Are fin whales at the mercy of available food?
A research project that was carried out in the early 2000s lifted the veil on how krill influences the dispersal of fin whales. It was observed that the more abundant the krill, the more fin whales were dispersed. The opposite was also shown to be true, the less krill available, the more fin whales tend to congregate. This study put forward the hypothesis that in years of low krill abundance, fin whales likely fed on a different prey: capelin. Is this hypothesis true?
To go through the looking glass
From 1998 to 2004, biopsies were carried out on 71 fin whales in the St. Lawrence Estuary. Furthermore, 14 potential prey species were harvested and their isotope signatures were analyzed. Krill abundance and fin whale distribution patterns were studied in parallel over a period of 10 years.
It was established that capelin and a species of krill that goes by the Latin name Thysanoessa sp. had very distinct isotope signatures representing different trophic levels in the food chain. It was therefore relatively easy to distinguish a diet rich in capelin from one rich in krill.
The fin whale biopsy samples, which were collected between 1998 and 2004, cover a period of low krill abundance. The hypothesis predicts therefore that the fin whale diet for these years be rich in capelin. Yet, isotope analyses of these biopsy samples did not show beyond all doubt that the fin whale diet was essentially made up of capelin. The samples may reflect fin whale diet prior to their arrival in the Estuary. Their diet may also have been made up of other prey species, such as sand lance or copepods. Fin whales have become rare in the Estuary since 2000 and this change likely reflects a change in their prey. The investigation continues!
Saguenay—St. Lawrence Marine Park, Fisheries and Oceans Canada, GREMM