Published in November 2017
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Research articles
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Michelle T. Christy, Julie A. Savidge, Amy A. Yackel Adams, James E. Gragg and Gordon H. Rodda
Experimental landscape reduction of wild rodents increases movements in the invasive brown treesnake (Boiga irregularis) (pp 455-467) |
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Experimental studies evaluating the effects of food availability on the movement of free-ranging animals generally involve food supplementation
rather than suppression. Both approaches can yield similar insights, but we were interested in the potential for using food suppression for
the management and control of invasive predators, in particular, the brown treesnake (Boiga irregularis) on Guam. However, understanding
a species’ response to food resources is critical before employing such a strategy. We studied the movements of 24 radio-tagged B. irregularis
initially caught within four 4-ha unfenced plots in rodent-abundant (control) and rodent-suppressed (treatment) grassland habitats over a 40-day period.
Because monitoring duration differed among snakes, we also analyzed short-term (16-day) activity areas. Over the 16 days, snakes associated with
rodent-suppressed plots had 86% larger activity areas (ha), 94% greater dispersal distances (m), and 43% greater movement rates (m/h) than snakes
associated with control plots. Boiga irregularis moved extensively, but these movements were not always reflected in the size of the snake’s
total activity area. Movement rates did not differ between sexes, but snakes in above-average body condition moved greater distances per hour
than those in below-average condition irrespective of treatment. Our study indicates that a relatively small prey suppression effort can cause
almost immediate and significant changes in B. irregularis movement. On Guam, prey suppression might enhance control efforts by either increasing
trap capture success or discouraging snakes from entering areas of conservation or management concern. However, the outcome of using prey suppression
as a control tool in areas threatened with the accidental introduction of the brown treesnake is more difficult to predict and might have negative
consequences such as elevated dispersal rates.
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Shane R. Siers, Julie A. Savidge and Robert N. Reed
Ontogenetic and ecological variation in invasion risk of Brown Treesnakes (Boiga irregularis) on Guam (pp 469-483) |
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Size structure within populations of invasive species may have consequences for relative risk at all stages of the invasion process,
with implications for management interventions such as interdiction, suppression, and eradication. To assess relative distributions
of invasive Brown Treesnakes (Boiga irregularis) among demographic categories of management interest, we undertook the most
comprehensive and controlled sampling in > 25 years of research into this ecologically and economically destructive introduced predator.
We collected a seasonally-balanced sample of 100 snakes from each of 18 sites, stratified by six habitat types, encompassing the species’
entire extralimital range. Samples indicated significant differences in distributions of female and male snakes among management classes
(juvenile, transitional, and mature) by site and habitat. We found substantial heterogeneity in localized population characteristics
over relatively small geographic distances, only modest influence of habitat type, higher prevalence of reproductively mature snakes
in savanna and urban habitats, and an alarmingly high proportion of snakes that are too small to be effectively targeted by current
rodent-baited control tools (mean = 38.2%, range = 19 to 72%). Failure to account for such variability in high risk demographic
fractions may hinder successful interventions.
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Joseph D. Lechelt, Matthew J. Kocian and Przemyslaw G. Bajer
Low downstream dispersal of young-of-year common carp from marshes into lakes in the Upper Mississippi River region and its implications for integrated pest management strategies (pp 485-495) |
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In lakes of the Upper Mississippi River Basin (UMRB), invasive common carp (Cyprinus carpio) employ a reproductive strategy
in which adults migrate out of lakes to spawn in seasonally unstable marshes that have few egg and larval predators. The rates with
which the juveniles outmigrate from marshes into adjacent lakes have critical management implications but have not been quantified
using direct approaches. We used passive integrated transponder (PIT) tags to quantify outmigration of young-of-year (YOY) carp from
marshes into lakes in two systems in UMRB. In both cases, marshes were located upstream of lakes and PIT antennas continuously monitored
the movement of carp. In the first system, which we monitored for three years, 0.2% to 5.5% of PIT-tagged YOY carp outmigrated to the lake
each year; highest outmigration occurred during mid-summer periods of low water level in the marsh. In the second system, which comprised
much more extensive area of deeper marshes, 0.2% of YOY carp outmigrated to the lake. Ageing and mark-recapture analyses confirmed that
relatively few YOY carp recruited into the lake populations from the marshes each year (between 5 and 50 per hectare). Our results show
that YOY carp outmigration rates are low (< 6%) but can vary an order of magnitude among years. These findings are important for removal-based
management strategies for carp in lakes of UMRB by showing what adult removal rates are needed to compensate for juvenile recruitment from marshy nurseries.
