The sad fate of the menhaden in the Hudson

A couple of readers have spotted dead fish floating in both the Pier 25 Marina and the North Cove Marina — and A. saw “many fish gasping for air and swimming in an erratic manner.” There are some natural migration patterns at work as well as, no surprise, longterm results from global warming.

Turns out the fish are menhaden — aka bunker — flat with a deeply forked tail and under 15 inches long.

The educators at the Hudson River Park Trust had this explanation: “We talked to an ichthyologist and he relayed that this is pretty natural for menhaden annually after they are spent from migrations. Menhaden are also very sensitive to changes in salinity and dissolved oxygen. There could have been some drastic localized changes with the recent flash rains / large CSO discharges over the last week (including right now!). Also, predators like striped bass and bluefish cause additional stress to menhaden and sometimes they even beach or exhaust themselves, which is another common reason for die offs, and both are entering the Hudson hungry right now.”

Riverkeeper — the non-profit that advocates for the health of the Hudson — explains that it is also the result of overheated water, which deprives fish of oxygen. See this or more here on their blog:
“The widespread deaths of Atlantic menhaden, and possibly other species, are most likely the result of prolonged heat and lack of rain, combined with other factors, which reduce levels of dissolved oxygen that the fish need to survive. Importantly, it’s a symptom of a compromised and fragile ecosystem in the river and harbor. It’s yet another warning about our need to restore the river to health and balance in the face of climate change.

During these long, sunny days in June and early July, sunlight is overheating the river. Periods of cool or cloudy weather are scarce. Warmer water holds less oxygen than colder water, due to the kinetic energy of the water molecules.

Low oxygen (hypoxia) or no oxygen (anoxia) can also occur in water bodies when excess organic materials, such as large algal blooms, are decomposed by microorganisms. During this decomposition process, oxygen in the water is consumed.

Ultimately, oxygen levels can become so low that fish suffocate.”

And this from the state Department of Environmental Conservation:
“Atlantic menhaden are very sensitive to environmental conditions. For more than a month, there had been little rainfall, very low freshwater input (flushing) into the system and a quick rise in water temperature, resulting in a drop in dissolved oxygen creating hypoxia. Adding these conditions to the sensitivity of the species, the estuary had become a very stressful environment. The result was death by a lack of sufficient dissolved oxygen. This type of fish die off incident occurs naturally this time of year when water temperatures warm and generally have little impact on region-wide fish population numbers.”

 

2 Comments

  1. I also noticed fish that were dying (or dead) and wondered why seagulls weren’t eating them. Then I noticed there are no seagulls around. Wondering what that’s about, too….

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