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Reassessment of Arkansas Crayfish Conservation Ranks

Arkansas Natural Heritage Commission - Thursday, July 16, 2020
by Dustin Lynch

The Arkansas Natural Heritage Commission (ANHC) has been working since its establishment in 1973 to protect and document the amazing biodiversity of the Natural State. This is accomplished through ANHC’s two major components -- the System of Natural Areas and the Heritage Program.

Bluff shelter pool at Devil's Eyebrow Natural AreaThe System of Natural Areas, comprised of 75 sites across the state, is a system of lands that are specifically managed to preserve, maintain, and restore the best remaining examples of the state’s rarest natural communities and species. ANHC’s natural areas offer a window into the pre-settlement past, when the landscape of Arkansas consisted of an intact mosaic of amazingly diverse natural community types, many of which have become all too rare in modern times.

Although the System of Natural Areas is more visible and well-known, the Arkansas Heritage Program is just as important. The Heritage Program maintains a dynamic biodiversity database that tracks the location and status of rare and imperiled species of plants and animals, as well as rare natural communities, across the state. Some of these species may be listed by the U.S. Fish and Wildlife Service (USFWS) as endangered or threatened (i.e. likely to become endangered), but many more species are not federally listed but still considered globally rare or rare in Arkansas. All these species are tracked by the ANHC as “elements of special concern.” The Heritage Program collects all known localities for these elements wherever they occur, not just at natural areas. Records in the database span a remarkable timeframe of natural observations, from the mid-1800s to the present. The database is continually updated from a variety of sources, as ANHC’s data specialists gather information from herbaria, museums, scientific publications, and research studies. At the same time, field biologists on ANHC’s research staff routinely travel across the state conducting on-the-ground (or in some cases, in-the-water) field surveys and biological inventories, continuously adding to our knowledge of Arkansas’s biodiversity.

ANHC’s Heritage Program is part of the greater Natural Heritage Network of 100 Heritage units (also known as Conservation Data Centers) that cover all 50 states, Canada, and many Latin American and Caribbean nations. All of these programs use a standardized methodology first developed by The Nature Conservancy in the 1970s. Consistency in methodology and cooperation among different Heritage programs throughout the network are crucial, because species ranges and natural communities do not adhere to political boundaries such as state or national borders. All this information is ultimately managed by NatureServe, a non-profit organization that maintains the world’s largest biodiversity information database and develops tools and methods to help us better interpret and understand it.

Ouachita Mountain crayfishA crucial part of this process of tracking elements of special concern is determining which species of plants and animals are most in need of protection so that we can expend effort surveying, mapping, and keeping close track of occurrences of those species. Prioritizing which species are most in need of protection involves the process of assigning conservation ranks to each species. Every species that occurs in Arkansas has both a global and a state conservation rank. The global rank (G-rank) describes how rare the species is globally, while the state rank (S-rank) describes how rare it is only in Arkansas. A species might be relatively common or widespread overall, i.e. have a relatively low G-rank, but be considered rare in Arkansas, i.e. have a relatively high S-rank. An example might be a widespread species at the periphery of its range in Arkansas that occurs only in one corner of the state. On the other hand, Arkansas is home to many rare regionally endemic species, i.e. those that occur only in one or two ecoregions, such as the Ozark Highlands, the Ouachita Mountains, or the Gulf Coastal Plain of Arkansas and adjacent states, and others that are state endemics, i.e. found only in Arkansas. These species typically have high G-ranks as well as high S-ranks. In the case of state endemics, the G and S ranks will be the same, since a globally rare species that only occurs in Arkansas is necessarily also rare in Arkansas.

NatureServe Conservation RanksConservation ranks range from 1 to 5. A rank of 1 is considered critically imperiled, 2 is imperiled, 3 is vulnerable, 4 is apparently secure, and 5 is secure. A crucial aspect of the ranking process is that these ranks must be dynamic, i.e. they are open to adjustment upward or downward. This might happen because a species has become rarer or more common, but it also may happen as we obtain new information about that species. In some cases, as new information becomes available, we may discover that a species we thought was very rare is more common than previously thought or vice versa. Conservation ranks are based on a large variety of factors, including range extent, number of occurrences, population size, ecological viability, environmental specificity, long and short-term trends, and the impact of all the threats facing a species across its range. ANHC actively tracks any species that has a G and/or S rank of 3 or higher as part of our official “Tracked Species List.”

Coldwater CrayfishThe first conservation ranks for crayfish in the state were assigned in 1986 to eight species with known conservation concerns. In 1989, 14 additional species were ranked, and in 2004 the first comprehensive ranking attempt was made for all crayfish species known in the state at the time. Rank revisions were made on some species as the need arose or as new information became available. These ranks were qualitative in nature and based on expert opinion utilizing a standardized set of contributing factors. Though these ranks were made based on the best available information at the time, this approach may lead to issues with consistency, repeatability, and transparency. Issues with some of the ranks included non-matching G and S ranks for state endemics, ranks that had not kept up with taxonomic changes, and some species that had simply never been formally ranked. Additionally, research in recent years has led to several new species being described in the state, all of which needed ranking.

For these reasons, one of the major projects I’ve been involved with for the past two years is a complete re-assessment of conservation ranks of every species and subspecies of crayfish, as well as the two freshwater shrimp species, that have been documented occurring in Arkansas or thought to potentially occur here. I’ve collaborated closely on this project with one of the state’s foremost crayfish experts, Brian Wagner, aquatic wildlife diversity biologist for the Arkansas Game and Fish Commission (AGFC), who has been studying crayfish in Arkansas for decades, and with Cindy Osborne, ANHC’s data manager and environmental coordinator. We’ve consulted throughout the process with a team of other aquatic biologists with crayfish expertise from a diverse assortment of organizations, including the University of Arkansas Cooperative Fish and Wildlife Research Unit, the AGFC’s Environmental Coordination Division, the USFWS, the Arkansas Department of Transportation, and Central Arkansas Water.

