Comments on "Analysis of permanent magnets as elasmobranch bycatch reduction devices in hook-and-line and longline trials"

Abstract

A recent study (Fish. Bull. 109:394-401 (2011)) purportedly tests two hypotheses: 1. that the capture of elasmobranchs would be reduced with hooks containing magnets in comparison with control hooks in hook-and-line and longline studies. 2. that the presence of permanent magnets on hooks would not alter teleost capture because teleosts lack the ampullary organ. Review of this paper shows some inconsistencies in the data supporting the first hypothesis and insufficient data and poor experimental design to adequately test the second hypothesis. Further, since several orders of teleosts are known to possess ampullary organs and demonstrate electroreception, grouping all teleosts in a study design or data analysis of magnetic hook catch rates is not warranted. Adequate tests of the hypothesis that permanent magnets or magnetized hooks do not alter teleost capture requires a more careful study design and much larger sample sizes than O'Connell et al. (Fish. Bull. 109:394-401 (2011)).