Federal Register / Vol. 88, No. 186 / Wednesday, September 27, 2023 / Proposed Rules 66351 

situations, such as general permits for 

specific source categories, to facilitate 

minor source emissions management in 

Indian country. Existing sources in 

Indian country may have PTE limits that 

preceded the EPA’s FIP for minor 

sources and, for that reason, were issued 

in a 40 CFR part 71 permit or FIP 

permitting provision applicable to 

Indian country. 

Consistent with EPA policy, the EPA 

will offer to consult with the potentially 

impacted tribes and other tribes upon 

their request. 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

The EPA interprets Executive Order 

13045 as applying only to those 

regulatory actions that concern 

environmental health or safety risks that 

the EPA has reason to believe may 

disproportionately affect children, per 

the definition of ‘‘covered regulatory 

action’’ in section 2–202 of the 

Executive Order. This action is not 

subject to Executive Order 13045 

because it does not directly regulate any 

emission source and will not have any 

direct impact on children’s health. The 

emissions reductions achieved by 

individual NESHAP are properly 

accounted for in those individual 

NESHAP rather than the General 

Provisions. This action will not change 

the level of emissions reductions 

achieved by those NESHAP. While we 

do not expect this action to have any 

direct impact on children’s health, 

preventing emissions increases will 

ensure protections achieved via any 

NESHAP that a source was subject to at 

the time of reclassification will provide 

continued protection achieved by any 

NESHAP that source was formerly 

subject to. 

H. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution, or Use 

This action is not a ‘‘significant 

energy action’’ because it is not likely to 

have a significant adverse effect on the 

supply, distribution, or use of energy. 

We have concluded that this action is 

not likely to have any adverse energy 

effects. 

I. National Technology Transfer and 

Advancement Act (NTTAA) 

This rulemaking does not involve 

technical standards. 

J. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations and Executive 

Order 14096: Revitalizing Our Nation’s 

Commitment to Environmental Justice 

for All 

The EPA believes that this action does 

not have disproportionate and adverse 

human health or environmental effects 

on communities with environmental 

justice concerns because it does not 

establish an environmental health or 

safety standard. The proposed 

amendments to the General Provisions 

are procedural changes and do not 

impact the technology performance nor 

level of control of the NESHAP 

governed by the General Provisions. 

While the EPA does not expect this 

action to directly impact the level of 

control of any particular NESHAP 

standards, this proposal is expected to 

enhance transparency, promote national 

consistency in EPA and citizen 

enforcement, and improve compliance 

assurance through clearer criteria for 

NESHAP reclassifications. The 

processes by which state programs and 

permits are approved under 40 CFR 

subpart E, includes requirements for 

public notice and comment as well as 

creating programs and permits that are 

federally enforceable by the EPA and 

citizens. These additional layers of 

oversight increase the likelihood that 

sources will continue to effectively 

operate air pollution control equipment 

and create a framework for the EPA and 

citizens to pursue enforcement actions if 

they do not. Additionally, the EPA finds 

that the safeguards proposed in this 

action will ensure that HAP emissions 

reductions are achieved, and the 

corresponding public health and 

environmental benefits from decreased 

HAP emissions, are maintained at 

sources that reclassify from major 

sources of HAP to area sources of HAP. 

List of Subjects in 40 CFR Part 63 

Environmental protection, Area 

sources, General provisions, Hazardous 

air pollutants, Major sources, Potential 

to emit. 

Michael S. Regan, 

Administrator. 

[FR Doc. 2023–21041 Filed 9–26–23; 8:45 am] 

BILLING CODE 6560–50–P 

DEPARTMENT OF THE INTERIOR 

Fish and Wildlife Service 

50 CFR Part 17 

[Docket No. FWS–R4–ES–2019–0069; 

FF09E21000 FXES11110900000 234] 

RIN 1018–BE14 

Endangered and Threatened Wildlife 

and Plants; Reclassifying the Virgin 

Islands Tree Boa From Endangered to 

Threatened With a Section 4(d) Rule 

AGENCY: Fish and Wildlife Service, 

Interior. 

ACTION: Proposed rule; withdrawal. 

SUMMARY: We, the U.S. Fish and 

Wildlife Service (Service), withdraw the 

proposed rule to reclassify the Virgin 

Islands tree boa (listed as Epicrates 

monensis granti) from endangered to 

threatened under the Endangered 

Species Act of 1973 (Act), as amended. 

This withdrawal is based on new 

information we received during the 

proposed rule’s public comment 

periods, specifically new survey results 

that indicate that the Virgin Islands tree 

boa is likely extirpated from Cayo 

Ratones. We also realized an error in 

calculations that reduced the resiliency 

of the Cayo Diablo population. After 

evaluating the status of the species 

following these changes, we find that 

the species still meets the Act’s 

definition of an endangered species. We 

have, therefore, determined that 

reclassification of this species is not 

appropriate at this time. Accordingly, 

we also withdraw the proposed 4(d) rule 

for the Virgin Islands tree boa. 

DATES: The proposed rule that 

published on September 30, 2020 (85 FR 

61700), to reclassify the Virgin Islands 

tree boa as threatened with a rule issued 

under section 4(d) of the Act is 

withdrawn on September 27, 2023. 

ADDRESSES: This withdrawal, comments 

on our September 30, 2020, proposed 

rule, and supplementary documents are 

available for public inspection on the 

internet at https://www.regulations.gov 

at Docket No. FWS–R4–ES–2019–0069 

and on the Service’s website at https:// 

www.fws.gov/office/caribbeanecological-services/library. 

FOR FURTHER INFORMATION CONTACT: 

Edwin E. Mun ̃iz, Field Supervisor, U.S. 

Fish and Wildlife Service, Caribbean 

Ecological Services Field Office, P.O. 

Box 491, Boquero ́n, PR 00622; 

telephone 787–405–3641; email: 

Caribbean_es@fws.gov. Individuals in 

the United States who are deaf, 

deafblind, hard of hearing, or have a 

speech disability may dial 711 (TTY, 


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TDD, or TeleBraille) to access 

telecommunications relay services. 

Individuals outside the United States 

should use the relay services offered 

within their country to make 

international calls to the point-ofcontact in the United States. 

SUPPLEMENTARY INFORMATION: 

Previous Federal Actions 

Please refer to the September 30, 

2020, proposed rule (85 FR 61700) to 

reclassify the Virgin Islands tree boa 

(which we refer to below as ‘‘Virgin 

Islands boa’’) for a detailed description 

of previous Federal actions concerning 

this species. The September 30, 2020, 

proposed rule opened a 60-day public 

comment period, ending November 30, 

2020. We then reopened the public 

comment period for an additional 30 

days, from April 26 to May 26, 2021, 

and held a public hearing on May 12, 

2021 (see 86 FR 22005; April 26, 2021). 

During both comment periods and at the 

public hearing, we accepted submission 

of new information and comments on 

the proposed reclassification. 

Summary of Justification for 

Withdrawal 

Based on the comments we received 

during both of the September 30, 2020, 

proposed rule’s public comment periods 

and at the May 12, 2021, public hearing, 

we made several changes and 

corrections throughout the species 

status assessment (SSA) report for the 

Virgin Islands boa (Service 2022, entire). 

