Assessing progress in regulation of aquatic nonindigenous species across the multijurisdictional waters of the Laurentian Great Lakes, with emphasis on the live trade pathways

Abstract

The inconsistency in regulated species lists across the shared waters of the Great Lakes undermines the collective prevention efforts of the region, resulting in a "weakest link" problem; some jurisdictions regulate more than 100 species, others fewer than 20. We examine progress over the last twelve years toward more consistent regulated species lists within the 10 Great Lakes jurisdictions. Using a risk assessment framework, we assess a suite of regulated and unregulated organisms that have been identified as having the potential for introduction. Using these species assessments, we determine how sufficient current regulated species lists are in protecting against high-risk species. We also use these species assessments to transparently identify potential high-risk candidates for regional regulatory consideration. A total of 136 aquatic species were regulated by at least one jurisdiction (69 plant species and 67 animal species). The number of species regulated by 5 or more jurisdictions has gone from 10 in 2008 to 44 in 2020. However, the majority (68%) of the currently regulated species are listed in less than half of the Great Lakes jurisdictions. The number of regulated species varies widely across jurisdictions for both taxonomic groups. Wisconsin regulates the largest number of plant and animal species (104 in total), followed by Minnesota (71), New York (59), Illinois/Indiana/Michigan/Ohio (45), Pennsylvania (34), Ontario (23) and Québec (19). We observed only a weak positive correlation between impact score and regulation status. Many of the most-regulated species have impact scores in the low or low-moderate categories, and several species with high impact scores are regulated by less than half of jurisdictions. Twenty-one species (17 plant and 4 animal) are identified as priorities for future regulatory listing.

Full text

Management of Biological Invasions (2021) Volume 12, Issue 3: 546–577
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 546
CORRECTED PROOF
Risk Assessment
Assessing progress in regulation of aquatic nonindigenous species across the
multijurisdictional waters of the Laurentian Great Lakes, with emphasis on
the live trade pathways
Alisha Dahlstrom Davidson1,*, Andrew J. Tucker2, W. Lindsay Chadderton2, Erika Jensen3, Cecilia Weibert3
and Russel Death4
1Great Lakes Aquatic Research and Management, glarm.org, Grand Rapids, MI, 49505, USA
2The Nature Conservancy, University of Notre Dame, IN, 46556, USA
3The Great Lakes Commission, Ann Arbor, MI, 48108, USA
4Innovative River Solutions, School of Agriculture and Environment, Massey University, Private Bag 11-222, Palmerston North 4442,
New Zealand
Author e-mails: alisha.dahlstrom@gmail.com (ADD), atucker@tnc.org (AJT), lchadderton@tnc.org (WLC), ejensen@GLC.org (EJ),
cweibert@glc.org (CW), R.G.Death@massey.ac.nz (RD)
*Corresponding author
Abstract
The inconsistency in regulated species lists across the shared waters of the Great Lakes
undermines the collective prevention efforts of the region, resulting in a “weakest
link” problem; some jurisdictions regulate more than 100 species, others fewer than 20.
We examine progress over the last twelve years toward more consistent regulated species
lists within the 10 Great Lakes jurisdictions. Using a risk assessment framework, we
assess a suite of regulated and unregulated organisms that have been identified as
having the potential for introduction. Using these species assessments, we determine
how sufficient current regulated species lists are in protecting against high-risk species.
We also use these species assessments to transparently identify potential high-risk
candidates for regional regulatory consideration. A total of 136 aquatic species
were regulated by at least one jurisdiction (69 plant species and 67 animal species).
The number of species regulated by 5 or more jurisdictions has gone from 10 in 2008
to 44 in 2020. However, the majority (68%) of the currently regulated species are listed
in less than half of the Great Lakes jurisdictions. The number of regulated species
varies widely across jurisdictions for both taxonomic groups. Wisconsin regulates the
largest number of plant and animal species (104 in total), followed by Minnesota (71),
New York (59), Illinois/Indiana/Michigan/Ohio (45), Pennsylvania (34), Ontario (23)
and Québec (19). We observed only a weak positive correlation between impact score
and regulation status. Many of the most-regulated species have impact scores in the
low or low-moderate categories, and several species with high impact scores are
regulated by less than half of jurisdictions. Twenty-one species (17 plant and 4 animal)
are identified as priorities for future regulatory listing.
Key words: risk assessment, impact, weakest link, binational, organisms in trade,
invasion
Introduction
Aquatic invasive species (AIS) threaten the ecology, economy, and quality
of life in regions throughout the world. Arrival of AIS can occur through a
variety of pathways, including shipping, recreational boating, and the live
Citation: Davidson AD, Tucker AJ,
Chadderton
WL, Jensen E, Weibert C,
Death
R (2021) Assessing progress in
regulation of aquatic
nonindigenous
species across the multijurisdictional
waters of the Laurentian Great Lakes, with
emphasis on the live trade pathways
.
Management of Biological Invasions
12(3)
:
5
46–577, https://doi.org/10.33 91/mbi.2021.1 2.3.04
Received:
28 October 2020
Accepted:
1 March 2021
Published:
19 April 2021
Handling editor:
Joana Dias
Copyright:
© Davidson et al.
This is an open acces s article distributed under terms
of the Cr eative Commons Attr ibutio n Licen se
(
Attribution 4 .0 International - CC BY 4.0).
OPEN ACCESS.

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 547
trade industries. Despite the historical focus within the Great Lakes region
on management of the shipping/ballast water pathway, the aquatic live
trade pathway has received increasing attention (Padilla and Williams
2004) and is the primary focus of this manuscript. Studies have found, for
example, that propagule pressure from the aquarium trade is high relative
to the recreational boating pathway for taxa such as fish and invertebrates
(Strecker et al. 2011). The live trade pathways include live bait, horticultural
and water-garden plants, biological supplies, pets, and live food (Keller and
Lodge 2007). In taxa such as reptiles and amphibians, the pet trade is
responsible for the largest proportion of introduced species (Kraus 2009).
For aquatic plants, releases include water hyacinth Eichhornia crassipes
(Mart.) Solms (1883) and purple loosestrife Lythrum salicaria L.
Species introduced through live trade cause impacts when they are
released (either intentionally or unintentionally) into the wild. The number
of releases are difficult to quantify, but they are likely high: Gertzen et al.
(2008) estimate over 10,000 fishes are released annually in Montréal
(Canada). Introductions via the live trade industry have occurred in nearly
all regions of the world (South Africa in Martin and Coetzee 2011, India in
Singh and Lakra 2011, U.S. Pacific Northwest in Strecker et al. 2011,
Poland in Lenda et al. 2014), including the Laurentian Great Lakes
(Funnell et al. 2009; Sturtevant et al. 2019). The importation and sale of
aquatic species is an important invasion pathway to the Great Lakes (Rixon
et al. 2005; Ricciardi 2006; Keller and Lodge 2007; Pagnucco et al. 2015).
Several U.S. federal regulations exist to manage invasive species within
the live trade pathway. The Federal Noxious Weed Act regulates trade and
import of federally listed noxious weeds, including several aquatic plants
(see Table 1). The Lacey Act gives the U.S. Fish and Wildlife Service the
authority to prohibit importation of animals identified as potentially harmful
to humans or other wildlife. However, this statute was weakened by the
2017 United States Association of Reptile Keepers, Inc. v. Zinke decision
that changed the interpretation and enforcement of the Lacey Act so that it
no longer prohibits transport of injurious wildlife between States within
the continental United States. With this increased responsibility on U.S.
States, and the fact the federal statutes cover a limited number of species,
much of the regulation is left to jurisdictions within the Great Lakes region
(Thomas et al. 2009).
Management of this pathway within the Great Lakes is complex, with
eight U.S. states and two Canadian provinces (collectively, “jurisdictions”)
having established individual regulations to prevent species introduction
and spread. Some jurisdictions regulate more than 100 plant and/or animal
species, and others regulate fewer than 20. This inconsistency in regulated
species lists across the shared waters of the Great Lakes undermines the
collective prevention efforts of the region, resulting in a “weakest link”
problem, wherein the success of AIS management efforts is limited to the

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 548
weakest regulatory approach (Peters and Lodge 2009). Regional policy
makers have recognized that successful closure of this pathway requires
greater coordination (Great Lakes Panel on Aquatic Nuisance Species
2014; GLEC 2019). In June 2013, the Council of Great Lakes [and St
Lawrence] Governors (now the Great Lakes St. Lawrence Governors and
Premiers or “GSGP”) identified a list of sixteen “least wanted” AIS that
they considered a grave threat to the region’s economy and ecology (GSGP
2013). On May 4, 2018, the GSGP announced the addition of five more
species to the “least wanted” list. The Governors and Premiers called for
specific steps to manage these “least wanted” species, including taking
executive action within each state or province to prohibit or restrict the
transfer of these species, and cross-jurisdictional collaboration to harmonize
related state and provincial policies and regulated species lists.
The application of consistent criteria to identify problematic species,
particularly via risk assessment, would aid efforts to improve cross-
jurisdictional collaboration and harmonization of regulated species lists.
Risk assessment has been repeatedly identified as an essential tool in
evidence-based identification, regulation, and management of live trade
species (Mandrak and Cudmore 2015; Chan et al. 2019). Risk assessment
also allows for the most efficient allocation of resources to pathways and
species posing the greatest risk (Mandrak and Cudmore 2015). The
agencies responsible for regulation and enforcement of species in trade at
the state, province and federal levels may require a formal risk assessment
framework to provide a detailed evaluation of a species’ risk in order to
justify removal from the trades and withstand potential judicial review.
Transparent and evidence-based risk assessment are particularly important
in the United States where the onus is on agencies to prove a species will
likely have impact before they can regulate (“innocent until proven guilty”,
or the “hindsight approach”) (Davidson et al. 2013). This contrasts with
the approach taken by countries like New Zealand, Australia, and those
within the European Union (EU), who employ rigorous risk assessment
frameworks, but use a more precautionary approach that allows regulation
even if data necessary to complete a risk assessment is scarce (“guilty until
proven innocent”) (Davidson et al. 2013).
Across the Great Lakes region, the development of risk assessment tools
has continued to evolve and diverge and now includes decision trees (Kolar
and Lodge 2002; Howeth et al. 2016), probabilistic models (e.g., Keller et al.
2007) as well as semi-quantitative questionnaire-based frameworks (e.g.,
Davidson et al. 2017) and formal literature reviews (e.g., Frederickson 2007;
Department of Fisheries and Oceans 2017). In the EU, in order to address
the challenges posed by the region’s shared borders and waterways, and the
need for harmonized risk assessment frameworks, Roy et al. (2018) reviewed
29 risk assessment schemes (including the World Trade Organization,
Convention on Biological Diversity and International Plant Protection

