Stable isotope analysis and fin whale subpopulation structure in the eastern North Atlantic

Abstract

The North Atlantic fin whale was subject to heavy exploitation in the past and, despite partial recovery, it is still considered endangered. Recent research has questioned its currently accepted subpopulation structure and migratory movements, challenging management and conservation efforts. Here we contribute to this discussion by presenting results of stable isotope analysis of fin whale bones and krill samples collected from fin whale stomachs from two exploited areas, west Iceland and northwest Spain, and comparing these results with North Atlantic isoscapes. In krill, d15 N values were highly variable and no significant differences in d C values in bone were higher than in krill, due to trophic enrichment, and were not significantly different between areas. Both krill and bone results were slightly inconsistent with the local isoscapes, maybe due to seasonal variations in local productivity and in krill diet and, in the case of bone, to its capability to integrate long-term isotopic values, derived from food consumed in distant areas. Conversely, d18 O values, which reflect the basal signal of sea water, were consistent with isoscapes and significantly higher in whales from northwestern Spain, possibly indicating migration to breeding grounds located at lower latitudes.

Isotopic niches of fin whales from the Mediterranean Sea and the Celtic Sea (North Atlantic)

“…18 O values analysed in bones of fin whales from northwestern Spain and Iceland suggested intricate structure of fin whale subpopulations exploiting different habitats and with latitudinal migrations that are still far to be completely understood (Vighi et al, 2016).…”

Modelling the spatial abundance of a migratory predator: A call for transboundary marine protected areas

“…In fact, from early August onwards, off‐shore French waters support a high biomass of age 0 fish (i.e., juveniles) of the European anchovy Engraulis encrasicolus (Boyra et al, ). This small pelagic fish could constitute the main food resource for fin whales during this period in the BoB as has been demonstrated for other areas such as the Celtic Sea, where fin whales feed on age 0 sprat Sprattus sprattus and herring Clupea harengus (Vighi et al, ).…”

“…There are no studies on fin whale diet in the inner part of the BoB, but their diet off north‐western Spanish waters is constituted by krill (mainly euphausiids) and small pelagic fish (Aguilar, ). Fin whales are reported to rely on krill when available and to prey on small pelagic fish otherwise (Vighi et al, ). In the BoB, plankton blooms take place in spring and late autumn, whereas in summer and winter this area reaches minimum plankton biomass (Pingree & Garcia‐Soto, ).…”

“…Geographical references are located in Figure 1 Figure 1 fish (Aguilar, 2009). Fin whales are reported to rely on krill when available and to prey on small pelagic fish otherwise (Vighi et al, 2015).…”

“…Lack of detailed knowledge about their migratory patterns partly stems from most research taking place in non-breeding high latitudes areas, while temperate latitudes have been less studied (Mizroch, Rice, Zwiefelhofer, Waite, & Perryman, 2009). Fin whale population structure in the NA is similarly poorly known, though recent studies suggest the existence of two subpopulations (Vighi, Borrell, & Aguilar, 2015). Fin whales present in the Bay of Biscay (BoB) are part of the British Isles-Spain-Portugal subpopulation, with an estimated abundance of 17,400 individuals in Aguilar & García-Vernet (2017).…”