Non-Native Does Not Equal Invasive



      Based on the nearly hysterical, national angst generated by fish escaping from broken cages on an Atlantic salmon farm in the San Juan Islands, an impartial observer might have concluded that there had been a jail break and dangerous criminals were “on the loose”.  In the minds of some environmental activists, Atlantic salmon escaping into the natural habitat of Pacific salmon is the ecological-environmental equivalent of a jail break by hardened criminals.  Many of these activists believe that any species that did not evolve naturally in a given ecosystem simply does not belong there.  Further, they believe that any fish escaping from a hatchery or farm are certainly invasive, will reproduce in vast numbers, and establish new colonies of the invaders; invaders that will destroy the “balance of nature”.  Really?  Is an escape of farm-reared fish always a catastrophe; important enough to draw media attention coast-to-coast?

     The only absolutely certain catastrophe when thousands of Atlantic salmon escaped from broken cages in waters near the San Juan Islands was the effect on the owner’s finances.  Estimates of the numbers of escaped fish varied from 160,000 to nearly 300,000.  The lower number is probably more accurate, inasmuch as, the owners recovered more than 140,000 fish that were still in the cages.  Never-the-less, the loss is devastating to the owners of the farm.  Whether or not the escaped fish will have serious negative effects on the Salish Sea-Puget Sound ecosystems, and potentially other adjacent systems, remains to be determined.  However, based on past experiences with other, smaller escapes in similar areas, it is highly unlikely that there will be serious, long-term damage.  What are the possibilities?  More importantly, what are the probabilities?

     Long before the term “alien invasive species” became popular with environmental activists, ecologists and other scientists used the term “colonizing species” when referring to species who found their way into new ecosystems and established self-sustaining populations in locations where they were not found previously.  Much of the intense, emotional arguments about whether or not a species “belongs” in a specific location depend on each individual’s beliefs about the “balance of nature” and their understanding, or lack thereof, of chance as a factor in ecosystem evolution.  Whether or not each person considers an ecosystem to be a functional system or a structural system can be central to the discussion.  Unfortunately, science has yet to provide a definitive answer to that question.  Is each natural ecosystem a perfect balance that will spiral out of control if anything is added, or subtracted?  Many believe this prediction, but confirming evidence is lacking.

     I consider ecosystems to be functional systems in which the current species structure was determined by the species and conditions that happened to be present thousands of years and events since then.  For example, the conditions and species present in northwest North America at the end of the last Ice Age favored salmonid fishes and they remained dominant over the next 10,000 to 15,000 years.  The idea that a different set of species would be present today if other species had been present initially is regarded as ecological heresy by many present-day environmental activists.  These activists contend that the ecosystems that existed prior to European, “invasive” humans gaining dominance were perfect in structure and function.  I disagree with ecological creationism, and argue that changes do not necessarily degrade ecosystem functions and should not be predicted as always producing catastrophes.

     Taking ecosystem flexibility and resilience a step further, I suggest that the continued existence of a functional system is more important than maintaining a specific species composition.  The belief that species structure is all important was certainly dominant in the media coverage of the San Juan cage break.  Pundits and would-be “experts” agreed…invasive aliens had escaped and the native fauna was in serious jeopardy.

     The role of Atlantic salmon in marine/aquatic ecosystems is very similar to that of the four major species of Pacific salmon in the Pacific Northwest.  IF, the escaped Atlantic salmon survive in open waters, avoid capture, avoid being eaten, find a river/stream in which to spawn, successfully migrate to suitable spawning grounds, hatch and survive to migrate back to salt waters, and mature to finally return to their natal streams; they would be in head-on competition with Pacific salmon inhabiting the same waters.  Inasmuch as the Atlantic salmon were reared in the same waters as native Pacific salmon, they certainly do not carry any pathogens and parasites that are new to these waters.  The probability of accomplishing all the life cycle actions successfully is extremely small.  Previous escapes of Atlantic salmon in western waters of Canada and the United States have not led to self-sustaining populations of Atlantic salmon, nor diminished populations of Pacific salmon. 

     Although it seems that the extensive publicity given to this fish escape is largely environmental hyperbole, questions remain as to whether or not the broken cages could have been prevented.  The farm owners acknowledge the cages and anchoring systems were in somewhat degraded condition and not capable of withstanding abnormally high currents.  The cost of repairing them would have been considerably greater than their value.  Plans to replace the entire system had been developed, but not initiated.  Whether or not the owners should have acted more quickly is not an appropriate aspect of the present discussion.

     The basic question of whether or not any species of fish should be reared in waters outside its native range is a valid question that should be addressed before beginning a new aquaculture operation.  In the case of Atlantic salmon in British Columbia and Washington State waters, marine scientists with extensive research experience with this question have concluded that there are very small, if any, risks.  Atlantic salmon and Pacific salmon do not interbreed; Atlantic salmon carried no disease agents other than those already established in the Salish Sea; and it is highly unlikely that the Atlantic salmon will reproduce successfully.  The ecosystems will continue to function normally.