Maine DEP found no permit violations in Cooke salmon die-off

The Maine Department of Environmental Protection (DEP) has officially closed its investigation into Cooke Aquaculture’s salmon mortality report on Aug. 27.

The decision, which was announced on Sept. 27, reported that the DEP did not find permit violations or violations of the Clean Water Act.

More than 100,000 salmon mortalities were reported to the DEP in August from Cooke Aquaculture’s Black Island (28,212) and Black Island South (87,607) net pen sites.

The DEP inspected both sites on Aug. 31 noting, “Visibility in the water was limited to about 5 to 8 feet and the net pens had been cleaned within the last week. DEP staff did not find evidence of excessive net pen fouling.”

The DEP concluded that the event was an issue of low oxygen in the pens, which is not a compliance issue.

Though the company is not required by the DEP to report its mortalities, Cooke provided the department with daily dissolved oxygen (DO) readings from July 1 to Aug. 31, within the 30-metre mixing zone outside the net pens of both sites.

The permit limit for DO is 6.0 mg per litre. Cooke’s lowest measure of DO was on Aug. 10 with a reading of 6.5 mg per litre at both sites. On Aug. 13, it reported 6.9 mg per litre and on Aug. 16, it reported an increase of 9.0 and 8.4 mg per litre.

“Cooke is not required by the DEP permit to track or report DO within the net pen sites. However, they were able to provide data for August 1st to 25th for a single pen at Black Island South. The lowest reported DO levels in the single pen on August 15 and 16 were 4.9 mg/L,” the DEP report continued.

“Additionally, all pen densities reported to the Department during June, July, and August were within permit limits.”