Diving into the diet of sperm whales (Physeter macrocephalus) off the northern Norwegian coast: Insights from fecal DNA metabarcoding

Abstract

Sperm whales are elusive creatures; they spend much of their time out of sight, deep in the oceans. This makes them difficult to study, and previously, studies of their diet have mainly been stomach content analyses of stranded or caught individuals. However, DNA metabarcoding has the potential for solving this problem. This thesis examines the diet of sperm whales in the Norwegian Sea, of which we know very little, and aims to investigate the diet by examining fecal samples utilizing DNA metabarcoding and using surface water samples as a reference. Two types of fecal samples were utilized: ethanol fecal samples, which are ethanol that was filtered from sample-containing jars, as well as regular fecal samples, which are extracted DNA from the fecal matter. For comparison, seven reference surface water samples were selected. For this study, the fecal samples were split into five different sample groups with the closest related water samples. The samples were amplified and sequenced with two primer sets: Leray XT for amplifying and sequencing a fragment of the mitochondrial Cytochrome c Oxidase subunit I (COI) gene, and MiFish-U for amplifying and sequencing a region of the 12S ribosomal RNA gene. The focus point in this study was metazoans, and more specifically, fish species. The 12S marker registered 20 unique fish taxa for fecal samples, of which four were exclusive to fecal samples. The genetic marker COI identified nine unique fish taxa for fecal samples, of which five were exclusive to fecal samples. Surface water samples generally exhibited more unique taxa than fecal samples. Analysis of similarities (ANOSIM) proved significant dissimilarities between the sample types for the overall dataset (including all taxonomic kingdoms), group one in the 12S dataset, group four and the combined group in the COI-Metazoa dataset, and the combined group for the COI-fish dataset. Similarity Percentage (SIMPER) analysis was carried out on the significant groups and illustrated which species were responsible for most of the dissimilarity between the groups. Based on all of the results, it seemed that benthic fish were a smaller part of the diet of sperm whales than previously believed, and that Gadus morhua (Atlantic cod), Sprattus sprattus (sprat), Clupea harengus (Atlantic herring), Trisopterus esmarkii (Norway pout), and Scomber scombrus (Atlantic mackerel) were likely to have been a part of the diet of the sperm whales in the Norwegian Sea in the area of Bleik Canyon, either as primary or secondary prey. Notably, T. esmarkii and S. sprattus had not been registered in the diet of sperm whales before. However, a definitive conclusion on the prey of sperm whales in the Bleik canyon area in the Norwegian Sea cannot be reached, but this study provided insight into the fecal sampling method and the potential diet of sperm whales.