Imagine you’re taking a walk one day with a group of friends. You’re enjoying the weather, the company of your friends and the adventure you’re on. You take a breath only to find that there’s no oxygen in the air. None. All of a sudden, all oxygen is gone. You have seconds, maybe minutes, to contemplate what’s happening to you. Can you even imagine how horrific an end that would be? If you were a fish swimming in the South River in Maryland this past week, that is exactly what you would have felt. Just prior, of course, to your untimely death.

A massive fish kill of over 100,000 juvenile fish occurred just south of Annapolis when a large school of menhaden encountered a dead zone along a tributary of the Chesapeake Bay. The fish kill is the largest in the region this year.

Well that sounds bad, but what exactly IS a fish kill? A fish kill is an area of oxygen depletion in the water that makes it impossible for fish to survive. One of the most common reasons for fish kills is elevated summer temperatures and reduced rainfall, often occurring in back creeks with slow-moving water. The increased temperatures and lower rainfall cause stratified layers in the water. On one layer, increased temperatures reduce the water’s ability to hold oxygen. On another layer, the lack of movement prevents the water from becoming aerated. On the bottom layer, the heavier, salty water is cut off from an oxygen supply and can result in a dramatic loss of oxygen.

Isn’t this just a naturally occurring phenomenon? Higher temperatures resulting from global warming have the potential to cause catastrophic imbalances to the entire ecosystem of this important region. There are also a number of other causes of fish kills, including algae blooms caused by Pfiesteria, lawn pesticides and farm runoff. Many menhaden have also been found with lesions and sores that scientists think may be a result of toxins, fungus or algal blooms.

Fine, but what’s the big deal about menhaden, anyway? Menhaden are small, oily fish that are part of the herring family. They are critical to the ecosystems up and down the coast of the Atlantic Ocean. They serve as a link between the upper and lower levels of the food chain and play several vital roles in the Chesapeake Bay’s ecosystem.

As filter feeders, they eat algae and help to clean the polluted waters of the Chesapeake Bay. There are two main natural filtration systems in this region. The menhaden compose one filtration system and the Atlantic, or American oyster, compose the other. Oyster levels have suffered a major decline for many years due to their demand in the US and international seafood markets. At one time, the American oyster was able to filter the entire volume of the Chesapeake Bay within one week (about 19 trillion gallons of water). Today, this process would take more than a year. Because of the decline in oyster populations, the need for menhaden has never been greater.

Additionally, menhaden are the main source of food for popular game fish like bluefish and rockfish (striped bass). Reduced numbers of menhaden mean fewer fish higher up the food chain.

Ok, so it sounds like an important fish to help pollution and that area’s food chain. But what if I don’t live along the Chesapeake Bay. Why should I care? The Chesapeake is the largest estuary in North America and the third largest in the entire world. This means that if you like fish or seafood, there’s a very good chance that you’ve enjoyed something from the Chesapeake Bay.

Menhaden are also harvested commercially in huge numbers to produce fish oil and fish meal that is used in paints, soaps, lubricants, cattle feed and some pet foods. Considering the widespread use of menhaden in so many products on the market today, it is likely that a number of items in your home contain menhaden by-products. At this time, it is unknown what kind of impact the health of the menhaden can have in the products we use and those we feed our animals.

What can I do to help? If you’re part of the Chesapeake Bay watershed, become a conscious consumer by purchasing organic fruits and vegetables and eliminating the use of toxic herbicides and pesticides in your garden. No matter where you live, choose sustainable seafoods. Become a part of a proactive community and support politicians working to help the environment. You can also donate to a major contributor like the Chesapeake Bay Foundation.

To learn more, check out the following links about the Chesapeake Bay, menhaden and fish kills and the water quality of the Chesapeake Bay.

Chart credited to Eco-Check. Menhaden lesion image credited to NIMS.