Endangered and Threatened Wildlife and Plants; Removing Chipola Slabshell and Fat Threeridge From the Federal List of Endangered and Threatened Wildlife

SUPPLEMENTARY INFORMATION:

Executive Summary

Why we need to publish a rule. Under the Act, a species warrants delisting if it no longer meets the definition of an endangered species (in danger of extinction throughout all or a significant portion of its range) or a threatened species (likely to become an endangered species in the foreseeable future throughout all or a significant portion of its range). The Chipola slabshell is listed as a threatened species and the fat threeridge is listed as an endangered species, and we are proposing to delist them. We have determined the Chipola slabshell and fat threeridge do not meet the Act's definition of an endangered or threatened species. Delisting a species can be completed only by issuing a rule through the Administrative Procedure Act rulemaking process (5 U.S.C. 551 et seq.).

What this document does. This rule proposes the removal of the Chipola slabshell and fat threeridge from the List of Endangered and Threatened Wildlife based on their recovery; if we finalize this rule as proposed, the prohibitions and conservation measures provided by the Act, particularly through sections 4 and 7 for the Chipola slabshell and sections 7 and 9 for the fat threeridge, would no longer apply to these species.

The basis for our action. Under the Act, we may determine that a species is an endangered or threatened species because of any of five factors: (A) The present or threatened destruction, modification, or curtailment of its habitat or range; (B) overutilization for commercial, recreational, scientific, or educational purposes; (C) disease or predation; (D) the inadequacy of existing regulatory mechanisms; or (E) other natural or manmade factors affecting its continued existence. The determination to delist a species must be based on an analysis of the same factors.

Under the Act, we must review the status of all listed species at least once every five years. We must delist a species if we determine, on the basis of the best available scientific and commercial data, that the species is neither a threatened species nor an endangered species. Our regulations at 50 CFR 424.11 identify four reasons why we might determine a species shall be delisted: (1) The species is extinct; (2) the species has recovered to the point at which it no longer meets the definition of an endangered species or a threatened species; (3) new information that has become available since the original listing decision shows the listed entity does not meet the definition of an endangered species or a threatened species; or (4) new information that has become available since the original listing decision shows the listed entity does not meet the definition of a species. Here, we have determined that the Chipola slabshell and fat threeridge have recovered to the point at which they no longer meet the definition of an endangered species or a threatened species; therefore, we are proposing to delist them.

Information Requested

We intend that any final action resulting from this proposal will be based on the best scientific and commercial data available and be as accurate and as effective as possible. Therefore, we request comments or information from other concerned governmental agencies, Native American Tribes, the scientific community, industry, or any other interested parties concerning this proposed rule.

We particularly seek comments concerning:

(1) Reasons we should or should not remove Chipola slabshell or fat threeridge from the List of Endangered and Threatened Wildlife.

(2) Relevant data concerning any threats (or lack thereof) to the Chipola slabshell or fat threeridge, particularly any data on the possible effects of climate change as it relates to habitat, as well as the extent of State protection and management that would be provided to these mussels as delisted species;

(3) Current or planned activities within the geographic range of Chipola slabshell and fat threeridge that may have adverse or beneficial impacts on these species; and

(4) Considerations for post-delisting monitoring, including monitoring protocols and length of time monitoring is needed, as well as triggers for reevaluation.

Please include sufficient information with your submission (such as scientific journal articles or other publications) to allow us to verify any scientific or commercial information you include.

Please note that submissions merely stating support for, or opposition to, the actions under consideration without providing supporting information, although noted, do not provide substantial information necessary to support a determination. Section 4(b)(1)(A) of the Act directs that determinations as to whether any species is an endangered species or a threatened species must be made solely on the basis of the best scientific and commercial data available.

You may submit your comments and materials concerning this proposed rule by one of the methods listed in ADDRESSES . We request that you send comments only by the methods described in ADDRESSES .

If you submit information via https://www.regulations.gov, your entire submission—including any personal identifying information—will be posted on the website. If your submission is made via a hardcopy that includes personal identifying information, you may request at the top of your document that we withhold this information from public review. However, we cannot guarantee that we will be able to do so. We will post all hardcopy submissions on https://www.regulations.gov.

Comments and materials we receive, as well as supporting documentation we used in preparing this proposed rule, will be available for public inspection on https://www.regulations.gov.

Our final determinations may differ from this proposal because we will consider all comments we receive during the comment period as well as any information that may become available after this proposal. For example, based on the new information we receive (and if relevant, any comments on that new information), we may conclude that Chipola slabshell should remain listed as a threatened species, or we may conclude that Chipola slabshell should be reclassified from a threatened species to an endangered species. We may conclude that the fat threeridge should remain listed as an endangered species, or we may conclude that the fat threeridge should be reclassified from an endangered species to a threatened species. We will clearly explain our rationale and the basis for our final decision, including why we made changes, if any, that differ from this proposal.

