Comment: Not all Biases are Created Equal—A Comment on the Snorkel Survey Bias Observed by Hessenauer et al. (2014)

In their recent paper, Hessenauer et al. (2014) address an important topic, the efficacy of snorkel surveys in detecting Largemouth Bass Micropterus salmoides nests. In their study they compared the observed numbers of reproductively successful and unsuccessful nests in the spring (identified via snorkel surveys) with the actual origin of young of the year collected in the fall as determined by genetic pedigree analysis. Based on that approach, the authors reported observational biases in two aspects of snorkel surveys: nest detection efficacy (where snorkelers missed 50% of the nests that produced young of the year) and nest success/failure determination (where snorkelers misclassified 40% of the nests as unsuccessful while genetic analysis indicated that those nests were actually successful in terms of raising broods to the swim-up stage). Because that study provided one of the few reports of nest or brood detection rates by snorkel surveys (see Shaw and Allen 2014), its findings are particularly relevant to other studies investigating black bass Micropterus spp. reproductive ecology. Unfortunately, the authors drew broad, generalized conclusions regarding bias in snorkel survey methods without acknowledging potentially important methodological differences among snorkel survey techniques. We wish to address some of the detection bias issues raised by Hessenauer et al. (2014) because we feel that the authors did not adequately acknowledge alternative sources of bias in their study and incorrectly cast aspersions on studies that in fact avoided or were unaffected by the biases identified by these authors.