ENVIRONMENTAL INFLUENCES ON THE MARINE MIGRATION OF ARCTIC CHAR AND BROOK TROUT (SALVELINUS SPP.)

Abstract

Environmental influences on the marine migration of Arctic char Salvelinus alpinus and brook trout Salvelinus fontinalis were determined by correlating movements, habitat use and diving behaviours to distance traveled from freshwater inputs, salinity, temperature, tides and prey availability. Using acoustic tracking, S. alpinus were detected either continuously (maximum 34 days) or intermittently in estuarine zones, on average residing approximately ⅓ of time tracked and returning once every 9 days. Low travel rates during flood tide suggested individuals staged before accessing intertidal flats. A portion of tagged individuals (19%) used two main estuaries situated 22 km apart. Extra-estuarine travel was within 3 km of shore ranging < 30 km straight line distance of either estuary. Higher estuarine residency prior to freshwater re-entry suggested a marine-fresh water transition phase. Tracking revealed S. alpinus spent the most of their time in surface waters (0 to 3 m). Inter/sub-tidal movements and consecutive repetitive dives (maximum 52.8 m) resulted in extreme body temperature shifts (-0.2 to18.1oC). Stomach contents analysis and diving suggested inter- and sub-tidal feeding. Although Salvelinus fontinalis continued to feed while overwintering within an estuary, near-zero body temperatures may have stopped gastric evacuation. Salvelinus alpinus mostly occupied warmer estuaries and surface waters, limiting time spent in colder environments, as part of thermoregulatory behaviours which enhanced feeding/digestion physiology. Both Salvelinus spp increased body condition by marine feeding in near-zero temperatures. Salmoninae adaptability to the marine environment was evaluated based on the following criteria: (1) extent, and (2) duration of migration; (3) horizontal and (4) vertical habitats; and (5) minimum and (6) maximum thermohaline limits experienced. The most-to-least marine adapted genera were Oncorhynchus, Salmo and Salvelinus. The lowest and highest thermohaline limits were reached by O. keta, S. salar, S. alpinus and S. malma; and O. kisutch, O. keta and O. nerka, respectively. Our top three ranked species, O. keta, O. nerka and O. gorbuscha, suggested recently evolved salmonids are more marine adapted. The plasticity of Salvelinus spp. marine migration strategies, demonstrated by wider thermal/habitat zone niches described within this thesis, may have allowed exploitation of extreme environments, offering a survival advantage when faced with rapid climate change.