Lyngbya wollei in western Lake Erie

We report on the emergence of the potentially toxic filamentous cyanobacterium, Lyngbya wollei as a nuisance species in western Lake Erie. The first indication of heavy L. wollei growth along the lake bottom occurred in September 2006, when a storm deposited large mats of L. wollei in coves along the south shore of Maumee Bay. These mats remained intact over winter and new growth was observed along the margins in April 2007. Mats ranged in thickness from 0.2 to 1.2 m and we estimated that one 100-m stretch of shoreline along the southern shore of Maumee Bay was covered with approximately 200 metric tons of L. wollei. Nearshore surveys conducted in July 2008 revealed greatest benthic L. wollei biomass (591 g/m² ± 361 g/m² fresh weight) in Maumee Bay at depth contours between 1.5 and 3.5 m corresponding to benthic irradiance of approximately 4.0–0.05% of surface irradiance and sand/crushed dreissenid mussel shell-type substrate. A shoreline survey indicated a generally decreasing prevalence of shoreline L. wollei mats with distance from Maumee Bay. Surveys of nearshore benthic areas outside of Maumee Bay revealed substantial L. wollei beds north along the Michigan shoreline, but very little L wollei growth to the east along the Ohio shoreline.     

Cylindrospermopsis in Lake Erie: Testing its Association with Other Cyanobacterial Genera and Major Limnological Parameters

We report the first documented observation of the potentially toxic cyanobacterium Cylindrospermopsis in Lake Erie and Sandusky Bay in 2005 (0.043–1.326 mg L^-1 wet weight, 16–1,942 trichomes mL^-1) and quantify the physical and chemical parameters and the cyanobacterial community composition contemporaneous to its occurrence. We hypothesize that the high temperature, low light intensity, and high nutrient content of Sandusky Bay, a shallow, drowned river mouth along the southwestern shore of Lake Erie, provides an ideal habitat for Cylindrospermopsis. This is consistent with published laboratory and field studies that show these physical and chemical conditions facilitate Cylindrospermopsis growth. Using multivariate statistics, we found that Cylindrospermopsis biomass correlated with high temperatures and shallow depths, conditions often found in Sandusky Bay. Light climate and nutrient concentrations were not associated with Cylindrospermopsis biomass, most likely because the light climate did not systematically change during the season and because nutrients exceeded demand. We propose that Cylindrospermopsis will increase in importance in Lake Erie, as previous research on climate change in the Great Lakes region predicts future higher water temperatures and lower water levels.     

Impact of the Alga Cladophora on the Survival of E. coli, Salmonella, and Shigella in Laboratory Microcosm

E. coli is an indicator of recent fecal contamination of freshwater beaches around the Great Lakes region. Elevated concentrations indicate that a fecal contamination has occurred, and that the risk for contact with fecal pathogenic organisms is heightened. The green algae, Cladophora, harbors populations of E. coli and potentially allows for prolonged survival and even replication of the bacterium in the lake environment. If presence of Cladophora mats on beaches is associated with persistence of E. coli in beach water, then E. coli would be a useful indicator organism only if pathogens also were able to survive and persist in the algae. This study utilized lab microcosms to study the persistence of E. coli, and of the fecal pathogens, Salmonella and Shigella, in lake water with and without the presence of Cladophora. E. coli was able to persist for extended periods in the presence of Cladophora (attached to algal mats for 45 days). Salmonella and Shigella, however, were unable to persist for this time period while in the presence of Cladophora (Salmonella attached to Cladophora was detectable for 10 days and Shigella was detectable for only 2 days). These data imply that E. coli is able to survive in the presence of Cladophora for greater times than are the fecal pathogens and that E. coli may not be an appropriate indicator organism for beaches with accumulations of algal material.     

