IUCN Red List Assessment
Red List Category
Red List Criteria
IUCN Evaluation of the Australian Sea Lion, Neophoca cinerea
Prepared by the 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.
Australian Sea Lions have a non-annual and asynchronous breeding system. The mean interval between successive breeding seasons is 17.5 months (range16.0-19.9). Subpopulations across the range of the species breed at different times. Populations as near as 20 km can be up to 6 months out of phase in the timing of breeding. There are 73 known breeding sites. 61 of these produce >5 pups, with a total breeding cycle pup production estimated at 3,455 (mean pup production 57, median 27). 80% of the population is located in South Australia, 20% in Western Australia. Based on an age-structured model, the number of mature animals in the population is ~6,600 (Females >4.5 years; males >6 years). Genetic population substructure in the species is extreme, with most colonies (subpopulations) having unique mtDNA lineages, demonstrating extreme philopatry and meeting the IUCN definition of a severely fragmented population.
Some age-structure data are available for one Australian Sea Lion population (Seal Bay, Kangaroo Island). The generation time has been estimated to be 12.4-12.8 years. Hence 3 generations is equivalent to ~38 years.
Robust data on trends in abundance (based on pup abundance per breeding season) are available for only the three largest subpopulations:
- Seal Bay (Kangaroo Island)- pup abundance estimates have declined by 12.6% over 13 breeding season (17.7 years), a decline of -0.77%/year (-1.14%/breeding season), and population modeling projects the subpopulation to decline ?50% within 3 generations 38 years.
- The Pages Islands - trends in pup abundance for 13 breeding seasons show no significant change (i.e. stable).
- Dangerous Reef- trends in pup abundance over 8 breeding seasons from 1994/95 to 2006/07 indicate an increase of 6.9%/breeding season (4.6%/year). Most of this increase has taken place since 2000.
The main threat to the Australian Sea Lion is bycatch in demersal gillnet and trap fisheries. The recovery of the Dangerous Reef population coincides with closures in the gillnet fishery in Spencer Gulf in 2000. Fishery closures also provide protection for most of the foraging space of The Pages Islands subpopulation (stable). There are no substantive gillnet fishery closures that provide protection for the foraging space of the Seal Bay subpopulation which is declining.
No accurate trend data are available for the majority of subpopulations with low pup production (>70% of populations produce <50 pups).
Historical reductions in range and population size from sealing (1800-1830) and subsequent take are inferred. Recent reductions (last 30-40 years) have been inferred or suspected from the high proportion of small and potentially declining subpopulations based on actual and potential levels of bycatch in gillnet and trap fisheries. The causes of reduction and threat are reversible and understood (but have not ceased); thus, this criterion is not applicable.
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 any of (a) to (e) under A1.
Declines have been detected at Seal Bay (12.6% decline over 13 breeding seasons, equivalent to a 25% decline over 3 generations). A population model suggests that this population will continue to decline at a level that will be ?50% within 3 generations.
The high proportion of small subpopulations in the species (50% produce ?27 pups per breeding season) is thought to be a consequence of systemic declines that have resulted from sustained fisheries by-catch over the last 40 years. However, trend data for these small populations are of poor quality or are totally lacking.
The major causes for reduction based on observed and potential levels of by-catch in gillnet and trap fisheries are known and have not ceased. As the rate of decline has only been estimated for one subpopulation and ranges from 25 to ?50% reduction over 3 generations, and declines are inferred in other (depleted) subpopulations, the Australian Sea Lion meets criterion A2b and A2d for Vulnerable (VU).
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 A1.
A population model suggests that the Seal Bay subpopulation will decline ?50% within 3 generations 38 years (indicating E). A population viability analysis indicates that many South Australian subpopulations (~30%) are vulnerable to extinction in the absence of additional by-catch mortality. With low levels of fishery by-catch mortality (egg. 1-2 additional female mortalities/year/subpopulation), 80% of subpopulations are projected to be declining, and 42% may be quasi-extinct (?10 females) within 25 years (<3 generations). Current estimated by-catch levels are likely to be within these ranges.
At a subpopulation level, under criterion A3d, 38% of South Australian subpopulations are assessed as either VU or EN, and at least 42% are assessed as Critically Endangered (CR) based on criterion A3 (d) CR if current by-catch levels remain.
