Provision of Services to Develop a Risk Assessment

Provision of Services to Develop a Risk Assessment Protocol for Alien Species and

Conduct Risk Assessment and Advise on Management of Alien Herpetofauna in

Hong Kong

Working Paper No. 3 (Final)

30 January 2020

Environmental Strategy, Conservation and Management Co. Ltd. Unit 1701, 17/F, Prosperity Millennia Plaza 663 King’s Road, North Point, Hong Kong T: (852) 2811 2278 | E: [email protected]

mailto:[email protected]

Working Paper No. 3

Table of Content

1. Introduction ..................................................................................................................................... 1

a) Background .................................................................................................................................. 1

b) Objectives of the Working Paper No. 3 ....................................................................................... 2

2. Study Approach ............................................................................................................................... 3

a) Evaluations of overseas examples of eradication/ management options for herpetofauna ...... 3

b) Rationales for species prioritisation ............................................................................................ 3

c) Best eradication/ management options ...................................................................................... 4

3. Results ............................................................................................................................................. 4

a) Evaluations of overseas examples of eradication/ management options for herpetofauna ...... 4

b) Rationales for species prioritization .......................................................................................... 10

c) Best eradication/ management options .................................................................................... 13

4. Discussion .................................................................................................................................... 177

5. References ................................................................................................................................... 199

List of Tables

Table 1 Matrix table for prioritisation of the four herpetofauna species with overall risk level of “medium”

or above.

Environmental Strategy, Conservation and Management Co. Ltd. i

Working Paper No. 3

Environmental Strategy, Conservation and Management Co. Ltd. 1

1. Introduction

a) Background

Invasive alien species (IAS) can cause serious impacts on native biodiversity (Rands et al., 2010) and there

are many documented cases of species extinction and population declines due to them (e.g. Clavero and

Garcia-Berthou, 2005; Molnar et al. 2008). Moreover, IAS impose enormous costs on agriculture, forestry,

fisheries and human health (Wittenberg & Cook, 2001). According to Article 8(h) of the Convention on

Biological Diversity (CBD), contracting parties are encouraged to prevent the introduction of alien species,

and to control or eradicate those alien species which threaten ecosystems, habitats or species as far as

possible and as appropriate. The Aichi Biodiversity Target 9 of CBD relates to the identification and

prioritization of IAS and invasion pathways, and their control and management. The Sustainable

Development Goal 15.8 also states that “by 2020, introduce measures to prevent the introduction and

significantly reduce the impact of invasive alien species on land and water ecosystems and control or

eradicate the priority species”.

Trade is one of the main means through which IAS can be introduced either intentionally or

unintentionally. Measures to restrict the introduction of IAS may be very trade restrictive and can have

devastative consequence on trade (Standards and Trade Development Facility, 2013). For instance, the

Asian longhorn beetle arrived in North America and Europe most likely through the infested wood

packaging material and killed many hardwood trees in forests. This led to new US rules requiring wooden

packing materials from China to be chemically or heat treated to prevent further infestations on local

trees. It was estimated that between $12 and $16 billion, or 17 to 22 percent of total imports from China

to US were affected (Meyer, 1998).

These impacts have led to various response measures in many countries and regions. For example, in

2010 it was found that 55% of the countries signatory to the CBD have adopted legislative tools to

regulate IAS (McGeoch et al., 2010). Some countries, such as Great Britain, have developed IAS strategies.

In the European Union, Regulation (EU) 1143/2014 on invasive alien species (the IAS Regulation) entered

into force on 1 January 2015, fulfilling Action 16 of Target 5 of the EU 2020 Biodiversity Strategy.

In Hong Kong, there are a number of established IAS in the terrestrial, freshwater and marine

environment and control measures are in place for some of them. Since Hong Kong is a free port, the

flow of goods, ships, vehicles, flights and people from around the world is immense and the risk of both

intentional and unintentional introduction of alien species is very high. Many live animals and plants are

imported for food, pets, agriculture, aquaculture, landscaping and ornamental purposes. Some of these

may escape or are intentionally released to the wild. To better understand the risks posed by the arrived

or potential alien species and to prioritize the species for management/preventative measures, a

standardized risk assessment tailored to the Hong Kong situation should be developed.

Working Paper No. 3


The purpose of this study “Provision of Services to Develop a Risk Assessment Protocol for Alien Species

and Conduct Risk Assessment and Advise on Management of Alien Herpetofauna in Hong Kong” (the

Services hereafter) is, in response to Action 7 of the Hong Kong Biodiversity Strategy and Action Plan

2016-2021, to develop a protocol for conducting risk assessment of IAS, making reference to

international best practices. The protocol should be applicable to a wide range of taxonomic groups.

