Redline darter

Redline darter
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Perciformes
Family:	Percidae
Genus:	Nothonotus
Species:	N. rufilineatus
Binomial name
Nothonotus rufilineatus (Cope, 1870)

The redline darter, Nothonotus rufilineatus, is a small freshwater fish found in the Southeastern United States. It is one of the 324 fish species found in Tennessee.^[2]

This fish, like most other darter species, tends to inhabit clear, rocky riffles of streams, creeks, and small rivers. Both currently and historically, this fish is known from only the Tennessee and Cumberland River drainages in Tennessee, Virginia, Kentucky, Alabama, North Carolina, Georgia, and Mississippi. The average length for this fish is 6.9 cm, with a maximum recorded length of 8.4 cm. The maximum recorded longevity in the wild for this species is four years. The redline darter feeds mainly on aquatic macroinvertebrates, including midge fly, black fly, and caddisfly larvae, as well as water mites and mayfly nymphs. These fish spawn in the spring and early summer, from May through August. Females reportedly lay between 21 and 131 eggs, which are fertilized by the male and buried in the substrate. Males then guard the nest until the eggs hatch.^[3][4] Redline darters are among the most common darter species throughout much of their range, so do not require any specialized management. These darters do benefit, however, from management activities that promote healthy streams and a diversity of other darter species, because of similar habitat requirements among species. Due to feeding and reproduction habits, these fish require flowing water, meaning that damming of creeks or streams by humans or beavers could result in extirpation of this species from those water bodies. Also, because this species needs clear water to feed, siltation and pollution that increase turbidity are detrimental to it.^[5]

Ecology

N. rufilineatus exhibits typical darter behavior, preferring to live in riffles of small to medium-sized creeks, streams, and rivers, and is rarely if ever found in pools. This fish is also known to inhabit shallow water shoals over bedrock, as long as some scattered cobble or gravel is available. Areas containing scattered larger rocks are also preferred, because these rocks give the fish refuge from predators.^[6] Living in shallow areas limits predation from larger fishes, such as smallmouth bass (Micropterus dolomieu), because these fish are often too large to venture into riffles to feed. However, living in shallower water may make this darter more susceptible to predation from terrestrial hunters, such as wading birds and raccoons (Procyon lotor). Another possible explanation for this fish’s choice of habitat is its feeding requirements. This fish feeds on aquatic and terrestrial insect larvae and other small invertebrates such as midgeflies, black flies, caddisflies, and water mites.^[7] These invertebrate species tend to be more abundant in areas inhabited by the redline darter, so are readily available as a food source. Availability of different food sources varies by season and location; the feeding habits of redline darters change accordingly. Because of its choice of food and habitat, the redline darter is often in direct competition with other species of darters, Nothotus spp. and many of the Etheostoma spp.^[8] The redline darter also competes with other small fish with similar habitat requirements.^[9]

Lifecycle

The breeding season for the redline darter extends from spring through early summer, with fish at higher elevations and more northerly latitudes breeding later than those at lower elevation and more southerly latitudes.^[10] During spawning, the female will lay between 21 and 131 eggs by depositing them directly into the gravel substrate to ensure they are well-protected from predators. The eggs will then be fertilized by the male, which will guard the nest until the eggs have hatched. This fish is believed to have a maximum lifespan of around four years in the wild and reaches sexual maturity after one year, meaning a single female could only produce a total of about 350-400 eggs during her lifetime.^[11] This is a fairly low number when compared to some other species of fish that may produce tens or even hundreds of thousands of eggs. However, redline darter eggs, fry, and offspring have a fairly high survival rate due to the concealment of eggs and the protection afforded by the males. Both man-made and natural siltation is thought to impact the survival rate of the eggs of the redline darter and many other species, because it can result in a reduction or complete lack of oxygen penetrating the egg membrane.

Management

Currently, no special programs or policies are put into place specifically to manage for the redline darter. Unlike several other darter species, this species is not threatened, and is believed to be one of the most common species of darter throughout its range, with a population perhaps over 1,000,000 individuals.^[12] Many state and federal agencies, such as US Fish and Wildlife Service, the National Park Service, the US Forest Service, the Tennessee Wildlife Resources Agency, and the North Carolina Wildlife Resources Commission, currently engage in stream monitoring activities aimed toward improving stream health and surveying populations of fishes. Although these programs do not specifically focus on management of the redline darter, population data on this species and many other species are collected, thus helping to avoid future population problems. Also, in an effort to curb siltation and pollution that have historically been an issue for many stream-dwelling fish, many states have begun to pass laws and to educate landowners on the prevention of siltation. A particular problem is the permission of cattle to wade in streams and creeks when feeding, because the high inputs of organic matter and silt that cattle can potentially contribute to a body of water often results in high levels of turbidity and reduced water quality.

The redline darter has been reclassified into a new genus, Nothonotus. Whereas Nothonotus was once considered a subspecies within the genus Etheostoma, genetic analysis has recently uncovered the need to designate Nothonotus as its own genus, and to move several darters from Etheostoma to Nothonotus. This resulted in the scientific name of the redline darter being changed from Etheostoma rufilineatum to Nothonotus rufilineatus.^[13]

Recommendations

Since the redline darter is one of the most common darters throughout most of its range, and is not currently under any immediate threats, intensive management for this species should not be necessary in the foreseeable future. The best way to manage this species would be to continue to ensure the health and well-being of the streams, creeks, and rivers it inhabits by limiting pollution and siltation. Increased pollution and siltation can result in higher water turbidity, making it difficult for this darter, and many other fish species, to forage for food, breed, and potentially decreasing the ability to avoid predators.^[14] Managing the pollution input into waterways can be as simple as educating private landowners who live near a body of water inhabited by this darter on proper use and disposal of chemicals and other substances, such as fertilizers and automotive oil. Siltation can also be limited through management practices such as allowing vegetation growth around streams, and by using streamside buffers during logging or agricultural activities. Another problem that may arise, particularly around areas of high human activity, such as campgrounds, is the creation of man-made rock dams in smaller creeks and streams. These dams are potentially very harmful, because they destroy the natural riffles needed by redline darters, and convert them into pools, which are of no use to this species. Removal of these dams is fairly simple, but education of the public as to why creation of rock dams can be harmful is critical to curbing this problem. Monitoring populations of the redline darter can be accomplished by a few manners. Backpack electroshocking in streams containing these fish may be one of the most effective ways to conduct surveys for the redline darter. Another way to monitor populations of this darter is to net this fish using a sample seine, and then recording the number of fish captured. Although the redline darter is not in current need of management, it is very important to continue to monitor populations of this darter species to ensure that any reduction in population can be detected in time to be reversed through management.

References