Decade-long Study Of Pacific Predators Shows İmportance Of Biological 'Hotspots'

An unprecedented decade-long study of apex predators in the Pacific Ocean found a wider range of distribution among some species than previously thought, unknown relationships between other species, and the importance of biological "hotspots" to the survival of most of these sea creatures. The field program, dubbed Tagging of Pacific Predators – or TOPP – looked at 23 species from 2000-09 and included researchers from multiple institutions.

Results of the study are being published this week in the journal Nature.

"One thing that quickly became apparent is that there are many similarities among top predators in the California Current System," said Bruce Mate, director of the Marine Mammal Institute at Oregon State University and co-author on the study. "There is a strong overlap in territory, for example, between blue whales and tuna. Blue whales eat krill; the tuna eat fish that eat the krill.

"But the krill, and the ocean conditions that promote its abundance, are key to both species," added Mate, who directed the cetacean portion of the TOPP study. "When there are hotspots of krill or other food, the apex predators need to find them."

Most of these hotspots result from upwelling, or the fertilization of surface waters with nutrient-rich deeper water as a result of wind-driven mixing. One such biological hotspot occurs just west of Santa Barbara, Calif., where the wind comes around Point Conception and triggers strong upwelling.

"When the winds there died, we watched whales eat literally all of the available food in three days, and then they just took off," Mate said. "Most of them moved to the Farallon Islands near San Francisco, which is another productive feeding area. Blue whales likely know these hotspots from experience. Instead of waiting for upwelling to renew the krill population, they'll travel 400 miles in three days to find a new food source."

The study also found, however, that some species have more difficulty with poor ocean productivity, as often happens during El Niño events. Coastal birds also depend on krill, and during an El Niño in 2006-07, most of their hatchlings failed, the researchers noted.

Pinnipeds – including seals and seal lions – normally experience a successful birth rate of 80 percent, but in El Nino years, that drops to 20 percent. "Most of the offspring die," Mate said, "because the mothers cannot produce enough milk."

The TOPP study was the first ocean basin-scale study of marine predator distribution and movement ever conducted, and the massive amount of data collected will help resource managers develop effective ocean protection strategies, the researchers say.