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Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 549
Convention) to identify a list of components necessary for a robust risk
assessment framework that covers species biology, assessment of likelihood
of introduction, survival and impacts, and measures of process efficiencies
and confidence.
Here, we examine progress over the last twelve years toward more
consistent regulated species lists within the 10 Great Lakes jurisdictions.
We compile and compare risk assessment frameworks for consistency with
the minimum standards listed by Roy et al. (2018). Finally, using the risk
assessment framework that best meets the minimum standards, we assess a
suite of regulated and unregulated species that have been identified as
having the potential for introduction to determine how sufficient current
regulated species lists are in protecting against high-risk species and to
transparently identify potential high-risk candidates for regional regulatory
consideration. We take a broad view of “regulated”, recognizing that
jurisdictional regulated species lists, statutes, and administrative codes are
complex and dynamic. Our intent is to focus on broad patterns that show
progress and remaining major gaps in regulatory species lists for the live
trade pathways, in particular.
For each section, we use the following definitions: consistent (the same
suite of species are regulated across all jurisdictions), sufficient (species
identified as highest risk are prioritized for regulation), and transparent
(species are listed for regulation based on the consistent application of an
objective and comprehensive risk assessment framework). By describing
the history and current status of regulated species, reviewing the
application of risk assessment in the regulatory process, and assessing
patterns of regulations against each species’ assessed risk, we aim to
identify gaps and priority species for future regulation, particularly within
the live trades.
Materials and methods
Progress toward consistent regulations
To assess regional progress toward more consistent regulated species lists,
we determined the number of regulated species at three points in time
(2008, 2014, and current (2020)) for each state and province included in
the Great Lakes region (Illinois-IL, Indiana-IN, Michigan-MI, Minnesota-
MN, New York-NY, Ohio-OH, Ontario-ONT, Pennsylvania-PA, Québec-
QBC, and Wisconsin-WI). We used 2008 because this represents the state
of regulated species lists when the key regional entity tasked with
coordinating AIS management (Great Lakes Panel on Aquatic Nuisance
Species, GLP) released their first assessment of the consistency between
Great Lakes jurisdictions of organisms in trade regulations. The year 2014
represents the state of regulated species lists a year after the announcement
of the first 16 “least wanted” AIS by the Council of Great Lakes [and St

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 550
Lawrence] Governors (now the Great Lakes St. Lawrence Governors and
Premiers or “GSGP”) in 2013. The use and definition of the term “regulated”
varies between jurisdictions, but here we use it to represent all regulation
types, e.g., prohibited, restricted, controlled, etc. Our intent is to encourage
harmonization of lists of regulated species for which import, sale, and
possession are controlled by statute. We recognize the need for a parallel
process to ensure that laws and regulations governing the importation,
sale, and possession of species are consistent and complementary; however,
an assessment of those is beyond the scope of this paper.
State and provincial administrative code and statutes were referenced to
compile a comprehensive list of regulated AIS (and dates for listing) for all
Great Lakes jurisdictions. The analysis was limited to the subset of aquatic
plants and animals for which sale, possession, and/or import is restricted,
prohibited, or otherwise regulated. For plants, those species designated as
obligate or facultative wetland plants (per U.S. Army Corps of Engineers
National Wetland Plant list for Northcentral and Northeast region) were
considered. If a plant was not listed by the U.S. Army Corps of Engineers,
other sources such as obligate aquatic or wetland designations by Great
Lakes jurisdictions and expert knowledge were used. For all species, only
those species able to arrive and establish in the Great Lakes region were
included (e.g., marine and tropical species were excluded; hereafter referred
to as the “establishment criteria”). Using our establishment criteria, we
excluded marine species such as Caulerpa taxifolia (Vahl) C. Ag., that
clearly couldn’t establish in the Great Lakes. However, the establishment
ability of genera Ulva (synonym Enteromorpha) is less clear. In 2003, it
reached bloom proportions in Muskegon Lake, a coastal lake of Lake
Michigan (Lougheed and Jan Stevenson 2004). The ability of a recognized
marine species to establish in freshwater was attributed to high nutrient
levels, a history of industrial activity that led to elevated salinity and
absence of grazing pressure. There is some uncertainty about its ability to
survive in similar environments around the basin with salinity levels in the
lower Great Lakes (Erie and Ontario) overlapping with Ulva’s lower
tolerance limits (Chapra et al. 2012). However, as Ulva hasn’t persisted or
spread since this event, we treated it as primarily a marine species and
excluded it from the initial list of regulated species. Overall, thirty species
regulated as “aquatic” were excluded due to their predicted inability to
arrive or establish in the Great Lakes (Supplementary Table S1).
Six algal species and the diatom Didymospenia geminata (Lyngbye) M.
Schmidt were also included on the list. For animals, all regulated mammals,
fish, aquatic invertebrates, reptiles and amphibians were included. The
state of Illinois publishes an Aquatic Life Approved Species List and
prohibits possession, sale, and import of any aquatic species not on the
approved list. However, for the purposes of this analysis, only those species
that were identified as “injurious species” under part 805 of the Illinois

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 551
Administrative Code and relevant plant species under the Illinois Exotic
Weed Act were considered regulated.
In order to obtain a clear species list and count, we only included species
that were explicitly mentioned by one or more jurisdictions. In instances
where entire families or genera of species were regulated by a jurisdiction,
all species within that group regulated in the Great Lakes were counted
towards that jurisdiction’s total number of regulated species. For example,
all individually listed snakehead species were counted as regulated in those
jurisdictions where Channa, Parachanna, or Channidae were regulated.
Likewise, although, Québec regulates the entire family Acipenseridae, only
sterlet Acipenser ruthenus Linnaeus, 1758 (regulated by Wisconsin) was
included for Québec. All regulated taxa had at least one named species
except for the genus Nymphaea (regulated by Minnesota). As highlighted
by Minnesota on their public outreach page for non-native waterlilies
(https://www.dnr.state.mn.us/invasives/aquaticplants/waterlilies.html), there
are many native waterlilies that look similar to non-native waterlilies.
Although some harmful non-native water lilies are relatively easy to
distinguish (e.g., Nymphaea mexicana Zucc.), without a clear guide on the
non-native waterlilies, a positive identification for most species is difficult
for pond retailers or the public. As such, we did not include this family.
Patterns in regulated species lists across jurisdictions were examined
over the last 12 years with non-metric multidimensional scaling (NMDS)
on a Bray-Curtis similarity matrix using the Vegan package in R 4.0.2.
Plant and animal species lists were assessed separately, and each jurisdiction
by time period, for 2008, 2014 and 2020, was treated as a separate point in
the analysis. Average dissimilarity between jurisdictions was calculated for
each time step and significance of differences between timesteps assessed
using a one-way ANOVA also in R.
Progress in coordinating regional risk assessment frameworks
We consulted regional policy reports and relevant AIS management
personnel to compile a list of risk assessments that are used by Great Lakes’
jurisdictions to inform state or provincial processes for listing regulated
species. We included frameworks that have been used by at least one
jurisdiction (state, regional or federal) for planning or regulatory purposes.
We limited the comparison to those frameworks able to assess broad
taxonomic groups (plants, animals or plants and animals). To compare
regional risk assessment frameworks against the minimum standards
described in Roy et al. (2018), three independent reviewers with risk
assessment background but not directly affiliated with any of the frameworks
scored each assessment according to how well it met each standard. They
used completed assessments and related standard operating procedures
(where available). These three scores were then reconciled to consensus,
for each criterion. Criteria were scored as “fully met” if the standard

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 552
operating procedures explicitly described a criterion, or if that criterion
was consistently considered in the completed assessments. Criteria were
scored as “partially met” if the standard operating procedures and/or
completed assessments mentioned but did not provide any detail relative
to a criterion. Criteria were scored as “not met” if there was no mention of
that criterion in standard operating procedures or the completed
assessments. Supporting information used to determine scores are
included in Appendix 1.
Progress toward sufficient and transparent regulations
To determine how well current regulated species lists protect the Great
Lakes, we assumed that in an ideal world, regulated species lists should give
priority to those species most likely to be introduced and cause the greatest
harm. We assumed that limited resources require prioritization of a
candidate pool of potential future introduced species. And that those
species with highest potential for impact(s) and likelihood of introduction
would be higher priority for regulation, and removal from the live trade
pathways. We used the Great Lakes Aquatic Nonindigenous Species Risk
Assessment (GLANSRA) to score potential environmental and socio-economic
impacts and likelihood of arrival. In the absence of a comprehensive data
set on all species in the live trade, we developed a candidate list of potential
regulated species by combining the list of all regulated species that met the
inclusion criteria above and a list of unregulated species that had been
identified as potential future invaders. The list of unregulated future invaders
is a subset of a list of “surveillance species” that were identified through a
separate regional process (Davidson et al. 2021). The surveillance species
are species that are not present in or widespread throughout the basin,
have a pathway through which they can arrive in the Great Lakes, are
capable of establishment and are predicted to cause impacts.
Significance of the relationship between impact scores and numbers of
jurisdictions regulating that species was assessed by Kendall rank correlation.
We also plotted species using their impact scores, likelihood of arrival
scores and current regulatory status to identify high risk species that may
be underregulated. Candidate species were divided into groups based on
the GLANSRA likelihood of arrival score (high, moderate, low, unknown,
unlikely, established) and then patterns between impact score (from
GLANSRA) and the number of regulating jurisdictions were compared
graphically. Species not regulated in all 10 states and provinces with high
(> 40) or moderate (20–39) impact scores were identified for consideration
as regional regulatory priorities. Thus, species recommended for regulation
all meet the following criteria: not yet regulated by all 10 jurisdictions;
meet minimum impact standards (impact of medium or high; total impact
score of ≥ 20); and likelihood of introduction of unknown, low, moderate
or high. We chose to take a precautionary approach to pathway score

