75 scientists have compiled 10 years’ worth of data on the migration patterns of 23 of the Pacific Ocean’s major species, including blue whales, bluefin tuna, sharks and albatrosses, to reveal two oceanic ‘hotspots’ that are teeming with marine life.
These two vast areas in the North Pacific Ocean, one off the west coast of the United States and the other between Hawaii and Alaska, provide migration corridors for large marine predators chasing seasonal concentrations of prey. These biological hotspots, rich in life, have been described as ‘marine counterparts of East Africa’s Serengeti plain’.
Chasing down predators
Between 2000 and 2009, the 23 marine species were tracked using electronic tags, to record their movements and the water conditions around them, including temperature, salinity and depth. In total, the programme deployed 4,306 electronic tags, yielding 1,791 individual animal tracks, and resulting in 265,386 days’ worth of tracking data.
This ambitious work is being hailed as the largest ever ‘biologging’ study.
The result is the most comprehensive view to date of how top predators follow and find the biological hotspots of the sea as seasons shift. The findings are published today in Nature.
“It is like asking, ‘How do lions, zebras and cheetahs use Africa as a whole continent?’, only we have done it for a vast ocean,” said Barbara Block, a marine scientist at Stanford University in California and lead author of the paper.
“We have had single-species papers before on a lot of the migration patterns, but they have never been put together as a whole.”
Records from the tags show two ‘hotspot’ regions where the predators’ migration routes concentrate in the North Pacific, which act like a trans-oceanic migration highway.
“These are the oceanic locations where food is most abundant, and that’s driven by high primary productivity at the base of the food chain. These areas are the savannah grasslands of the sea,” added Block.
Upwelling nutrient-rich cold waters create an abundance of plankton, which itself supports huge swarms of krill, the founding layer of the marine food chain. This brings in many other predators, including those that feed directly on the krill like blue whales, to those that are after the fish that also feast on the krill, such as bluefin tuna.
The results also showed that slightly different preferences for water temperature prevent closely related species (e.g. salmon sharks, white sharks and mako sharks) from treading on one another’s fins. Many species with very long migratory paths, such as yellowfin tuna, bluefin tuna, white sharks, elephant seals and salmon sharks, were also found to faithfully return from their migration to the same region every season.
The study data has left scientists excited, “we can now predict when and where individual species are likely to be,” said Daniel Costa, an ecologist at the University of California, Santa Cruz, and a co-author of the paper.
The ability to map the ocean’s main predators’ migration paths allows conservationists to focus their efforts to protect and conserve the biodiversity of the hotspots.
Block says that “knowing where and when species overlap is valuable information for efforts to manage and protect critical species and ecosystems”.
Read the paper in nature – ‘Tracking apex marine predator movements in a dynamic ocean’
Alex Royan, ARKive Species Text Author