Public Hearing

Section 4(b)(5) of the Act provides for a public hearing on this proposal, if requested. Requests must be received by the date specified in DATES . Such requests must be sent to the address shown in FOR FURTHER INFORMATION CONTACT . We will schedule a public hearing on this proposal, if requested, and announce the date, time, and place of the hearing, as well as how to obtain reasonable accommodations, in the Federal Register and local newspapers at least 15 days before the hearing. We may hold the public hearing in person or virtually via webinar. We will announce any public hearing on our website, in addition to the Federal Register . The use of these virtual public hearings is consistent with our regulations at 50 CFR 424.16(c)(3).

Peer Review

Species status assessment (SSA) teams prepared separate SSA reports for the Chipola slabshell and fat threeridge. The SSA teams were composed of Service biologists and staff from Texas A&M Natural Resource Institute, who consulted with subject area experts for both species. Each SSA report represents a compilation of the best scientific and commercial data available concerning the status of these species, including the impacts of past, present, and future factors (both negative and beneficial) affecting the species.

In accordance with our joint policy on peer review published in the Federal Register on July 1, 1994 (59 FR 34270), and our August 22, 2016, memorandum updating and clarifying the role of peer review of listing and recovery actions under the Act, we solicited independent scientific reviews of the information contained in each of the SSA reports. We sent the Chipola slabshell SSA report to three independent peer reviewers and received two responses. We sent the fat threeridge SSA report to four independent peer reviewers and received two responses. Results of these structured peer review processes can be found at https://www.regulations.gov. In preparing this proposed rule, we incorporated the results of these reviews, as appropriate, into the final SSA report for each species, which are the foundation for this proposed rule.

Summary of Peer Reviewer Comments

As discussed in Peer Review above, we received comments from two peer reviewers on each of the draft SSA reports. We reviewed all comments we received from the peer reviewers for substantive issues and new information regarding the information contained in the SSA reports. The peer reviewers generally concurred with our methods and conclusions, and provided additional information, clarifications, and suggestions, including clarifications in terminology and discussions of survey information related to detection versus no detection, and other editorial suggestions. Otherwise, no substantive changes to our analysis and conclusions within either of the SSA reports were deemed necessary, and peer reviewer comments are addressed in versions 1.0 of each SSA report (Service 2020, entire; Service 2021, entire).

Previous Federal Actions

On March 16, 1998, the Chipola slabshell was listed as a threatened species (63 FR 12664) and the fat threeridge as an endangered species (63 FR 12664) under the Act. On October 1, 2003, we completed a recovery plan for both species (68 FR 56647). A 5-year review of 37 Southeastern species, including Chipola slabshell and fat threeridge, was completed on September 27, 2006 (71 FR 56545). Critical habitat was designated for the Chipola slabshell in the Chipola River main stem and seven tributaries comprising a stream length of approximately 228 km (142 mi) (72 FR 64286; November 15, 2007). Critical habitat was designated for the fat threeridge in the lower Flint River system (397 km (247 mi)), the Apalachicola River system (161 km (100 mi)), and the Chipola River system (228 km (142 mi)) (72 FR 64286; November 15, 2007). We published notices of initiation of periodic status reviews for both species as required under section 4(c)(2) of the Act in 2018 (83 FR 38320, August 6, 2018); this proposed rule serves as completion of those status reviews. Recovery plan revisions were completed for both species on August 6, 2019 (84 FR 38284). The referenced documents and additional details can be found using our Environmental Conservation Online System (ECOS): https://ecos.fws.gov/.

Background

Species Information

Both the Chipola slabshell and fat threeridge are members of the family Unionidae, a large group of freshwater mussels represented by 298 species in North America. Both species are endemic to the Apalachicola-Chattahoochee-Flint River (ACF) River Basin of Alabama, Georgia, and Florida. The ACF River Basin extends approximately 620 kilometers (km) (385 miles (mi)) and spans 50 counties in Georgia, 8 in Florida, and 10 in Alabama (see figure 1, below). For more details about the ACF River Basin, refer to the SSA reports (Service 2020, pp. 12-15; Service 2021, pp. 26-50).

The Chipola slabshell occurs in the mainstem of the Chipola River and several large tributaries. The fat threeridge occurs in the mainstems of the Flint River, Chipola River, and Apalachicola River. Neither species has known occurrences within the Chattahoochee River basin.

