Long range seasonal movements of northern pike (Esox lucius L.) in the barbel zone of the River Ourthe (River Meuse basin, Belgium)
Michaël OVIDIO & Jean-Claude PHILIPPART
University of Liège, Department of Life Science, Laboratory of Fish Demography and Hydroecology, 10 Chemin de la Justice, 4500 Tihange, Belgium Phone: +32 85 27 41 57; Fax: +32 85 23 05 92, email: M.Ovidio@ulg.ac.be
Biotelemetry studies on movements and migrations of northern pike (Esox lucius) have almost exclusively been performed in lakes and reservoirs but rarely in river ecosystems.
In order to study the annual activity cycle and reproductive ecology of E. lucius in the River Ourthe (Belgian Ardennes), 6 pikes (579-742mm FL, 1605-4090g, 2 females and 4 males) were captured by electric fishing in November 2000 and January 2001. They were surgically equipped with a radio-transmitter and intensively tracked for 149 to 349 days in a 30-km river stretch.
During the pre-spawning period in winter, most movements corresponded to alternate occupation of well distinct resting-places spaced out from 40 to 550 m. All the pikes started an upstream spawning migration between the 8 February and the 30 Marsh 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 pikes travelled upstream, over distances ranging from 0.75 km to 15.7 km to reach their potential spawning sites and were sometimes confronted to small weirs that they succeeded in clearing. The duration and dynamic of the migration were highly variable between individuals. Some pikes performed a direct migration, while others moved upstream by stages. Pikes arrived on their potential spawning sites between the 13 February and the 02 April 2001 and stayed over there from 5 to 25 days when the daily mean water temperature ranged from 2.9 to 10.0 °C. Individuals used a distinct spawning site and were distributed in different parts of the river system. Three pikes entered into the River Amblève, a tributary of the Ourthe and three others stayed in the main course of the Ourthe or in a secondary branch for reproduction. The six pikes moved downstream after spawning and showed similar behaviour to those observed prior to spawning, but the distances travelled between two locations were longer (resting-places spaced out from more than 1,500 m) than during the winter pre-spawning period. When considering the entire tracking period, individual home ranges ranged from 1,421 to 24,798 m (mean 12,050 m).
This exploratory study provided original observations on northern pike mobility in a barbel river of the River Meuse basin. Results contrasted with the widely established view of pike being a sedentary predator and brought data on its biological cycle and behavioural tactics throughout the annual cycle. Further studies in river environments are needed to plan effective management programmes for this species which is highly affected by habitat deterioration. By the end of 2001, about 150 young of the year were pit-tagged in order to study their dispersal and possible return as adult to their natal site (homing behaviour).