Science Advisory Report 2009/051

Recovery Potential Assessment for Atlantic Whitefish (Coregonus huntsmani)

Summary

• The absolute abundance of wild Atlantic whitefish is unknown but is considered to be low. They are currently thought to be restricted to the Petite Rivière watershed, with reproduction occurring primarily within the approximately 16 km² combined area of Minamkeak, Milipsigate, and Hebb lakes.
• Atlantic whitefish survival depends upon its continued production within Minamkeak, Milipsigate, and Hebb lakes; thus, this habitat is considered necessary for its survival and subsequent recovery. There is no evidence to suggest that any part of this small area is not utilized by Atlantic whitefish, and further habitat fragmentation or loss of function should be avoided.
• At present, information about past abundance or productivity of Atlantic whitefish populations is not sufficient to form a basis for establishing watershed-specific abundance recovery targets or the number of populations required to ensure long-term viability.
• The minimum census population size required to maintain genetic diversity is estimated to be in the vicinity of 550 – 2,000 mature individuals. An interim watershed specific abundance target above the mid-point of this range (e.g., above 1,275 mature individuals) is proposed.
• There are reasons to expect that establishing several populations in diverse habitats, i.e., in several watersheds as a distribution target, will increase the probability that the species will be self-sustaining in the long term.
• Both the proposed interim watershed specific abundance target and distribution target will need to be revisited once knowledge about the dynamics of the recovering species is obtained.
• Current potential sources of direct mortality for Atlantic whitefish include: bycatch in recreational angling and other fisheries, entrainment of fish into water intakes, and removals or mortality from sampling for scientific purposes. Current indirect sources of mortality and impacts to habitat currently include: fluctuations in lake levels from municipal water drawdown or irrigation; acidification from acid run-off or acid rain; activities causing increased siltation, eutrophication, or substrate alteration; and barriers to fish passage. Unauthorized introduction and spread of non-native fish species (e.g., smallmouth bass, chain pickerel) may pose competitive, disruptive, or predation risks for Atlantic whitefish.
• A number of measures have already been put in place to mitigate threats to the existing population of Atlantic whitefish. However, the potential for survival of this population may be higher if fish passage and anadromy is an option within the Petite Rivière, and abundance of smallmouth bass within Minamkeak, Milipsigate, and Hebb lakes is managed. The overall survival and recovery of Atlantic whitefish requires enabling anadromy and range extension outside the Petite Rivière lakes.
• Activities to establish the anadromous form of Atlantic whitefish will need to consider the above cited sources of direct and indirect mortality, as well as the direct impact of passage through hydroelectric turbines, indirect effects of water management for hydroelectric generation, and native fish species (e.g., brook trout) recreational angling fishery enhancement activities.
• The recovery of Atlantic whitefish is considered to be both biologically and technically feasible. However, the time to recovery will be dependent both upon the current status of the remaining population and the timing/extent of human intervention.
• At a minimum, future monitoring activities should aim to establish whether Atlantic whitefish continue to produce new individuals annually in Minamkeak Lake, determine the response of Atlantic whitefish in Milipsigate Lake to a likely increase in smallmouth bass abundance, and establish indices of current status within Hebb Lake in advance of smallmouth bass becoming established.

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