I agree that overpopulation is a subjective determination, but in some cases, the increase in goose populations has been shown to have negative impacts on species whose populations have decreased in recent years.
Linked here is a study that found that the increase in light goose populations (Chen caerulescens, C. rossii) has had a negative impact on Arctic-nesting shorebird populations. See the article for a more nuanced discussion of the proposed causal relationships, but the reduction of ground cover and attraction of predators to areas surrounding goose colonies are the primary ones. I believe this is one of several articles looking at this same phenomenon, as I previously read one looking more specifically at the issue of predator attraction to nesting sites.
Ecological relationships are often complex, and I am sure that increases in goose populations are just one contributing factor in the overall decline of Arctic-nesting shorebirds (cf. climate change). However, I think that when human actions lead to a dramatic increase in native species’ populations, “negative” impacts on the broader ecosystem can result, even if they are more latent than those brought on by introduced species. Whether ecological changes are “good” or “bad” is an artificial determination based on the effects we are able to perceive and how we as humans are impacted. Based on my understanding, however, ecosystems are “healthier” (more resilient, etc.) when they are more balanced, which is why most biodiversity indices include metrics of species richness, evenness, and dominance instead of simple abundance. While it is not a statement of fact to say that these geese are overabundant in the Arctic, the article implies that without effective management, the increasing trend of goose populations will fuel the decreasing trend in shorebird populations and will further the dominance of geese in the ecosystem.
As far as it relates to the discussion of waterfowl hunting, the article brings up some points (not necessarily answers) that I found relevant:
Recent estimates of Central and Eastern Arctic light goose breeding colonies indicate that breeding populations increased by more than 400% between 1973 and 2008
- Based on this figure, it is clear that the light goose population in this part of the world has grown dramatically in recent history. Based on this statistic alone, it is difficult to determine the extent to which this applies to other waterfowl species/populations in North America and how these numbers compare to previous eras. However, I think it is safe to say that, at the very least, the growth in goose populations has outpaced that of most other bird species in the same time frame.
- The article mentions that due to the “overabundance” of white geese, bag limits were increased and a spring season was added, but this had little effect on the overall population. To me, the lack of population response to more liberal hunting regulations is indicative of a few things. First, current hunting practices and harvest numbers for these species in North America (I don’t want to overgeneralize) are likely sustainable, and hunting pressure is not a limiting factor on overall population size. Second, in this particular case, land-use changes have an impact on the goose population that outsizes the impact of hunting. This suggests that hunting is not always an effective method of population management, per se. I would say that for light geese in these areas, hunting does not remotely threaten the light goose population but has only a negligible positive impact on nesting shorebird populations.
- The article points to wintering site food subsidies from agriculture as the primary cause of the population increase. These claims are made with linked citations, though I have not personally read through them yet. Even if these claims are true (feel free to critique this claim; I myself am skeptical that goose populations only began to benefit from winter subsidies in the 1970s), I don’t think that this devalues the importance of wetland management practices and game refuges. However, I wonder whether the population increase from the availability of winter food from agriculture fields overblows the impacts of the perceived conservation bias toward waterfowl as game species. As a note, I think this bias certainly exists, but might not be proportionally reflected by the increase in wetland birds relative to other groups since 1970.
Finally, on a somewhat separate note, I think that there are valid arguments against hunting on a personal basis, and I myself am not a hunter. However, I think the argument against hunting as a practice on the grounds of non-interventionism in the natural world overlooks the fact that we are passively altering ecosystems throughout our everyday life. Effective management requires intervening in the natural world, frequently to correct for anthropogenic ecological problems. Hunting is probably not always the best or most effective way to deal with species whose populations have grown large enough to negatively impact the populations of rare or declining species. However, in cases where scientific findings show that population control is in the best interest of maintaining a diverse environment, I think that hunting to manage the overpopulation of a native species is no different than hunting to eradicate destructive invasive species.
P.S. This post probably seems long and ranty but I just found the discussion of the term “overpopulation” to be interesting, and it reminded me of this article