;and grouse (1993) 15: 18-36.

Impact of Gulf War oil spills on Saudi

Arabian breeding populations of terns

Sterna in the Arabian Gulf, 1991

P. SYMENS and M EVANS

Summary The breeding populations of terns Sterna on five Saudi Arabian islands (Harqus, Karan,Kurayn, Jana, and Jurayd) in the Arabian Gulf were investigated during May-June 1991. Anestimated total of 66,660 pairs of terns was found, comprising 3,229 pairs of Swift Tern S.bergii, 20,501 pairs of Lesser Crested Tern S. bengalensis, 34,000 pairs of Bridled Tern S.anaethetus, and 8,930 pairs of White-cheeked Tern S. repressa. The numbers of Lesser CrestedTern and Bridled Tern are of international importance. Compared to a previous survey in1986, tern numbers overall had increased by 39% and Bridled Terns. by 270%, while LesserCrested and White-cheeked Terns had decreased by 22% and 28% respectively. Reasons forthe changes cannot yet be advanced, but it was obvious that the massive oil and smokepollution of the marine environment during the 1991 Gulf War did not have any major impacton overall breeding success, which ranged from 720;0 to 910;0 in the different species. Thiswas because most of the pollution occurred well before the terns arrived on their breedinggrounds. Conservation of the breeding tern populations is discussed.

O NE OF the most important ornithological aspects of the Arabian Gulf is thelarge number of breeding seabirds on the offshore islands (e.g. Gallagher et

al. 1984), and the northern coral islands off Saudi Arabia are known to be of inter-national importance for breeding Sterna terns (Zwarts 1987; Bundy et al. 1989).

In 1991 the National Commission for Wildlife Conservation and Development ofSaudi Arabia (NCWCD) and BirdLife International (known at the time as the Inter-national Council for Bird Preservation) set up a joint project to assess the extent ofdamage to birds caused by the massive oil spills that occurred that year in theGulf during the Iraq-Kuwait conflict (the Gulf War) and to gather further data on

Plate 1. Kurayn island in the Arabian Gulf, c. 300 m across. (Arnoud B. van den Berg)

18

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P. Symens and M. I. Evans Sand grouse 15

bushes and (only on Karan and Kurayn)the annual Mesembryanthemum nudi-florum. In some places the vegetation isup to 1 m high and very dense. Thevegetated, central area of the islands issurrounded by a narrow, bare beachplatform, covered in nesting pits of seaturtles, from which a moderately steepsand beach descends to the water (Fig-ure 2). Around much of the perimeterof the islands a storm berm occurs atthe top of the beach slope, and on mostislands the densest vegetation lies in theprotected zone just behind this. Beachrock occurs in some areas of Karan and Plate 3. Swift Tern Sterna bergii, Karan (SaudiJana along the lower portion of the Arabia), June 1991. (Arnoud B. van den Berg)beach and in the upper intertidal zone.

All islands except al-Arabiyah are aligned near the edge of the Gulf's increase indepth to 35 m, and their distances from the mainland vary from 35 to 90 kIn. Al-Arabiyah is located in deeper seas, 125 kIn from the coastline, and close to Iranianterritorial waters. Although this island had important breeding colonies of seabirdsin the past (Gallagher et al. 1984), it has been taken over by a coastguard stationwhich occupies almost the entire surface and; has consequently been abandonedby all breeding seabirds.

A preliminary survey of the islands by helicopter on 10 March 1991 revealedthat huge quantities of oil had stranded on Karan, but the other islands escapedmajor impact by the oil spills except for some pollution by fresh tar balls, mainly

on their northern beaches. However, onJa~a, as well as on Karan, the northernrocky parts of the islands were coveredby a thick layer of old tar, accumulatedduring spills that occurred mainly in19~3-4 during the Iran-Iraq War.During April and the first half of May

1991, a specialist company cleaned upthe oil on the sandy beaches of Karanby burying it in pits along the peripheryof the island, and beaches were sub-sequenUy re,levelled with sand from thecentral part of the island. Due to a short-age of time, tar on the rocky parts ofthe beaches was not removed, as it was

..necessary for clean-up operations to fin-Plate 4. The oll clean-up m progress on Karan ish before the beginning of the turtles'(Saudi Arabia), May 1991. (Arnoud B. van den d t ' b d .Berg) an ems ree mg seasons.

