Evaluation of stochastic gravity model selection for use in estimating non-indigenous species dispersal and establishment

Predicting dispersal of nonindigenous species (NIS) is an essential component of risk analysis and management, as preventative measures are most readily applied at this stage of the invasion sequence. Gravity models provide one of the most useful techniques available to model dispersal of nonindigenous invasive species (NIS) across heterogeneous landscapes, as these models are able to capture transport patterns of recreational boaters who are dominant vectors responsible for aquatic NIS dispersal. Despite the widespread use of gravity models in forecasting biological invasions, different classes of gravity models have not been evaluated regarding their comparative ability to capture recreational transport patterns and subsequent use in predicting NIS establishment. Here we evaluate model selection between unconstrained, total-flow-constrained, production-constrained and doubly-constrained stochastic gravity models to assess dispersal of the spiny waterflea Bythotrephes between Ontario lakes. Differences between the models relate to the amount of data required and constraints under which calculations of source/destination interactions are made. For each class of gravity model, we then estimated the probability of a lake having established Bythotrephes populations by modeling the relationship between empirical presence/absence data and inbound recreational traffic (i.e. propagule pressure) via boosted regression. The unconstrained gravity model provided the best fit to observed traffic patterns of recreational boaters. However, when output from the gravity models was used to predict Bythotrephes establishment, the doubly-constrained gravity model provided the strongest relationship between inbound recreational traffic and observed Bythotrephes presence/absence, followed by the production-constrained model. Our results indicate production-constrained gravity models offer an acceptable balance between modeling recreational boater traffic and their utility to estimate establishment probabilities.     

Lake morphometry determines Dreissena invasion dynamics

Predicting the ecosystem effects of invasive species and the best control strategies requires understanding population dynamics and population regulation. Invasive bivalves zebra and quagga mussels (Dreissena spp.) are considered the most aggressive invaders in freshwaters and have become major drivers of ecosystem processes in the Laurentian Great Lakes. Combining all lake-wide studies of Dreissena spp. conducted in the Great Lakes, we found that invasion dynamics are largely governed by lake morphometry. Where both species are present, quagga mussels generally become dominant in 8–13 years. Thereafter, zebra mussels remain common in shallow lakes and embayments and lake-wide Dreissena density may remain similar, while in deep lakes quagga led to a near-complete displacement of zebra mussels and an ensuing dramatic increase in overall dreissenid density. In deep lakes, overall Dreissena biomass peaked later and achieved?~?threefold higher levels than in shallow lakes. Comparison with 21 waterbodies in North America and Europe colonized by both dreissenids confirmed that patterns of invasion dynamics found in the Great Lakes are very consistent with other waterbodies, and thus can be generalized to other lakes. Our biophysical model predicted that the long-term reduction in primary producers by mussel grazing may be fourfold less in deep compared to shallow lakes due to thermal stratification and a smaller proportion of the epilimnion in contact with the bottom. While this impact remains greatest in shallow areas, we show that when lakes are vertically well-mixed, dreissenid grazing impact may be greatest offshore, revealing a potentially strong offshore carbon and phosphorus sink.

     

Recreational boats as a vector of secondary spread for aquatic invasive species and native crustacean zooplankton

Recreational boats in tow between lakes are a known vector of the spread of aquatic invading species (AIS), but we have no test of the hypothesis that recreational boats are also a vector of secondary spread of AIS among freshwater ecosystems via in-water transport i.e., while boating between interconnected waterways. In this study, we surveyed recreational boaters travelling into Lake Simcoe (44°25′N, 79°20′W), Ontario, Canada, on their recreational activities, boat maintenance, and travel destinations, measured the degree of vessel fouling, and sampled all standing water and attached macrophytes associated with their vessels. A total of 321 zooplankton individuals comprising 15 different species were collected from the standing water in vessels, including veligers of the invasive zebra mussel Dreissena. The volume of water collected within the vessels significantly increased the number of zooplankton transported. Zooplankton species from pelagic habitats or with planktonic life stages were collected more frequently than species that occupy littoral or benthic habitats, likely reflecting the recreational activities of boaters. Patterns of boater activities, movements and hygiene habits, suggest recreational boating in the Lake Simcoe region is contributing to the spread of native and invasive species into nearby waterways. Our study validates the widespread assumption that recreational boats are an important in-water vector for the secondary spread of both native and invasive zooplankton species. Future management strategies to reduce the spread of AIS should be aimed at increasing awareness of boater hygiene practices, particularly the frequent draining of standing water.     