We received substantive comments 

regarding the probable extirpation of 

Virgin Islands boas due to colonization 

of rats on Cayo Ratones, and we have 

included that information in all 

descriptions of that population and 

addressed it in our analysis. Results 

from a survey effort in September 2021 

by Puerto Rico Department of Natural 

and Environmental Resources (DNER) 

and other boa experts were provided to 

the Service; no boas or indirect evidence 

of boas were observed (Puente-Rolo ́n et 

al. 2021, p. 1) and the DNER affirms that 

the Cayo Ratones population is most 

likely extirpated (DNER 2019, p. 3). We 

also received comments on the 

characterization of the resiliency of the 

Cayo Diablo population, and upon 

reexamination of the current resiliency 

score, we realized we made an error in 

our calculations and subsequently have 

changed the resiliency of that 

population from moderately high 

resiliency to moderate resiliency. Upon 

incorporating these changes, we have 

determined that there are not sufficient 

data to support reclassifying the Virgin 

Islands boa from an endangered species 

to a threatened species. Accordingly, we 

are withdrawing our proposed rule to 

reclassify the Virgin Islands boa as a 

threatened species with a rule issued 

under section 4(d) of the Act (16 U.S.C. 

1531 et seq.). 

Proposal to Update the Scientific Name 

of the Virgin Islands Tree Boa 

In the September 30, 2020, proposed 

rule (85 FR 61700), we proposed to 

correct the Federal List of Endangered 

and Threatened Wildlife (List) to change 

the scientific name of the Virgin Islands 

tree boa from Epicrates monensis granti 

to Chilabothrus granti to reflect the 

currently accepted taxonomy. Virgin 

Islands boa is a distinct species, not a 

subspecies, and Epicrates is no longer 

the scientifically accepted genus for this 

species. However, because we are 

withdrawing the September 30, 2020, 

proposed rule (85 FR 61700), the Virgin 

Islands boa’s scientific name will 

remain Epicrates monensis granti in the 

List until we, in the future, publish a 

final rule recognizing the new 

taxonomy. 

Background 

A thorough review of the taxonomy, 

life history, ecology, and overall 

viability of the Virgin Islands boa is 

presented in the SSA report (Service 

2022, entire; available at https:// 

www.regulations.gov under Docket No. 

FWS–R4–ES–2019–0069). A summary 

of this information follows. 

The Virgin Islands boa is endemic to 

Puerto Rico and the Virgin Islands (U.S. 

and British). The Virgin Islands boa is 

a medium-length, slender, 

nonvenomous snake. The largest snoutvent lengths (SVL) recorded for the 

species were 1,066 millimeters (mm; 42 

inches (in)) for females and 1,112 mm 

(44 in) for males (total body lengths 

1,203 mm (47 in) and 1,349 mm (53 in), 

respectively; Tolson 2005, entire), 

although most specimens range between 

600 and 800 mm (24 and 31 in) SVL, 

with an average mass of 165 grams (6 

ounces) (USVI Division of Wildlife, 

unpublished data). Adults are graybrown with dark-brown blotches that 

are partially edged with black, and 

feature a blue-purple iridescence on 

their dorsal surface; the ventral surface 

is creamy white or yellowish white. 

Newborns, on the other hand, have an 

almost grayish-white body color with 

black blotches and weigh 2.0–7.2 grams 

(0.07–0.25 ounces) with SVLs of 200– 

350 mm (approx. 8–14 in) (Tolson 1992, 

entire; Tolson 2018, pers. comm.). 

The Virgin Islands boa occurs in 

subtropical dry forest and subtropical 

moist forest (Service 2009, p. 11). 

Subtropical dry forest covers 

approximately 14 percent (128,420 

hectares (ha); 317,332 acres (ac)) of 

Puerto Rico and the U.S. Virgin Islands 

(USVI), typically receives less than 750 

mm (29 in) rainfall annually (Ewel and 

Whitmore 1973, pp. 9–20), and is 

characterized by small (less than 5 

meter (m; 16 feet (ft)) deciduous trees 

with high densities of interlocking 

branches and vines connecting adjacent 

tree canopies (Ewel and Whitmore 1973, 

p. 10). Subtropical moist forest covers 

approximately 58 percent (538,130 ha; 

1,329,750 ac) of Puerto Rico and USVI 

and typically receives more than 1,100 

mm (43 in) of annual rainfall. It is 

dominated by semi-evergreen and 

evergreen deciduous trees up to 20 m 

(66 ft) tall with rounded crowns. The 

Virgin Islands boa has also been 

reported to occur in mangrove forest, 

thicket/scrub, disturbed lower 

vegetation, and artificial structures 

(Harvey and Platenberg 2009, p. 114; 

Tolson 2003, entire). 

Habitat needs for Virgin Islands boa 

can be divided into those for foraging 

and those for resting. Factors 

contributing to foraging habitat quality 

are tree density and connectivity, 

presence of arboreal and ground-level 

refugia, prey density, and rat presence/ 

density (Tolson 1988, pp. 234–235). 

Tree density is more important than tree 

species or diversity; Virgin Islands boas 

do not appear to prefer a particular tree 

species after accounting for availability 

and structure (Platenberg 2006, pers. 

comm.). The highest densities of Virgin 

Islands boas are found where there are 

few or no exotic predators and high 

densities of lizard prey (Tolson 1988, p. 

233). Resting habitat includes refugia for 

inactive boas to use during the day. 

Refugia can be the axils (angles between 

trunk and branches) of Cocos or Sabal 

species, tree holes, termite nests, or 

under rocks and debris (Tolson 1988, p. 

233). 

The Virgin Islands boa forages at night 

by gliding slowly along small branches 

in search of sleeping lizards (Service 

1986, p. 6). The primary prey for the 

Virgin Islands boa is the Puerto Rican 

crested anole (Anolis cristatellus), and 

the greatest concentrations of Virgin 

Islands boa are found where Anolis 

densities exceed 60 individuals/100 m2

(1,076 ft2; Tolson 1988, p. 233). Other 

prey species include ground lizard 

(Ameiva exsul), house mouse (Mus 

musculus), small birds, iguana (Iguana 

iguana) hatchlings, and likely other 

small animals encountered (MacLean 

1982, pp. 30–31, 37; Tolson 1989, p. 

165; Tolson 2005, p. 9; Platenberg 2011, 

p. 3). The Virgin Islands boa may also 

compete for prey and other niche 

components with the green iguana 

(Iguana iguana) and the Puerto Rican 


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racer (Borikenophis portoricensis), a 

snake native to Puerto Rico, USVI, the 

British Virgin Islands, and surrounding 

cays (small, low islands). 

Much of what is known about the 

Virgin Islands boa’s life history comes 

from studies in captivity. Lifespans in 

captivity often exceed 20 years, and 

sometimes exceed 30 years (7 percent of 

captive Virgin Islands boas exceeded 30 

years of age; Smith 2018c, pers. comm.), 

but typical lifespans in the wild are not 

known. Sexual maturity is reached at 2 

to 3 years of age (Tolson 1989, pp. 165– 

166; Tolson and Pin ̃ ero 1985, pp. 5–6), 

and boas are still reproductive at up to 

20 years of age (Tolson 2018, pers. 

comm.). Females breed biennially, but 

studies have suggested that annual 

breeding may occur in some conditions 

(Tolson and Pin ̃ ero 1985, pp. 6–7). 

Courtship behaviors and copulation 

occur from February through May, and 

interaction with conspecifics of the 

opposite sex appears to be necessary for 

reproductive cycling (Tolson 1989, p. 

