Patterns and impacts of oiling of African penguins Spheniscus demersus: 1981–1991

Biological Conservation 68 (1994) 35-41

PATTERNS A N D IMPACTS OF OILING OF A F R I C A N P E N G U I N S Spheniscus demersus: 1981-1991 Nigel J. Adams* Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Private Bag, Rondebosch 7700, Republic of South Africa (Received 14 November 1992; revised version received 30 March 1993; accepted 10 May 1993)

Akstraet A total of 4 215 oiled African penguins Spheniscus demersus recovered from beaches and at breeding localities around the southern African coast were admitted to the SANCCOB rescue station over the period 1981-1991. This is 24 % less than recorded during the previous 11 years. The admission rate of 2.47 individuals per 1000 in the 1970s is similar to the 2.35 individuals per 1000 recorded in the 1980s in spite of a substantial decrease in the volume of oil transported around the South African coast over the last decade. This may be explained by a regional shift in the distribution of the penguin population. Seventy-seven percent of the total population now breeds along the south coast of the subcontinent in an area where the risk of encountering oil is highest. The #lcreased risk is a consequence of important shipping lanes passing close to the major concentrations of penguins at Dyer and St Croix Islands and probably the system of currents which moves oil onshore, at least east of Cape Agulhas. A winter peak in the incidence of oiling of penguins is probably related to breeding and associated commuting to and from feeding areas at sea. This increases the likelihood of penguins encountering oil in the vicinity of nesting sites. Impacts of oiling at the population level apparently remain similar to that noted in the previous decade, with a minimum annual admission rate of oiled penguins to the rescue station of 0.24 % of the total population. However, the risk of a single incident affecting a substantial part of the population has increased markedly.

1989) and is subjected to contamination of its coastal waters by oil originating from passing vessels. Penguins spend much of their time at sea on the surface, where they are particularly susceptible to oiling compared to volant birds (Morant et al., 1981; Kerley & Erasmus, 1987). Substantial numbers of African penguins Spheniscus demersus, endemic to southern Africa, have been oiled over the last three decades (Frost et al., 1976; Morant et al., 1981). The closure of the Suez canal in 1967 and a dramatic increase in the average size of bulk carriers which were too large to pass through the canal resulted in a large increase in shipping around the Cape (Morant et al., 1981). The corresponding increase in the number of oiling incidents involving penguins led to the establishment of the South African National Foundation for the Conservation of Coastal Birds (SANCCOB) in 1968. This organization has as its primary aim the cleaning and rehabilitation of oiled penguins. The task has been conducted with gratifying success and is one of the most successful operations of its kind in the world (Randall et al., 1980; Morant et al., 1981). However, there has been some debate about the ultimate value of this exercise. The annual oiling rate of African penguins was estimated at only 10 % of the probable annual mortality rate for adults (Frost et al., 1976, see also Morant et al., 1981). Frost et al. (1976) contended that although rehabilitation efforts served a humanitarian and educational function, they contributed little to the species conservation. It is of note that oil pollution in the North Sea is considered to have had little effect on populations of seabirds (Dunnet, 1987). Such a view was contested by Randall et al. (1980), who noted substantial mortality of adult penguins by oiling at St Croix Island, Algoa Bay. However, these authors made no assessment of the impact at the level of the population. Total population counts of African penguins conducted within the last decade indicate that numbers have continued to decrease (Crawford et al., 1990) particularly at sites in the centre of the species range. Consequently, an increased proportion of the penguin population now occurs at sites on the south-east coast

Keywords: African penguins, Spheniscus demersus, southern Africa, oiling. INTRODUCTION The coast of southern Africa is adjacent to one of the world's major shipping routes (Moldan & Dehrman, * Present address: Mitrani Center for Desert Ecology, Jacob Blaustein Institute for Desert Research, Ben Gurion University of the Negev, Sede Boker Campus 84990, Israel. Biological Conservation 0006-3207/94/$07.00 © 1994 Elsevier Science Limted, England. Printed in Great Britain 35

36

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towards the eastern extremity of the species' range. It is at these sites that the risk of penguins encountering oil close to breeding sites is highest (Moldan & Dehrman, 1989). Oiling records of penguins collected by SANCCOB over the last decade are reviewed to assess whether oiling is now having a relatively more severe impact on penguin populations than during the period 1971-1981 (Morant et al., 1981). In addition, we examine seasonal and distributional patterns of oiling.

