The Most Important Fish in the Salt Marsh

By KENNETH W. ABLE | May 23, 2018
Courtesy of: Kenneth W. Able Large numbers of birds congregate on the salt marsh surface around ponds or pools to feed on mummichogs, an important source of food. This especially noticeable in the early mornings of summer.

While there has been increasing recognition of menhaden as “the most important fish in the sea,” I offer, with somewhat less lofty ambitions, that the mummichog is the most important fish in the salt marsh.

Others refer to these fish as “minnows” or “killifishes,” but mummichog is the official name. These small fish are distinctly colored with the males having brighter hues, at least during the spawning season, then the drab green females.

The mummichog’s importance is derived from several factors. First, it is extremely abundant in salt marshes. For example, in a series of trap collections at the Rutgers University Marine Field Station marsh-rimmed boat basin in Little Egg Harbor, in twice a week collections from 1992 up to the present, this fish has consistently been the most frequently collected.

Its abundance is understandable when we recognize that marshes dominate much of the margin around the Mullica River and Great Bay. In addition, while it is typically found in marshes, it also occurs along shallow shorelines such as beaches, in coves and on tide flats. It is well adapted to the variety of marsh habitats including the marsh surface, marsh pools and intertidal and subtidal creeks and dominates in all of these independent of whether it is high or low tide.

Second, they are tough. They tolerate extremely high and low temperatures. For the former, we have recorded them in water greater than 90 degrees Fahrenheit. For the latter, they can often be observed swimming around under the ice in frozen-over marsh pools, a location where they often spend the winter. They also tolerate very low levels of oxygen in the water in summer, levels that would kill other fish, including other kinds of killifishes. And salinity is not an issue. They do well in full ocean salinities and all the way into fresh waters, but they have to have time to adjust to changing salinities for reproduction. 

Third, this species is very productive. That is, it grows fast, survives well, and is abundant enough that it produces more fish per square foot of marsh than any other fish. All of these factors explain why there has been some effort by the University of Delaware to produce a canned sardine-like product from this abundant fish. (Apparently, while it is fine to eat after processing, it never caught on, which is why you can’t find them in the grocery store.)

Fourth, it is an important predator in the marshes and influences the abundance and survival of many invertebrates. For many of us who spend time in and around marshes, its greatest value is that it is a great predator of larval mosquitoes, thus reducing the number that are around to plague us and eliminating the need to have marshes treated with pesticides to control them. 

Fifth, because of its abundance it is an important food item, including for many of the estuarine fish that we want to harvest, including striped bass, bluefish, fluke or summer flounder, and likely blue crabs as well. This predation on mummichogs extends into tidal fresher waters by white perch and chain pickerel. Other predators include mummichog juveniles and adults from seven-tenths of an inch to 3½ inches, which cannibalize their young from two-tenths of an inch to 1½ inches, as we learned from specialized examination of stomach contents. This frequent predation is an increasingly important issue for managing fisheries with an ecological perspective.

But its predators are not just under water. This is most obvious when a variety of birds collect around marsh pools to feed on them. We have observed this phenomenon over 30 years, most often in early morning in the summer. At these times, dissolved oxygen is low in the pools and fish are closer to the surface to skim the surface layer for oxygen coming from the air. As a result, a multitude of birds, such as blue herons and great and snowy egrets, gather around or wade through the pools while other species including terns and laughing gulls dive into the pools for fish and shrimp. Occasionally, little blue herons, double-crested cormorants and brown pelicans are attracted to these gatherings as well. Mummichog predators also include mink and river otters.

Sixth, it is a valuable baitfish. The waters of the Mullica Valley have part-time and full-time bait fishermen who collect mummichogs for their own fishing or to sell to others. Their value is especially notable when, in some years, they are less abundant and those who use them to fish for fluke and other species cannot find them.

However, a general warning to bait fishermen – don’t eat them live. Several years ago there was a well-documented account of some fishermen in Maryland who, after a hot day in the sun and retiring to a local bar, decided to swallow some of their mummichog bait, presumably as a challenge – like swallowing goldfish. Apparently, they did not know that some mummichogs have a roundworm or nematode in their body cavity. They are red and can get surprisingly long, a couple of inches. Bottom line: The worms burrowed into the fishermen’s stomach linings. One had to have surgery.

And lastly, we value mummichogs from the scientific point of view because their small size and tolerance make them great laboratory animals. Many years ago someone calculated that there have been over 1,000 publications on this species. We have contributed substantially to the number since then. This extends to their value as “sentinel” species in marshes and estuaries as an index of the quality of marsh and estuarine habitats.  

All of this contributed to my surprise when someone suggested that the species of fish that should represent the state of New Jersey should be the mudminnow. What better way to encourage further jokes on late night television or online about New Jersey! Instead, I strongly support the nomination of the mummichog as the state fish. Why not, given its ecological and economic importance?

Kenneth Able is director of the Rutgers University Marine Field Station in Little Egg Harbor. This story is part of his upcoming book on the underwater natural history of the Mullica Valley by Rutgers University Press.

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