165). The gestation period, observed 

from a single known copulation 

between two individuals, is about 132 

days (Tolson 1989, p. 165). Virgin 

Islands boas give birth to live young 

from late August through October to 

litters of 2 to 10 young, and litter size 

increases with female body size (Tolson 

2018, pers. comm.). 

The exact historical distribution of the 

Virgin Islands boa is unknown, but its 

present disjointed distribution suggests 

that it was once more widely distributed 

across small islands within its range. In 

the 1970s, when the Virgin Islands boa 

was listed under the Endangered 

Species Conservation Act of 1969, its 

range was identified as three islands: 

Puerto Rico (no specific site); St. 

Thomas, USVI (from a single record); 

and Tortola in the British Virgin Islands 

(BVI) (from one report) (44 FR 70677; 

December 7, 1979). When the recovery 

plan was written (1986), 71 individuals 

were reported in two populations: one 

on the eastern side of St. Thomas in the 

USVI, and one at Cayo Diablo, an 

offshore islet in Puerto Rico (Service 

2009, p. 6). 

Currently, the Virgin Islands boa 

occurs on six islands between Puerto 

Rico, USVI, and BVI: the eastern Puerto 

Rican islands of Cayo Diablo and 

Culebra; Rı ́o Grande on the Puerto Rican 

main island; eastern St. Thomas and an 

offshore cay in USVI (USVI Cay; an 

introduced population); and Tortola. 

The occurrence of a seventh population 

(also an introduced population) on the 

Puerto Rican cay of Cayo Ratones is 

considered uncertain after the 

reestablishment of rats on this island 

possibly sometime after 2004 (Service 

2022, p. 24). Surveys in April 2018 and 

September 2021 did not find Virgin 

Islands boas on Cayo Ratones (Island 

Conservation 2018, pp. 5, 17; DNER 

2021, unpublished data; Puente-Rolo ́n 

et al. 2021, entire), indicating this 

population is likely extirpated. Lastly, 

there is also one report from 2004 that 

the species occurs on Greater St. James 

Island in St. Thomas, but nothing is 

known about that potential population 

(Dempsey 2019, pers. comm.). In 2009, 

based on all known populations in 

Puerto Rico and the USVI, an estimated 

1,300–1,500 Virgin Islands boas were 

thought to occur (Service 2009, p. 8). 

However, some population numbers 

used for that estimate are speculative. 

The current overall estimate of the 

species is unknown, particularly with 

the likely extirpation of the Cayo 

Ratones population. Based on the 2022 

SSA report (Service 2022, entire), 

current population trend estimates for 

Puerto Rico and USVI are either 

declining, potentially declining, 

considered rare, or unknown, and most 

populations are small or considered rare 

(Service 2022, p. 30). 

The population on Tortola Island, 

BVI, was confirmed in 2018, but there 

are no specific data regarding the status 

of that population (McGowan 2018, 

pers. comm.). In addition, according to 

anecdotal reports, the species is thought 

to occur on Jost Van Dyke, Guana 

Island, Necker Cay, Great Camanoe, and 

Virgin Gorda of the BVI (Mayer and 

Lazell 1988, entire), but data and 

confirmed observations are limited. 

There is not enough information to 

reliably assess the status of Virgin 

Islands boa populations on those 

islands, and they are not included in 

our analysis. 

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. In 2019, 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 the criteria for designating 

listed species’ critical habitat (84 FR 

45020; August 27, 2019). On the same 

day, the Service also issued final 

regulations that, for species listed as 

threatened species after September 26, 

2019, eliminated the Service’s general 

protective regulations automatically 

applying to threatened species the 

prohibitions that section 9 of the Act 

applies to endangered species (84 FR 

44753; August 27, 2019). 

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. 

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 


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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 Act’s 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. The term 

‘‘foreseeable future’’ extends only so far 

into the future as we can reasonably 

determine that both the future threats 

and the species’ responses to those 

threats are likely. In other words, the 

foreseeable future is the period of time 

in which we can make reliable 

predictions. ‘‘Reliable’’ does not mean 

‘‘certain’’; it means sufficient to provide 

a reasonable degree of confidence in the 

prediction. Thus, a prediction is reliable 

if it is reasonable to depend on it when 

making decisions. 

It is not always possible or necessary 

to define foreseeable future as a 

particular number of years. Analysis of 

the foreseeable future uses the best 

scientific and commercial data available 

and should consider the timeframes 

applicable to the relevant threats and to 

the species’ likely responses to those 

threats in view of its life-history 

characteristics. Data that are typically 

relevant to assessing the species’ 

biological response include speciesspecific factors such as lifespan, 

reproductive rates or productivity, 

certain behaviors, and other 

demographic factors. 

Analytical Framework 

The SSA report (Service 2022, entire) 

documents the results of our 

comprehensive biological review of the 

best scientific and commercial data 

regarding the status of the species, 

including an assessment of the potential 

threats to the species. The SSA report 

does not represent a decision by the 

Service on whether the species should 

be listed as an endangered or threatened 

species under the Act. It does, however, 

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. The following 

is a summary of the key results and 

conclusions from the SSA report; the 

full SSA report can be found at Docket 

FWS–R4–ES–2019–0069 on https:// 

www.regulations.gov. 

To assess Virgin Islands boa’s 

viability, we used the three conservation 

biology principles of resiliency, 

redundancy, and representation (Shaffer 

and Stein 2000, pp. 306–310). Briefly, 

resiliency supports the ability of the 

species to withstand environmental and 

demographic stochasticity (for example, 

wet or dry, warm or cold years), 

redundancy supports 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 the species’ ecological 

requirements for survival and 

reproduction at the individual, 

population, and species levels, and 

described the beneficial and risk factors 

influencing the species’ viability. 

The SSA process can be categorized 

into three sequential stages. During the 

first stage, we evaluated the individual 

species’ life-history needs. The next 

stage involved an assessment of the 

historical and current condition of the 

species’ demographics and habitat 

characteristics, including an 

explanation of how the species arrived 

at its current condition. The final stage 

of the SSA involved making predictions 

about the 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 a species to 

sustain populations in the wild over 

time. We use this information to inform 

our regulatory decision. Our SSA was 

revised to reflect the comments and new 

information we received during both of 

the September 30, 2020, proposed rule’s 

public comment periods and at the May 

12, 2021, public hearing. 

Summary of Biological Status and 

Threats 

In this discussion, we review the 

biological condition of the species and 

its resources, and the threats that 

influence the species’ current and future 

condition, in order to assess the species’ 

overall viability and the risks to that 

viability. In the SSA report (Service 

2022, pp. 12–18), we reviewed all 

factors (i.e., threats, stressors) that could 

be affecting the Virgin Islands boa now 

or in the future. However, in this 

document, we will focus our discussion 

only on those factors that could 

meaningfully impact the status of the 

species. The risk factors affecting the 

status of the Virgin Islands boa vary 

from location to location, but generally 

include habitat loss and degradation 

from development, introduced 

predators, sea level rise (SLR) and a 

changing climate, and public attitudes 

towards snakes. Where habitat is 

available but the species is not present 

(i.e., most of the small islands in the 

eastern Puerto Rico bank and USVI), it 

is believed that absences are due to local 

extirpation resulting from habitat 

degradation and colonization of exotic 

species (Service 2009, p. 11). We 

discuss each of the risk factors below. 

Habitat Loss and Degradation— 

Development 

Virgin Islands boas occur on both 

privately and publicly owned land. 

Virgin Islands boas have been observed 

living in developed areas around 

residences and can persist within 

developed areas if habitat patches are 

available, but only if no cats or rats are 

around (Platenberg and Harvey 2010, p. 