Economic effects and the efficacy of intervention: exploring unintended effects of management and policy on the spread of non-indigenous species

Models have been well developed describing human movements as vectors of the spread of non-indigenous species (NIS). However, to be maximally useful, predictions need to be integrated with management models of how different policies change human behaviour and lead to concurrent changes in invasion risk. Using the dispersal of freshwater organisms by recreational boaters as our study system and mandatory boat washing as our management strategy, we conducted a survey of recreational boaters (n = 580 respondents, t = 2354 boating trips) in Ontario, Canada, and performed counterfactual analysis of boater behavior across different management options. We developed a model to quantify three responses to mandatory boat washing policies: (1) the continued use of a policy lake; (2) switching to a non-policy lake (“trip redistribution”); or, (3) a reduction in boating trips (“trip loss”). We found that boater and locational traits did not have a significant effect, but even modest user fees at washing stations greatly influenced trip redistribution and loss, explaining 87% of the variation in boater choices. These results indicate that user fees can strongly reduce the effectiveness of boat washing programs to mitigate invasion risk and could have unintended local economic effects, supporting the need to minimize boater expense as a program goal. In contrast, only minor redistribution and loss occurred if users washed but did not pay, and when taken together with the lack of effect for boater and locational traits, suggest that simple human-mediated dispersal models would be sufficient to prioritize management actions under “zero fee” scenarios. Simulating management scenarios using an existing spread model for 10 aquatic NIS in Ontario further emphasized the benefit of zero fees. Although averted invasions increased monotonically with effort (number of lakes with washing stations), the relative effectiveness (number of invasions averted per unit effort) was high even with management of a single lake, given zero fees, but required washing stations at far more lakes to maximize relative effectiveness when user fees were imposed.     

Evolution and diversity of two cisco forms in an outlet of glacial Lake Algonquin

The diversity of Laurentian Great Lakes ciscoes (Coregonus artedi, sensu lato) arose via repeated local adaptive divergence including deepwater ciscoes that are now extirpated or threatened. The nigripinnis form, or Blackfin Cisco, is extirpated from the Great Lakes and remains only in Lake Nipigon. Putative nigripinnis populations were recently discovered in sympatry with artedi in a historical drainage system of glacial Lake Algonquin, the precursor of lakes Michigan and Huron. Given the apparent convergence on Great Lakes form, we labeled this form blackfin. Here, we test the hypothesis that nigripinnis may have colonized this area from the Great Lakes as a distinct lineage. It would then represent a relict occurrence of the historical diversity of Great Lakes ciscoes. Alternatively, blackfin could have evolved in situ in several lakes. We captured more than 600 individuals in the benthic or pelagic habitat in 14 lakes in or near Algonquin Provincial Park (Ontario, Canada). Fish were compared based on habitat, morphology, and genetic variation at 6,676 SNPs. Contrary to our expectations, both cisco and blackfin belonged to an Atlantic lineage that colonized the area from the east, not from the Great Lakes. Sympatric cisco and blackfin were closely related while fish from different lakes were genetically differentiated, strongly suggesting the repeated in situ origin of each form. Across lakes, there was a continuum of ecological, morphological, and genetic differentiation that could be associated with alternative resources and lake characteristics. This study uncovers a new component of cisco diversity in inland lakes of Canada that evolved independently from ciscoes of the Laurentian Great lakes. The diversity of cisco revealed in this study and across their Canadian range presents a challenge for designating conservation units at the intraspecific level within the framework of the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).     