Specific objectives stated in the service specifications are as follows:

To review international best practices in managing IAS

To develop a generic risk assessment protocol for alien species

To assess the risks of potential and arrived alien herpetofauna using the protocol developed

To recommend management options for priority herpetofauna species

In addition to above, the Contractor will also attend meetings to present preliminary findings and

respond to views expressed by participants of the meetings.

b) Objectives of the Working Paper No. 3

Environmental Strategy, Conservation and Management Co. Ltd. (ESCM, the Contractor) was awarded by

Agriculture, Fisheries and Conservation Department (the Proponent) on 19 November 2018 to carry out

the Services. The Services will be implemented within a period of 12 months. Following the submission of

Working Paper No. 1 - Review of international IAS Strategies and recommendations to the formulation of

an IAS strategy for Hong Kong, Working Paper No. 2 - Protocol for Risk Assessment and Risk Assessment

for Herpetofauna, was prepared according to the tender document and submitted in Month 8 of the

contract period. The paper included a generic risk assessment protocol for Hong Kong, explained in

details the information requirements and outlines the procedure of risk assessment. It also documented

the assessment results of the arrived and potential herpetofauna and several alien plants and animals

that were used to test the assessment protocol. An expert workshop was also arranged on 29 October

2019 to discuss the herpetofauna assessment, and the protocol and assessment were revised based on

the comments received during the iterative process. The overall risk of four IAS herpetofauna species

ranked as “Moderate” (no species ranked as high) during the assessment exercise would be subject to

recommendations of management options in Working Paper No. 3. These are Rhinella marina,

Eleutherodactylus planirostris, Lithobates catesbeiana and Trachemys scripta elegans.

The objectives of this Working Paper No. 3 - Recommendations of Eradication/ Management Options are

to evaluate overseas examples of eradication/ management options for herpetofauna, identify the best

eradication/ management options and explain the rationales for species prioritisation. Due to the time

required to address comments and revise both the protocol and the Working Paper No. 2 after the expert

meeting, it was agreed that Working Paper No. 3 would be delivered in Month 12 instead of original

programme (Month 11) of the contract period.

Working Paper No. 3


2. Study Approach

a) Evaluations of overseas examples of eradication/ management options for

herpetofauna

Overseas examples of eradication and management options for herpetofauna in general, including

preventing their introductions (Kraus, 2009) and those that are specific to the four selected species are

reviewed (D’Amore, 2012; Ficetola et. al., 2012; Shine, 2012; CABI, 2019; Global Invasive Species

Database, 2019). No management or eradication programme targeting Eleutherodactylus planirostris can

be found in the literature (Kraus, 2009; CABI, 2019; Global Invasive Species Database, 2019).

Eleutherodactylus coqui (Sin and Radford, 2007; Beard and Pitt, 2012), a closely related species with

rather similar biology and invasion pathway, was used as a surrogate to gain useful information on the

management measures that can be applied to E. planirostris. Particular attentions were paid to the

appropriateness of the management/ eradication options in the Hong Kong context.

b) Rationales for species prioritisation

The assessed alien herpetofauna species with overall risk level of ‘Medium’ or above were selected for

consideration of the best eradication/ management options. Four species were short-listed (see above).

Management/eradication measures are resource-demanding and often require sustained efforts to be

effective. Therefore, prioritisation is needed to ensure the limited resources are committed to actions

that are likely to be most cost-effective. The ranking of alien species based on (1) their relative

environmental and socio-economic impacts and (2) the relative priority of actions to effectively and

efficiently prevent or mitigate the impacts (McGeoch et. al., 2016) was used as a prioritizing tool.

For the four selected species, they are in different stages of the invasion process. Rhinella marina is a

potential IAS that has not yet arrived in Hong Kong. Lithobates catesbeiana has been in the food/pet

trade and individuals have been recorded in the wild but not yet established. While Eleutherodactylus

planirostris and Trachemys scripta elegans have already established and widespread locally. The priority

management options should be targeted to effectively and efficiently deal with the three stages of the

invasion process. That is (1) preventing introductions of R. marina, (2) early-detection and rapid-response

to eradicate incipient populations of L. catesbeiana, and (3) eradicating/controlling well-established E.

planirostris and T. scripta elegans to reduce the negative impacts.

For the relative environmental and socio-economic impacts, the Impact Scores in the risk assessment of

the four selected species were compared. The effectiveness and efficiency of the management options

for each species were based on the resources required, the duration of actions, the likelihood of success

and public support. Overseas experiences of the management measures for the target IAS or the

surrogate (covered in 3a) were used to provide the information. A matrix capturing all these sub-

categories were created for the management actions for each species. These together with the impact

Working Paper No. 3


scores were used to prioritise species for eradication/management. Detailed eradication/management

actions best suited for each priority species will be elaborated in the following section.

c) Best eradication/ management options

Based on the overseas examples of eradication and management measures (including preventing

introductions) relevant to the selected herpetofauna species (in 3a) and the species prioritization (in 3b),

recommendations would be made on the best eradication/ management options against these IAS in

Hong Kong.

As mentioned in 2(b), the four selected species are in different stages of the invasion process. Therefore,

the best eradication / management options recommended for each of them target the respective

invasion stage they are currently at.

3. Results

a) Evaluations of overseas examples of eradication/ management options for

herpetofauna

General Approach

Similar to other IAS, the most effective way to reduce impacts from alien amphibians and reptiles are

having a prevention programme. However, as shown in the review in Working Paper 1, very few places

have a strict biosecurity policy and legislation restricting the importation of alien species. Herpetofauna

attracts even less attention than plants and insect pests in this regard. Only New Zealand and Australia

ban the importation of amphibians and reptiles. Hawaii allows the importation of dozens of species that

are approved for commercial sale, permits the importation of several dozen additional species by

scientific and educational institutions and ban the remaining (Kraus, 2009). Other places do not have any

import control or just have restriction on a handful of herpetofaunal species known as pests, such as the

prohibition of import of Brown Tree Snake, three tortoise species, turtles under four inches and large

constrictors in USA (Kraus, 2009) and the ban on importation of Lithobates catesbeiana to E.U. in 1990’s

(D’Amore, 2012). Very different results were obtained from the different approaches. New Zealand has

not had a naturalized alien amphibian or reptile since the 1960’s while USA, Europe and Asia have seen

many amphibian and reptile introductions (Kraus, 2009).