552; Platenberg 2011, p. 11). 

Development continues to impact 

populations via habitat destruction, 

especially in St. Thomas, Rı ́o Grande 

(Puerto Rico), and Culebra Island where 

habitat has declined over decades. In St. 

Thomas, available habitat has declined 

due to development for resorts, condos, 

and related infrastructure, and habitat 

has become more constricted and 

isolated (Platenberg and Harvey 2010, p. 

552). In Puerto Rico, human populations 

are decreasing, but residential 

development continues to increase 

island-wide, including around protected 

areas (Castro-Prieto et al. 2017, entire). 

Consequences of human development 

on the boa and its habitat not only 

include habitat loss and fragmentation 

due to deforestation, but also mortality 

from vehicular strikes, an increase in 

predators such as cats and rats, and an 

increase in human–boa conflicts that 

results in snakes being killed because of 

fear of snakes (Service 2022, pp. 13–14). 

Predation and Competition 

One of the primary threats to Virgin 

Islands boa populations is predation by 

exotic mammalian predators, mainly 

cats and rats, and possibly, to a lesser 

degree, mongoose. Mongoose are not 

likely a major predator of Virgin Islands 

boa because mongoose are terrestrial 

and active during the day, while Virgin 


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Islands boas are arboreal and active 

primarily at night, although not 

exclusively (Service 2022, p. 14). Feral 

cats are known to prey upon boas 

(Tolson 1996b, p. 409), and cat 

populations around human 

development are further bolstered by cat 

feeding stations set up by residents. 

There has not been direct evidence of 

rats preying upon Virgin Islands boas, 

but boas are not present on islands with 

high densities of rats (Tolson 1986ab, 

unpaginated; Tolson 1988, p. 235). Rats 

likely negatively impact Virgin Islands 

boas by competing for prey, or by 

inducing behavioral changes in Anolis 

prey that make them less likely to be 

encountered by boas (Tolson 1988, p. 

235). However, rats may also predate on 

neonate boas (Service 1986, p. 12). 

Complete predator removal on large, 

developed islands is challenging, but is 

feasible on smaller cays. Prior to 

reintroduction of the boas, rats were 

eliminated from Cayo Ratones and the 

USVI Cay using anticoagulant poison 

(Tolson 1996b, p. 410), although Cayo 

Ratones was recolonized by rats 

sometime after August 2004, 

highlighting the importance of ongoing 

monitoring for rat presence after a 

removal project. Cayo Ratones was 

thought to harbor one of the most robust 

Virgin Islands boa populations, but 

during the April 2018 survey (Island 

Conservation 2018, p. 20) and more 

recent September 2021 survey (DNER 

2021, unpublished data; Puente-Rolo ́n 

et al. 2021, entire), no boas were found. 

Effects of Climate Change, Including 

Sea Level Rise 

Climate change will continue to 

influence the Virgin Islands boa’s 

viability into the future. Species such as 

the Virgin Islands boa, that are 

dependent on specialized habitat types 

or limited in distribution, are the most 

susceptible to the impacts of climate 

change (Byers and Norris 2011, p. 22). 

The climate in the southeastern 

United States and Caribbean has 

warmed about 2 degrees Fahrenheit (°F) 

from a cool period in the 1960s and 

1970s, and temperatures are expected to 

continue to rise (Carter et al. 2014, pp. 

398–399). Projections for future 

precipitation trends in this area are less 

certain than those for temperature, but 

they suggest that overall annual 

precipitation will decrease and tropical 

storms will occur less frequently but 

with more force (i.e., more category 4 

and 5 hurricanes) than historical 

averages (Carter et al. 2014, pp. 398– 

399; Knutson et al. 2010, pp. 161–162). 

With increasing temperatures and 

decreasing precipitation, drought could 

negatively influence Virgin Islands boa 

populations. After a severe drought in 

eastern Puerto Rico, Anolis populations 

crashed on Cayo Diablo, and body 

condition indices of the boas 

plummeted (Tolson 2018, pers. comm.). 

Sea levels are expected to rise 

globally, ranging from 0.2 m (7.9 in) to 

over 1 m (3 ft) of SLR by the end of the 

century (Reynolds et al. 2012, p. 3; 

Service 2022, p. 38). Local SLR impacts 

in the Caribbean will depend on how 

much the ocean level itself rises, and on 

land subsidence or changes in offshore 

currents, but are predicted to range from 

0.17 m (6.7 in) to 0.38 m (15.0 in) by 

2065 (Carter et al. 2014, p. 400; Service 

2022, p. 38). Impacts on terrestrial 

ecosystems can be temporary, via 

submergence of habitat during storm 

surges, or permanent, via saltwater 

intrusion into the water table, 

inundation of habitat, and erosion. SLR 

and hurricane storm surges in the 

Caribbean are predicted to inundate 

low-lying islands and parts of larger 

islands (Bellard et al. 2014, pp. 203– 

204). The low-lying islands of Cayo 

Diablo and the USVI Cay, which 

support Virgin Islands boa populations, 

and the island of Cayo Ratones, where 

we are uncertain if the island still 

supports a population, are all vulnerable 

to SLR and storm surges in the future. 

Boa populations on Rı ́o Grande, 

Culebra, and St. Thomas are not 

considered at risk from SLR; however, 

the three cays (Cayo Diablo, Cayo 

Ratones, and USVI Cay) could see 10– 

23 percent loss of low-lying habitat due 

to SLR over the next 30 years (Service 

2022, pp. 38–46). Past and current 

observations suggest that the species can 

survive major hurricane events, 

although lasting impacts to habitat, 

particularly die-off of vegetation 

inundated by storm surges, have been 

observed (Platenberg 2018, pers. comm.; 

Smith 2018c, pers. comm.; Tolson 1991, 

pp. 12, 16; Yrigoyen 2018, pers. comm.). 

Loss of habitat due to storm surge 

impacts is similar to loss of habitat due 

to development; loss of low-lying forest 

habitat could result in decreased habitat 

availability for the Virgin Islands boas 

and their prey. 

Persecution by Residents 

Intentional killing of the more 

common and larger sized Puerto Rican 

boa (Chilabothrus inornatus) due to fear 

or superstitious beliefs has been well 

documented (Bird-Pico ́ 1994, p. 35; 

Puente-Rolo ́n and Bird-Pico ́ 2004, p. 

343; Joglar 2005, p. 146). Thus, Virgin 

Islands boas in proximity to developed 

areas where people fear snakes are 

susceptible to intentional killings. 

Public encounters with Virgin Islands 

boas in the more populated Rı ́o Grande 

and Culebra locations are considered 

questionable because of the rarity of 

boas in those populations, and there are 

only a couple of anecdotal records of 

intentional killings in those areas 

(Service 2009, pp. 15–16). In the highly 

developed east side of St. Thomas, 

about 10 percent of the Virgin Islands 

boa records in St. Thomas are from boas 

killed by humans on private property 

(Platenberg 2006, unpublished data). We 

have no further information to assess 

the magnitude of this threat, but it is 

likely that intentional killings of Virgin 

Islands boas still occur, are not being 

documented, and would be particularly 

detrimental to rare populations such as 

in Rı ́o Grande. The Service is not aware 

of a law enforcement case related to the 

boa in Puerto Rico or the USVI. 

Populations that occur within protected 

areas are not expected to be exposed to 

this threat. 

