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Marine Pollution Bulletin 47 (2003) 313–318

Impacts of the Jessica oil spill on sea lion(Zalophus wollebaeki) populations

Sandie Salazar *

Charles Darwin Foundation, Puerto Ayora, Gal�aapagos, Ecuador

Abstract

Following the Jessica oil spill, a total of 79 oiled Gal�aapagos sea lions (Zalophus wollebaeki) were recorded around the islands of

San Crist�oobal, Santa F�ee, Isabela and Floreana. Almost half of these animals required washing and other treatment. One sea lion

death and a high incidence of conjunctivitis and burns were detected during the period of the oil spill. Sea lion populations exhibited

a tendency for decline in the first months following the spill at all three colonies monitored close to the grounding site on San

Crist�oobal. By comparison, declines of similar magnitude occurred at only one of six sea lion colonies monitored on islands more

distant from the spill. However, no significant decreases in population numbers were detected for any colony in the year following

the spill. Gal�aapagos sea lion populations were partially recovering from the much more catastrophic impact of the 1997/98 El Ni~nno.� 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Gal�aapagos; Jessica; Impacts; Oil spill; Sea lion; Zalophus wollebaeki

1. Introduction

On the early morning of 16 January 2001, the oiltanker Jessica ran aground on a reef off the point of

El Ca~nn�oon, at the entrance to Bah�ııa Naufragio, San

Crist�oobal. The tanker contained approximately 300

tonnes of bunker fuel and 600 tonnes of diesel. Part of

this fuel was rescued from the ship, but over 60% of the

total cargo was lost at sea during the following two-

week period.

In order to minimize and assess the impact of oilreleased by the Jessica, the Charles Darwin Research

Station and Gal�aapagos National Park Service formu-

lated a contingency and monitoring plan for affected

wildlife. Because sea lions live in large colonies near the

grounding site, numerous oiled animals were observed,

and studies elsewhere indicated substantive impacts of

oil spills on marine mammals (e.g., Hall et al., 1996;

Spies et al., 1996; Peterson, 2000). The Gal�aapagos sealion (Zalophus wollebaeki) was ranked amongst the

highest priority species for remediation and study. The

present report describes the principal actions under-

* Fax: +593-5-527013x3.

E-mail address: ssalazar@fcdarwin.org.ec (S. Salazar).

0025-326X/03/$ - see front matter � 2003 Elsevier Science Ltd. All rights re

doi:10.1016/S0025-326X(03)00160-7

taken and assessment of trends in population numbers

following the spill.

2. Methods and results

2.1. Survey of oiled animals

During the first two weeks following the spill (17–30

January 2001), counts were made of animals marked by

oil along the beaches of the different islands affected.Four colonies of Gal�aapagos sea lions were found to be

most affected: La Lober�ııa and El Malec�oon on San

Crist�oobal (with 22 animals oiled), Bah�ııa Santa F�ee on

Santa F�ee (with 41 animals affected) and Playa de los

Perros on Floreana (with seven animals oiled) (Fig. 1).

The proportion of oiled animals in most of the colonies

was less than 10% except in Bah�ııa Santa Fe, where 19%of individuals exhibited oiling. Other surveys recordedtwo oiled adults and one oiled pup on Isabela, two

(including one dead pup) on Floreana, and two at El

Miedo (Santa F�ee). In the colony at El Malec�oon an ad-

ditional two sea lions were observed with chemical

burns, presumably caused by solar heating of oil ex-

posed on skin. Therefore, a total of at least 79 sea lions

were considered affected by the oil spill. The two San

served.

Fig. 1. Locations of sea lion colonies affected by the Jessica oil spill.

314 S. Salazar / Marine Pollution Bulletin 47 (2003) 313–318

Crist�oobal colonies were located immediately adjacent to

the Jessica grounding site.