Occurrence of the Great Lake's most recent invader, Hemimysis anomala, in the diet of fishes in southeastern Lake Ontario

The Ponto-Caspian mysid, Hemimysis anomala, was first observed in southeastern Lake Ontario in May 2006. During July and August 2007, gill nets were fished in 6 to 8 m of water at two locations of known Hemimysis colonization in southeastern Lake Ontario to determine if fish that consume macroinvertebrates were beginning to include this new invasive mysid in their diets. Of nine fish species captured in August, September, and October 2007, three species had consumed Hemimysis: alewife (Alosa pseudoharengus), rock bass (Ambloplites rupestris), and yellow perch (Perca flavescens); and six species had not: round goby Apollonia melanostoma, smallmouth bass Micropterus dolomieu, spottail shiner Notropis hudsonius, gizzard shad Dorosoma cepedianum, white perch Morone americana and log perch Percina caprodes. Diets of alewives from all samples were composed predominantly of Hemimysis (69.6% -100% frequency of occurrence, 46.0%–74.5% dry weight diet composition). Two of 6 rock bass stomachs sampled in August contained ≥ 98.9% Hemimysis (10 and 40 individuals each) and one of 61 yellow perch stomachs sampled in September contained 10.0% Hemimysis (6 individuals) and 90.0% fish. While Hemimysis were observed only sparsely in the diet of most nearshore fish, their predominance in alewife diets and their omnivorous feeding behavior indicated that they have the potential to alter energy flow in Great Lakes' foodwebs.     

Escherichia coli toxin and attachment genes in sand at Great Lakes recreational beaches

The United States Environmental Protection Agency recommends density thresholds for the fecal indicator organism Escherichia coli in order to ensure the safety of recreational waters. A number of studies published over the past ten years indicate that E. coli is encountered frequently in sand at recreational beaches. While a majority of the sand-associated E. coli may be commensal or environmental strains, the potential for pathogenic strains of E. coli to be present exists. Therefore, the aim of this study was to assess the presence of attachment and virulence genes associated with enteropathogenic and enterohemorrhagic strains of E. coli (EPEC and EHEC) in populations of E. coli recovered from swash zone sand from seven recreational beaches along Lake Huron and Lake St. Clair in eastern Michigan, USA. Genes coding for attachment proteins in EPEC and EHEC were very prevalent in sand E. coli, but genes coding for toxin genes were uncommon. The paucity of genes associated with E. coli toxins suggests that the EPEC and EHEC pathotypes are not common in sand; however, the high prevalence of genes associated with attachment in E. coli pathotypes suggests that these genes are being retained within the beach sand E. coli population.     

Trends in Diporeia populations across the Laurentian Great Lakes, 1997-2009

Benthic communities in the Laurentian Great Lakes have been in a state of flux since the arrival of dreissenid mussels, with the most dramatic changes occurring in population densities of the amphipod Diporeia. In response, the US EPA initiated an annual benthic macroinvertebrate monitoring program on all five Great Lakes in 1997. Although historically the dominant benthic invertebrate in all the lakes, no Diporeia have been found in Lake Erie during the first 13 years of our study, confirming that Diporeia is now effectively absent from that lake. Populations have almost entirely disappeared from our shallow (< 90 m) sites in lakes Ontario, Huron, and Michigan. In Lake Ontario, three of our four deep (> 90 m) sites still supported Diporeia populations in 2009, with densities at those sites ranging between 96 and 198/m². In Lake Michigan, populations were still found at six of our seven deep sites in 2009, with densities ranging from 57 to 1409/m². Densities of Diporeia in 2009 at the four deep sites in Lake Huron were somewhat lower than those in Lake Michigan, ranging from 191 to 720/m². Interannual changes in population size in Lake Huron and Lake Michigan have shown a degree of synchrony across most sites, with periods of rapid decline (1997-2000, 2003-2004) alternating with periods of little change or even increase (2001-2002, 2005-2009). There has been no evidence of directional trends at any sites in Lake Superior, although substantial interannual variability was seen.     

Stock assessment and fishery management of Henicorhynchus spp., Cyclocheilichthys enoplos and Channa micropeltes in Tonle Sap Great Lake,Cambodia

Tonle Sap Great Lake, in the lower Mekong River basin, contributes 60% of Cambodia's inland fisheries catch. There are four types of fisheries, including the middle-scale fishery. The major species comprising the middle-scale fishery are Henicorhynchus spp. (16%), a small-bodied fish caught mainly with small-mesh nets, and Cyclocheilichthys enoplos (13%), and Channa micropeltes (7%) which are caught with a variety of gear. Here we apply the Schaefer surplus production model to the middle-scale fisheries using monitoring data collected between 1995 and 1999. Model simulations determined that the maximum sustainable yield (F_MSY) for Henicorhynchus spp., was obtained with the use of 47,206 gillnets (mesh size < 50 mm) and 4269 and 1605 fishing boats for C. enoplos and C. microplestes, respectively. Over 1995–1999, there was a strong trend of increase in fishing effort and decrease of catch-per-unit-effort in the waters of Pursat, Siem Riep and Kampong Chnnang provinces. These provinces have large population centres located close to the fishing grounds; fishing in these areas should be more strictly regulated.     

