Point Piedras Blancas Northern Elephant Seal Monitoring
- Brian Hatfield
United States Geological Survey (USGS)
We have monitored, by systematic counts, the growth in population numbers and distribution of breeding Northern Elephant Seals at Piedras Blancas since the colony’s inception in the fall of 1990. A number of weaned seals are flipper tagged with white tags each year. Members of Friends of the Elephant Seal and college students have participated in the tag re-sighting effort.
Summary to Date
Summary data and figures for each year from 2011 to 2016 are under the 'Documents' tab.
2016 summary from Brian Hatfield, USGS:
The number of adult females counted at the rookery (and therefore the number of estimated births) this breeding
season was up by more than 400, resulting in an estimate of the number of births being up approximately 8% from
last year (to roughly 5,700). Although the number of live young-of-the-year seals counted at the end of the season
was a record high (~5,000, Figure 1), this number was up only 2.5% from last year. The difference between the
number of estimated births and the number of live pups/weaners/orphans indicates that mortality was approximately
12% this year (compared to approximately 7% last year). The higher mortality this year is almost certainly due to
the prolonged periods of large ocean swells that often coincided with high tides. In addition to the direct mortality,
it is likely these conditions were responsible for mother-pup separations and the high number of very small orphaned
pups seen during the pup/weaner/orphan count this year. Although a subjective measure, the estimate of “very
small” seals this year (almost 300) is about three times the number counted last year. As in 2015, deaths of
pups/weaners that appeared to be in good body condition were rare (unlike 2014).
The two coastal segments with the biggest increases in pup production this year compared to last year were from Pt.
Piedras Blancas to South Point (the first rocky headland down coast from Pt. Piedras Blancas) and from South Point
to – but not including – VP-3. There was also an increase at the southern end of the rookery (Arroyo Laguna and
south, Figure 2). The segment with the largest decline was the area north of Pt. Piedras Blancas. Fewer numbers at
Arroyo del Corral this year compared to last year accounted for this decline (Figure 3). Slightly fewer pups/weaners
were counted at VP-3. There were actually more counted off the south end of VP-3, but much fewer off the north
end compared to last year.
There was no expansion of the breeding range of the colony this year. Only two pups were counted at the mouth of
Arroyo de la Cruz this year, down from 5 last year. Again this year, no pups were born south of Pt. San Simeon.
- There has been a dramatic increase in the number of pups born at Piedras Blancas, with 1 pup born in 1992 versus roughly 5,700 born in 2016. For annual summaries, click on the 'Documents' tab above.
- The rate of colony growth at Piedras Blancas is higher than at other elephant seal colonies in California.
- Elephant seals from all major rookeries in California have been seen breeding at Piedras Blancas.
- Individuals that were tagged during this monitoring effort at Piedras Blancas have been documented at other colonies in California, and as far away as the Aleutian Islands in Alaska.
- Movements within and among colonies
Figures and Images
Figure 2: Map of the Piedras Blancas area with generalized coastal geomorphic features. At the northern and southern ends of the study area, about 90 and 130 pups were born in the 2004/2005 season, respectively.
- 2016 Elephant Seal summary at Piedras BlancasSummary for 2016 provided by Brian Hatfield, USGS.
68 KB PDF
- 2015 Elephant Seal summary at Piedras BlancasSummary provided by Brian Hatfield, USGS.
50.2 KB PDF
- 2014 Elephant Seal summary at Piedras BlancasSummary provided by Brian Hatfield, USGS.
52.0 KB PDF
- Lowry et al. (2014)Abundance, Distribution, and Population Growth of the Northern Elephant Seal (Mirounga angustirostris) in the United States from 1991 to 2010.
4.1 MB PDF.
- 2013 Elephant Seal summary at Piedras BlancasSummary provided by Brian Hatfield, USGS.
16.5 KB PDF
- 2012 Elephant Seal summary at Piedras BlancasSummary provided by Brian Hatfield, USGS.
14.8 KB PDF
- 2011 Elephant Seal summary at Piedras BlancasSummary provided by Brian Hatfield, USGS.
70.9 KB PDF