Ecological Archives E096-248-A1

Alastair M. M. Baylis, Rachael A. Orben, John P. Y. Arnould, Fredrik Christiansen, Graeme C. Hays, and Iain J. Staniland. 2015. Disentangling the cause of a catastrophic population decline in a large marine mammal. Ecology 96:28342847. http://dx.doi.org/10.1890/14-1948.1

Appendix A. Detailed description of archipelago-wide census methods and count error and southern sea lion (Otaria flavescens) breeding colonies at the Falkland Islands.

A1: Archipelago-wide census methods and count error.
Southern sea lion breeding colonies were identified by surveying the coast line from a boat. Where possible, observers walked the coast line and interior of each island to ensure all breeding groups were found. Most breeding colonies (80 %) were direct counted from land. Direct counts from the boat (or zodiac) were the preferred method for seven breeding colonies (Table A1). We were unable to land at seven breeding colonies because access was not granted (Table A1). One breeding colony (Beauchêne Island) (n = 3 pups) was counted in 2011 by Falklands Conservation (unpublished data), but not in 2014 due to logistical constraints. Five small breeding colonies reported in 2003 (≤ 30 pups) did not exist in 2014. However, we found six new breeding colonies (Table A1).

Several potential sources of count error exist. These are (1) pups were born after visiting breeding colonies, (2) pups died prior to counting and the carcass was not detected and (3) live pups at some breeding colonies may have been hidden by tussac grass (i.e., had moved away from the main breeding beach) (Hamilton 1939, Thompson et al. 2005).

We cannot account for the first two sources of error, although previous studies suggest they are less than 5 % (Hamilton 1939, Thompson et al. 2005). To explore potential count error associated with pups hidden by tussac grass, we used the average number of pups counted in tussac grass as a proxy for potential error. In 1995, the number of pups counted in tussac was 4 % (based on breeding colonies counted after 31 January 1995) (Thompson et al. 2005). In 2014, all pups remained on breeding beaches until the 24 January. After the 24 January, pups at 14 breeding colonies were found in tussac grass on the periphery of breeding beaches (Table A1). Based on these 14 breeding colonies, the number of pups in tussac grass was, on average, 14 ± SD 12 % of the total count. We estimated the potential count error for all breeding colonies counted after 24 January. Count error was derived by drawing a fractional error from a uniform distribution, assuming the uncertainty of the original count was between 4 % and 14 %. A value (count) was then randomly drawn from a sampling distribution based on the error. The procedure was repeated 10,000 times and the resulting 10,000 possible estimates generated for each breeding colony were summed. The 2.5 and 97.5 percentiles calculated as the lower and upper band of the 95 % confidence interval.

One known breeding colony (Port Louis) was not counted in 2014 because of issues associated with site access. In 2003, 64 pups were counted at Port Louis. To estimate the number of pups at Port Louis in 2014, we used the same bootstrap approach detailed above, but with an error range that was based on the population change between 2003 and 2014 for colonies of a similar size (>60 pups). The lower and upper error used was 17 % and 94 %, respectively.

For 36 breeding colonies counted on or after 24 January 2014, the total number of pups estimated using a count error of between 4 % and 14 % to account for pups that could have moved from the beach into surrounding tussac grass, ranged between 2,923 and 2,951 (lower and upper 95 % CI). Therefore, the total number of pups born in 2014 could be as high as 4,591 or a 66 % increase in the number of pups since 2003, using upper 95 % confidence intervals for breeding colonies counted before (1,513) and after (2,951) 24 January and Port Louis.


Table A1. Breeding colonies of southern sea lions at the Falkland Islands counted in 2014, 2003, 1995, 1965 and the 1930s. Dead pups are included in the total column, and reported as the value within parenthesis. D = direct count. DB = preferred method, direct count from boat.

Date

Location

Sea lion pups

Latitude

Longitude

Pups in

Count

2014

2003

1995

1965

1930s

tussock

method

4,443

2,765

2,042

5,506

80,555

01-Mar-11

Beauchêne Island

3

 

-52.91

-59.19

0

D

16-Jan-14

Bills Islet

125 (1)

94 (2)

 

-51.35

-59.82

0

D

16-Jan-14

North West Island

74

48

37

 

838

-51.58

-59.21

0

D

16-Jan-14

Penguin Point

42

27

27

 

350

-51.35

-59.44

0

D

16-Jan-14

Penguin Point (rocks)

44

22

 

-51.35

-59.44

0

D

16-Jan-14

Rabbit Island

101

113

52

 

161

-51.31

-59.73

0

D

17-Jan-14

Dry Island

1

 

-51.37

-59.89

0

DB

17-Jan-14

Government Island

22

10

12

 

-51.22

-59.9

0

D

17-Jan-14

Monday Islet

11

 

-51.37

-59.91

0

D

17-Jan-14

Port Egmont Cays

65 (2)

29

25

 