Coexistence of the native benthic amphipod Diporeia spp. and exotic dreissenid mussels in the New York Finger Lakes

Populations of the benthic amphipod Diporeia spp. have sharply declined since the early 1990s in all North America's Great Lakes except Lake Superior. The onset and continued decline coincides with the invasion of these lakes by zebra (Dreissena polymorpha) and quagga (Dreissena rostriformis bugensis) mussels and the spread of quagga mussels to deep habitats. The six deepest Finger Lakes of central New York (Seneca, Cayuga, Skaneateles, Canandaigua, Keuka, and Owasco) have historically been Diporeia habitat and have had dreissenids for more than a decade. These lakes represent a wide range of trophic state, maximum depth, and dreissenid invasion history. We hypothesized that Diporeia abundance would be negatively impacted by dreissenid mussel expansion in the Finger Lakes. During 2006–2010, we sampled Diporeia and mussel populations in these six lakes. Diporeia was present in all six lakes, and was abundant (2000/m²) in Owasco Lake that has only zebra mussels and in Cayuga and Seneca Lakes that have had zebra and quagga mussels since 1994. Diporeia abundance was lowest (1000/m²) in Skaneateles, Canandaigua, and Keuka Lakes where quagga mussels have recently expanded. Productivity indicators explained much of the variability of Diporeia abundance. The persistence of Diporeia with quagga mussels in these lakes may be because of available alternative food resources. Fatty acid tracers indicate that Diporeia from Owasco Lake, the lake without quagga mussels, utilize diatoms, but Diporeia from Cayuga Lake that coexist with abundant quagga mussels also use food resources associated with terrestrial detritus that cannot be intercepted by dreissenids.     

Is reduced benthic flux related to the Diporeia decline? Analysis of spring blooms and whiting events in Lake Ontario

Benthic monitoring by USGS off the southern shore of Lake Ontario from October 1993 to October 1995 provides a detailed view of the early stages of the decline of the native amphipod Diporeia. A loss of the 1994 and 1995 year classes of Diporeia preceded the disappearance of the native amphipod at sites near Oswego and Rochester at depths from 55 to 130 m. In succeeding years, Diporeia populations continued to decline in Lake Ontario and were nearly extirpated by 2008. Explanations for Diporeia's decline in the Great Lakes include several hypotheses often linked to the introduction and expansion of exotic zebra and quagga mussels (Dreissena sp.). We compare the timeline of the Diporeia decline in Lake Ontario with trends in two sources of organic matter to the sediments — spring diatom blooms and late summer whiting events. The 1994–95 decline of Diporeia coincided with localized dreissenid effects on phytoplankton in the nearshore and a year (April 1994 to May 1995) of decreased flux of organic carbon recorded by sediment traps moored offshore of Oswego. Later declines of profundal (> 90 m) Diporeia populations in 2003 were poorly associated with trends in spring algal blooms and late summer whiting events.     

Evidence for Remote Effects of Dreissenid Mussels on the Amphipod Diporeia: Analysis of Lake Ontario Benthic Surveys, 1972–2003

The status of invasive dreissenid mussels (Dreissena polymorpha and D. bugensis) and native amphipods (Diporeia spp.) in Lake Ontario was assessed in 2003 and compared with historical data. D. polymorpha (zebra mussels) were rarely observed in 2003, having been displaced by D. bugensis (quagga mussels). D. bugensis expanded its depth range from 38 m depth in 1995 to 174 m in 2003 and this dreissenid reached densities averaging 8,000/m² at all sites < 90 m. During the same time period, Diporeia populations almost completely disappeared from 0–90 m depth, continuing a declining trend from 1994–1997 reported in previous studies. The average density of Diporeia in the 30–90 m depth interval decreased from 1,380/m² to 63/m² between 1997 and 2003. Prior to 2003, areas deeper than 90 m represented a refuge for Diporeia, but even these deep populations decreased, with densities declining from 2,181/m2 in 1999 to 545/m2 in 2003. Two common hypotheses for the decline of Diporeia in the Great Lakes are food limitation and a toxin/pathogen associated with dreissenid pseudofeces. The Diporeia decline in deep waters preceded the expansion of D. bugensis to these depths, and suggests that shallow dreissenid populations remotely influence profundal habitats. This pattern of decline is consistent with mechanisms that act from some distance including nearshore dreissenid grazing and downslope transport of pseudofeces.     