There are not many eradication and/or management programme for alien herpetofauna and such control

operations have met with relatively little success when compared with plants or mammals (Kraus, 2009).

Eradication and or management methods can be broadly divided into (1) physical removal by using

different traps, nets, hand, shooting, electrofishing and sometimes with the assistance of trained

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detector dogs, (2) chemical treatment using lethal chemicals or hot water, (3) biological control using

parasites, and, (4) habitat alteration to kill the alien herpetofauna present and/or to make the habitats

unavailable or unsuitable. Quite often, an integrated approach employing a combination of the methods

is used to eradicate or control invasive herpetofauna.

(1) Physical Removal

Physical removal is often used in the eradication or long-term control of alien herpetofauna but they are

resource demanding and volunteers/communities are often involved to provide the necessary

manpower. This is because invasive alien herpetofauna often have cryptic habits, with high reproductive

rates and high densities (Kraus, 2009). It would be a huge challenge to catch all the individuals in a big

area and successful eradication have only been achieved for incipient populations over relatively small

areas. Some successful examples, other than the selected species, listed in Kraus (2009) are:

- Eradication of Limnodynastes dumerilii in northern New Zealand that involved surveys in all the

catchments of the mountain range within two months of its discovery and all tadpoles and

metamorphs found were destroyed.

- Eradication of Bufo gargaizans in northern Okinawa by removal of adults, eggs and tadpoles from

late 1980’s through to mid-1990’s.

- Eradication of an isolated population of Xenopus laevis in USA by trapping that may have been helped

by severe winter freezing.

More often, physical removal is used in combination with other methods to control the population

density or to prevent the IAS from spreading into sensitive sites/habitats. The Guam programme in

controlling the Brown Tree Snake, Boiga irregularis, is a good example. Much of the efforts have been

directed to reduce snake densities surrounding airports and seaports, and, to search hitch-hiking snakes

in out-bound cargo and vehicles in order to prevent this invasive snake from spreading to other Pacific

Islands. Dense array of custom-designed, flap-door traps with live mouse as bait is used to capture snakes

in order to reduce its population and is supplemented by nighttime searches of fences which are often

used by this arboreal species (Engeman and Vice, 2002). Cargo searches are largely carried out by the dog

team with trained Jack Russell Terriers and snake detection rate can reach 50-80% (Engeman and Vice,

2002). Reduction of rat populations through the use of bait stations and the use of cage traps to reduce

exotic bird numbers help to lower prey populations around ports and increase the efficacy of snake traps

(Engeman and Vice, 2002). In addition, other methods, such as deploying barriers, devising attractants,

repellents, toxicants and toxicant-delivery systems are also being used or developed to control Brown

Tree Snakes on Guam (Engeman and Vice, 2002; Kraus, 2009).

Amphibians and reptiles are highly diverse groups in terms of habitats, food habits, reproductive biology

and activity pattern. Effective physical removal methods have been documented for only a very small

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number of them (see Kraus, 2009) and these methods cannot be copied and expected to work similarly

well on other species. In general, trapping is often more effective than hand-collecting (e.g. Muller and

Schwarzkopf, 2018) and the type of trap used depends on the biology and behavior of the species. For

instance, the use of basking trap seems to be more effective in catching T. scripta elegans than funnel

traps (Ficetola et al., 2012) but this may not work on many Asian turtles that seldom bask. Effective

means of locating and removing targeted alien amphibians and reptiles have to be investigated. Some

notable measures are covered in the species-specific examples.

(2) Chemical and Hot Water Treatment

Chemical treatment may involve applying lethal chemicals or hot water to kill amphibians. Over 90

chemical agents have been tested by US Department of Agriculture as potential frog toxicants and

caffeine, citric acid and hydrated lime were found to be effective and approved for frog control (Beard

and Pitt, 2012). Caffeine was later retracted for use as control because of human health effects. Citric acid

is the minimum risk chemical and is used legally in Hawaii to control E. coqui. It has been used

successfully in killing Eleutherodactylus coqui frogs and eggs both in nursey plants cargo and also in the

wild (Beard and Pitt, 2012). However, it has phytotoxic effects on plants and can leave white to yellow

dots on leaves (Pitt and Sin, 2004). Hot water spray or vapour (45oC for three minutes) is also effective in

eliminating frogs and their eggs from potted plants during quarantine but may have effects on some

plants (Beard and Pitt, 2012).

Toxicants have also been tested and used to control Brown Tree Snake on Guam. A large variety of

chemicals have been examined and Rotenone, propoxur, natural pyrethrins, allethrin, resmethrin,

diphacinone, warfarin and aspirin were found to be orally toxic to brown tree snakes (Brooks et al. 1998).

Other compounds have been tested and acetaminophen is highly effective and delivered through frozen

pinky mice (Savarie et al., 2001). Due to the much depleted bird fauna on Guam as a result of Brown Tree

Snake predation, the only concern of poisoning of non-target native wildlife include the Mariana Crow,

Coconut Crab and land hermit crabs. Monitoring showed that there were no primary or secondary

hazards and this type of toxic baits have been used on Guam (Engeman and Vice, 2002) and large-scale

aerial delivery has been tested and found to be effective (Clark et al., 2018).

