While the old adage insists, “ … in Spring, a young man’s thoughts turn to Love,” the Global Warming variant may change that antiquated lyric to, “ …in Summer, a young trout’s thoughts turn to Hybridization.”
A recent study of wild trout intermingled with hatchery fish, based on lakes and hydroelectric dams in Norway – suggests that wild fish and hatchery trout rarely inter-breed. It’s thought the high mortality rate of pen-raised, pellet-fed, fish – coupled with the inability of hatchery fish to make use of spawning creeks – means the two strains rarely occupy the same space at the same time, and interbreeding is negligible as a result.
Released trout accounted for nearly 30% of the sexually mature fish in the reservoirs and it was assumed that the prolonged use of non-indigenous and previously released fish in hatcheries posed a risk to the genetic integrity of wild fish. However, it appears that wild fish maintain their natural, genetic structure, principally due to the high mortality of indigenous and released hybrids and to the fact that released fish do not migrate when spawning.
My tortured blend of humor and lay science suggests this phenomenon could be due to their “fast food” diet. How inhaling pellets shat from a cannon leaves hatchery trout couch-prone and listless – versus chasing a shapely wild female up the riffle and into the Gravels of Lust.
But Global Warming and its corresponding changes in water temperatures apparently changes this delicate relationship. With elevated temperatures, “Couch Potato” fish suddenly mount everything, including beer cans and sunken grocery carts and the gene pool resulting is a crazy mash up of hybridized fish.
Despite widespread release of millions of rainbow trout over the past century within the Flathead River system5, a large relatively pristine watershed in western North America, historical samples revealed that hybridization was prevalent only in one (source) population. During a subsequent 30-year period of accelerated warming, hybridization spread rapidly and was strongly linked to interactions between climatic drivers—precipitation and temperature—and distance to the source population. Specifically, decreases in spring precipitation and increases in summer stream temperature probably promoted upstream expansion of hybridization throughout the system. This study shows that rapid climate warming can exacerbate interactions between native and non-native species through invasive hybridization, which could spell genomic extinction for many species.
As I’m one of those horribly insensitive louts that claim to have tread lightly on his environment, (which we now realize as “having our way with the Old Gal,”) and after leaving what few scraps of the watershed that remains to the New Breed of fly fishermen, can only cackle at your indignity when you see some obese Grass Carp mounting that silvery, noble Rainbow (as it lies panting in the hot water), and how righteous you’ll sound when you insist we kill everything with Rotenone, so the gene pool is kept sacrosanct …
In addition to leaving you whatever we couldn’t eat, along with the discarded plastic wrapper of everything we did consume, we’ve imparted to you our antiquated snooty attitude towards salmonids. No doubt you’ll cling to this last bit of purism despite rising hemispheric temperatures, and with the Trout-centric enviro-lobby’s urging – will launch a Genetic Cleansing, or watery Jihad … whichever Politically Correct term you’ll devise for eradicating all the warm water fish that don’t mind hybridizing with lawnmowers or Salmo Salar …