Small Boreal Lakes Research Articles

Productivity-diversity relationships in lake plankton communities.

One of the most intriguing environmental gradients connected with variation in diversity is ecosystem productivity. The role of diversity in ecosystems is pivotal, because species richness can be both a cause and a consequence of primary production. However, the mechanisms behind the varying productivity-diversity relationships (PDR) remain poorly understood. Moreover, large-scale studies on PDR across taxa are urgently needed. Here, we examined the relationships between resource supply and phyto-, bacterio-, and zooplankton richness in 100 small boreal lakes. We studied the PDR locally within the drainage systems and regionally across the systems. Second, we studied the relationships between resource availability, species richness, biomass and resource ratio (N∶P) in phytoplankton communities using Structural Equation Modeling (SEM) for testing the multivariate hypothesis of PDR. At the local scale, the PDR showed variable patterns ranging from positive linear and unimodal to negative linear relationships for all planktonic groups. At the regional scale, PDRs were significantly linear and positive for phyto- and zooplankton. Phytoplankton richness and the amount of chlorophyll a showed a positive linear relationship indicating that communities consisting of higher number of species were able to produce higher levels of biomass. According to the SEM, phytoplankton biomass was largely related to resource availability, yet there was a pathway via community richness. Finally, we found that species richness at all trophic levels was correlated with several environmental factors, and was also related to richness at the other trophic levels. This study showed that the PDRs in freshwaters show scale-dependency. We also documented that the PDR complies with the multivariate model showing that plant biomass is not mirroring merely the resource availability, but is also influenced by richness. This highlights the need for conserving diversity in order to maintain ecosystem processes in freshwaters.

Phylogenetic composition of bacterial communities in small boreal lakes and ombrotrophic bogs of the upper Volga basin

Fluorescent in situ hybridization (FISH) with rRNA-specific oligonucleotide probes was used to assess the numbers and phylogenetic diversity of prokaryotic microorganisms in the water of small boreal lakes and peatland catchments of the swampy upper Volga basin. The abundance of bacterioplankton in lake water was found to vary from 1.6 to 8.7 × 106 cells ml−1, with the highest values detected in neutral eutrophic lakes. The total cell numbers in the peat of ombrotrophic bogs were 3.9–4.3 × 108 cells g−1 of wet peat. The proportion of bacteria identified by the group-specific probes decreased from 79–85% in neutral (pH 6.6–6.9) mesotrophic and eutrophic lakes to 65–69% in acidic (pH 4.4–5.5) dystrophic lakes and to 51–58% in the peat of acidic (pH 3.6–3.9) ombrotrophic bogs. The diversity of bacterial communities was highest in lakes with neutral water. These communities were dominated by members of the phylum Actinobacteria (31–44% of the total bacterial number), while the contribution of Alphaproteobacteria (16–19%), Bacteroidetes (6–16%), Betaproteobacteria (6–7%), Planctomycetes (2–8%), and Gammaproteobacteria (4–5%) was also significant. In acidic dystrophic lakes, Actinobacteria (25–35%) and Betaproteobacteria (25–34%) predominated, while peatland catchments were dominated by the Alphaproteobacteria (20–23%). The presence of acidobacteria and some planctomycetes common for bogs in the water of acidic dystrophic lakes, as well as the high proportion of bacteria (31–49%) that were not identified by the group-specific probes, suggest the impact of microbial processes in peatland catchments on the microbial composition of the receiving waters.

Diatom-inferred depth models in 8 Canadian boreal lakes: inferred changes in the benthic:planktonic depth boundary and implications for assessment of past droughts