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 553
because the live trade pathway continues to grow, and these scores are only
likely to increase (Pagnucco et al. 2015).
Results
Progress toward consistent regulations
A total of 136 aquatic species established in or predicted to be capable of
establishing in the Great Lakes are regulated by at least one jurisdiction (69
plant species and 67 animal species; Tables 1, 2). The number of species
regulated by 5 or more jurisdictions has gone from 10 in 2008 to 44 in 2020
(Figure 1). In 2008, only 43 species were regulated; by 2020, 136 species
were regulated, with 53 new species regulated in one or more jurisdictions
between 2008 and 2014 and a further 40 new species added to one or more
states or provinces after 2014 (Figure 1). However, the majority (68%) of
the currently regulated species are listed in less than half (i.e., < 5) of the
Great Lakes jurisdictions (Figure 1). No plant species are regulated by all
ten jurisdictions (as Québec does not regulate any plant species). However,
hydrilla Hydrilla verticillata (L.f.) Royle and water chestnut Trapa natans
L. are regulated by nine jurisdictions. The nine animal species listed in all
ten jurisdictions are: northern snakehead Channa argus (Cantor, 1842), grass
carp Ctenopharyngodon idella (Valenciennes in Cuvier and Valenciennes, 1844),
ruffe Gymnocephalus cernuus (Linnaeus, 1758), silver carp Hypophthalmichthys
molitrix (Valenciennes in Cuvier and Valenciennes, 1844), bighead carp
Hypophthalmichthys nobilis (Richardson, 1845), black carp Mylopharyngodon
piceus (Richardson, 1846), round goby Neogobius melanostomus (Pallas,
1814), tubenose goby Proterorhinus marmoratus (Pallas, 1814) and rudd
Scardinius erythrophthalmus (Linnaeus, 1758) (Tables 1, 2).
The number of regulated species varies widely across jurisdictions for
both taxonomic groups. Wisconsin regulates the largest number of plant
and animal species (104 in total), followed by Minnesota (71), New York
(59), Illinois/Indiana/Michigan/Ohio (45), Pennsylvania (34), Ontario (23)
and Québec (19) (Figures 2, 3). Between 2014 and 2020, nine out of ten
jurisdictions (all except Quebec) increased the number of regulated plants,
and nine out of ten jurisdictions (all except Pennsylvania) increased the
number of regulated animals. The regulation of plants can be broken into
four major groups: 1) few regulated species by 2008, with a jump by 2014
(IL, IN, MN, WI – with WI having another jump by 2020); 2) few regulated
species by 2014, with a jump by 2020 (NY, OH, ONT, PA); 3) many
regulated species by 2008, with steady increase throughout (MI); and 4) no
regulated species (QBC) (Figure 2). Notably, the pattern in regulation of
animals was similar for all jurisdictions, with mostly steady growth from
2008–2020 (except for PA, which stayed constant) (Figure 3). The frequency
of “least wanted” species listings has increased over time. Prior to the

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Table 1. Alphabetical list of 69 regulated plant/algae species with GLANSRA environmental (Env), Social/Cultural (Soc/Cult)
and total (combined) impact scores. Note: *Indicates a species included on the GSGP “least wanted” list. ^Indicates a species listed
as federal noxious weed under the Plant Protection Act of 2000 (7 U.S.C. 7701 et seq.). s Indicates species on the GLANSRA
surveillance species list. For Env impact or Soc/Cult impact categories, if impact score was 0–1, impact category is considered
Low or Unknown (based on number of unanswered questions, indicated by a U); if impact score was 2–5, impact category is
considered Moderate; if impact score was ≥ 5, impact category is considered High.
Species name Common name
Jurisdictions
regulated
GLANSRA Env
Impact Score
GLANSRA Soc/Cult
Impact Score
Total impact
score
Alnus glutinosas
European alder
1
9
1
10
Alternanthera sessilis ^s
Sessile joyweed
1
1
6
7
Arthraxon hispidus
Small carpet grass
1
1
0
1
Arundo donaxs
Giant reed
1
19
3
22
Azolla pinnata^s
Mosquito fern
5
9
3
12
Butomus umbellatuss
Flowering rush
6
2
4
6
Cabomba carolinianas,a
Carolina fanwort
4
4
4
8
Cirsium palustres
Marsh thistle
1
8
0
8
Conium maculatum
Poison hemlock
4
2
2
4
Crassula helmsiis
Australian stonecrop
2
6
2
8
Cylindrospermopsis
raciborskii
Cylindro 2 1 2 3
Didymosphenia geminatas
Didymo
2
12
19
31
Egeria densa*s
Brazilian elodea
8
18
25
43
Eichhornia azurea^s
Anchored water hyacinth
5
3
2
5
Eichhornia crassipess
Water hyacinth
2
15
26
41
Epilobium hirsutums
1
3
0
3
Glossostigma cleistanthum
Mudmats
1
0(U)
0(U)
0
Glyceria maximas
Reed manna grass
2
12
2
14
Hydrilla verticillata*^s
Hydrilla or water thyme
9
19
30
49
Hydrocharis morsus-ranae*s
European frogbit
8
8
7
15
Hydrocotyle ranunculoidess
Floating marsh pennywort
1
13
6
19
Hygrophila polysperma^s
Miramar weed, Indiana
swampweed
5 3 8 11
Impatiens balfourii
Balfours touch-me-not
1
0(U)
0
0
Ipomoea aquatica^s
Chinese waterspinach or
swamp morning-glory
5 6 8 14
Iris pseudacorus
Yellow flag iris
5
8
3
11
Lagarosiphon major^s
Oxygen weed or African
elodea
6 14 13 27
Ludwigia hexapetala s
Uruguayan primrose willow
2
18
10
28
Ludwigia peploidess
Floating primrose willow
1
19
9
28
Lysimachia nummularia
Creeping jenny
1
1(U)
0
1
Lysimachia vulgariss
Garden loosestrife
2
8
0
8
Lythrum salicaria
Purple loosestrife
8
9
0
9
Lythrum virgatums
Wanded loosestrife
5
18
12
30
Melaleuca quinquenervia^s
Broad-leaved paperbark
2
13
18
31
Monochoria hastata^
Monochoria, arrowleaf, or
false pickerelweed
4 0 6 6
Monochoria vaginalis^
Heartshape or false
pickerelweed
4 2 6 8
Murdannia keisaks
Marsh dewflower
1
12
2
14
Myosotis scorpioides
True forget-me-not
1
O(U)
0
0
Myriophyllum aquaticums*
Parrot feather
8
18
3
21
Myriophyllum heterophyllum
Broadleaf water-milfoil
1
9
7
16
Myriophyllum heterophyllum
x M. laxum
s
Broadleaf water-milfoil
hybrid
1 8 18 26
Myriophyllum spicatum
Eurasian watermilfoil
6
6
10
16
Najas marina
1
0(U)
1
1
Najas minors
Brittle naiad
4
7
2
9
Nelumbo nuciferas
Sacred lotus
1
12
1
13
Nitellopsis obtusas
Starry stonewort
4
19
7
26
Nymphaea spp.b
Non-native water lilies
1
3
1
4
Nymphoides peltata*s
Yellow floating heart
6
2
3
5
Oenanthe javanicas
water-celery
1
3
2
5

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Table 1. (continued).
Species name Common name
Jurisdictions
regulated
GLANSRA Env
Impact Score
GLANSRA Soc/Cult
Impact Score
Total impact
score
Ottelia alismoides^
Duck lettuce
5
0
0
0
Phalaris arundinacea
Reed Canary grass
1
14
3
17
Phragmites australis
Common reed
6
18
5
23
Pistia stratiotess
Water lettuce
1
14
30
44
Potamogeton crispus
Curlyleaf pondweed
6
5
4
9
Prymnesium parvums
Golden algae
2
13
18
31
Sagittaria sagittifolia^s
Arrowhead
5
1
14
15
Salix atrocinereas
Gray florist’s willow
1
13
1
14
Salvinia auriculata^
Eared watermoss, African
payal, and butterfly fern
5 1 1 2
Salvinia biloba^
Giant salvinia
5
0
0
0
Salvinia molesta^s
Giant salvinia
6
18
31
49
Silphium perfoliatum
Cup-plant
1
12
0
12
Solanum tampicense^s
Wetland nightshade
2
3
1
4
Solidago sempervirens
Seaside goldenrod
1
1
0
1
Sparganium erectum^
Exotic bur-reed
4
1
0
1
Stratiotes aloides*s
Water soldier
6
3
2
5
Trapa natans*s
Water chestnut
9
14
12
26
Typha angustifolia
Narrow leaf cattail
3
8
0
8
Typha domingensiss
Southern cattail
1
14
15
29
Typha laxmanniis
Graceful cattail
1
6
1
7
Typha x glaucas
2
18
0
18
Valeriana officinalis
Garden valerian
1
1
0
1
a Cabomba, while not native to the Great Lakes basin, is native to some portion of at least four Great Lakes states.
b This species was not counted toward the total because there are no species identified in the associated regulation.
announcement of a list of “least wanted” species in 2012 (GSGP 2013) only
5 of these high-risk species were regulated in at least half of all jurisdictions,
but by 2020, 19 of the 21 species were regulated across the majority of
jurisdictions. Exceptions are New Zealand mudsnail (Potamopyrgus
antipodarum J.E. Gray, 1853) (4 jurisdictions) and marbled crayfish
(Procambarus virginalis Hagen, 1870) (1 jurisdiction) which was only
announced as “least wanted” in May 2018. No jurisdiction regulates all 21
“least wanted” species.
For animals (Figure 4), by 2020, the lists appear to be converging into
two locations in the ordination. A group of seven jurisdictions (IL, IN, MI,
MN, OH, ON, QBC) appear to show an increasing level of similarity
towards the top of axis 2 between 2008 to 2020. The second smaller group
of states (NY, WI) in contrast, is showing similarity towards the far right of
axis 1, and Minnesota is intermediate between these two groups. This latter
group (NY, WI) differs from the main cluster in that they regulate stone
moroko (Pseudorasbora parva, Temminck and Schlegel, 1846), Wels
catfish (Silurus glanis L., 1758) and yabby (Cherax destructor Clark 1936).
For plants (Figure 5) all jurisdictions appear to be moving towards a similar
list of taxa to the far right of axis 1. Average dissimilarity was significantly
different between 2008 timestep and 2014 or 2020 for both animals and
plants (F2,115 = 2.52, P = 0.085 and F2,76 = 6.82, P = 0.002 respectively), but
there were no significant differences between 2014 and 2020 for either
plants or animals.

