The effect of the krill length to wetmass relationship on the scaling of acoustic data

Here we examine the variability in the conversion factor, C, that scales Nautical Area Scattering Coefficient (NASC) values of krill echoes to krill areal biomass density. Specifically, we examine variation in C due to the krill length to wetmass relationship. Using example data from a krill survey conducted in the East Antarctic, we used a linear mixed effects model with a fixed effect of log(krill length) and random effect of net haul on the log(wetmass) response variable. We use biased-corrected backed-transformed predictions of krill wetmass and associated to calculate C and 95% confidence intervals of C. Using an example krill length frequency distribution and 120 kHz target strength we calculate mean C = 0.347 with a 95% confidence interval [0.286, 0.408].