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Jaewoo Kim and Nicholas E. Mandrak
Effects of vertical electric barrier on the behaviour of common carp (pp 497-505) |
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When managing invasive fishes, permanent barriers may be best in preventing spread; however, they may not be feasible due to costs
and logistical constraints. Alternatively, non-permanent barriers using electricity, light, sound, pressure, bubbles, CO2, and other
stimuli are being developed and deployed in efforts to limit the spread of aquatic invasive species or to achieve fish guidance and conservation.
However, the effectiveness of these barriers is quite variable and testing is often lacking for both target and non-target species. We conducted
a series of laboratory trials to examine the effects of a vertical electric barrier on behaviour of common carp Cyprinus carpio (Linnaeus, 1758).
In response to the electric field, common carp reduced passing the electric barrier significantly, exhibiting different behaviours when interacting with
the electric barrier, and spent more time away from the electric barrier when it was turned on during the stimulus period compared to pre- and post-stimulus
periods. Our results suggest that a relatively weak electric gradient (i.e., voltage gradient: 0.2–0.4 V•cm-1, power density: 3–42 µW•cm-3)
can inhibit the movement of common carp. Our results also highlight the importance of detailed examination of behavioural responses of target species when
evaluating and considering fish-deterrent technologies.
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Hana Colwell, Jane Ryder, Robert Nuzzo, Matthew Reardon, Rachel Holland and Wai Hing Wong
Invasive Asian clams (Corbicula fluminea) recorded from 2001 to 2016 in Massachusetts, USA (pp 507-515) |
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Invasive Asian clams (Corbicula fluminea) recorded from 2001 to 2016 in Massachusetts were mapped to have a better understanding
of the status of this species in this state. The map will help the general public in preventing the further spread of the clams to new water
bodies by increasing the awareness of infested waters, as well as aid water resource managers track the extent of infestations in Massachusetts.
The first sighting of Asian clams in Massachusetts was in a section of the Charles River in Watertown, MA. Currently there are 29 sites
(representing 28 water bodies) reported to have the invasive Asian clam in Massachusetts. These recent infestations may reflect the warming
temperature in this region because all clams were found in the warmer parts of the state where water temperature is above the clams’ long-term
incipient lower thermal limit. In an infested unnamed tributary in Forest Park, Springfield, MA, a high abundance of 6,124 clams/m² was recorded.
The maximum shell length was 22.64 mm and most individuals were estimated to be about one year old.
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Bridgett N. Pickman and Matthew A. Barnes
Preliminary analysis reveals sediment burial decreases mass loss and increases survival of the aquatic invasive plant
Hydrilla verticillata following desiccation over short time scales (pp 517-522) |
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Aquatic plants represent a key target in the management of biological invasions due to their ability to outcompete native species,
interfere with human water use, and modify nutrient cycles. Studying desiccation tolerance of aquatic plants can improve understanding
of their survival in habitats with fluctuating water levels, as well as response of invasive aquatic plants to management practices such as drawdowns.
In a preliminary study, using Hydrilla verticillata as a case study, we desiccated plant fragments for 3 hours on top of sediment,
buried beneath sediment, and in the absence of sediment in laboratory mesocosms to quantify the effects of sediment burial on survival
and growth upon reintroduction to a common aquatic environment. In the absence of sediments, fragments experienced the greatest mass loss
during desiccation and highest mortality rates upon reintroduction to the aquatic environment. Burial decreased plant fragment mass loss
during desiccation, and upon return to a common aquatic environment, buried fragments demonstrated rates of new growth indistinguishable
from undried control fragments. Overall, our results suggest that the presence of sediments can play an important role in the ability
of aquatic plants to withstand desiccation stress at short time scales. Future studies should consider longer time scales and conditions
most representative of field settings, as an understanding of sediments can inform management practices aimed at the control and eradication
of hydrilla and other invaders.
