The Life History and Status of the California Sea lionThe Life History and Status of the California Sea lion
•• Life HistoryLife History
•• Population StatusPopulation Status
•• Population RegulatorsPopulation Regulators
Sharon RSharon R. . MelinMelin NOAANOAA//National Marine Fisheries ServiceNational Marine Fisheries Service
Alaska Fisheries Science CenterAlaska Fisheries Science Center National Marine Mammal LaboratoryNational Marine Mammal Laboratory
SeattleSeattle, , WAWA
Canada
Washington
Oregon
California
Mexico
California Sea Lion Distribution
Western Baja California Stock
Gulf of California Stock
U.S. Stock
California sea lion U.S. rookery locations
45%
45%
6%
4%
Canada
Washington
Oregon
California
Mexico
California Sea Lion Life History
Year round Sardine Anchovy
Pacific hake Market squid
Mackerel
September
to May
Pacific hake eulachon Salmon squid
••PolygynousPolygynous ••Sexually dimorphicSexually dimorphic
Annual Reproductive Cycle of a California sea lion
J J A S O N D J F M A M Breeding Non-breeding
Females
Males
Pupping Breeding Gestation
Lactation Implantation Migration
From Pup to Predator • Dependent on mother for
nutrition until 6 months old • Begin swimming at 8
weeks • Begin feeding at 6-7
months • Wean at 11 months old • Pup survival is less than
50% to the first birthday • Causes of mortality are
starvation and disease
• Once weaned, first year survival is 77%
• Annual survival after age 2 increases to 95%
• Primary causes of mortality are predation, interactions with humans and diseases
From Pup to Predator
From Pup to Predator
• Reproductive at 4 or 5; all by age 7 • 77% give birth each year • Site fidelity once reproductive, little
emigration • Survival declines after 11 years • Reproduction declines after 15 years • Life span at least 24 years in the wild
From Pup to Predator • Can reproduce at 4-5 years;
most don’t • Must develop physical and
social maturity • Mean reproductive age is 13
years • Only 10% of males born
survive to reproductive age • Longevity ~19 years
More on Males
• Present at breeding colonies May-early August, then migrate north
• Mean territorial tenure 10 days (range 1 day – 2 months)
• Males breed with one to many females depending on location, tenure, and female choice
• Fidelity to territory over time
• May hold territory up to 6 consecutive years
Population Status and Trends • Historical population level unknown • Protected under MMPA in 1972 • Monitoring population since 1975
- Live pup counts at all breeding colonies since 1975 - Pup mortality surveys at San Miguel Island since1990 - Marking at San Miguel Island for estimating survival, natality
and longevity since1987 • California sea lions are not listed as “threatened” or
“endangered” under the ESA and are not listed as “depleted” or as a “strategic” stock under the MMPA
• Potential Biological Removal (PBR) is 8,511 animals
Live Pup Count 1975 – 2005
Source: NMFS Draft Stock Assessment Report 2007
How many sea lions are there?
A correction factor to estimate total population from live and dead pup counts has been developed using the life table for the northern fur seal and the growth rate of the California sea lion population. From a live pup count of 48,277 and early pup mortality of 15% in 2005
and a correction factor of 4.28, we predict a total population size of 238,000 sea lions in U.S. waters. (NMFS Draft Stock Assessment Report 2007) In 2000, the Western Baja California Stock was estimated at 74,000 (Lowry and Maravilla-Chavez 2000)
Population Regulators
• Population growth is currently regulated by pup and yearling survival
- Environmental changes (e.g. El Niño, Pacific Decadal Oscillations)
- Disease (e.g. parasites) • Juvenile (2-3 years) and adult mortality is low
- Predation - Biotoxins - Disease - Human interactions
El Niño and Disease: First Year Mortality
0.000.100.200.300.400.500.600.700.800.901.00
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
Year
Surv
ival
Rat
e
5% growth rate 1% growth rate
El Niño Hookworm
Warm Phase Cold Phase
Biotoxins and Disease
• Domoic acid - Neurotoxin produced by Pseudo-nitzschia australis, attacks the nervous system and leads to seizures and brain damage that can lead to death
- 74% of documented adult female mortalities
- Sub-lethal doses lead to reproductive failure
• 20% of stranded adult population positive for urogenital cancer leading to reproductive failure and death
Human Interactions
• ≥ 159 annual fishery related mortalities
• ≥ 74 annual non-fishery related mortalities
• Minimum 233 annual mortalities
Source: NMFS Draft Stock Assessment Report 2007
Estimated human-caused mortality between 2000 and 2004:
•• UU..SS. . population breeds in California Channel Islandspopulation breeds in California Channel Islands •• Life historyLife history: : longlong--livedlived, , slow reproducersslow reproducers •• 20052005 population estimate population estimate 238,000238,000 •• Population is at or near KPopulation is at or near K •• Population growth is mostly driven by pup and yearling Population growth is mostly driven by pup and yearling
survivalsurvival •• Other factors that may influence population growth include El Other factors that may influence population growth include El
NiNiññoo, , biotoxinsbiotoxins, , and human interactionsand human interactions •• Current human caused mortality poorly estimated but likely Current human caused mortality poorly estimated but likely
below PBR of below PBR of 8,5118,511 •• California Current in cold phase which should favor California Current in cold phase which should favor
California sea lions but positive effects are currently mitigatCalifornia sea lions but positive effects are currently mitigated ed by diseaseby disease
SummarySummary
Questions?