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Present-day environments and anticipated future conditions often pose a significant challenge to efforts to reintroduce extirpated species, highlighting the need for collaborative, thorough approaches to reintroductions. Such is the case in Michigan, where numerous partners are working to reintroduce Arctic Grayling Thymallus arcticus with hopes of reestablishing self-sustaining populations. With > 47,000 km of coldwater stream habitat in the state and limited numbers of eggs for reintroductions, a prioritization framework was needed to provide a standardized, fine-scale method for rating suitability of streams for reintroductions. Through facilitated discussions with stakeholders and experts, we developed an overall prioritization framework for rating Michigan streams with components evaluating a reach's thermal, instream habitat, biological, and connectivity characteristics. Within the context of this broader framework, we developed the habitat rating component for assessing suitability of instream conditions for egg, fry, juvenile, and adult life stages of Arctic Grayling. Life-stage-specific habitat metrics and scoring criteria from this effort were used to rate habitat conditions for 45 reaches in tributaries of Michigan's Manistee River, enabling identification of reaches likely having instream habitat most suitable for Arctic Grayling. Numbers of reaches meeting or exceeding 60%, 70%, and 80% of the maximum score for overall habitat suitability were 31, 8, and 1. Upon completion of the fish assemblage and connectivity components, the prioritization framework and habitat rating process described here will be used for comparing suitability among streams throughout the historical range of Arctic Grayling in Michigan and guiding reintroduction efforts. Though it will take considerable time before instream habitat suitability criteria can be evaluated for all life-stages of Arctic Grayling in Michigan, the collaborative stream prioritization framework developed for Arctic Grayling reintroduction can be readily adapted to reintroduction efforts for other species elsewhere.

Introduced salmonines (Oncorhynchus spp. and Salmo spp.) are important components of recreational fisheries in the Great Lakes. These fishes were stocked heavily following the fishery collapse of lake trout (Salvelinus namaycush) due to sea lamprey (Petromyzon marinus) predation and commercial overharvest. While salmonine introductions occurred in all five of the Great Lakes, Lake Superior is less productive than the lower Great Lakes restricting most introduced salmonines to a small percentage of available habitat. This suggests the potential for high resource overlap between salmonines, yet little information has been published related to the trophic ecology of introduced salmonines in Lake Superior. Furthermore, hybrid splake (S. namaycush × S. fontinalis) are also stocked by various state agencies while little information on their trophic ecology exists. To address uncertainties associated with introduced salmonines, we assessed the diet composition and isotopic niche overlap of fish collected from two south shore ports of Lake Superior. Introduced salmonines consumed similar prey items including rainbow smelt (Osmerus mordax), coregonines, and three-spined stickleback (Gasterosteus aculeatus) in varying amounts, with a notable percentage of diet comprising terrestrial invertebrates. These results are further supported by stable isotope analysis which indicated high isotopic niche overlap among introduced salmonines suggesting a mixed diet attributed to benthic, pelagic, and terrestrial sources. Our characterization of the salmonine community provides important information that will inform fisheries research and management in Lake Superior.

The above article from the Ecology of Freshwater Fish, published online on 20 December 2019 in Wiley Online Library (https://onlinelibrary.wiley.com/doi/abs/10.1111/eff.12527), has been retracted by agreement between the journal Editor‐in‐Chief; the symposium editor, Phaedra Budy; and the author, Troy Zorn. The retraction has been made due to a mistake in the classification (accessible vs. landlocked) of one of the survey locations in Table 1, which affected the accuracy of other analyses in the article.