METHODS SANCCOB keeps detailed records of all birds recovered alive along the southern African coast and received at its rescue station near Cape Town. Details include date and the locality where the bird was found, severity of oiling, fate of penguin and length of rehabilitation period. All rehabilitated birds are banded and records of subsequent recoveries are collated by the South African Avian Demography Unit, University of

Oiling in penguins, South Africa Table 1. Estimates of numbers of African penguins (non-chick individuals) in different areas of their southern African breeding range estimated in the 1970s and 1980s (Shelton et al., 1984; Crawford et a/., 1990; 1991).

Locality

1978-79

1984-88

Northern Namibia Southern Namibia Western South Africa Southern South Africa

33 262 13 691 57 826 100 378

16 243 4 380 16 821 125 327

Total

205 157

162 771

Cape Town. We scanned the data base for relevant records. RESULTS

37

Table 3. Average number of oiled penguins admitted to SANCCOB per annum (1981-1991) and relative numbers of oiled penguins as a percentage of total population resident in the area

Locality

Ave

% of total

Northern Namibia Southern Namibia Western South Africa Southern South Africa

1.5 0 35 345

0.01 0 0.21 0-28

Total

382

0-24

Fig. 1). In contrast, although 12.7 % of the population was associated with breeding sites along the Namibian coast only 0.4 % of the total number of oiled birds admitted to the rescue station came from this area (Table 2).

Total numbers of African penguins oiled

During the ll-year period 1981-1991, 4 215 oiled penguins captured alive at breeding sites and from beaches along the southern African coast were admitted to the rescue station. This figure is a minimum estimate of the number of penguins affected by oiling. Westphal and Rowan (1971) assumed that for every penguin recovered eight birds would have perished at sea. Frost et al. (1976) suggested that given the absence of reports of large numbers of oiled penguins out at sea or dead oiled penguins washed ashore the numbers of unrecorded birds affected is considerably lower than this. However, the total number of birds affected remains unknown. Admission numbers to SANCCOB remain the only estimate of the impact of oiling on penguins for which comparative time series data are available (Morant et al., 1981). The worst single incident in the review period occurred in Algoa Bay (Fig. 1). A total of 923 penguins were admitted to SANCCOB after being oiled when the Kapodistrias ran aground at Cape Recife during August 1985. However, most penguin oilings during the review period could not be related to particular vessels and were mostly a consequence of illegal and undetected tank washing and bilge pumping by passing ships (Moldan & Dehrman, 1989).

Annual and seasonal patterns of oiling

On average, between 1981 and 1991,208 oiled penguins per annum were admitted to SANCCOB, representing 0.24 % of the total population (Table 3) (population

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Regional patterns of oiling

Ninety percent of all oiled African penguins are recovered from sites along the south coast where 77 % of the breeding population is concentrated (Table 1, Table 2. Numbers and origin of oiled penguins received at the SANCCOB rescue station, 1981-1991

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% of total

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16 0 389 3 793 16

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Fig. 4. Frequency of oiling events involving 20 penguins or more recorded monthly along the south coast of South Africa. estimated by Crawford et al. (1991) in the mid 1980s). There was no apparent trend in annual numbers of oiled penguins recovered (Fig. 2). A minimum of 92 oiled penguins were recovered in 1981 (0.01% of total population) and a maximum of 1192 in 1985 (0.73 % of the total population). Seventy-one percent of all penguins admitted from Dyer Island were recovered during July-September (Fig. 3). The frequency of incidents involving greater than 20 individuals indicated a similar seasonal pattern (Fig. 4). No penguins were recovered in November, January or February (Figs 3 and 4). DISCUSSION The 4 215 oiled penguins admitted to the SANCCOB rescue station over the period 1981-1991 is 24 % less than the 5 565 recorded in the previous 11 years. However, total population counts indicate a decrease in African penguin numbers between 1978-1979 and 1984-1988 of 2 1 % . Consequently, average annual admission rates of oiled penguins have remained similar (2.47 individuals per 1000 birds in the 1970s and 2.35 per 1000 birds in the 1980s). This is despite a substantial decrease in the tonnage of oil transported around the Cape coast. Between 1970 and 1980 annual amounts transported averaged 536 x 10 6 tonnes with a peak of 630 × 10 6 tonnes in 1977 (Moldan & Dehrman, 1989). In contrast, an average of only 197 X 10 6 tonnes passed around the Cape between 1981 and 1987. Oil tankers are not the only source of oil slicks along the southern African coast. Many small, chronic, operational spills that affect penguins are discharged from vessels other than tankers. The numbers of these vessels are also likely to have decreased in response to the same factors that have resulted in a decrease in oil traffic. That the proportion of the penguin population affected by oiling has remained similar, in spite of a decrease in traffic over the last decade, is probably a