Approximately 42 sea lions were cleaned (26 at Santa

F�ee, nine at San Crist�oobal and seven at Floreana). All of

the treated animals were pups (less than a year old) and

small juveniles. The treated animals were cleaned withliquid detergent and excess water, the mucous linings

were cleaned with milk, and some sea lions on Santa F�eewere hydrated by administration of a subcutaneous

physiological solution with vitamin B. Of the 73 sea

lions where the degree of oiling was known, 27 were

severely oiled (>50% of the body), 12 were moderately

oiled (<10%) and 34 lightly oiled. Fortunately, the ap-

plication of euthanasia was not necessary during thisemergency.

During monitoring, various pups and juveniles in all

the colonies were observed to be affected by an eye in-

fection, the severity of which varied between colonies.

The colonies with highest levels of infection (>50% of

pups with severe cases) were La Lober�ııa (San Crist�oobal),Bah�ııa Santa F�ee (Santa F�ee), Caama~nno (Santa Cruz) and

Punta Mangle (Fernandina). During the final weeks ofJanuary to mid February, specimens of blood and tears

were collected for assay from a total of 25 sea lions in

the following colonies: La Lober�ııa, Isla Lobos, Ca-

ama~nno and Bah�ııa Santa F�ee. Preliminary diagnosis in-

dicated that the disease was severe conjunctivitis, related

to the presence of bacillo-cocci bacteria.

A direct relationship between the oil spill and this

disease cannot be shown, given that outbreaks of the

disease were seen prior to the spill and historical records

exist for this disease in Gal�aapagos.

2.2. Population monitoring

Since 1997 the Charles Darwin Research Station hasmaintained regular population surveys of 12 sea lion

colonies in Gal�aapagos (Fig. 2). All of the colonies mostaffected by the oil spill were included in this population

monitoring programme, except Playa de los Perros on

the island of Floreana.

During November 2001 a general pinniped survey

was conducted throughout the archipelago (except

Darwin and Wolf islands, where negligible animals live).Total populations of 14,000 Galap�aagos sea lions and

6000 fur sea lions were estimated in this survey, taking

into account that the proportion of the counted animals

in a breeding colony was about 50% of the true popu-

lation. This correction is normally used for estimation of

populations of a medium size species, considering the

probability of observation (observability) and the census

method used (Nichols and Corroy, 1996). Few differ-ences were found between data collected during No-

vember 2001 compared with the average number of the

animals recorded in surveys earlier in this year at the

reproductive colonies of Z. wollebaeki that are moni-

tored regularly. Thus, the census data can be considered

reasonably representative of general patterns and not

influenced greatly by the particular conditions on the

days of sampling.

Fig. 2. Sea lion colonies monitored in Gal�aapagos since April 1997.

S. Salazar / Marine Pollution Bulletin 47 (2003) 313–318 315

Population trends over the short term (between spill

date, or immediately prior to spill, and surveys six

months later) were negative for two of the three colonies

with oiled animals observed (La Lober�ııa and El Ma-

lec�oon), and positive for the colony at Bah�ııa de Santa F�ee(Fig. 3). The colony at Playa de los Perros is not a re-

productive colony and the number of animals variesgreatly between monitoring periods for this site.

The downward trend at two oiled colonies was gen-

erally unusual for Gal�aapagos, given that most colonies

in Gal�aapagos showed increasing population numbers as

a recovery response to the severe mortality encountered

during the 1997/98 El Ni~nno event. Other sites monitoredwhere no animals were observed with effects of oil are

useful as reference sites for comparison with the oiledsites. Amongst these sites (Fig. 3), the trend in popula-

tion numbers over the three months following the spill

was generally positive. Only at Isla Lobos (San

Crist�oobal), a site only 8 km from the wreck site but with

no animals observed with oiling, and at Plaza Sur off

Santa Cruz, was the population trend substantially

negative. It is particularly notable that all three colonies

on San Crist�oobal showed population declines, whereasonly one of six sites monitored on islands more distant

from the spill showed a similar trend.

