To fast or feed: an alternative life history for anadromous brook trout Salvelinus fontinalis overwintering within a harbour

Abstract

The seasonal feeding pattern of sea-run brook trout Salvelinus fontinalis was studied from November to May 2010-2012 in Antigonish Harbour, Nova Scotia, Canada (45° 38' N; 61° 55' W). Sixty-three S. fontinalis (mean ± s.d. fork length = 330 ± 70 mm and mass = 536 ± 351 g) captured had fed predominantly on fishes (Fundulidae and Gasterosteidae). Percentage of empty stomachs was highest during autumn (18%) and winter (22%) and lowest in spring (7%). Stomach fullness increased from autumn to a maximum during winter, relating to near-zero body temperatures which may have effectively stopped gastric evacuation. Although feeding occurred during winter (December to March), consumption rates were calculated as negative values, and subsequently returned to positive values in spring (April to May). The over-winter life-history strategy of this sea-run S. fontinalis population appears to be a feeding marine migration in which fish continually increase body condition, representing an alternative to the more common overwintering strategy of starvation in fresh water until spring.

A critical review of marine adaptability within the anadromous Salmoninae

“…osmoregulation at higher temperatures; Pennell and Barton 1996). Yearround acoustic tracking of S. fontinalis in the southern Gulf of St. Lawrence found individuals foraged within the estuarine environment from autumn to spring with body temperatures ranging from -0.5 to 20.1°C and returned to fresh water during summer (Spares et al 2014) where the majority of individuals tracked occupied cool, spring-fed pools (unpublished data Spares et al). This behaviour suggests high estuarine temperatures during summer (mean ± SD, 18.7 ± 3.4°C, n = 231, maximum = 25.8°C; unpublished data Spares et al) were the main influence for individuals to return to fresh water as marine primary productivity was highest during this period (personal observation).…”

“…The Salmoninae migrants which ventured closest to their lowest thermohaline limits were O. keta, S. salar, S. alpinus and S. malma, as all encountered full saltwater with temperatures ranging from 0 to -1.5°C (Table 6). The highest temperatures at the highest salinities were tolerated by O. kisutch, O. keta and O. nerka, even though the highest temperatures at lower salinities were experienced by O. clarki (23.7°C; Table 7) and S. fontinalis (20.1°C; Spares et al 2014). Ambient salinity measurements were obtained from conductivity-temperature-depth profiles conducted during tracking, or temporally and spatially similar oceanographic studies; thus cited salinities may not accurately represent actual conditions experienced by migrants.…”

“…1). Although these species demonstrated a marine migration strategy of remaining near shore and fresh water inputs (Curry et al 2006;Morinville and Rasmussen 2006;Rikardsen et al 2007;Spares et al 2012Spares et al , 2014, the circumpolar S. alpinus's versus temperate S. fontinalis's distribution ranked the former higher due to extreme thermohaline adaptations (Jensen and Rikardsen 2012;Spares et al 2012). …”

“…In spite of these advances, there has been relatively little research conducted on the marine migration of some salmonids (Goetz et al 2004;Jensen and Rikardsen 2012;Spares et al 2012Spares et al , 2014, and on the better studied Atlantic salmon Salmo salar L. 1758 (Spares et al 2007;Dadswell et al 2010;Chittenden et al 2013;Lacroix 2013) and steelhead trout Oncorhynchus mykiss (Walbaum 1792) (Nielsen et al 2011).…”

“…Recent electronic tracking has recorded temperature and salinity encountered by marine migrating salmonids and results cast doubt on the current salinity tolerance hierarchy (Goetz et al 2004;Jensen and Rikardsen 2012;Lefèvre et al 2012;Spares et al 2012Spares et al , 2014. Long-distance migratory Salmoninae (Oncorhynchus and Salmo) have demonstrated salinity tolerance in oceanic environments for months to years (Quinn 2005.…”