Inverse trends in relative abundance of muskellunge and northern pike have been reported for numerous lakes and one large river. In each case, muskellunge appeared to decrease in abundance while northern pike appeared to increase. Most instances involved colonization of native muskellunge lakes by northern pike but shifts in relative abundance of populations with a history of co-occurrence also have been noted. These trends have been interpreted as evidence of a negative interaction between the two species. Predation, competition and hybridization are possible mechanisms of interference. Earlier spawning in the spring, shorter generation time, a more aggressive nature and greater food conversion efficiency have been suggested as possible advantages for northern pike.
Predation by young-of-the-year (YOY) northern pike on YOY muskellunge was proposed as a likely mechanism of interactions nearly 35 years ago and it remains the most attractive hypothesis, more on the basis of its intuitive appeal and explanatory power than on actual field evidence. Under this hypothesis the apparent compatibility of muskellunge and northern pike in some waters can be explained by the availability of sufficient spawjning habitat to permit spatial separation of the species, either because of differences in preferred spawning habitat or because eggs are spread over a large enough area that encounters between YOY muskellunge and northern pike and minimized . The existence of one mechanism of interaction does not preclude the existence of others.
Circumstantial evidence of a negative interactions between the two species is persuasive and not to be discounted. However, negative associations in relative abundance might arise even in the absence of any direct species interactions. For example, changing environmental conditions could affect the two species quite differently if they have different tolerances or optima for certain environmental variables. Base on zoogeographic evidence it appears that northern pike might be favoured by cooler temperatures and more lentic conditions Cultural development more often results in the conversion of lotic habitat to lentic habitat than vice versa. Sequelae of human settlement such as increased turbidity, siltation and accumulation of organic sediments might be expected to have a more severe impact on a species adapted for life in flowing water than on one which evolved for life in still water habitats. Differences in the environmental requirements of the two species have been postulated but nor proven.
Effective muskellunge management in waters containing northern pike will require deeper understanding of how the two species interact, what factors modify the intensity and outcome of the interaction and how environmental conditions and fishing pressure can otherwise favour one species over the other.