Marine feeding patterns of anadromous brook trout (Salvelinus fontinalis) inhabiting an estuarine river fjord

Abstract

This study describes the ontogenetic and seasonal feeding patterns of anadromous brook trout (Salvelinus fontinalis, also known as sea trout) inhabiting the estuarine Saguenay River (Quebec, Canada) using both stomach content and stable isotope analyses. Sea trout of the Ste. Marguerite River (Quebec, Canada) entered the saline waters of the Ste. Marguerite Bay in early May before venturing into the Saguenay River fjord for the remainder of the summer period. Upon their arrival, first-year migrants stayed relatively close to river mouths and initially fed on freshwater aquatic invertebrates. However, they quickly shifted their diet to marine prey items such as amphipods and mysids for the rest of their first summer at sea. These prey items were generally larger than freshwater prey; the prey spectrum at sea was both larger and wider than that found in freshwater and, as such, likely contributed to the trout's rapid growth rates at sea. The diet of migrants in subsequent years at sea (second-year migrants) consisted primarily of marine crustaceans and fish, the latter being most important when feeding in the upper Saguenay River. Trout shifted to piscivory at all marine sites at a size of 25 cm, regardless of time spent at sea, although the importance of piscivory varied with season and site.Résumé : Notre étude décrit les patrons ontogéniques et saisonniers d'alimentation de l'omble de fontaine anadrome (« truite de mer »; Salvelinus fontinalis) qui habite l'estuaire du Saguenay (Québec, Canada) à l'aide à fois de l'étude des contenus stomacaux et de l'analyse des isotopes stables. La truite de mer de la rivière Sainte-Marguerite (Québec, Canada) pénètre dans les eaux salines de la baie de Sainte-Marguerite au début de mai avant de s'aventurer dans le fjord du Saguenay pour y passer le reste de l'été. À leur arrivée, les migrateurs d'un an restent relativement près des embouchures des rivières et se nourrissent au départ d'invertébrés aquatiques d'eau douce. Ils changent cependant rapidement de régime et utilisent des proies marines telles que des amphipodes et des mysidacés pour le reste de leur premier été en mer. Ces proies sont généralement de plus grande taille que les proies d'eau douce; la gamme de proies en mer est aussi plus importante et plus étendue que celle d'eau douce et elle contribue ainsi aux taux élevés de croissance de la truite en mer. Le régime alimentaire des migrateurs des années subséquentes en mer (les migrateurs de seconde année) comprend surtout des crustacés et des poissons marins, ces derniers étant particulièrement importants lorsque la truite de mer se nourrit dans le Saguenay supérieur. Dans tous les sites marins, la truite de mer devient ichtyophage à une taille de 25 cm, quel que soit le temps passé en mer, bien que l'importance de l'ichtyophagie varie en fonction de la saison et du site.[Traduit par la Rédaction] Morinville and Rasmussen 2027

Estimating the scale of fish feeding movements in rivers using δ13Csignature gradients

“…2005); dashed circles, stream resident trout above waterfalls and other physical barriers impassible to migratory salmon (Kline et al. 1990; Morinville & Rasmussen 2006b); no circles, fish above likely barriers (e.g. beaver dams).…”

“…2003) were necessary. Further analytical details were outlined by Rasmussen & Trudeau (2007) and Morinville & Rasmussen (2006b) for SMR samples and in the cited references for samples from other rivers.…”

“…Our own published and unpublished results on the SMR includes signatures of periphyton (rock scrapings mostly diatoms) (Rasmussen & Trudeau 2007), as well as unpublished data on grazing mayflies (mostly Heptageniidae, Baetidae and Ephemerellidae), filter feeders (mostly Hydropsychidae) and collector-gatherers (mostly chironomids), as well as juvenile Atlantic salmon (Trudeau 2004). All of these taxa were collected along the river gradient from headwater streams down to the river mouth (Morinville & Rasmussen 2006b). The rivers from which literature data were obtained were free flowing, like the SMR, are located at similar latitude, and have similar biota.…”

“…Neither samples from the SMR nor those from other literature studies were lipid or acid extracted, and therefore no signature corrections for effects of such procedures (McCutchan et al 2003) were necessary. Further analytical details were outlined by Rasmussen & Trudeau (2007) and Morinville & Rasmussen (2006b) for SMR samples and in the cited references for samples from other rivers.…”

A critical review of marine adaptability within the anadromous Salmoninae

“…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). …”