There is debate in the literature as to whether scales of fishes require acidification to remove inorganic carbonates prior to stable isotope analysis. Acid-treated and untreated scales from 208 Atlantic salmon from nine locations on both sides of the Atlantic were analysed for δ 13 C and δ 15 N. Linear mixed-effect models determined the effect of acid treatment to be statistically significant. However, the mean difference was small (δ 13 C 0.1 ± 0.2‰, δ 15 N −0.1 ± 0.2‰) and not of biological relevance. This study concludes that Atlantic salmon scales do not need to be acidified prior to stable isotope analysis.

The P/B and P/Q values for meso-and macrozooplankton were based on Hutchings et al. (1991), and the P/B value for microzooplankton from Hutchings et al. (1995). The Q/B ratio of microzooplankton and the diet of the micro-, meso-and macrozooplankton were derived from the Southern Benguela model (Shannon et al. 2020). For gelatinous zooplankton, the biomass, P/B and Q/B values from the Southern Benguela model (Shannon et al. 2020) were used. Benthos (8, 9)Meiobenthos and macrobenthos biomass was estimated by EwE using the P/B, Q/B and EE (0.95) values for the southern Benguela model (Shannon et al. 2020). Diet information was also derived from this model. Chokka squid (10) and other cephalopods (11)The biomass of chokka squid was derived from the demersal trawl surveys for the south coast of South Africa using information from years 2010, 2011 and 2014 for the depth stratum 0-100 m. The abundance estimate (in tons) was divided by the stratum area (nm 2 ), and then converted from t nm 2 to t km 2 . The average over the 2010-2014 period was input in the model. The P/B and P/Q values from the southern Benguela model were used. Diet information was obtained from Sauer and Lipiński (1991).In terms of other cephalopods, Augustyn et al. (1995) reported that the most common species of Sepioidea in the