The feeding habits of anadromous arctic char, (Salvelinus alpinus L.) in Frobisher Bay, Baffin Island in the Eastern Canadian Arctic: Diet, parasites and stable isotopes

Chapter One tested the hypothesis that there is trophic structuring (TS) among Arctic char populations feeding in the marine environment based on published data and the hypothesis was rejected. A comprehensive study was undertaken to test the hypothesis further, by collecting data on diet, parasites and using stable isotopes. Anadromous Arctic char consume diet items that occur in different trophic levels and their endohelminth parasite community, transmitted by a broad range of food items, is consists of mostly non-host specific parasites. Based on 2002 data, char samples from several sites (Chapter Two) were similar with respect to length, weight age and sex and can be combined for statistical analyses. Moreover, male and female char diets were similar between sites and while diet varied among sample sites, char condition were comparable. Chapter Three compared char samples collected during 2002, 2004 and 2005 and assessed diet, parasites and stable isotope ratios (SIR) to determine if TS occurs. Diet and parasite data were unable to show clear cut evidence for TS as char were infected by non-host specific parasite species which in turn is a reflection of their diet. Controlled feeding experiments (Chapter Four) were designed to confirm if food particle size affected growth of char, if shifts in stable isotope values could be correlated with a diet shift and if the stable isotope half-lifes (HLs) from experimentally fed and wild char were comparable. Young-of-the-year (YOY) char were used because this is when char growth is considered the fastest and when the greatest shift in food particle size occurs in natural populations. Char length was not correlated with diet particle size for experimentally fed char but there was correlation for wild char feeding on Mysis spp., and Onesimus littoralis.;Data from my experimental studies, in general, corroborates my findings from wild char and provides further evidence that even if quality of diet and particle size change there is little support for trophic structuring i.e. a permanent shift in diet, during the marine phase of char feeding, regardless of char size.;Estimates of gross energy (GE) of diet items (Chapter Six) available to char showed that char growth is dependent on nutrient and total energy content and proportions of important diet items. The GE invested into growth by YOY was comparable to that of old wild char hence the similarity in their SGR. Furthermore, the stomach emptying time of old wild char is comparable to that of YOY since both groups have comparable rates of gastric evacuation.;Contrary to my hypothesis 1 (stating absence of trophic structuring), my results have shown that TS occurs in wild char but this cannot be generalized, since it was dependent on specific diet type (e.g. Mysis spp., O. littoralis and Arctic cod). The homogenization of diet as a nutrient source and as transmitters of endohelminthes assures stability and predictability of feeding patterns of Arctic char in the marine environment. Moreover, the homogenization processes and apparent stability of feeding indicates that predictive energy models for Arctic char will likely work in a changing Arctic environment. (Abstract shortened by UMI.);Since SGR of char is high in the marine environment, at low temperatures, the quantity and quality of food plus the length of time food remains in the intestine are needed to assess energy needs and possible shifts in diet preference (Chapter Five). Bomb calorimetry and proximate analysis of diet items found that the major food items varied in their nutrient content and could lead to a diet item preference but not a trophic shift. The relationship describing rate of gastric evacuations in YOY char is linear and this is similar to the results obtained from wild char in Chapter Three.