Assessment of past drought in boreal regions, a region predicted to be strongly affected by climate warming, can provide insights into future availability of water. However, limited instrumental data and paleoclimatic data are available for this assessment. To address this lack of data in the boreal region of northwest Ontario, a regional study of lakes in the Winnipeg River Drainage Basin was initiated. Diatom-inferred (D-I) depth models were developed based on surface samples collected along a depth gradient within 8 small boreal lakes. Weighted-averaging and modern analog approaches provided robust within-lake depth models for each of the study lakes, with bootstrapped r 2 values ranging from 0.90 to 0.98, and root-mean-squared-errors of prediction (RMSEP) between 1.1 and 2.5 m. Large differences in the estimated depth optima for three representative, but common diatom species across our 8 study lakes suggested that within-lake calibration datasets are more appropriate for inferring past drought based in depth models than a regional multi-lake calibration dataset, and that light and related variables are controlling factors governing the maximum depth of benthic taxa. A down-core application of the D-I depth models on a near-shore core from Meekin Lake, retrieved near the present-day ecotone between the benthic and planktonic diatom assemblages indicated highly similar trends in inferred depth ( r = 0.96). The models have significant correlations with other metrics of changes in depth including diatom species richness ( r = 0.74–0.78) and evenness ( r = 0.76–0.8), thereby allowing a check on the strength and direction of the depth inferences down-core. Near-shore cores located near the benthic:planktonic transition is a sensitive region that can provide estimates of past droughts in lakes where such inferences have been difficult to estimate.

Long-term energy flux measurements and energy balance over a small boreal lake using eddy covariance technique

[1] Measurements of the energy balance components of a small boreal lake (area 0.041 km2, mean depth 2.5 m) in southern Finland were performed during four open water periods (April–October) in 2005–2008. Turbulent fluxes of sensible and latent heat acquired using the eddy covariance technique were accompanied by net radiation and water heat storage measurements. In April the lake was near isothermal, whereas in May the development of a thermocline was enabled by dark water color and a sheltered location. The thermocline continued to deepen until September down to the depth of 3.5 m and prevented the deeper water from interacting with the atmosphere. The sensible heat flux was governed by the air-water temperature difference and had its minimum in the afternoon (values down to −45 W m−2) and peaked in the early morning (values up to 32 W m−2). The monthly means ranged from −9 W m−2 (April 2005) to 24 W m−2 (July 2008). The diurnal variation of the latent heat flux, controlled by vapor pressure deficit, had an opposite diurnal phase with a maximum in the afternoon (values up to 120 W m−2) and minimum in the morning (values down to ∼2 W m−2). The monthly averages ranged from 4 W m−2 (October 2008) to 77 W m−2 (July 2006). Furthermore, the lake acted as a heat sink until July and August when the maximum heat content was about 230 MJ m−2. The monthly energy balance closure varied from 57% to 112%, and the average closure was 82% (residual 16 W m−2) and 72% (residual 23 W m−2) for 2006 and 2007, respectively.

Climate induced thermocline change has an effect on the methyl mercury cycle in small boreal lakes

We conducted a whole-lake experiment by manipulating the stratification pattern (thermocline depth) of a small polyhumic, boreal lake (Halsjärvi) in southern Finland and studying the impacts on lake mercury chemistry. The experimental lake was compared to a nearby reference site (Valkea–Kotinen Lake). During the first phase of the experiment the thermocline of Halsjärvi was lowered in order to simulate the estimated increase in wind speed and in total lake heat content (high-change climate scenario). The rate of methyl mercury (MeHg) production during summer stagnation (May–August) was calculated from water profiles before the treatment (2004), during treatment (2005, 2006) and after treatment (2007). We also calculated fluxes of MeHg from the epilimnion and from the hypolimnion to the sediments using sediment traps. Experimental mixing with a submerged propeller caused a 1.5–2 m deepening of the thermocline and oxycline. Methyl mercury production occurred mostly in the oxygen free layers in both lakes. In the experimental lake there was no net increase in MeHg during the experiment and following year; whereas the reference lake showed net production for all years. We conclude that the new exposed epilimnetic sediments caused by a lowering of the thermocline were a major sink for MeHg in the epilimnion. The results demonstrate that in-lake MeHg production can be manipulated in small lakes with anoxic hypolimnia during summer. The climate change induced changes in small boreal lakes most probably affect methyl mercury production and depend on the lake characteristics and stratification pattern. The results support the hypothesis that possible oxygen related changes caused by climate change are more important than possible temperature changes in small polyhumic lakes with regularly occurring oxygen deficiency in the hypolimnion.

