The foraging ecology of minke whales (Balaenoptera acutorostrata) in Northeast Scottish waters using stable isotope analysis

The marine environment is undergoing rapid change, impacting the entire food web. Monitoring the ecology of trophic factions that utilise the ecosystem resources is therefore crucial in tracking change and assessing its key drivers. Baleen whales, as mid-trophic level predators, are indicator species that reflect pressure-driven changes at both higher and lower trophic levels. As such, understanding their foraging ecology is critical to informing effective conservation and management during a time of rapid environmental change. The waters of Northeast Scotland provide rich feeding opportunities for large marine vertebrates, such as cetaceans. Migratory baleen whales exploit these productive areas during the summer months to replenish energy reserves lost over winter. The minke whale (Balaenoptera acutorostrata) is the most abundant baleen whale in Scottish waters, yet key aspects of its foraging ecology remain poorly understood. Using bulk minke whale skin tissue, and muscle tissue from their putative prey, stable isotope analysis was conducted to derive δ13C and δ15N values. The aims of this thesis were to: (i) determine the contribution of known prey species to the diet of minke whales in Northeast Scotland and assess prey preferences between adult and juvenile age classes; (ii) establish if age-related dietary differences are reflected in trophic position estimates; (iii) investigate seasonal (spring-summer) variation and overlap in the isotopic niche between adults and juveniles; and (iv) interpret these new findings in the context of emerging threats such as prey stock decline and evaluate their implications for management within the Scottish Marine Protected Area (MPA) network. Minke whale δ13C and δ15N values (mean ± SD) were -17.6 ± 1.4 ‰, and 13.0 ± 1.1 ‰, respectively. Prey δ13C differed between species (sand eel: -18.27 ± 0.68 ‰; sprat: -18.09 ± 0.2 ‰; herring: -18.25 ± 0.53 ‰; mackerel: -19.02 ± 0.45 ‰; whiting: -18.03 ± 0.78 ‰; zooplankton: -18.79 ± 0.28 ‰) as did their δ15N values (sand eel: 11.25 ± 1.60 ‰; sprat: 11.98 ± 0.23 ‰; herring: 11.87 ± 0.57 ‰; mackerel: 11.83 ± 1.01 ‰; whiting: 13.52 ± 1.38 ‰; zooplankton: 10.81 ± 0.63 ‰). Mixing model results (median, low–high 95% credibility intervals) revealed that adult and juvenile minke whales primarily consumed sand eel (Ammodytidae sp.) (0.34, 0.03 - 0.68 and 0.36, 0.03 - 0.74, respectively). Isotopic niche analysis (SEAB ‰2, low–high 95% credibility intervals) showed that adults occupy a smaller niche area than their juvenile counterparts, (1.89, 1.08 – 3.29 ‰2; 4.66, 3.28 – 6.95 ‰2), respectively. The analyses highlight that minke whale foraging behaviour in Northeast Scotland is closely tied to the availability of key prey species, linking their ecology to commercially important fisheries for sand eel. These findings emphasise the need for adaptive management of the Scottish MPA network to account for seasonal prey availability and to ensure that populations of ecologically important forage fish remain sufficient to meet the energetic demands of minke whales during the summer feeding season.<p></p>

Author dc:creator

• Ciaran Dolan (21041687)

• Mixing models
• Diet
• Strandings
• Age class
• MPAs
• Isotopic niche
• Trophic level
• Fisheries

Statement dc:rights

• All rights reserved
• Open Access after 2027-12-01

Identifier

10779/exe.32493600.v1

OAI identifier oai:identifier

oai:figshare.com:article/32493600