Lake Trout (Salvelinus namaycush) Growth Potential Predicted from Cisco (Coregonus artedii) Population Structure and Conductivity

Abstract

Trophic dynamics between lake trout (Salvelinus namaycush) and cisco (Coregonus artedii) were examined in a set of 10 northwestern Ontario lakes that ranged in conductivity by nearly an order of magnitude. Diets revealed the possibility of interspecific competition for invertebrate prey prior to initiation of piscivory by lake trout at approximately 200 mm fork length (FL). Von Bertalanffy growth equations (based on otolith ages) were used to estimate time to attain this length (1.4–3.0 yr). Contrary to anticipated results, lake trout reached this size more rapidly in lakes with high cisco abundance. Presumably, this relationship was caused by improved food conditions for young trout in some of the more productive waterbodies. However, after removing the collinearity between lake conductivity and nonpiscivorous growth by regression analysis, there was no relationship between the time for lake trout to reach 200 mm and cisco abundance. Piscivorous growth varied (L_∞ = 508 to 740 mm) extensively among the 10 populations and was likely a function of growth efficiency from different food sources. Using stepwise multiple regression, 81% of the L_∞ variation among lakes was explained by cisco abundance and mean size. Linear regression between L_∞ and mean size of trout (but not trout abundance) on conductivity generated significant positive relationships.