Species Status Assessment Report for the Barrens Darter (Etheostoma Forbesi)

Species Status Assessment Report for the
Barrens Darter (Etheostoma forbesi)

Version 2.0

Acknowledgements: This Species Status Assessment would not have been possible without the research and assistance of Dr. Richard Harrington, Yale University Department of Ecology and Evolutionary Biology, Dr. Hayden Mattingly and his students, Tennessee Tech University School of Environmental Studies, Dr. John Johansen, Austin Peay State University Department of Biology, and Mark Thurman, Tennessee Wildlife Resources Agency.

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TABLE OF CONTENTS

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Chapter 1: Introduction

The Barrens Darter (Etheostoma forbesi Page and Ceas 1992) is a small fish endemic (restricted to a locality or region) to streams in the Collins River watershed on the Barrens Plateau in middle Tennessee. The Barrens Darter was designated a Category 2 Candidate species in 1994 (59 FR 58982), and remained such until that list was discontinued in 1996 (61 FR 64481). A species assessment and listing priority form was completed for the Barrens Darter in 2006, but due to the limited amount of data available on the species at the time, it was not determined to be a candidate for listing at the time (USFWS 2006). The Barrens Darter was petitioned to be listed under the Endangered Species Act of 1973, as amended (Act), by the Center for Biological Diversity as part of the 2010 Petition to List 404 Aquatic, Riparian and Wetland Species from the Southeastern United States (CBD 2010, p. 432-433).

This SSA Report for the Barrens Darter provides the biological support for the decision on whether or not to propose to list the species as threatened or endangered and, if so, where to propose designating critical habitat. Importantly, the SSA Report is not the decision by the Service on whether this species should be proposed for listing as a threatened or endangered species under the Act. Instead, this SSA Report provides a review of the available information strictly related to the biological status of the Barrens Darter. The listing decision will be made by the Service after reviewing this document and all relevant laws, regulations, and policies, and the results of a proposed decision will be announced in the Federal Register, with appropriate opportunities for public input.

For the purpose of this assessment, we generally define viability as the ability of the Barrens Darter to sustain natural populations in its native range over time. Using the SSA framework (Figure 1.1), we consider what the species needs to maintain viability by characterizing the status of the species in terms of its resiliency, redundancy, and representation (Shaffer and Stein, 2000, entire; Wolf et al. 2015, entire).

• Resiliency describes the ability of populations to withstand stochastic events (arising from random factors). We can measure resilience based on metrics of population health; for example, birth versus death rates and population size. Highly resilient populations are better able to withstand disturbances such as random fluctuations in birth rates (demographic stochasticity), variations in rainfall (environmental stochasticity), or the effects of anthropogenic activities.

• Representation describes the ability of a species to adapt to changing environmental conditions. Representation can be measured by the breadth of genetic or environmental diversity within and among populations and gauges the probability that a species is

3capable of adapting to environmental changes. The more representation, or diversity, a species has, the more it is capable of adapting to changes (natural or human caused) in its environment. In the absence of species-specific genetic and ecological diversity information, we evaluate representation based on the extent and variability of habitat characteristics across the species’ geographical range and other factors as appropriate.

• Redundancy describes the ability of a species to withstand catastrophic events. Measured by the number of populations, their resilience, and their distribution (and connectivity), redundancy gauges the probability that the species has a margin of safety to withstand or can bounce back from catastrophic events
Figure 1-1 Species Status Assessment Framework

(such as a rare destructive natural event or episode involving many populations).
To evaluate the biological status of the Barrens Darter, both currently and into the future, we

assessed a range of conditions to allow us to consider the species’ resilience, redundancy, and

representation (together, the 3Rs). This SSA Report provides a thorough assessment of biology and natural history and assesses demographic risks, stressors, and limiting factors in the context of determining the viability and risks of extinction for the species. The format for this SSA Report includes: (1) the resource needs of individuals and populations (Chapter 2); (2) the Barrens Darter’s historical distribution and a framework for determining the distribution of resilient populations across its range for species viability (Chapter 3); (3) the likely causes of the current and future status of the species and determining which of these risk factors affect the species’ viability and to what degree (Chapter 4); and (4) a description of the viability in terms of resilience, redundancy, and representation (Chapter 5). This document is a compilation of the best available scientific and commercial information and a description of past, present, and likely future risk factors to the Barrens Darter.

