Ocean health depends more on whales than we thought
Baleen and sperm whales, known collectively as the great whales, include the largest animals in the history of life on Earth. Though large in size, whales have long been considered too rare to make much of a difference in the ocean, and the focus of much marine ecological research has been on smaller organisms, such as algae and planktonic animals. While these small organisms are essential to life in the sea, they are not the whole story. As great whales recover from centuries of overhunting, scientists are beginning to appreciate their roles as ecosystem engineers of the ocean.
A recent synthesis, published in Frontiers in Ecology and the Environment, evaluates decades of research on the ecological role of great whales. The authors, led by Joe Roman at the University of Vermont, suggest that the influence of these animals has been substantially undervalued because, until now, scientists have underestimated the degree to which the decline in whale population has altered marine ecosystems.
Commercial whaling dramatically reduced the abundance of great whales — by at least 66% and perhaps as high as 90%, according to some estimates — but recovery is possible, and potentially critical for ocean resiliency.
Among their many ecological functions, whales recycle nutrients and enhance primary productivity, locally and on a regional scale. Whales mix the water column, and after feeding at depth, release surface plumes of fecal material. This "whale pump" supplies iron and nitrogen - essentially fertilizers - to primary producers in the surface ocean. Further, the migrations of baleen whales between highly productive, high-latitude feeding and low-latitude calving grounds are among the longest annual movements of mammals. By fasting in these winter calving grounds near the equator, humpback whales, for example, release nitrogen in the form of urea into comparatively nutrient-poor areas — transporting nutrients nearly 10,000 kilometers on the "great whale conveyor belt."
Sometimes, commercial fishermen have seen whales as competition. But this new paper summarizes a strong body of evidence that indicates the opposite can be true: whale recovery "could lead to higher rates of productivity in locations where whales aggregate to feed and give birth," supporting more robust fisheries.
Sperm whale image via Shutterstock.
Read more at University of Hawai'i at Mānoa