Long-term patterns in pH and colour in small acidic boreal lakes of varying hydrological and landscape settings

Changes in water pH and colour since the late 1980s were studied in 35 small boreal lakes of varying hydrological and landscape settings but similar climate and acid deposition. The data was collected during the autumnal overturn on the annual basis except in lake with weekly sampling during the ice-free period. In addition to the deposition data information about catchment soil types as well as local meteorological and hydrological conditions were used for the long-term data interpretation. The lakes are situated in a small area in southern Finland, 130 km north from Helsinki, where sulphate deposition declined by >60% in one decade since the mid-1980s. The results showed that water colour increased in most lakes while pH did not. In lakes dominated by surface runoff there was a distinct upward shift in colour, with an initial increase after the mid-1990s and a second increase in 2004. The first shift appeared when the sulphate deposition reached a level ca. 25% of that in 1988. However, the upward shift in colour also coincided with a change in hydrological conditions after several dry summers. In contrast, the second shift in colour clearly coincided with a switch in hydrology due to the abnormally wet summer of 2004 after severe drought in 2002–2003. Although the hydrological conditions indisputably had a key role in determining the annual variability in colour, a distinct negative relationship between acid deposition and water colour in 90% of the lakes strongly suggested that reduction in sulphate deposition fostered the leaching of coloured organic substances from the catchment soils. Increase in colour, in turn, strongly influenced lake water pH, and the present day higher organic matter concentrations seemingly depress pH values more than in the 1980s, before the reduction in acid deposition.

Diurnal variations of trace metals and heterotrophic bacterioplankton concentration in a small boreal lake of the White Sea basin

This work represents a concerted effort aimed at understanding the microbiological and chemical evolution of a small boreal lake during the diurnal cycle of photosynthesis. We studied diurnal variation of ∼40 dissolved macro- and trace elements, organic carbon and bacterial population dynamics in the surface and bottom water layer of the shallow Vilno Lake in the White Sea basin. Four-days continuous measurements with 6 h sampling steps both at the surface (0.5 m) and on the bottom (4.0 m depth) during no-bloom periods revealed constant concentrations (within ±20–30%) of all major elements (Na, Mg, Si, K, Ca), organic and inorganic carbon and most trace elements (B, V, Cr, Fe, Cu, Ga, As, Rb, Sr, Y, Zr, Sb, Cs, Ba, all REEs, Hf, Pb, Th, U). At the same time, the concentration of some biologically important trace metals (Mo, Mn, Co, Cd) was subjected to variations partially reflecting the change of bacterioplankton concentration. This work enables two types of element behavior to be distinguished during photosynthesis in the water column – constant concentration and sinusoidal variations – depending on their speciation in solution and their affinity to aquatic microorganisms.

Diets of crustacean zooplankton, inferred from stable carbon and nitrogen isotope analyses, in lakes with varying allochthonous dissolved organic carbon content

We used stable carbon and nitrogen isotope analyses to estimate the relative proportions of three putative food sources (1) algae, (2) allochthonous organic matter (but including also heterotrophic bacteria and green-sulphur bacteria having similar isotopic values) and (3) methane-oxidizing bacteria (MOB) in the diets of crustacean zooplankton in five small boreal lakes representing a gradient of dissolved organic carbon (DOC) concentration from ca. 5 to 40 mg C l−1. The lakes were sampled in May, after establishment of stratification, and again in October during autumnal mixing of the water column. IsoSource mixing model outputs indicated that the proportion of algae in the diets of zooplankton was generally higher in May than in October, and that bacteria contributed to the diets of both cladocerans and copepods. Our results indicate that bacteria, especially MOB, can make an appreciable contribution to zooplankton diets in these small lakes, even in those with relatively low DOC concentrations.