Toxic fumigants had also been looked at to treat outbound cargo to kill stowaway Brown Tree Snake.

Several pyrethrin/pyrethroid insecticide foggers were found to be not effective while methyl bromide is

effective, it is highly toxic, expensive and time consuming to apply (Engeman and Vice, 2002). Hence

cargo fumigation to control Brown Snake Tree has not been commercially adopted (Clark et al., 2018).

Chemical treatment has the potential to be an effective control method because it can have a widespread

effect on a habitat (e.g. the poison of a pond in USA to eradicate the aquatic Xenophrys laevis cited in

Kraus, 2009) or a population. However, chemicals tend not to have a species-specific effect and the

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impact on non-target species have to be carefully considered. In the control of Eleutherodactylus coqui in

Hawaii and Brown Tree Snake on Guam outlined above, chemicals have been used both in the wild and

also to treat cargo/nursery materials. These two places are somewhat unique in that Hawaii does not

have any native herpetofauna and Guam does not have any native snakes, thus limiting the risks of toxic

chemicals to non-target species. Choosing a good attractant (e.g. bait) for the target species may also

help to reduce unintended impacts on native wildlife.

The application of chemicals/hot water to kill alien species can be controversial. In Hawaii where E. coqui

is a well-known invasive causing much ecological and economic damages, there are a lot of support to

control this alien but there are also individuals who opposing it (see Beard and Pitt, 2012). Opposition to

killing alien herpetofauna may arise from people that generally oppose to killing of any vertebrates

(Kraus, 2009). Such sentiment is to be expected among a certain proportion of the general public.

Hopefully through good communication and engagement, understanding of the issue can be improved

and results in less opposition.

(3) Biological Control

Using living organisms to control pest species has been most common in insects and plants. Successful

applications to vertebrates has been limited and there is no report of successful case of biological control

on invasive alien herpetofauna. Introducing new predators as a control would be highly risky and this is

the pathway through which a number of notorious IAS (e.g. Javan Mongoose and Cane Toad) were

introduced across the world.

Using parasites as biological control against Cane Toad, Eleutherodactylus coqui and Brown Tree Snake

has been considered but not progressed very far (Kraus, 2009; Beard and Pitt, 2012; Shine 2012). There

have also been suggestions on using chytrid fungus to control E. coqui in Hawaii (Beard and Pitt, 2012)

and using Paramyxovirus to control Brown Tree Snake on Guam (Engeman and Vice, 2002) but the risks of

the pathogen spreading to other areas and species are high.

The efficacy of a biological agent depends on its ability to reproduce, disperse, find and have a significant

impact on the target species preferably without subsequent human assistance (Howarth, 1999). The

difficulty of guaranteeing host specificity, vector availability, and their significance in regulating host

population make biological control highly risky, success uncertain, development costs high and difficult to

justify the funding (Kraus, 2009). Biological control remains the least applied method in dealing with alien

herpetofauna and its potential is limited when compared to other methods.

(4) Habitat Manipulation

There are a number of successful eradication of alien herpetofauna by habitat manipulation. For

instance, Xenophrys laevis infested ponds in USA were drained in autumn so that all individuals froze over

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in winter (Kraus, 2009). Other examples of its use in combination with other methods in the eradication

of isolated populations of Rhinella marinus, Lithobates catesbeiana, Eleutherodactylus coqui and

Trachemys scripta elegans are covered in the species-specific section below.

Ponds as habitats and/or breeding sites for target alien herpetofauna allow control operations at well-

defined space. Barriers around the ponds may be put up to prevent the access of the target alien species

and those individuals present inside can be removed by trapping, netting, hand-capture, shooting,

electrofishing etc. Ponds may even be drained or filled to eradicate the aliens and, in the latter case, to

eliminate the habitat altogether. This approach is particularly suitable for the management of amphibians

and reptiles that live or breed in small, lentic habitats.

Terrestrial habitats can also be modified to reduce its attractiveness to the alien herpetofauna. For

example, clearing of vegetation was used to reduce the habitat of E. coqui but this method can have

lasting impact on native wildlife if applied in natural habitat as a long-term control method.

Species-specific Approach

(1) Rhinella marina

Rhinella marina were successfully eradicated from Nonsuch Island in Bermuda by installation of a high

density polyethylene barrier fence around the only freshwater pond on the island to prevent them from

breeding and toads were removed both outside the fence and in the pond (Wingate, 2011). In Viwa

Island in Fiji, some ponds were fenced to exclude toads from breeding and rehydrating while other ponds

were filled. The measures were quite effective but faced funding uncertainty (Kraus, 2009).

In Australia, this species was first introduced to control invertebrate pests in Queensland and has been

spreading southwards to New South Wales and westwards to Northern Territory and Western Australia. It

would appear impossible to eradicate this species from Australia and control efforts focus on research

into effective means of long-term control, preventing the establishment of new populations along the

invasion fronts and public education (Kraus, 2009). Research includes searching for a viral control but

failure to find toad-specific pathogen within the toad’s native range or to create an effective and

environmentally acceptable genetically modified viral control resulted in termination (Shine, 2012).

Genetic manipulation so that only males are produced or release of sterile males have been suggested

but these face technical difficulties and have not been investigated in details (Shine, 2012). The high

profile of this invasive toad resulted in active participation of the local communities in removal such as

hand-collecting, trapping using artificial light to attract insects as bait, fencing of ponds and even spraying

household disinfectant onto newly metamorphosed toadlets gather around water edge (Shine, 2012).