1859

-51.18

-60.04

0

D

17-Jan-14

Sedge Island

6

7

 

2782

-51.15

-60.38

0

D

17-Jan-14

Skip Rock

12

23

10

 

-51.44

-60.14

0

DB

17-Jan-14

Wreck Island

66 (1)

35 (1)

34

 

1941

-51.16

-60.25

0

D

18-Jan-14

Dunbar Island

36

51

38

 

768

-51.37

-60.37

0

D

18-Jan-14

Low Island

23

42 (2)

43

 

3316

-51.34

-60.46

0

D

18-Jan-14

Low Island rocks

59

 

-51.34

-60.48

0

D

18-Jan-14

Twins South

68

44 (1)

13

 

1495

-51.25

-60.64

0

D

19-Jan-14

Gibraltor Rock

28

14

7

 

-51.32

-60.76

0

DB

19-Jan-14

Twins North

49 (1)

15

15

 

-51.25

-60.64

0

D

20-Jan-14

Elephant Jason

20

26

23

 

684

-51.17

-60.85

0

D

20-Jan-14

North Fur Island

39

34 (1)

 

8158

-51.13

-60.74

0

D

20-Jan-14

South Fur Island

3

5 (1)

7

 

5010

-51.26

-60.84

0

D

20-Jan-14

South Jason

13

5

4

 

17

-51.2

-60.84

0

D

21-Jan-14

Flat Jason

51

17

23

 

6041

-51.09

-60.9

0

D

21-Jan-14

The Fridays

68

29

25

 

25641

-51.06

-60.97

0

D

21-Jan-14

Steeple Jason Islet

132

46

61 (1)

 

414

-51.06

-61.15

0

D

22-Jan-14

3rd Passage Island3

45

30

 

7777

-51.57

-60.83

0

Photo

22-Jan-14

Cliff Island

86

85

36

 

400*

-51.48

-60.56

0

DB

22-Jan-14

Sea Lion Island

50

43

38

 

-52.44

-59.09

0

D

22-Jan-14

Split Island

21

31 (2)

13

 

3325

-51.47

-60.72

0

D

23-Jan-14

Gibbs Island

22

30 (1)

53

 

-51.65

-60.3

0

D

23-Jan-14

Rabbit Island

10

 

-51.55

-60.49

0

DB

23-Jan-14

Shallow Harbour Islet

100

68 (1)

66

 

-51.79

-60.51

0

D

23-Jan-14

Town Point Rocks

14

 

-51.66

-60.25

0

DB

24-Jan-14

Circum Island

71

37 (1)

36 (2)

 

1247

-51.93

-60.87

0

D

24-Jan-14

Outer Island

45

45

25 (1)

 

1938

-51.86

-60.53

0

D

24-Jan-14

West Double Creek

34

18

2

 

-51.97

-60.59

2

D

25-Jan-14

Hill Islet3

48

24

27

 

-51.8

-61.08

0

DB

25-Jan-14

Hill Main3

27

19 (1)

22

 

-51.8

-61.08

0

DB

25-Jan-14

Weddell Island

45

15

11

 

2061

-51.78

-61.03

0

D

26-Jan-14

Stinker Island

135

20

 

-51.83

-61.19

65

D

26-Jan-14

Stuck in the mud

95

84 (1)

98 (2)

 

-51.85

-61.17

0

D

27-Jan-14

Tussack Island

71

37

26

 

1217

-52.02

-60.95

13

D

29-Jan-14

Bare Island

39

29

1

 

-52.2

-60.68

0

D

29-Jan-14

Peat Island

39

31

16

 

246

-52.18

-60.48

4

D

30-Jan-14

Calista Island3

24

20

21

 

2073

-52.02

-59.86

0

DB

30-Jan-14

North Wedge Island3

39

24

26

 

201

-52

-59.8

0

DB

31-Jan-14

Clump Island

2

15 (1)

21

 

720

-52.03

-59.75

0

DB

31-Jan-14

Mike's Island

57

28

2

 

-52.1

-59.75

0

D

31-Jan-14

Sandy Tyssen

56

13

24

 

291

-51.88

-59.63

0

D

31-Jan-14

West Tyssen

126

81

60

 

647

-51.89

-59.67

0

D

01-Feb-14

Cape Dolphin

172

74 (1)

82

 

3393

-58.95

-51.25

30

D

01-Feb-14

Blind Island

159 (3)

86

70

 

274

-52.27

-59.54

20

D

01-Feb-14

East Cay3

30

29

24

 

2569

-52.16

-59.84

6

Photo

01-Feb-14

Sandy Elephant Cay

130 (1)

64

57

 

150*

-52.13

-59.84

0

D

01-Feb-14

Speedwell Islet

70

30

 

37

-52.3

-59.74

0

D

01-Feb-14

Speedwell Pass Point

77

92

88

 

-52.31

-59.74

0

D

02-Feb-14

Cattle Point Island

5 (1)

