The tiny Southeastern fish that caused delays to Tellico dam construction for years – and inspired an epic Endangered Species Act battle – has finally been removed from the list, though more work remains.
Hill and Metcalf know darters enjoy direct sunlight, so they built culverts resembling skylights over sections of their stream. Their efforts are paying off: darters have begun coming closer to shore.
Stream Habitat
Streams are dynamic environments that offer organisms diverse conditions to live and flourish. Most natural streams feature sequences of faster riffle and slower pool habitats, providing oxygenated water and coarse sedimentary substrates that resist movement during high flow times; slow pool habitats offer shelter during low flow times while providing nursery areas for young aquatic organisms. Both riffle and pool habitats offer cover that protects against predators, competitors, and sediment erosion.
Pure, clean streams provide shelter to an abundance of fish species including the School of Darter (Pomacanthus gairdneri). Furthermore, streams provide refuge to other threatened or endangered species such as Okaloosa darters, Florida bullheads, native crayfishes, and the Ringed Map Turtle.
Beyond the physical characteristics of a stream, it’s also crucial to understand how its chemistry interacts with biological communities to form the ideal habitat for these organisms. Habitat and water chemistry play an essential role in fish-species distribution at both regional and local scales.
For example: stream size and channel dimensions have been shown to correlate directly to water quality and their ability to support aquatic biota (Kaufmann et al. 1999). These relationships may also depend on other environmental variables and vary depending on location.
Physical characteristics of stream habitat can be assessed more reliably at a local scale by studying an entire stream reach and its associated biota. Thus, the USGS NAWQA Program emphasizes physical habitat assessments within streams. To do so, three types of data were linked with stream reaches: bedrock geology, stream gradient, and watershed size. Finally, each stream reach was evaluated based on physical criteria and classified into one of three categories – good, fair, or poor. The three stream reaches under consideration each exhibited distinct environmental settings, land use, and habitat characteristics that significantly affected fish communities and streams. Our classification system was then utilized to identify physical criteria that most significantly impact habitat and fish communities in these reaches.
Food
Darters feed on aquatic insects, crustaceans, snails, and aquatic plant leaves; as well as submersed aquatic vegetation and algae. Although darters usually inhabit shallow stream beds when food sources are plentiful, when food shortages occur they will move deeper waters for food sources. Darters’ bodies are designed for fast gliding with two dorsal fins – one featuring spines while the second soft rays. Their body color ranges from straw-olive and their dorsal and caudal fins being blue with males having well-developed dorsals while females having less developed or no dorsals with only faint versions featuring blue spots along their dorsals; blue and red patterns cover the pectoral and dorsals while red stripes appear on anal fins.
River darters (Percina shumardi) in Alabama often preyed heavily on pleurocerid snails found in Brushy Creek and Sipsey Fork Black Warrior rivers, feeding predominantly on hatchling snails during July (80% of their diet). Snail consumption decreased during April and May but increased again when hatchling snail numbers peaked again at around 80% of the diet; similarly, darter species fed opportunistically on insect larvae and adults; with chironomids, trichopterans and ephemeropterans being preferred over other taxa; females tend to partition diet more according to prey size than males when snail abundance was high – effect less prominent during April/ July when abundance was high.
The Watercress Darter (Etheostoma spectabile) can be found inhabiting deep, slow-moving backwaters of spring outflows in Wisconsin that support dense aquatic vegetation – specifically Nasturtium officinale). A study indicated this fish primarily feeds on immature stages of aquatic insects like midges and caddisflies, in particular. Males typically court receptive females before claiming small nesting territories on rocks, logs, or other objects in shallow protected environments that they defend from other males by pushing them away several times their own size!
At home aquariums, one of the key considerations should be creating an environment similar to that of a darter’s natural habitat. A tank should feature gentle flow through its main part and powerhead or outside filter outflow located across its width – this will hasten water circulation while still leaving enough shallow areas for darters to forage and nest in shallow pools. Aquatic plants and minnows make excellent additions.
Habitat Predators
The school of darter is a very small stream fish with an olive green body adorned with dark eyes and an 11-spot black circle lateral band. It prefers inhabiting streambeds of small to medium-sized rivers with rubble, boulder, or bedrock bottoms as well as shallow pools with moderate to fast flow rates.
