Interspecific and spatial variation in muscle sulphur compositions and their relation to mercury concentrations for northern freshwater fishes

We explored patterns in muscle sulphur to nitrogen ratio (S:N) and sulphur stable isotope ratios (δ 34 S) and their relationships with muscle total mercury concentrations ([THg]) for fishes of 13 coastal rivers and 18 inland lakes ( n = 1370 fish) from northern Ontario, Canada. Muscle S:N decreased and δ 34 S increased with increasing latitude across populations but neither showed consistent ontogenetic variation within populations. Relative differences among species were similar between rivers and lakes for S:N, but not for δ 34 S. The piscivore walleye ( Sander vitreus) had distinctly higher S:N than other species. In coastal rivers, muscle δ 34 S was highest in purported anadromous species, whereas in lakes muscle δ 34 S was most frequently highest in walleye. Within populations, [THg] was positively related to δ 15 N and δ 34 S, particularly in lakes. Within food webs, [THg] was positively related to δ 15 N in both coastal rivers and inland lakes, and positively related to S:N in coastal rivers, but not related to δ 34 S in either habitat. Our results further our understanding of sulphur in freshwater food webs and its association with mercury dynamics.