We’ve approached this project by using the NatureServe Rank Calculator, first developed by a NatureServe work group in 2004. While the rank calculator has not yet been implemented at all state Heritage Programs, it represents a much more well-defined process than the way ranks have been assigned in the past, automating the process to result in more consistent assignment of ranks using the full suite of ranking factors. The ranks produced by the calculator are weighted 70 percent by the rarity of the species, based on range extent, area of occupancy, number of occurrences, population size, and ecological integrity; and 30 percent by the threats facing the species. Threat assessment considers the impact, scope, and severity of all manner of threats, ranging from urban or agricultural development and other forms of ecosystem modification to direct exploitation to geologic events and the impacts of climate change.

Since we began this project in September 2018, we have examined all 64 taxa (species or subspecies) of crayfish known or thought to potentially occur in the state, as well as the two species of freshwater shrimp, taking into account all known distribution and occurrence data. We’ve used the rank calculator to produce a new S-rank for every taxa in Arkansas, as well as a new G-rank for all species that have limited ranges, such as regional endemics shared with one or two other neighboring states. These newly proposed G-ranks will be reviewed by our counterparts in the other states that have those species.

At the same time that we’ve re-calculated and re-assessed these conservation rankings, we’ve also written new accounts for every species in the AGFC’s Arkansas Wildlife Action Plan (AWAP), which heavily relies on the G and S ranks in the formula it uses to generate a priority score for every species. These priority scores heavily influence which species may receive State Wildlife Grant (SWG) funding for efforts to study and protect them. We’ve made an effort to revamp these accounts using citations from all the relevant scientific literature for each species, much of which has been published since the last time the accounts were written.

In June 2020, we completed our evaluations of all 66 taxa. In the process, we generated 63 S-ranks, 40 G-ranks, and 63 new AWAP species summaries. We generated S-ranks, G-ranks, and AWAP species accounts for four newly described species, and we reviewed three species of questionable or disputed occurrence in the state and determined there was not sufficient evidence to include these three species in the official list of crayfish species in Arkansas. We generated new S-ranks and AWAP species accounts for 22 species previously known from Arkansas that were unranked for the state and lacked AWAP accounts. Of the 37 species that were previously S-ranked for Arkansas, nine increased in rank (i.e. were ranked as rarer than before), 17 decreased in rank (i.e. were ranked as more common than before), and 11 remained the same. Of the 36 previously described and ranked species for which we proposed new G-ranks, 14 increased in rank (i.e. were ranked as rarer than before), seven decreased in rank (i.e. were ranked as more common than before), and 15 remained the same.

Williams' crayfishSpecific examples can illustrate just a few of the factors that might play a role in this process. An example of a species which increased in rank is the narrow-range endemic Coldwater Crayfish (Faxonius eupunctus), formerly ranked G2S1, which occurs only in northeast Arkansas and southeast Missouri. The species was formerly considered to occur in three watersheds – the Spring, Eleven Point, and Strawberry Rivers – but was recently split into three species with even smaller ranges, and true F. eupunctus is now considered restricted to the Eleven Point River. This species’ G-rank increased from G2 to G1, while its S-rank remained at S1. An example of a species which decreased in rank is Williams’ Crayfish (Faxonius williamsi), which occurs in northwest Arkansas and southwest Missouri. This species was formerly ranked G3S1, but surveys in recent years have uncovered many new populations in Arkansas, considerably expanding both the number of occurrences and the range extent. This species S-rank decreased from S1 to S3, while its G-rank remained the same.

Mena crayfishWhile it has been a massive undertaking, working on this project has been a rewarding experience. The meticulous nature of the project has often meant that in our ranking sessions, which typically last all day and are held about once a week, we only get to one or two species at a time. But focusing so intently on each species has provided a great opportunity to study each in detail. These ranking sessions have also frequently served as a springboard to plan fieldwork that helps us fill specific knowledge gaps, as it did when we decided to make a trip to some Ouachita Mountain streams to ascertain the identity of a pair of confusingly similar-looking “leopard-spotted’ crayfish species in the winter of 2019 (see The Mystery of the Leopard-spotted Crayfish).

The important conservation efforts of the ANHC and the many partners we work with across the state can only be effective when they are informed by accurate, precise, and up-to-date scientific information. In the case of conserving our rarest species, this is only possible through a dynamic and constantly updated database and periodic efforts such as this one to re-assess and adjust what we are doing as biologists and conservationists.

Photos (top to bottom):

Bluff shelter pool at Devil's Eyebrow Natural Area (NA). Photo by Dustin Lynch.

Ouachita Mountain Crayfish (Fallicambarus tenuis). Photo by Dustin Lynch.

NatureServe ranking key of global and state ranks. Those in red are tracked by the ANHC.

Coldwater Crayfish (Faxonius eupunctus), formerly ranked G2S1, but has recently been increased globally to G2, while the state ranking remains at S1. Photo by Dustin Lynch.

Williams' Crayfish (Faxonius williamsi), formerly ranked G3S1, but surveys in recent years have uncovered new populations in Arkansas, expanding both the number and occurrences and the range extent. Its S-rank decreased from S1 to S3, while its G-rank remained the same. Photo by Dustin Lynch.

The Mena Crayfish (Faxonius menae), which caused a trip to some Ouachita Mountain streams to ascertain the identity of a pair of confusingly similar looking "leopard-spotted" crayfish. Photo by Dustin Lynch. See The Mystery of the Leopard-spotted Crayfish to read more.

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