General Mussel Biology

Freshwater mussels, including Chipola slabshell and fat threeridge, have a complex reproduction process involving parasitic larvae, called glochidia, that are wholly dependent on host fish. Mussels release sperm into the water column, which is taken in by the female, wherein fertilization and development of glochidia occurs in a restricted portion of the gills, called the brood pouch or marsupium. When mature, the glochidia are released to the water column to attach on the gills, head, or fins of fishes. Glochidia die if they fail to attach to a host fish, attach to an incompatible fish species, or attach to the wrong location on a host fish (Neves 1991, p. 254; Bogan 1993, p. 599). Once attached to the host, glochidia draw nutrients from the fish's tissue as they develop (Arey 1932, pp. 214-215). Time to development, from attachment of glochidia to maturation, ranges from just over 1 week to 6 weeks or more (Parmalee and Bogan 1998, p. 8).

Depending on the species, mussels are either short-term or long-term brooders. In short-term brooders, such as Chipola slabshell and fat threeridge, fertilization occurs in the spring or summer and glochidia are released shortly after they are fully developed. In long-term brooders, fertilization occurs in late summer or fall, and developed glochidia are held over winter and released in the following spring or summer (Haag 2012, pp. 39-40). Mature glochidia drop off their hosts and, if they settle in suitable habitat on the stream bottom, continue the remainder of their existence as free-living mussels. Newly released glochidia are juveniles that are reproductively immature but otherwise resemble adults, with both halves (valves) of the shell developed and poised for growth.

Freshwater mussels are relatively sedentary and, under their own power, capable of moving only short horizontal distances, typically up to a few yards or less in a year (Haag 2012, pp. 34-35). Given mussels' limited mobility, host fish are their primary mode of dispersal, and the hosts are essential for maintaining population connectivity. Host specificity varies, with some mussel species being compatible with a few fish species while others can transform from glochidia to juveniles on several fish species.

Chipola Slabshell

A thorough review of the taxonomy, life history, and ecology of the Chipola slabshell is presented in chapter 1 of the SSA report (Service 2020, pp. 3-24).

The Chipola slabshell is a freshwater mussel that does not exhibit sexual dimorphism in shell characters (Service 2020, p. 4). The species can attain a length of 85 millimeters (mm) (3.35 inches (in)), but typical length is between 47 to 76 mm (1.85 to 2.99 in). The Chipola slabshell has a chestnut colored periostracum (outer shell) with 1 to 4 dark annuli (growth) bands (Service 2020, p. 4). Within its range, Chipola slabshell is the only species with light and dark bands on periostracum and with salmon-colored nacre (inner layer of shell) inside the shell. The umbos (shell protrusions near the hinge) are prominent, well above the hingeline, thus inside the umbo cavity is deep.

Based on the size, shell characteristics, and traits from similar species in the genus Elliptio, the Chipola slabshell is thought to reach sexual maturity within 3-5 years and has an average lifespan of 15-20 years (Service 2020, p. 8). The Chipola slabshell is a short-term brooder (tachytictic), meaning immature mussels ( i.e., glochidia) are carried in the female's gills for a short time following spawning and released that same season. Females are gravid from early June to early July. The Chipola slabshell is a host-fish specialist, requiring a Centrarchid ( i.e., sunfish) host.

Currently, the Chipola slabshell is widespread within its range and common at some localities. A lack of consistent survey methods across observers and through time limits the discussion of abundance trends for Chipola slabshell, however historical data indicate approximately 32 records whereas current records (from 2005 onward) indicate approximately 138 (Service 2020, p. 62). The species' distribution is primarily continuous in one river system, including the Chipola River and its tributaries. The species inhabits silty sand substrates of large creeks and the main channel of the Chipola River, in slow to moderate current. Chipola slabshell appears to be more tolerant of soft sediments than other mussel species in the ACF River Basin. It co-occurs with more silt-tolerant species in stream bank habitats with slower currents, thus it has more available habitat than mid-channel-dwelling species (Service 2020, p. 15).

Fat Threeridge

A thorough review of the taxonomy, life history, and ecology of the fat threeridge mussel is presented in chapter 2 of the SSA report (Service 2021, pp. 14-25).

The fat threeridge is an almost square, inflated, solid, and heavy shelled freshwater mussel that typically reaches up to 102 mm (4 in) in length. Older, larger individuals are quite inflated, where their width approximates their height. The dark brown to black shell is strongly sculptured with seven to eight prominent horizontal parallel ridges. The prominent, parallel ridges and inflated shell (older specimens, especially) distinguish this species from other mussels within its range (Service 2021, p. 15).

