Lake Whitefish Research Articles

How to Manage Data to Enhance Their Potential for Synthesis, Preservation, Sharing, and Reuse—A Great Lakes Case Study

ABSTRACTProper data management (applying coordinated standards and structures to data collection, maintenance, retrieval, and documentation) is essential for complex projects to ensure data accuracy and accessibility. In this article, we used a recent project evaluating changes in Lake Whitefish (Coregonus clupeaformis) growth, condition, and recruitment in the Great Lakes as a case study to illustrate how thoughtful data management approaches can enhance and improve research. Data management best practices described include dedicating personnel to data curation, setting data standards, building a relational database, managing data updates, checking for and trapping errors, extracting data, documenting data sets, and coordinating with project collaborators. The data management actions taken ultimately resulted in a rich body of scientific publication and a robust database available for future studies. Investing in data management allowed this project to serve as a model for taking the first steps toward a common goal of sharing, documenting, and preserving data that are collected and reported during the scientific research process.

Experimental Evaluation of Size‐Dependent Predation by Adult Post‐Spawned Rainbow Smelt on Larval Lake Whitefish

AbstractIntroduced landlocked Rainbow Smelt Osmerus mordax are hypothesized to be a major factor in the decline of Lake Whitefish Coregonus clupeaformis populations in many lakes. We sought to identify the size of Lake Whitefish preyed upon by adult Rainbow Smelt and how the efficiency of Rainbow Smelt predation changes Lake Whitefish ontogeny. In a laboratory setting, we exposed larval Lake Whitefish of increasing sizes to groups of seven Rainbow Smelt (>100 mm) for a 1‐h period and observed predation behaviors and efficiencies. In each trial, the group of Rainbow Smelt consumed at least one larval Lake Whitefish, which were up to 45 mm in length (up to 89% of Rainbow Smelt gape width). Predation efficiency, the total number of Lake Whitefish consumed by Rainbow Smelt during trials, was 100% after Lake Whitefish hatching and followed a decreasing sigmoidal response to increasing lengths of Lake Whitefish. The apparent predatory window of Rainbow Smelt on Lake Whitefish is from Lake Whitefish size at hatch (∼12 mm) to approximately 34 mm. Rainbow Smelt generally required multiple attacks to capture a single Lake Whitefish. The capture efficiencies of Rainbow Smelt decreased from 30% as Lake Whitefish length increased and were highly variable within each Lake Whitefish size‐group. The overall impact that Rainbow Smelt predation will have on Lake Whitefish populations is dependent on the growth rate of Lake Whitefish, environmental conditions that cause the Lake Whitefish hatching period to coincide with Rainbow Smelt spawning events, and the degree of overlap in habitat use between spawning Rainbow Smelt, nonspawning subadult Rainbow Smelt, and hatching Lake Whitefish.Received August 29, 2011; accepted November 7, 2012

Variable extent of parallelism in respiratory, circulatory, and neurological traits across lake whitefish species pairs

Parallel adaptive radiation events provide a powerful framework for investigations of ecology's contribution to phenotypic diversification. Ecologically driven divergence has been invoked to explain the repeated evolution of sympatric dwarf and normal lake whitefish (Coregonus clupeaformis) species in multiple lakes in eastern North America. Nevertheless, links between most putatively adaptive traits and ecological variation remain poorly defined within and among whitefish species pairs. Here, we examine four species pairs for variation in gill, heart, and brain size; three traits predicted to show strong phenotypic responses to ecological divergence. In each of the species pairs, normals exhibited larger body size standardized gills compared to dwarfs – a pattern that is suggestive of a common ecological driver of gill size divergence. Within lakes, the seasonal hypoxia experienced in the benthic environment is a likely factor leading to the requirement for larger gills in normals. Interestingly, the morphological pathways used to achieve larger gills varied between species pairs from Québec and Maine, which may imply subtle non-parallelism in gill size divergence related to differences in genetic background. There was also a non-significant trend toward larger hearts in dwarfs, the more active species of the two, whereas brain size varied exclusively among the lake populations. Taken together, our results suggest that the diversification of whitefish has been driven by parallel and non-parallel ecological conditions across lakes. Furthermore, the phenotypic response to ecological variation may depend on genetic background of each population.