However, native frogs were mistaken and also killed and collateral damage to native wildlife from

spraying poison and fencing of ponds are likely to happen (Shine, 2012).

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Other novel approaches include making spawning sites unsuitable by planting dense vegetation around

ponds, introducing nematode lungworm to the toad invasion front, attracting predatory ants to toad

metamorphosing sites and application of alarm pheromone to spawning sites (Shine, 2012). The

feasibility of these are not clear yet. For these to reduce the ecological impact of Cane Toad, they would

need to have a negative impact on toad abundance and the toad impact is density-dependent but this

may not be true (Shine, 2012).

(2) Lithobates catesbeiana

There was a case of successful eradication of Lithobates catesbeiana in East Sussex, U.K. Surveys

identified seven ponds infested by American Bullfrog and these were fenced and frogs were captured by

aquatic traps, pit-fall traps, hand, shooting and electro-fishing in late 1990’s. At the end of 1999, the

ponds were drained to exterminate remaining tadpoles, allow the removal of surviving adults and have

the pond silt excavated and buried (Kraus, 2009). Similar approaches were adopted to eradicate several

populations in Germany and in Netherlands (Kraus, 2009).

Similar methods have been used in an attempt to eradicate/control this IAS in areas where it is already

widespread but the long-term effectiveness is not known because of its very high reproductive potential

and recolonization from adjacent ponds (Kraus, 2009). The poor success may also be explainable because

population growth rate in American Bullfrog is most influenced by tadpole development rate and early

postmetamorphic survival rate (Govindarajulu et al., 2005) while control mostly target adult removal

which may increase metamorphs survival by reducing cannibalism. Modeling suggests removal of

metamorphs in autumn together with removal of egg masses in spring may be more effective in

controlling this IAS (Govindarajulu et al., 2005).

(3) Eleutherodactylus coqui (similar to E. planirostris in biology and invasion pathway)

Hawaii launched a major campaign to control the Coqui Frog around 2005 and it was successfully

eradicated from Oahu by a combination of frequent citric acid spraying and hand-capture (Beard and Pitt,

2012). On Kauai, thick vegetation was cleared to reduce suitable habitat and citric acid was sprayed to

reduce the population to a very small area (Beard and Pitt, 2012). On Molokai, infestation was avoided by

immediate response to frogs arriving in nursery materials (Kraus, 2009). Long-term surveillance against

further incursions from established nursery populations on other Hawaii islands will be necessary. This is

helped by regulatory requirement that all exported shipments from known infested nurseries be treated

with citric acid or hot water spray to kill hitch-hiking frogs (Kraus, 2009).

Beard and Pitt (2012) provided a detailed account of the control measures on Big Island where at least

25,000 ha has been infested. Yearly ground and aerial operations of citric acid, hydrated lime and

mechanical techniques to eradicate populations from isolated areas such as greenhouses have been

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used. Traps are effective where natural retreats are rare such as in resort areas. However, the area

treated each year has been declining due to reductions in fund. On the other hand, a considerable

amount of control has been undertaken by community groups who raise funds and invest lots of

volunteer time to monitor and control local populations.

(4) Trachemys scripta elegans

O’Keeffe (2009) documented the cooperative efforts between government agencies, landowners and

community groups in the eradication of two populations of Red-eared Sliders in Queensland. A

combination of techniques including draining water bodies, intensive trapping and netting, and using

trained dogs to detect nests (O’Keeffe, 2009) have been used. Infested ponds have also been filled in and

compacted, or drained, desilted and fenced to prevent re-colonisation. The largest population was

successfully eradicated while the second small population has been reduced and required additional

effort to complete the work. Reliable detection of this turtle is the greatest hurdle and the use of eDNA

technology may solve this problem.

Ficetola et al. (2012) outlined the control approach for Red-eared Sliders. Floating basking traps and

funnel hoop traps are the most frequently used method and basking traps seem particularly effective.

However, small juveniles are more difficult to capture especially when using hoop traps. Other methods

include the use of nets, draining of wetlands followed by removal of sliders, and the use of sniffer dogs to

detect sliders and their eggs. However, if sliders are still being released by people, this will hamper the

removal efforts.

b) Rationales for species prioritization

The four species with overall risk level of ‘Medium’ or above selected for consideration of the best

eradication/ management options are: Rhinella marinus, Lithobates catesbeiana, Eleutherodactylus

planirostris and Trachemys scripta elegans (Table 1). These four species are in different stages of the

invasion process. The management option considered is targeted towards dealing with their specific

stage of the invasion process: (1) preventing introductions, (2) early-detection and rapid-response to

eradicate incipient populations, and (3) eradication/control of well-established IAS to reduce the negative

impacts.

Prioritisation is based on (1) their environmental and socio-economic impacts and (2) the effectiveness

and efficiency of management options measured by the resources required, the duration of actions, the

likelihood of success and public support. Below is the matrix table capturing these two aspects and the

sub-categories. Species with a comparatively higher impact score and a good degree of effectiveness and

efficiency for the targeted management option will be accorded a higher priority. The important factors

to consider for effectiveness/efficiency of the management options are “Resources Required” and

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“Success Likelihood”. Those required relatively lower resources and higher likelihood of success would be

deemed of higher effectiveness and efficiency. As shown from many overseas cases of managing IAS and

also in the matrix table, the duration of management actions are often long-term and this factor is mainly

for planning the management option, rather than determining the prioritisation. Public support is

important when animals need to be removed from the wild. Public view can be steered with good

communication and early engagement with stakeholders. This factor is captured in the matrix table to

flag those species or management options that will likely generate opposition from the public so that

communication and stakeholder engagement will be included as part of the management package.

