Baleen and sperm whales, known collectively as the great whales, include the largest animals in the history of life on Earth. With high metabolic demands and large populations, whales can play an important role in ecosystem dynamics in several ways, including the vertical and horizontal transport of nutrients, as detrital sources of energy and habitat in the deep sea, and as predators and prey of other marine animals. Whales facilitate the transfer of nutrients by releasing fecal plumes near the surface after feeding at depth and by moving nutrients from highly productive, high-latitude feeding areas to low-latitude calving areas. Methods to examine these processes include field measurements of prey consumption and nutrient cycling using electronic tags, drones, prey mapping, and remote sensing. Whales can influence the carbon cycle by storing carbon in their biomass; sequestering it in deep-sea whale falls; and stimulating primary productivity, though there is uncertainty regarding the fate of carbon in marine food webs.
Baleen whales undertake the longest seasonal migrations of any mammal, generally moving from high-latitude feeding grounds to low-latitude breeding grounds. In this talk, I will discuss how these migrations can mediate the transport of nutrients and energy from productive to nutrient-limited ecosystems. My colleagues and I have quantified the latitudinal translocation of nutrients through whale carcasses, placentas, and urea—a process we refer to as the great whale conveyor belt—focusing on the migration of four species that exhibit clear annual migration: gray whales, humpback whales, and North Atlantic and southern right whales. In addition to biomass from carcasses and placentas (estimated at 31,791 tons yr-1 for mothers and calves and 55,176 tons yr-1 for the entire population), migrating whales release nitrogen through urea, placentas, and carcasses (6,213 tons N yr-1 for mothers and calves, 7,164 tons N yr-1 for the entire population). To our knowledge, this movement is the largest long-distance animal subsidy on the planet, a flux that would have been about three times higher before commercial whaling. Such subsidies can support entire trophic webs, from primary producers to scavengers, including benthic and pelagic organisms. In areas such as the Hawaiian Islands Humpback Whale National Marine Sanctuary, humpback whales transport nitrogen that is approximately double the vertical flux, or upwelling, in the region. Although whales face threats from fisheries, shipping, climate change, and other human activities, conservation efforts can improve populations and help restore nutrient movement and other ecological functions.