Chapter 2: Biology and Life History

Taxonomy

The Barrens Darter was first described from Duke Creek (Figure 2-4) as Etheostoma forbesi by Page and Ceas in a larger review of the E. squamiceps (Spottail Darter) species complex that described five new species (Page et al. 1992, pp.633-634). Previous collections had be assigned to Spottail Darter, Dirty Darter, E. olivaceum, or Fringed Darter, E. crossopterum (Page et al. 1992, p.633). Near and Keck formally defined the Spottail Darter complex as the clade Stigmacerca in the subgenus Catonotus, the egg clustering darters (Near et al. 2011, p.595). This is a very diverse group of darters and includes the only species in the perch family (Percidae)

4known to produce sounds (Johnston and Johnson 2000, p.475). The Catonotus darters are also notable for the level of parental care the male provides by guarding the eggs (Etnier and Starnes 1993, pp.449-450).

Also within the Stigmacerca clade is the Fringed Darter, Etheostoma crossopterum, which is slightly larger than the Barrens Darter and is found in tributaries of the lower ends of Tennessee and Cumberland River systems. This species occurs as a disjunct population in the Barren Fork, primarily downstream from stream reaches where the Barrens Darter historically occurred.

Genetic Diversity

Endemic to headwater streams in the Collins River system, the Barrens Darter has a naturally narrow distribution. There have been no published population genetic studies on this species; however analysis of the mitochondrial gene, cytochrome b (cyt b), shows only a single common haplotype (set of genes inherited together) found in all populations across its range, with very few individuals bearing cyt b haplotypes that differ from this common one by one or two mutations (Richard Harrington, pers. comm.). Analyses of molecular variation of Barrens Darter cyt b haplotypes show no significant correlation of this limited genetic diversity with geographic distribution. Preliminary analysis of the nuclear gene S7, shows a similar pattern, with two common haplotypes distributed throughout the Barrens Darter range and no support for geographic structuring of the genetic variation. Ongoing work using a genomic sequencing technique (RADseq) may provide increased resolution. Given the limited geographic range of this species, this low level of genetic diversity is not unexpected, but may also point to adequate connectivity between watersheds.

Genetic analysis has also shown evidence of potential hybridization between Barrens Darters and Fringed Darters. A small number of specimens collected in Hickory Creek (Figure 2-4) that were initially identified morphologically as Fringed Darters were found to have Barrens Darter mitochondrial haplotypes. Preliminary nuclear genome analysis of these specimens showed that the nuclear genes matched Fringed Darters. Since the mitochondrial genome is maternally inherited, the data available at this time may indicate unidirectional hybridization. Without a larger sample size of nuclear data, it is not possible to tell whether this mitochondrial introgression happened recently or longer ago (Richard Harrington, pers. comm.).

Morphological Description

The Barrens Darter is a small, drab-colored, benthic darter, with an observed maximum length of 97 millimeters (mm) (3.8 inches (in)) (Hansen et al., 2006). As is typical of the subgenus Catonotus, Barrens Darters are laterally compressed (taller than wide), have rounded caudal (tail) fins, and, denoting their placement in the clade Stigmacerca, they have three dark spots in a vertical line on the base of the tail (Page et al. 1992, p.623). Barrens Darters are tan overall with brown mottling. Nuptial males, which are larger than females, become much darker with swelling developing in the head and nape region. The fins become mostly black, and the second dorsal fin shows 4-5 distinctive clear or yellow bars and a yellow-gold margin. The Fringed Darter is very similar in appearance to the Barrens Darter and occurs in some of the same stream systems, making identifications in the field problematic. Nuptial males are distinguishable by the pattern on the second dorsal fin, with Fringed Darters having 6-7 rows of clear or light yellow crescents and a white margin compared to the Barrens Darter described

