IUCN Red List Assessment
Red List Category
Red List Criteria
IUCN Evaluation of the California Sea Lions, Zalophus californianus
Prepared by Pinniped Specialist Group
A. Population reduction Declines measured over the longer of 10 years or 3 generations
A1 CR > 90%; EN > 70%; VU > 50%
Al. Population reduction observed, estimated, inferred, or suspected in the past where the causes of the reduction are clearly reversible AND understood AND have ceased, based on and specifying any of the following:
(a) direct observation
(b) an index of abundance appropriate to the taxon
(c) a decline in area of occupancy (AOO), extent of occurrence (EOO) and/or habitat quality
(d) actual or potential levels of exploitation
(e) effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
Exploitation during the 19th and 20th centuries caused population reductions. The distribution range has not changed since the exploitation era but population numbers have increased mainly in California where the population estimate is around 238,000. The population in Mexico occupies both side of the Baja California Peninsula: the west coast has an estimated population of 75,000 – 87,000, whereas the Gulf of California population is near 30,000. The total population of California sea lions is therefore around 355,000 individuals. The population in California is reaching carrying capacity. Some colonies in the Central Gulf of California have declined by approximately 35% in the last 15 years.
A2, A3 & A4 CR > 80%; EN > 50%; VU > 30%
A2. Population reduction observed, estimated, inferred, or suspected in the past where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.
California Sea Lions are abundant; they are likely reaching carrying capacity in California.
A3. Population reduction projected or suspected to be met in the future (up to a maximum of 100 years) based on (b) to (e) under A1l.
A4. An observed, estimated, inferred, projected or suspected population reduction (up to a maximum of 100 years) where the time period must include both the past and the future, and where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.
No population reduction is inferred in the near future in California or in west coast Baja California. However, some rookeries in the Gulf of California are declining and are likely to continue to decline in the near future.
B. Geographic range in the form of either B1 (extent of occurrence) AND/OR B2 (area of occupancy)
B1. Extent of occurrence (EOO): CR
Considering recent, frequent sightings of California Sea Lion in the Gulf of Alaska and the end of the Gulf of California as the northern and southern limits of its occurrence (around 6800 km) and a typical coastal distribution of 50 km, the EOO of California Sea Lions is around 340,000 km².
B2. Area of occupancy (AOO): CR
The AOO for the California Sea Lion, determined for the locations in which they breed (around 2,845 km) and 50 km offshore is about 142,250 km².
AND at least 2 of the following:
(a) Severely fragmented, OR number of locations: CR + 1; EN (b) Continuing decline in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) area, extent and/or quality of habitat; (iv) number of locations or subpopulations; (v) number of mature individuals.
(c) Extreme fluctuations in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) number of locations or subpopulations; (iv) number of mature individuals.
The California Sea Lion has 13 rookeries from the Channel Islands to the south of Baja California and 13 rookeries inside the Gulf of California. The populations in California and Baja California show population declines during severe El Niño event, but they tend to recover to previous levels within 4-5 years. The Gulf of California does not show such fluctuations; it is genetically isolated from the remaining geographic distribution.
C. Small population size and decline
Number of mature individuals: CR
AND either C1 or C2:
C1. An estimated continuing decline of at least: CR + 25% in 3 years or 1 generation; EN = 20% in 5 years or 2 generations; VU = 10% in 10 years or 3 generations (up to a max. of 100 years in future)
C2. A continuing decline AND (a) and/or (b):
(a i) Number of mature individuals in each subpopulation: CR or
(a ii) % individuals in one subpopulation: CR = 90–100%; EN = 95–100%; VU = 100%
(b) Extreme fluctuations in the number of mature individuals.
D. Very small or restricted population
Number of mature individuals: CR AND/OR restricted area of occupancy typically: AOO
E. Quantitative Analysis
Indicating the probability of extinction in the wild to be: Indicating the probability of extinction in the wild to be: CR > 50% in 10 years or 3 generations (100 years max.); EN > 20% in 20 years or 5 generations (100 years max.); VU > 10% in 100 years
Some quantitative analysis for the probability of extinction is available for rookeries of California sea lions in the Gulf of California, indicating that at least one of the 4 clusters of rookeries shows a risk for being CR > 50% in 15 years.
Listing recommendation — The California Sea Lion population is abundant and probably reaching carrying capacity in most of its wide geographic distribution. A category of Least Concern should be assigned for the global status. However, the Gulf of California Sea Lion population is genetically isolated, relatively small and some colonies have shown recent declines. Some of the local stocks in the Gulf of California should be considered Near Threatened.
- 1996Lower Risk/least concern