Scott Benson in Monterey Bay, CA. During the late summer and fall, leatherback turtles usually arrive in coastal California waters to feed on schools of jellyfish that multiply by the millions when nutrients upwell from the deep. But, each year, variability in ocean conditions affects the number of turtles and where they feed. Some leatherbacks swim across the Pacific Ocean from Indonesian nesting beaches to stop more than 40 miles from the coast without ever moving into nearshore areas.

Many of these turtles are influenced by prominent fronts where cool, recently upwelled waters collide with warmer offshore waters. To determine the current distribution of leatherbacks in offshore waters, I recently conducted an aerial survey with local colleagues aboard a NOAA Twin Otter aircraft. The Twin Otter is well-suited for this assignment because it can fly for a long time, so it allows us to explore these distant waters. Here's a photo taken by Daniel Palacios, an oceanographer from NOAA's Southwest Fisheries Science Center in Pacific Grove.

Our survey area was large, from Cape Mendocino to Point Sur and more than 130 miles from the coast. Each survey was a seven-hour marathon over an electric blue seascape, devoid of the abundance of marine life that is found nearer the coast. Dall’s porpoise were the most commonly sighted marine mammal, located in the recently upwelled plumes of nutrients that extended far from the coast. Here's a photo I took of Pt. Arena lighthouse -- it's between Bodega Bay and Mendocino.

Our perseverance through the long flights was rewarded with an exceptional sighting of sperm whales in flat calm seas (see photo below). We found one leatherback way out there, located among a loose aggregation of another jelly-eating species, the sun fish or mola-mola, and moon jellyfish. These three species hanging out int he same place told us that we were in the right neighborhood.

Following our offshore wanderings, we moved back into the coastal waters. It was nice to be back in a familiar place with the abundant humpback whales, white-sided dolphins, harbor porpoise, and thousands of seabirds. Off the San Mateo coast, we saw many leatherbacks feeding on abundant sea nettles in murky red water that resembled a frothy tomato soup. Between the Russian River and Monterey, we had one last look beyond the coastal shelf and found another leatherback, swimming with purpose to join the coastal menagerie in search of a well-deserved feast after a 7,000 mile swim.
We are encouraged by the turtle sightings and jellyfish aggregations, and we are now preparing to begin our telemetry studies of free-swimming leatherbacks as soon as weather conditions permit.

The details:

Leatherbacks sighted: six

Number of flights: four days (August 26, 28-30), seven hours each day

People who came along on at least one of the flights:

Erin LaCasella (National Marine Fisheries Service-Southwest Fisheries Science Center)
Tomo Eguchi (National Marine Fisheries Service-Southwest Fisheries Science Center)
Katherine Whitaker (local expert)
Kelly Newton (University of California, Santa Cruz)
Tanya Graham (Moss Landing Marine Lab)
Brian Hoover (Moss Landing Marine Lab)
Julia Burrows (Moss Landing Marine Lab)
Daniel Palacios (Southwest Fisheries Science Center)

Pilots:
Nickie Lambert
Nicole Cabana