5above. The third branch of the dorsal fin rays are greatly elongated in male Fringed Darters, but roughly equal with the other branches in the Barrens Darter. Females and juveniles of the two species are distinguishable meristically (using scale and fin ray counts) within the Caney Fork drainage as given by the counts in Table 2-1. The Barrens Darter also co-occurs with a third species of Catonotus, the Fantail Darter (Etheostoma flabellare), in Charles Creek, but the two species are distinguishable by the three spots on the base of the tail fin in Barrens Darters (Layman et al. 1993, p.68).

Table 2-1. Counts of second dorsal fin rays in Barrens Darter and Fringed Darter. Putative Fringed Darter from McMahan Creek and Barrens Darter from Scott Creek included. (Table provided by Rich Harrington, from meristic data collected by Tom Near).

Habitat

Barrens Darters inhabit small headwater streams with slab rock cobble substrates and strong groundwater influence (Figure 2-1). In a habitat association study, Zuber (2014, pp. 36-51) found Barrens Darters only in streams with a link magnitude of 5 or less. From a point in a stream, link magnitude is the number of unbranched source streams located upstream. Thus, a low link

magnitude measure, such as 5 or less, indicates the Barrens Darter’s affinity for small streams

and headwater habitats. Barrens Darters were also found to have an association with lower than average dissolved oxygen levels, which may be an indication of groundwater influence. As a headwater specialist species, tolerance of lower than average oxygen levels would be advantageous because headwaters are likely to become intermittent, with only stagnant pools available during the warmest periods of the year and during periods of drought. In times of drought, if the discharge of groundwater is severely reduced, Barrens Darters may move downstream into more permanent water if suitable habitat is available. No correlation was found with microhabitat variables outside of the spawning season (Zuber 2014, p. 46). During the spawning season, Barrens Darters congregate in shallow riffle and run areas with roughly 4- to 12-in slab rock cobble with cavities underneath. Barrens Darters, in comparison to Fringed Darters, have been observed using smaller nest rocks in shallower water (Bergen 2012, p. 436).

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This difference could be due to what was available where the observations occurred rather than a true difference of nest rock size and depth preference.

Figure 2-1. Barrens Darter Habitat. Left: Charles Creek, illustrating the slab rock cobble. Right: McMahan Creek, a stream with strong groundwater influence.

Lifecycle

The lifecycle of the Barrens Darter (Figure 2-2) and other members of its subgenus, Catatnotus, includes a unique reproductive strategy. Catonotus darters are cavity nesting egg clusterers that exhibit parental care. Life stage needs (Table 2-2) include nest guarding, whereby the male establishes a territory around a cavity under a flat rock and, based on its body size and quality of its nest cavity, attracts females. The males will also produce knocks, drums and purrs to court females as well as to defend the nest cavity from other males (Johnston and Johnson 2000, p.477). Once a female has chosen to spawn with a male, the pair will invert under the rock and the female will adhere eggs to underside of the rock in a single layer. Multiple females will lay eggs in a single in a single nest, and there may be over 900 in a nest. The male will clean the eggs and guard them from predators until they hatch in 5 - 11 days (Page 1974). Nesting occurs from mid-March to early June (Bergen et al 2012, p. 435)

Barrens Darter larvae are non-pelagic and stay near the substrate. The species matures in one to two years, though males may not breed until their second year due to female preferential selection of bigger males and the competition for nest cavities. Barrens Darters have a roughly three year lifespan and may rarely live to age four (Hansen 2006, pp. 65, 67). Prey items likely include midge, mayfly, and caddisfly larvae as well as microcrustaceans, similar to the known prey items consumed by Fringed Darters (Page 1974, entire).