Fatty acids in Great Lakes lake trout and whitefish

Fish are an excellent source of lean protein and omega-3 polyunsaturated fatty acids (PUFAs) but there is inadequate information on the levels of PUFAs in freshwater fish and specifically Great Lakes fish. Knowledge of PUFAs is necessary to make informed decisions regarding the balance between the benefits of fish consumption due to these factors versus risks of adverse health effects associated with elevated levels of contaminants known to be present in some Great Lakes fish and linked to increased risk of cancer and adverse neurological effects to both infants and adults. Our goal was to determine the lipid profiles in two species of Great Lakes fish, lake trout and whitefish. Total fat and the percentage of total and omega-3 PUFAs were with one exception significantly higher in lake trout than whitefish. Average concentrations of EPA+DHA were 11.2 and 9.7g/100g lipid in lake trout and whitefish, respectively. The concentrations of EPA+DHA in fatty marine fish (22.7, 23.9 and 30.2g/100g lipid, respectively) are about double those found in Great Lakes lake trout and whitefish. Nevertheless a 100g serving of Great Lakes lake trout provides more than 500mg of EPA+DHA, which is the daily intake level recommended by the American Dietetics Association for the prevention of coronary heart disease.

Lake Whitefish Diet, Condition, and Energy Density in Lake Champlain and the Lower Four Great Lakes following Dreissenid Invasions

AbstractLake Whitefish Coregonus clupeaformis support some of the most valuable commercial freshwater fisheries in North America. Recent growth and condition decreases in Lake Whitefish populations in the Great Lakes have been attributed to the invasion of the dreissenid mussels, zebra mussels Dreissena polymorpha and quagga mussels D. bugensis, and the subsequent collapse of the amphipod, Diporeia, a once‐abundant high energy prey source. Since 1993, Lake Champlain has also experienced the invasion and proliferation of zebra mussels, but in contrast to the Great Lakes, Diporeia were not historically abundant. We compared the diet, condition, and energy density of Lake Whitefish from Lake Champlain after the dreissenid mussel invasion to values for those of Lake Whitefish from Lakes Michigan, Huron, Erie, and Ontario. Lake Whitefish were collected using gill nets and bottom trawls, and their diets were quantified seasonally. Condition was estimated using Fulton's condition factor (K) and by determining energy density. In contrast to Lake Whitefish from some of the Great Lakes, those from Lake Champlain Lake Whitefish did not show a dietary shift towards dreissenid mussels, but instead fed primarily on fish eggs in spring, Mysis diluviana in summer, and gastropods and sphaeriids in fall and winter. Along with these dietary differences, the condition and energy density of Lake Whitefish from Lake Champlain were high compared with those of Lake Whitefish from Lakes Michigan, Huron, and Ontario after the dreissenid invasion, and were similar to Lake Whitefish from Lake Erie; fish from Lakes Michigan, Huron, and Ontario consumed dreissenids, whereas fish from Lake Erie did not. Our comparisons of Lake Whitefish populations in Lake Champlain to those in the Great Lakes indicate that diet and condition of Lake Champlain Lake Whitefish were not negatively affected by the dreissenid mussel invasion.

Spatial and temporal genetic diversity of lake whitefish (Coregonus clupeaformis (Mitchill)) from Lake Huron and Lake Erie

Spatial and temporal genetic diversity of lake whitefish (Coregonus clupeaformis (Mitchill)) from Lake Huron and Lake Erie

Absence of mercury effects on fish populations of boreal reservoirs despite 3 to 6 fold increases in mercury concentrations

At the La Grande hydroelectric complex located in northern Quebec, Canada, mercury concentrations were measured in over 25 000 fish as part of an ongoing environmental effects monitoring program. Five fish species were monitored over a 30-year period: the non-piscivorous lake whitefish (Coregonus clupeaformis) and longnose sucker (Catostomus catostomus) and the piscivorous northern pike (Esox lucius), walleye (Sander vitreus) and lake trout (Salvelinus namaycush). Total mercury concentrations were measured by standard cold vapour atomic absorption spectrophotometry. Fish population characteristics, such as fishing yields, growth rates and condition factors were also monitored over a 20-year period. In reservoirs, mercury concentrations in all species increased rapidly after impoundment, peaking after 5 to 9 years in non-piscivorous fishes, and after 9 to 11 years in piscivorous species, at levels 3 to 6 times those measured in surrounding natural lakes, then significantly and gradually declined. Concentrations in most species have returned to levels typical of natural lakes, 10 to 30 years after flooding. Despite such increases, the monitored fish showed no mercury-related ill effects at the population level. For most species, increases were observed in fishing yields (by factors ranging from 2 to over 20), in growth rates and in condition factors (for more than a decade). The fishing yield increase was highest for northern pike of the Robert-Bourassa Reservoir, for which the highest average mercury concentrations were measured (3.28 µg g -1 (ww) for 700-mm fish). The biological boom usually observed after reservoir impoundment, resulting from increased nutrients, may have prevented potential mercury-related ill effects.