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Table 2. Alphabetical list of 67 regulated animal species with GLANSRA environmental (Env), Social/Cultural (Soc/Cult) and
total (combined) impact scores. *Indicates a species included on the GSGP “least wanted” list. ^Indicates a species listed as
“injurious wildlife” under the Lacey Act (18 U.S.C. 42). s Indicates species on the GLANSRA surveillance species list. For Env
impact or Soc/Cult impact categories, if impact score was 0–1, impact category is considered Low or Unknown (based on number
of unanswered questions, indicated by a U); if impact score was 2–5, impact category is considered Moderate; if impact score was
≥ 5, impact category is considered High.
Species name Common name
Jurisdictions
regulated
GLANSRA Env
Impact Score
GLANSRA Soc/Cult
Impact Score
Total impact
score
Acipenser ruthenus
Sterlet
2
18
6
24
Alosa aestivaliss
Blueback herring
1
6
0
6
Alosa pseudoharengus
Alewife
2
18
14
32
Bithynia tentaculate
Faucet snail
3
7
2
9
Bythotrephes longimanus
(cederstroemi)
Spiny waterflea 3 7 1 8
Carassius auratus
Goldfish
3
1(U)
0
1
Carassius carassius^
Crucian carp
2
0
0
0
Carassius gibelio^s
Prussian carp
2
9
6
15
Cercopagis pengoi
Fishhook waterflea
2
7
1
8
Channa argus*^s
Northern snakehead
10
7
2
9
Cherax destructor*s
Yabby
6
2
1
3
Cherax tenuimanuss
Marron
1
2
0
2
Cipangopaludina chinensis
Chinese mystery snail
3
0(U)
0(U)
0
Cipangopaludina japonica
Japanese trap door snail
3
1
1(U)
2
Corbicula fluminea
Asian clam
3
2
2
4
Ctenopharyngodon idella*s
Grass carp
10
20
1
21
Cyprinella lutrensiss
Red shiner
2
14
0
14
Cyprinus carpio
Common carp
3
12
1(U)
13
Daphnia lumholtzis
Water flea
2
2
0
2
Dikerogammarus villosus*s
Killer shrimp
5
7
0
7
Dreissena bugensis
Quagga mussels
9
25
20
45
Dreissena polymorpha^
Zebra mussel
9
30
25
55
Eriocheir sinensis^s
Chinese mitten crab
5
8
8
16
Faxonius rusticus
Rusty crayfish
6
19
7
26
Fundulus diaphanus diaphanous
Eastern banded killifish
1
0(U)
0
0
Gambusia affiniss
Western mosquitofish
3
9
1
10
Gambusia holbrookis
Eastern mosquitofish
2
19
9
28
Gasterosteus aculeatus
Three spine stickleback
2
3
1
4
Gymnocephalus cernuuss
Eurasian river ruffe
10
12
12
24
Hemimysis anomalas
Bloody red shrimp
2
7
0
7
Hypophthalmichthys molitrix*^s
Silver carp
10
15
7
22
Hypophthalmichthys nobilis*^s
Bighead carp
10
8
12
20
Lepomis microlophuss
Redear sunfish
1
8
0
8
Leuciscus idus
Ide
3
0
0
0
Limnoperna fortunei*s
Golden mussel
5
30
9
39
Misgurnus anguillicaudatuss
Weatherfish
4
14
0
14
Morone americana
White perch
4
18
2
20
Mylopharyngodon piceus*s
Black carp
10
7
0
7
Myocastor coypus
Nutria
3
6
13
19
Neogobius melanostomus
Round goby
10
13
13
26
Oncorhynchus gorbuscha
Pink salmon
1
1(U)
1
2
Oncorhynchus kisutch
Coho salmon
1
3
0
3
Oncorhynchus mykiss
Rainbow trout
1
9
0
9
Oncorhynchus tshawytscha
Chinook salmon
1
2
0
2
Osmerus mordax
Rainbow smelt
2
12
0(U)
12
Perca fluviatilis^s
European perch
3
18
2
20
Perccottus glenii^s
Amur sleeper
2
8
1
9
Petromyzon marinus
Sea lamprey
4
12
18
30
Phoxinus phoxinus^s
Eurasian minnow
2
2
1
3
Potamopyrgus antipodarum*s
New Zealand mud snail
4
13
0
13
Procambarus clarkiis
Red swamp crayfish
3
24
7
31
Procambarus virginalis*s
Marbled crayfish
1
14
2
16

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 557
Table 2. (continued).
Species name Common name
Jurisdictions
regulated
GLANSRA Env
Impact Score
GLANSRA Soc/Cult
Impact Score
Total impact
score
Proterorhinus marmoratus
Tubenose goby
10
1
0
1
Pseudorasbora parva*^s
Stone moroko
7
19
1
20
Rhodeus sericeuss
Bitterling
3
6
0
6
Rutilus rutilus^s
Roach
2
11
2
13
Salmo salar
Atlantic salmon
1
5
0
5
Salmo trutta
Brown trout
1
9
0
9
Salvelinus alpinus
Arctic char
1
1
0
1
Sander lucioperca*^s
Zander
9
8
0
8
Scardinius erythrophthalmuss
Rudd
10
4
0
4
Silurus glanis*^s
Wels-catfish
7
6
0
6
Tinca tinca*s
Tench
5
2
0
2
Trachemys scripta elegans
Red eared slider
2
13
6
19
Valvata piscinalis
European valve snail
1
1
0
1
Viviparus georgianus
Banded mystery snail
2
1
0
1
Xenopus laevis
African clawed frog
1
9
0
9
Figure 1. The cumulative number of species (out of 136 unique species) regulated by one to all
(ten) jurisdictions. The “zero” jurisdiction column represents species that are regulated in 2020
but were not regulated in 2008 (93 species) or 2014 (40 species).

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 558
Figure 2. Number of plant species regulated by jurisdiction, as of the start of 2008, 2014 and 2020, with the total number of
unique species regulated in one or more jurisdiction (69) and the number of regulated “least wanted” species (out of 7).
Figure 3. Number of animal species regulated by jurisdiction, as of the start of 2008, 2014 and 2020 with the total number of
unique species regulated in one or more jurisdiction (67) and the number of regulated “least wanted” species (out of 14).
Progress in regional risk assessment framework development
In all, six risk assessment frameworks are identified and assessed (Table 3;
Appendix 1). Three risk assessments evaluated risk for both plants and
animals and three were specific to just plants. The assessments range from
semi-quantitative questionnaire-based assessments, to screening level
assessments based on literature review and a climate matching tool. In
addition to different formats, the frameworks were designed to achieve

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 559
Figure 4. Plot of axis 1 and 2 from a Nonmetric multidimensional scaling ordination (NMDS: stress = 0.12) based on Bray-Curtis
dissimilarity of jurisdictional regulated aquatic animal species lists in 2008, 2014 and 2020. The lists in each jurisdiction are joined
in sequence from 2008 to 2020. IL = Illinois, IN = Indiana, MI = Michigan, MN = Minnesota, NY = New York, OH = Ohio, ONT
= Ontario, PA = Pennsylvania, QBC = Québec and WI = Wisconsin.
Figure 5. Plot of axis 1 and 2 from an NMDS (stress = 0.08) based on Bray-Curtis dissimilarity of jurisdictional regulated aquatic
plant species lists in 2008, 2014 and 2020. The lists in each jurisdiction are joined in sequence from 2008 to 2020. IL = Illinois,
IN = Indiana, MI = Michigan, MN = Minnesota, NY = New York, OH = Ohio, ONT = Ontario, PA = Pennsylvania, QBC = Québec
and WI = Wisconsin.
different goals (Appendix 1). The frameworks that most closely met the full
suite of risk assessment standards from Roy et al. (2018) are the Great
Lakes Aquatic Nonindigenous Risk Assessment (GLANSRA), United
States Department of Agriculture Animal and Plant Health Inspection
Service plant protection and quarantine weed risk assessment protocol