Recent increases in the large glacial-relict calanoid Limnocalanus macrurus in Lake Michigan

Since 2004, population density of the large hypolimnetic calanoid Limnocalanus macrurus Sars. has increased dramatically in Lake Michigan. The average summer biomass of this species between 2004 and 2006 was roughly three times that of the period 1984–2003, and at levels unprecedented in our 22-year dataset, making L. macrurus the dominant zooplankter in the lake in terms of biomass. These increases have been accentuated by coincident population declines of the main daphnid, Daphnia mendotae, in the lake with the result that in 2006, L. macrurus accounted for 75% and 50% of the large (> 0.9 mm) crustacean biomass in the northern and southern basins of Lake Michigan, respectively. The increases in L. macrurus populations have closely coincided with equally dramatic increases in summer water clarity. Recent extinction coefficients are among the lowest recorded for the lake, and deepening light penetration has permitted increases in the size of the deep chlorophyll layer. In addition, planktivorous fish populations have declined coincidently with the increases in L. macrurus. It seems likely that an increase in sub-epilimnetic production has resulted in increased food resources for the deep-living L. macrurus, while low planktivore abundances have reduced predation loss, permitting L. macrurus to respond to these increases in sub-epilimnetic production.     

Glyphosate influence on phytoplankton community structure in Lake Erie

In this study we investigated the effect of the phosphonate herbicide glyphosate (N-(phosphonomethyl)glycine) on the phytoplankton community structure in Lake Erie using lake water incubations, laboratory growth experiments and phylogenetic analysis of phosphonate metabolism genes. In microcosms, addition of glyphosate to Sandusky Bay water resulted in a significant increase in phytoplankton abundance, specifically causing an increase in the abundance of Planktothrix spp. In microcosms using Maumee Bay water, glyphosate did not stimulate phytoplankton growth but caused a decrease in Microcystis spp. abundance. The difference in the ability of Planktothrix spp. and Microcystis spp. to grow in the presence of glyphosate was confirmed in laboratory growth experiments. Further, an examination of the molecular pathways involved in phosphonate metabolism demonstrated that heterotrophic bacteria may be critical in allowing this proliferation. The results indicate that glyphosate has both positive and negative influences on phytoplankton community structure, serving as a nutrient source to microbes able to tolerate the herbicidal effects of the compound while killing those less tolerant. Moreover, this work highlights that in natural environments microorganisms function as communities, and the metabolic abilities of individual species are often less important than the collective ability of the community.     

Distribution of nuisance Cladophora in the lower Great Lakes: Patterns with land use, near shore water quality and dreissenid abundance

Selected shorelines and offshore shoals in Lakes Erie, Huron and Ontario were surveyed with a high frequency hydroacoustic system to investigate current spatial patterns of nuisance benthic filamentous algal (e.g., Cladophora) cover and stand height. Cladophora reached nuisance levels at all sites in Lakes Erie and Ontario, but not in Lake Huron or Georgian Bay. Despite clear gradients in coastal land cover, near shore water quality gradients were generally weak, and for Lakes Erie and Ontario, measures of near shore water quality were similar to that at offshore shoals. Hierarchical partitioning analysis suggested that while dreissenid mussel abundance appeared to be important in determining the magnitude of Cladophora standing crop, the joint contribution of catchment land cover, near shore water quality (nutrient levels and suspended matter) and dreissenid mussel abundance explained nearly 95% of the total variance in nuisance Cladophora standing crop observed in this study. Although the results from this study are necessarily correlative in nature and definition of causal relationships is not possible, these results provide corroborating evidence from sites across a gradient within and across the lower Great Lakes that is consistent with the operation of the near shore shunt model.     