Mechanisms of oiling The large volume of shipping that passes close to the south Cape coast, and more particularly the distribution of oil spills, places penguins in the area at increased risk (Moldan & Dehrman, 1989). West of Cape Point most shipping veers away from the coast in order to round the bulge of Africa or to set course for the Americas. Legal restrictions controlling the movement of shipping around the South African coast have been enacted. Most recently and since 1979, laden tankers travelling westwards and not trading with South African ports are obliged to maintain a distance of more than 25 nautical miles (46.3 km) offshore during summer. In winter such tankers must conform to the load line convention (Moldan & Dehrman, 1989). In contrast, unladen tankers have not been confined to any particular shipping lane since 1973 and tend to travel close inshore to take advantage of the eastwardflowing currents along the south and east coasts (Shannon & Chapman, 1983). There are additional controls. The Prevention and Combating of Pollution of the Sea by Oil Act prohibits the discharge of any oil within 12 nautical miles (22.2 km) of the coast and mixtures of oil and water which contain more than 100 ppm of oil within 50 nautical miles (92.6 km) of the coast (Morant et al., 1981, Shannon & Chapman, 1983, Moldan & Dehrman, 1989). These limits are probably beyond the areas generally utilized by foraging African penguins (Heath & Randall, 1989, Wilson, 1985, Wilson et al., 1988). This suggests that most penguins are encountering illegally or accidentally discharged oil. However, other factors may be implicated. High concentrations of tar washed up on beaches or entrained in inshore waters, particularly east of 20°E, suggest that winds and currents also play an important role in increasing the risk of oiling of penguins along part of the southern Cape coast (Shannon & Chapman, 1983) by increasing the residence time of oil in areas close to breeding sites. The system of currents around the major penguin concentration at Dyer Island (19°20'E is complex (Harris, 1978; Shannon & Chapman, 1983). The main relevant feature is a zone of divergence between 20 ° and 21°E that divides an onshore advection (Fig. 5). Oil entering the system from an oil spillage further offshore would be moved shorewards and eastwards. A nearshore anticyclonic eddy east of the divergence would also keep oil entrained in the region (Shannon & Chapman, 1983). On the basis of data collected at other African penguin colonies (Wilson, 1985; Heath & Randall, 1989) this would be within the potential foraging range of penguins breeding at Dyer Island although the precise areas utilized by birds are unknown. Oil advected towards the coast west of the

Oiling in penguins, South Africa

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divergence would move westwards towards Cape Point and finally out of the divergent west coast upwelling region. A small convergence zone near Danger Point and Dyer Island may further increase the chance of penguins at Dyer Island encountering oil close to the island (Shannon & Chapman, 1983). Patterns

of oiling

There are no seasonal trends in the number of oil spillages recorded along the southern Cape coast (Moldan & Dehrman, 1989). Consequently, the observed seasonal patterns of oiling (Figs 3 and 4) may reflect (1) predictable changes in local currents and wind patterns that determine the movement of oil and attendant risk of penguins encountering oil slicks; (2) changes in the activity patterns and bchaviour of penguins that affect their susceptibility to oiling. The prevailing wind regime off the south coast is southerly in summer and northerly in winter. Accordingly, there is a greater frequency of surface onshore flow during summer. Such conditions are likely to increase the risk of penguins encountering oil during summer (Shannon & Chapman, 1983). This was not observed, suggesting instead that seasonal changes in penguin activity patterns are a more likely cause of the higher incidence of oiling in winter. Penguin populations are most vulnerable to oiling when individuals concentrate to breed. African penguins breed over an extended period, caused partly by the high incidence of replacement laying (Randall &