Prediction and error in multi‐stage models for spread of aquatic non‐indigenous species

Aim Predictions of spread of non‐indigenous species allow for greater efficiency in managing invasions by targeting areas for preventative measures. The invasion sequence is a useful concept in predictions of spread, as it allows us to test hypotheses about the transport and establishment of propagules in novel habitats. Our aims are twofold: (1) to develop and validate multi‐stage invasion models for the introduced fishhook waterflea, Cercopagis pengoi, and (2) to assess how variability in the transport patterns of the propagules influences the accuracy and spatial extent for predictions of spread. Location New York State, USA. Methods We developed a two‐stage model for the spread of C. pengoi. First, we developed a stochastic gravity model for dispersal based on surveys of recreational boat traffic in New York State as a proxy for propagule pressure. We then modelled the probability of establishment based on predicted levels of propagule pressure and measures of lakes’ physicochemistry. In addition, we used Monte Carlo simulations based on the gravity model to propagate variability in boater traffic through the establishment model to assess how uncertainty in dispersal influenced predictions of spread. Results The amount recreationalists were willing to spend, lake area and population size of the city nearest to the destination lake were significant factors affecting boater traffic. In turn, boater traffic, lake area, specific conductance and turbidity were significant predictors of establishment. The inclusion of stochastic dispersal reduced the rate of false positives (i.e. incorrect prediction of an invasion) in detecting invasions at the upper 95% prediction interval for the probability of establishment. Main conclusions Combinations of measures of propagule pressure, habitat suitability and stochastic dispersal allow for the most accurate predictions of spread. Further, multi‐stage spread models may overestimate the extent of spread if stochasticity in early stages of the models is not considered.     

Temperature,recreational fishing and diapause egg connections: dispersal of spiny water fleas (<Emphasis Type="Italic">Bythotrephes longimanus</Emphasis>)

The spiny water flea (Bythotrephes longimanus) is spreading from Great Lakes coastal waters into northern inland lakes within a northern temperature-defined latitudinal band. Colonization of Great Lakes coastal embayments is assisted by winds and seiche surges, yet rapid inland expansion across the northern states comes through an overland process. The lack of invasions at Isle Royale National Park contrasts with rapid expansion on the nearby Keweenaw Peninsula. Both regions have comparable geology, lake density, and fauna, but differ in recreational fishing boat access, visitation, and containment measures. Tail spines protect Bythotrephes against young of the year, but not larger fish, yet the unusual thick-shelled diapausing eggs can pass through fish guts in viable condition. Sediment traps illustrate how fish spread diapausing eggs across lakes in fecal pellets. Trillions of diapausing eggs are produced per year in Lake Michigan and billions per year in Lake Michigamme, a large inland lake. Dispersal by recreational fishing is linked to use of baitfish, diapausing eggs defecated into live wells and bait buckets, and Bythothephes snagged on fishing line, anchor ropes, and minnow seines. Relatively simple measures, such as on-site rinsing of live wells, restricting transfer of certain baitfish species, or holding baitfish for 24 h (defecation period), should greatly reduce dispersal.     

Exploration of sample size and diatom-based indicator performance in three North American phosphorus training sets

Three large training sets were investigated to determine optimal sample sizes for diatom-based inference models. The sample sets represented (1) assemblages from Great Lakes coastlines, (2) phytoplankton from the pelagic Great Lakes and (3) surface sediment assemblages from Minnesota lakes. Diatom-based weighted average models to infer nutrient concentrations were developed for each training set. Training set sample sizes ranging from 10 to the maximum number of samples were created through random sample selection, and performance of each model was evaluated. For each model iteration, diatom-inferred (DI) nutrient data were related to stressor data (e.g., adjacent agricultural or urban development) to characterize the ability of each model to track human activities. The relationships between model performance parameters (DI-stressor correlations and model r ², error and bias) and sample size were used to determine the minimum sample size needed to optimize models for each region. Depending on the training set, at least 40–70 samples were needed to capture the variation in diatom assemblages and environmental conditions to such a degree that non-analog situations should be rare and so should provide an unambiguous result if the model was applied to any sample assemblage from the region. It is recommended that one exercises caution when dealing with smaller training sets unless there is certainty that the selected samples reflect the regional variability in diatom assemblages and environmental conditions.     

