Away from selected breeding colonies there have been no coordinated and comprehensive studies of migrant seabirds in Korean waters. The status of many seabird species therefore remains largely unknown or underestimated - with records pre-2000 based largely on specimens collected as by-catch in fishing nets, or from short periods of land-based observations. As a result, although five species of skua/jaeger are listed by the Oriental Bird Club checklist for the broader Oriental/East Palerarctic region (Brown Skua Catharacta antarctica, South Polar Skua Catharacta maccormicki, Pomarine Jaeger Stercorarius pomarinus, Parasitic Jaeger Stercorarius parasiticus and Long-tailed Jaeger Stercorarius longicaudus), there is almost no published information on the status of any of these five species in Korean waters. No species of Skua or Jaeger is listed for the Democratic Peoples' Republic of Korea (DPRK/North Korea) by Tomek (1999), for example; and only one species, the Parasitic Jaeger, is listed for the Peninsula as a whole by Lee, Koo and Park (2000), and that as a vagrant. This online note therefore aims to present updated information on the status of the four species so far recorded (South Polar Skua and Pomarine, Parasitic and Long-tailed Jaegers), based primarily on the personal observations of the author in South Korean waters. Almost all such records were made from commercial ferries, taken as part of research into passerine and other migration on offshore islands.

Geography and Other Considerations

The Korean Peninsula forms an obvious barrier for seabirds, including Skuas and Jaegers, moving along the eastern flank of the Asian mainland. To move south from high latitude breeding or feeding areas, for example, such species must either cross the Peninsula, to enter the West/Yellow Sea; or instead follow the long and curving East Sea/Sea of Japan coastline southwards before entering the 200 km wide South Sea/Korea Straits. From here, presumably joined by seabirds moving along the western coastline of the Japanese archipelago, such species would then be able to enter the warmer East China Sea, or for longer distance migrants, migrate beyond the Ryukyu Islands and Taiwan into the open waters of the Pacific Ocean.

Despite its extensive coastline and this apparently strategic location on migrant flyways, observations of seabirds on the Peninsula have been significantly limited by a combination of political and geographical factors. Most coastal and marine areas in the north of the Peninsula have highly restricted access; while in the south of the Peninsula, where there are fewer access restrictions, there are still very few obvious points (such as exposed headlands) to conduct observation of migrant seabirds. The largely shallow and turbid inshore waters of the Yellow Sea have both extensive tidal-flats and numerous offshore islands greatly limiting observation of seabirds; the South Sea coastline is highly indented, also with numerous offshore islands; and the deep East Sea has a largely “straight” coastline, with one very remote but massive accessible offshore island (Ulleung) and only a single 10 km long Peninsula (the Guryongpo: headland at approximately 36 D 04' N 129 D 33'E), which both forms the easternmost point of the southern Korean peninsula and also offers conditions suitable for funneling migrant seabirds in onshore winds.

Most observations of seabirds in the southern part of the Peninsula at least therefore need to be made either from the Guryongpo Peninsula (and to a much lesser extent from other less-exposed headlands), or from commercial ferries - which run between South Korea and Japan across the South Sea/Korea Strait, and also to offshore islands in all three seas.

Observations of Skuas and Jaegers: Method and Bias

As a result the most significant observations of jaegers (most especially Pomarine, with lesser numbers of Parasitic) have been made from both the Guryongpo Peninsula and also from ferries running to offshore islands - with the largest number of records being made by Nial Moores from commercial ferries in the Yellow Sea. There is, however, very considerable bias in such observations (both in timing and distribution), with over 50 ferry journeys taken since 2000 by Nial Moores in the southern Yellow Sea (all to research migrant birds on offshore islands, rather than as part of a coordinated attempt to survey seabirds), compared with only 2 ferry journeys in the East Sea, and less than 10 in the Korean Straits. Most observations from ferries were made (with binoculars) from the back of high speed commercial hydrofoils that run between Mokpo and Gageo Island (most especially in 2000 and 2001), between Incheon Port and Socheong Island (all in 2003), and from a slower ferry between Gunsan and Eocheong Island (in 2002 and 2003), with limited additional observations made also from inside high-speed hydrofoils between Busan and the Japanese city of Fukuoka (on ten occasions between 1995 and January 2004). Most journeys were timed to coincide with the peaks of spring and autumn passerine migration - i.e. mid-March to late May, and again between August and early November - with only very limited ferry travel in the mid-summer or mid-winter period.

