104Wildlife Conservation Plan for Seabirds

104 Wildlife Conservation Plan for Seabirds

No recent data from Bishop and Clerk Islets, Heard or McDonald Islands (Woehler 2006) but Heard Island population is believed to have decreased, based on disappearance of surface colonies between 1940s–1950 and early 2000s (E. Woehler pers. comm). Globally, this species has been classified as vulnerable under IUCN criteria owing to rapid population decreases, which, although they have been ongoing for perhaps a century, appear to have worsened in recent years.

Climate change appears to be a factor driving population decreases. Survival of adult Rockhopper Penguins appears to be sensitive to sea surface temperatures, with highest survival probabilities under moderately-cold to long-term average temperature, and reduced survival probabilities under increasingly cold or warm ocean temperatures (Raya Rey et al. 2007, Dehnhard et al. 2013). Rockhopper Penguins at the Falkland Islands (Islas Malvinas) delayed breeding under warmer environmental conditions and laid lower mass eggs, with potential impacts on breeding success (Dehnhard et al. 2015a, b). Temperature extremes have caused collapse in accessible food resources in the past, and these are part of an ongoing trend in more frequent unusual oceanographic conditions recurring in the area (Dehnhard et al. 2013).

Penguins and their habitats may also be threatened by increased frequency of storm events at breeding sites (Wolfaardt et al. 2012). Severe mortality was recorded in moulting birds found unusually far from colonies in 2016, which appeared to be related to a set of poorly understood oceanographic conditions, leading to lowered primary productivity near breeding sites immediately before moult (Morgenthaler et al. 2018). Climate change may also lead to top-down changes in food web structure, causing increased inter-specific competition and secondary predation, e.g. competition and predation by the rapidly increasing pinniped (fur seal and sea lion) populations (Barlowet al. 2002, Raya Rey et al. 2012, Morrison et al. 2017). Overwintering conditions are thought to influence the proportions of birds skipping breeding at Marion Island (Crawford et al. 2006) and potentially elsewhere.

The number of Rockhopper Penguins returning to Marion Island to breed decreased by about 20 per cent between 1994/95 and 2007/08 and was significantly correlated with breeding success (Crawford et al. 2008). Another potential threat stems from interaction with fisheries; levels of bycatch mortality appear to be insignificant, but resource competition and indirect changes to the food web through modification of ecosystems may have more extensive impacts (Crawford et al. 2017). Land-based human threats at breeding sites, such as tourism, research and land management, are considered low, and although it may vary on local scales, disturbance from such activities is currently deemed not significant at an overall population level at the Falkland Islands (Islas Malvinas) (Crofts 2014). Tourism is strictly regulated with visits only to a small percentage of the global population.