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Zohar Yanai, Tamar Dayan, Henk K. Mienis and Avital Gasith
The pet and horticultural trades as introduction and dispersal agents of non-indigenous freshwater molluscs (pp 523-532) |
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Understanding the introduction pathways and patterns of distribution of non-indigenous species is essential for minimizing future invasions.
In the aquarium and aquatic ornamental plant trades lies the potential for importing freshwater molluscs and dispersing them. We surveyed 37 pet
shops and 24 aquatic plant nurseries throughout Israel in search for freshwater molluscs. The survey yielded 29 taxa, of which 15 are offered
for sale (deliberate introduction) and 14 are stowaways (accidental introduction). The species offered for sale are alien species not yet established
in Israeli natural systems, whereas the stowaways are mainly established species that have already invaded and maintain stable populations in natural
habitats. Six species were documented for the first time in Israel. Taxon richness was not correlated with any geographic or socioeconomic variable.
We attribute this to the small size of Israel, which enables people from different locations and social classes to travel easily across the country
to buy plants or pets. The findings of this study imply that the import of freshwater molluscs deliberately for commerce or on aquatic plants as stowaways
is an important mode of introduction for these species. In order to prevent, or at least reduce, the extent of this phenomenon, we recommend establishing
more effective restrictions on the import of live material, preventing deliberate import and commerce of freshwater molluscs, and confiscating and eliminating
non-indigenous freshwater molluscs once found, before they reach nature.
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Pablo E. Allen, Marco D. Barquero, Esteban Bermúdez, Jose Carlos Calderón, Branko Hilje, Willy Pineda, Guido Saborío-Rodríguez, Viviana Arguedas and Eduardo Chacón-Madrigal
Calling for more accurate information in aquarium trade: analysis of live-fish import permits in Costa Rica (pp 533-542) |
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Ornamental fish trade is a growing business around the world, but also a major pathway for the introduction of potentially invasive species.
Trade patterns and policies have been evaluated in high-income countries while developing countries in tropical regions have been overlooked,
even when they are especially vulnerable to invasions by aquarium fishes. We analyzed the live fish import data and regulations in Costa Rica
as a study case for a tropical country that regularly trades with many countries. We evaluated the quality of the taxonomic information given
in live fish import permits issued by the Costa Rican Ministry of Environment between 1998 and 2004. We used FishBase to extract information
about geographical distribution, habitat, historical introduction records, and taxonomic information on all the species we cataloged.
A total of 834,624 live individuals were imported into Costa Rica from six countries with the scientific name absent for many individuals
(40.6%) and correctly written in only 29.6% of the cases. We estimated that 352 different species were imported into the country.
Most species imported were freshwater fishes and South America natives. We found that regulations of ornamental fish imports
in Costa Rica are usually not enforced. The lack of accurate information in the live fish permits does not allow the full understanding
and scope of live animal imports and their potential impacts. We call for more accurate information in the global aquarium trade by aiming
to have much better tools to regulate the traffic of ornamental fishes.
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Stein Mortensen, Torjan Bodvin, Åsa Strand, Mark W. Holm and Per Dolmer
Effects of a bio-invasion of the Pacific oyster, Crassostrea gigas (Thunberg, 1793) in five shallow water habitats in Scandinavia (pp 543-552) |
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Management of invasive species is addressed in both national and international regulations regarding the protection of marine habitats
and biodiversity and in regulations of aquaculture. The geographical range of the invasive Pacific oyster, Crassostrea gigas, is expanding,
both through human mediated vectors and by natural dispersal. The species is now spreading in Scandinavia. In order to optimize the management of the oyster,
including targeted monitoring and mitigation activities, knowledge on the present and future distribution and impact on the ecosystem is important.
The development of the population and the potential impacts on native ecosystems were analyzed, based on the present scientific knowledge
on the distribution in Scandinavia, data on new settlements and existing literature. Data was first evaluated by 14 experts (including the authors)
during a workshop, relating the current status of habitats where Pacific oysters are found in Scandinavia (Low energy rock, Littoral sand and mudflats,
Littoral biogenic reefs, Sublittoral sand and Sublittoral biogenic reefs) to a predicted development, thereafter assessed in relation to impact on the habitats.