Table 1 Matrix table for prioritisation of the four herpetofauna species with overall risk level of

“medium” or above.

Species Impact

Score

Management Options Specific to IAS Invasion Stage Priority for

Management

Option Resources

Required*

Duration Success

Likelihood*

Public

Support

Other Factors to

Consider

Rhinella marina 12 Prevention +

Early

detection &

Rapid

response

Low; become

Medium

when

incursions

occur

Long-term High Needed,

possibly

positive

Incursions may repeat,

sustained surveillance

needed.

Modification of

breeding sites likely

affect native

biodiversity.

High

Lithobates

catesbeiana

11 Early

detection &

rapid

response

Low; become

Medium

when

incursions

occur

Long-term High Needed,

possibly

positive

Incursions may repeat,

sustained surveillance

needed.

Modification of

breeding sites likely

affect native

biodiversity.

High

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Species Impact

Score

Management Options Specific to IAS Invasion Stage Priority for

Management

Option Resources

Required*

Duration Success

Likelihood*

Public

Support

Other Factors to

Consider

Eleutherodactylus

planirostris

8 Eradication/

Control

Very High for

complete

eradication;

Medium to

High for

prevention in

not yet

infested areas

Long-term Very Low for

complete

eradication;

Medium to

High for

prevention in

not yet

infested areas

Needed,

possibly

positive

Reinvasion highly likely.

Eradication by citizen

scientists may affect

Liuixalus romeri due to

confusion.

Medium

Trachemys scripta

elegans

8 Eradication/

Control

Very High for

complete

eradication;

High for

control in

targeted areas

Long-term Very Low for

complete

eradication;

Medium for

control in

targeted areas

Needed,

may be

negative

Reinvasion highly likely.

Habitat modification

may affect native

aquatic biodiversity

Medium

* important factors used to assess the effectiveness and efficiency of management options

Based on the matrix above, Rhinella marina and Lithobates catesbeiana should be accorded high priority

for management. These two IAS have relatively higher Impact Score and their respective management

options have high effectiveness and efficiency.

For Eleutherodactylus planirostris and Trachemys scripta elegans, the priority would be medium because

of lower Impact Score, higher resource requirement and lower likelihood for success especially for

complete eradication. However, it has to be stressed that the impacts of these last two established and

widespread species on Hong Kong biodiversity and the ecological function have not been scientifically

studied. Their actual ecological impact may be higher than that reflected in the current low Impact Score

and there is a need for research, as captured in their risk assessment. Once relevant research is

completed regarding their ecological impacts, there may be strong support to adjust the impact score

upward and the priority to manage them will be raised.

Working Paper No. 3


c) Best eradication/ management options

The best management options for the four short-listed alien herpetofauna according to their current

invasion stage are covered below. Due to the paucity of information available on the ecological impacts of

Eleutherodactylus planirostris and Trachemys scripta elegans, research is also considered as part of the

management package.

(1) Rhinella marina

Since Rhinella marina has not yet arrived and there is no current pathway for this species to Hong Kong,

the best management option is to prevent the introduction of this potential IAS. As mentioned in

Working Paper 1, prevention is regarded as the most effective measures in dealing with IAS and this also

applies to alien herpetofauna (Kraus, 2009) but the import of amphibians into Hong Kong is currently not

covered by existing legislations.

As shown in the species risk assessment, there are three likely pathways through which the species can

arrive in Hong Kong. One of them is the intentional release and the others are the unintentional transport

of this species as contaminant nursery material or as stowaway in container/bulk. To minimize the

intentional import of this species into Hong Kong and its subsequent release, its import should be

discouraged. If a new legislation with a list of serious IAS under import control (i.e. a Black List) would be

enacted in the future, R. marina should be included in the list.

To counter the unintentional transport of this species into Hong Kong, heightened vigilance in ports and

airport against this species in nursery materials and containers originated from source and infested

countries, such as the Caribbean Islands, Australia and Pacific Islands, would help.

Despite these preventive measures, it is probable that some individuals may eventually arrive and reach

the wild. Hence, a rapid detection and early response programme is needed to prevent its establishment

and spread in Hong Kong. This programme should include collaboration with field biologists, NGOs and

citizen scientists such as those using iNaturalist to report and even remove individuals found in the wild.

Active communication, together with capacity building in detection, species identification, handling etc.

when this species has arrived in HK, to these groups is essential for the programme to be effective.

As mentioned in section 3(a) above, isolated breeding populations can be successfully eradicated. If a

breeding population is located in Hong Kong, effective eradication measures from successful case study

elsewhere should be implemented in a timely manner. This will include putting up a Cane Toad-specific

barrier fence around the breeding site and active removal of adults, juveniles, tadpoles and eggs inside

the fence. Night-time patrol along the fence should also be conducted to capture adults trying to enter

the breeding site. If infestation is serious, draining, removal of silt and/or filling of the breeding site can

be considered. However, collateral damage to native biodiversity must be assessed before such drastic

Working Paper No. 3


habitat modification technique is undertaken. Monitoring is needed to assess the effectiveness of the

eradication measures and the status of the alien toad. This species probably matures in one to two years

in invaded areas (Shine, 2012) and if no more individual is detected two years in a row, the eradication

programme can be a called a success and the management measures can be scaled back to keeping a

vigilance of its presence in the wild.

