Thiamine concentrations in lake whitefish eggs from the upper Great Lakes are related to maternal diet

Interpreting stable isotope patterns with depth: A comment on Riley et al. (2011)

“…Thus, lake whitefish feeding in deeper habitats should display more depleted carbon signatures. Though Riley et al (2011) observe in their results that "Isotopic carbon signatures (δ 13 C) were significantly more 13 C depleted in lake whitefish from Lake Huron than from Lake Michigan" (page 734), they contradict this observation by concluding in their discussion that "…lake whitefish in Lake Huron tend to feed in more near shore environments than those in Lake Michigan as indicated by the more enriched δ 13 C signatures of fish from Lake Huron" (page 735).…”

“…In their recent article, Riley et al (2011) discuss isotopic differences between adult female lake whitefish collected from lakes Michigan, Huron and Superior and how those differences relate to potential differences in habitat use. In their discussion, the authors interpret their isotopic evidence as indicating a greater reliance on near shore resources for lake whitefish collected in Lake Huron compared to those collected from Lake Michigan.…”

“…To be sure which is the correct conclusion, I digitized the stable isotope data presented by Riley et al (2011) in their Fig. 1 (while the caption of the figure indicates that these are stable isotope signatures of lake whitefish eggs, the isotopic signatures are actually for adult female lake whitefish; S. Riley, personal communication).…”

“…Even without the contradictory statements in their discussion, conclusions by Riley et al (2011) regarding differences in resource use between Lake Huron and Lake Michigan based on lake whitefish δ 13 C are unsupported. Baseline isotopic carbon signatures can vary greatly among lakes, even within taxa (Foster and Sprules, 2010).…”

“…Baseline isotopic carbon signatures can vary greatly among lakes, even within taxa (Foster and Sprules, 2010). To interpret isotopic differences between lakes as indicative of differences in resource use, Riley et al (2011) make an unstated (and untested) assumption that lake whitefish from both lakes have similar isotopic baselines (i.e., the isotopic signatures of their prey are identical over depth in both lakes). Riley et al (2011) do present data that show the range of values for dreissenids encountered in Lake Huron and Lake Michigan (both references to unpublished data) were similar.…”