The Atlantic Menhaden (Brevoortia tyrannus) a member of the herring (Clupeidae) family is found in huge schools along our east coast from Maine to northernmost Florida. Menhaden are a “forage fish” and perhaps one of the most important fish species in the Atlantic Ocean. A forage fish serves as prey and a food source for other species in the food chain. They are the first steps of the food chain (or trophic level) and serve by converting the ocean’s primary producers ( algae or phytoplankton) into edible food for larger species. And yet, despite its essential and critical import this common fish is the most under rated, maligned, misidentified, mismanaged, misused and misunderstood fish species in our local waters.
Menhaden is one of the few species which has retained the name used by native Americans. The term “Menhaden” is said to be a corruption of the Algonquian unprepossessing term for this species which means: “that which is used as fertilizer”. The first colonists, who were befriended by Algonquian-speaking native Americans introduced the new-comers to the hugely abundant Menhaden and to the fact that this fish was also essential to insure a good corn crop. The English colonists assumed it was not necessarily good for much else, and this negative view of the species has continued on though history. ( Though later colonists in the 1800s realized that since so many other critters were consuming it, it was probably good to eat too, and began preparing it and consuming it as Europeans prepared sardines.)
Locally , here on Long Island’s north shore, these fish are called “bunker”, short for another name for this fish: “Mossbunker”. Like so many other local New York names and words, this term is of colonial Dutch origin. The “horse mackerel” of the Netherlands, called by the local Dutch colonists of New York “marsbanker” has a passing resemblance to our local Brevoortia. The early Dutch colonists simply applied this name to a similar though unrelated fish. It has remained in the vernacular...shortened often to simply “bunker”.
The Atlantic Menhaden or “bunker” is by any account an attractive fish. It is bluish black above and white below, its silvery sides are tinged with a brassy luster. The sea- blue color of its dorsal surface probably makes it nearly invisible from above, protecting from its many avian predators, while the white of its belly helps to camouflage it against predators from below. The fins and lovely deep forked tail are tinged with yellow. A large black spot is located behind the eye and often several smaller spots are found along its sides. Its mouth is large with the lower “jaw” continuing to a point behind the level of the eye. The mouth is rigid and horny. The jaws are toothless to the touch. With the mouth pried open one can observe its “gill rakers” arising as two lines of closely spaced, soft, pliable “comb teeth ” likely composed of cartilage-covered! soft tissues which apparently also exude a sticky mucous. The gill raker “comb teeth” are close spaced (@ 1-2 mm apart) and these arise from both sides of the inner jaw. In the anterior of the mouth one observes what appears to be the developmental remnant of a short tongue. Another bulbous double “U” shaped organ is located in the back of the mouth, and perhaps may be used to sweep the gill rakers clean when the fish swallows the trapped plankton which has accumulated on the raker teeth.
These gill rakers reveal why Bunker, as any fisherman knows, will not take a baited hook or a lure, since they are wholly filter feeders (animals which filter food from the water which surrounds them) just like the great baleen or Right Whales of the North Atlantic, as well as basking sharks and even invertebrates such as mussels and oysters.
Menhaden feed only on plankton, those living organisms which float just below the surface of the water in the sunlit zone. The Menhaden swim with their mouths open in this level, through the clouds of microscopic plankton on which they feed. It is well documented that the Atlantic Menhaden feeds on both phytoplankton (plants like algae) as well as zooplankton. The former is the “green grass” of the sea, and the latter, are tiny floating organisms (ostracods, copepods, tiny crabs, larvae of shellfish etc.) which feed directly on the algae.
The phytoplankton ( green plants) use sunlight and chlorophyll as well as the nutrients dissolved in the sea water in the presence of sunlight to produce complex carbohydrates, oils and proteins which constitute the living, floating organism. Like any green garden plant, besides water and sunlight they require copious levels of nutrients such as nitrates and phosphates to flourish.
In the open ocean, there is obviously no scarcity of water and oxygen, but just as in our home gardens, bright sunlight is essential. That variable is controlled by the seasons.. So we would expect blooms of algae and the filter feeder fish which feed on algae and other plankton to appear in the spring. As expected, the algal blooms coincide with high concentrations of nutrients in the water and the increased sunlight-duration (longer days) and sunlight-intensity ( sun higher above horizon resulting in more intense solar radiation overhead). For these reasons schools of Menhaden and shoals other filter feeder fish arrive in the spring,, encouraging the commercial and sports fisherman to oil up their equipment and head out to sea or shoreline.
But these same Menhaden reappear again in the Fall. Why?
It seems counter intuitive. In fall the temperatures decline, sunlight duration and intensity are decreasing, and storms churn up the surface waters. So what attracts the Menhaden back into Long Island Sound every Fall?
The answer to that is besides water and sunlight, green plants (like the tomato plant in your home garden) are dependent on adequate nutrients. After a summer of flourishing growth a gardener would be wise to replenish the nutrients in the soil for their fall plantings. And in this same manner the ocean phytoplankton are also dependent upon an adequate concentration of nutrients in the water column.
All spring and summer sea water nutrients are slowly used up as they are converted by algae into other organisms in the food chain—zooplankton, small fish, and bigger fish. These organisms which feed on the primary producers —live in the water and release metabolic wastes, which sink to the bottom, and then they are eaten by others, or they die and sink to the bottom where further decay and nutrient releases occur. All of these processes result in nutrients sinking from the top of the water column to concentrate at depth, often out of the photic sunny zone.
