| Eastern sand darter | |
|---|---|
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Perciformes |
| Family: | Percidae |
| Genus: | Ammocrypta |
| Species: | A. pellucida |
| Binomial name | |
| Ammocrypta pellucida (Agassiz, 1863) |
|
Contents |
Ammocrypta pellucida, also known as the eastern sand darter, is a species of the Percidae family. The eastern sand darter is a relatively small, perch-like fish that has recently been listed as globally threatened in the areas in occupies throughout Canada and the eastern United States.[1] It is most plentiful in the Mississippi and Ohio rivers, as well as Lakes Champlain, Erie, Huron, Michigan, and Ontario. It prefers sandy bottomed streams and sandy shoals in the lakes.[2] The Eastern sand darter feeds on larvae of black flies and other small insects that live in the water. They also feed on zooplankton in small portions due to their small mouth size limiting their gape ability.[3] Their average body size is around 1.5-2 inches long and it prefers to breed in the spring and summer months in sandy bottomed waters.[4] Along with pollution from humans, the main biological factor that is deterring the population growth of this fish can be contributed to siltation, which reduces the amount of oxygen available for them to breathe and can also lead to the smothering of their eggs they bury after they breed.[1] The highest concentration of Eastern sand darters can be found throughout Lake Erie, however, the population has slightly decreased over the last few years. In order to maintain and hopefully increase the population of the Eastern sand darter, the species should be monitored every six months while making sure litter and other forms of pollution are not invading their habitat. Another form of protection could also be offered by sampling with fish nets in designated parts Mississippi and Ohio Rivers, as well as the five lakes mentioned above to see how often offspring is produced. By sampling in the designated habitats of the Eastern sand darter, ecologists will be able to see if the population is staying constant or fluctuating. This will then reveal if the sedimentation problem is worsening or actually improving.
The Eastern sand darter can be found in many areas throughout the United States and into southern Canada. In addition to the Mississippi and Ohio Rivers it can be found in great concentration in Lake Champlain, Erie, Huron, Michigan and Ontario. They can also be found in the St. Lawrence River drainage in Canada along with the Lake Champlain drainage in Vermont down into New York, Pennsylvania, West Virginia, Kentucky, Illinois, and Indiana.[4] Currently, the greatest concentration of Ammocrypta pellucida occurs in northern Alabama and eastern Tennessee. Distribution has slowly decreased over the last few decades and there are two key factors that could be the cause of this. The eastern sand darter requires clean sand substrates; hence siltation is a major factor in their decline the past few decades. Siltation decreases the quality of habitat for both egg development and adult darters by decreasing the oxygen levels within the sand in which they bury themselves. Furthermore, silted habitats can cause adult darters to not fully burrow or decrease their time burrowed which then causes them to waste energy reserves. Channel or water flow alterations, nutrient enrichment, or any other habitat modification can completely change the amount and quality of the shifting sand bars which can then turn detrimental for the Eastern sand darter.[5]The increased construction of dams also has been a major factor in contributing to the elimination of their respective habitats. Dams reduce river levels and flow, decrease oxygen levels in reservoir waters, and alter water temperatures making it difficult for the Eastern sand darter to reproduce at a comfortable temperature.[1] Dam construction adds a whole new dimension to decreasing the reproduction and survival rate for the Ammocrypta pellucida.
Ammocrypta pellucida seeks its prey from the sand along the bottom of the stream or lake. “Their prey items usually range in size up to 3/16 inches, but prey selection varies depending on the age of the darter. Juvenile Eastern sand darters consume small crustaceans, while adults prefer midge larvae, blackfly larvae, mayflies, and caddisflies.” [5] Ammocrypta pellucida has several species of fish predators which include: Rainbow Trout, Large and Smallmouth Bass, and Rock Bass. However, due to extensive time periods spent buried in the sand and its translucent body, the Eastern sand darter usually tends to stay unharmed from predators.[1] Minnows are the Eastern sand darters biggest competitor for food, but little conflict arises between the two due to the darter occupying the lowest depths of the rivers and lakes while the minnows occupy the upper part of the water column. [6] Dam construction added with human pollution has caused an increased problem with siltation in their habitats, which has reduced the abundance of the species.
The average life span for the Ammocrypta pellucida is about 2–3 years, but if the siltation and pollution continue to worsen, the average life span will gradually decrease. Ammocrypta pellucida reproduces in the sandy shoals at the bottom of the lakes and rivers it inhabits during the spring and summer months when the water is at its warmest temperature. It reaches sexual maturity around age one and the males are able to mate once during the breeding season while females mate twice producing about 350 eggs with an average clutch size of 71 eggs.[2] Furthermore, spawning activity increases during the warmer months and females may spawn several times during the reproductive season. These numbers are likely to drastically decrease unless a solution is created to stop the siltation problem. If the problem continues to worsen, much of the eggs will be smothered resulting in a loss of births, further hindering the Eastern sand darters' population count.[5]
Due to the Ammocrypta pellucida population decreasing over the last few years in the rivers and lakes it inhabits, actions need to be taken to decrease the human impact on their population. The Eastern sand darter is on the brink of being endangered, but it is currently listed as threatened in much of the areas it occupies. Lake Champlain’s wildlife management staff has come up with several factors that are contributing to the Eastern sand darter’s population decline, which are stocking more predators than the forage basin can sustain, failing to control undesirable non-native species, and a loss of critical habitats caused by changes in flow, dredging, and sedimentation. The staff plans to stock the fish in monitored fisheries in order to develop spawning populations and rehabilitate the species until the population increases enough to be set back into their natural habitats.[3] The U.S. Fish and Wildlife Services have also set aside a few refugees across the country in an attempt to increase the Eastern sand darter population through breeding in a pollution-free environment. They also have been continuously monitoring the areas the Eastern sand darter occupies to make sure the maintenance of a quality habitat is maintained for the darter community. Ending human pollution is their first priority which will then help decrease the severity of the other threatening problems including sedimentation and siltation.[7]The preservation and restoration of their habitat must be the foremost concern for achieving an increased abundance within this species. [6]
Although the Ammocrypta pellucida has developed an efficient way to hide from its predators, it unfortunately cannot hide from pollution and other serious siltation problems that seem to be worsening over time. In order to ensure that the Ammocrypta pellucida population does not continue to decrease, current monitoring practices with the refugees and fisheries should continue to be conducted by the wildlife management staffs. A plan to reduce the amount of invasive species in the areas inhabited by the Eastern sand darter would also help to increase the population of the darter by decreasing the number of its predators. Using gill nets to gather large amounts of fish could be used to capture invasive species that are threatening to the Ammocrypta pellucida. Once an invasive species is found in the net, it should be captured and later released in its own refugee, away from the Eastern sand darter. Sampling every six months using gill nets in designated areas throughout the United States and Canada that the Eastern sand darter occupies would allow researchers to formulate a hypothesis about how the population is fairing. Only sampling twice a year will allow time for eggs to develop into juveniles which can then be counted as part of the population when the sampling is conducted. This will give a more accurate reading of its abundance as opposed to doing it every week when the numbers are unlikely to fluctuate. This process will permit the agencies to target the most threatened areas and act quickly in order to help correct the possible problem.