Toward a better understanding of Lake Simcoe through integrative and collaborative monitoring and research

This special section of Inland Waters features the first of numerous papers that highlight trends and insights emerging from decades of ecological monitoring and research activities on Lake Simcoe, Canada. Lake Simcoe is the largest lake in southern Ontario after the Laurentian Great Lakes. Like most large lakes, Simcoe has been negatively impacted over the past century by human activities, which accelerated dramatically around the 1930s (Hawryshyn et al. 2012). Phosphorus (P) loading from point and nonpoint sources caused excessive growth of plants and algae that consume hypolimnetic oxygen during decomposition, which limited coldwater fish habitat and contributed to the recruitment failure of popular sportfish such as lake trout ( Salvelinus namaycush ) and lake whitefish ( Coregonus clupeaformis ; Evans et al. 1996). The establishment in recent decades of invasive fish, invertebrates, and plants is changing lake habitat, food webs, and native species dynamics (Evans et al. 2011, Ginn 2011, Ozersky et al. 2011). Increasing air temperature associated with climate change has prolonged thermal stratification and shortened the period of ice cover (OMOE et al. 2009, Stainsby et al. 2011). Metals and organic pollutants originating from urban and industrial sources have accumulated in lake and tributary sediments (Helm et al. 2011, Landre et al. 2011), potentially affecting aquatic biota and increasing the risk associated with human fish consumption (Gewurtz et al. 2011, Lembcke et al. 2011). Additionally, the cumulative effects of these and other stressors have drastically altered aquatic communities (Depew et al. 2011, Ginn 2011, Jimenez et al. 2011, Winter et al. 2011). In response to public concern about the ecological health of the lake, the Lake Simcoe Protection Act was approved by the Government of Ontario in 2008 with a mandate to protect and restore the Lake Simcoe watershed (Government of Ontario 2008). The Act established the Lake Simcoe Protection Plan (LSPP; OMOE et al. 2009) that identifies a number of targets and indicators to characterize environmental health in the Lake Simcoe watershed and details 119 policies and actions to achieve these targets. Scientific monitoring and research play an integral role in the success of the LSPP, which supports an ecosystem approach to informing policies and actions, taking into account the interconnectedness of the lake and watershed. The LSPP mandates the enhancement of current monitoring programs, development of new monitoring programs, and the promotion and implementation of research projects that build upon existing science to continually update management decisions as part of an adaptive management approach. The challenges posed by the LSPP necessitate collaborative research efforts and sharing of responsibilities, resources, and knowledge among federal, provincial, and local governments, academics, conservation authorities, agricultural, commercial, and industrial sectors, First Nations communities, the general public, and other stakeholders. The collection of papers shows the value of a collaborative approach and demonstrates how strong partnerships can facilitate integrative approaches to scientific monitoring and research efforts being used to protect Lake Simcoe.

Using LiDAR to reconstruct the history of a coastal environment influenced by legacy mining

LiDAR (light detection and ranging) data can be used to create fine digital elevation and bathymetric models (DEMs). Here we examine natural coastal erosion in Grand Traverse Bay, Michigan, a part of Keweenaw Bay in Lake Superior, and discuss how a variety of geological features (submersed river bed and channels associated with the Houghton Low; Nipissing dunes) interact with long-term sediment accumulation patterns. The geological features also modify migrating tailings from a legacy mining site. The combination of LiDAR derived images and aerial photographs allowed us to reconstruct the historical movement of tailings along the coastline. A total of 22.8million metric tonnes (Mt) of stamp sand were discharged into the coastal environment off Gay, MI. Over a span of 80years, beaches to the southwest of Gay have progressively received 7.0Mt (30.7%) of the mass eroded from the original pile, whereas 11.1Mt (48.7%) have moved into the bay. The total amount accumulated along the beaches now greatly exceeds the mass remaining on the original tailings pile (3.7Mt; 16.2%). Bathymetric differences between two LiDAR surveys (2008 and 2010) were also used to estimate the mass, and to track the movement of migrating underwater stamp sand bars. These bars are moving southwesterly towards Buffalo Reef, creating a threat to the lake trout and lake whitefish breeding ground.