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Figure 2-2. Barrens Darter Lifecycle Life stage Egg

Needs

Sources

Page 1974, entire Page 1980, entire Page 1974, entire Page 1980, entire Page 1974, entire Page 1980, entire
• Male Guarding • 60-75℉
Larvae
• Clean Gravel substrate
Juveniles
• Gravel or other suitable cover
• Small aquatic arthropods for food
• Appropriate water quality

Adult

Page 1974, entire

Page 1980, entire Hansen 2006, entire Bergen 2012, entire Zuber 2012, entire
• Clean water quality • Available cover • Stable hydrograph • Aquatic arthropods for food
• Clean slab rock cobble for spawning habitat
Table 2-2. Barrens Darter life stage needs

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Population Needs

Each Barrens Darter population needs to be able to withstand, or be resilient to, stochastic events or disturbances. Although they are infrequent, stochastic events are reasonably likely to occur and they can drastically alter the ecosystem where they happen. Classic examples of stochastic events include drought, major storms (hurricanes), fire, and landslides (Chapin et al. 2002, pp. 285-288). To be resilient to stochastic events, populations of Barrens Darter need to have an abundance of several hundred individuals and occupy multiple sites in multiple watersheds (spatial extent). Additionally, populations need to exist in locations where environmental conditions provide suitable habitat and water quality such that adequate numbers of individuals can be supported. Without all of these factors, a population has an increased likelihood for localized extirpation.

Species Needs

For a species to persist and thrive over time, it must exhibit attributes across its range that relate to either representation or redundancy (Figure 2-3). Representation describes the ability of a species to adapt to changing environmental conditions over time and encompasses the

“ecological and evolutionary patterns and processes that not only maintain but also generate

species” (Shaffer and Stein, p. 308). It is characterized by the breadth of genetic and environmental diversity within and among populations. For the Barrens Darter to exhibit adequate representation, resilient populations should occur in the ecoregion to which it is native (Eastern Highland Rim); these populations should occur at the widest extent possible across the historic range of the species; and they should occupy multiple tributaries in drainages where they are native. The breadth of morphological, genetic, and behavioral variation should be preserved to maintain the adaptive capacity of the species. Finally, natural levels of connectivity should be maintained between representative populations because it allows for the exchange of novel and beneficial adaptations where connectivity. Situations where connectivity is naturally lower and the species is more isolated can function as a mechanism for localized adaption and variation.

Redundancy describes the ability of a species to withstand catastrophic events. It “guards against

irreplaceable loss of representation” (Redford et al. 2011, p. 42; Tear et al. 2005, p. 841) and

minimizes the effect of localized extirpation on the range-wide persistence of a species (Shaffer and Stein, p. 308). Redundancy for the Barrens Darter is characterized by having resilience in multiple streams across the native range of the species. In terms of redundancy connectivity is important, because it allows for immigration and emigration and increases the likelihood of recolonization should a population become extirpated.

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Figure 2-3. How resiliency, representation, and redundancy are related to species viability

Historic Range and Distribution

The Barrens Darter is a highly endemic species with a very narrow distribution in Middle Tennessee in the headwaters of the Collins River, which is a tributary of the Caney Fork River in the Cumberland River Drainage. The range of this species lies in portions of Coffee, Cannon, Warren, and Grundy Counties. This species is limited to the headwaters of the Barren Fork and Collins Rivers and the upper portions of Charles Creek, a direct tributary to the Collins River. At the time of description, this species was known from six subwatersheds (Figure 2-4). Each of these subwatersheds acts as a separate management unit (MU), where the change within the unit is likely to outpace significant movement of Barrens Darters between the units (Mattingly and Johansen, 2017 interim report, p.2; Hayden Mattingly and Rich Harrington, pers. comm.). Barrens Darters were found in a seventh subwatershed in the headwaters of the Collins River during the preparation of this report which validates the record of a single Barrens Darter taken from Scott Creek in Grundy County during 2003 (Rich Harrington, pers. comm.).