Conservation Measures and Regulatory 

Mechanisms That Affect the Species 

Positive influences on the Virgin 

Islands boa’s viability have been habitat 

protection, predator control, and captive 

breeding and reintroduction. Two 

populations of Virgin Islands boa were 

reintroduced to protected cays after 

predators had been removed, one on 

Cayo Ratones (Puerto Rico) in 1993, and 

another on USVI Cay in 2002. Founders 

for these reintroductions came largely 

from a cooperative captive-breeding 

program initiated in 1985 between the 

Service, Puerto Rico DNER, U.S. Virgin 

Islands Department of Planning and 

Natural Resources (VIDPNR), and 

Toledo Zoological Garden. Cayo Diablo 

provided the founding individuals for 

the captive population that was 

reintroduced to Cayo Ratones (6 

kilometers (3.5 miles) away from Cayo 

Diablo), and St. Thomas provided the 

founding individuals for the captive 

population that was reintroduced to the 

USVI Cay (4 kilometers (2.5 miles) away 

from St. Thomas). 

The Cayo Ratones population 

originated from 41 captive-born boas 

(offspring of Cayo Diablo boas) released 

between 1993 and 1995. Post-release 

survival was high: 82.6 percent of 

individuals and 89 percent of neonates 

survived at least 1 year (Tolson 1996a, 

unpaginated). By 2004, the population 

had grown to an estimated 500 boas 

(Tolson et al. 2008, p. 68). 

Unfortunately, since 2004, Cayo Ratones 

has been recolonized by rats, and no 

boas were found during surveys in April 

2018 (Island Conservation 2018, pp. 5, 

20) and September 2021 (DNER 2021, 

unpublished data; Puente-Rolo ́n et al. 

2021, entire). However, because Virgin 

Islands boas are difficult to find, 


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additional surveys are needed to 

confirm whether a few individuals still 

persist or to conclude that the 

population is extirpated. 

The USVI Cay reintroduction was 

initiated with the release of 42 Virgin 

Islands boas in 2002 and 2003, 11 from 

captivity and 31 from St. Thomas. 

Follow-up surveys in 2003–2004 

provided an estimate of 168 boas (202 

boas per hectare), which researchers 

suspected was near carrying capacity for 

the island (Tolson 2005, p. 9). More 

recent surveys in March 2018 detected 

20 boas over 2 nights and 44 boas over 

3 nights in November and December 

2018 (Smith 2018ab, entire). These 

recent surveys revealed a potential 

decline in abundance and the loss of 

two prey species (Smith 2018ab, entire), 

possibly as a result of density 

dependence as the population 

approached carrying capacity after 

reintroduction. Differences in survey 

and analysis methodologies complicate 

direct comparisons of population size 

between the surveys. Recent surveys 

also indicate that there are no rats on 

the island. Additional surveys are being 

conducted by the VIDPNR that will help 

continue to monitor this population and 

refine current estimates. Factors for 

consideration for future reintroduction 

sites include the presence and amount 

of suitable habitat (e.g., appropriate 

forest structure, adequate prey base, 

available refugia), protection status or 

threat of development, the presence/ 

absence/eradication of exotic predators, 

and geomorphology that provides 

protection from SLR and hurricane 

storm surges that are likely to affect the 

persistence of low-lying habitat. 

Potential sites for new introductions 

have been suggested (Reynolds et al. 

2015, p. 499) and need to be further 

assessed, with one offshore island in St. 

Thomas as one of the primary sites. 

Some areas may require that predators 

be removed before boas are reintroduced 

and future monitoring is ensured to 

prevent recolonization by predators. In 

addition to reintroductions to new sites, 

augmentation of existing populations 

may prove beneficial or necessary for 

the persistence of existing populations, 

particularly on developed islands and 

cays where predators have become 

reestablished. 

Both Puerto Rico and the USVI have 

regulatory mechanisms established to 

protect the species and its habitat 

through consultation processes for the 

authorization of development projects. 

Presently, the Virgin Islands boa is 

legally protected under Puerto Rico’s 

Commonwealth Law No. 241–1999 (see 

title 12 of the Laws of Puerto Rico at 

section 107 et seq. (12 L.P.R.A. sec. 107 

et seq.)), known as Nueva Ley de Vida 

Silvestre de Puerto Rico (New Wildlife 

Law of Puerto Rico). This law has 

provisions to protect habitat for all 

wildlife species, including plants and 

animals. In addition, the species is 

protected by Puerto Rico DNER’s 

Regulation 6766 (Reglamento para Regir 

el Manejo de las Especies Vulnerables y 

en Peligro de Extincio ́n en el Estado 

Libre Asociado de Puerto Rico 

(Regulation 6766: To govern the 

management of threatened and 

endangered species in the 

Commonwealth of Puerto Rico)). Article 

2.06 of Regulation 6766 prohibits 

collecting, cutting, and removing, 

among other activities, listed plant and 

animal individuals within the 

jurisdiction of Puerto Rico (DRNA 2004, 

entire). In the USVI, Act No. 5665, 

known as the Virgin Islands’ Indigenous 

and Endangered Species Act, which is 

enforced by the VIDPNR, protects the 

species. 

Despite these regulations being in 

place, including the requirement for 

developers to conduct environmental 

assessments and mitigate damage to the 

species and habitat, the regulations have 

proved difficult to enforce, they are 

often ignored by developers, and they 

do not cover all development activities 

in all Virgin Islands boa habitat 

(Platenberg 2011, pp. 11–13). For 

example, in St. Thomas, major permit 

applications submitted for projects in 

the coastal zone require an 

environmental impact assessment that 

addresses endangered species and 

protected habitat, but these 

requirements do not apply to smaller 

projects or those outside of the coastal 

zone. Furthermore, as noted in one 

study, even though a protocol was 

developed and applied to delineate 

habitat on protected sites and identify 

mitigation strategies, the absence of a 

legal mechanism to enforce mitigation 

has led to varying success as developers 

are slow to accept, and often ignore, the 

mitigation process (Platenberg and 

Harvey 2010, pp. 551–552). 

Most offshore cays within the species’ 

range are part of the Territorial 

Government or protected as wildlife 

refuges, thus formally protecting Virgin 

Islands boa habitat for three of the six 

populations (i.e., Cayo Diablo, Cayo 

Ratones, and USVI Cay). Cayo Ratones 

and Cayo Diablo are included in La 

Cordillera Natural Reserve managed by 

the Puerto Rico DNER, and the offshore 

cay in USVI is managed and protected 

by the VIDPNR. Furthermore, even 

though Virgin Islands boa habitat on 

privately owned land on Culebra Island 

is currently under pressure from urban 

and tourism development and 

deforestation, more than 1,000 acres of 

suitable habitat on the island are 

protected within the Service’s Culebra 

National Wildlife Refuge. 

In conclusion, the Virgin Islands boa 

still faces the threat of development on 

St. Thomas, Rı ́o Grande, and Culebra 

Island, and regulatory mechanisms 

addressing this threat are difficult to 

enforce or do not cover all development 

actions affecting the species. Human 

development results in habitat loss from 

deforestation and fragmentation, 

mortality from vehicular strikes, and 

increased predation by cats and rats. In 

addition, impacts from changes in 

climate could affect habitat. Drought 

could negatively influence Virgin 

Islands boa populations through loss of 

prey. SLR and storm surges are expected 

to inundate low-lying islands, such as 

Cayo Diablo, Cayo Ratones, and the 

USVI Cay, which currently support 

Virgin Islands boa populations. Finally, 

persecution of boas by citizens, due to 

fear or superstition, can affect 

individual boas, although there has 

never been a systematic study of the 

impact of these events on the overall 

population. 