The assessment was done as a function of climate change in a long-term IPCC climate scenario (A1B). We conclude that Littoral biogenic reefs are at risk
to obtain the highest expected increase, while all other habitats are at risk of low to moderate development of the oyster populations. Accordingly,
Littoral Biogenic reefs was assessed as the habitat type at risk of the largest ecosystem effects as high densities of oysters already exist in these areas,
and the densities are expected to increase rapidly until reaching a threshold density. Low energy rock and Littoral sand and mud were assessed as being
subjected to moderate to high ecosystem effects. Sub-littoral sand and Sub-littoral biogenic reefs were assessed as currently being at risk of moderate
ecosystem effects as there are low densities of oysters in these habitats, although densities in sublittoral biogenic reefs has the potential to increase.
We discuss management and mitigation strategies based on the forecasted development and effects of the Pacific oyster populations.
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Louis F. Ferguson, John D.P. Davidson, Thomas Landry, Jeff C. Clements and Thomas W. Therriault
Didemnum vexillum: invasion potential via harvesting and processing of the Pacific oyster (Crassostrea gigas) in British Columbia, Canada (pp 553-558) |
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Routine shellfish aquaculture practices in British Columbia (BC) result in cultured Pacific oysters (Crassostrea gigas (Thunberg, 1793))
being moved from tunicate infested culture areas to non-infested areas for processing, thereby posing a potential risk of spreading the colonial
ascidian Didemnum vexillum Kott, 2002 and other nuisance species, to new areas. Three intervention points (IPs; i.e., stages
of the processing regime) were identified in existing aquaculture practices where clusters of C. gigas received manipulation or stress that
could alter the cover of epibionts, notably D. vexillum. These IPs were: IP1) harvesting, IP2) transportation (from harvesting areas
to processing plants), and IP3) processing (shucking of the oysters). The percentage coverage of D. vexillum on oyster clusters was evaluated
at each IP for products originating from two aquaculture sites in BC, Lemmens Inlet and Okeover Inlet. A total of 60 clusters were sampled from Lemmens
Inlet and 46 from Okeover Inlet. Results demonstrated a significant loss (P < 0.05) of D. vexillum coverage on C. gigas clusters from IP1
to IP3 for both sites. Although variations existed between the sites, the mean percentage coverage decreased from 48% post-harvest
to 30% post-transportation and 17% post-shucking. Since shucked oyster shells still have a substantial cover of D. vexillum on them
and are disposed of in areas exposed to tidal waters of un-infested bays, the risk of secondary introduction related to shellfish aquaculture practices
remains high. Based on these results, thresholds could be set to reduce the risk of introducing D. vexillum into new areas, and new research
is recommended to determine the risk of dispersal of D. vexillum should it be inadvertently introduced via shellfish movements.
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Michelle L. Marraffini, Gail V. Ashton, Chris W. Brown, Andrew L. Chang and Greg M. Ruiz
Settlement plates as monitoring devices for non-indigenous species in marine fouling communities (pp 559-566) |
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Non-indigenous species (NIS) are one of the leading forces of change in coastal marine ecosystems and are often associated with fouling communities,
especially the artificial structures of marinas and ports. As a result, monitoring of marine fouling communities is crucial to evaluate the introduction
and spread of NIS as well as assess the efficacy of legislation aimed to prevent further introductions. Settlement plates have long been used as a means
of studying fouling communities. Many factors such as orientation, movement, and substrate type have been shown to influence the number and type
of organisms present in fouling communities, but one key question remains poorly studied: how well do settlement plates represent the established
fouling community of a marina, especially regarding NIS? We investigated this question, by examining the sessile invertebrates on both marina
structures and settlement plates from three marinas in San Francisco Bay (California, USA). Total species richness, NIS richness, and community
composition on settlement plates were found to be similar to those on existing marina floating docks. Our results indicate that settlement plates
can provide a sensitive and standardized measure of the NIS richness and composition in fouling communities.