The need for decision‐support tools for a changing climate: application to inland fisheries management

AbstractLarge‐scale environmental impacts, such as those of climate change on fisheries, require policy and management action not only at the local level, but at regional, national and international levels. Fisheries biology and ecology, along with social, political and economic considerations, can influence policy design and implementation. Decision‐support tools can integrate these sciences to distil often complex, mechanistic and synergistic processes into a format that the public, policy makers and managers can use when designing strategies to ensure fisheries sustainability in the face of large‐scale environmental perturbations, such as climate change. Harvest management of lake whitefish, Coregonus clupeaformis (Mitchill), in the Laurentian Great Lakes provides an excellent case study to examine the value and utility of a decision‐support tool for inland fisheries management when considering the effects of climate change because this fishery is expected to be impacted by future changes in water temperature, ice cover and wind speed.

Mapping phenotypic, expression and transmission ratio distortion QTL using RAD markers in the Lake Whitefish (Coregonus clupeaformis)

The evolution of reproductive isolation in an ecological context may involve multiple facets of species divergence on which divergent selection may operate. These include variation in quantitative phenotypic traits, regulation of gene expression, and differential transmission of particular allelic combinations. Thus, an integrative approach to the speciation process involves identifying the genetic basis of these traits, in order to understand how they are affected by divergent selection in nature and how they ultimately contribute to reproductive isolation. In the Lake Whitefish (Coregonus clupeaformis), dwarf and normal species pairs sympatrically occur in several North American postglacial lakes. The limnetic dwarf whitefish distinguishes from its normal benthic relative by numerous life history, behavioural, morphological and gene expression traits, in relation with the exploitation of distinct ecological niches. Here, we have applied the RAD-Sequencing method to a hybrid backcross family to reconstruct a high-density genetic linkage map and perform QTL mapping in the Lake Whitefish. The 3061 cM map encompassed 3438 segregating RAD markers distributed over 40 linkage groups, for an average resolution of 0.89 cM. We mapped phenotypic and expression QTL underlying ecologically important traits as well as transmission ratio distortion QTL, and identified genomic regions harbouring clusters of such QTL. A narrow genomic region strongly associated with sex determination was also evidenced. Positional and functional information revealed in this study will be useful in ongoing population genomic studies to illuminate our understanding of the genomic architecture of reproductive isolation between whitefish species pairs.

Coexistence and origin of trophic ecotypes of pygmy whitefish,Prosopium coulterii, in a south‐westernAlaskan lake

Ecologically, morphologically and genetically distinct populations within single taxa often coexist in postglacial lakes and have provided important model systems with which to investigate ecological and evolutionary processes such as niche partitioning and ecological speciation. Within the Salmonidae, these species complexes have been well studied, particularly within the Coregonus clupeaformis-C. laveratus (lake and European whitefish, respectively) group, but the phenomenon has been less well documented in the other whitefish genera, Prosopium and Stenodus. Here, we examined the morphology, feeding biology and genetic structure of three putative forms of the pygmy whitefish, Prosopium coulterii (Eigenmann & Eigenmann, 1892), first reported from Chignik Lake, south-western Alaska, over 40 years ago. Field collections and morphological analyses resolved a shallow water (< 5 m depth) low gill raker count form (< 15 first arch gill rakers), a deepwater (> 30 m), low gill raker form and a deepwater, high gill raker count (> 15 gill rakers) form. The two low gill raker count forms fed almost exclusively on benthic invertebrates (mostly chironomids), while the deepwater, high gill raker count form fed almost exclusively on zooplankton; differences in diet were also reflected in differences both in δ(13) C and δ(15) N stable isotopes. All three forms were characterized by the same major mitochondrial DNA clade that has been associated with persistence in, and postglacial dispersal from, a Beringian glacial refugium. Analysis of variation at nine microsatellite DNA loci indicated low, but significant differentiation among forms, especially between the two low gill raker count forms and the high gill raker count form. The extent of differentiation along phenotypic (considerable) and genetic (subtle) axes among the Chignik Lake forms is similar to that found among distinct taxa of Prosopium found in pre-glacial Bear Lake (Utah-Idaho, USA) which is probably at least ten times older than Chignik Lake. Our analyses illustrate the potential for the postglacial differentiation in traits subject to divergent natural selection across variable environments.