149 Distribution and Invasion of Bangia Atropurpurea (Rhodophyta) in the Laurentian Great Lakes

Müller et al. (1998) noted that freshwater collections of the genus Bangia formed a distinct group separate from marine entities in gene sequence analyses. Recently, the species epithet B. atropurpurea has been resurrected to represent this freshwater lineage. This taxon is one of many invasive species within the Laurentian Great Lakes. B. atropurpurea was first observed in Lake Erie in 1964 and by 1982 was observed in all of the Great lakes except Lake Superior. The present study was initiated to examine the further spread of B. atropurpurea and determine the origin of these populations. Hence, a survey of all the Great Lakes was conducted in 1995 (86 sites) and again in 2002 (104 sites). Bangia was observed at 43 sites in 1995 and 39 sites in 2002. For the first time, this alga has been observed to be present in the St. Lawrence River (1995), Georgian Bay on Lake Huron (2002) and Lake Simcoe (eastern shore, 2002) and hence this alga appears to be spreading into new locations. Cluster analyses of morphological data reveal three distinct groupings that do not separate according to location or lake basin. Preliminary analyses of ITS 1 and 2 sequences show differences among samples within Lake Ontario and among all Lakes; however, collections from Lake Simcoe are very similar in sequence. We are continuing to examine the relationship of Great Lakes populations with freshwater collections from Europe.     

Distribution of recreational boating across lakes: do landscape variables affect recreational use?

1. Because people impact lake ecosystems, it is important to consider factors influencing the human use of freshwater resources. We investigated the influence of the landscape position, as well as lake area, recreational facilities, and distance to highways and urban centres, on lake use by boaters in the Northern Highland Lake District of Wisconsin, U.S.A.
2. In aerial surveys of ninety-nine randomly selected lakes, we did not see boats on over half of the lakes. Of the lakes with boats, we found a strong correlation between the number of boats and lake area. Recreational boats tended to be found on large, accessible lakes with good boating facilities. Boats were not seen on small, stained lakes with few recreational facilities.
3. Regression models showed that lake size and landscape position explained 63% of the variability in the average number of boats per lake and landscape position explained 24% of the variability in boat density on all ninety-nine lakes. Social variables representing the quality of boating facilities and the perception of good fishing explained 70% of the variability in number of boats per lake and 54% of the variation in boat density on all lakes. A combined model using both physical and social variables increased the explanatory power for both number and density. Lake use by boaters was correlated with landscape position, the quality of fishing and the availability of recreational facilities. When the analysis was restricted to the forty-six lakes where boats were found, only the availability of recreational facilities proved a significant predictor of boat density.
4. Our results suggest that lake choice by recreational boaters may be best predicted by a combination of the location of a lake in a regional hydrologic landscape, and considerations of available facilities and perceptions regarding fishing.     

Can filter‐feeding Asian carp invade the Laurentian Great Lakes? A bioenergetic modelling exercise

1. There is much concern that filter‐feeding Asian carp will invade the Laurentian Great Lakes and deplete crucial plankton resources. We developed bioenergetic models, using parameters from Asian carp and other fish species, to explore the possibility that planktonic food resources are insufficient to support the growth of silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis) in the Great Lakes. 2. The models estimated basic metabolic requirements of silver and bighead carp under various body sizes, swimming speeds and reproductive stages. These requirements were then related to planktonic food resources and environmental temperature to predict when and where silver and bighead carp may survive in the Great Lakes, and how far they may travel. 3. Parameter values for respiration functions were derived experimentally in a coordinated study of silver and bighead carp, while consumption parameters were obtained from the literature on silver carp. Other model parameters lacking for Asian carp, such as those for egestion and excretion, were obtained from the literature on other fish species. 4. We found that full‐sized bighead carp required 61.0 kJ d^?1 just to maintain their body mass at 20 °C, approximately equivalent to feeding in a region with 255 μg L^?1 macrozooplankton (dry) or 10.43 μg L^?1 chlorophyll a. Silver carp energy requirements were slightly higher. 5. When applied to various habitats in the Great Lakes, our results suggest that silver and bighead carp will be unable to colonise most open‐water regions because of limited plankton availability. However, in some circumstances, carp metabolism at lower temperatures may be low enough to permit positive growth even at very low rations. Positive growth is even more likely in productive embayments and wetlands, and the modelled swimming costs in some of these habitats suggest that carp could travel >1 km d^?1 without losing biomass. 6. The simulation (and firmly hypothetical) results from this modelling study suggest when and where Asian carp could become established in the Great Lakes. Given the potential consequences to Great Lakes ecosystems if these filter feeders do prove capable of establishing reproducing populations, efforts to keep Asian carp out of the Great Lakes must not be lessened. However, we do encourage the use of bioenergetic modelling in a holistic approach to assessing the risk of Asian carp invasion in the Great Lakes region.     

