Fin Whales, Balaenoptera physalus: At Home in a Changing Mediterranean Sea?

Abstract

Abstract 1. The relationship of Mediterranean fin whales ( Balaenoptera physalus ) to their Atlantic conspecifics has puzzled zoologists for centuries. Recent data indicate the occurrence of two distinct populations, one resident in the Mediterranean Sea and the other a seasonal visitor to the western Mediterranean from the northeastern North Atlantic Ocean. 2. Resident Mediterranean fin whales are nomadic opportunists that have adapted to exploit localised mesoscale hotspots of productivity that are highly variable in space and time. These appear to be fairly widespread across the region during winter, whereas in summer favourable feeding habitat is dramatically reduced, concentrating mostly in the western Ligurian Sea and Gulf of Lion. This prompts a reinterpretation of the movement pattern of resident fin whales, based on a contraction/dispersion hypothesis caused by seasonal variability in available feeding habitat, as opposed to a pattern of migrations occurring along defined directions as is common in other Mysticetes. 3. Calving peaks in autumn but has been observed year-round throughout the Mediterranean, suggesting that resident fin whales engage in breeding activities whenever favourable physiological conditions occur. It can be assumed that the Mediterranean environment, which is relatively forgiving in comparison to oceanic habitats, combined with negligible predation pressure and high potential for sound-mediated socialisation due to the region's relatively small size, might have provided year-round resident fin whales an extended and more flexible calendar of breeding and feeding opportunities. 4. Considering the Mediterranean fin whales’ small and possibly decreasing population size, low survival rate and the high pressure from many threats deriving from human activities such as vessel traffic, noise, chemical pollution and likely climate change, their status raises considerable concern and conservation measures should be urgently implemented.