Control rule performance for intermixing lake whitefish populations in the 1836 Treaty waters of the Great Lakes: A simulation-based evaluation

We conducted a simulation-based evaluation exploring the effects of population intermixing on the current 65% total annual mortality control rule used to manage lake whitefish (Coregonus clupeaformis) fisheries in the 1836 Treaty waters of the Laurentian Great Lakes. The simulations incorporated intermixing among four populations with characteristics similar to those of lake whitefish in northern lakes Huron and Michigan. Dynamics of each population were simulated for 100years with each stock exploited by a single fishery. An age-structured assessment of each stock was conducted every third year, with the abundance, mortality, and recruitment estimates used with the current control rule to set future harvest limits. Overall aggregate yield of the modeled system was generally not affected by intermixing, but did depend on assumed productivity levels. Mean annual yields for individual fisheries were sensitive to mixing levels, with yields from fisheries coinciding with low productivity spawning populations often similar to those coinciding with high productivity populations when intermixing occurred. Variability in yield tended to decrease slightly as mixing rates increased. Intermixing did not have a large influence on measures of spawning population sustainability, but detection of declining population sizes in low productivity populations may be difficult when intermixing occurs because of fishery yields remaining high due to immigration of fish from other spawning areas. This raises concern about the current control rule given that low productivity populations had spawning population sizes less than 20% of the unfished level in most years.

Speciation leads to divergent methylmercury accumulation in sympatric whitefish

Central European lake whitefish (Coregonus spp.) colonized Swiss lakes following the last glacial retreat and have undergone rapid speciation and adaptive radiation. Up to six species have been shown to coexist in some lakes, and individual species occupy specific ecological niches and have distinct feeding and reproductive ecologies. We studied methylmercury (MeHg) accumulation in sympatric whitefish species from seven Swiss lakes to determine if ecological divergence has led to different rates of MeHg bioaccumulation. In four of seven lakes, sympatric species had distinctly different MeHg levels, which varied by up to a factor of two between species. Generally, species with greater MeHg levels were smaller in body size and planktivorous, and species with lower MeHg were larger and benthivorous. While modest disparities in trophic position between species might be expected a priori to explain the divergence in MeHg, δ15N of bulk tissue did not correlate with fish MeHg in five of seven lakes. Results of a nested ANCOVA analysis across all lakes indicated that only two factors (species, lake) explained substantial portions of the variance, with species accounting for more variance (52 %) than inter-lake differences (32 %). We suggest that differences in MeHg accumulation were likely caused by diverging metabolic traits between species, such as differences in energy partitioning between anabolism and catabolism, potentially interacting with species-specific prey resource utilization. These results indicate substantial variability in MeHg accumulation between closely related fish species, illustrating that ecological speciation in fish can lead to divergent MeHg accumulation patterns.

Oxidative phosphorylation gene transcription in whitefish species pairs reveals patterns of parallel and nonparallel physiological divergence

Across multiple lakes in North America, lake whitefish (Coregonus clupeaformis) have independently evolved 'dwarf' and 'normal' sympatric species pairs that exhibit pronounced phenotypic and genetic divergence. In particular, traits associated with metabolism have been shown to be highly differentiated between whitefish species. Here, we examine the transcription of genes associated with the five mitochondrial and nuclear genome-encoded oxidative phosphorylation (OXPHOS) complexes, the primary physiological mechanism responsible for the production of ATP, in whitefish species pairs from Cliff Lake and Webster Lake in Maine, USA. We observed OXPHOS gene transcription divergence between dwarf and normal whitefish in each of the two lakes, with the former exhibiting transcription upregulation for genes associated with each of the OXPHOS complexes. We also observed a significant influence of lake on transcription levels for some of the genes, indicating that inter-lake ecological or genetic differences are contributing to variation in OXPHOS gene transcription levels. Together, our results support the hypothesis that metabolic divergence is a critical adaptation involved in whitefish speciation and implicate OXPHOS gene upregulation as a factor involved in meeting the enhanced energetic demands of dwarf whitefish. Further studies are now needed to evaluate the contribution of genetically vs. plasticity driven variation in transcription associated with this critical physiological pathway.

