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Sighting data of Mustelus mustelus in the Canary Islands

Citation

Espino, Fernando et al. (2022), Sighting data of Mustelus mustelus in the Canary Islands, Dryad, Dataset, https://doi.org/10.5061/dryad.pvmcvdnpq

Abstract

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.

Methods

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

Usage Notes

Refer to README file