MOUNTAIN LIFE - Blue Mountains | Fall 2017

FALL 2017 ML BLUE 53 APOCALYPSE, MAYBE Back in 2013 , I was having a beer with my friend Nick Mandrak, an Associate Professor in Biological Sciences at the University of Toronto. Mandrak’s beat is Species at Risk, and we were discussing one of the main forces putting native fish at risk in the Great Lakes. “Invasive species rank second only to habitat loss as a major driver of species extirpations and extinctions,” he told me. “But if you asked a member of the public what they thought the biggest threats to Great Lakes biodiversity were, they might say pollution or habitat loss.” That such a pervasive, bi-national issue remained so generally invisible was perhaps not surprising. As Mandrak reminded me, neither a century- long battle with sea lamprey, high-profile problems like zebra mussels, nor even the occasional tabloid-worthy piranha fished from Lake Ontario (true—I saw it) had sufficiently impacted public consciousness to add “Do Not Introduce Nonnative Species into Native Waters” to the ledger of things you taught children—and fishermen. In fact, if vast schools of tuna-sized silver carp didn’t have a bizarre predilection for leaping clear of the water at the sound of a boat engine—and into headlines (e.g., bit.ly/2gqGyhM )— current public knowledge concerning such threats might be even lower. Silver carp ( Hypophthalmichthys molitrix ) is one of four species referenced by invasion scientists under the rubric of “Asian carp(s).” The remaining trio—a taxonomic mouthful—comprise bighead carp ( Hypophthalmichthys nobilis ), grass carp ( Ctenopharyngodon idella ), and black carp ( Mylopharyngodon piceus ). The more familiar (and pronounceable) common carp ( Cyprinus carpio )—also native to Asia and introduced widely in Europe and North America—isn’t included; not only because it is now naturalized on this continent, but because the others form a de facto cultural unit. Known as the “Four Domesticated Fish” in China, silver, bighead, grass and black carp are that country’s most important freshwater collective in use for food and traditional medicine. Though all attain sizes in excess of 40kg and a metre in length, each is physically and ecologically distinct. Feeding on, respectively, phytoplankton, zooplankton, aquatic vegetation, and molluscs, these fish were originally imported to the southern U.S. beginning in the 1960s for control of weeds, algae or parasites in scenarios ranging from reservoirs to waste-treatment to aquaculture. Lodged in ponds along the Mississippi River, each was introduced into the wild on numerous occasions, particularly during the repeated heavy flooding of the early 1990s. Silver, bighead and grass carp made their way up the Mississippi and tributaries as far as Minnesota; black carp, with a predilection for deeper water, stuck to the main channels of the Central Mississippi. The spread of silver and bighead carp was slow to start, but once dispersed sufficiently northward, an ecological inflection point was reached; whatever this constituted, it radically increased spawning success because around the millennium, mid-continent populations of silver and bighead carp exploded. On a few notorious stretches of the Illinois River, that meant 60 per cent of all individuals and over 90 per cent of fish biomass. Straining up to 20 per cent of their body weight from the water daily, these filter-feeding machines weren’t just messing up an ecosystem, they were becoming it—their abundant waste contributing to algal blooms and excessive turbidity. Biologists immediately fretted over the possibility that this piscine juggernaut would enter the Great Lakes, whose heavily compromised ecosystems were already vulnerable. But wait, you might say, the Mississippi drains into the Gulf of Mexico, not the Great Lakes—so why the concern? Well, there wouldn’t be… were it not for the Chicago Area Waterway System (CAWS). Not only does CAWS control the flow of water around metropolitan Chicago, but its ageing locks offer a critical direct ASIAN CARP DOORSTEPPING THE GREAT LAKES words :: Leslie Anthony BIO PHILIAC