The glochidia of fat threeridge, like most freshwater mussels, are obligate parasites on fish, and must attach to a host to transform into juvenile mussels; this parasitism serves as the primary dispersal mechanism for this relatively immobile group of organisms. To facilitate attachment, fat threeridge hookless glochidia are broadcast in a web-like mass that expands and wraps around a host. This method often is seen in host generalists because passive entanglement is nonselective. Reproductive studies confirm that fat threeridge is a host generalist, completing transformation on 23 species of fishes (Service 2021, p. 17). The fat threeridge is a short-term summer brooder. Females appear to be gravid when water temperatures reach 23.9 degrees Celsius (°C) (75 degrees Fahrenheit (°F)), usually in late May and June.

Because freshwater mussels are relatively long-lived and have limited mobility, habitat stability is a requirement shared by all unionids. Fat threeridge appears to be sensitive to the effects of sediment instability and completely reliant on stable fine sediment habitat patches. Excessive amounts of sediment and particulate matter can interfere with key aspects of mussel biology. The availability of stable sediment patches may help explain the restricted distribution in mainstem versus tributary environments, as the fat threeridge has never been found in a tributary stream. By their nature, tributaries are smaller in size than mainstems and have more dynamic flows and sediment transport (Fritz et al. 2018, p. 6). Thus, the fat threeridge is ecologically restricted/isolated to large river systems in low gradient areas with stable, very fine sediment patches (Service 2021, pp. 22-23).

Within its range in the ACF River Basin, fat threeridge is found in mainstem habitats in the Flint, Apalachicola, and Chipola rivers; there are no known collections from the Chattahoochee River (Service 2021, p. 26). At the time the fat threeridge was listed in 1998, there were very few existing records of the species, with the most seen at a site being 6 individuals (63 FR 12666). Current estimates in the middle Appalachicola alone are upwards of 7.7 million individuals (Service 2021, p. 47).

Regulatory and Analytical Framework

Regulatory Framework

Section 4 of the Act (16 U.S.C. 1533) and the implementing regulations in title 50 of the Code of Federal Regulations set forth the procedures for determining whether a species is an endangered species or a threatened species, issuing protective regulations for threatened species, and designating critical habitat for endangered and threatened species. On April 5, 2024, jointly with the National Marine Fisheries Service, the Service issued a final rule that revised the regulations in 50 CFR part 424 regarding how we add, remove, and reclassify endangered and threatened species and what criteria we apply when designating listed species' critical habitat (89 FR 24300). This final rule is now in effect. The Act defines an “endangered species” as a species that is in danger of extinction throughout all or a significant portion of its range, and a “threatened species” as a species that is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range. The Act requires that we determine whether any species is an endangered species or a threatened species because of any of the following factors:

(A) The present or threatened destruction, modification, or curtailment of its habitat or range;

(B) Overutilization for commercial, recreational, scientific, or educational purposes;

(C) Disease or predation;

(D) The inadequacy of existing regulatory mechanisms; or

(E) Other natural or manmade factors affecting its continued existence.

These factors represent broad categories of natural or human-caused actions or conditions that could have an effect on a species' continued existence. In evaluating these actions and conditions, we look for those that may have a negative effect on individuals of the species, as well as other actions or conditions that may ameliorate any negative effects or may have positive effects. The determination to delist a species must be based on an analysis of the same five factors.

We use the term “threat” to refer in general to actions or conditions that are known to or are reasonably likely to negatively affect individuals of a species. The term “threat” includes actions or conditions that have a direct impact on individuals (direct impacts), as well as those that affect individuals through alteration of their habitat or required resources (stressors). The term “threat” may encompass—either together or separately—the source of the action or condition or the action or condition itself.

However, the mere identification of any threat(s) does not necessarily mean that the species meets the statutory definition of an “endangered species” or a “threatened species.” In determining whether a species meets either definition, we must evaluate all identified threats by considering the species' expected response and the effects of the threats—in light of those actions and conditions that will ameliorate the threats—on an individual, population, and species level. We evaluate each threat and its expected effects on the species, then analyze the cumulative effect of all of the threats on the species as a whole. We also consider the cumulative effect of the threats in light of those actions and conditions that will have positive effects on the species—such as any existing regulatory mechanisms or conservation efforts. The Secretary determines whether the species meets the definition of an “endangered species” or a “threatened species” only after conducting this cumulative analysis and describing the expected effect on the species now and in the foreseeable future.