Spatial and temporal variation in the distribution of burrowing mayfly nymphs (Ephemeroptera: Hexagenia limbata and H. rigida) in western Lake Erie

In the early 1990s, burrowing mayfly species reappeared in sediments of the western basin of Lake Erie after an absence of over 30 years due to episodic hypoxia at the sediment–water interface. Long-term monitoring of adult mayflies at shoreline areas had revealed that Hexagenia rigida was more abundant than Hexagenia limbata during the initial recolonization period, but was gradually replaced by H. limbata. We hypothesized that this shift in dominance would be confirmed by the distribution and abundance of nymphs. We identified nymphs collected each spring throughout western Lake Erie from 1997 to 2004. The relative abundances of H. rigida and H. limbata nymphs exhibited the same temporal sequence as adults. Furthermore, the number of sites in the western basin in which H. rigida occurred decreased as the occurrence frequency of H. limbata increased. H. limbata were dominant in the basin by 2004. Hexagenia limbata nymphs persisted in the center-most part of the basin, whereas H. rigida did not, possibly due to differences in tolerance to hypoxia. There were no significant differences in body size between the two populations. Differences in dispersal distance from source populations and the timing and success of egg hatching likely accounted for the initial colonizing success of H. rigida, but the differential ability of H. limbata eggs to overwinter in sediments and possible tolerance of nymphs to hypoxia has possibly led to its current dominance in the western basin.     

Shifting status and distribution of range margin chorus frog (Pseudacris) populations in eastern Great Lakes watersheds

Contiguous with their range across major rivers into Canada, two different species of chorus frogs are now thought to inhabit the Great Lakes watersheds of New York. Pseudacris triseriata is found along the western Lake Ontario and Lake Erie plains while P. maculata (tentatively a new frog species in NY) inhabits the lowlands of eastern Lake Ontario and the St. Lawrence River. Both species are on their extreme range margins in NY. In 2010 we detected distributional declines of both putative chorus frog species based on a broad survey following standardized occupancy detection protocols. Causes are unclear but could relate to reforestation and urbanization of formerly more extensive agricultural lands, climate change, pathogenic fungal outbreaks and/or the contaminant effects of intensive agriculture. On the other hand, the prior overestimation of ranges because of misidentification may have inflated earlier perceived distributions (positive survey bias) because false positives are problematical for this cryptic frog. At broad geographical scales, chorus frog (meta)populations are highly dynamic and are likely shifting their ranges in response to rapidly changing overall environmental conditions in the northeastern U.S. and Canada.     

A model laboratory system to study the synergistic interaction and growth of environmental Escherichia coli with macrophytic green algae

Escherichia coli, an important fecal indicator bacterium, is known to persist and reproduce in association with Cladophora and other macrophytic algae and environmental substrates. Recent increases in the growth of Cladophora and other macrophytic algae in many of the Laurentian Great Lakes result in the accumulation of large amounts of algal biomass along the shoreline and on beaches. While the Cladophora–E. coli association may pose substantial public health risks, detailed laboratory-based studies have not been done to investigate the bases of the interaction. This is due, in large part, to past inabilities to culture many macrophytic algae under near axenic conditions. Here we describe the development and experimental use of laboratory microcosms to study the synergistic interaction and growth of the green alga Pithophora, a close relative of Cladophora, with environmental E. coli. In the absence of exogenous organic carbon supply, the E. coli population attached to algal filaments increased approximately three orders of magnitude within 72 h of inoculation. Growth of E. coli on Pithophora appeared to be limited by dissolved nitrogen with a concentration of ≥ 66 μg/mL N allowing maximal bacterial growth. In contrast, an environmental strain of Salmonella did not grow under identical conditions in the microcosms, suggesting that this bacterium requires additional growth factors not provided by Cladophora. Since the alga can be maintained in the laboratory for long periods of time, this system allows for further experimentation and understanding of macroalga–microbe interactions.     

Assessment of Microcystis growth rate potential and nutrient status across a trophic gradient in western Lake Erie