When considering conservation 

actions and how they influence the 

viability of Virgin Islands boa, about 

half of known localities where Virgin 

Islands boas occur are on small offshore 

islets managed for conservation. In 

addition, predator removal has been 

successful at smaller cays, such as USVI 

Cay, although the reestablishment of 

rats on Cayo Ratones illustrates the need 

for continued monitoring and removal 

efforts. Lastly, successful 

reintroductions of Virgin Islands boas 

occurred on these islands after the 

eradication of predators. 

Current Condition 

For the Virgin Islands boa to maintain 

viability, its populations, or some 

portion thereof, must be resilient. For 

the SSA report (Service 2022, entire), 

our classification of resiliency relied 

heavily on habitat characteristics in the 

absence of a certain population size for 

most populations or trend estimates. 

The habitat characteristics we assessed 

were degree of habitat protection (or, 

conversely, development risk), presence 

of introduced predators, and 

vulnerability to storm surges (Service 

2022, p. 31). 

Representation can be measured by 

the breadth of genetic or environmental 

diversity within and among populations 

and gauges the probability that a species 

is capable of adapting to environmental 

changes. A rangewide genetic analysis 

of the Virgin Islands boa showed there 

was little genetic variation; however, the 


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same study found that each sampled 

locality had unique mtDNA haplotypes, 

indicating a lack of gene flow between 

islands (Rodrı ́guez-Robles et al. 2015, 

entire). Therefore, in the SSA report we 

used genetics to delineate representative 

units. 

The species also needs to exhibit 

some degree of redundancy in order to 

maintain viability. Catastrophic events 

that could affect both single and 

multiple populations of the Virgin 

Islands boa include drought, hurricanes, 

and colonization or recolonization of 

exotic predators. This species occurs in 

geographically isolated groups and does 

not disperse from island to island to 

interact and interbreed; therefore, for 

purposes of analyzing redundancy, all 

boas within each island were 

considered to be individual 

populations. 

Resiliency 

Because resiliency is a populationlevel attribute, the key to assessing it is 

the ability to delineate populations. As 

discussed above, we considered all boas 

within each island to be single 

populations. On small offshore cays, 

what we define as a population might 

consist of a single interbreeding deme 

(or subdivision) of Virgin Islands boas. 

On larger islands, what we define as a 

population functions more as a 

metapopulation, with multiple 

interbreeding groups in isolated habitat 

patches that may interact weakly via 

dispersal and recolonization of 

extirpated patches. Alternately, multiple 

occupied patches on large islands may 

be completely isolated from one another 

(Service 2022, p. 20). 

Six island populations were 

considered: Cayo Diablo, Cayo Ratones, 

Culebra Island, Rı ́o Grande (Puerto 

Rico), St. Thomas, and USVI Cay 

(USVI). Further, one or more 

populations exist in the BVI (e.g., 

Tortola), but data are severely limited, 

and for the SSA report, we lacked 

sufficient data from these islands to 

incorporate them into our viability 

analysis. In addition, other populations 

may occur on other offshore islands in 

Puerto Rico and USVI, but most have 

not been searched for Virgin Islands 

boas and we could not confirm any to 

be extant at the time we completed our 

analysis. 

Resiliency scores for each population 

were generated by combining scores for 

three habitat metrics ((1) protection/ 

development risk, (2) exotic mammals, 

and (3) storm surge risk) and one 

population metric (population size and/ 

or trend, dependent on availability). 

Each metric was weighted equally, with 

the overall effect that habitat (three 

metrics) was weighted three times 

higher than population size/trend (one 

metric). For each metric, populations 

were assigned a score of ¥1, 0, or 1, as 

described below in table 1. 

The scores were based on the best 

available information for each 

population, gathered from the literature 

and species experts. Monitoring data are 

scarce. The Virgin Islands boa recovery 

plan (Service 1986, pp. 16–19) called for 

periodic monitoring to estimate 

population sizes and trends, but surveys 

since then have been few and far 

between. Survey methodology and 

reporting have varied from population 

to population, with survey results given 

as estimated abundances, estimated 

densities, or encounter rates per personhour of searching. The above-described 

factors in combination contribute to 

high levels of uncertainty in current and 

past population sizes, and how they 

have changed over time. Accordingly, 

resiliency classifications relied more 

heavily on habitat conditions than 

population size and trend estimates. 

TABLE 1—DESCRIPTION OF HABITAT AND POPULATION FACTOR SCORES TO DETERMINE THE VIRGIN ISLANDS BOA’S

POPULATION RESILIENCY

Score 

Habitat metrics Population metric 

Habitat protection/development 

risk 

Exotic 

mammals Storm surge risk Population Size/Trend * 

¥1 .................. Habitat not protected, at risk of 

being developed.

Exotic mammals present Topography and elevation 

leaves population vulnerable 

to storm surges.

Relatively low population size 

and/or declining trend. 

0 ...................... Some habitat protected, some 

at risk of being developed.

Not applicable (not 

present).

Not applicable (not an issue) ... • Relatively moderate population size and stable trend, 

or 

• High degree of uncertainty in 

population size/trends. 

1 ...................... Habitat protected in identified 

protected area.

Exotic mammals absent Protected by topography and 

elevation.

Relatively high population size 

and/or growth. 

* Population size/trend scores are relative and were based on the best available information for each population, gathered from the literature 

and species experts. 

The scores for each population across 

all metrics were summed, and final 

population resiliency categories were 

assigned as follows: 

Low Resiliency: ¥4 to ¥2 

Moderately Low Resiliency: ¥1 

Moderate Resiliency: 0 

Moderately High Resiliency: 1 

High Resiliency: 2 to 4 

Applying these resiliency categories 

to the six populations of Virgin Islands 

boa, we determined that two 

populations have moderate resiliency 

(Cayo Diablo and USVI Cay), one has 

moderately low resiliency (Culebra), 

two have low resiliency (Rı ́o Grande 

and St. Thomas), and one has no 

resiliency because it is presumed to be 

extirpated (Cayo Ratones). 

One of the populations classified as 

having moderate resiliency (Cayo 

Diablo) occurs on a small offshore 

island that is free of exotic rats and cats 

and is protected for conservation. Boas 

have been consistently found on Cayo 

Diablo, with an April 2018 survey 

detecting 10 boas (Island Conservation 

2018, entire), one in November 2018 

that detected 14 boas (DNER 2018, 

unpublished data), and one in April 

2022 that detected 2 boas (Smith 2022, 

unpublished data). Using the April 2018 

data, extrapolating the density within 

the transect area (2.9 boas per hectare) 

to the entire island, the model provides 

an estimate of 20 boas on the island (95 

percent confidence interval 13–39). This 

number is lower than earlier 

unpublished survey results; however, 

direct comparisons cannot be made with 

past surveys because of different survey 

and analytical methodologies (Service 

2022, p. 23). The previous efforts in 

1993 had marked over 250 snakes in 

Cayo Diablo (Tolson 1996b, p. 411), 


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with an estimate of approximately 500 

boas in the cay. Because of the protected 

and exotic-mammal-free state of the 

habitat, but with potentially declining 

numbers, this Cayo Diablo population is 

considered to have moderate resiliency 

to demographic and environmental 

stochastic events and disturbances (e.g., 

fluctuations in demographic rates, 

variation in climatic conditions, illegal 

human activities). 

