Ecomorphological Diversity of Lake Trout at Isle Royale, Lake Superior

Abstract

Four Lake Trout Salvelinus namaycush morphs were identified from Isle Royale, Lake Superior; the morphs differed in shape, traits linked to feeding and locomotion, buoyancy, and physical habitat use. Lean, humper, and siscowet Lake Trout generally conformed to previous descriptions, and we report, for the first time, quantitative evidence of a fourth morph, previously described anecdotally as the “redfin.” Jackknife classification of individuals to morphs based on body shape were 94% correct. High variation within and low variation among morphs led to moderately low percent agreement among visual identifications and high uncertainty in Bayesian model groupings of morphs. Eight linear measures of phenotypic traits linked to feeding (i.e., head and eyes) and locomotion (i.e., fin lengths and caudal peduncle shape) varied among morphs, consistent with specialized adaptations for trophic and physical resource use. Habitat differed among morphs with leans being most abundant in the 0–50‐m depth stratum and siscowets most abundant in two deeper strata (50–100 and 100–150 m). Differences in capture depth and percent buoyancy reflected physical habitat and known trophic resource partitioning among morphs. While the historical fingerprint of morphological and ecological diversity in Lake Superior Lake Trout persists, it is unknown whether the contemporary low level of differentiation is due to ecological release without subsequent reorganization or to a complete breakdown of differentiation. Received July 11, 2013; accepted February 7, 2014

Juvenile divergence in adaptive traits among seven sympatric fish ecomorphs arises before moving to different lacustrine habitats

“…In Lake Kronotskoe, adults of the L morph have the longest migration path and their feeding strategy of being a chase predator requires the greatest swimming ability. In contrast, the S morph is less mobile, and a high content of spare lipids in muscles has been suggested to provide the flotation needed for a pelagic lifestyle, as previously shown for S. namaycush pelagic morphs (Muir et al ., ).…”

Factors Affecting Postrelease Survival of Coded‐Wire‐Tagged Lake Trout in Lake Michigan at Four Historical Spawning Locations

“…), the present rehabilitation strategy calls for the stocking of primarily Seneca Lake strain fish on the Southern Refuge, with a recent addition of some Superior Klondike strain Lake Trout (a “humper” morphotype; other strains stocked in Lake Michigan belong to the “lean” morphotype; see Muir et al. , for context on different Lake Trout ecomorphotypes in the Great Lakes). The Seneca Lake strain can help buffer against effects of Sea Lamprey mortality and may contribute a disproportionately high amount to parental stock and recruitment of wild fish (Page et al.…”

Life history differences between fat and lean morphs of lake charr (Salvelinus namaycush) in Great Slave Lake, Northwest Territories, Canada

“…Nets were in the water overnight for about 24 h. Data collected from each fish included a full-body photograph (for shape and fin measures), total length (mm), weight in air (grams), weight in water (grams) with the swim bladder deflated (for buoyancy), sex (male or female), and maturity status (immature or mature; Zimmerman et al, 2006Zimmerman et al, , 2009. From full-body photographs (Muir et al, 2012b), most fish were assigned to a morph using a combination of statistical analysis of head and body measures and visual assignment, as described by Muir et al (2014). However, for some fish, statistical assignments differed between head and body measures, and visual consensus was not reached, so these fish were classified by visual comparison to the library of statistical and visual assignments (Hansen et al, 2012).…”

“…Numerous sympatric lake charr S. namaycush morphs were recognized centuries ago in the Laurentian Great Lakes of North America by aboriginal people (Agassiz, 1850), early Jesuit missionaries (Goodier, 1981), and French voyageurs (Roosevelt, 1865), and lean, fat, humper, and redfin morphs are presently recognized (Muir et al, 2014(Muir et al, , 2015. The lean morph typically uses shallow waters\50 m in depth, is streamlined in form, low in fat content, and is often a piscivore when [460 mm in length (Krueger & Ihssen, 1995;Muir et al, 2015).…”

“…The humper morph has a small head, short snout, short maxilla, large eye, short and narrow caudal peduncle, and uses isolated offshore reefs surrounded by water [90 m in depth or steep-sided sloping banks in Lake Superior (Burnham-Curtis & Smith, 1994;Krueger & Ihssen, 1995;Muir et al, 2015). The redfin morph is the most robust morph, with the largest head, snout, eyes, longest and deepest caudal peduncle, and longer pelvic and pectoral fins than other morphs (Muir et al, 2014). Lean, fat, and humper morphs are genetically differentiated (Dehring et al, 1981;Krueger et al, 1989;Page et al, 2004).…”