Temporal changes in the dietary niche of sympatric seals provides insight into the role of competition in population declines (dataset)

Temporal changes in the dietary niche of seals has been quantified from analysis of prey hard parts retained in scat samples. The study utilised six datasets collected over summer months (June, July and August) between 1987 and 2011 from haulout sites in two regions of Scotland (Moray Firth and southeast Scotland). The attached data file underpins the publication "Temporal changes in the dietary niche of sympatric seals provides insight into the role of competition in population declines". Data are stored in a csv file which can be opened in various programmes, including Microsoft Excel (dietData.csv). Seal species - Samples were assigned to seal species following three rules developed and tested in previous studies (Matejusová et al. 2013; Wilson 2014): (1) if the seals hauled out were from a single species, it was assumed that all samples collected on that visit were from that species, (2) if the haulout composition was mixed, and one species represented more than 80% of the total number of seals hauled out, then samples were assigned to that dominant species, and (3) if neither species represented more than 80% of the total number of seals hauled out, collected samples were processed in Reed et al. (1997) where predator species was molecularly assigned. Prey species - Fish sagittal otoliths and cephalopod beaks were identified to the lowest possible taxonomic level (Härkönen 1986; Clarke 1986; Leopold et al. 2001). Prey size - The size of prey consumed can be back-calculated from the size of prey hard parts using known allometric relationships. To allow estimation of prey size, the length and width of otoliths, and the lower rostral or lower hood length of beaks, were measured when possible.