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Sea Otter Savvy

Sea Otter Science And Community Outreach

Sea Otters on the Island of Blue Dolphins, Part 2

sni raft ottersA rare photo of a raft of sea otters at the remote San Nicolas Island, CA

By Gena Bentall

Read Part 1 of this series.

rock crusher fog 350x263    Fog blankets the shore and sleepy elephant seals at San Nicolas IslandThe San Nicolas Island sea otter research team drives down the winding road to the beach aptly called Rock Crusher to take a first look for sea otters. Rock Crusher, at the southwest end of the island, is known for pounding surf, otherworldly rock formations, northern elephant seals and the most likely place to find the sea otters of San Nicolas. The kelp beds here can extend from shore out 2 kilometers, forming optimal habitat for a growing sea otter population. On this first day of our survey, however, few of those features are visible in the dense fog that rests heavily on the water. The winds have calmed, the air is still, and the marine layer settles in. Only the closest rocks and resting elephant seals are visible. Beyond that, all fades to pearly grey. For today, San Nicolas will keep his secrets hidden in the mist.

 

San Nicolas Island sea otter counters hits the trails with their Questar telescopesSan Nicolas Island sea otter counters hit the trails with their Questar telescopesAfter a good night’s sleep, we are all up at dawn to check the weather and plan for the day. From our quarters on an island plateau a wispy crown of fog is visible, hinting that viewing may still be obscured. The oversight of the San Nicolas Island sea otter census has been the responsibility of Brian Hatfield of the US Geological Survey Western Ecological Research Center for 30 years. As expected, he assigns each team member a section of the rugged coastline, dividing the island neatly into uneven quarters: the southeast side, the southwest side, the north side, and the offshore reef known as The Boilers. San Nicolas Island is the second smallest of the Channel Islands at only 8 km from west to east tip of its leaf shape. Each hiker must search meticulously for sea otters in their section and mark them on a map. Despite the wisps of fog, the team is excited to hit the trails in search of otters.

 

sni scope boilers 350x263Questar telescope pointed at The Boilers kelp bed in the distanceMy assigned section is The Boilers which is notorious among the sea otter biologists coming to the island. This shallow rocky outcrop rises 3.5 km (2.2 mi) from the island’s southwest tip, providing a foothold for a vast bed of giant kelp, Macrocystis pyrifera, and habitat for a myriad of other species including sea otters. Surveyors assigned to this location must have expert “otter spotting” skills to not only spot, but count, sea otters as distant as 4 km (2.5 mi). Our most trusted tool for accomplishing this is the Questar telescope---not a standard spotting scope but a true telescope designed for looking at celestial, rather than mustelidal bodies.

As I reach my hilltop vantage point east of the Boilers, I can see I am in a race for visibility against the fog, and the fog has a head start. Within minutes, any chance of spotting sea otters in the kelp bed is lost in a dense fog bank riding the wind to shore. For the two hours I must wait for the fog to clear, I at least have the soundtrack of the barking sea lions, croaking elephant seal bulls, and breaking surf to keep me company. At last, under the heat of the noon sun, the fog recedes, and the kelp of The Boilers reef rolls out before my scope like a vast carpet. 

Slowing panning the scope from the east end of the kelp bed to the other, my eye seeks the tiny search image of a sea otter, dark against the kelp—where there is one, there are often others---two, three, eight, twelve in raft—I find four rafts and several single otters. By the end of my day I have counted over 40 adult sea otters with 5 pups at The Boilers. After meeting up with my teammates, I discover that my section contained half of the total number of sea otters counted that day. Only once since the translocation occurred in the late 1980s, has the total count of sea otters at San Nicolas Island topped 100. Today, it will be fewer.

sni raft otters pupsSea otter moms and pups with a territorial male at San Nicolas IslandThe sea otters at San Nicolas Island seem to thrive. They find high-calorie prey abundant and easily acquired. Vast beds of giant kelp encircle the island, offering habitat for prey, shelter from predators, and security for pups. The crowds of mainland Southern California are 100 miles away. Understanding why populations thrive or decline is rarely simple, and even arriving at a sound theory can be a bit like putting together a 500-piece puzzle. We expect the San Nicolas sea otter population to expand to fill the available habitat and yet, 30 years after the translocation, the otters have not approached the island’s carrying capacity.

Because their metabolism (and thus, their appetite) runs so high, one key piece of the puzzle for sea otter populations everywhere is prey. What is available and abundant in the habitat and what are the otters selecting to eat? For this reason, an important goal of these quarterly expeditions is the acquisition of foraging data, much the same as it was during my thesis work in 2003. Team members visually locate foraging sea otters and, with the help of our trusty Questars, follow them for as long as possible to identify, count, and estimate size of prey. As a comparison point, we know what they were eating back in 2003 (see Part 1). Has that changed? Are the big, calorie-rich red urchins still a mainstay? How does that relate to changes we see in the habitat itself? With urchin barrens on the rise on the mainland of California, the otters of San Nicolas Island may help scientists unlock deeper mysteries of the relationship between sea otters and their sea urchin prey.  Look for Part 3 of Sea Otters at the Island of the Blue Dolphins to learn more about the interwoven stories of the sea otters, urchins, and kelp of coastal California. 

sni purps 450x320Purple urchins (Strongylocentrotus purpuratus) in a San Nicolas Island tidepool. Urchins slowly grind their own caves in the sandstone.

All photos by Gena Bentall