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.
A population decline has been detected in the recent past at Seal Bay (12.6% decline over 13 breeding seasons, equivalent to a 25% decline over 3 generations) and is projected to continue (?50% decline within 3 generations). The only subpopulation known to be increasing has only done so since gillnet fisheries were closed within its foraging grounds in 2000. The high proportion of small subpopulations in the species is suspected to result from systemic declines that have resulted from fisheries bycatch. Current rates of by-catch are high and have not ceased, and population modeling of South Australian populations suggests that even low levels of by-catch will lead to quasi-extinctions of some subpopulations (42% quasi-extinct within 3 generations) and continuing declines in others (38%). Hence, subpopulations range from VU to CR under A3 and A4d, though it is not possible to make an accurate global assessment for the species with available data.
B. Geographic range in the form of either B1 (extent of occurrence) AND/OR B2 (area of occupancy)
B1. Extent of occurrence (EOO): CR
EOO for Australian Sea Lions is > 20,000 km²
B2. Area of occupancy (AOO): CR
AOO for Australian Sea Lions is > 2,000 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.
None of the criteria (a), (b) or (c) is satisfied.
C. Small population size and decline
Number of mature individuals: CR
Based on an age-structured model and estimates of pup production for the species, the number of mature individuals is estimated to be ~6,600 (Females >4.5 years; males >6 years). This meets criterion C for Vulnerable (VU).
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)
For the Seal Bay subpopulation a continuing decline is projected for the future (?50% decline within 3 generations) satisfying V. For subpopulations vulnerable to fisheries by-catch, with by-catch of ?1-2 females per year, declines are expected that would satisfy the EN or VU criteria for many subpopulations, and CR to quasi-extinct for some others.
C2. A continuing decline AND (a) and/or (b):
(a i) Number of mature individuals in each subpopulation: CR
For the 61 subpopulations that produce ?5 pups per breeding season, based on the number of mature individuals, most (48%) are categorized as CR , 39% as EN and 13% VU. The median number of mature individuals in each subpopulation is 52. If the breeding sites that producer <5 pups per breeding season are included, the median number of mature individuals per subpopulation would be <50, which satisfies a classification of CR.
(a ii) % individuals in one subpopulation: CR = 90?100%; EN = 95?100%; VU = 100%
The largest subpopulation contains ~20% of individuals of the species.
(b) Extreme fluctuations in the number of mature individuals.
Based on C, C1 and C2(ai), the species is categorized as VU, although under some criteria, EN and CR could be justified.
D. Very small or restricted population
Number of mature individuals: CR AND/OR restricted area of occupancy typically: AOO
The number of mature individuals in the Australian Sea Lion population is estimated to be ~6,600. This does not meet any of the above criteria.
E. Quantitative analysis
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
A population viability analysis has been undertaken for South Australian subpopulations (assuming a stable population structure, r = 0). PVAs were undertaken on individual subpopulation because of the extreme philopatry in the species. These determined that with no additional bycatch mortality, ~30% of subpopulations are presently categorized as EN or CR, based on criterion E. With low levels of fishery by-catch mortality (e.g., 1-2 additional female mortalities/year/subpopulation), 80% of subpopulations are categorized as either EN or CR, with 42% quasi-extinct (?10 females) within 25 years. Current estimated bycatch levels are likely to be within these ranges. Based on these quantitative analyses, at least 42% of South Australian populations would meet the criterion for Critically Endangered (CR), and 38% meet the criterion of either Endangered (EN) or Critically Endangered (CR).
Listing recommendation ? The Australian Sea Lion population is thought to be significantly reduced in size from historical levels. It is a non-annual, asynchronous breeder that exhibits extreme site fidelity to its multiple, small colonies within its fragmented population. Based on: levels of fishing effort over the last 40 years; current estimates of fishery by-catch rates of sea lions; the high proportion of small, depleted subpopulations; quantitative analyses, which suggest that until fishery by-catch is manage, subpopulations will continue to decline or disappear; and projected declines in abundance in excess of 50% for major colonies - the Australian Sea Lion should be classified as Endangered (EN).
- 1996Lower Risk/least concern
- 1994Rare(Groombridge 1994)