The Great Lakes are conceded to the round goby. The argument now is for spending upstream

Two researchers at the University of Toronto Scarborough have published a paper in the Journal of Great Lakes Research arguing that round goby management should be redirected away from the Great Lakes and toward the rivers, streams and isolated lakes the fish is now entering ^[2]. Their premise is blun: the lakes are a lost position, and the only places where effort still buys an outcome are upstream ^[3].

The arithmetic behind that concession is not subtle. Round goby arrived in the Great Lakes in the early 1990s in ships' ballast water, having come from its native range in the Black and Caspian seas, and it is now established in all five lakes ^[5]. Scientists put the population in the billions, which makes eradication unrealistic ^[1]. Professor Nick Mandrak says the fish are established throughout the lakes and will never be fully removed, and that the open question is the connected and isolated waters they are moving into now ^[4]. A fish roughly the length of a smartphone ^[7] competes with native species for food and habitat, eats their eggs and young, and rearranges food webs ^[6].

The operationally useful number in the paper is a rate. Using more than two decades of river monitoring data collected by conservation agencies in the Greater Toronto Area, Marques and Mandrak found the fish advancing between a fraction of a kilometre and about two kilometres per year ^[10]. Postdoctoral researcher Piatã Marques dates the upstream phase of the invasion to roughly the last 15 years ^[8]. Taken together, those figures put the outer bound on how far any given front has travelled at around 30 kilometres ^[18]. That is a manageable length of stream, and it is why the authors think trapping, electrofishing, physical barriers and rapid-response programs could suppress local populations and in some cases remove them outright ^[11]. Rivers are smaller and more accessible than a lake, which is the whole point ^[11].

What is at stake inland is not interchangeable with what was lost in the lakes. Marques notes that these freshwater systems hold some of Ontario's richest biodiversity, including endangered species ^[8]. One of them is the redside dace, an endangered fish in streams across the GTA that researchers expect round goby to outcompete for food ^[9].

The paper is a reallocation argument, and it is worth being precise about what it does and does not contain: the source material does not put a dollar figure on current round goby spending or on what an inland program would cost ^[19]. What it offers instead is the shape of the work. Marques says the aim is practical guidance for resource managers on which methods work and how much effort is needed to cut populations ^[14]. The team is testing environmental DNA, which detects fish from genetic material in water samples, to find invasions where capture is difficult ^[12]. It is also examining whether urban development is helping the invasion, since road salt and other pollutants raise dissolved ions in streams and may suit a fish native to brackish water ^[15].

Watch whether conservation authorities holding those GTA monitoring datasets fund removal trials rather than more surveys, and whether the eDNA work sets a detection threshold early enough to act on ^[12][14].