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 560
Table 3. Comparison of regional risk assessment frameworks: Great Lakes Aquatic Nonindigenous Species Risk Assessment
(GLANSRA); United States Department of Agriculture, Animal and Plant Health Inspection Service (USDA APHIS); Ecological Risk
Screening Summaries, U.S. Fish and Wildlife Service (ERSS); Wisconsin Literature Review (WI); Great Lakes Aquatic Weed Risk
Assessment (GL AqWRA); and New York State Ranking System (NY). The rows represent each standard: (1) basic species
description; (2) likelihood of invasion; (3) distribution, spread and impacts; (4) assessment of introduction pathways; (5) assessment of
impacts on biodiversity and ecosystems; (6) Assessment of impact on ecosystem services; (7) assessment of socio-economic
impacts; (8) consideration of status (threatened or protected) of species or habitat under threat; (9) assessment of effects of future
climate change; (10) completion possible even when there is a lack of information; (11) documents information sources; (12) provides
a summary in a consistent and interpretable form; (13) includes uncertainty; (14) includes quality assurance (Roy et al. 2018).
A score of 0 = did not meet; 0.5 = partially met; 1 = fully met.
GLANSRA
USDA APHIS
ERSS
WI (SAGs/lit review)
GL AqWRA
NY
Spp. description (1)
1
1
1
1
0.5
0.5
Invasion likelihood (2)
1
1
0.5
0.5
0.5
1
Distribution, spread, impacts (3)
1
1
1
1
0.5
1
Introduction pathways (4)
1
0.5
0.5
0.5
0.5
0
Biodiversity/ecosystems impacts (5)
1
1
1
1
1
1
Ecosystem services impacts (6)
0.5
1
0.5
0.5
0.5
0.5
Socio-economic impacts (7)
1
0.5
1
1
0.5
0
Impacts to critical spp./habitats (8)
0.5
1
1
0
0
0
Climate change (9)
1
0
0.5
1
0
0
Results despite information gaps (10)
1
1
1
0
0
1
Documents information sources (11)
0.5
0.5
0.5
0.5
0.5
0.5
Provides usable summery (12)
1
1
1
0.5
1
1
Includes uncertainty (13)
1
1
1
0
1
0
Includes quality assurance (14)
0.5
0.5
0.5
0.5
0.5
0.5
Total score (out of 14)
12
11
11
8
7
7
(USDA APHIS) and United States Fish and Wildlife Service Ecological
Risk Screening Summary (ERSS) tool. These frameworks included assessment
of ecosystem services, threatened species/habitat and climate change,
whereas the lower scoring frameworks did not. The U.S. Fish and Wildlife
Service’s Ecological Risk Screening Summary tool recently revised their
standard operating procedure to provide for a supplementary assessment
of future climate scenarios, upon request. However, this is not included as
part of the core assessment so was scored as partially met.
Only two states (Michigan and New York) use risk assessment frameworks
to identify and justify listing of both plants and animals, with Michigan the
only state to legislatively mandate these frameworks (Heathcote 2015).
Michigan initially mandated the U.S. Fish and Wildlife Service’s Ecological
Risk Screening Summary tool (US Fish and Wildlife Service 2020) for
animals and the USDA’s plant protection and quarantine weed risk
assessment protocol (USDA APHIS 2020) for plants, although the state has
since expanded the list of potential risk frameworks. New York has developed
their own scoring tool that includes ecological and socio-economic benefits
and impacts (New York Invasive Species Council 2010). Indiana has used
the U.S. AqWRA tool for plants (Gordon et al. 2012; Gantz et al. 2015) and
is developing a tool for animals. Other jurisdictions apply risk assessments
more informally, using different approaches based on the species, or
instead relying on an expert panel process (e.g., MN, OH). Wisconsin uses
a standardized literature review and formalized species assessment group
to identify and assess species for regulation (Wisconsin Invasive Species
Council 2018). Some jurisdictions are attempting to standardize their risk

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 561
assessment approach by legislating the use of specific risk assessment
frameworks (e.g., Pennsylvania) (Stahlman pers. comm.).
Progress toward sufficient and transparent regulated species lists
Based on the GLANSRA surveillance list (Davidson et al. 2021), 58 surveillance
species are not regulated by any jurisdiction (Table 4; plotted as “0”
jurisdictions in Figures 6, 7). There was a weak correlation between impact
score and number of jurisdictions regulating all animal species (Tau = 0.26,
P = 0), and all species (animals and plants) (Tau 0.21: P = 0) known to be
in the live trade pathways, but not for plants (Tau = 0.14: P = 0.08). Many
of the most-regulated species have impact scores in the low or low-moderate
categories, and several species with high impact scores are regulated by less
than half of jurisdictions (Figures 6, 7). Twenty-one species (17 plant and 4
animal) are identified as priorities for future regulatory listing because they
meet the criteria for minimum impact (moderate or high) and likelihood of
arrival from GLANSRA (excluding shipping/ballast pathway-only species)
and are not yet regulated by all ten Great Lakes’ jurisdictions (Table 5).
Discussion
The Great Lakes has been at the forefront of the scientific development of
aquatic risk assessment methods and has demonstrated invasive species
can be accurately predicted through trait-based analysis (Kolar and Lodge
2001; Keller et al. 2007). Management uptake of these methods was initially
slow, and in 2008 when the GLP assessed interjurisdictional patterns in
regulated species, many jurisdictions were reliant on expert panels to identify
potential species for listing. At the time, state and federal prevention efforts
were focused on the shipping pathway and awareness of the risk posed by
the live trade pathways was low (Padilla and Williams 2004; Rixon et al.
2005; Keller and Lodge 2007). It is therefore not surprising that in 2008,
regulated species lists were a disparate collection of species with limited
similarity across the jurisdictions. Twelve years later, in concert with a
growing number of risk assessment methods (Mandrak 2014; Gantz et al.
2015; Howeth et al. 2016; Davidson et al. 2017; Marcot et al. 2019), there is
increasing recognition of the need for regional coordination and
information sharing. These efforts have led to the establishment of two risk
assessment clearinghouses (Great Lakes Aquatic Nonindigenous Species
Information System 2020; Invasive Species Centre 2020) and regionally
agreed-upon lists of “least wanted” species (GSGP 2013). Nevertheless,
despite the region’s wealth of risk assessment tools and species risk
assessments, there remains both significant differences in regulated species
lists between jurisdictions and under-regulation of potentially harmful AIS
in most jurisdictions. This “weakest link” dilemma is shared by other
regions where multiple jurisdictions share management of large aquatic
ecosystems (e.g., the Colorado and Murray-Darling River basins; Wheeler

Progress in regulating Great Lakes aquatic nonindigenous species
Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 562
Table 4. List of surveillance species not regulated by any jurisdictions (58), assessed using the GLANSRA framework. The
surveillance species list includes species present in at least one introduction pathway and would represent novel introductions to the
Great Lakes basin, as well as established species with localized distribution in the Great Lakes (in ≤4 Great Lakes) but capable of
range expansion. Species with no known history of invasion, plants not generally associated with aquatic habitats, and plants or
animals not suited to temperate freshwater habitats are also excluded from this list.
Taxa Species name Common name
GLANSRA Env
Impact Score
GLANSRA Soc/Cult
Impact Score
Total impact
score
Bryozoan
Fredericella sultana
8
12
20
Bryozoan
Lophopodella carteri
3
1
4
Crustacean
Apocorophium lacustre
2
0
2
Crustacean
Argulus japonicus
Japanese fishlouse
6
6
12
Crustacean
Calanipeda aquaedulcis
6
0
6
Crustacean
Chelicorophium curvispinum
Caspian mud shrimp
3
0
3
Crustacean
Cyclops kolensis
3
0
3
Crustacean
Daphnia galeata galeata
Waterflea
7
0
7
Crustacean
Dikerogammarus haemobaphes
2
0
2
Crustacean
Echinogammarus warpachowskyi
2
0
2
Crustacean
Gmelinoides fasciatus
Baikalian amphipod
8
0
8
Crustacean
Limnomysis benedeni
4
0
4
Crustacean
Obesogammarus crassus
6
0
6
Crustacean
Obesogammarus obesus
8
0
8
Crustacean
Faxonius limosus
Spinycheek crayfish
1
2
3
Crustacean
Pacifastacus leniusculus
Signal crayfish
14
3
17
Crustacean
Paramysis ullskyi
7
0
7
Crustacean
Paramysis lacustris
3
0
3
Crustacean
Podonevadne trigona ovum
2
0
2
Crustacean
Pontastacus leptodactylus
Danube crayfish
2
1
3
Crustacean
Pontogammarus robustoides
4
0
4
Crustacean
Schizopera borutzkyi
Oarsman
6
0
6
Fish
Acanthogobius flavimanus
Yellowfin goby
7
0
7
Fish
Alburnus alburnus
Alver, bleak
14
0
14
Fish
Atherina boyeri
Big-scale sand-smelt
2
0
2
Fish
Babka gymnotrachelus
Racer goby
2
1
3
Fish
Benthophilus stellatus
Starry goby
3
0
3
Fish
Gobio gobio
Gudgeon
6
0
6
Fish
Hypomesus nipponensis
Wakasagi
6
0
6
Fish
Ictalurus furcatus
Blue catfish
2
1
3
Fish
Leuciscus leuciscus
Dace
7
6
13
Fish
Menidia beryllina
Inland silverside
7
0
7
Fish
Morone saxatilis x chrysops
Hybrid striped bass/wiper
3
0
3
Fish
Neogobius fluviatilis
Babka goby
3
0
3
Fish
Oncorhynchus keta
Chum salmon, Keta salmon
3
0
3
Fish
Osmerus eperlanus
European smelt
7
0
7
Fish
Siniperca chuatsi
Mandarin fish
6
1
7
Mollusk
Sinanodonta woodiana
Chinese pond mussel
8
0
8
Mollusk
Lithoglyphus naticoides
Gravel snail
7
0
7
Mollusk
Mytilopsis leucophaeata
Dark false mussel
14
7
21
Plant
Alternanthera philoxeroides
Alligator weed
18
24
42
Plant
Aponogeton distachyos
Cape pondweed
2
0
2
Plant
Azolla filiculoides
Pacific mosquitofern
8
14
22
Plant
Cyperus difformis
Variable flat sedge
1
6
7
Plant
Egeria najas
3
2
5
Plant
Juncus compressus
Flattened rush
2
1
3
Plant
Juncus gerardii
Black-grass rush
7
2
9
Plant
Juncus inflexus
European meadow rush
2
1
3
Plant
Limnobium spongia
American spongeplant
2
3
5
Plant
Ludwigia adscendens
Water primrose
2
4
6
Plant
Ludwigia grandiflora
18
10
28
Plant
Oxycaryum cubense
Cuban bulrush
7
1
8
Plant
Rotala rotundifolia
Roundlaf toothcup
2
1
3
Plant
Sagittaria platyphylla
Delta arrowhead
12
13
25

Progress in regulating Great Lakes aquatic nonindigenous species
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Table 4. (continued).
Taxa Species name Common name
GLANSRA Env
Impact Score
GLANSRA Soc/Cult
Impact Score
Total impact
score
Plant
Salvinia minima
Water spangles
8
8
16
Plant
Typha orientalis
Bullrush/raupo
6
0
6
Plant
Vallisneria spiralis
Eelgrass
7
2
9
Platyhelminthes
Ichthyocotylurus pileatus
Digenean fluke
7
0
7
Figure 6. Plot of regulated and surveillance (unregulated) plant/algae species capable of arriving and establishing in the Great Lakes
basin, showing total impact score (environmental plus social/cultural, based on GLANSRA framework) against number of regulating
jurisdictions. Likelihood of arrival is highest score from all pathways in GLANRA assessment. Those species established in the
Great Lakes did not receive a likelihood of arrival score. “Least wanted” indicates a species included on the GSGP “least wanted” list.
Figure 7. Plot of regulated and surveillance (unregulated) animal species capable of arriving and establishing in the Great Lakes
basin, showing total impact score (environmental plus social/cultural, based on GLANSRA framework) against number of
regulating jurisdictions. Likelihood of arrival is highest score from all pathways in GLANRA assessment. Those species
established in the Great Lakes did not receive a likelihood of arrival score. “Least wanted” indicates a species included on the
GSGP “least wanted” list.

