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Maybe I’m getting old, but it seems that lately for every piece of good news I get, there is an equal and opposite dose of bad news that cancels it out. Just as we were reveling in the relative abundance of big fish that came back to our rivers in 2003, a couple of dark clouds crossed our sun.
One bit of bad news was released by Lee Sochasky, of the St. Croix International Waterway Commission. Lee and her collaborators have been trying to restore Atlantic salmon to this historic watershed, which forms part of the border between the USA and Canada. For a number of years they have been stocking the river, and collecting returning adults as brood fish, to try and recreate a “St. Croix strain,” and a self-sustaining run.
This year, massive algae blooms occurred along the marine migration route of the St. Croix fish in parts of the Bay of Fundy. As they passed through the algae, some apparently had their gills damaged by oxygen supersaturation. Supersaturation occurs when the phenomenal densities of algae (> 600,000 – 700,000 Alexandrium cells per liter in this case) release phenomenal quantities of oxygen as part of the photosynthesis process. All plants, including algae, use photosynthesis to capture energy from the sun, which they use to run their metabolism.
While oxygen released by plants makes life possible on our planet, a superabundance of oxygen can have a corrosive effect, destroying sensitive tissues like gills. Three big females, about half of the brood fish Lee’s river is struggling to produce, died soon after their return to fresh water, and post-mortems showed that their gills had been destroyed, most probably by oxy- gen supersaturation. Fish heading to other rivers in the region, including populations listed as endangered in Maine and the Bay of Fundy, might also have passed through the bloom and been affected.
The second bit of bad news began surfacing in late October. Up on the Restigouche River, dead salmon enveloped in fungus were found. The fungus, probably of the genus Saprolegnia, is ubiquitous in nature. Generally speaking, it is a “secondary” problem. It attacks when a fish is already weakened by stress, or another infection. The fungus is readily evident as a “cotton- wool” coat on the body. The larger the body area affected, the more dangerous it is to the fish’s life.
It would seem that the 2003 fungus problem was not confined to Atlantic salmon, or the Restigouche system. Sea run brook trout within the Restigouche and Nouvelle watersheds were infected, as were some of the gaspereau (a.k.a. alewives or river herring) from the St. John and Magaguadavic Rivers in southern New Brunswick. Additional reports of infected Atlantic salmon have come from the Bonaventure and Nouvelle Rivers.
The worst hit rivers seemed to be the Patapedia and Nouvelle, where up to 75-80% of the salmon observed in certain sections had fungus. Fish with 90% of the body covered with “cotton-wool” coats were seen on the Patapedia.
On the bright side, divers counting spawners in the Matapedia observed only 2% of the fish with fungus. Therefore, infections occurred patchily, even in some of the most heavily hit watersheds like the Restigouche. In regions where the fish were heavily infected, they seemed to be spawning normally, and successfully. The eggs should not be affected by their parent’s plight. This seems to be a disease that the salmon have historically lived with and will have evolved some sort of natural resistance to it. Hence, we are not worried about the kind of massacre that occurs when a foreign pathogen, to which the species has no natural immunity, finds its way to a river.
What triggered the problem this year remains a mystery. One clue, at least for the Restigouche River, may lie in the pattern of water temperatures that occurred during the summer. During June, low flows were combined with a rapid increase in water temperature. Indeed, this year’s maximum temperatures occurred in June, which is very early. These environmental conditions could have stressed the fish, and tilted the balance in favor of the infection. No other diseases have been identified so far in fish that had fungus.
On the Restigouche River, Jay Casey and the Listuguij First Nation hope to implement a fungus screening program in 2004. This will provide an early warning system to let us know if 2004 will also be a fungus year.
Dr. Frederick Whoriskey, Jr. was the Atlantic Salmon Federation’s Vice-President, Research and Environment at the time this article was written.