Interannual variability in feeding rate and niche breadth of radiated shanny (Ulvaria subbifurcata) larvae from coastal Newfoundland

Using 6 years of data for radiated shanny (Ulvaria subbifurcata) larvae from coastal Newfoundland, we examine relationships between prey availability, specific consumption rates (SPC) and niche breadth (S) as a function of both larval size and cohort. We also examine the extent to which specific consumption rates correlate with interannual variations in otolith-based estimates of average growth rate (mm day(-1)) and variability in individual growth rates. In all years, we observed an ontogenetic dietary shift, from nauplii to larger copepods, as the Ulvaria larvae grew. There were significant differences in SPC both across size categories and among years. There was also a significant increase in S with increasing body size in most years. There was a positive, but variable, correlation between SPC and average growth rates for small- and intermediate-sized fish, but no significant relationship with variability in individual growth rates. Overall, we found that foraging success increased with larval size, whereby the majority of large larvae were feeding above maintenance levels while small larvae fed at or below maintenance levels. Food limitation may therefore be an important factor that directly affects the mortality of small, but not necessarily large, larvae. Coupled with the observed ontogenetic change in diet, quantifying the relationship between food availability and larval growth will thus depend not only on prey availability, but also on the size-based foraging abilities of larval fish.