In addition, some land-based counts of migrant seabirds were conducted by Nial Moores at Guryongpo or at the Taejongdae headland in Busan (the southeastern-most point of the Peninsula), mostly between late November and March - at a time of year when rather few jaegers have been recorded from ferries.

The present status review should therefore not be considered as comprehensive in any way: rather, a small step forward in understanding.

South Polar Skua Catharacta maccormicki

The South Polar Skua was first recorded in Korean waters by Nial Moores with a single on November 4th, 1995 ca 20 km south of Busan in the Korean Straits, followed by 1 or 2 on October 10th, 2001, near Gageo Island in the southwestern approaches (both records are described in more detail. Go to: South Polar Skua. 04 November 1995. At Sea).

In 2003, a further seven records at least of South Polar Skua were made between Incheon and Socheong Island, at sea largely between 2km and 50 km south or southeast of the island:

All eight records so far have been made in autumn, between September 26th and November 4th; and all have been coincident with dates on which Pomarine Jaeger were also recorded. The spread of records in the south and west, with no records yet from the East Sea, however, appears rather different from the pattern shown by Pomarine or Parasitic Jaegers. Brazil (1991) states that South Polar Skua in the Pacific Ocean off Japan often follow flocks of shearwaters, particularly Short-tailed Shearwater Puffinus tenuirostris. It is perhaps of interest that both the record near Gageo island in 2001 and the series of records in 2003 also coincided with records of “southern-type” or ocean-associated seabirds (including Brown Booby Sula leucogaster in 2001) and a run of records of both Short-tailed and Flesh-footed Shearwaters Puffinus carneipes in 2003. Rather than migrating purposefully through Korean waters, it seems possible that small numbers of South Polar Skua are instead attracted to significant concentrations of other seabirds, following them up into the Yellow Sea or the Korean Straits.

Pomarine Jaeger Stercorarius pomarinus

Pomarine Jaeger, Nov 02 2003,
at sea near Socheong,
Photos © Nial Moores

The Pomarine Jaeger is the most recorded and numerous jaeger occurring in Korean waters with records from January through to November, and an obvious peak of migration in October. The species has been recorded from all three seas. On the east coast at least 200 per hour were counted passing south within sight of land from the Guryongpo Peninsula on October 19th, 2002, with 100 per hour also passing south also on October 20th (van Den Berg and M. Robb in lit.). A further 3 were also noted by Nial Moores there on November 22nd, 2002. In the South Sea/Korean Straits there have been at least two records at sea between about 5 km and 15 km offshore from Busan, with 10 on November 4th, 1995, and 1 on January 10th, 2004; and there have been numerous records in the West/Yellow Sea. There have been at least nine records involving 18 individuals (dates spanning March 14th and May 23rd in the first half of the year, and August 24th and November 10th in the second half) between Mokpo and Gageo Island in the far southwest (on approximately 20 crossings); three records of singles between Gunsan and Eocheong in 16 ferry crossings (one in May 2002, and one each in August 2002 and 2003); and numerous records on 16 ferry journeys made by Nial Moores between Incheon and Socheong Island, the first in 2003. (Most records prior to 2003 are listed on this site: go to: Pomarine Skua: 04 November 1995:At Sea.) In addition, a single concentration of 40 were noted from the same ferry on October 26th, 2003, by Kim Dong-Won and Nam Ki-Baek.

Records in 2003: All between Incheon and Socheong Island.

Records of Pomarine Jaeger from all ferry journeys made by Nial Moores between Incheon Port and Socheong Island (some as multi-observer records) in 2003.

