DOI: 10.5061/dryad.pvmcvdnpq
title: Sighting data of Mustelus mustelus in the Canary Islands

description: These data were generated to investigate the distribution and population
 structure of Mustelus mustelus across the Canarian archipelago. This shark
 is widely found in the eastern Atlantic Ocean and catalogued as
 'Vulnerable'  by the IUCN European assessment. Data on
 the distribution and population structure of this species across the
 islands of the Canarian archipelago, located along an east to west
 gradient in the north-eastern Atlantic, were collected by taking advantage
 of 'Local Ecological Knowledge', in terms of sightings in
 coastal waters. This source of qualitalitve and quantitative data
 (sightings) demonstrated that adults of M. mustelus has a significantly
 larger presence in the eastern and central, than in the western of the
 archipelago. Adult smooth-hound sharks were significantly more observed in
 sandy and sandy-rocky bottoms, with idividuals seen throughout the entire
 year, whereas juveniles aggregate on very shallow waters in spring and
 summer. Such aggregations requiere a special management strategy, as they
 pley a key role in critical life stages; these sites should be protected
 from human perturbations. We also suggest a temporal fishing ban between
 April and October, when individuals tend to concentrate on earshore
 waters. Because of the large differences in presence of this shark among
 the Canarian Islands, management of the species should be adapted to th
 specific peculiarities of each island, rather than adopting a management
 policy at the entire archipelago-scale. Overall, this study sets the basis
 for further investigation to promote conservation of this vulnerable shark
 in the study region.
description: 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 R<sub>4.0.2</sub> 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
description: Refer to README file