Justification of Red List Category
This species has a very large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <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). The population trend is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The population trend is difficult to determine because of uncertainty over the extent of threats to the species.
The Rock Shag breeds on the southern coasts of Argentina and Chile, including Tierra del Fuego and the Falkland Islands (Islas Malvinas). It can be found wintering as far north as Uraguay (del Hoyo et al. 1992).
Behaviour The Rock Shag is a foot-propelled pursuit diver widely distributed in southern South America. It generally forages within 5 km of the colony, and eats a variety of primarily benthic prey. It principally forages during daylight hours, with occasional night time trips during moonlit nights when birds forage in similar locations and depths as during the day (Sapoznikow and Quintana 2002). It forages solitarily, in strictly coastal areas, and feeds at the sea bed (Punta et al. 1993). Diet At Punta Loma, Argentina, the main prey are benthic fish Riberoclinus eigenmant and the polychaete Eunice sp., both associated with sandy seafloors and seaweeds (Quintana 2001). At Bahias Bustamante and at Melo, Argentina, the species fed mainly on Rock Cod (Notothenia spp.), which were present in 87% of breeding and 91% of non-breeding regurgitated pellets (Punta et al. 1993). Foraging range At Punta Loma, Argentina, during the chick-rearing period, birds spent 36% of daylight hours away from the colony on feeding trips, and 92% of the foraging trip was spent diving (Quintana 2001). Shags fed mainly in water less than 10m deep, with a gravelly sand bottom and within 5 km of the shore (Quintana 2001). The mean foraging ranges were 3.8 ± 2.6 km and 2.6 ± 2.3 km in 1996 and 1997 respectively (Quintana 2001). These results are consistent with observations made in Bahia Bustamante, Argentina, where the observed foraging range was between 50-2000 m from the coast (Punta et al. 1993). Typically, the species forages in inshore waters less than 20m deep (Quintana 1999). Using a published relationship between dive depth and dive duration in Shags (depth (m) = (dive time (s)-35)/1.28), the mean diving depth for Rock Shags was estimated at 12.7 ± 7.5 m, with 86% of dives under 20 m (Quintana 1999). In Port Stanley Harbour, Falklands, birds foraged mainly in or just outside giant kelp beds (Macrocystis spp. and Lessonia spp.), within 50 m of shore and where the water was 1-6 m deep (Wanless and Harris 1991). Fewer birds foraged up to 100 m out, in water 7-13 m deep but not over kelp beds (Wanless and Harris 1991). The mean water depth for dives was 4.5 m (Wanless and Harris 1991). At Bahia Bustamante and Melo, Argentina, birds either foraged within bays, or else at a distance of less than 200 m from the shore and among kelp (Macrocystis pyrifera) beds (Punta et al. 1993). They foraged in areas which were 2 - 12 m deep, and contained algae (Punta et al. 1993). Foraging occurred at the bottom throughout the year, but occasionally also in mid-water during the breeding season (Punta et al. 1993). At Punta Loma, Argentina, the seabed in all the foraging areas consisted of bands of shallowly-sloping, gravelly sand sediments, with tuffs and wave cut platforms in some areas (Quintana 2001). The features of the seabed at foraging sites were consistent with the habitat requirements of the principal prey species, i.e. sandy sea floors and seaweeds (Quintana 2001). Shags used the same feeding areas during the two study years (Quintana 2001).
Intense fishing pressures on anchovy and numerous other fish species may increase competition for food for this species (Skewgen 2007). However, the primary prey sources is benthic fish and invertebrates and hence the species is less likely to be severely impacted by the anchovy fishery and food limitation is not thought to have caused any significant declines in the population thus far. Disturbance from recreational activities may threaten the species, possibly explaining the declining population trend in the Fuegian channel. The response of the Rock Shag to tourism contrasted strongly with other studied species and it has therefore been regarded as more sensitive to disturbance than other breeding species in the area (Raya Rey et al. 2014).
Text account compilers
Ekstrom, J., Fjagesund, T., Calvert, R., Butchart, S., Hatchett, J., Martin, R.
BirdLife International (2019) Species factsheet: Leucocarbo magellanicus. Downloaded from http://www.birdlife.org on 22/08/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/08/2019.