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P. Symens and M. I. Evans Sand grouse 15

severely impacted by the Gulf War oil spills. Oil pollution can cause damage toseabirds during various stages of their life cycle. Large numbers of adults can bekilled by oil-fouling, as so many sad examples have demonstrated. Oiling of eggsbya contaminated incubating bird can also cause serious problems (Freedman 1989),10-20 ,ul of fresh oil on a freshly laid larid egg being enough to kill the embryo(White et al. 1979; Lewis and Malecki 1984). Furthermore, oil can have a severeimpact on flightless chicks forming creches on beaches near the colonies. In orderto assess the direct impact of the Gulf War spills on the breeding populations ofterns, careful observations were made on each stage of their life cycle.

Plate 7. Creche of Lesser Crested Terns Sterna bengalensis, samamik island (eastern SaudiArabia), June 1984. (Duncan Brooks)

Oil spills can also affect seabirds indirectly through the food chain, for toxichydrocarbons may damage the ecosystems within which the birds' food resourcesare produced. Disruption of the breeding cycles of certain fish species could causea drastic decline in seabirds' breeding success.

As there was no previous baseline information available on the breeding andfeeding ecology of these tern populations, the present study initiated longer-termmonitoring of chick growth rates, daily activity patterns, hunting success, and feed-ing ecology , with the aim of assessing any indirect impact that might become evi-dent in future years. The methods and results of these studies will be discussedwhen data from several seasons are available.

METHODS

Censuses

As there exist specific differences in the distribution patterns of terns on their breed-ing grounds, different methods were used to estimate as accurately as possible thetotal numbers of nests of each species. Swift and Lesser Crested Terns have aclustered nest distribution and form large, dense, and very localized colonies onbare ground. Bridled Terns are known to have an even distribution, covering the

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P. Symens and M. I. Evans Sand grouse 15

Table 2. Total numbers of breeding pairs of terns Sterna on islands in the northern ArabianGulf, Saudi Arabia. Breeding densities are averaged over the whole surface area of each is-land. Data for 1991 are from the present study, those for 1986 from Zwarts (1987). Surfaceareas of islands are from Basson et al. (1981).

Dates of survey (1991)~ area (km2) 1.915

In colonies of Swift and Lesser Crested Terns nests were counted individually. Ifcolonies were too extensive to permit complete counts, the area of the colony wasdetermined and the density of nests within the colony was estimated by countingnests within a number of 1 x 1 m squares placed evenly throughout the colony.Harqus was not visited but was twice overflown by helicopter, in May and July.As there is no vegetation on this island it was possible to count the numbers ofbreeding terns from aerial photographs (Plate 8).

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Sand grouse 15Symens and M Eva

season transect counts were made on Karan to estimate the number of survivingchicks of Bridled Terns. In mid-August, when the majority of the chicks of LesserCrested Tern, Swift Tern, and White-cheeked Tern had just started attempting tofly and were close to fledging, the total number of these chicks was counted on thebeaches of Karan in order to estimate fledging success.

RESULTS

The numbers of each species and theoverall breeding densities for each is-land are summarized in Table 2.

Census of Swift and Lesser CrestedTerns I

Totals of 20,501 pairs of Lesser CrestedTern and 3,229 pairs of Swift Tern werefound. Lesser Crested Terns werebreeding in large colonies on Harqus,Karan, and Kurayn, and a muchsmaller colony was found on Jana.Swift Terns were found in large colo-nies on Harqus and Kurayn, whilesmaller numbers bred in association Iwith the colonies of Lesser CrestedTern on Karan, Kurayn, and Jana. The Figure 3. Distribution of breeding colonies ofcolonies of these two species were all terns on Karan island, Saudi Arabia (in 1991,on areas of bare sand (Figure 2). On except as shown).

Plate 11. Lesser Crested Terns Sterna bengalensis, Samamik island (eastern Saudi Arabia), June1984. (Duncan Brooks)

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P. Symens and M. Evans Sand grouse 15

Plate 13. White-cheeked Tern Sterna repressa, Karan (Saudi Arabia), June 1991. (Arnoud B. vanden Berg)

Census of White-cheeked and Bridled Terns

White-cheeked Terns totalled 8,930 pairs. They were in small colonies spread overthe islands of Karan, Jana, and Jurayd, on small sandy patches sparsely vegetatedwith low annuals (Figure 2). Averaged over the entire surface of the islands, they

occurred in densities ranging from 11 to171 nests/ha. Working on a basis oftransects divided into 8-m-long units of40 m2 each (here called 'surface units',and equivalent to the Step Count Unitsof Zwarts 1987), the proportion of eachisland that was actually used for breed-ing by this species was found to rangefrom 1.5% on Karan to 12-40;0 on Jana,and nest densities within the coloniesranged from 1,428 nests/ha on Jana to765 nest/ha on Jurayd (Table 4). Thehighest density of nests recorded in asurface unit on the different islandsranged from 8 to 23 nests, or from 1 nestper 8 m2 to 1 nest per 1.74 m2.

