Reproductive success of sympatric northern pike and muskellunge in an upper St. Lawrence River bay

A change in the use of spawning habitats linked with water-level management may explain differences in reproductive success among sympatric St. Lawrence River northern pike Esox lucius and muskellunge Esox masquinongy. Reproductive success in a shared spawning and nursery bay was compared based on egg (embryo) and age-0 abundance estimates before the fall emigration of young. Historically, northern pike were noted to commence spawning runs in shallow flooded areas soon after ice-out. I found that more than 87% of the estimated northern pike egg deposition in 1994 occurred in offshore, deep-water habitats (2–5 m) and that 99% did in 1995. Northern pike began spawning 17 d before muskellunge in 1994 and 31 d earlier in 1995. Spawning peaks occurred during the interval of 16–23 May. Muskellunge mostly spawned near shore (<1.5-m depth) in submerged aquatic vegetation growth that was absent during northern pike spawning. Muskellunge spawning began and peaked between 23 May and 4 June in 1994 and between 23 May and 1 June in 1995. Estimated egg deposition by northern pike was over 40 times that of muskellunge for the 2 years combined. Despite greater egg deposition, minimum survival estimates of northern pike from egg to fall juvenile were very low: 0.00008% in 1994 and 0.00010% in 1995. By comparison, minimum muskellunge survival estimates (egg to fall juvenile) were greater: 0.034% in 1994 and 0.105% in 1995. In seine surveys age-0 muskellunge catch per unit effort was negatively correlated with that of northern pike (r = −0.77), and muskellunge dominated catches for 9 of 10 years sampled. Growth of inshore submergent habitat during muskellunge spawning and the low abundance of northern pike may have contributed to the greater reproductive success of muskellunge.