Climate-related eutrophication of a small boreal lake in northwestern Ontario: a palaeolimnological perspective

A palaeolimnological investigation of changes in water quantity and quality in Lake 239, Experimental Lakes Area, in northwestern Ontario indicates marked changes in limnological conditions during the Holocene. Water quantity changes are based on the analysis of diatoms and inferences of lake-level changes from a nearshore sediment core. Changes in water quality are based on the analysis of diatom assemblages and associated quantitative inferences of total phosphorus (TP) from a deep central core, as well as changes in diatom accumulation rates, the proportion of chrysophyte scales to diatoms and changes to organic matter content. Lake levels at least 8 m lower than today were inferred from the nearshore core and were concurrent with an increase in nutrient-rich diatom assemblages, an increase in diatom accumulation and a decrease in the chrysophytes relative to diatoms in the central core. Fragilaria crotonensis and Aulacoseira subarctica were two of the dominant nutrient-rich taxa that contributed to an increase in diatom-inferred TP during the mid Holocene. Results from this study provide strong empirical evidence that water levels much lower than today can dramatically change trophic status, as occurred during the dry mid Holocene, and may provide a good analogue for understanding future impacts of climatic changes due to anthropogenic activities.

Predicting the spatial mud energy and mud deposition boundary depth in a small boreal reservoir before and after draw down

We predicted the distribution of coarse- and fine-grained substrata in a small boreal lake at natural lake level and then assessed if the extents of sediment focusing due to water level manipulation could be predicted. The littoral substratum and upper limit to the distribution of mud was mapped completely prior to experimental draw down and the upper depth limit of mud was mapped in each of the first 2 years of a new water level regime. Six published equations for estimating the position of the mud boundary and the lower limit of surface wave energy were applied using maps of fetch, slope, and depth. At natural lake level, the agreement between observed and estimated mud boundaries in deep water was remarkable (<5 m horizontal). Agreement between the depth of mixing by surface waves and mud boundaries in shallow water was closest, at times exact, for equations with estimates similar to maximum wave height. However, the size of waves responsible for the shallow sediment boundaries remains unclear due to natural variation of lake level. All models overestimated energy in shallow depositional settings where exposure and slope was low. Refocusing of sediment due to maximum winter draw down of 3 m resulted in contraction and expansion of the profundal zone; a net decrease in area of 3% was evident after 2 years. Our results demonstrate that mud deposition models can be used in deep lake basins to map the littoral and profundal zones. Sediment refocusing in the first few years of winter draw down is forced mainly by falling lake levels. The interpretation of littoral habitat complexity can be simplified by understanding the lake-wide spatial pattern of erosion, transport, and deposition of sediments.

Sedimentation in Boreal Lakes—The Role of Flocculation of Allochthonous Dissolved Organic Matter in the Water Column

We quantified sedimentation of organic carbon in 12 Swedish small boreal lakes (< , 0.48 km(2)), which ranged in dissolved organic carbon (DOC) from 4.4 to 21.4 mg C l(-1). Stable isotope analys ...

Paleolimnological assessment of the impact of logging on small boreal lakes

In Finland a great number of forest lakes are affected by silvicultural practices such as logging. Logging affects water chemistry and thus the ecological state of lakes by causing nutrient loads and increasing erosion and humic substances in water. Water quality assessment requires definition of natural background conditions and ecological status of water bodies. Therefore it is necessary to determine the impact of these practices on aquatic organisms. In the absence of long-term monitoring data, paleolimnological methods provide a powerful tool for determining human-induced changes in lakes. In this study diatom assemblages, diatom-inferred water total phosphorus and total organic carbon, and sediment chemistry were analyzed from the sediments of six lakes with a logged catchment area (11–53%). According to one-way analysis of similarities (ANOSIM) the diatom communities of three lakes were different before, immediately after and more than 10 years after logging and diatom assemblages in remaining three lakes did not show statistically significant differences between these times. However, all changes were minor, and at present the diatom assemblages and diatom-inferred water chemistry of all the lakes are close to the pre-logging conditions. The minor alterations are probably due to the wide protective zones around the lakes.

Contribution of trophic position to the mercury content of pike (Esox lucius) in small boreal lakes

Contribution of trophic position to the mercury content of pike (<i>Esox lucius</i>) in small boreal lakes

Sediment respiration and lake trophic state are important predictors of large CO2 evasion from small boreal lakes