If the recommended measures will be adopted, a detailed plan should be formulated so that all the

parties and stakeholders involved will fully understand the objective and actions required for this long-

term programme.

(2) Lithobates catesbeiana

Lithobates catesbeiana can sometimes be found in the pet and/or food trade in Hong Kong but seems to

be not popular in recent years. Individuals had also been encountered in the wild before. Preventing its

entry to Hong Kong is not possible under the existing legislations (see Working Paper 1). If a new

legislation with a list of serious IAS under import control (i.e. a Black List) would be enacted in the future,

L. catesbeiana should be included in the list because of the potential major impact on native aquatic

biodiversity and as a vector of chytrid fungus.

If import and trade of live individuals of this species into Hong Kong resumes to a substantial level, it is

possible that some individuals will reach the wild and this alien frog may eventually become established

if given the opportunity. Therefore, a rapid detection and early response programme should be in place

to prevent this. An import/market monitoring is helpful to provide an early warning when considerable

number of this species is imported into Hong Kong. When that happens, an early detection and rapid

response programme similar to the one on Rhinella marina should be launched in collaboration with field

biologists, NGOs and iNaturalist citizen scientists to report and remove this species. Communication and

capacity building activities can be combined for both species if the timing overlaps.

If a breeding population is located, successful eradication measures based on overseas experience should

be implemented in a timely manner. The breeding ponds/wetlands will be fenced and frogs, tadpoles and

eggs removed by traps, hand, nets, and even shooting and/or electro-fishing if deemed appropriate.

Draining and de-silting of the ponds/wetlands can be considered to exterminate remaining tadpoles and

to capture surviving frogs if the breeding site is small in size and collateral damage to native biodiversity

is acceptable. Monitoring is needed to assess the effectiveness of the eradication measures and the

status of the alien frog. This species can reach sexual maturity in two years after metamorphosis (CABI,

2018) and in warmer climate tadpoles can metamorphose in the same year (D’Amore, 2012). If no more

individual is detected in three consecutive years, the eradication programme can be a called a success

and the management measures can be scaled back to keeping a vigilance of its presence in the wild.

Working Paper No. 3


If the recommended measures will be adopted for this alien, a detailed plan should be formulated so that

all the parties and stakeholders involved will fully understand the objective and actions required for this

long-term programme.

(3) Eleutherodactylus planirostris

This species is already widespread in disturbed areas and forest edges in Hong Kong and quite well-

established. It undergoes direct development, i.e. does not have an aquatic tadpole stage and any control

measures have to target the terrestrial frogs.

There is no attempted eradication and/or management measures reported in the literature. For the

surrogate E. coqui, intensive eradication efforts targeting small population can be successful as explained

in 3(b). However, the two most commonly used control measures against E. coqui, i.e. citric spray and

hand capture would deem not appropriate or ineffective to use against E. planirostris in Hong Kong. The

use of harmful chemical spray (such as citric acid or hydrated lime) or hot water spray would have

negative impacts on native amphibians and other wildlife. E. coqui is much larger in size and more

conspicuous because of its very loud call and lives in undergrowth vegetation, while E. planirostris is tiny

in size, produces a very soft call and lives among leaf litter and debris on the ground, making it much

more difficult to detect. Hand-capture of E. planirostris would not be an effective control measure as it is

difficult to find and capture all the individuals. Since this species is already widespread locally,

management measures should focus on reducing its negative impacts.

As shown in the risk assessment, the biggest potential impact of E. planirostris is on the similarly-sized

endemic Liuixalus romeri. The Greenhouse Frog already occurs in New Territories, Hong Kong Island,

Lantau Island and Lamma Island where there are native or translocated populations of L. romeri. The two

species have been found to co-exist in some sites but there have been no scientific reports on the

impacts of this alien frog. What is most sensitive is probably Po Toi Island where the native L. romeri

population is smallest and genetically most distinct (Lau, 1998) and the alien seems not to have reached

yet. Po Toi Island is comparatively drier than the other places that support L. romeri but E. planirostris is

adapted to live in both wet and dry habitats (CABI, 2019). If this alien frog reaches Po Toi, it may exert a

negative impact L. romeri that is not experienced by other populations on more favourable environment.

As a precautionary principle, control measures should be put in place to prevent this alien from arriving

to Po Toi by targeting its major pathway of contaminant on plants for landscaping projects. Planting

materials to be used on Po Toi should be isolated and pre-treated with citric acid or hot water spray just

before their transport to the island. Field monitoring should also be carried out on the island for early

detection. If E. planirostris reaches Po Toi, intensive search and capture should be mobilized quickly with

an aim to eradicate this alien before it can establish on the island. The window of opportunity for

eradication is narrow and timely action is the essence of success. Such effort is labour intensive but there

are likely to be interested volunteers and NGOs who would like to take part in conservation work. Prior

Working Paper No. 3


communication and engagement with these parties would be needed to quickly mobilize this human

resource into action. Support, training and coordination are also integral to such volunteer participation.