Beyond its habitat needs, this species must also avoid various predators. To lessen the risk of predation, they can hide under the substrate or within structural shelters to reduce predation risk – though this may become difficult with multiple habitat components that hinder movement or increase detection rates by predators.
However, without adequate structural shelters, this fish may need to move more often and is at greater risk of predator detection. To lower this risk a school of darters can seek cover in dense vegetation and avoid high-velocity areas of their stream.
Additionally, they utilize currents to escape predators by traveling upstream or downstream and inhabiting different water depths or flow velocities. Furthermore, this species often favors streamside brush clumps and boulders which provide additional hiding and foraging habitats.
As the fish migrates between habitats, its chances of predation increase greatly, due to seasonal patterns in predator migration and seasonal migration of prey fish. To mitigate this risk, darter schools have been seen traveling together in groups of four or more to increase survival odds when predators are concentrated at certain places within a stream.
Multiple mechanisms influence darter assemblage assembly, including phylogenetic clustering, abundance weighting, functional morphological similarity, and habitat filtering. Unfortunately, it is difficult to ascertain their magnitude and progression given they operate at such a fine temporal scale; for example, changes in behavior such as avoidance of certain lemming habitats during active movements while others become selectively selected when resting foxes are nearby can significantly alter space use patterns.
Breeding
Studies have been undertaken to identify breeding habitats for variegate darters. Their preferred spawning sites can be found along the Highland Rim in riffle areas of free-flowing streams with limestone or chert bedrock and coarse sand and gravel bedcover, where eggs are typically laid by females on gravel bed surfaces buried at the edge of pools and run downstream from pools or runs and in their margins. Spawning eggs occur by burying eggs in gravel deposits at these riffle areas in which many eggs may also be laid by multiple females who may then lay multiple egg nests within pools or runs that contain multiple riffles located downstream from pools or runs where eggs may also be laid within multiple pools or run to reach these highland Rim waters where limestone or chert bedrock surfaces are present containing coarse sand gravel deposits containing limestone or chert bedrock layers composed of limestone/chert bedrock with coarse sand gravel deposits where eggs buried into gravel beds where eggs burying occurs via burial into gravel beds beneath layers of coarse sand gravel bedrock layers beneath layers of loose-flowing streams on this Rim area typically comprising limestone/chert bedrock as well as coarse sand gravel beds where single female may deposit her eggs. Sometimes within one pool/run multiple females may lay eggs within its margins to place multiple eggs laid by multiple females she uses multiple times on multiple riffles located downstream from where pools/run margins are located downstream from pools/run margins by multiple females may lay eggs through multiple riffle areas downstream pool/run margins within that pool/run in which eggs laid directly below pools/run.
Darters face many threats that limit the availability of breeding habitat, such as water withdrawal and the overall degradation of river ecosystems from impoundments, dredging, gravel mining operations, poor land use practices, or waste discharge. Being adaptable and responsive is crucial for long-term survival; adaptability will be key.
To gauge population size and trend, each year 10 randomly selected riffles are sampled using mark-recapture and transect data from along the Levisa Fork mainstem between Dismal Creek confluence and Virginia/Kentucky border for mark-recapture data and mark-recapture transect data collection. Furthermore, small samples of fin tissue from every variegate darter captured are collected in order to assess DNA variation among captured fish allowing comparison among samples collected at various locations and years.
Darter schools present in specific stream reaches are an indicator that physical and biological conditions are conducive to their reintroduction. Although blue mask darter has been eradicated from Calfkiller River, if physical/chemical improvements allow successful reintroductions then suitable watersheds could become available, potentially making reintroduction possible again.
Understanding how environmental variables influence variegate darter occupancy is key to making informed restoration decisions. A variety of predictive models is utilized to assess this relationship: from simple estimates of abundance (naive estimates or model-averaged), through mark-recapture sessions and subsequent transect sampling, up to model averaged abundance estimates from mark-recapture sessions, estimated abundance from mark-recapture sessions or transect sampling and estimated abundance from mark-recapture sessions (with model averaged abundance estimates or estimate from mark-recapture sessions or subsequent transect sampling).
No matter the estimating technique employed, results demonstrate a positive relationship between mark-recapture estimates and subsequent transect sampled abundances of darter fish and mark-recapture estimates; and subsequent transect sampled abundances. This relationship can be explained by darters being more likely to occur at other riffles within their site if one has already been occupied by schools of darter.