AbstractWe show that sediment respiration is one of the key factors contributing to the high CO2 supersaturation in and evasion from Finnish lakes, and evidently also over large areas in the boreal landscape, where the majority of the lakes are small and shallow. A subpopulation of 177 randomly selected lakes (&lt;100 km2) and 32 lakes with the highest total phosphorus (Ptot) concentrations in the Nordic Lake Survey (NLS) data base were sampled during four seasons and at four depths. Patterns of CO2 concentrations plotted against depth and time demonstrate strong CO2 accumulation in hypolimnetic waters during the stratification periods. The relationship between O2 departure from the saturation and CO2 departure from the saturation was strong in the entire data set (r2=0.79, n=2 740, P&lt;0.0001). CO2 concentrations were positively associated with lake trophic state and the proportion of agricultural land in the catchment. In contrast, CO2 concentrations negatively correlated with the peatland percentage indicating that either input of easily degraded organic matter and/or nutrient load from agricultural land enhance degradation. The average lake‐area‐weighted annual CO2 evasion based on our 177 randomly selected lakes and all Finnish lakes &gt;100 km2 (Rantakari &amp; Kortelainen, 2005) was 42 g C m−2 LA (lake area), approximately 20% of the average annual C accumulation in Finnish forest soils and tree biomass (covering 51% of the total area of Finland) in the 1990s. Extrapolating our estimate from Finland to all lakes of the boreal region suggests a total annual CO2 evasion of about 50 TgC, a value upto 40% of current estimates for lakes of the entire globe, emphasizing the role of small boreal lakes as conduits for transferring terrestrially fixed C into the atmosphere.

The biology of pygmy whitefish, Prosopium coulterii, in a closed sub-boreal lake: spatial distribution and diel movements

Using gillnets and trap nets, we examined the spatial distribution, diel movements, and environmental tolerances of pygmy whitefish, Prosopium coulterii, in a small boreal lake in north-central British Columbia. Most gillnets were set below the thermocline but we also fished a shore net in the littoral zone. During the ice-free season (May to November) there was a strong diel onshore–offshore movement: during the day pygmy whitefish were offshore and below the thermocline (water temperatures of 4–6°C) but at night they were inshore and above the thermocline (water temperatures of 12–18°C). This onshore–offshore movement occurred close to the bottom and, regardless of where they were caught, most fish were <4 m off the bottom. Oxygen concentrations in most of the hypolimnion dropped to <5.0 mg l−1 in June and by late August to <1.0 mg l−1; indicating pygmy whitefish can tolerate low oxygen conditions. The catch of pygmy whitefish in gillnets set below the thermocline was highly skewed: 53% of the nets were empty, 37% caught 18 or less fish, and 10% caught 70% of the total catch (742 fish). Trap nets produced similarly skewed results: most trap net sets caught no pygmy whitefish but one set caught over 2,000 individuals. Our catch data suggest that in Dina Lake #1 some pygmy whitefish aggregate.

Coupling of boreal forests and lakes: Effects of conifer pollen on littoral communities

Conifer pollen deposition is a visually striking spring event in boreal lakes, representing a potentially major allochthonous input of limiting nutrients. We conducted a lake survey and mesocosm experiment at the Experimental Lakes Area in northwestern Ontario to test the hypothesis that jack pine (Pinus banksiana) pollen inputs subsidize littoral nutrient levels and stimulate algal growth and zooplankton abundance. A series of floating litterfall collectors were deployed along transects that span a 0.27-km2 headwater lake (Lake 373) and monitored after ice-out to quantify pollen deposition over a 45-d period. Lake 373 (L373) received 11–56 µmol P m−2 d−1 from pollen, or an annual total of about 10 kg of P. These data were used to determine pollen amendment levels (ambient, 3×, 10×) for an experiment involving 18, 1-m3 littoral mesocosms distributed over three lakes (L239, L373, and L442). Pollen amendments significantly increased total phytoplankton and herbivorous zooplankton biomass, resulting in greater abundance of inedible filamentous green algae and large diatoms. Pollen also exerted a positive lake-specific effect. Periphyton biomass also increased in response to pollen additions, especially filamentous green algae and diatoms in L239 and L442. Conifer pollen subsidizes nutrient levels and promotes production in small boreal lakes.