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Table 5. List of 17 plant and 4 animal species for regulatory consideration and “least wanted” status. ^Indicates a species listed as
“injurious wildlife” under the Lacey Act (18 U.S.C. 42). s Indicates species on the GLANSRA surveillance species list. Pathway
score is for the trade pathways. * indicates a score for a non-trade pathway if a species scores unlikely for a trade pathway; ()
indicates a higher-scoring non-trade pathway. Unk = unknown. Risk assessments include: Great Lakes Aquatic Nonindigenous
Species Risk Assessment (GLANSRA); United States Department of Agriculture, Animal and Plant Health Inspection Service
(USDA APHIS); Ecological Risk Screening Summaries, U.S. Fish and Wildlife Service (ERSS); Wisconsin Literature Review
(WI); Great Lakes Aquatic Weed Risk Assessment (GL AqWRA); and New York State Ranking System (NY).
Taxa Species name Common name Jurisdictions
regulated
GLANSRA
Total impact
score
GLANSRA
pathway score
Completed risk
assessments
Plant Salvinia molesta^s Giant salvinia 6 49 L*
GLANSRA, ERSS,
WI, NY
Plant Pistia stratiotess Water lettuce 1 44 H
GLANSRA, ERSS,
GL AqWRA, WI, NY
Plant
Alternanthera
philoxeroides
Alligator weed 0 42 L (H*)
GLANSRA, ERSS,
GL AqWRA
Plant Eichhornia crassipess Water hyacinth 2 41 H
GLANSRA, ERSS,
GL AqWRA, WI, NY
Plant
Didymosphenia geminatas
Didymo
2
31
H*
GLANSRA, WI
Plant
Melaleuca quinquenervia^s
Broad-leaved paperbark
2
31
L*
GLANSRA, ERSS
Plant
Prymnesium parvums
Golden algae
2
31
M*
GLANSRA, WI
Plant
Lythrum virgatums
Wanded loosestrife
5
30
H
GLANSRA, WI
Plant
Typha domingensiss
Southern cattail
1
29
L (M *)
GLANSRA, WI
Animal Gambusia holbrookis Eastern mosquitofish 2 28 H
GLANSRA, ERSS,
WI
Plant Ludwigia grandiflora Water primrose 0 28 L*
GLANSRA, ERSS,
GL AqWRA, NY
Plant Ludwigia hexapetala s
Uruguayan primrose
willow
2 28 H
GLANSRA, GL
AqWRA, NY
Plant
Ludwigia peploidess
Floating primrose willow
1
28
H
GLANSRA, NY
Plant Lagarosiphon major^s
Oxygen weed or African
elodea
6 27 Unk (L*)
GLANSRA, ERSS,
GL AqWRA, WI
Plant
Myriophyllum
heterophyllum x M. laxum
s
Broadleaf water-milfoil
hybrid
1 26 Unk (L*) GLANSRA
Plant
Sagittaria platyphylla
Delta arrowhead
0
25
L
GLANSRA
Animals
Acipenser ruthenus
Sterlet
2
24
H
GLANSRA, WI
Plant Arundo donaxs Giant reed 1 22 H
GLANSRA, USDA
APHIS, ERSS, WI
Plant
Azolla filiculoides
Pacific mosquitofern
0
22
H
GLANSRA, ERSS
Animal
Mytilopsis leucophaeata
Dark false mussel
0
21
M*
GLANSRA, ERSS
Animal
Fredericella sultana
Branching bryozoan
0
20
H*
GLANSRA
et al. 2018). In addition to the “weakest link” issue, interpreting the codes
and statutes covering each jurisdiction’s regulated species can be
challenging. For example, one of the jurisdictions regulates crayfish three
different ways: a general legislative code that is extremely difficult to find
and interpret, a list from the fishing department and a list related to
aquaculture. The fact that interpreting these conflicting lists posed a
significant challenge in the writing of a manuscript dedicated to this topic
has implications for how these statutes are interpreted by the wider public.
To continue progress in harmonization of regulated species, a key
challenge is how to objectively identify the next set of regional priorities.
Here we discuss progress toward species’ regulation that is consistent (the
same suite of species is regulated across all jurisdictions), sufficient (species
identified as highest risk are prioritized for regulation), and transparent
(species are listed for regulation based on the consistent application of an
objective and comprehensive risk assessment framework).

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Progress toward consistent regulated species lists
Great Lakes jurisdictions have regulated many high impact species; in fact,
all species for which risk assessment predicted the highest impact (total
impact score of 40–60; Tables 1, 2; Figures 6, 7) are regulated by at least
one jurisdiction, except one (alligator weed Alternanthera philoxeroides
Mart. Griseb., discussed below). Brazilian elodea (Egeria densa Planch.)
and hydrilla (Hydrilla verticillata (L.f.) Royle) are regulated by eight and
nine jurisdictions, respectively. State and provincial regulated species lists,
and the number of species within these lists included by the majority of
Great Lakes jurisdictions, have increased over the last 12 years (Figures 1–3).
We venture that this is due in part to the increasing use of evidence-based
decision-making. There appears to be a general trend towards increasing
similarity across animal and plant regulated species lists. For animals there
appear to be two clusters of jurisdictions developing. Average dissimilarity
is decreasing but was not significantly different across years, probably
because these two groups appear to be diverging. The two outlying
jurisdictions (WI, NY) and Minnesota (intermediate between these two
groups) are also the jurisdictions with the greatest number of regulated
animal species (Figure 4) and their divergence is presumably driven by the
regulation of a group of unique species across these three jurisdictions. For
plants, three states (MN, IL, IN) form a tight cluster, noting that the Illinois
regulated species lists was based off Indiana’s list and the same risk
assessment data. All other jurisdictions appear to be trending towards this
group, but average dissimilarity does not appear to be declining. However,
the higher similarity in 2008 is an artefact of the few species listed then,
and the absences (zeros) making these jurisdictions appear similar in
ordination space. Unlike animals, those states with the highest similarity
have intermediate numbers of listed species. The two jurisdictions with the
fewest listed species (ON, OH) are two of the least similar lists by 2020,
whereas Wisconsin (most comprehensive list) appears to be trending
towards the IL, IN, MN cluster. New York seems to be the other outlier,
and while it has a reasonably comprehensive list of species, the differences
may in part reflect the marine coastal geography of the state and different
introduction risks associated with neighbouring eastern seaboard states. As
state and provincial regulated species lists are informed by regional risk
assessment and clearinghouse data, and there is a more deliberate effort to
complement neighboring regulatory efforts, we would expect these two groups
to continue to come together and the average level of dissimilarity to decline.
Additional gains towards regional efforts to harmonize regulated species
lists across the region could be achieved through progress on aquatic plants
by a subset of jurisdictions (notably Ontario and Québec). Some Great
Lakes jurisdictions have initiated discussions to inform regional
harmonization efforts across neighboring states and provinces, but to date

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there do not appear to have been any formal resolutions. For animals, most
states have made progress to list additional high-risk species and continued
progress towards consistent regulation of the agreed upon “least wanted”
species is evident. A notable exception is Pennsylvania, where no “least
wanted” species that were not already regulated by the state in 2013 have
been listed since publication of the “least wanted” list (but as noted above
efforts to develop AIS listing criteria are underway in that state). Existing
gaps in the “least wanted” list may be due to socio-political factors, given
that regionally recognized scientific evidence for risk would appear to
provide the evidential basis to justify prohibition (for example, current
“least wanted” species New Zealand mudsnail Potamopyrgus antipodarum
and marbled crayfish Procambarus virginalis are regulated by only four and
one jurisdictions, respectively).
Progress toward sufficient regulated species lists
Despite substantial progress, there remain 21 species with GLANSRA impact
scores of medium or high (total impact score of 20–60) and likelihood of
introduction of unknown, low, moderate or high that are not yet regulated
across all jurisdictions. Notably, the two species predicted to have the
greatest impact and a high likelihood of arrival are regulated by very few
jurisdictions (water hyacinth Eichhornia crassipes – 2 and water lettuce
Pistia stratiotes – 1). These two species are economically valuable to the live
trade industry, and there has been some uncertainty about the ability of
these plants to over winter in the Great Lakes or produce viable seeds
(Adebayo et al. 2011). However, repeated detections in the same locations
in Frank and Poet Drain (Detroit River) may provide anecdotal evidence of
seed production; understanding if and under what circumstances sexual
reproduction occurs in the Great Lakes is a critical research need (Cahill et
al. 2018). Furthermore, as the region warms these species are more likely to
be able to overwinter in sheltered locations and spread rapidly in spring.
Given their global history of invasion and damages (E. crassipes listed on
the “100 of the World’s Worst Invasive Alien Species” by the Global
Invasive Species Database, with P. stratioties having similar effects), their
predicted high impact in the Great Lakes, and the success of “least wanted”
designation in increasing the number of regulating jurisdictions, all Great
Lakes states and provinces could consider these two as future “least wanted”
species to increase consistency (and subsequent likelihood of prevention).
But this will require consultation with the aquarium and water garden
industries.
Alligator weed (Alternanthera philoxeroides) is one high risk species that
is not regulated by any jurisdiction, despite its presence in Illinois and
states on the southern border of the Great Lakes states. It is another species
for which the Great Lakes may be at the northern limits of its range, given
its intolerance of extended periods of freezing (Shen et al. 2017). Nevertheless,

