Cooke didn’t break the rules at die-off sites, says Maine environment watchdog

Staff from the state’s Department of Environmental Protection (DEP) inspected the Black Island and Black Island South net pen sites on August 31, after Cooke reported mortalities of 28,212 fish at Black Island and 87,607 at Black Island South. The company blames a precipitous fall in dissolved oxygen (DO) levels for the die-off.

“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 said in a press release.

Dissolved oxygen

The DEP said Cooke provided daily (DO) readings collected in the 30-metre 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, and all were above the minimum limit of 6.0 milligrams per litre (mg/L).

On August 16, when the mortalities were reportedly discovered, Cooke measured mixing zone DO at both sites of 8.1mg/L. Although Cooke is not required to provide DO levels for inside the pens, it was able to provide data for August 1 to 25 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.

Pen densities

All pen densities reported to the DEP 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,” stated the DEP.

“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 Aquaculture’s cooperation in this matter, and having found no infractions, has therefore closed the investigation into this matter.”