Work

Harbour porpoise feeding ecology in Portuguese waters

Year: 2026

Type: article

Abstract: The harbour porpoise ( Phocoena phocoena ) was recently classified at national level as “Critically Endangered” in Portugal, emphasising the urgent need for a dedicated conservation action plan for the population (commonly known as the Iberian porpoise population). A better understanding of the porpoise’s feeding ecology can inform appropriate conservation measures and, therefore, a combination of stomach content analysis and Stable Isotope Analysis was used to estimate the feeding ecology of harbour porpoises in Portugal over the past two decades (2003-2020). The analysis of 157 stomach contents identified Common dragonet ( Callionymus lyra ), Trisopterus spp. and Chelon spp. as the main prey species of Iberian harbour porpoise in Portuguese waters. Moreover, isotopic ratios suggested that porpoises have coastal feeding habits. Muscle isotopic ratios also suggested Trisopterus ( Trisopterus luscus were used in analysis) as the main potential prey, while hepatic stable isotopes revealed dietary variations depending on the trophic enrichment factors. Temporal and seasonal diet variations suggest that harbour porpoises may replace the predominant prey species in response to prey availability, movements within their distribution range, and/or seasonal requirements. Overall, the diet inferred from Stable Isotope Analysis was consistent with that derived from stomach content analysis, highlighting a long-term consumption of Trisopterus spp. (probably Pouting) in Portugal. In addition, this study highlights a marked overlap between fishing grounds and porpoise feeding areas, which may explain the high porpoise bycatch rates observed in northern Portugal.

Source: Marine Environmental Research

DOI: 10.1016/j.marenvres.2026.108479