The Act does not define the term “foreseeable future,” which appears in the statutory definition of “threatened species.” Our implementing regulations at 50 CFR 424.11(d) set forth a framework for evaluating the foreseeable future on a case-by-case basis which is further described in the 2009 Memorandum Opinion on the foreseeable future from the Department of the Interior, Office of the Solicitor (M-37021, January 16, 2009; “M- Opinion,” available online at https://www.doi.gov/sites/doi.opengov.ibmcloud.com/files/uploads/M-37021.pdf ). The foreseeable future extends as far into the future as the U.S. Fish and Wildlife Service and National Marine Fisheries Service (hereafter, the Services) can make reasonably reliable predictions about the threats to the species and the species' responses to those threats. We need not identify the foreseeable future in terms of a specific period of time. We will describe the foreseeable future on a case-by-case basis, using the best available data and taking into account considerations such as the species' life-history characteristics, threat-projection timeframes, and environmental variability. In other words, the foreseeable future is the period of time over which we can make reasonably reliable predictions. “Reliable” does not mean “certain”; it means sufficient to provide a reasonable degree of confidence in the prediction, in light of the conservation purposes of the Act.

Analytical Framework

The SSA reports document the results of our comprehensive biological review of the best scientific and commercial data regarding the status of the Chipola slabshell and fat threeridge, including assessments of the potential threats to these species. The SSA reports do not represent our decisions on whether these species should be proposed for delisting. However, they do provide the scientific basis that informs our regulatory decisions, which involve the further application of standards within the Act and its implementing regulations and policies.

To assess Chipola slabshell and fat threeridge viability, we used the three conservation biology principles of resiliency, redundancy, and representation (Shaffer and Stein 2000, pp. 306-310). Briefly, resiliency is the ability of the species to withstand environmental and demographic stochasticity (for example, wet or dry, warm or cold years); redundancy is the ability of the species to withstand catastrophic events (for example, droughts, large pollution events); and representation is the ability of the species to adapt to both near-term and long-term changes in its physical and biological environment (for example, climate conditions, pathogens). In general, species viability will increase with increases in resiliency, redundancy, and representation (Smith et al. 2018, p. 306). Using these principles, we identified each species' ecological requirements for survival and reproduction at the individual, population, and species levels, and described the beneficial and risk factors influencing these species' viability.

The SSA process can be categorized into three sequential stages. During the first stage, we evaluated individual species' life-history needs. The next stage involved an assessment of the historical and current condition of these species' demographics and habitat characteristics, including an explanation of how these species arrived at their current condition. The final stage of the SSA involved making predictions about each species' responses to positive and negative environmental and anthropogenic influences. Throughout all of these stages, we used the best available information to characterize viability as the ability of these species to sustain populations in the wild over time. We use this information to inform our regulatory decisions.

The following is a summary of the key results and conclusions from the SSA reports; the full SSA reports can be found at Docket No. FWS-R4-ES-2024-0051 on https://www.regulations.gov.

Summary of Biological Status and Threats

In this discussion, we review the biological condition of each species and their resources, and the threats that influence these species' current and future conditions, in order to assess both species' overall viability and the risks to that viability. In addition, the SSA reports (Service 2020, entire; Service 2021, entire) document our comprehensive biological status review for each species, including an assessment of the potential threats to each species. The following is a summary of these status reviews and the best available information gathered since that time that have informed these decisions.

Species Needs

Both Chipola slabshell and fat threeridge share similar habitat needs, including stable stream channels; permanently flowing water to adequately deliver oxygen, enable passive reproduction, support host fish, deliver food items to the sedentary juvenile and adult life stages, and remove wastes; and good water quality ( i.e., free from harmful toxicants (such as chlorine, unionized ammonia, heavy metals, salts, pesticides), or at low enough concentrations to avoid adverse effects). The Chipola slabshell prefers predominantly sand, gravel, and/or cobble stream substrate with low to moderate amounts of silt and clay (Service 2020, pp. 15-16), whereas the fat threeridge prefers stable fine sediment habitat patches (Service 2021, p. 22).

Analysis Units

The Chipola slabshell consists of a single, panmictic population within the Chipola River basin; we delineated three subpopulations ( i.e., management units, MUs) to account for the two natural breaks in connectivity (Service 2020, pp. 64-65). Although these breaks do not prevent dispersal of infected host fish between subpopulations of the Chipola slabshell, we delineated the MUs based on the potential barriers to dispersal and genetic exchange. Since our knowledge of the level of genetic diversity is limited, it is possible MUs exhibit some natural variation in genetic diversity. Each subpopulation was broken into U.S. Geological Survey (USGS) 10-digit hydrologic unit codes (HUC-10s) as MUs (see table 1, below). These units reflect a spatial scale for which mussel survey data were available.