A fast, highly sensitive double‐nested PCR‐based method to screen fish immunobiomes

Efficient methods for constructing 16S tag amplicon libraries for pyrosequencing are needed for the rapid and thorough screening of infectious bacterial diversity from host tissue samples. Here we have developed a double-nested PCR methodology that generates 16S tag amplicon libraries from very small amounts of bacteria/host samples. This methodology was tested for 133 kidney samples from the lake whitefish Coregonus clupeaformis (Salmonidae) sampled in five different lake populations. The double-nested PCR efficiency was compared with two other PCR strategies: single primer pair amplification and simple nested PCR. The double-nested PCR was the only amplification strategy to provide highly specific amplification of bacterial DNA. The resulting 16S amplicon libraries were synthesized and pyrosequenced using 454 FLX technology to analyse the variation of pathogenic bacteria abundance. The proportion of the community sequenced was very high (Good's coverage estimator; mean = 95.4%). Furthermore, there were no significant differences of sequence coverage among samples. Finally, the occurrence of chimeric amplicons was very low. Therefore, the double-nested PCR approach provides a rapid, informative and cost-effective method for screening fish immunobiomes and most likely applicable to other low-density microbiomes as well.

Habitat use by fishes of Lake Superior. I. Diel patterns of habitat use in nearshore and offshore waters of the Apostle Islands region

Diel patterns of distribution of fishes in nearshore (15–80 m depth) and offshore (&amp;gt;80 m) waters of the Apostle Islands region of Lake Superior were described using bottom trawls, mid-water trawls, and acoustic gear during day and night sampling. These data revealed three types of diel migration: diel vertical migration (DVM), diel bank migration (DBM), and no migration. DVM was expressed by fishes migrating from benthopelagic to pelagic strata and DBM was expressed by fishes migrating horizontally from deeper waters in the day to shallower waters at night while remaining within the benthopelagic stratum. Most fishes that did not exhibit diel migration showed increased nighttime densities as a result of increased activity and movement from benthic to benthopelagic strata. Rainbow Smelt (Osmerus mordax), Cisco (Coregonus artedi), Bloater (C. hoyi), Kiyi (C. kiyi), juvenile Trout-Perch (Percopsis omiscomaycus), and adult siscowet (Salvelinus namaycush siscowet) exhibited DVM. Lake Whitefish (C. clupeaformis), lean Lake Trout (Salvelinus namaycush namaycush), and juvenile siscowet exhibited DBM. Adult Trout-Perch and adult Pygmy Whitefish (Prosopium coulteri) exhibited a mixture of DBM and DVM. Burbot (Lota lota), Slimy Sculpin (Cottus cognatus), Spoonhead Sculpin (C. ricei), and Deepwater Sculpin (Myoxocephalus thompsonii) did not exhibit diel migration, but showed evidence of increased nocturnal activity. Ninespine Stickleback (Pungitius pungitius) exhibited a mixture of DVM and non-migration. Juvenile Pygmy Whitefish did not show a diel change in density or depth distribution. Species showing ontogenetic shifts in depth distribution with larger, adult life stages occupying deeper waters included, Rainbow Smelt, lean and siscowet Lake Trout, Lake Whitefish, Pygmy Whitefish, Ninespine Stickleback and Trout-Perch. Of these species, siscowet also showed an ontogenetic shift from primarily DBM as juveniles to primarily DVM as adults. Across all depths, fishes expressing DVM accounted for 73% of the total estimated community areal biomass (kg ha−1) while those expressing DBM accounted for 25% and non-migratory species represented 2% of the biomass. The proportion of total community biomass exhibiting DVM increased with depth, from 59% to 95% across ≤30 m to &amp;gt;90 m depth zones. Along the same depth gradient, the proportion of total community biomass exhibiting DBM declined from 40% to 1%, while non-migrators increased from 1% to 4%. These results indicate that DVM and DBM behaviors are pervasive in the Lake Superior fish community and potentially provide strong linkages that effect coupling of benthic and pelagic and nearshore and offshore habitats.

