On the lack of scientific evidence for the Ontario cormorant cull and other cormorant management actions: a response to Dorr et al. (2022)

Abstract

In their recent essay in Avian Conservation and Ecology, Dorr et al. (2022) were compelled to clear up apparent misunderstandings they felt were perpetrated by the separate editorials of Hobson (2021) and Cooke (2021) dealing specifically with the Ontario government’s decision to allow a province-wide public cull of Double-crested Cormorants (Nannopterum auritum) in response to perceived conflicts with fisheries, conservation objectives, and human recreation. They claim to have addressed “misconceptions about cormorant and fishery interactions, summarize the current state of knowledge on the issue, and discuss a different approach based on collective experience in the United States.” They further suggest that both editorials imply that “cormorants rarely, if ever, are an issue for any reason, and that management is rarely warranted.” While we welcome the debate, it is clear to us (now including Ludwig, the senior author of this report) that such premises are simply not true; a more careful reading of our papers would have revealed a more dispassionate and scientific approach to the question and that we had very clearly focused almost entirely on the Great Lakes region vs. Double-crested Cormorants everywhere. Rather, the Dorr et al. (2022) response reflects the authors’ long careers in cormorant “management” and an apology for the record of the US government (and various state agencies) with respect to cormorant fisheries concerns. The apparent need by Dorr et al. (2022) to defend cormorant management in light of the irrational Canadian province-wide hunt /cull by an ill-informed public is revealing. Readers will know that we clearly acknowledged that certain situations justify cormorant management and should be conducted by professionals (as in fact quoted by Dorr et al. [2022] from Hobson’s editorial). Moreover, we never labeled cormorant management universally as “persecution.” Indeed, Hobson (2021) devoted considerable summary background on the myriad of environmental issues involved in the health of the Great Lakes that obscures any direct linkage between cormorants and fisheries in this region. The obvious take-home message from the Hobson (2021) and Cooke (2021) essays was how complex these natural systems are and how such complexity has hitherto been ignored by public advocates for cormorant control, governments, and several fisheries biologists. The Dorr et al. (2022) essay raises important issues but is afflicted by the same tunnel vision that has tainted many studies of fisheries and cormorants published by fisheries and wildlife biologists for decades. This included ignoring examples of any beneficial interactions of cormorants with game species, cherry-picking data sets to include only those data that suggest cormorants harm fisheries, creating models replete with unjustified or known false assumptions, the ignoring or outright misuse of published data, and a common tendency to assume the only important change in ecosystems where conflicts exist are changes in fish stocks (usually game fish) and cormorant numbers. The most egregious oversights are the implicit assumptions that the explosions of invasive species and their interactions with fisheries did not influence the observed declines of economically important fish species where cormorants were present (Bunnell et al. 2017). Early research on the Great Lakes indicated cormorants ate very few game fish (Eck and Brown 1987, Ludwig et al. 1989, Madenjian et al. 1995, MDNR Fisheries 17), but this research has been ignored by proponents of controls.