Long range seasonal movements of northern pike (Esox lucius L.) in the barbel zone of the River Ourthe (River Meuse basin, Belgium).

In order to study the annual activity cycle and reproductive ecology of northern pike (Esox lucius L.) in the River Ourthe (Belgian Ardenne), 6 fish (579-742mm FL, 1605-4090g, 2 females and 4 males) were captured by electric fishing in November 2000 and January 2001. They were surgically implanted with a radio-transmitter and tracked for 149 to 349 days in a 30-km river stretch. During the pre-spawning period in winter, most movements were between distinct holding areas spaced from 40 to 550 m. All the pike began the upstream spawning migration between 8 February and 30 March 2001, when the mean water temperature varied from 6.7°C to 8.7 °C and the water flow from 52 to 199 m3s-1. The six pike travelled upstream, over distances ranging from 0.75 km to 15.7 km to reach their potential spawning sites. Pike arrived on their potential spawning sites between the 13 February and the 02 April 2001 and remained there from 5 to 25 days when the daily mean water temperature ranged from 2.9 to 10.0 °C. The six pike moved downstream after spawning and showed similar behaviour to those observed prior to spawning, but the distances between holding areas were more extended than during the winter pre-spawning period. When considering the entire tracking period, the longitudinal extension of the activity domains ranged 1 421 to 24 798 m (mean 12,050 m). This exploratory study provided original observations on northern pike movements in a barbel zone of the River Meuse basin. Results contrasted with the widely established view of pike being a sedentary predator and provides data on its behaviour throughout the annual cycle