Lean, fat, and humper morphs are genetically distinct (Dehring et al., 1981, Goetz et al., 2010, Guinand et al., 2003, Guinand et al., 2012, Krueger et al., 1989, Page et al., 2004), with heritable physiological differences in fat content (Eschmeyer and Phillips, 1965, Goetz et al., 2010, Thurston, 1962), swim bladder gas retention (Ihssen and Tait, 1974), and developmental rates of fertilized eggs and fry (Horns, 1985). The redfin morph is the most full-bodied, with the largest head, snout, and eyes, longest and deepest caudal peduncle, and longer pelvic and pectoral fins than other morphs (Muir et al., 2014). The humper morph has a small head, short snout, short maxilla, large eye, short and narrow caudal peduncle, and often uses isolated offshore reefs surrounded by water > 90 m in depth or steep-sided sloping banks. and Myoxocephalus thompsonii) and burbot Lota lota (Conner et al., 1993, Ray et al., 2007). The siscowet (fat) morph is deep bodied with a rounded snout, uses deep waters > 80 m, is high in fat content, and feeds in pelagic habitat by following diel vertical movements of Mysis diluviana and Coregonus species (Hrabik et al., 2006) and in benthic habitat on sculpins ( Cottus sp. The lean morph uses shallow waters 460 mm in length (Conner et al., 1993, Dryer et al., 1965, Ray et al., 2007). Recently, lake trout recovery plans have expanded to include other forms that occupy deep offshore waters (e.g., Lake Michigan, Bronte et al., 2008 Lake Erie, Markham et al., 2008).Īlthough lake trout morphological diversity in Lake Superior is currently reduced from historical conditions, lean, siscowet (fat), humper, and redfin morphs are currently recognized (Bronte et al., 2003, Burnham-Curtis and Smith, 1994, Khan and Qadri, 1970, Krueger and Ihssen, 1995, Moore and Bronte, 2001, Muir et al., 2014, Muir et al., 2015, Peck, 1975, Thurston, 1962). However, hatchery production and stocking were focused on the lean form of lake trout that occupied shallow inshore waters where fisheries were focused. Subsequently, fishery managers attempted to restore lake trout stocks by stocking hatchery-reared fish, restricting fisheries, and controlling sea lamprey populations. However, much of this morphological diversity was lost in the middle of the 20th century when over-fishing, predation by the invasive sea lamprey Petromyzon marinus, and habitat degradation caused lake trout stocks to collapse throughout much of the basin (Hansen, 1999, Krueger and Ebener, 2004, Muir et al., 2012a). Many visually-distinct and easily-identified sympatric morphs of the lake trout Salvelinus namaycush were recognized more than a century ago in the Laurentian Great Lakes of North America (Agassiz, 1850, Goodier, 1981, Roosevelt, 1865).
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