Randall, 1981), with most present at colonies from January to September (Randall & Randall, 1981; Wilson, 1985). Indices of the total numbers of penguins breeding at Stony Point, a mainland colony within 30 km of Dyer Island, peak in June or July (Fig. 6) (FitzPatrick Institute unpublished data). The relatively large number of penguins commuting to and from foraging areas during winter may partly explain the high rates of oiling observed. There are few relevant data on dispersal of penguins. However, outside of

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40

N. d. Adams

breeding and moulting both adult and juvenile penguins may be widely dispersed along the coast. The impact of a particular oiling incident on the penguin population is to a large measure dictated by its location in relation to breeding sites and may explain the inter-annual variability in numbers of penguins affected by oiling. The lack of any significant correlation between the relative number of oil spillages detected over the period 1985-1988 from aircraft patrols and numbers of oiled penguins recovered along the south coast (r2=0.21, p>0.05) is probably similarly explained. However, the small number of data points necessitates some caution in interpretation.

shipping around the Cape coast in the vicinity of the major penguin concentrations at Dyer and St Croix Islands, particularly in winter when penguins appear most at risk from oiling. Such regulations should enforce ships to passage farther offshore. The initiation of coastal patrols coupled with increased penalties for illegal oil discharges has reduced the number of spills. Such patrols should be maintained. The natural establishment of new penguin colonies along the southern Cape coast and at Robben Island suggests that artificial seeding of colonies may be feasible (see also Crawford et al., 1990). Such colonies would mitigate the effects of catastrophic events at major population centres.

Impacts of oiling The annual adult mortality rate of breeding African penguins at St Croix Island was estimated at 8.9 % (Randall, 1983; La Cock et al., 1987). The number of penguins admitted to SANCCOB annually between 1981 and 1991 has averaged 0.24 % of the total population (estimated 1984-1988, Crawford et al., 1991). This is 2.6 % of the annual adult mortality rate. The figure for Dyer Island alone was slightly higher at 0.28 % of the island population. These percentages are lower than the 0.7-0.9 % of the total population found oiled at breeding sites and beaches over six years in the late 1960s and early 1970s (Frost et al., 1976). During this period 69 % of penguins found oiled were admitted to SANCCOB for treatment. That 40.3 % of 295 penguins deaths recorded at St Croix Island over 3.5 years were directly attributable to oiling led Randall et al. (1980) to conclude that oiling was a significant factor in influencing population trends. However, dead penguins found at the island represent only a small fraction of those actually dying. Consequently, until mortality factors at sea are quantified a more cautious interpretation is required. On the basis of numbers of oiled penguins admitted to SANCCOB, there is no evidence of a substantial increase in the impact of oiling in penguin populations between 1981-1991 and the previous decade. It is of note that numbers of penguins breeding along the south coast have increased or have remained stable in an area of high oiling risk. However, there is now a greater risk of a single incident affecting a substantial proportion of the population on the south coast of South Africa. It is likely that the recovery of African penguin populations from a single catastrophic oiling event at one of the major breeding sites on the south coast of South Africa is likely to be slow (Cairns & Elliot, 1987). Breeding colonies are far from any other source of colonization and African penguins rarely recruit to non-natal colonies (Randall et al., 1987), although the rapid increase in the penguin colony at Robben Island (Crawford et al., 1990; R. J. M. Crawford & B. M. Dyer, pers. comm.), greater than that possible by intrinsic growth, suggests that the phenomenon may be more widespread than previous data suggest. On this basis, there are sufficient grounds for reviewing regulations controlling the movement of

