How Chemicals and the Menhaden Affect the Chesapeake Bay

How Chemicals and the Menhaden Affect the Chesapeake Bay

By: Justin Dawson

Introduction

The Atlantic Menhaden is one of the most important and abundant species of fin-fish in estuarine and coastal Atlantic waters. They are the second most important species harvested in the United States in terms of quantity. They are processed for their oil, made into fish meal, protein meal and solubles, and used as bait for commercial and recreational fishing. As fishmeal the Menhaden are a valuable ingredient in poultry and livestock feeds because of their high protein content, they constitute approximately sixty percent of the feed product. Menhaden are consumers of phytoplankton and plant detritus and in turn are fed upon by many predatory fish, mammals, and birds.

A healthy Atlantic menhaden population has the potential to consume up to twenty five percent of the Chesapeake Bay's normal nitrogen content for one year. Nitrogen Arrives in the Chesapeake Bay from run offs from farms, sewer systems, and many other sources. An increased nitrogen supply to the Chesapeake Bay is the cause of a major problem for the Menhaden population. The increased amount of nitrogen in the water has an effect on the phytoplankton that the Menhaden eat. Nitrogen causes the phytoplankton to grow at an increased rate. This increased rate of growth causes a reduced production of oxygen by the phytoplankton. The reduced oxygen content in the water is insufficient to fulfill the needs of the phytoplankton and that of the fish that come to feed on the phytoplankton. This problem is more severe when the sun is down, because at that time of day the phytoplankton makes no oxygen. This causes the dissolved oxygen content of the water to drop even further, which can cause mass fish kills. Large numbers of fish are killed, due to the reduced oxygen content below what they need for survival.

Dead Zones

A "dead zone" is an area in which a fish kill is contained. There are many reasons for dead zones. They can be caused by a toxic spill or they can be caused by an algae bloom in an area were the fish are eating. For the purposes of this paper primarily dead zones caused by an algae bloom will be discussed.

Algae blooms are primarily caused by an over abundance of nitrogen in the area. Nitrogen comes into a bay or an estuary through

run off from homes and farms that use the nitrogen as a fertilizer. Nitrogen can also arrive by means of raw sewage. The nitrogen in conjunction with a run off of fresh water causes the phytoplankton to grow exponentially. The growth causes increased algae blooms which the menhaden are attracted to, the algae being their main source of food. However, the over abundance of algae has a negative down side for the Menhaden. The increased algae growth consumes more oxygen then it produces. When there are a large number of Menhaden in the area the concentration of dissolved oxygen is insufficient for their survival causing asphyxiation.

Low Concentration of Menhaden

Do in a large part to the over fishing of the Menhaden there is another type of 'dead zone' created. This is a dead zone in which no fish can survive because of the low amount of dissolved oxygen in the water. The low dissolved oxygen content is caused when there are too few menhaden to sufficiently eat the algae that grow in the bays and estuaries along the Atlantic coast. This type of dead zones does not just have an effect on the Menhaden, but on all forms of marine life in the particular area. Similar to the previous type of dead zones nitrogen is again a big contributor. With a low concentration of Menhaden in the area and a high concentration of nitrogen the phytoplankton (algae) tend to expand exponentially creating zones deficient in adequate concentrations of dissolved oxygen in the water. This causes a drastic reduction of marine life in most of the bays and estuaries along on the Atlantic coast.

Value of the Menhaden

The Menhaden are not harvested by the fishing industry because of their value as a food product. They are instead harvested for their value as bait to lure other larger game fish (shark, blue fish, tuna and other predator fish species) that feed on the Menhaden and for their value to the animal feed industry. Additionally without the Menhaden the bays and estuaries along the Atlantic coast would become clogged with a very thick growth of algae. This would make it nearly impossible for most boats to navigate without extreme difficulty.

Another particularly significant problem in the bays and estuaries is the excess amount of nutrients (nitrogen and phosphorus) that end up there. The majority of nutrients enter the bay and estuaries from power plants and factories, sewage treatment plants, commercial and residential development, agriculture, septic systems, large scale animal operations (chicken and pig operations), roadway runoff, and excessive fertilizer use. In overabundance they set off a chain reaction causing phytoplankton to grow explosively or "bloom" only to die and sink to the bottom. Bacteria decompose the dead algae and in the process use up much or all of the water's dissolved oxygen. Such areas of low or no dissolved oxygen cannot support other marine life (plant or animal) This is due in part to the phytoplankton restricting the amount of light needed for to help them to perform photosynthesis and to the reduced dissolved oxygen in the surrounding area. The lack of oxygen production and the dead zones could over time increase the greenhouse gasses.

Each year approximately one hundred sixty five thousand tons of nitrogen and ten thousand tons of phosphorus reach the bays and estuaries of the eastern seaboard. In bays and estuaries nitrogen containing compounds act as nutrients providing growth. An overabundant supply of nitrate (NO3-) in fresh water can cause reactions which lead to oxygen depletion. Because of this, aquatic organisms that depend on oxygen and fish, especially the Menhaden, experience detrimental effects when nitrite (NO2-) or nitrogen levels reach 90 milligrams per liter or nitrate (NO3-) levels reach 0.5 milligrams per liter. Bacteria in the water quickly convert nitrites (NO2‑) to nitrates (NO3-). Nitrites can produce a serious condition in fish called "Brown Blood" disease. The nitrites also react directly with hemoglobin in human blood and in other warm blooded animals to produce met-hemoglobin. Met-hemoglobin destroys the ability of red blood cells to transport oxygen in humans. This condition is especially dangerous in infants under the age of three months.