Arctic Wildlife
The Arctic Species Trend Index: A Barometer for Arctic Wildlife

M. J. Gill ¹, C. Zöckler ², L. McRae³, J. Loh³, and B. Collen ³

¹Environment Canada, Circumpolar Biodiversity Monitoring Program Office 91780 Alaska Highway, Whitehorse, Yukon, Canada Y1A 5B7.
²UNEP World Conservation Monitoring Centre, 219 Huntingdon Road, Cambridge, CB3 0DL United Kingdom
³Institute of Zoology, Zoological Society of London, Regent's Park, London, NW1 4RY, United Kingdom

This report card summarizes results from the Arctic Species Trend Index report,
released by CAFF’s Circumpolar Biodiversity Monitoring Program in March 2010. : www.asti.is

October 18, 2010

Introduction

Dramatic changes (e.g., sea ice loss) in the Arctic’s ecosystems are predicted to occur over the next century (ACIA 2005). Understanding how the Arctic’s living resources, including its vertebrate species, are responding to these changes is essential in order to develop effective conservation and adaptation strategies. Arctic species that are adapted to these extreme environments are expected to be displaced, in part, by the encroachment of more southerly species and ecosystems (Post et al 2009). As Arctic ecosystems are characterized by low species diversity, they are at heightened risk of experiencing dramatic changes, as the loss of a single species could have dramatic and cascading effects on an ecosystem’s state and function (Post et al 2009). The current, mostly, single species approach to monitoring with a bias towards charismatic species over functional species limits our ability to detect and understand critical changes in the Arctic’s ecosystems. A broader and more integrated approach is needed to facilitate a better understanding of how biodiversity is responding to a changing Arctic and how these changes might reflect or counter global biodiversity trends.

Status and Trends

A total of 965 populations of 306 species (representing 35% of all known Arctic vertebrate species) were used to generate the ASTI. In contrast to the global LPI (Loh et al 2008), whose overall decline is largely driven by declines in tropical vertebrate populations, the average population of arctic species rose by 16% between 1970 and 2004. This pattern is very similar to the temperate LPI (Loh et al 2008) and is consistent in both the North American and Eurasian Arctic. The overall increasing trend in the Arctic is thought to be partly driven by the recovery of some vertebrate populations (e.g., marine mammals) from historical overharvesting ( George et al 2006) as well as from recent changes in environmental conditions both inside (e.g. Bering Sea Pollock (Overland 2008)) and outside of the Arctic (e.g. Lesser Snow Geese ( Abraham et al 1997)) resulting in dramatic increases in some species’ populations. This increasing trend, however, is not consistent across biomes, regions or groups of species.

Populations in the High, Low and Sub-Arctic boundaries (Figure W1), for instance, show markedly different trends. High Arctic vertebrate abundance has experienced an average decline of 26%. Despite an initial growth period until the mid-1980s, Sub Arctic populations (mostly terrestrial and freshwater populations) have, on average, remained relatively stable (-3% decline) whereas Low Arctic populations, largely dominated by marine species, show an increasing trend (+46%). This pattern may reflect, to some extent, varying and predicted responses (ACIA 2005; Post et al 2009) to changing pressures such as climate change and harvest patterns, but may also reflect natural, cyclic patterns for some species and populations. However, caution is needed in interpreting these results.

Figure W1. Location of datasets in the Arctic Species Trend Index.

The High Arctic has experienced the greatest increases in temperature to date and even greater temperature increases are expected resulting in further loss of sea ice extent and range contraction of high arctic ecosystems and species (ACIA 2005; Anisimov et al 2007). However, 34 years is too limited a time series to attribute these changes to declining trends in High Arctic vertebrates. For example, wild barren-ground caribou and reindeer herds are known to naturally cycle over long time periods and recent, largely synchronous declines across the Arctic are thought to be natural and in part, responsible for the declining High Arctic index. However, declines in other species populations such as lemmings in Greenland, Russia and Canada may be in part, the beginning of a negative response to a dramatically changing system. In contrast, increasing trends in Low Arctic populations are biased by dramatically increasing fish populations in response to changing marine conditions (Overland 2008) and recovering marine mammal populations (George et al 2006) in the eastern Bering Sea. More data are needed in other arctic marine systems before an accurate picture regarding arctic marine vertebrate population trends can be developed.