 

-52.2

-59.26

0

D

02-Feb-14

Fanny Island

61

55

34

 

-52.25

-59.33

0

D

02-Feb-14

Tussock Point Island

64

10

 

-52.34

-59.4

2

D

03-Feb-14

Motley Island

18

32

17

 

-52.15

-58.6

0

D

03-Feb-14

Outer Triste Island

91

46

53

 

-52.15

-58.71

0

D

03-Feb-14

Sisters

60

36

30

 

-52.19

-58.99

0

D

03-Feb-14

Turn Island

51

41

34

 

-52.12

-58.92

5

D

04-Feb-14

Green Island

181

125

93 (1)

 

-51.96

-58.51

35

D

04-Feb-14

North East Island

48

3

 

-52.01

-58.36

2

D

04-Feb-14

Sal Island

83

47

51

 

-52.06

-58.53

1

D

05-Feb-14

Kelp Island

260 (3)

166 (1)

138

 

-51.85

-58.19

21

D

06-Feb-14

Port Harriet

93

 

-51.74

-57.85

0

D

12-Feb-14

Big Shag Island

328 (3)

125

73

 

-51.39

-58.32

60

D

Not visited

Port Louis3

-

64

32 (1)

 

350

-51.39

-58.17

-

-

Breeding colony reported in 1995 or 2003, but not in 2014

26-Jan-14

Letterbox

 

24

24

 

 

-51.83

-61.15

24-Jan-14

North Harbour Is

 

1

3

 

 

-51.87

-60.88

08-Feb-14

Diamond Cove

 

30

19

 

 

-51.54

-57.92

29-Jan-14

Kelp Lagoon

 

15

 

 

-52.24

-60.62

16-Jan-14

Bullock Is

 

7

 

 

-51.35

-59.61

02-Feb-14

Bull Point

 

 

2

 

 

-52.357

-59.373

29-Jan-14

North Arch Is

 

 

2

 

19

-52.219

-60.451

1-Feb-14

Elephant NW Cay

 

 

1

 

 

-52.13

-59.87

Eroded tussack island2

 

 

27

 

 

?

?

Breeding colony reported in 1934–1937, but not in 1995, 2003, or 2014

22-Jan-14

Fourth Passage Is

 

 

 

 

5779

-51.56

-60.87

26-Jan-14

Pitt Is

 

 

 

 

4087

-51.81

-61.06

31-Jan-14

Tyssen Islet

 

 

 

 

1494

-51.875

-59.648

26-Jan-14

unnamed off Weddell

 

 

 

 

951

-51.79

-61.04

Not visited

Jason West Cay

 

 

 

 

500*

-50.999

-61.45

Not visited

Pebble Islet

 

 

 

 

302

-51.239

-59.892

Not visited

Pebble West Islet

 

 

 

 

272

-51.217

-59.906

Not visited

Jason East Cay

 

 

 

 

250*

-51

-61.307

25-Jan-14

Quaker Is

 

 

 

 

248

-51.77

-61.04

Not visited

Carcass reef

 

 

 

 

226

-51.31

-60.579

22-Jan-14

Second Passage Is

 

 

 

 

200*

-51.57

-60.77

1-Feb-14

South East Elephant Cay

 

 

 

 

200*

-52.164

-59.829

1-Feb-14

South Elephant Cay

 

 

 

 

150*

-52.157

-59.84

26-Jan-14

Bald Is

 

 

 

 

130

-51.778

-60.966

16-Jan-14

White Is

 

 

 

 

108

-51.23

-59.776

29-Jan-14

Cape Meredith

 

 

 

 

85

-52.222

-60.667

Not visited

West Is

 

 

 

 

77

-51.975

-59.838

Not visited

Channel Is

 

 

 

 

75*

-51.806

-61.196

Not visited

New Island seal rocks

 

 

 

 

35

-51.778

-61.298

Not visited

New Is

 

 

 

 

19

-51.7

-61.31

Not visited

Stop Is

 

 

 

 

12

-51.983

-60.965

Not visited

Barren Is

 

 

 

 

12

-52.362

-59.709

Not visited

North Is

 

 

 

 

4

-51.65

-61.23

29-Jan-14

Saddle Is

 

 

 

 

4

-51.67

-61.24

29-Jan-14

Arch Is

 

 

 

 

2

-52.231

-60.478

1 Includes 750 pups ‘estimated’ rather than direct counted
2 Location unknown. Description rather than name of island.
3 Access not granted.
*Counts were ‘estimates’ rather than direct counted

Literature Cited

Hamilton, J. E. 1939. A second report on the southern sea lion (Otaria byronia) (de Blainville). Discovery Reports 19. Pages 121–164.

Thompson, D., I. Strange, M. Riddy, and C. Duck. 2005. The size and status of the population of southern sea lions Otaria flavescens in the Falkland Islands. Biological Conservation 121:357–367.


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