Reproduction strongly drives annual variation in Arctic fox abundance (Tannerfeldt and Angerbjörn 1998; Samelius and Alisauskas 2017), and Arctic fox harvest in winter is positively related to fox reproductive output the previous summer (McDonald et al. 2017). Thus, trends observed in Arctic fox harvest likely reflect changes in Arctic fox population dynamics. Our results suggest Arctic fox harvest in Churchill has declined over time (Fig. 2). However, inflation-adjusted pelt price lagged 1 year was positively related to Arctic fox harvest after accounting for trapping effort. Due to the negative relationship between pelt price and year, and the positive relationship between pelt price and Arctic fox harvest, the decline in Arctic fox harvest found in our analysis was likely influenced in part by declining pelt value in the longer time series (1955–2012). However, in the shorter time series (1980–2012) pelt price was not significantly related to Arctic fox harvest, suggesting that although pelt price influenced Arctic fox harvest when evaluated across the full-time series, its influence on Arctic fox harvest patterns was weaker in the later portion of the time series where the largest declines in Arctic fox harvest were observed.
Contrary to our prediction, red and Arctic fox harvests were positively related. Our hypothesis that interspecific competition between the species may be promoting declines in Arctic fox abundance may not be supported. Moizan et al. (2022) showed resources competition for denning sites was greater driven by spacing needs than interference competition between the species. Arctic and red foxes have been demonstrated to coexist in our study area (Lai et al. 2022; Moizan et al. 2022); therefore, another driver may be promoting changes in Arctic fox harvest dynamics.
Our analysis on harvest suggests a decline in Arctic fox numbers, whereas red fox harvest has remained stable. The different harvest responses of red and Arctic foxes suggest these species may be responding differently to cryosphere changes near the Arctic treeline. Similarly, interference between Arctic foxes and red foxes in the Canadian High Arctic is low (Lai et al. 2022). Gallant et al. (2012) suggested red fox population growth on Herschel Island, Yukon, may be limited by winter prey availability as reproduction and relative abundance of Arctic and red foxes did not change significantly over four decades, despite increased temperatures and a longer growing season. Similar to Gallant et al. (2012), variables associated with a warmer climate, including warmer summer temperatures and the last day snow was present in late spring, were not significantly related to fox harvest.
Decreased sea ice duration on Hudson Bay may be contributing to the recent decline in Arctic fox abundance (Fig. 3), likely because shorter sea ice duration constrains Arctic foxes’ access to important supplementary marine food resources. Considering sea ice is an important habitat for polar bears to hunt seals, a reduction in polar bear hunting success in response to sea ice freezing later in fall and breaking up earlier in spring may consequently reduce the availability of seals for foxes (Stirling and McEwan 1975; Lunn et al. 2016; Descamps et al. 2017). Shorter sea ice duration may further contribute to declines in Arctic fox abundance by causing a trophic mismatch. Delayed sea ice freeze-up may create a lag in reliable food resources for foxes between the departure of migratory birds in fall and when seals carcasses can be scavenged on the sea ice, potentially lowering the survival of juveniles shortly after they become independent and disperse from their natal dens. Furthermore, limited food availability on sea ice may impact Arctic fox reproduction, given litters are produced before migratory birds arrive in spring, and access to marine resources during this critical and energetically-costly period for Arctic foxes (Audet et al. 2002) may increase foxes’ body condition during pregnancy and lactation. Tannerfeldt et al. (1994) estimated 21% of juvenile mortality from weaning to 6 weeks of age was attributed to starvation and only 8% of juveniles survived to reproductive age, so food availability at this time, when energetic requirements are high but terrestrial resources are still scarce, may be an important factor for early juvenile survival. The increasing trend of the number of days without sea ice coverage in Hudson Bay is well documented (e.g., Boonstra et al. 2020), and this trend is likely responsible in large part for the negative relationship we found between ice free days and Arctic fox harvest.
In contrast, red fox abundance appeared unaffected by changes to sea ice duration on Hudson Bay. Previous studies have demonstrated marine resources have been used by red foxes. Killengreen et al. (2011) showed that marine resources were important alternative food sources for coastal red foxes that lived within 20–25 km of the coast, but foxes that lived further from the coast were less reliant on marine resources. In our study area, Warret Rodrigues (2022) detected marine resources in the red fox diet, but other species (including rodents, snowshoe hares, and migratory birds) were relied on much more. Further, red foxes use the marine habitat much less than Arctic foxes (Warret Rodrigues 2022), which may explain the difference in response of fox harvest records between the two species to changes in the ice-free period (i.e., red foxes have an overall reduced reliance on marine subsidies for late-winter food).
Arctic fox harvest was not affected by the length of time snow persisted in late spring, suggesting goose reproductive success had minimal influence on the observed Arctic fox decline. The snow-free date was included as a climate variable as persistent spring snow was shown to influence goose nesting success (Reed et al. 2004; Madson et al. 2007). However, MacDonald et al. (2017) demonstrated that juvenile goose density, although an important alternative food source for Arctic foxes, was not related to their reproductive success, suggesting the seasonal abundance of geese may not be sufficient to minimize declines in Arctic fox abundance. Similarly, in Svalbard, Eide et al. (2012) also did not measure a numerical response of Arctic foxes’ reproductive success to goose abundance. Goose abundance is hypothesized to be less impactful on Arctic fox reproductive success in these regions because geese migrate annually and are therefore not available during late winter, a critical period for Arctic fox reproduction (Roth 2002; Eide et al. 2012; McDonald et al. 2017).
Although our results are based on correlations and indices, these data are the only available sources within the Churchill region to evaluate long-term population changes of these important Arctic predators. Further comparisons of direct relationships may strengthen the support of our results. However, the long-term trends in our indices parallel those of shorter-term research in our study area, and thus have further support for their use here. Moizan et al. (2022) demonstrated that Arctic fox den occupancy decreased while red fox den occupancy remained stable in late winter between 2011–2021 in the Churchill region. These trends parallel our results using local harvest data: a decline in Arctic foxes continuing from the mid-1990s, while red fox harvest appeared stable during the same time period.
Arctic foxes, similar to other tundra-adapted species, may experience continued stress from changing climate and cryosphere as marine habitat is less reliable with shortened sea ice duration (Gagnon and Gough 2005) and the continued northward encroachment of shrubs and forest reducing tundra habitat (Sturm et al. 2005). As our study area is coastal and along the southern edge of the Arctic fox distribution, these rapid environmental changes appear to be having a detrimental effect on Arctic foxes. Continued alteration to Arctic ecosystems may result in the future exclusion of Arctic foxes within regions of their historical circumpolar distribution (Fuglei and Anker Ims 2008). Conversely, although red fox harvest has remained stable in our study area so far, as the climate continues to change, the area may be able to support higher red fox densities. Arctic and red foxes appear able to coexist in areas of North America (Lai et al. 2022; Moizan et al. 2022), but future climatic trends may lead to greater resource competition and disrupt the balance between the two species. Through greater exploration of the mechanisms that drive population trends, we may better understand the effects of climate change on northern species and predict how these changes may continue to affect wildlife going forward.