Migratory and reproductive activity of radio-tagged Arctic char (Salvelinus alpinus L.) in northern Labrador

Abstract

Migratory and reproductive activities of Arctic Char (Salvelinus alpinus L.) were studied using radio-telemetry in two adjacent river systems in northern Labrador, Canada. A total of 154 Arctic char were radio-tagged. Coded radio tags were surgically implanted into the body cavity of char, in the Summer and Fall of 1996. Individuals movements were monitored using 3 solar powered, fixed data logging stations, that recorded the time, date, channel and code of any transmitter within a predetermined distance (150 m) of the antenna (every 5 seconds). Movements of fish throughout the remaining sections of the 2 rivers were monitored on a weekly basis using aerial and manual tracking techniques. Gonadosomatic indices of spawning females increased throughout the Summer to peak between 20–36% in mid September, and dropped to <2% when spent, indicating that spawning occurred in the last week of September. Arctic char radio-tagged within the smaller river, Reid Brook (n = 125), exhibited a complex range of migratory behaviors. Initially, the majority of Reid Brook char migrated to spawning areas located throughout the mid to upper reaches of the river, where they remained until spawning was completed. Only 8 radio-tagged fish, (35.9–56.4 cm) successfully negotiated a waterfall called Reid Falls, to enter Reid Pond where they remained for the duration of the study. Immediately following spawning, during river ice up at water temperatures 0–3 °C, most of the radio-tagged Arctic char made abrupt downstream migrations and 61% of Reid Brook radio-tagged char moved through into the adjacent river system, Kogluktokoluk Brook. Final tracking data (29th October 1996), indicated that 8 fish remained in Reid Pond, 8 in the pool below Reid Falls, 62 char had moved through to adjacent river systems and the remaining char were generally located close to the mouth of Reid Brook. Char radio-tagged in Ikadlivik Brook, dispersed throughout that river system to spawn. Throughout October radio-tagged individuals from both river systems congregated in large deep pools (≈30 m deep) in the Ikadlivik and these sites were considered suitable habitats in which to over-winter. This strategy whereby Arctic char spawn in one river system but over-winter in a larger neighboring system (within a single year) has been postulated for other char species but never previously proven, highlighting the value of radio-telemetry for remotely studying complex migratory patterns.