Plankton tow samples collected from 2002 through 2009 indicate that Microcystis biovolume in western Lake Erie is often most dense in transition zone (TZ) waters between Maumee Bay and the center of the western basin. TZ waters are generally high in nutrients and turbidity, and concentrations of each decrease with distance from Maumee Bay. High Microcystis biovolume in the TZ suggests the possibility that the conditions in these waters support a greater Microcystis growth rate relative to the open lake. To test this hypothesis, during the 2008 bloom, Microcystis was collected from western Lake Erie for measurements of total protein content (TPC) as an indicator of growth rate potential and cellular nutrient content to indicate nutrient deficiencies. TPC results indicate that Microcystis in the TZ had a higher potential growth rate compared to offshore waters. TPC values in Maumee Bay were intermediate but not significantly different from the TZ and offshore. Nitrogen content of Microcystis remained high over the summer at all sites, despite very low dissolved nitrate concentrations and low total nitrogen-to-total phosphorus ratio in late summer in the lake. Ammonium level in the lake was constant during the summer, and likely provided the nitrogen source for Microcystis. Cellular phosphorus content varied between site and sample date suggesting that Microcystis was moderately phosphorus deficient. Quotas of micronutrient indicated that Microcystis was not deficient of micronutrients. Results of this study suggest the waters in and adjacent to Maumee Bay provide more favorable growth conditions for Microcystis than offshore waters.     

The Zebra Mussel Dreissena polymorpha Found in North America in 1986 and 1987

The zebra mussel Dreissena polymorpha was first detected in the western basin of Lake Erie, Ontario, Canada, on natural gas wellheads and well markers between April and November 1986. It was found again in 1987 on the north shore of Lake Erie in a water treatment plant, and in vessel fouling. The population increased in Lake Erie in 1988. Dreissena may have spread from Lake Erie to Lake St. Clair, where it was then discovered on 1 June 1988.     

Historic occurrence of parthenogenetic Artemia in Great Salt Lake,USA, as demonstrated by molecular analysis of field samples

Great Salt Lake (GSL), USA is the main source of the commercially important Artemia franciscana Kellogg (1906) cysts used in larviculture. Our objective was to document the presence of parthenogenetic Artemia in GSL analysing a series of non-commercial samples harvested over the period 1997–2005. Laboratory cultures suggested that sex ratios were skewed in some years. Species-specific restriction fragment length polymorphisms in the exon-7 of the Na/K-ATPase α-1 subunit nuclear gene and of a fragment of exon-2 of the heat shock protein HSP26 gene were used to identify samples of individual adults and pooled cysts. Additionally, denaturing gradient gel electrophoresis using the Na/K-ATPase marker and individual adults was used because of its greater power for detecting different alleles. Finally, the exon of the Na/K-ATPase α-1 subunit was sequenced in selected individuals to validate the results. All results indicated that there were parthenogenetic Artemia in the samples from the period 2000 to 2002. Our data do not provide evidence on the autochthonous or allochthonous nature of this population, although an anthropogenic origin seems most likely. The transitory character of the incidence of parthenogenetic Artemia can be linked to unusual environmental conditions in the lake around the turn of the century. The subsequent disappearance of the parthenogenetic population would then be due to the competition with the more productive A. franciscana population as conditions returned back to normal. A systematic genetic study of the GSL Artemia population is recommended as it may provide valuable complementary information about population changes undetected in traditional monitoring programmes.     

First occurrence of the mysid Hemimysis anomala in an inland lake in North America,Oneida Lake,NY

Hemimysis anomala (Crustacea, Mysidae) is a recent invader to North America that until now was reported only from the Laurentian Great Lakes and their immediate embayments, along with the St. Lawrence River. In August 2009, we identified Hemimysis in diets of white perch and yellow perch in Oneida Lake, NY. Night time vertical plankton net tows detected Hemimysis at four sites across the lake. Hemimysis in fish diets (5.5–8.6 mm) were larger than in net tows (2.2–7.0 mm) and reproduction is occurring as some females had brood sacs. This is the first documented introduction of Hemimysis to an inland lake in North America, outside the Great Lakes. Oneida Lake is located 53 river km upstream from Lake Ontario, the nearest known source of Hemimysis. No genetic differences were found between Hemimysis in Oneida Lake and Lake Ontario, indicating this is likely the source of introduction. Several large rapids, locks, and dams separate the two lakes, and as a result the most likely vector of introduction to Oneida Lake is pleasure boat or light commercial traffic via the canal system or overland transport. The presence of Hemimysis in Oneida Lake 3 years after it was first found in Lake Ontario suggests this species may spread rapidly throughout the basin. Despite an intensive monitoring program on Oneida Lake directed at fish, zooplankton, and limnology, Hemimysis was only detected in fish diets and night time zooplankton tows, indicating it may go undetected in lakes for some time using traditional daytime net tows.