The USVI Cay population, also on a 

protected offshore island with no exotic 

mammals, was also determined to have 

moderate resiliency. Previous survey 

efforts from 2004 resulted in a 

population estimate of 168 snakes 

(Tolson 2005, p. 9). Recent surveys have 

revealed a potential decline in 

abundance and the loss of two prey 

species (Smith 2018ab, entire), possibly 

as a result of density dependence as the 

population approached carrying 

capacity after reintroduction. Over two 

separate survey efforts in 2018, 

researchers found a total of 64 boas, 

including 10 recaptures (Smith 2018ab, 

entire). Additional surveys are being 

conducted by the VIDPNR, and although 

we do not have the results, additional 

boas have been detected (VIDPNR 2022, 

unpublished data). 

The Culebra population, with some 

portions of habitat protected as part of 

Culebra National Wildlife Refuge, was 

determined to have moderately low 

resiliency. Surveys in 2018 found no 

boas (Island Conservation 2018, p. 20); 

however, two individuals were 

documented in February 2019 within 

the Culebra National Wildlife Refuge 

(Puente-Rolo ́n and Vega-Castillo 2019, 

p. 18). In October 2019, another 

individual was confirmed in an area 

outside of the refuge (Roma ́n 2019, pers. 

comm.). 

Three of the populations (Rı ́o Grande, 

Culebra, and St. Thomas) with 

moderately low or low resiliency occur 

on larger and higher elevation islands, 

which provide more protection from 

storm surges, but have more human–boa 

interactions, habitat loss and 

fragmentation from development, and 

exotic cats and rats. Recent surveys in 

2018 on Rı ́o Grande found three boas 

(three survey nights) (Island 

Conservation 2018, p. 20). For St. 

Thomas, there have been no recent 

systematic surveys for the species as 

much of eastern St. Thomas is 

inaccessible due to private ownership or 

impenetrable habitat. Previous 

uncertain conservative estimates for this 

population ranged from 300 to 400 

individuals (Tolson 1991, p. 12) to 

fewer than 100 individuals based on 

effective population size estimates 

(Reynolds et al. 2015, p. 498). 

The remaining Cayo Ratones 

population is classified as not having 

resiliency because of the recolonization 

of rats on the island and subsequent 

declining trend of boas, which we 

presume to be extirpated, as no boas 

were detected during recent survey 

efforts conducted in April 2018 and 

September 2021. 

Representation 

A rangewide genetic analysis of 

Virgin Islands boa showed that there 

was little genetic variation within the 

species (Rodrı ́guez-Robles et al. 2015, p. 

150), supporting the idea that there is 

only one representative unit of Virgin 

Islands boa. However, each sampled 

island, and each sampled locality 

within the same island, had unique 

mtDNA haplotypes, indicating a lack of 

gene flow between islands/populations 

(Rodrı ́guez-Robles et al. 2015, p. 150). 

These results suggest that each 

population has a different genetic 

signature, perhaps as a result of genetic 

adaptations to their local environment, 

or genetic drift with increasing isolation 

of small populations. The 

reintroduction program took this view, 

and managed captive populations 

sourced from Cayo Diablo and St. 

Thomas separately (Tolson 1996b, p. 

412). To minimize the chances of 

introducing individuals poorly suited to 

their new environment, the captive 

population sourced from Cayo Diablo 

founded the reintroduced population on 

nearby Cayo Ratones, and the captive St. 

Thomas population founded the 

reintroduced population on the nearby 

USVI Cay (Tolson 1996b, p. 412). 

In addition to genetic differences, the 

six populations also have noticeable 

phenotypic differences. These are not 

just limited to coloration differences 

between USVI and Puerto Rican 

populations (Tolson 1996b, p. 412); 

Cayo Diablo reportedly has lighter 

coloration than the Rı ́o Grande and 

Culebra populations (Tolson 2018, pers. 

comm.). The Rı ́o Grande population also 

occurs in a different habitat type 

(subtropical moist forest) than the others 

(subtropical dry or littoral forest; Tolson 

1996b, p. 410). 

In light of this information, we 

considered each of the four natural 

populations in Puerto Rico and USVI as 

a representative unit (see table 2, 

below). The Cayo Diablo population is 

considered to have moderate resiliency. 

As this was the source for the now 

presumed extirpated Cayo Ratones 

population, there is only one population 

representing the Cayo Diablo genetic 

signature. The USVI Cay population was 

sourced from St. Thomas, so there are 

two populations with St. Thomas 

representation, with neither considered 

to have high resiliency. The other two 

natural populations, Culebra and Rı ́o 

Grande, both characterized as having 

moderately low or low resiliency, have 

not been used for captive breeding and 

reintroduction, and so have no 

additional populations on other islands 

with the same genetic characteristics. 

Overall, two of four representative units 

have at least one moderately resilient 

population. 

TABLE 2—REPRESENTATION: NUMBER OF VIRGIN ISLANDS BOA POPULATIONS OF EACH RESILIENCY CLASS IN EACH REPRESENTATIVE UNIT, CORRESPONDING TO NATURAL (NOT INTRODUCED) POPULATIONS, WHICH THEMSELVES CORRESPOND TO UNIQUE GENETIC SIGNATURES

Natural population 

(genetic signature) 

High or 

moderately 

high resilience 

populations 

Moderate 

resilience 

populations 

Low or 

moderately 

low resilience 

populations 

or extirpated 

Cayo Diablo ................................................................................................................................. 0 1 1 

Culebra ........................................................................................................................................ 0 0 1 

Rı ́o Grande .................................................................................................................................. 0 0 1 

St. Thomas .................................................................................................................................. 0 1 1 

While currently we could consider 

the USVI Cay reintroduced population 

(currently with moderate resiliency) to 

be a redundant population sharing the 

same genetic signature and adaptive 

potential as its source population, all 


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islands occupied by Virgin Islands boa 

are isolated from each other. Without 

human-mediated movement of boas 

between islands, reintroduced 

populations are expected to diverge 

genetically from their source 

populations over time, and may at some 

point in the future (decades to centuries; 

Reynolds et al. 2015, entire) be different 

enough to be considered their own 

unique representative unit. 

Redundancy 

Redundancy describes the ability of a 

species to withstand catastrophic 

events. Measured by the number of 

populations, their resiliency (ability of a 

species to withstand environmental and 

demographic stochasticity (e.g., wet or 

dry years)) and their distribution (and 

connectivity), redundancy gauges the 

probability that the species has a margin 

of safety to withstand or return from 

catastrophic events (such as a rare 

destructive natural event or episode 

involving many populations). 

The exact historical distribution of the 

Virgin Islands boa is unknown, but its 

present disjointed distribution suggests 

that it was once more widely distributed 

across small islands within its range, 

which have been subject to local 

extirpations from habitat degradation, 

invasive species, and historical climate 

and sea level changes. However, for 

current redundancy, we identified the 

five populations in Puerto Rico and 

USVI. As discussed above, two of these 

populations are considered to have a 

moderate level of resiliency, which 

provides some ability to withstand the 

effects of catastrophic events. However, 

these populations are considered small 

and potentially declining or trend 

unknown. Therefore, overall 

redundancy for the species is low. 

Current Condition Summary 

Of the six assessed populations, the 

Cayo Diablo population and the USVI 

Cay population have moderate 

resiliency and the Culebra population 

has moderately low resiliency. The 

other three assessed populations 

currently have low resiliency or are 

likely extirpated (Cayo Ratones). 

