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vol.30 número1  suppl.SympLong-Term Effects of "El Niño" on The Structure of Soft-Bottom Macrozoobenthos Communities in Northern ChileBiological Background of "El Niño" and "La Niña" in Intertidal and Subtidal Communities of the Northern Zone of Chile índice de autoresíndice de materiabúsqueda de artículos
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Investigaciones marinas

versión On-line ISSN 0717-7178

Investig. mar. v.30 n.1 supl.Symp Valparaíso ago. 2002

http://dx.doi.org/10.4067/S0717-71782002030100059 

Effect of El Niño 1997/98 on a
Population of the Southern Sea Lion
(Otaria flavescens Shaw) from Punta
Patache/Punta Negra (Iquique, Chile)

Walter Sielfeld, Ana Guzmán

Departamento Ciencias del Mar, Universidad Arturo
Prat, Casilla 121, Iquique, Chile
E-mail: wsielfeld@cec.unap.cl

In order to study the eventual regulation effect of ENSO events on the population dynamics of the Southern Sea Lion in Northern Chile, a long term monitoring program is being carried out at Punta Negra and Punta Patache, about 70 km south of the port of Iquique: I Region of Chile.

Punta Negra is a breeding place and Punta Patache represents a resting site during the non-reproductive season. Both localities have been studied during breeding seasons since 1986, and seasonally since 1994, with complete census of pups, yearlings, females, subadult and adult males.

The Southern sea lion population during 1994 _ 1997 inter El Niño

Punta Negra and Punta Patache were used during the 1994/97 inter-El Niño period by a population of 1200 _ 1500 Southern Sea Lions (Table 1). During this period, 452 (93/94), 464 (95/96), 521 (96/97) and 64 (97/98) females reproduced at Punta Negra, with an annual production of 411 to 464 pups, with an estimated mortality of 8,2 - 20,8 % during the breeding season (Sielfeld et al. 1993; Acevedo, 1996 and 1999).

Table 1: Population structure during breeding seasons (M = males; H = females; P = pups;
J = yearlings; I = indeterminate; * = no information).

PUNTA NEGRA

PUNTA PATACHE

BOTH SITES

Season

M

H

P

J

Total

M

H + J

I

Total

M

H + J

P

I

Total

1985/86

1120

517

368

28

953

0*

0*

*

0*

0*

0*

0*

*

00*

1993/94

14

452

411

0-

877

1990

332

-

531

213

784

411

-

1408

1995/96

55

464

464

21

10940

0*

0*

*

0*

0*

0*

0*

*

00*

1996/97

57

521

464

3370

15530

84

332

-

416

141

11900

464

-

1969

1997/98

18

064

045

0-

127

35

962

860

10830

053

10260

045

860

1210

1998/99

47

248

215

33

571

71

607

-

678

118

888

115

-

1249

1999/00

52

292

278

43

713

68

554

-

628

120

889

278

-

1341

2000/01

12

272

227

0-

511

15

593

670

675

027

865

227

670

1186

2001/02

09

250

295

0-

554

51

304

160

471

060

554

295

160

1025

El Niño 1997/98 effect on the breeding population

The following effects on the sea lion population were detected: 1. Increase of the local population during the second semester of 1997, probably because of animals migrating from the north; 2. Abortion and premature birth, outside of the normal breeding places, since October 1997, with a maximum intensity in December 1997; 3. Mortality of yearlings and adults since January 1998 and until May 1998; 4. Strong reduction of birth rates at Punta Negra during January/March 1998.

The increase of the local population of 1997 involved principally young animals (individuals of 1-3 years), probably migrating from the north. This affected principally Punta Patache, where an increase of 160% of females + young was observed in summer 1997/98.

From 15 directly observed premature births, only 3 cases (20%) showed interest of the females for their pups. 100 % of them died during the following 24 hours. 35,7% of these pups were males and 64,3% females. Their total length varied between 63 and 74 cm.

The general mortality of young and adult individuals was apparently caused by lack of food resources (mainly anchoveta, Sielfeld et al., in presst). The sex, age and death date of 83 bodies is presented in the following tables, where age structure was inferred from the growth curve established previously for this species (Fondo de Investigación Pesquera FIP - 95-28).

Table 2: Fortnight distribution of carcasses studied during the 1997/98 period

MONTH

JAN 98

FEB 98

MAR 98

MAY 98

TOTAL

Day

1 - 15

16 - 30

1 – 15

16 - 30

1 – 15

16 - 30

1 – 15

16 - 30

4 month

Males

-

10

2

6

1

-

2

-

21

Females

-

23

6

16

4

-

2

-

51

Indeterminate

-

10

-

1

-

-

-

-

11

TOTAL

-

43

8

23

5

-

4

-

83

Table 3: Sex and age structure of the carcasses studied during the period 1997/98
(indeterminate specimens are excluded)

M A LE S

FEMALES

T O T A L

AGE

N

%

AGE

N

%

AGE

N

%

0

5

23,6

0

9

17,6

0

14

19,4

1

6

28,6

1

6

11,8

1

12

16,7

2

9

42,9

2

13

25,5

2

22

30,6

3

1

4,8

3

9

17,6

3

10

13,9

4

-

-

4

9

17,6

4

9

12,5

5

-

-

5

-

-

5

-

-

6

-

-

6

-

-

6

-

-

7

-

-

7

4

7,8

7

4

5,6

8

-

-

8

1

2,0

8

1

1,4

TOTAL

21

100,0

TOTAL

51

100,0

TOTAL

72

100,0

Table 4: The 1997/98 breeding season of Punta Negra

Month

Males

Females

Pups

Yearlings

Total

DEC 97

-

-

-

-

-

JAN 98

18

64

45

5

132

FEB 98

6

20

12

-

38

MAR 98

-

39

12

-

53

APR 98

-

-

-

-

-

MAY 98

-

27

19

-

46

JUN 98

-

7

3

-

10

Table 5: Reproductive females and pup production
at punta Negra after El Niño 1997/98

Category

1998/
1999

1999/
2000

2000/
2001

2001
2002

Pups

215

278

227

295

Females

248

292

272

250

Males

36

43

12

9

The normal reproductive process (January-May) on the Punta Negra breeding place was very irregular during 1997/98. Only 45 pups could be reported at the beginning of the breeding season (about 10% of the production of previous normal seasons), of which only 19 (57,8% mortality) survived the breeding period. The following table sumarizes the breeding season.

The sea lion population during the 1998/ 2002 post El Niño period:

After El Niño 97/98 the pup production of the colony recovered. At the first post-El Niño breeding season (98/99) the birth of 215 pups was registered. During the following seasons and up to date this number rose to around 300 pups during the present 2001/02 season, not reaching the historical numbers before the 97/98 El Niño. Details on post-El Niño pup production can be found in the following table:

Conclusions

ENSO events were shown to have a strong regulatory effect on the Southern Sea Lion population of Northern Chile, affecting recruitment rates because of high mortality of pups (100% of premature; 56% of normal birth) and young between 1 and 3 years of age. During the 1997/98 season the normal breeding process declined, and pup production went down to rates close to 10% of normal seasons. The effect of El Niño on the recruitment rates persists during the present time, whereby the death of pups (females reaching maturity after 3 years), 1 year old young (females reaching maturity after 2 years) and 2 year old young (females reaching maturity after 1 year) resulted in a reduction of the reproductive female population, that actually maintains low pup production.

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