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given its high potential for impact, proximity to the basin, and the
likelihood that climate change-induced milder winters and warmer
summers will increase the chance for establishment throughout the Great
Lakes basin (Stefan et al. 2001), this species would seem to be a high
priority for regulation and advanced planning could allow industry to find
an alternative during the regulatory process.
There are also species in the moderate impact category that are either
not regulated or appear to be underregulated (less than 5 jurisdictions).
Those unregulated live trade species with total impact scores of 20–39
include Pacific mosquitofern Azolla filiculoides Lam. and Delta arrowhead
Sagittaria platyphylla (Engelm.) J.G. Sm. Those underregulated live trade
species with total impact scores of 20–39 include broadleaf water-milfoil
hybrid Myriophyllum heterophyllum Michx. × M. laxum Shuttlw. ex
Chapm., floating primrose willow Ludwigia peploides (Kunth) P.H. Raven,
eastern mosquitofish Gambusia holbrooki Girard, 1859, Uruguayan
primrose willow Ludwigia hexapetala (Hook. & Arn.) Zardini, H.Y. Gu &
P.H. Raven, southern cat-tail Typha domingensis Pers., giant reed Arundo
donax L., sterlet Acipenser ruthenus Linnaeus, 1758 and red swamp
crayfish Procambarus clarkii (Girard, 1852). While it is up to each
jurisdiction’s risk management staff to determine the impact threshold
warranting regulation, some jurisdictions have often used moderate or
high impact scores to justify regulation (e.g., New York Invasive Species
Council 2010). Regulating species with predicted high or moderate impacts
may be particularly relevant for species, like those listed above, with a high
likelihood of arrival via the live trade pathway.
Progress toward transparent regulated species lists
One of the most challenging aspects about regulating the live trade
pathway is that the outcomes of a risk assessment are not usually the only
factor considered when deciding to mitigate risk and regulate a species. All
species in trade have a varying degree of economic value that influences
whether they are regulated even when evidence suggests the species will
have negative impacts to the environment and/or human health. For
example, in the U.S., revenues from reptile sales are estimated at US$1.4
billion (Collis and Fenili 2011), with each additional species sold generating
about US$90,000 in profit (Springborn et al. 2011). While many suppliers,
retailers and consumers are interested in preventing harmful AIS impact,
sectors of the aquarium industry such as the Pet Industry Joint Advisory
Council have opposed past proposals on importation restrictions for
nonnative wildlife species (Strecker et al. 2011). As such, adding species to
regulated species lists already perceived as overly long requires transparency
on behalf of the responsible agency, as well as coordination with the live
trade industry.

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As noted above, of the 136 regulated plant and animal species, the 6th
(Pistia stratiotes, water lettuce) and 9th (Eichhornia crassipes, water hyacinth)
highest-scoring species are only regulated by one (Wisconsin) and two
(Wisconsin and Minnesota) jurisdictions, respectively. Both of these are
popular commercial plants. In contrast, while there are several species with
high impacts that justify their status as “least wanted”, over half (11 of 21)
of the “least wanted” species have low total impact scores. Several other
species could be considered “overregulated”. For example, tubenose goby
Proterorhinus marmoratus is regulated by all 10 jurisdictions despite
having a total impact score of one. Of the 73 regulated species with total
impact less than 10 (“very low” impact category), 18 are regulated in at
least half of the jurisdictions. Of the 136 regulated species, 74% have low
impacts; only seven have high impacts (note: this is for all regulated
species, not just those in trade). In addition, three of the regulated species
(arrowleaf Monochoria hastata (L.) Solms, heartshape pickerelweed
Monochoria vaginalis (Burm. f.) C. Presl ex Kunth and giant salvinia
Salvinia biloba Raddi) are predicted to be unlikely to arrive via any
pathway, the latter likely regulated by jurisdictions due to its status as a
species within a federally regulated taxon (genus Salvinia). Finally, several
species unlikely to establish due to abiotic conditions in the Great Lakes
(freshwater or cold winter temperatures) are regulated by multiple
jurisdictions (e.g., marine Caulerpa taxifolia (Vahl) C. Ag. is regulated by
four jurisdictions without marine coastlines). While we do not necessarily
suggest that species like Caulerpa be de-regulated (especially for those
Great Lakes jurisdictions that also contain Atlantic coast marine habitats
that would be vulnerable to marine species), it is important to note this
issue of species with potentially low impacts (or low likelihood of arrival or
establishment) being regulated, while others with the ability to arrive,
survive and have larger impact are not.
There are several species not present in the live trade pathway (e.g.,
zebra mussel Dreissena polymorpha Pallas, 1771) that are regulated by at
least one jurisdiction. Although presence in the live trade pathways is the
primary reason to regulate a species, other reasons exist that justify regulation.
For example, New Zealand mud snail and starry stonewort are found in the
hitchhiking/fouling pathway and are commonly transported on recreational
boats. Regulation of these species would ensure, e.g., that inspection officers
and volunteers would be able to identify them during watercraft inspections,
thus limiting their transfer between water bodies. While regulation of
individual species is appropriate for pathways such as live trade and even
hitchhiking/fouling, we acknowledge that regulation of individual species
may not be appropriate for pathways such as shipping (ballast water). As
such, we did not include species as candidates for regional regulatory
consideration whose only pathway of introduction is ballast water (full
pathway scores included in Supplementary Table S2.

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Resources for regulation and enforcement are limited; effort spent
focusing on a low impact species is effort not spent on a higher impact
species. In addition, if a species is predicted to have no or very low impact,
regulation may harm the live trade industry unnecessarily. To some extent,
existing patterns may reflect the role that “expert panels” played in
identifying species for regulation in the early efforts to manage this
pathway. It is therefore encouraging that there appears to be an evolution
to increasing adoption of semi-quantitative and formal data driven
assessment processes, that are less prone to individual bias. This is perhaps
a function of both management’s acceptance of the science of risk
assessment and the development of risk assessment tools that provide the
range of information needed for regulatory processes.
Notably, while academic risk assessment efforts have been directed to
more statistical-based and parsimonious models (e.g., Keller et al. 2007;
Howeth et al. 2016), in part assuming that reduced data needs results in a
more efficient screening process, the frameworks developed by management
agencies have tended towards semi-quantitative systems that cover a broad
range of information consistent with recommendations of Roy et al. (2018;
Leung et al. 2012). We speculate that this is not due to reluctance by the
agencies to adopt these parsimonious models, but rather, the agencies’
need for detailed assessments that document the full spectrum of factors
related to invasion (e.g., introduction, establishment, and both ecological
and socio-economic impact).
Given the economic and social value of aquatic live trade activities, it is
important to maintain the sale of a variety of organisms. Yet, given the
environmental costs of harmful live trade releases, and value of prevention
vs. control, it is also important to regulate those species that should not be
traded. Therefore, it is essential that the regulatory process for listing
species be transparent, objective and consistent. Risk assessment is a
rigorous tool that can inform the risk management process when
attempting to list species for regulation (Mandrak and Cudmore 2015) and
provide justification for limitations on live trade (Roy et al. 2018). For the
Great Lakes, a range of risk assessment methods exist that meet Roy et al.
(2018) recommendations to varying degrees (Table 3).
Progress in regional risk assessment framework development
Despite the availability of risk assessment frameworks relevant to the Great
Lakes region (Table 3), only Michigan and New York legislate the use of a
risk assessment framework as part of the regulatory decision making
process. New York uses the same framework for both plants and animals,
whereas Michigan uses two frameworks, one for plants and another for
animals. Indiana, which is close to finalizing a risk assessment process for
both plants and animals, will also use a different framework for the two

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groups. The application of a multitude of assessments across the basin
likely results in duplication of effort and may impede knowledge sharing
and the ability to reach regional consensus. The GLANSIS Risk Assessment
Clearinghouse has developed a Methods Explorer that allows a side-by-side
comparison of a variety of frameworks, which further demonstrates the
number and variety of risk assessments.
The fact that some jurisdictions currently implement risk assessment as
part of the regulatory decision making process and that other jurisdictions
are currently working towards adoption of a similar model presents an
opportunity for jurisdictions to work together to ensure that the same (or
very similar) frameworks are selected for use across the region. Adopting
the same risk assessment framework would allow jurisdictions to save
resources and use (or use with modifications) existing species risk
assessments completed by other jurisdictions in the region (Heathcote
2015). This is a model that has been implemented in the European Union
(EU), where a consistent risk assessment framework is applied across
Member States to inform an agreed upon list of regulated species. In 2018,
the European Commission (executive body of the EU) approved a risk
assessment template that met 14 minimum standards, as described in Roy
et al. (2018). This template is used to assess priority species, to decide
whether they should be included on the list of invasive species under
Regulation (EU) 1143/2014 on the prevention and management of the
introduction and spread of invasive alien species (European Commission
2020). The list of invasive species (and any related management actions)
applies across all Member States (H. Roy pers. comm.).
Although none of the risk assessments we evaluated meet all of the
criteria laid out by Roy et al. (2018), some measure up well (GLANSRA,
APHIS, and ERSS) and all of them meet at least half of the minimum
standards. GLANSRA, which can be used to assess both plants and
animals, scored highest, yet is not widely used for regulatory decision
making across Great Lakes’ jurisdictions. USDA APHIS, which is used by
Michigan to inform invasive plant listings, meets most of the criteria, but
does not assess animals. The ERSS can assess both plants and animals but
does not assess likelihood of introduction. The ERSS is intended as a risk
screening tool to identify species that merit additional and more detailed
risk screening (S. Jewell pers. comm.). If a species scores highly in an ERSS,
and is considered for listing under the Lacey Act, a more in-depth analysis
is completed and published in the Federal Register (US Fish and Wildlife
Service 2001, e.g., US Office of the Federal Register 2016). Furthermore,
the Ontario Ministry of Natural Resources and Forestry is also developing
its own risk assessment tool. No assessment is perfect and no single
assessment is likely to meet every jurisdictions’ wants and needs.
Nevertheless, a regional process to consider how existing risk assessment
tools could be adopted or adapted to meet regional needs and an agreed

