Effects of exotic common reed invasion on northern pike spawning and growth in two wetlands of the St. Lawrence River system

The invasion of wetland by the exotic common reed Phragmites australis is well documented, but knowledge about fish and wildlife use in freshwater systems is generally lacking. We compared the use of exotic common reed for northern pike Esox lucius spawning and growth to control habitats characterized by a mix of vegetation types (Phalaris arundinacea, Scirpus sp., Carex sp. and Typha sp.) in two St. Lawrence River’s wetlands. Eggs deposition was three times lower in the common reed invaded area. From mid-May to the end of June, weekly abundance of age-0 fish was highly variable, without being found different over the whole period between the habitat types. At equal fish weight, the digestive tract weight of age-0 northern pike was higher in the control habitats suggesting better feeding conditions in these habitats. Growth and condition differences were observed but they were slight and their direction varied among the two wetlands. The exotic common reed invasion of freshwater wetland will likely affect the quality of the northern pike spawning habitats in the St. Lawrence River wetlands but its impact on its nursery habitats remain unclear.