DEP finds no permit violations associated with recent mortalities at Cooke Aquaculture pens

September 27, 2021

Cooke Aquaculture discovered high mortalities of fish on August 16, 2021 at Black Island and Black Island South net pen sites. Although Cooke is not required to report mortalities to the Maine Department of Environmental Protection (DEP), on Friday August 27, 2021, they notified DEP Compliance staff that Cooke had removed and disposed of carcasses and cleaned the net pens at each site. Cooke reported to DEP the mortalities in August for Black Island were 28,212 and Black Island South were 87,607.
DEP staff inspected the Black Island and Black Island South net pen sites on August 31, 2021. 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.

Cooke Aquaculture provided to DEP daily dissolved oxygen (DO) readings collected in the 30-meter mixing zone outside the net pens at Black Island and Black Island South net pen sites for the period of July 1, 2021 - August 31, 2021. The permit limit for DO within the mixing zone is 6.0 mg/L. Cooke's lowest measure of DO in the mixing zone for the period submitted was on August 10, with a reading of 6.5 mg/L at both sites. On August 13, 2021 they reported DO readings of 6.9 mg/L and the DO increased over the weekend to 9.0 and 8.4 mg/L. On August 16, when the mortalities were reportedly discovered, Cooke measured mixing zone DO at both sites of 8.1mg/L. 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.

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

On September 23, 2021, DEP Enforcement and Compliance staff met to review the permit requirements and the data submitted by Cooke to the Department. As a result of that examination, DEP did not identify any permit violations or violations of the Clean Water Act in relation to the reported fish kill. The Department acknowledges Cooke Aquacultures cooperation in this matter, and having found no infractions, has therefore closed the investigation into this matter.

For additional information, contact: David R. Madore, Deputy Commissioner