Redundancy for the species includes 

populations on five islands in Puerto 

Rico and USVI, and possibly more in 

the BVI, although islands in the BVI are 

not part of this assessment. 

Representation consists of four 

representative units, one of which has 

two populations representing its genetic 

signature, and two of the four units have 

populations with moderate levels of 

resiliency. 

The Virgin Islands boa has 

demonstrated some ability to adapt to 

changing environmental conditions over 

time from both anthropogenic threats 

(e.g., habitat disturbance due to 

development) and natural disturbances 

(e.g., predation and hurricanes). 

Compared to the species’ distribution at 

the time of listing (see 35 FR 16047; 

October 13, 1970), which included three 

locations (Puerto Rico, St. Thomas, and 

Tortola), the species currently has five 

populations (potentially more if others 

are eventually confirmed). Two of the 

five current populations exhibit 

moderate levels of resiliency, whereas 

three exhibit moderately low to low 

resiliency. One other assessed 

population is presumed extirpated 

(Cayo Ratones). 

We note that, by using the SSA 

framework to guide our analysis of the 

scientific information documented in 

the SSA report, we have not only 

analyzed individual effects on the 

species, but we have also analyzed their 

potential cumulative effects. We 

incorporate the cumulative effects into 

our SSA analysis when we characterize 

the current and future condition of the 

species. Our assessment of the current 

and future conditions encompasses and 

incorporates the threats individually 

and cumulatively. Our current and 

future condition assessment is iterative 

because it accumulates and evaluates 

the effects of all the factors that may be 

influencing the species, including 

threats and conservation efforts. 

Because the SSA framework considers 

not just the presence of the factors, but 

to what degree they collectively 

influence risk to the entire species, our 

assessment integrates the cumulative 

effects of the factors and replaces a 

standalone cumulative effects analysis. 

Future Conditions 

Because we determined that the 

current condition of the Virgin Islands 

boa is consistent with an endangered 

species (see Determination of Status, 

below), we are not presenting the results 

of the future scenarios in this 

withdrawal. For more information on 

the future condition, future threats, and 

future scenarios for the Virgin Islands 

boa, see the SSA report (Service 2022, 

pp. 36–60). 

Determination of Virgin Islands Boa’s 

Status 

Section 4 of the Act (16 U.S.C. 1533) 

and its implementing regulations (50 

CFR part 424) set forth the procedures 

for determining whether a species meets 

the definition of ‘‘endangered species’’ 

or ‘‘threatened species.’’ 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 a 

species meets the definition of 

‘‘endangered species’’ or ‘‘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. 

Status Throughout All of Its Range 

Compared to the species’ distribution 

at the time of listing (see 35 FR 16047; 

October 13, 1970), which included three 

locations (Puerto Rico, St. Thomas, and 

Tortola), Virgin Islands boa currently 

has five extant populations (potentially 

more if others are eventually 

confirmed), and one presumed 

extirpated population. None of the 

populations exhibit high resiliency; 

only two of the six current populations 

exhibit moderate level of resiliency 

(Cayo Diablo and USVI Cay), one has 

moderately low resiliency (Culebra), 

two exhibit low resiliency (Rio Grande 

and St. Thomas), and one is considered 

presumed extirpated (Cayo Ratones). 

Recent surveys indicate that current 

population trend estimates are either 

declining, potentially declining, 

considered rare, or unknown and most 

populations are small or considered rare 

(Service 2022, p. 30). Three of the 

populations are currently impacted by 

habitat loss and degradation by 

development, three populations are at 

high risk from storm surges, and three 

of five populations are under imminent 

threat by exotic mammal predation. The 

species does not have enough current 

redundancy, lacking highly resilient 

populations and having only two 

moderately resilient populations; thus, 

the species is at risk from catastrophic 

events. In addition, as the species lacks 

multiple resilient populations that 

contribute to the genetic diversity of the 

species, thus limiting species 

representation or overall future adaptive 

capacity. 

In summary, due to the new 

information we received during both of 

the September 30, 2020, proposed rule’s 

public comment periods and at the May 

12, 2021, public hearing, we find that 

there is no longer sufficient evidence to 

justify reclassifying the Virgin Islands 

boa as a threatened species, and the 


ddrumheller on DSK120RN23PROD with PROPOSALS1
66360 Federal Register / Vol. 88, No. 186 / Wednesday, September 27, 2023 / Proposed Rules 

species still meets the Act’s definition of 

an endangered species. The new 

information included the probable 

extirpation of Virgin Islands boas due to 

colonization of rats on Cayo Ratones, 

and an error in calculations affecting the 

current resiliency score for the Cayo 

Diablo population. Based on our revised 

SSA report (Service 2022, entire) 

incorporating this new information, 

estimates of current resiliency for the 

Virgin Islands boa are low, as are 

estimates for representation and 

redundancy. The Virgin Islands boa 

faces a variety of ongoing threats from 

habitat loss and degradation from 

development, introduced predators, SLR 

and a changing climate, and public 

attitudes towards snakes. Given current 

rates of resiliency, populations are 

vulnerable to extirpation from stochastic 

events, in turn, resulting in concurrent 

losses in representation and 

redundancy. For these reasons, the 

Virgin Islands boa is in danger of 

extinction throughout its range. 

Status Throughout a Significant Portion 

of Its Range 

Under the Act and our implementing 

regulations, a species may warrant 

listing if it is in danger of extinction or 

likely to become so in the foreseeable 

future throughout all or a significant 

portion of its range. We have 

determined that the Virgin Islands boa 

is in danger of extinction throughout all 

of its range and accordingly did not 

undertake an analysis of any significant 

portion of its range. Because the Virgin 

Islands boa warrants listing as 

endangered throughout all of its range, 

our determination does not conflict with 

the decision in Center for Biological 

Diversity v. Everson, 435 F. Supp. 3d 69 

(D.D.C. 2020) (Everson), which vacated 

the provision of the Final Policy on 

Interpretation of the Phrase ‘‘Significant 

Portion of Its Range’’ in the Endangered 

Species Act’s Definitions of 

‘‘Endangered Species’’ and ‘‘Threatened 

Species’’ (79 FR 37578; July 1, 2014) 

providing that if the Service determines 

that a species is threatened throughout 

all of its range, the Service will not 

analyze whether the species is 

endangered in a significant portion of its 

range. 

Determination of Status 

Our review of the best available 

scientific and commercial information 

indicates that the Virgin Islands boa 

continues to meet the Act’s definition of 

an endangered species. Therefore, in 

accordance with section 4(b)(6)(A)(i)(IV) 

of the Act, we withdraw our proposed 

rule to reclassify the Virgin Islands boa 

as a threatened species with a rule 

issued under section 4(d) of the Act. 

References Cited 

A complete list of references cited in 

this document is available on the 

internet at https://www.regulations.gov 

and upon request from the Caribbean 

Ecological Services Field Office (see FOR

FURTHER INFORMATION CONTACT). 

Authors 

The primary authors of this document 

are the staff members of the Fish and 

Wildlife Service’s Species Assessment 

Team and the Caribbean Ecological 

Services Field Office. 

Authority 

The authority for this action is the 

Endangered Species Act of 1973, as 

amended (16 U.S.C. 1531 et seq.). 

Martha Williams, 

Director, U.S. Fish and Wildlife Service. 

[FR Doc. 2023–20946 Filed 9–26–23; 8:45 am] 

BILLING CODE 4333–15–P 


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