Despite the six-monthly trends, no major changes

attributable to oiling were detected during the year fol-

lowing the spill for any of the sites studied. This was

indicated by a lack of significant effects shown in t-testswhere population numbers of sea lions were compared

during the year before and year after the spill for the

various colonies monitored (Table 1). Only one signifi-

cant effect was found, an increase rather than a decrease

in numbers at the oil-affected El Malec�oon site. While

numbers at this colony, located only 2 km from the

wreck site, apparently doubled during the year following

the spill, the increase occurred between the last survey

pre-spill and the first survey post-spill (Fig. 3), and thusprobably occurred prior to the spill. During the year

following the spill from 14 February to 14 November

2001, population counts at El Malec�oon in fact declined

from 258 to 136 individuals.

It is important to note that the sample sizes (dates

sampled) and power for t-tests described in Table 1 werelow, hence few conclusions can be made because of the

likelihood of Type II statistical errors (i.e., a change inpopulation number occurred between years but was not

detected because of insufficient sample size). Neverthe-

less, none of the colonies showed a major decrease in

population numbers, and the trend overall was for in-

crease rather than decrease, including the overall trend

in population numbers for oil-affected sites combined.

3. Discussion

The effects of oil spills on sea mammals are difficult to

predict, but largely depend on the level of skin exposure

and ingestion. Pinnipeds generally appear quite resistant

to external oiling because the presence of blubber layers

minimizes impacts on thermoregulation. By contrast,

sea otters can suffer considerably from hypothermia

Affected: San Cristóbal Island:La Lobería

0

50

100

150

200

250

300

350

No

.in

div

idu

als

1997 1998 1999 2000 2001

El Malecón

0

50

100

150

200

250

300

350

No

.in

div

idu

als

1997 1998 1999 2000 2001

Affected: Santa Fé Island:Santa Fe Bay

0

50

100

150

200

250

300

350

No

.in

div

idu

als

1997 1998 1999 2000 2001

No reports: San Cristóbal Island:Isla Lobos

0

50

100

150

200

250

300

350

400

No

.in

div

idu

als

1997 1998 1999 2000 2001

No reports: Isla Española:Gardner Bay

0

50

100

150

200

250

300

350

No

.in

div

idu

als

1997 1998 1999 2000 2001

Punta Suárez

0

50

100

150

200

250

No

.in

div

idu

als

1997 1998 1999 2000 2001

No reports: Isla Santa Cruz:Caamaño

0

50

100

150

200

250

300

350

400

450

500

No

.ind

ivid

ual

s

1997 1998 1999 2000 2001

Plaza Sur

0

100

200

300

400

500

600

700

800

900N

o.i

nd

ivid

ual

s

1997 1998 1999 2000 2001

Mosquera

0

200

400

600

800

1000

1200

1400

1600

1800

No

.In

div

idu

als

1997 1998 1999 2000 2001

Fig. 3. Changes over time in maximum number of animals sighted per visit for three colonies affected by the oil spill and six colonies with no reports

of oiled animals. A vertical line indicates the date of the oil spill.

316 S. Salazar / Marine Pollution Bulletin 47 (2003) 313–318

when oiled (Geraci and St. Aubin, 1990; Overton et al.,1994; Michel et al., 2000). Following the Exxon Valdez

spill, impacts on harbor seals were less severe than on

sea otters, although eye illness (Michel et al., 2000) and

some decline in population size was observed for seals

(Frost et al., 1999; but see Hoover-Miller et al., 2001).Effects of internal ingestion of oil remain largely un-

known (Michel et al., 2000); however, kidney failure,

intestinal lining destruction, neural disorders and bio-

accumulation are likely in extreme cases (Overton et al.,

Table 1

Mean densities of sea lions at sites during the 12-month period prior to the Jessica oil spill (19 January 2001), and in 2001 following the spill, with

