Areason the fish are dying

One thing that was missing from the article on dead fish washing ashore in Darien was the behavior of the fish themselves and how that can kill them as well as how oxygen gets into water and stays there. Schooling fish such as menhaden (bunker) are active fish. They need oxygen levels usually well above 3 parts per million of dissolved oxygen in the water.

The reality of large schools getting into bays, harbors and inlets is that they can use up the oxygen in the water and suffocate. This is so serious that aquariums that keep them need to put them in circular tanks and keep the water oxygenated and circulating, otherwise, they would follow the leader, and go into a corner in a square tank, and suffocate unless there was a strong current removing the water from the corners that has been deoxygenated by the fish and replaced it with oxygenated water.

The oxygen in local harbors can only be replaced by photosynthesis, strong wave action, and sometimes rain and runoff from rivers and this could take hours and even days. The temperature and salinity of the water determine how much oxygen can dissolve in the water to be available for the life in the water.

Even though these fish had lots of oxygen when they came into a bay or harbor, which is the case right now, they use the oxygen up faster than it can be replaced. And, like any other animal, they do not do well as far as thinking with low levels of oxygen, so they can swim to where there is actually less oxygen, and then die. The larger, more tightly packed schools, the more oxygen is used up, and the more fish that die unless they can get to unused water.

The menhaden that I am seeing are well fed, and that is probably why so many are here — there is food and Long Island Sound has enough plankton to attract them. As alarming as this is, it is part of a natural process and the crabs on the bottom of the Sound are thankful for the extra food.

Joe Schnierlein

Chairman, Norwalk Mayor’sWater Quality Committee