Optimizing fishing time: One vs. two-night fyke net sets in Great Lakes coastal systems

Synoptic surveys of fish assemblages captured using fyke nets typically use a soak time of one night. We questioned whether enough information was gained from maintaining the nets for a second night to justify both the additional effort and the resulting reduction in sites sampled per field season. We compared fyke net catches from one-night and two-night sets at Great Lakes coastal margin ecosystems. Re-setting nets for a second night increased species richness by an average (± SE) of 12 ± 0.06%. This translated to an average of 2.5 ± 0.25 additional species captured. Ordinations of the assemblage data revealed that one-night and two-night catches from the same site (catch pairs) were much more similar to each other than were catches from different sites: the Kendall's kappa concordance values between one-night catches and their two-night pairs measured along the first three ordination axes were 80%, 88%, and 87%, respectively. Catch pairs plotted more closely, Sorensen's distances were smaller, and assemblages were much more concordant than were pairs of catches randomly selected from different sites. Bootstrap analyses of catch species richness indicated that there was little difference between adding effort by increasing soak time versus adding effort by increasing the number of nets. Our data indicate that one- and two-night sets generally produce comparable assemblage data. For synoptic studies, the increase in statistical power gained by increasing the number of sites sampled will typically be more important than the moderate amount of additional information acquired by fishing sites for a second night.