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The North Atlantic blue whale was depleted by modern whaling and it is still considered to be highly endangered. Despite its protection in 1954, catches continued in the South European Atlantic Shelf (SEAS) region and immediately adjacent waters until 1979. We compiled catches and investigate abundance trends in the region using original data from whaling (1921–1985) and scientific surveys around the last years of exploitation (1981–1987). The struck and lost rate was estimated at 3.2% for sperm whales and 2.3% for baleen whales. The compiled records include 60 catches, with an additional 1–2 blue whales likely struck and lost. From these, 29 individuals had been correctly reported as blue whales but 31 were mislabelled as fin whales. After correcting for loss rates, the number of blue whales killed in the region was estimated at 61 in 55 years (1.12 individuals/year). The data from the 1950s shows some oversized fin whales but it is unclear whether they are due to an incorrect reporting of species or to incorrect measurements, so it cannot be discarded that the actual number of blue whales caught was slightly higher than estimated. Mean body length of reported blue whales was lower than in higher latitudes of the North Atlantic, probably reflecting geographical stratification with higher proportion of immatures in the SEAS. The ratio between catches or sightings of blue whales and those of fin whales was 5.9% in the southern part of the SEAS previous to exploitation, it declined to 0.02–0.18% in the 1920s, and increased thereafter up to 1.6% in the 1980–1990s. Taking as reference the population size of fin whales in the SEAS, that of blue whales at the end of the 1980s can be guessed to be at ca337-497 individuals. Considering accepted population estimates in other areas as well as the observed rates of increase, current abundance is thought to be over a thousand whales in the SEAs and at in the order of 4000–5000 individuals for the whole eastern North Atlantic basin. [ABSTRACT FROM AUTHOR]

[Display omitted] • δ13C, δ15N and δ34S were analysed in skin from 5 Icelandic baleen whale species. • MixSiar model showed that krill was the main prey for all species except common minke whales. • In humpback whales, dependence on krill may reduce entanglement risk in fishing gear. • Isotopic niche overlap between species was small, except between blue and fin whales. • Niche overlap between fin and blue whales suggests strong interspecific competition. The highly productive waters off Iceland are an important feeding ground for baleen whales. Five balaenopterid species coexist there during the summer feeding season: the blue whale, the fin whale, the sei whale, the humpback whale and the common minke whale. For capital breeders such as baleen whales, niche partitioning and reduced interspecific competition during their stay in the feeding grounds may be critical for the completion of their annual cycles and the long-term stability of populations. Coexistence often entails spatio-temporal or trophic segregation to avoid competitive exclusion. With the aim of studying how these species share habitat and trophic resources, we analyzed the δ13C, δ15N and δ34S values in skin samples. Bayesian stable isotope mixing models to calculate compositional mixture of food sources showed that most species segregate by consuming different prey. Segregation was further enhanced by some degree of spatio-temporal exclusion. Overall, clear ecological niche partitioning was apparent between all species except between blue and fin whales. All the species consumed krill and, except for the common minke whale, this was the dominant prey. Among baleen whales, common minke whales and humpback whales were the major predators of sand eel, capelin and herring. In humpback whales, a strong reliance on krill may explain the apparently low rates of local entanglement in fishing nets as compared to other areas. Except for the blue whale, all species have shown evidence of adapting to shifts in prey availability and thus suggested capacity to cope with variability. However, in a scenario of increasing environmental variability associated to global warming, the overlap between ecological niches may have to decrease to allow long-term coexistence. [ABSTRACT FROM AUTHOR]