results of t-tests

Island Site Year pre-spill Year post-spill t-value df

Reference sites

Caama~nno Caama~nno 254.5 331.7 2.23 7

Espa~nnola Bah�ııa Gardner 186.3 267.0 2.02 3

Espa~nnola Punta Cevallos 34.3 64.0 2

Espa~nnola Punta Su�aarez 184.7 187.5 0.06 3

Floreana Champion 197.7 321.5 1.83 3

Mosquera Mosquera 576.5 538.5 0.74 4

Plaza Sur Plaza Sur 630.8 435.7 1.68 8

Seymour Norte Seymour Norte 117.3 52.0 2

San Crist�oobal Isla Lobos 231.8 230.7 0.01 5

Oil-affected sites

San Crist�oobal La Loberia 145.0 110.5 0.40 4

San Crist�oobal El Malec�oon 90.3 198.7 3.03� 5

Santa F�ee Santa F�eeBay 224.8 253.3 1.06 5

* p ¼ 0:029.

S. Salazar / Marine Pollution Bulletin 47 (2003) 313–318 317

1994; Seal Conservation Society: http://www.pinnipeds.fsnet.co.uk/species/steller.htm). Chronic pollution of

small quantities of oil from shipping and coastal dis-

charges also appears to cause long term impacts in

pinnipeds, as is evident with grey seals (Halichoerus

grypus) where the skeletal and the reproductive systems

can be affected (Jenssen, 1996). Exposure to persistent

chemical compounds has also been suggested as the

cause of declines in Baltic grey seal populations (Jens-sen, 1996).

A medium-term impact of oiling was observed for

the Australian fur seal (Arctocephalus pusillus doriferus)

following the Iron Baron oil spill in Australia (July

1995), with the number of pups born at the Tenth Island

(an affected area) reduced during the year following the

spill. A negative relationship also was detected between

the productivity of fur seal colonies and proximity ofisland colonies to the spill site (Pemberton, 1998).

In Gal�aapagos, short-term impacts of the Jessica oil

spill were apparent in terms of numerous sea lions with

oiling observed and treated during the two-week period

following the wreck of the Jessica; however, no major

long-term negative impacts were detected. Counts of sea

lion numbers declined at all three colonies located on

San Crist�oobal near the spill site over the following sixmonths; however, this was more likely caused by tem-

porary emigration or stochastic sampling variation ra-

ther than by direct mortality. Amongst the sea lion

colonies where oiled individuals were observed, a decline

in population numbers over the year following the spill

was detected only at La Lober�ııa, San Crist�oobal, and the

decline at that colony was not statistically significant

(Table 1). Population numbers at the site closest to thespill (El Malec�oon) were considerably higher overall in

2001 than during the previous year, however, a down-

ward trend was experienced through 2001. Part of this

decline was presumably caused by the unrelated deaths

of at least nine sea lions through illegal killing for re-productive organs (Salazar and Edgar, 2001).

For all sites, any changes in population numbers in

2001 were minor compared to the huge declines in

population numbers in 1998 associated with the severe

El Ni~nno that concluded in that year. Impacts of the

Jessica oil spill were therefore well within the range of

natural environmental variability in the region.

Acknowledgements

I am grateful to Ian Robinson, who designed theprotocol for treatment of oiled sea lions, Godfrey Mer-

len, Martin Haulena, Alejandro Ulloa, Marilyn Cruz

and others who shared their knowledge to help with

this unexpected experience. Thanks also to the teams

of people from the Charles Darwin Foundation and

Gal�aapagos National Park Service who washed the ani-

mals and collected data in Santa F�ee colony, and to CDFstaff in Puerto Baquerizo Moreno for their collabora-tion. My special thanks to Graham Edgar and Lynn

Lougheed for helpful comments and English translation.

This study was supported by GEF PNUD, the British

Embassy, Ernest Kleinwort Charitable Trust and the

Gal�aapagos National Park Service. I also wish to thank

the Laboratory of Erasmus University in Holland for

conducting the pathological analyses.

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