Divergent patterns are also observed between the different biomes (marine, freshwater, terrestrial). Whereas the freshwater and marine indices increase over the time period (52% and 53% respectively), the terrestrial index shows an overall decline of 10% despite increasing in the late 1970’s to mid-1980’s. The data behind the freshwater index is currently too sparse (51 species, 132 populations) to fully reflect the circumpolar freshwater situation and whilst the marine index is robust (107 species, 390 populations) it is largely driven, as is the Low Arctic index, by an overweighting of population data from the eastern Bering Sea. The moderate decline in the terrestrial index (-10%) is largely a reflection of declines (-28%) in terrestrial High Arctic populations (mostly herbivores such as caribou and lemmings), whereas terrestrial Low Arctic populations (e.g. Lesser Snow Geese ( Abraham et al 1997)) have increased by 7% and Sub Arctic populations have declined (-5%) slightly (Figure W2). Terrestrial Low Arctic population increases are driven, in part, by dramatically increasing goose populations, but may also reflect ecological response to climatic changes whereby species with more southerly distributions are responding favourably to these climatic changes (Post et al 2009). This northward movement of southern species (e.g. Red Fox (Killengreen et al 2006) coupled with increasing incidence of severe weather events in the High Arctic (Post et al 2009; Miller et al 2003) and changing tundra vegetation (Sturm et al 2001; Wahren et al 2005) may explain, in part, the declines in terrestrial High Arctic populations and the expected negative impact on herbivorous species.

Figure W2. Index of terrestrial species disaggregated by Arctic boundary for the period 1970-2004. (High Arctic, n=25 species, 73 populations; Low Arctic, n=66 species, 166 populations; Sub Arctic, n=102 species, 204 populations)

The major Arctic taxa (birds, mammals and fish) also exhibit divergent trends. Birds, which comprise 52% of the ASTI populations are revealing a very flat trend overall (-2%), whereas mammal populations increased fairly steadily (+33%) over the same time period. The fish index experienced the greatest increase (+96%), but, again, this is primarily driven by marine fish population increases in the Eastern Bering Sea. Within the bird taxa, freshwater birds have increased dramatically (+43%) and is largely a reflection of increases in some waterbird populations, likely in response to stricter hunting regulations and land-use changes on their wintering grounds (Drent et al 2007). The terrestrial bird index, despite a doubling in the numbers of geese, has experienced a moderate decline (-10%) over the past 34 years, whereas marine birds, although fluctuating, have remained relatively steady (-4%). An analysis of migrant versus non-migrant birds showed an increasing trend for non-migrants (+20%) and a slight decline (-6%) for migrants although there was no significant differences between the two groups. However, the slight decline in migrant birds would have likely become a more significant decline if the increasing geese populations were not included and we were able to include shorebird population trend data derived from non-Arctic survey sources². Declines in migrant shorebirds to date is mostly regarded as a response to pressures (land-use changes, etc.) found on wintering and stop-over sites (Stroud et al 2006; Piersma et al 2001; Niles et al 2009), but expected changes to arctic breeding habitat as a response to climate change may also become a factor in the long-term as most High Arctic species and populations would be at risk (Post et al 2009; Meltofte et al. 2007).

While the ASTI offers some initial insight into recent trends in Arctic vertebrate populations, careful interpretation of the ASTI is required as it does not yet adequately represent all populations, taxa, biomes and regions. The large number of Bering Sea populations in the Marine index and the recent recovery of marine mammal populations from historical overharvesting illustrate how the index can be influenced and reveals the shortcomings that a restricted timeline of biodiversity change presents. While rapid, human-induced changes in Arctic ecosystems are already likely resulting in winners and losers among arctic species and populations (Post et al 2009), more data coverage and longer-time series are needed to give an accurate, unbiased picture. Despite the limited time series for the index, the large and diverse collection of data in the index, representing a multitude of taxa across regions, biomes and longitudes does allow some insight into potential responses to human-induced pressures, outside of natural variation. This index will improve with the scale, number and breadth of contributions and future analyses will be more robust in their messages.

Endnotes

¹ 1970 was used as the baseline as pre-1970 data in the ASTI was limited making trend results uncertain for years preceding 1970.
² Population trend data derived from non-arctic surveys were not included in the analyses.

References

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