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upon set of minimum standards could help to move the region towards
more consistent, sufficient, and transparent regulated species lists, and
reduce duplication of effort.
Beyond risk assessment: other issues facing live trade pathway regulations
and enforcement
Adoption of a uniform framework and process to apply risk assessment in
a regulatory context will improve consistency, sufficiency, and transparency
of regulated species lists. But regulatory challenges may be caused by
factors unrelated to risk assessment, per se, such as inconsistent risk
management, jurisdictional prerogative, insufficient funding, species native
ranges, enforcement terminology and authority, and supplier/distributor
issues. These issues will also need to be addressed for effective management
of the live trade pathway.
In general, risk assessment is the understanding of likelihood and
impact; risk management is the action taken based on this understanding
(e.g., regulation). Risk management includes both the decision-making
body and other stakeholders in order to identify value judgements and
determine the risk tolerance (also known as the acceptable level of risk).
This may present a challenge because the acceptable level of risk can differ,
so that one jurisdiction may aim to regulate any species with an impact of
low, moderate or high, while another may only aim to regulate species with
a high impact (Davidson et al. 2015). Thus, jurisdictions must not only apply
consistent risk assessment outcomes, but also make consistent decisions on
how “strong” their link will be in the proverbial chain of protection.
Jurisdictional prerogative reflects the fundamental differences in regulatory
philosophy that exist across the basin. Most jurisdictions take a prohibited
species approach (only species listed in specific legislation are regulated),
while one (Illinois) takes a mostly allowable species list approach (only
species listed in specific legislation are allowed in trade) (Sturtevant et al.
2016). Allowed lists are a precautionary option to regulating species
(Padilla and Williams 2004) but can be difficult to implement and enforce
due to the large number of species in some aspects of live trade, e.g., the
aquarium industry (Heathcote 2015). When neighboring jurisdictions vary
between allowed and prohibited species lists approach, it can be challenging
to understand what, and how, species are regulated. Regional agreement on a
risk assessment and framework for application could help to alleviate this issue.
Insufficient funding is another impediment to the development and
enforcement of regulated species lists. In the U.S., most jurisdictions have
little to no funding to support their invasive species programs apart from
federal assistance funding. Several jurisdictions have relatively significant
budgets due to monies specifically allocated to AIS management, e.g.,
Minnesota uses a portion of boat and trailer license fees, New York uses a

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portion of real estate transfer taxes and unclaimed bottle deposit bottles,
and Wisconsin uses a portion of the gas tax (Heathcote 2015). Relatively
well-funded jurisdictions (and especially those relying on “soft money”) are
nevertheless constrained by budgets insufficient to implement jurisdictional
AIS management plans. Significant time is required to assess species for
regulatory consideration; insufficient funding to support this endeavor is
also a contributing factor to inconsistent regulations, including jurisdictions
that do require risk assessments. Finally, even after regulations are passed,
such laws are rendered ineffective without funding to hire trained staff to
enforce them (Heathcote 2015).
Species native ranges can make universal regulation difficult. For
example, the ghost shiner Notropis buchanani Meek, 1896 is native to the
southern Great Lakes basin (and endangered in Pennsylvania), but it is
invasive in other parts of the basin (Sturtevant et al. 2016). Four cryptogenic
species (rusty crayfish Faxonius rusticus Girard, 1852, red swamp crayfish
Procambarus clarkii, broadleaf water-milfoil Myriophyllum heterophyllum
Michx. and spiny naiad Najas marina L.) are on the regulated species list in
the Great Lakes, despite being considered by some jurisdictions to be
native. The regulation of these species in jurisdictions where they have
native and non-native populations is inconsistent. For example, rusty
crayfish is regulated by IL (where it has native populations, though not in
the basin, and non-native populations in the basin) and MI (where it has
native and non-native populations, both in the basin) but not IN and OH
(where is also has native and non-native populations in the basin). Although
these species are considered native to a subset of Great Lakes jurisdictions,
and thus would not be expected to be regulated in these jurisdictions, the
number of these native species are small and wouldn’t be expected to
change the observed patterns in regulation.
Even when there is a consistent list of species between jurisdictions, the
terminology surrounding the regulation may vary, with “injurious”,
“restricted” and “prohibited” having different definitions and penalties.
Addressing such differences in legislative terminology and definitions have
reduced confusion and increased compliance in other areas of AIS
management, including recreational boating (Otts and Nanjappa 2014).
Furthermore, responsibility for regulation of species may be split between
agencies within a jurisdiction. For example, in Pennsylvania, the authority
for regulation of aquarium fish is under the State Fish and Boat Code, but
enforcement is under the Department of Agriculture. Enforcement of this
pathway is already difficult owing to the vast number of bait/aquarium/
pond/aquaculture retailers and the associated suppliers and consumers, as
well as the vast number of species in trade and the associated difficulty in
identifying them. Attempting to coordinate such efforts across agencies
only increases the burden (Heathcote 2015).

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Regulation is important because awareness of the potential for species in
live trade to become invasive is limited (Seekamp et al. 2016). However,
regulation alone has not been effective at reducing trade in regulated
species (Diaz et al. 2012; June-Wells et al. 2012; Patoka et al. 2018). If profit
from trade in regulated species exceeds the associated fines, for example,
retailers may continue to offer banned species for sale (Drew et al. 2010).
The proliferation of online commerce also makes enforcement difficult
and complex (Lenda et al. 2014). Kay and Hoyle (2001) found sites selling
nearly every aquatic or wetland plant listed in the United States as either a
Federal Noxious Weed or as a noxious weed in one or more states.
Even if retailers attempt to comply, they often face additional barriers to
success. Inconsistent regulations pose challenges for multi-state retailers or
their suppliers (Peters and Lodge 2009; Drew et al. 2010). Unlabeled or
mislabeled specimens hinder retailers’ (and inspection officers’) ability to
identify regulated species and remove them from trade; the presence of
“hitchhikers” associated with the intended species makes this even more
difficult (Maki and Galatowitsch 2004; Keller and Lodge 2007). For
example, in a study of eDNA from bait and pond stores in the Great Lakes,
88% of bait stores had AIS present in stocked bait. Samples from pond stores
found eDNA from species such as bighead carp, silver carp, European ide,
zebra mussels, invasive bryozoans, and invasive snails (Snyder et al. 2020).
Educational efforts focused on existing regulations, species identification
and best management practices for nonindigenous species could help to
improve compliance and overall effectiveness of regulations (Oele et al.
2015), especially if coupled with regular surveillance of the pathway. New
high throughput sequencing eDNA survey methods are becoming cost
effective and overcome the reliance on visual inspections that can have low
levels of detection sensitivity and be time and cost prohibitive (Nathan et
al. 2015).
Conclusion
Live trade is a major pathway for the introduction of non-indigenous
species, with thousands of species from a variety of taxa transported
globally (Lockwood et al. 2019). In addition, climate change will shift the
suite of plants and animals able to establish in many regions of the world,
including the Great Lakes, and therefore risk-screening should be applied
to new species and reviewed for species currently allowed for sale (Bradley
et al. 2012). To address the threat of invasive species in trade in a “weakest
link” regional management context, the Great Lakes needs to harmonize
and increase the number of species listed for regulation. In the near-term,
we have identified the next suite of priority high-risk species for
consideration for regulation across the region. In the long term, we believe
the region should work towards investing in a consistent (set of) risk
assessment(s) that meet the minimum criteria for risk assessments, and

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Davidson et al. (2021), Management of Biological Invasions 12(3): 546–577, https://doi.org/10.3391/mbi.2021.12.3.04 574
whose results can be used by all jurisdictions. Adoption of a consistent risk
assessment(s) would help establish a transparent process for state and
federal stakeholders to consistently regulate live trade species. It would aid
data sharing and reduce duplication of efforts related to assessing species.
Such transparency and efficiency are essential given the economic
importance of the live trade industries and the limited resources available
to manage new and established AIS.
Acknowledgements
This manuscript has evolved out of an initial assessment by the Research committee of the
Great Lakes Panel on Aquatic Nuisance Species, and from discussions by the panels Ad Hoc
Trade in live organisms subcommittee. We thank David Hamilton, Katie Kahl, Sarah LeSage
and Eric Fischer for their advice, and many discussions over the last 12 years, that have helped
inform our thinking. We would like to acknowledge several individuals who provided input and
data used in this study. Rochelle Sturtevant and GLANSIS provided risk assessment data for
several species. Kristina Davis (Notre Dame Center for Research Computing) formatted the
figures included in this manuscript. Patrick Canniff assisted in the risk assessment framework
review. Comments from Katherine Wyman-Grothem and an anonymous reviewer significantly
improved the manuscript.
Funding Declaration
ADD, AJT, WLC, CW and EJ contributions were partially funded through the Blue Accounting
Initiative. Blue Accounting receives funding support from the Charles Stewart Mott
Foundation, the Fred A. and Barbara M. Erb Family Foundation, the Joyce Foundation, and the
Herbert H. and Grace A. Dow Foundation. The funders had no role in study design, data
collection and analysis, decision to publish, or preparation of the manuscript.
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Supplementary material
The following supplementary material is available for this article:
Appendix 1. Description of risk assessment frameworks relevant to the Great Lakes region.
Table S1. Table of regulated aquatic species not expected to arrive or establish in the Great Lakes basin.
Table S2. Table of GLANSRA pathway scores for all species.
This material is available as part of online article from:
http://www.reabic.net/journals/mbi/2021/Supplements/MBI_2021_Davidson_etal_SupplementaryTables_2.xlsx
http://www.reabic.net/journals/mbi/2021/Supplements/MBI_2021_Davidson_etal_Appendix_1.pdf