Adult Pomarine Jaeger
Photo © Nial Moores

Allowing for the present bias in observations, the pattern of records strongly suggests that the Pomarine Jaeger is primarily an autumn migrant through Korean waters, with one major migration route along the East coast into the South Sea (following the coast past the Guryongpo Peninsula, past Busan and then southwest through the Korean Straits past the Heuksan islands, including Gageo); and another shorter route presumably cutting across the DPRK into the West/Yellow Sea. This second route likely follows a Northwest-Southeast axis along the coast of the Russian Maritimes and northeastern DPRK, before cutting across the narrow neck of the peninsula (a distance of ca 175 km) into the West Sea - for example between Hamheung and Wonsan Bays on the east Coast and Daedong River estuary on the west coast. The existence of this hypothetical route is supported by the present paucity of records of Pomarine Jaeger on the Hebei coast in the far northern part of the Yellow Sea, and by the comparative paucity of observations in the Yellow Sea near Eocheong Island and between Mokpo and Gageo (the latter island lying at almost the same latitude as Socheong): i.e. large numbers of Pomarine Jaeger seem not to be reaching Socheong Island in autumn from either the northernmost part of the Yellow Sea, or from waters far to the south. The scarcity of records further south in the Yellow Sea in late autumn near the west coast also seems to suggest that the majority of Pomarine Jaeger after reaching the Yellow Sea then move into deeper and more open central waters, rather than moving south near to the west coast.

4 Pomarine Jaegers, October 20, 2002. Guryong-po Peninsula.
Photo © Arnoud Van den Berg

The peak of the southward migration appears to be in mid-October, with migration continuing with reduced intensity into late November. Although there is only one mid-winter record up to the present, it seems quite likely that very small numbers of Pomarine Jaeger also spend the boreal winter in Korean waters - not only in the Korean Straits. As in Japan (e.g. Brazil, 1991) it seems likely that they might be associated with Black-legged Kittiwake Rissa tridactyla flocks, a species that both also peaked in waters between Incheon and Socheong Island in October 2003 (similarly suggesting an overland crossing: go to Status and Distribution of Gulls in South Korea), and that occurs throughout all seas in mid-winter. The timing and pattern of northward migration in spring is less clear. However, at least some Pomarine Jaeger have been recorded in the Yellow Sea at this time - where they might either over-summer, or again move overland to more northern breeding areas.

Parasitic Jaeger Stercorarius parasiticus

Parasitic Jaeger. Photo © Choi Soon-Kyoo

The Parasitic Jaeger is the second commonest of the Skua/Jaeger group recorded in Korean waters, with records in both the East and Yellow Seas, as well as in the southwestern approaches. The highest count appears to be of 6 on September 23rd.

Records span mid-March to late-October, with an autumn peak occurring rather earlier than that shown by Pomarine Jaeger. There appears to be too little data to ascertain clearly the possible migration routes of the species, but on present evidence it seems likely to mirror those outlined in the Pomarine Jaeger account above.

There at least 15 records in South Korea known to the author between 2000 and 2003:

Long-tailed Jaeger Stercorarius longicaudus

There is only one record of this species in Korean waters so far known to the author - that on May 14th, 2002, between Mokpo and Daeheuksan Island (for details read: Long-tailed Skua: 14 May 2002: At Sea). It seems, however, based on records in Japan, that the species occasionally moves through the Korean Straits in significant numbers during migration.

Summary

There have been no coordinated or comprehensive surveys of migrant seabirds in Korean waters, beyond local studies of several nesting species. As a result there is very little data available on many seabird species - and very few records pre-2000 of any skuas or jaegers in Korean waters, with only the Parasitic Jaeger considered to occur - as a vagrant. Observations made from commercial ferries as well as from headlands since 2000 reveal that the Pomarine Jaeger is actually a relatively numerous species in both spring and especially in autumn (with evidence suggesting an overland migration route as well as one along the East coast); that the Parasitic Jaeger is also regular in lesser numbers in both spring and autumn; that the South Polar Skua occurs probably regularly in the Yellow Sea, especially in autumn; and that the Long-tailed Jaeger has also occurred.

Acknowledgements

The author would like to thank the following observers for sharing observations or making their records of jaegers available: Charlie Moores, Arnoud van den Berg, Magnus Robb, Choi Soon-Kyoo, Tim Edelsten, Kim Su-Kyung, Mathias Ritschard, Manuel Schweizer, Werner Mueller, Mario Camici, Dave Parmenter, Diana Briel, Claudio Koller, Andreas Taschler, Paul Walser, Dennis Buss, Kim Dong-Won, Nam Ki-Baek, and Choi Yu-Seong.

References:

• Brazil, M. (1991). The Birds of Japan. Helm, London.
• Lee, W., Koo, T. & J-Y Park.(2000). A Field Guide To the Birds of South Korea. Evergreen Foundation.
• Tomek , T. (1999). The birds of North Korea. Non-Passeriformes. Acta zool.cracov. 42 (1): 1-217.