Miramichi spruce budworm spraying

Miramichi spruce budworm spraying carried a forest-protection campaign into the Northwest Miramichi watershed and turned a seasonal effort against a native insect into a disaster for stream life and salmon. The consequences were immediate in the treated streams and more extensive where spraying was repeated: the campaign’s chemical method damaged not only fish but the aquatic food web on which their survival depended.

The campaign and its objective

The spraying was part of a Canadian government program begun the previous year to protect forests from spruce budworm, a native insect that attacks several kinds of evergreen. In eastern Canada, budworm populations surged at intervals of roughly 35 years; an upswing in the early 1950s prompted the campaign. DDT use began on a limited scale, then expanded abruptly in 1953 from thousands of forest acres to millions. The principal economic concern was the balsam, a mainstay of the pulp and paper industry.

The scale and purpose of the operation reflected a wider postwar reliance on persistent pesticides in agricultural and other control programs. In the Northwest Miramichi, the forest was treated as the target to be saved, while the watershed through which the treatment would pass was also a living habitat. That distinction mattered: the same application intended to protect evergreens could reach the streams and destroy organisms that had no part in the budworm outbreak.

The June 1954 application and its immediate effects

In June 1954, aircraft crossed the forests of the Northwest Miramichi in a crisscross pattern, leaving white clouds of settling mist. The mixture delivered half a pound of DDT per acre in an oil solution. The pilots made no effort to avoid the streams or turn off the spray nozzles while flying over them. Even if they had done so, the spray could drift a considerable distance in a slight movement of air, making the stream’s exposure difficult to prevent through flight precautions alone.

The damage became unmistakable soon after the operation ended. Dead and dying fish, including young salmon, appeared along the banks within two days. Brook trout were among the dead; birds were dying along roads and in the woods. The poisoning also removed the small stream organisms that formed the fish’s food: caddisfly larvae, stonefly nymphs clinging to rocks in the current, and blackfly larvae along stones beneath riffles and cascades. The stream was not simply losing individual fish; its food supply and the surrounding web of life were being stilled as well.

By August, none of the young salmon that had emerged from gravel beds that spring remained. An entire year’s spawning had come to nothing. Older young salmon fared only somewhat better. The losses thus reached beyond the fish visible on the banks: the spraying erased a new generation before it could mature, while the death of stream insects threatened the food base for those fish that survived.

Repeated spraying and a changing watershed

A detailed record of conditions before spraying made it possible to assess the damage with unusual precision. The survey showed that the effects extended beyond the first visible fish kill. Repeated applications had substantially altered stream environments, killing the aquatic insects on which salmon and trout fed. The evidence linked the chemical treatment not only to immediate mortality but also to a changed habitat in which the fish’s ordinary sources of food had been removed.

The budworm did not diminish as expected. Spraying was repeated in different parts of New Brunswick and Quebec from 1955 to 1957, with some places treated as many as three times. By 1957, nearly 15 million acres had been sprayed. Repetition made restoration precarious: any attempt to return aquatic insects to barren reaches would be undone by another application. The control campaign therefore posed a dilemma of its own making—rebuilding the stream’s food supply could not succeed while the treatment that had destroyed it continued.

Salmon returns and the cost of repetition

The difference between one year of spraying and repeated treatment appeared in the salmon populations. The Northwest Miramichi remained in relatively good condition because it had been sprayed in only one year. Many young salmon there grew rapidly in the stream, went to sea early, and returned in 1959 in large runs of grilse. Their return showed that a damaged fish population could still produce a recovery when the stream was spared repeated applications.

Other streams in the watershed told a harsher story. In sprayed streams, young salmon of every size were scarce, and biologists described the youngest as practically wiped out. The main Southwest Miramichi, sprayed in 1956 and 1957, produced its lowest catch in a decade in 1959. Fishers reported an extreme scarcity of grilse; at the estuary sampling trap, the count was only one quarter of the previous year’s. Across the whole Miramichi watershed, production in 1959 was about 600,000 smolt—young salmon descending to the sea—and less than one third of the runs recorded during the preceding three years.

The campaign’s significance lies in the contrast between its intended protection of forest resources and its consequences for connected waters. A treatment applied over millions of acres did not remain confined to the insect it was meant to control. In the Miramichi, the path from aircraft to stream insects, from stream insects to young salmon, and from repeated spraying to depleted runs made the ecological cost legible: safeguarding balsam forests with DDT could undermine the conditions needed for salmon fisheries in New Brunswick to persist.