Is vessel hull fouling an invasion threat to the Great Lakes?

Aim  Hull fouling is a leading vector for the introduction of marine, non‐indigenous species (NIS) worldwide, yet its importance to freshwater habitats is poorly understood. We aimed to establish the complement of NIS transported via this vector to the Great Lakes and to determine if they pose an invasion risk. Location  Laurentian Great Lakes. Methods  During 2007 and 2008, we collected scrapings from exterior surfaces as well as underwater video‐transects from 20 vessels shortly after their arrival in Great Lakes’ ports. Invertebrates present were sorted and identified in the laboratory. Results  Total estimated abundance averaged > 170,000 invertebrates per ship belonging to 109 taxa. Most (72%) of these taxa were freshwater species already present in the Great Lakes, whereas 11 and 31% were native to estuarine and marine habitats respectively, and would not be expected to survive in this habitat. Abundance was dominated by barnacles (51%), cladocerans (19%), bivalves (12%) and amphipods (11%). Sea‐chest grating and the rudder were hot‐spots for biofouling. Invertebrate diversity and total abundance were positively associated with total time spent in port during the last year and time in Pacific South American ports and negatively related to time in high latitudes and sailing speed. Although we found some live, established invaders such as Gammarus tigrinus and Dreissena rostriformis bugensis, only one individual of a freshwater NIS (Alexandrovia onegensis, Oligochaeta) not yet reported in the Great Lakes was detected. The animal’s poor condition and seemingly low population abundance indicated the risk of live introduction by this vector was likely quite low. Main conclusion  Our results indicate that hull fouling appears to pose a low risk of introductions of new species capable of surviving in the Great Lakes, unlike foreign‐sourced freshwater ballast water that historically was discharged by these transoceanic vessels.     

Domestic ships as a potential pathway of nonindigenous species from the Saint Lawrence River to the Great Lakes

Ballast water moved by transoceanic vessels has been recognized globally as a predominant vector for the introduction of aquatic nonindigenous species (NIS). In contrast, domestic ships operating within confined geographic areas have been viewed as low risk for invasions, and are exempt from regulation in consequence. We examined if the St. Lawrence River could serve as a source of NIS for the Laurentian Great Lakes by surveying ballast water carried by domestic vessels and comparing biological composition in predominant St. Lawrence River—Great Lakes port-pairs in order to determine the likelihood that NIS could be transported to, and survive in, the Great Lakes. Thirteen potential invaders were sampled from ballast water, while 26 taxa sampled from St. Lawrence River ports are not reported from the Great Lakes. The majority of NIS recorded in samples are marine species with low potential for survival in the Great Lakes, however two euryhaline species (copepod Oithona similis, and amphipod Gammarus palustris) and two taxa reported from brackish waters (copepod Microsetella norvegica and decapod Cancer irroratus) may pose a risk for invasion. In addition, four marine NIS were collected in freshwater samples indicating that at least a subset of marine species have potential as new invaders to the Great Lakes. Based on results from this study, the ports of Montreal, Sorel, Tracy and Trois Rivières appear to pose the highest risk for new ballast-mediated NIS from the St. Lawrence River to the Great Lakes.     

Microbial communities of the Laurentian Great Lakes reflect connectivity and local biogeochemistry

The Laurentian Great Lakes are a vast, interconnected freshwater system spanning strong physicochemical gradients, thus constituting a powerful natural laboratory for addressing fundamental questions about microbial ecology and evolution. We present a comparative analysis of pelagic microbial communities across all five Laurentian Great Lakes, focusing on Bacterial and Archaeal picoplankton characterized via 16S rRNA amplicon sequencing. We collected samples throughout the water column from the major basins of each lake in spring and summer over 2 years. Two oligotypes, classified as LD12 (Alphaproteobacteria) and acI-B1 (Actinobacteria), were among the most abundant in every sample. At the same time, microbial communities showed distinct patterns with depth during summer stratification. Deep hypolimnion samples were frequently dominated by a Chloroflexi oligotype that reached up to 19% relative abundance. Stratified surface communities differed between the colder, less productive upper lakes (Superior, Michigan, Huron) and warmer, more productive lower lakes (Erie, Ontario), in part due to an Actinobacteria oligotype (acI-C2) that averaged 7.7% of sequences in the lower lakes but <0.2% in the upper lakes. Together, our findings suggest that both hydrologic connectivity and local selective pressures shape microbial communities in the Great Lakes and establish a framework for future investigations.     