A total of 34,000 pairs of Bridled Ternswere breeding on the islands in 1991.No Bridled Terns were breeding on

Plate 14. White-cheeked Tern Sterna repressa,Karan (Saudi Arabia), June 1991. (Arnoud B.van den Berg)

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P. Symens and M. I. Evans Sand grouse 15

Table 6. Outch sizes and hatching dates for terns Sterna on Karan (Saudi Arabia), 1991.

Date of first

hatching

Sample size(nests)

Clutch size (%)1 egg 2 eggs 3 eggs

Swift TernLesser Crested TernWhite-cheeked TernBridled Tern

99.799.856.599.7

0.3

0.2

43.3

0.3

26 June28 June19 June27 June

445

2,890853

1,294

0.2

one Swift Tern egg (out of 447) werefound with visible spots of oil. Both theWhite-cheeked Tern eggs hatched, whilethe Swift Tern egg was found destroyedbefore hatching. Of 274 marked nests ofBridled Terns, all containing a singleegg, 257 chicks hatched, giving a hatch-ing success of 93.8%; 15 eggs proved tobe infertile and the two other nests were

Plate 15. Nest of White-cheeked Tern Sterna destroyed before hatching. From the 586repressa with oiled egg, Karan (Saudi Arabia), nests of White-cheeked Terns, contain-June 1991. (Arnoud B. van den Berg) ing 837 eggs, 781 eggs hatched (93.3%),

, the others remaining unhatched in thenests. Of the 540 eggs of Lesser Crested Tern and the 64 eggs of Swift Tern, 19 and8 respectively were lost during the incubation period; 513 Lesser Crested and 49Swift Tern chicks hatched, resulting in hatching successes of 94.8% and 76.5%respectively (Table 7).

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On 14 August the total number of surviving chicks of Lesser Crested Tern onKaran was estimated at 8,340 (this may include a small number of Swift Tern chicks,

Table 7. Breeding success of terns Sterna on Karan (Saudi Arabia) in 1991. (Hatching success:percentage of eggs hatching. Fledging success: percentage hatching eggs which eventuallyproduced fledged young. Overall success: percentage of eggs resulting in fledged young.)

?

86.5%

77.2%

96.7%

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?

8,340

2,390

10,150

30

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P. Symens and M. I. Evans Sand grouse 15

largest ever recorded for this region (Gallagher et a[. 1984), may indicate that thespecies is expanding its range in this area.

The breeding population of Bridled Terns made a spectacular increase of morethan 270% from 9,130 pairs in 1986 to 34,000 pairs by 1991. Whereas in 1986 it wasthe least numerous tern on the islands, in 1991 it had become the most abundant.In 1986, Zwarts (1987) found only 1240;0 of the surface of Karan occupied by breed-ing Bridled Terns with an average colony density of 1.26 nests per 40 m2 and amaximum density of 5 nests per 40 m2.1n 1991, 16% of Karan was used, while theaverage density had increased to 2.3 nests per 40 m2 and the maximum to 10 nestsper 40 m2 (Table 4). A similar increase took place on the other islands. At presentit is not clear why the numbers of Bridled Terns increased so dramatically between1986 and 1991, but as they depend on well-developed vegetation for breeding it isassumed that changes in the plant cover may be part of the explanation. Accord-ing to local fishermen, the general condition of the islands' vegetation was betterthan average in 1991. The amount of rainfall during the previous months was saidto be quite high, while the smoke clouds resulting from the oil well fires in Kuwaitreduced the strength of the summer sun, thereby reducing summer temperaturesand allowing the plants an extended period of growth.

According to Cramp (1985), summarizing studies on breeding Bridled Terns, thehighest nesting density recorded for this species is 1 nest per 6 m2, but in 1991 themaximum density on the different islands in our study area ranged from 1 nestper 4.5 m2 to 1 nest per 2.9 m2 (Table 4). These high densities might indicate thatthis species is close to the maximum that the islands can sustain, though on theother hand the very high breeding success of 910;0 in 1991 (Table 7) suggests that

Plate 17. Nesting Swift Terns Sterna bergii, with some Lesser Crested Terns S. bengalensis be-hind, Karan (Saudi Arabia), June 1991. (Arnoud B. van den Berg)