NOAA Determines Likely Cause of Ca. Sea Lion Strandings

Information on Recent Strandings and Non-traditional Haulout Site Use by Pinnipeds in California
Presented by NOAA’s National Marine Fisheries Service Southwest Regional Office
August 11, 2009


There was a disruption in the coastal upwelling process off central
 and northern California during May and June, at a time when it is
 normally strong.

It is possible that this disruption may have affected the ecosystem

adversely and therefore it may be tied to
 the unusual animal mortalities observed along the coast. Coastal
 upwelling along the U.S. West Coast is driven by equatorial winds,
 so changes in the normal wind pattern would lead to disrupted
 upwelling. It is still not known what caused the anomalous wind
 pattern, but in the absence of upwelling and wind-driven mixing,
 the water column will tend to stratify, leading to warming and
 decreased primary production in surface waters. This would, in
 turn, result in an impoverished food web. Stratification and
 warming of the surface waters nearshore may also lead to
 dinoflagellate red tides and possibly harmful algal blooms, as a
 secondary effect.
 California sea lions have been stranding at a very high rate in
 central and southern California so far in 2009, especially since
 May. Many stranding network facilities have already admitted more
 animals this year than in all of 2008, and some are fully extended
 and reaching capacity. Most of the stranded animals coming into
 the mainland are yearlings, following last year’s record number of
 59,000 California sea lion pups born on the rookeries.

In addition
 to the stranded yearlings, the highest pup mortality in the first
 month of life ever recorded was observed in 2009 at two offshore
 California sea lion rookeries (San Miguel Island and San Nicolas
 Island) by NMFS National Marine Mammal Laboratory scientists. On
 San Miguel Island, 6,000 pup mortalities were observed where the
 typical average is 1,000-1,500 for the same time period. On San
 Nicolas Island, 1,900 pup mortalities were observed where the
 typical average is 250 for the same time period. On both Islands,
 the pup production this year was lower than what is expected (on
 San Miguel typically 18,000 pups are born and on San Nicolas 10,000
 pups are born). Starvation appears to be the primary cause;
 stranded animals are weak and emaciated. Additionally, reports of
 large numbers of sea lions hauled out (but not yet stranded) in
 non-traditional areas, including docks and harbors, are increasing,
 particularly for this time of year.

 We anticipate that this situation could continue through next year,
 particularly if El Niño conditions persist or strengthen, which
 would begin impacting Californian waters in the next few months. We
 would also anticipate an increase in northern fur seal (Callorhinus
 ursinus) strandings in October through December of this year. The
 numbers of California sea lion strandings began to increase beyond
 typical levels in May and peaked in June and while the numbers of
 animals stranding have decreased in July, they are still higher
 than historical levels at this time of year. Harbor seal and
 northern elephant seal (Mirounga angustirostris) strandings are
 fairly typical for this time of year; however, an unusual parasite
(Otostrongylus circumlitis) was recorded in both elephant seals and
 harbor seals in April, May, and June of this year and was likely
 transmitted via prey. The last time this parasite was observed was
 in 1998. NMFS staff continue to consult with other NOAA staff and
 external colleagues to investigate oceanographic or climate
 phenomena that may further explain what is currently being
 documented with these marine mammals.

Jeffrey R. Boehm
Executive Director

The Marine Mammal Center 

Categories: California Sea Lion Deaths, Condition of Oceans, Marine Mammal Rescue

Tags: , , , , ,

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