information will also be needed to inform other aspects of Recovery Planning should LURS-LbP be added to Schedule 1 of SARA. 

The objectives of this Science Response process are to:

• Provide a population abundance estimate for the Lake Utopia Rainbow Smelt (large-bodied) Population based on work undertaken in 2014.
• Provide an updated recovery abundance objective for the Lake Utopia Rainbow Smelt (large-bodied) Population to replace the interim recovery abundance objective proposed in the Recovery Potential Assessment (DFO 2011).
• Provide the likelihood that the updated abundance objective for the Lake Utopia Rainbow Smelt (large-bodied) Population can be achieved under current levels of mortality.
• Provide the maximum level of allowable harm that the Lake Utopia Rainbow Smelt (large-bodied) Population can sustain without jeopardizing survival or recovery.

To address these objectives, a mark-recapture study to estimate population abundance within Mill Lake Stream and Trout Lake Stream-Spear Brook, both identified as containing LURS-LbP, was initiated in 2014.

This Science Response Report results from the Science Response Process of November 19, 2015, on Estimating Lake Utopia Rainbow Smelt (Large-bodied) Population Abundance and Allowable Harm.

Complete document (PDF, 291 KB)

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