Chemical and isotopic composition of karstic lakes in Jamaica,West Indies

Lakes in the limestone region of Jamaica exhibit a range of chemical characteristics that reflect varying inputs from precipitation, surface runoff and groundwater, together with the subsequent evolution of the water within the limnic environment. Detailed spatial and temporal sampling was conducted on one lake, Wallywash Great Pond. Chemical data, together with D/H, ¹⁸O/¹⁶O, ¹³C/¹²C and ⁸⁷Sr/⁸⁶Sr ratios confirm that the karstic spring waters entering the lake evolve chemically through degassing, mixing with rainfall and runoff, biogenic decalcification (resulting mainly from bicarbonate assimilation by the high biomass of submerged macrophytes), and evaporation. Modern carbonate sedimentation in Wallywash Great Pond is largely of high-Mg calcite. This is consistent with Mg/Ca molar ratios >2 within much of the lake. However, aragonite forms on the adaxial leaf surfaces of Potamogeton spp. This may be explained either as a result of locally elevated Mg concentrations or a high degree of supersaturation favouring very rapid carbonate precipitation. Two small lakes to the north of Wallywash Great Pond show minor influence of the Na-Cl dominated coastal aquifer, suggesting that coastal lakes are sensitive to variations in the boundary between fresh and brackish groundwater caused by changes in climate or sea level. Their ¹³C/¹²C ratios are strongly influenced by biogenic CO₂ derived from plant respiration or decay.     

The Round Goby, Neogobius melanostomus, a Fish Invader on both sides of the Atlantic Ocean

During the past decade, a bottom-dwelling, aggressive, multiple-spawning fish, the round goby (Gobiidae: Neogobius melanostomus), has spread from its native region in the Ponto-Caspian throughout Europe and to the Laurentian Great Lakes in North America. An international workshop, held at the Hel Marine Station, Poland, was organized to summarize population features of the round goby. Common fish predators of round gobies in the Great Lakes and in native regions are obligate and facultative benthic fishes and occasionally, pelagic fishes. In contrast, the main predator of the round goby in the Gulf of Gdansk is the Great Cormorant (Phalacrocorax carbo). In the Great Lakes, round gobies have lead to the decline of mottled sculpin (Cottus bairdi) and logperch (Percina caprodes) and reduced the hatching success of native fishes by feeding on their eggs. In the Gulf of Gdansk, round gobies have increased in abundance, while three-spined sticklebacks (Gasterosteus aculeatus) have declined. Round gobies have a broad diet throughout their range; larger specimens are molluscivores. There are fewer species of parasites and lower infection rates of round gobies in recently colonized areas than in native areas. Overall, newly colonized round gobies in brackish waters and lakes are smaller, mature earlier, have a male biased operational sex ratio and are more short-lived compared with round gobies from marine (native) habitats.     

Optimizing the location of watercraft inspection stations to slow the spread of aquatic invasive species

The accidental spread of aquatic invasive species (AIS) by recreational boaters is a major concern of state and county environmental planners in the USA. While programs for watercraft inspection to educate boaters and slow AIS spread are common practice, large numbers of boats and waterbodies, together with limited budgets, make program design difficult. To facilitate program design, we developed an integer programming model for allocation of scarce inspection resources among lakes. Our model uses species-specific infestation status of lakes and estimates of boat movement between lakes. The objective is to select lakes for inspection stations to maximize the number of risky boats inspected, where risky boats are ones that move from infested to uninfested lakes. We apply our model in Stearns County in central Minnesota, USA, to prioritize lakes for inspection stations and evaluate alternative management objectives. With an objective of protecting uninfested lakes within and outside Stearns County, the optimal policy is to locate stations at infested lakes having the most boats departing for uninfested lakes inside and outside the county. With an objective of protecting only Stearns County lakes, the optimal policy is to locate stations at both infested and uninfested lakes having the riskiest boats arriving from within and outside the county and departing to in-county lakes. The tradeoff between these objectives is significant.