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Aaron R. Cupp, John A. Tix, Justin R. Smerud, Richard A. Erickson, Kim T. Fredricks, Jon J. Amberg, Cory D. Suski and Robert Wakeman
Using dissolved carbon dioxide to alter the behavior of invasive round goby (pp 567-574) |
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Fisheries managers need effective methods to limit the spread of invasive round goby Neogobius melanostomus in North America.
Elevating carbon dioxide (CO2) in water at pinch points of rivers (e.g., inside locks) is one approach showing potential to deter
the passage of invasive fishes, such as bigheaded carps Hypophthalmichthys spp., but the effectiveness of this method to alter
round goby behavior has not been determined. The goal for this study was to determine CO2 concentrations that alter round goby behavior
across a range of water temperatures. Free-swimming avoidance (voluntary response) and loss of equilibrium (involuntary response) were
quantified by exposing round goby to increasing CO2 concentrations at 5, 15, and 25 °C using a shuttle box choice arena and static tank.
Water chemistry was measured concurrent with behavioral endpoints and showed that round goby avoided a threshold of 99–169 mg/L CO2
(79,000–178,000 µatm) and lost equilibrium at 197–280 mg/L CO2 (163,000–303,000 µatm). Approximately 50% lower CO2 concentrations were
found to modify behavior at 5 °C relative to 25 °C, suggesting greater effectiveness at lower water temperatures. We conclude that CO2
modified round goby behavior and concentrations determined in this study are intended to guide field testing of CO2 as an invasive fish deterrent.
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Ingunn Alne Hoell, Ranveig Ottoey Olsen, Ole-Kristian Hess-Erga, Gunnar Thuestad and Aud Larsen
Application of flow cytometry in ballast water analysis—biological aspects (pp 575-588) |
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Ballast water may, when discharged, cause the spread of nonindigenous and potentially invasive species. International ballast water treatment
regulations have accelerated the development of new methods to detect, enumerate and assess the status of organisms in the water to be discharged.
Flow cytometry (FCM) is a powerful technique with a broad range of applications with the possibility for multi-parametric analysis and the potential
of combining it with other techniques being two strong advantages. This review will discuss whether FCM is suitable for ballast water analysis according
to international ballast water regulations, and sum up the advantages and disadvantages. It will also give an overview of available labeling techniques.
Finally, a discussion on the knowledge gaps and future potential for FCM within ballast water analysis is presented.
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Lucy G. Anderson, Jennifer K. Chapman, Daniela Escontrela and Charlotte L.A. Gough
The role of conservation volunteers in the detection, monitoring and management of invasive alien lionfish (pp 589-598) |
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Across the Caribbean, targeted fishing is gaining momentum as a cost-effective method to control invasive alien lionfish
(Pterois volitans and Pterois miles) by suppressing population numbers below site-specific threshold levels i.e. a population density
that is predicted to cause declines in native fish biomass. Yet in marine reserve no take zones (NTZs) or reefs at depths of >18 m) where commercial
fishing is either not permitted or impractical, alternative methods of lionfish control are required. This study evaluates the potential for conservation
volunteers to act as citizen scientists monitoring invasive lionfish populations and to support removal efforts in Bacalar Chico Marine Reserve (BCMR),
Belize. Two underwater visual census techniques were trialled with conservation volunteers, each with associated benefits and drawbacks. A log
of opportunistic lionfish sightings on SCUBA dives has been used to record sightings per unit effort (SPUE) data 2011–2015. In 2014, more rigorous
lionfish focused searches (lionfish-adapted belt transects) were introduced. Opportunistic lionfish sightings contributed to a five year SPUE dataset
that suggests that lionfish population growth rate has slowed in BCMR, where a lionfish removal program was also carried out by conservation volunteers
over the same timeframe. However, lionfish focused searches showed that the mean density in 2014 was high (mean = 27.05 ± 8.77 fish ha-1, 1–30 m)
relative to lionfish populations in their native ranges, particularly at sites at depths > 18m (mean = 43.39 ± 13.76 fish ha-1, 18–30 m).
Drawing on lessons from Belize, we discuss the potential for conservation volunteers to support invasive alien species (IAS) monitoring and control
efforts in marine environments.
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