What's on the menu? Diet of common minke whales (Balaenoptera acutorostrata) stranded on the Atlantic Iberian coast

Abstract

There is little information regarding the ecology of common minke whales (Balaenoptera acutorostrata) in southern waters of the Northeast Atlantic. As such, stomach contents from common minke whales stranded in the west Iberian Peninsula were analysed (n = 27, 2005–2024) to improve the knowledge about the foraging ecology of this species. Overall, small pelagic fish species (Sardina pilchardus, Trachurus sp., Scomber sp.), that are also targeted by fisheries in this region, were predominant in the diet of common minke whales. In particular, Sardina pilchardus and Trachurus sp. were predominant in Portugal (n = 20; %N: 39.4 and 18.2; %W: 32.9 and 27.9; %IRI: 52.2 and 22.2 respectively), while Scomber sp. prevailed in Northwest Spain (Galicia) (n = 7; %N: 28.7; %W: 53.1; %IRI: 48.8), closely followed by Sardina pilchardus (%N: 40.9; %W: 34.6; %IRI: 45). Despite the similarity in the predominant species (Alosidae and Scombridae families) between sexes, females showed a less diverse diet compared to males. Results suggest a temporal shift in the diet of common minke whales in the west Iberian Peninsula (2005–2015 vs. 2016–2024), possibly related with changes in sardine abundance in this region, resulting from prolonged poor recruitment over several years associated with fishing mortality above sustainable levels. In addition, the estimated length of the main prey ingested by common minke whales was within the legal landing size allowed for fisheries in the west Iberian Peninsula. Finally, both minke whales and fisheries target the same energy-rich species, required to meet the high metabolic cost of living of minke whales. As such, the results of this study suggest the potential for minke whale-fisheries resource competition (in terms of species, size class and quality), stressing the potential indirect or direct threat that this socioeconomic activity may represent for common minke whales. This information may be relevant for the definition of efficient conservation strategies for this Vulnerable population. This study presents the first description of the diet composition of common minke whales in the southern part of their distribution range, in the North Atlantic.