By Dr. Rob Moir
Last Saturday, September 24, 2021, thousands of menhaden fish, locally known as pogie, were found dead in the Mystic River, resting up against the Amelia Earhart Dam between Somerville’s Draw Seven State Park next to Assembly Row and Costco in Everett.
On the surface, literally floating belly-up, it looked like a repeat of the menhaden fish kill in the Mystic that happened in July of2018. Then striped bass chased menhaden out of Boston Harbor and up the Mystic River. Near the dam, fish swam into an ocean dead zone caused by a harmful algal bloom. All fish and suffocated quickly. Standing on a very rank Everett Shore, I could see larger striped bass floating in a raft of ten-to-twelve-inch menhaden carcasses.
Harmful algal blooms in New England are summer events when the length of daylight is longest and weather warmest. In these conditions, algae grow and die when there are sufficient nutrients. Without nutrients, mostly nitrogen, algae will not grow. Clear tropical waters lacking in nutrients despite high temperatures will not suffer algae blooms.
We need only stop or greatly reduce the flow of nutrients into waterways to prevent harmful algal blooms. Nutrient loading comes from septic/sewage, agriculture and fertilizer. Don’t feed the beast, or rather algae, and there’ll be no harmful blooming algae killing fish and fouling our waters.
Looking down at the dead menhaden floating in water and strewn along the shore, I assumed that the extraordinarily hot September weather due to climate change it was the culprit. Then differences between this event and the July 2018 fish kill began to emerge. There were no striped bass mixed in with the menhaden. A fish circled just offshore of the rotting fish. I tried hard to see its shape but the bright light reflected off the water. I waited to no avail for the Jaws moment of a predator taking a chomp out of flesh. Instead, I was observing the distinctive ripple action of a lone pogie.
In front of the Encore casino, eight men and women with nets on the ends of long poles pulled fish from the waters. Noon was approaching and they had been at work since six in the morning for three days. Fish were scooped and turned into a black plastic trash barrel on wheels. I looked into the barrel and only saw menhaden with their characteristic big heads comprising nearly a third of body length. One of the fish flopped. This one was clearly alive but on its last fins.
The foreman pointed across the river to where the dam meets Draw Seven State Park in Somerville. There was the greatest concentration of menhaden. This also differed from the July 2018 fish kill. At that event, the fish died on an incoming tide when the tidal gates were open. The prevailing Southwest wind pushed the fish onto the Everett Shore with a few above the dam and the majority on the harborside in the cove before the Costco Tire store.
The current fish mortality event was not the result of being chased up river by a predator because people observed the fish mingling in front of the dam alive a few days earlier. Five days after the appearance of many dead fish, I witnessed menhaden still alive flopping, swimming in circles, and head pointing upwards spinning about.
Bigelow and Schroeder’s Fishes of the Gulf of Maine reports that “mass mortalities of menhaden occurred from spinning disease, which is caused by a virus named for the erratic swimming behavior and disorientation of infected fish.”
The life and death of schooling fish is much more complex than we think. With climate change the impacts of our action become more difficult to find causal connections.
Dr. Rob Moir is a nationally-recognized and award-winning environmentalist. He is president & executive director of Ocean River Institute, a nonprofit providing expertise, services, resources, and information unavailable on a localized level to support efforts of environmental organizations. Please visit www.oceanriver.org for more information.