This discussion was first published as part of the 2012 Red List update, but remains open for comment to enable reassessment in 2015.
Streaked Shearwater Calonectris leucomelas breeds on islands and some mainland coastal areas in Japan, eastern Russia, North Korea, South Korea and China at least, and ranges widely when not breeding, reaching the territorial waters of countries in South-East Asia and Australasia. It is currently listed as Least Concern on the basis that it was not thought to approach the thresholds for Vulnerable under any of the IUCN criteria.
This species has a very large non-breeding range, but a very small breeding range that is not thought to approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence of less than 20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline was not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (at least a 30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (fewer than 10,000 mature individuals with a continuing decline estimated to be at least 10% over ten years or three generations, or with a specified population structure).
In Japan, where it is thought that the majority of the species’s world population breeds, there are 11 islands that are inhabited by more than 10,000 breeding pairs of this species (Oka 2004). Some level of negative impact from alien rat species on Streaked Shearwaters can be expected at least on three of these islands (M. Sato in litt. 2011). The species appears to suffer significant impacts from rats on Mikura-jima, which is populated by c.300 people and is popular with tourists, thus making an eradication programme problematic and the reintroduction of rats more likely (Oka et al. 2002, J. Croxall in litt. 2011). Both black rats Rattus rattus and brown rats R. norvegicus are potentially affecting a colony of c.150,000 Streaked Shearwaters breeding on Okino-shima Island (M. Takeishi per M. Sato in litt. 2011). On Sasudo, South Korea, the species is threatened mainly by predation by R. norvegicus (Lee 2010). Rats, cats and human disturbance may threaten the species on Socheong Island (Birds Korea 2010). In addition to the threat from introduced predators, the species is also susceptible to fisheries bycatch (Birds Korea 2010, J. Croxall in litt. 2011). The prevalence of these threats suggests that the species is in population decline; however, further data and observations are required from throughout the species’s range to better assess the current trend.
Under criterion A, a decline approaching 30% (typically 20-29%) over the last three, or projected over the next three, generations, might make the species eligible for uplisting to Near Threatened. A decline of at least 30% over three generations would probably warrant uplisting of the species to Vulnerable. BirdLife estimates the generation length of this species to be c.19.3 years, giving a three-generation trend period of c.58 years.
Birds Korea (2010) Streaked Shearwater Calonectris leucomelas. The Birds Korea Blueprint 2010 for the conservation of the avian biodiversity of the South Korean part of the Yellow Sea. Busan, South Korea: Birds Korea.
Lee K.-G. (2010) The status of seabirds on Sasu and Chilbal islands, and the management of invasive species. The Birds Korea Blueprint 2010 for the conservation of the avian biodiversity of the South Korean part of the Yellow Sea. Busan, South Korea: Birds Korea.
Oka, N. (2004) The distribution of Streaked Shearwater colonies, with special attention to population size, area of sea where located and surface water temperature. Journal of the Yamashina Institute for Ornithology 35: 164-188.
Oka, N., Suginome, H., Jida, N. and Maruyama, N. (2002) Chick growth and fledgling performance of streaked shearwaters Calonectris leucomelas on Mikura Island for two breeding seasons. Journal of the Yamashina Institute for Ornithology 34: 39-59.