Choice of baseline affects historical population trends in hunted mammals of North America

Abstract

Establishing historical baselines of species' populations is important for contextualising present-day population trends, identifying significant anthropogenic threats, and preventing a cultural phenomenon known as 'shifting baseline syndrome'. However, our knowledge of historical baselines is limited by a lack of direct observation data on species abundance pre-1970. We present historical data of species-specific fur harvests from the Canadian government and Hudson's Bay Company as a proxy for estimating species abundance over multiple centuries. Using stochastic stock reduction analysis originally developed for marine species, we model historical population trends for eight mammals, and assess population trends based on two different baseline years: 1850 and 1970. Results show that population declines are significantly greater when using an 1850 baseline, as opposed to a 1970 baseline, and for four species, the population trend shifted from a population increase to a decrease. Overall, the median population change of the eight species changed from a 15% decline for 1850, to a 4% increase for 1970. This study shows the utility of harvest data for deriving population baselines for hunted terrestrial mammals which can be used in addition to other historical data such as local ecological knowledge.Results highlight the need for developing historically relevant population baselines in order to track abundances over time in threatened species and common species alike, to better inform species conservation programs, wildlife management plans and biodiversity indicators.

Historical reconstruction of the population dynamics of southern right whales in the southwestern Atlantic Ocean

“…, when the model projections start after the stock has been subject to unknown previous catches) are imprecise 96 . Recently, Collins et al 101 demonstrated that for eight species of Canadian mammals the use of 1850 rather 1970 as the baseline year resulted in a shift of four species from an increase to a decrease in population since 1970. For the SRW, in 2001, the IWC performed a global assessment to obtain an estimate of the initial population size 19 setting the pre-exploitation baseline in 1770.…”

Past, present, and future of the Living Planet Index

“…In Europe, for example, a significant amount of habitat destruction and overexploitation of some species had occurred prior to the 1970s and therefore the LPI baseline is set at a significantly depleted reference point 37 . The year chosen as a baseline can affect the interpretation of the state of biodiversity in a particular region 149 . Without taking this into consideration, it is possible to underestimate the gravity of the decline in biodiversity or overestimate a recovery within any given landscape.…”

A global indicator of utilised wildlife populations: regional trends and the impact of management

“…However, comparisons between regions should be interpreted with care because the baseline of 1970 set for this analysis sets relatively different starting points for the state of species abundance for each region. The baseline year chosen can be important for assessing long-term trends (Collins, Böhm et al 2020), particularly in regions where high human impact has been prevalent over centuries. In the case of North America and Western Europe, the baseline of 1970 hides historical declines in species abundance which occurred as land use was transformed after the Industrial Revolution (Ellis, Klein Goldewijk et al 2010); post-1970 trends may therefore show fewer declines as populations stabilise but at lower numbers.…”