Niche partitioning, distribution and competition in North Atlantic beaked whales
This study aimed to investigate the ecology of the six species of beaked whales that occur in the North Atlantic, and define and compare the niches that each species occupies in this area in relation to a number of factors. To counteract the difficulties of studying beaked whales in the wild, a variety of different approaches were used to investigate their ecology. From these analyses, a general beaked whale niche could be identified, covering the niches of all members of the family Ziphiidae in the North Atlantic, as deep-diving oceanic predators of deep-water squid, fish and to a much lesser extent other organisms, in areas with a sloping seabed and in all latitude and temperature ranges. However, no one species occupies this entire general beaked whale niche and each species occupies its own niche partition defined by individual species preferences for specific ranges of different niche factors. The primary partitioning of the general beaked whale niche is based on prey size, with one group of species, the large prey consumers (LPCs), consisting of two species that consume all prey sizes but preferentially take larger prey, and a second group, the small prey consumers (SPCs), consisting of four species that specialise in consuming smaller prey items. Within the LPCs, the two species are segregated geographically, probably by water temperature preferences, with Cuvier’s beaked whale (Ziphius cavirostris) only occurring in warmer, more southern waters and northern bottlenose whale (Hyperoodon ampullatus), only occurring in colder, more northern waters. Within the SPCs, there is a similar geographic partitioning, with Sowerby’s beaked whale (Mesoplodon bidens) only occurring in the coldest, most northern waters, Gervais’ beaked whale (Mesoplodon europaeus) in warmest, most southern waters and True’s beaked whale (Mesoplodon mirus) in intermediate waters between these two species. The last beaked whale species in the North Atlantic, Blainville’s beaked whale (Mesoplodon densirostris) differs from al other species in the habitat if occupies, preferentially occurring in over steeper areas of seabed and in relatively shallow waters, especially around oceanic islands, while all other species preferentially occur over areas with more gentle gradients and deeper water depths.