ACKNOWLEDGEMENTS The South African Foundation for the Conservation of Coastal Birds, through their chairperson Anton Moldan, kindly made available their detailed oiling records. Financial support was provided by the University of Cape Town and the South African Foundation for Research and Development. REFERENCES Cairns, D.K. & Elliot, R.D. (1987). Oil spill impact assessment for seabirds: The role of refugia and growth centres. Biol. Conserv., 40, 1-9. Crawford, R.J.M., Williams, A.J., Randall, R.M., Randall, B.M., Berruti, A. & Ross, G.J.B. (1990). Recent population trends of Jackass penguins Spheniscus demersus off southern Africa. Biol. Conserv., 52, 229-43. Crawford, R.J.M., Ryan, P.C. & Williams, A.J. (1991). Seabird consumption and production in the Benguela and western Agulhas ecosystems. S. Afr. J. mar. Sci., 11, 357-75. Dunnet, G.M. (1987). Seabirds and North Sea oil, Phil. Trans. R. Soc. Lond., B 316, 513-24. Frost, P.G.H., Siegfried, W.R. & Cooper, J. (1976). Conservation of the Jackass penguin Spheniscus demersus (L.). Biol. Conserv., 9, 79-99. Harris, T.F.W. (1978). Review of coastal currents in southern African waters. S. Afr. National Sci. Prog. Rep., 30, 1-103. Heath, R.G.M. & Randall, R.M. (1989). Foraging ranges and movements of jackass penguins Spheniscus demersus established through radio telemetry. J. Zool., Lond., 217, 367-79. Kerly, GTH. & Erasmus, T. (1987). The management of oiled penguins. In Proceedings 1987 Oil Spill Conference: Prevention, behaviour, control, clean-up, Baltimore, pp. 465--8. La Cock, G.D., Duffy, D.C. & Cooper, J. (1987). Population dynamics of the African penguin Spheniscus demersus at Marcus Island in the Benguela upwelling ecosystem. Biol. Conserv., 40, 117-26. Moldan, A. & Dehrman, A. (1989). Trends in oil spill incidents in South African coastal waters. Mar. Pollut. Bull., 20, 565-67. Morant, P.D., Cooper, J. & Randall, R.M. (1981). The rehabilitation of oiled Jackass penguins Spheniscus demersus, 1970-1980. In Proceedings of the Symposium on Birds of the Sea and Shore, 1979, ed. J. Cooper. African Seabird Group, Cape Town, pp. 267-301. Randall, R.M. (1983). Biology of the Jackass penguin Spheniscus demersus at St Croix Island. PhD thesis, University of Port Elizabeth, South Africa.

Oiling in penguins, South Africa Randall, R.M. & Randall, B.M. (1981). The annual cycle of Jackass penguins at St Croix Island. In Proceedings of the Symposium of Birds of the Sea and Shore, 1979, ed. J. Cooper. African Seabird Group, Cape Town, pp. 427-50. Randall, R.M., Randall, B.M. & Bevan, J. (1980). Oil pollution and penguins--Is cleaning justified? Mar. Pollut. Bull., 11,234--37. Randall, R.M., Randall, B.M., Cooper, J., La Cock, G.D. & Ross, G.J.B. (1987). Jackass penguin Spheniscus demersus movements, inter-island visits and settlement. J. FieM Ornithol., 58, 445-455. Shannon, L.V. (1985). The Benguela ecosystem Part 1. Evolution of the Benguela, physical features and processes. Oceanogr. Mar. Biol. Ann. Rev., 23, 105-82. Shannon, L.V. & Chapman, P. (1983). Suggested mechanism

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for the chronic pollution by oil of beaches east of Cape Agulhas, South Africa. S. Afr. J. mar. Sci., 1, 231-44. Shelton, P.A., Crawford, R.J.M., Cooper, J. & Brooke, R.K. (1984). Distribution, population size and conservation of the Jackass penguin Spheniscus demersus. S. Afr. J. mar. Sci., 2, 217-57. Westphal, A & Rowan, M.K. (1971). Some observations on the effects of oil pollution on the Jackass penguin. Ostrich, Suppl. 8, 521-26. Wilson, R.P. (1985). The Jackass penguin Spheniscus demersus as a pelagic predator. Mar. Ecol. Progr. Ser., 25, 219-27. Wilson, R.P., Wilson, M-P.T. & Duffy, D.C. (1988). Contemporary and historical patterns of African penguin Spheniscus demersus: Distribution at sea. Estuar. Coast. Shelf Sci., 26, 447-58.