The recovery of southern sea otters appears to have taken an
upturn, according to results from the annual California sea otter
survey released by the U.S. Geological Survey. Yet despite an
overall increase in sea otter abundance, sharks have been
“taking a bite” out of the portion of the population that could
fuel expansion into new areas.
“There’s much more to the story here than the main finding
would suggest,” said Dr. Tim Tinker, a research ecologist who
leads the USGS sea otter research program. “We are looking
into various factors that may be affecting the survey results,
including a boom in urchin abundance from Big Sur to
Monterey that may explain the uptick in numbers in the range
center, and high levels of shark bite mortality that are likely
responsible for continued declines at the north and south ends
of the range.”
This year’s survey results suggest an increasing trend over
the last five years of almost 2 percent per year and the
population index, a statistical representation of the entire
population calculated as the three-year running average of
census counts, has climbed to 3,054 from 2,711 in 2010. The
growth is accounted for by an unexpected jump in numbers in
the center of the sea otter’s range, an area that spans from
Monterey south to Cambria.
While the population index continues to trend upward, the
northern and southern subsets of the population continue a five-
year decline, dropping 2 percent and 3.4 percent per year,
respectively, numbers consistent with increased shark bite
induced mortality in these same areas.
Since the 1980s, USGS scientists have computed the annual
population index and evaluated trends in the southern sea otter,
“Enhydra lutris nereis,” a federally listed threatened species
found in California. For southern sea otters to be considered for
removal from threatened species listing under the Endangered
Species Act, the population index would have to exceed 3,090
for three consecutive years.
upturn, according to results from the annual California sea otter
survey released by the U.S. Geological Survey. Yet despite an
overall increase in sea otter abundance, sharks have been
“taking a bite” out of the portion of the population that could
fuel expansion into new areas.
“There’s much more to the story here than the main finding
would suggest,” said Dr. Tim Tinker, a research ecologist who
leads the USGS sea otter research program. “We are looking
into various factors that may be affecting the survey results,
including a boom in urchin abundance from Big Sur to
Monterey that may explain the uptick in numbers in the range
center, and high levels of shark bite mortality that are likely
responsible for continued declines at the north and south ends
of the range.”
This year’s survey results suggest an increasing trend over
the last five years of almost 2 percent per year and the
population index, a statistical representation of the entire
population calculated as the three-year running average of
census counts, has climbed to 3,054 from 2,711 in 2010. The
growth is accounted for by an unexpected jump in numbers in
the center of the sea otter’s range, an area that spans from
Monterey south to Cambria.
While the population index continues to trend upward, the
northern and southern subsets of the population continue a five-
year decline, dropping 2 percent and 3.4 percent per year,
respectively, numbers consistent with increased shark bite
induced mortality in these same areas.
Since the 1980s, USGS scientists have computed the annual
population index and evaluated trends in the southern sea otter,
“Enhydra lutris nereis,” a federally listed threatened species
found in California. For southern sea otters to be considered for
removal from threatened species listing under the Endangered
Species Act, the population index would have to exceed 3,090
for three consecutive years.