Parallelism in the oxygen transport system of the lake whitefish: the role of physiological divergence in ecological speciation

In North America, populations of lake whitefish (Coregonus clupeaformis) have evolved sympatric 'dwarf' and 'normal' ecotypes that are associated with distinct trophic niches within lakes. Trophic specialization should place diverging physiological demands on individuals, and thus, genes and phenotypes associated with energy production represent ideal candidates for studies of adaptation. Here, we test for the parallel divergence of traits involved in oxygen transport in dwarf and normal lake whitefish from Québec, Canada and Maine, USA. We observed significant differences in red blood cell morphology between the ecotypes. Specifically, dwarfs exhibited larger nuclei and a higher nucleus area/total cell area than normal whitefish in all of the lakes examined. In addition, isoelectric focusing gels revealed variation in the haemoglobin protein components found in whitefish. Dwarf and normal whitefish exhibited a similar number of protein components, but the composition of these components differed, with dwarf whitefish bearing a greater proportion of cathodic components compared to the normals. Furthermore, dwarf whitefish showed significant haemoglobin gene upregulation in the brain compared with the levels shown in normals. Together, our results indicate that metabolic traits involved in oxygen transport differ between the whitefish ecotypes and the strong parallel patterns of divergence observed across lakes implicates ecologically driven selection pressures. We discuss the function of these traits in relation to the differing trophic niches occupied by the whitefish and the potential contributions of trait plasticity and genetic divergence to energetic adaptation.

Trophic relationships of two species of grebe on a prairie lake based on stable isotope analysis

We used stable isotope analysis of carbon and nitrogen to investigate the trophic relationships of Western (Aechmophorus occidentalis (Lawrence)) and Red-necked (Podiceps grisegena (Boddaert)) Grebes from Lake Wabamun, a large prairie lake in north-central Alberta, Canada. We collected tissue samples (i.e., pectoralis muscles and primary feathers) from 42 Western and 22 Red-necked Grebes (adults and juveniles) that had died in captivity after an oil spill on Lake Wabamun on 3 August, 2005. We also collected fish and invertebrates, focusing on taxa known to serve as prey for grebes. Based on comparisons of 15N enrichment in muscle tissue, Western Grebes, northern pike (Esox lucius Linnaeus), yellow perch (Perca flavescens (Mitchill)), and lake whitefish (Coregonus clupeaformis (Mitchill)) were top consumers in Lake Wabamun, as were Red-necked Grebes. Adult Western Grebe muscle was more enriched with 15N than adult Red-necked Grebe muscle by 1.5‰, indicating that Western Grebes foraged at a slightly higher trophic position on Lake Wabamun than Red-necked Grebes. Red-necked Grebe muscles and feathers were also less depleted in 13C than Western Grebe muscle, indicating that Red-necked Grebes likely spent more time foraging in the littoral zone than Western Grebes. There were no differences in muscle or feather isotopic signals between juvenile and adult Western Grebes, suggesting that both age groups fed on similar prey items and in similar habitats. Muscle tissues and primary feathers of larger Red-necked Grebes were more enriched in both 15N and 13C than smaller grebes likely because larger grebes consume more or larger fish.

Characterizing Seasonal Habitat Use and Diel Vertical Activity of Lake Whitefish in Clear Lake, Maine, as Determined with Acoustic Telemetry

AbstractSeasonal and daily vertical activity of lake whitefishCoregonus clupeaformiswas studied in Clear Lake, Maine (253 ha), using acoustic telemetry from November 2004 to June 2009. Twenty adult lake whitefish were tagged with acoustic tags that had either a depth sensor or both depth and temperature sensors to assess vertical habitat use at a seasonal and daily resolution. Vertical habitat selection varied seasonally and was strongly influenced by temperature. Between December and April, when the lake was covered with ice, surface temperature was below 2°C and tagged individuals occupied deep areas of the lake (∼15 m). After ice‐out, fish ascended into shallow waters (∼5 m), responding to increased water temperature and possibly to greater foraging opportunity. When surface water temperatures exceeded 20°C, fish descended below the developing thermocline (∼9 m), where they remained until surface temperatures fell below 20°C; fish then ascended into shallower depths, presumably for feeding and spawning. Through the winter, fish remained in thermal habitats that were warmer than the surface temperatures; in the summer, they selected depths with thermal habitats below 15°C. Though the amplitude varied greatly across seasons, lake whitefish displayed a strong diurnal pattern of activity as measured by vertical velocities. Fish were twofold more active during spring, summer, and fall than during winter. Lake whitefish exhibited diel vertical migrations, rising in the water column during nighttime and occupying deeper waters during the day. This pattern was more pronounced in the spring and fall and far less prominent during winter and summer. The strong linkage between temperature and habitat use may limit the current range of lake whitefish and may be directly impacted by climatic change.