Sea otters may return to Lake Clark: measuring razor clams and bears before they do

Sea otters are a keystone species: remove them and an ecosystem unravels; let them return and you can watch it change again. They were hunted to near extinction in the northern Gulf of Alaska in the late 1700s and 1800s, and with conservation they are recolonizing much of their old range. They have been seen in bays near Lake Clark National Park and Preserve, but not yet along its coast. A National Park Service project is measuring the coast now, before they arrive.

Researchers use pumped water and large metal sieves to collect, count and measure clams. NPS photo.

Why razor clams

Sea otters reduce invertebrate numbers and boost kelp and eelgrass productivity, and the effects cascade through the ecosystem. They love razor clams, which can make up as much as 60 to 80% of their diet. Without otters, razor clams probably flourished, especially in the soft-sediment shores along the park's coast.

Others have a stake too. The coast is home to brown and black bears, which eat razor clams along with salmon and sedges. Clam-eating bears draw some 10,000 visitors a year, and growing, bringing millions of dollars to the local economy, and razor clams are a subsistence and commercial resource in the region.

A sea otter chews on a bivalve. NPS photo.

Measuring the baseline

A marine ecologist with the park service's Southwest Alaska Inventory & Monitoring Network and colleagues spent several weeks on the coast in summer gathering baseline data, a snapshot before conditions change. They are asking:

• Otters: are any here, what are they eating and how hard do they work for it?
• Clams: how many, how big and how old?
• Bears: which habitats do they use, and how many clams, salmon, sedges and marine mammals do they eat?

Baseline data are the "before" in a before-and-after comparison, and in ecology they are often missing because nobody collects them until it is too late.

A brown bear digs for razor clams. NPS photo.

What Katmai suggests

The project builds on Changing Tides in Katmai National Park and Preserve, where sea otters have recently reached carrying capacity after near-extirpation. There the team found clam populations falling as otters stabilized. Brown bears appear to be "prey switching," relying more on sedges than salmon, while their clam eating has stayed stable but low, and some bears have begun to hunt sea otters. Lake Clark may differ because it has extensive soft-sediment habitat, ideal for clam beds, and many brown and black bears.

The team hopes the baseline will help managers decide how to provide recreation, subsistence and commercial opportunities with the least harm to natural resources in a future that will likely also bring more tourism, commercial pressure, sea ice retreat and other changes. The ecologist pointed to the 1989 Exxon Valdez oil spill: no one really knew what natural resources existed before it, and it would have been nice if they had.

Sources

• National Park Service article by Alix Pfennigwerth, biologist and science communicator with the National Park Service (https://www.nps.gov/articles/000/lake-clark-a-keystone-quandary.htm), a U.S. government work in the public domain. Staff are not named in the text.
• National Park Service; rewritten in hubnx's own words.