Sighting data of Mustelus mustelus in the Canary Islands

This dataset was collected through personal surveys in the Canary Islands; the survey is included in the README file. All statistical modelling and testing were implemented in the R4.0.2 statistical environment (R Core Team). A t-test checked whether the mean depth at which adults were sighted differed from the mean depth at which juveniles and subadults were sighted. Contingency tables and associated χ2 tests checked for differences in the proportions of sightings according to the seasons (winter, spring, summer and autumn) and habitats of sightings, separately for juveniles and subadults and adults, respectively, for the overall study. Mixed-effects Generalized Linear Models (GLMs) were fitted to the number of sightings by means of the ‘lmerTest’ R package (Kuznetsova, Brockhoff & Christensen, 2017), to test for differences among the three island groups (eastern, central, and western islands), as a fixed factor, and years and islands within each group as random factors. All models were fitted using a ‘negative binomial’ family distribution of residuals, with a ‘log’ link function, which is robust for overdispersed data. Diagnosis plots of residuals and Q–Q plots were visually inspected to check the appropriateness of the fitted models (Harrison et al., 2018). We used the function ‘relevel’ to run models with varying reference levels to assess significant differences between each pair of island groups. References Harrison, X.A., Donaldson, L., Correa-Cano, M.E., Evans, J., Fisher, D.N., Goodwin, C.E.D. et al (2018). A brief introduction to mixed effects modelling and multi-model inference in ecology. PeerJ, 6, e4794. https://doi:10.7717/PEERJ.4794 Kuznetsova, A., Brockhoff, P.B. & Christensen, R.H.B. (2017). lmerTest package: tests in linear mixed effects models. Journal of Statistical Software, 82(13), 1-26. https://doi.org/10.18637/jss.v082.i13