     

Phenotypic variation of walleye, <Emphasis Type="Italic">Sander vitreus</Emphasis>, in Canadian Shield lakes: New insights on percid polymorphism

Synopsis Literature on colour dimorphism in walleye has concerned only the blue form, Sander vitreus glaucum (formerly Stizostedion vitreum glaucum), historically found in lakes Erie and Ontario and considered to be extinct from the fish fauna since the 1960s. In this paper, we report unusual observations of a blue form of walleye living in sympatry with the yellow form, Sander vitreus (formerly Stizostedion vitreum), in five lakes of the Canadian Shield, northern Québec. We compared head morphology, diet, and growth of the two forms to determine if there are any variations in characteristics other than colour and to examine the potential adaptive value of the two phenotypes. The blue form has a significantly longer head than the yellow form but does not differ in diet; the blue form also exhibits slower growth. The existence of a blue form of walleye in lakes of the Canadian Shield provides new insights into percid polymorphism and gives important information about their occurrence outside the Great Lakes area. ¹ Morrison, C. L. & T. L. King. 2003. Taxonomic status of blue pike Stizostedion vitreum glaucum: a molecular systematic comparison of nuclear and mitochondrial DNA regions. Pages 59 In Percis III, The Third International Percid Fish Symposium, Madison, Wisconsin.     

Recreational fishing depredation and associated behaviors involving common bottlenose dolphins (Tursiops truncatus) in Sarasota Bay,Florida

Odontocete depredation involves stealing or damaging bait or prey already captured by fishing gear. The increase in depredation is of concern for small stocks of cetaceans because interactions with fishing gear can lead to serious injury or mortality through entanglement or ingestion. Using long‐term data sets available for the bottlenose dolphin (Tursiops truncatus) community in Sarasota Bay, Florida, we investigated recreational fishing gear interactions by (1) examining temporal patterns in depredation and associated behaviors from 2000 to 2007; (2) quantifying the behavior of dolphins that depredate or engage in associated behaviors; and (3) identifying factors associated with the rise in depredation locally. The number of incidents of dolphins (primarily adult males) interacting with recreational anglers and boaters increased following 2004. Depredation and associated behaviors increased during red tide lags and tourist seasons during times of prey depletion and heightened angler and boater activity. Dolphins with a history of fishing gear interactions shifted away from natural activity patterns and were more likely to be within 50 m of fishing lines. Recreational fishing gear interactions were attributed to a two percent population decline in Sarasota Bay in 2006 and need to be considered along with other cumulative human impacts in the development of conservation measures for dolphins.     

Survival of the exotic Chinese mystery snail (<Emphasis Type="Italic">Cipangopaludina chinensis malleata</Emphasis>) during air exposure and implications for overland dispersal by boats

The exotic Chinese mystery snail (Cipangopaludina chinensis malleata) has invaded lakes and rivers across North America and is particularly widespread in northern Wisconsin. Although deliberate introductions and aquarium releases have likely been important, recreational boats may speed the spread of this snail into lakes. Prior research indicated boater access to be a significant predictor of invasion by C. chinensis and other invasive species in Wisconsin. To mimic the process of boater transport between lakes, I examined the tolerance of juvenile C. chinensis to air exposure in a series of field and laboratory experiments. Field experiments under mesic conditions indicated that this snail can survive exposure to air for at least 4 weeks. Larger juveniles were more resistant than smaller juveniles, an effect that was also observed in the laboratory during short-term (3–14 days) experiments. Tolerance of small juveniles to air exposure appeared to be unaffected by temperature, but was affected by humidity, with higher survival at 64% than 34% relative humidity (RH). Results from the current study suggest that C. chinensis is highly resistant to air exposure and could be readily transported by boats moving between lakes, particularly in cool mesic environments. Since juvenile C. chinensis are common around the roots of emergent macrophytes, hitchhiking with boats should be particularly common with boats or trailers infested with aquatic plants.