But beside the fact that all summer long living organisms slowly deplete nutrients in the upper portion of the water column, but in addition, the top layer of the water column has been warming up as well. Sunlight penetrates into the upper layer, warming it, while summer storms also tend to mix warm air into the top warm layer of water. Warm water is less dense than the cooler deep water. The warm water forms a discrete layer which sits on top of the water column. In L I Sound it by mid summer it produces a stable “warm water cap” of perhaps 30 feet thick in this “layer cake effect” water column. Below this warm water cap temperatures fall quickly, this boundary zone, where temperature changes most rapidly is called the “thermocline” .
As noted above in LI Sound this boundary occurs at perhaps thirty feet ( @10 m) or thereabouts below the surface and varies from year to year. Since the warm water is of a lower density than the deeper cooler more dense water, the two layers do not mix. Swimmers and divers can often observe this sharp change in temperature. It is within this upper warm layer that most of the biological activity takes place during the spring and summer seasons.
The result of the presence of the “warm water cap” and the algal blooms and zooplankton growth which occur there is that critical nutrients for plant growth are soon depleted in this warm zone. By late summer and early fall, nutrient levels in this upper layer are at their lowest point. As fall approaches there is still enough light for plants to grow, but the limiting factor for plant growth is the low level of “fertilizer” nutrients such as nitrates, nitrites and phosphates in the upper warm water layer.
But at this time in the fall, something very interesting happens—it is known as the “Fall Turnover”. As the cool season proceeds storms churn up the top water layer, sun light decreases and air temperatures drop, all of which tend to lower the temperature of the surface water cap. By mid November the average temperature of Sound surface waters have fallen almost 20 degrees F (11C) from their high in August. At some point in this period of the year the upper warm water layer cools to the temperate of the deeper water, the thermocline dyiappears and the two zones mix as the warm water cap or “layer cake” pattern breaks down. At that point deeper, nutrient rich, water can then mix freely with the top nutrient poor water. This Fall Turnover is the moving of nutrient rich bottom to thr top into sun light. This is a time for fishermen and others to mark on their calendars.
At the time of the Fall Turnover surface water temperatures are still well above their winter minimums, nutrient levels are restored to spring levels, sunlight is still more than adequate for photosynthesis and algae are present in the water. All these factors set the stage for a resurgence of algal growth and a similar rise in zooplankton populations. That sets the stage for the return of the Menhaden which feed on these plankton blooms.
Then the surface waters are rippled from below and sparkle in the sun as the subsurface movement of vast impressive schools of Menhaden —the Bunker— begin the fall run. As boats approach the densely packed blue back dorsal surfaces of bunker schools descend to deeper water and then raise again to continue their open mouthed pursuit of plankton during their fall run in the Sound. The huge schools, hundreds or thousands of feet across. enter the estuaries and bays where they furrow the water like cat’s paws of wind. . They attract predator fish such as Weakfish, Bluefish, Striped Bass and mammals such as seals, and in early days even dolphins and toothed whales. But the massive number crowding into tight harbors and shallow water often reduces water oxygen concentrations, and some fish die or become disoriented and strand on shore. Others are attacked by predators from above and below. With such large numbers in the water many die and waves wash them to shore.
During the fall, fisherman and beach walkers often observe large numbers of Menhaden dead or dying along the strand lines of our north shore Long Island beaches. Over several excursions counting stranded fish and estimating distances covered I reckon that tens of thousand s of fish are stranded on our Long Island beaches each time the Menhaden make their seasonal runs.
Though the number estimates of stranded fish seems like a lot of “dead fish”, it is only a tiny fraction of the the commercial landings of this important, nay critical, forage fish species which is so important over such a an extensive geographic range comprising all of the Atlantic east coast, Some recent data (Wikipedia: Atlantic Menhaden dl: 12/2020) indicate that commercial purse seiners in 2015 were permitted to take approximately 200,000 metric tons off this fish, or roughly 400,000,000 pounds ( or about that many individual one lb fish). Other estimates indicate as much as 500,000 metric tons or half a million metric tons of fish were landed annually in earlier dates.
The federal agencies which partly control commercial fishing as well as commercial fishermen themselves suggest that the stocks of menhaden are not “overfished”. There is a technical definition for this term. But one does not have to be an expert on fish management to understand that by removing the huge numbers (in hundreds of thousands of tons) of a major forage fish from the coastal ocean to make fish oil, lipstick, animal feed, and fish oil pills —simply denies this same amount of hundreds of thousands of metric tons of of food resource to the many species which have evolved over the millennia to depend on the menhaden as a source of sustenance. Clearly, if we remove this much food from the sea, we must expect we are denying food to other species and thus must expect a decline in those species of fish and other creatures which depend on that species for survival.
Keep in mind all wild species live on the knife edge between bare survival and starvation. Even very small changes in population of a first line forage fish such as the Atlantic Menhaden can be expected to have a deleterious effect on those species which have evolved over thousands of years to depend on the seasonal abundance of these fish. Thus we must expect such species as the weakfish, striped bass, bluefish, seals, dolphins, and other species which depend on bunker for sustenance to respond by falling in population levels.
There is no “free lunch” in the sea. There is no “excess fish stocks” which we can remove without effect on the entire ecological system. In nature every species is part of a tightly connected food web of predator and prey, of food and energy distribution Change the system somewhere and you will alter the system. The alterations may be irreversible and catastrophic to certain dependent species.
So when a fisherman asks: Where did the stripers and bluefish go? The answer may be: “Sorry but we made a choice, we chose lipstick and fish oil supplement pills!
Make your choice.Which would you rather have?
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