Monitoring the distribution and spread of E. planirostris are also needed to determine if there are any

important L. romeri (e.g. the largest population of this species on Ngong Ping) or invertebrate

populations in not yet infested areas but will potentially be threatened in the future. In such cases,

control measures similar to those used for Po Toi outlined above should be adopted to reduce the

potential impacts.

Research is needed to look into the negative impacts, if any, of this alien frog on L. romeri and leaf litter

fauna (particularly threatened ants) in good forests. If negative impacts are detected, then the respective

impact score and the priority for management should be adjusted accordingly. Targeted management

measures outlined above for L. romeri should be implemented whenever appropriate. For important leaf

litter invertebrates, specific management measures should be designed to reduce and/or mitigate the

impacts from this alien frog.

There is a Species Action Plan for Liuixalus romeri and it will soon be reviewed. The potential threat of

Eleutherodactylus planirostris should be covered in the plan. The recommended management measures

outlined above should be carefully considered and, if adopted, should be included the plan.

(4) Trachemys scripta elegans

Successful eradication has been documented for small and isolated populations of Red-eared Slider in

Queensland. However, it is deemed not possible to eradicate this alien species in Hong Kong because it is

already established and occurs in many wetlands throughout the territory. Moreover, it remains to be the

most popular pet turtle species and many individuals are subsequently released after being purchased.

Research is needed to look into the negative impacts, if any, of this alien on native lowland turtles,

particularly Mauremys reevesii and possibly Pelodiscus sinensis. If negative impacts are detected, then

management measures including intensive trapping (basking traps and funnel hoop traps) and draining

water bodies to remove individuals should be carried out to reduce the population (or even eradicate this

alien in small isolated sites) and its impacts in sites that support good populations of native turtles. Using

trained dogs to detect nests should also be explored and if effective, can be used both to reduce the

nesting success and to monitor the breeding of this alien. Efforts should also be made to prevent the

release of sliders into these important sites.

Possible candidate sites are Long Valley and Deep Bay wetlands where both native turtle species occur.

However, not much information is available regarding their population size and there is a need for field

research to identify the best habitats and sites for them. As both Mauremys reevesii and Pelodiscus

sinensis are globally threatened, it will be very useful if these knowledge gaps can be filled in the near

Working Paper No. 3


future. The recommended management measures against Trachemys scripta elegans outlined above

should be carefully considered and adopted if this IAS is found to have significant negative impacts on

these native turtles.

Monitoring is required to assess the effectiveness of the control measures and also to determine if the

impacts on the native turtles have been reduced or even reversed. The intensive trapping can yield such

valuable information and it should be designed in such a way that scientific data can be obtained. The use

of eDNA technology will probably help in detecting this alien and native turtles and should be tested for

different habitats in the field.

One note about the management of Red-eared Sliders is that this turtle is a popular pet species. In many

places, the removal of this turtle has faced resistance and how to handle the captured animals can be

controversial (Ficetola et al., 2012). Hence, a well-planned stakeholders’ engagement, in particular with

conservation NGOs, animal welfare groups and academics should be carried out before any actions are

taken. A communication strategy should also be designed and implemented if large-scale removal will be

attempted.

4. Discussion

This Working Paper has reviewed overseas practices in the management and eradication of alien

herpetofauna, prioritized the risky alien amphibians and reptiles and gave recommendations on the best

control measures for them.

There are not many cases of eradication and management of alien amphibians and reptiles and they met

with relatively little success when compared with mammals and plants (Kraus, 2009). The control

methods covered in Section 3 are based on overseas cases. Development and refinement of management

measures for alien species in Hong Kong, not just herpetofauna but also other taxa groups, would be

highly useful to formulate effective control methods suitable for the local context.

Before considering the available risk management options, a judgement on the acceptability of the risk

identified in the risk assessment is required (EPPO, 2011). The potential impacts of the four prioritized

aliens on Hong Kong biodiversity have not been properly studied and research into this area will help in

making that judgement. Moreover, prioritization for actions should simultaneously consider many species

from different taxa groups in order to ensure the best use of limited resources to generate the optimum

results in reducing the IAS impacts. Therefore, before costly, long-term eradication/management

measures are implemented, prioritization of multiple alien species that pose significant potential risk

based on risk assessment should be undertaken. The matrix used in this Working Paper to prioritise alien

herpetofauna can be a useful reference for this exercise.

Working Paper No. 3


During the review of overseas examples, there are cases in which control efforts were compromised by

inability to guarantee long-term investment in funding and personnel. Political will in treating the risks

posed by IAS seriously is needed. Risk communication is crucial not only to get policy and resources

support from within the Government, but also to gather public support for the eradication/management

actions which can be controversial. Risk communication is outside the scope of this consultancy study but

its importance must be stressed.

Kraus (2009) summarized neatly that effective IAS control would require positive research particularly on

eradication and control methods; comprehensive planning; sufficient funds and dedicated personnel

trained in wildlife control. These enabling conditions also apply to all the IAS management work in Hong

Kong.

Working Paper No. 3


5. References

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(ed.) A Handbook of Global Freshwater Invasive Species. Earthscan, London, pp 311-319.

Brooks, J.E., P.J. Savarie, and J.J. Johnston, J.J. (1998) The oral and dermal toxicity of selected chemicals

to brown tree snakes. Wildlife Research 25, 427–35.

CAB International (2018) Invasive Species Compendium, Rana catesbeiana (American Bullfrog).

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Clark, L., C.S. Clark and S. Siers (2018) Brown Tree Snakes Methods and Approaches for Control. USDA

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