Adaptation Actions for a Changing Arctic: Perspectives from the Barents Area

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Chapter 6 · Impact analysis and consequences of change

Box 6.2 Cumulative impacts and consequences for seabird populations Many seabird populations in the Barents area have shown a significant and steady decline (see Chapter 2). Studies have been attributing this not just to one factor (such as loss of prey base due to human influence or natural variation, disease, or increase in contaminant loads), but rather to a cumulative effect of multiple stressors.

Svalbard,the risk of extinction increases as all of these colonies may crash concurrently (Heino et al., 1997). This decline in population has coincided with a major shift in oceanographic conditions (Descamps et al., 2013).The 1995 shift in the sub- polar gyre and consequent changes in the subarctic waters of the NorthAtlantic are very likely to have played an important role (Descamps et al., 2013). Brünnich’s guillemots may be vulnerable to pollution and to human impact on the availability of their prey through climate change and overfishing (Fauchald et al., 2014). Since the mid-1980s, levels of polychlorinated biphenyls (PCBs) have been reported for Brünnich’s guillemot from Svalbard (Norheim and Kjoshanssen, 1984; Mehlum and Daelemans, 1995). Levels correspond to those for other auk species and are lower than for glaucous gull (Norheim and Kjoshanssen, 1984; Mehlum and Daelemans, 1995; Borgå et al., 2005; Letcher et al., 2010; Verreault et al., 2010). Although lower pollutant concentrations have been measured in Brünnich’s guillemot, negative effects on vitamin status have been observed (Murvoll et al., 2007).However, taken in context the findings for glaucous gull indicate that pollutants, even at low levels, act as a stressor enhancing the negative effect of other stressors (Bustnes et al., 2006). It is possible that pollutants are playing a role in the decline of the Brünnich’s guillemot population, or are making these birds more vulnerable to other changes related to climate and food availability. Ivory gull ( Pagophila eburnea ) is the least studied species in the Arctic, with an estimated global population of 14,000 pairs (deWit et al., 2003).This species has a strong and year- round association with pack ice and its scavenging habits,and thus is vulnerable to changes in sea ice cover and exposure and the accumulation of high levels of organic pollutants, including mercury (Braune et al., 2006, 2007; Miljeteig et al., 2009; Lucia et al., 2015). Global warming and pollution have been identified as the major threats to ivory gull and how this species will progress in the future is unknown.

The breeding population of glaucous gull ( Larus hyperboreus ) at Bjørnøya, which is home to the largest colony in the Barents area, has drastically declined; by 65% over a 30-year period. Autopsy and chemical analyses of dead and dying birds showed very high levels of chlorinated pollutants in their brain and liver (Sagerup et al., 2009). The elevated chlorinated pollutant levels are likely to have affected the gulls directly (physiological) or indirectly (suppression of condition) (Sagerup et al., 2009) and could be one of the main causes of mortality in glaucous gull. According to Erikstad et al. (2013), the Bjørnøya glaucous gull population is currently declining at 8% per year. This indicates a median time to quasi-extinction of 19 years for this species. However, a third of the population decline is estimated to be due to the effect of pollutants in the adult population. In the absence of pollution, median time to population quasi-extinction is 50 years (Erikstad et al., 2013). See also Figure 6.4. In 1980 and 2006, total counts indicated population sizes of 2000 and 650 breeding pairs, respectively. Temporal trend assessment suggests that although several organochlorines are declining in Svalbard glaucous gull samples (Verreault et al., 2010), environmental factors such as atmospheric variability may modulate the influx and thus the food chain transfer of these compounds in the Arctic ecosystem (Verreault et al., 2010).The effects of pollutants are more severe in years when the environmental conditions are worse (Bustnes et al., 2006). Even low levels of pollution in combination with other stress factors, such as food shortage or increased competition for nesting sites, can be critical (Erikstad et al., 2013). As well as pollution, other explanations for the decline in the breeding population of glaucous gull include reduced prey availability, increasing predation from Arctic foxes ( Vulpes lagopus ) and competition from a growing number of great skua ( Stercorarius skua ) (Erikstad et al., 2013).There is agreement that climate change may result in reduced food availability and in an increase in adverse weather events.The effects of these factors on the glaucous gull population, in combination with pollutants, are not yet clear. Allmonitored colonies of Brünnich’s guillemot ( Uria lomvia ) at Bjørnøya and Svalbard (Descamps et al., 2013; Fauchald et al., 2014) began to decline during the same period (1994–1998). The annual rate of decline has since varied from 2–5%, and during the past decade Brünnich’s guillemot colonies have decreased by about 15-45%.If this trend continues at the same rate, the Svalbard population has an almost one in two chance (43%) of becoming quasi-extinct within the next 50 years and extinct in the next 100 years (Descamps et al., 2013). Further, because there is high synchrony between colonies at west

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Figure 6.4. Nests occupied by glaucous gull at Bjørnøya between 1987 and 2010 at a study plot. No monitoring was undertaken in 1989, 1990, 1994, 1996 and 1997. Open symbols indicate explorations based on the PROC EXPAND procedure which is a tool to work with time series. Erikstad et al. (2013).