Carbon burial and infill rates in small Western Boreal lakes: physical factors affecting carbon storage

Effects of depression depth (ZT), lake surface elevation (ES), catchment area:lake surface area (AT:AO), trophic status, and surficial geology on sediment burial rates in small Western Boreal Plain lakes were assessed using content and chronology of cores from a relatively large and small lake on each of moraine (M), glaciofluvial (GF), and glaciolacustrine (GL) deposits. Aquatic and terrestrial plant and sediment carbon:nitrogen (C:N) suggested most buried C was aquatic. The rate of long-term total C burial averaged 31 g·m–2·year–1 (range: 0–84 g·m–2·year–1); this was recently 79 g·m–2·year–1 (range: 40–180 g·m–2·year–1) (higher and more variable rates than previously reported for Boreal lakes). Long-term C accrual rate and sediment depth increased with increasing ZT. In each landform, a relatively low base elevation (EB = ES – ZT) lake began accumulating sediment thousands of years before a high EB lake. GF depressions were deeper and had accrued more C·m–2 (and infilled) faster than M and GL lakes; a large GF lake had no organic sediment, perhaps because of large groundwater inputs. Increasing AT:AO corresponded with increasing C accrual rates where precipitation and evaporation dominated (surface runoff infrequent) (M and GL) but not where groundwater dominated (GF lakes) lake water budgets, illustrating the importance of landform and depression characteristics in regionalizing lake-C burial estimates.

Historical pollution of seldom monitored trace elements in Sweden—Part A: Sediment properties and chronological indicators

Sediment cores from four small oligotrophic boreal lakes, with minor acidification, in remote regions of central Sweden were used for historical interpretation of their metal content, with focus on Cu, Cd, Pb and Zn in Lake Stensjön, which has the longest sediment record (at least two centuries according to (210)Pb dating). Comparison is made with the other three lakes. Major and trace elements in lake water, porewater and the acid-leached (HNO(3)) solid sediment phase was analysed with ICP-MS. In addition, general lake water chemistry, TOC and principal anions were measured in the aqueous phases. Redistribution processes were interpreted from geochemical modelling. The solid/solution distribution of pe/pH sensitive elements, indicates a minor diagenetic redistribution and the concentration profiles are therefore suitable for chronological evaluation. The ratios of Al, Ti, Sc and V, indicated a qualitative shift of sedimenting material a century ago, which did not have any impact on the retention of trace elements. Lead had a concentration profile, supported by the (206)Pb/(207)Pb ratio, where it was possible to distinguish preindustrial conditions, early industrialisation in Europe, industrialisation in Sweden, and the use of leaded petrol after the Second World War. Cadmium showed a similar concentration pattern. The zinc profile resembled that of cadmium, but with less enrichment. Local lithogenic sources are believed to be quantitatively important. The solid/solution distribution (K(d)) was independent of depth for all four elements. The sediment concentrations of copper and zinc are not related to early industrialisation but its concentration has doubled since the Second World War.

Invertivory by northern pike (Esox lucius) structures communities of littoral macroinvertebrates in small boreal lakes

AbstractRecent comparative studies suggest that macroinvertebrates in small Boreal Plains lakes respond to large fluctuations in fish densities caused by winterkill and subsequent recovery even when such fluctuations involve the normally piscivorous northern pike (Esox lucius). We introduced pike into a boreal lake made fishless by a past winterkill to isolate experimentally the effects of pike on littoral macroinvertebrates. We compared postmanipulation macroinvertebrate data from the experimental lake (EXP) to premanipulation data from the same lake, to parallel data from 2 unmanipulated reference lakes (R1 and R2) containing pike, and to data from mesocosms within EXP. Pike in all 3 lakes preyed heavily upon macroinvertebrates; diets consisted predominantly of the amphipod Gammarus lacustris in R1 and R2 and erpobdellid leeches in EXP. Principal components analysis (PCA) of macroinvertebrate communities distinguished between systems with and without fish and detected a shift in the macroinvertebrate co...

The Response of Lake Trout to Manual Tracking

AbstractThe use of telemetry is widespread in fisheries research, and manual tracking of fish is considered acceptable for data collection. However, it has never been shown whether the use of boats with powered engines, which is common in manual tracking, influences the distribution and behavior of fish. We examined whether general boat traffic or focused manual tracking activity altered movement patterns of adult lake trout Salvelinus namaycush in a small boreal lake at the Experimental Lakes Area of northwestern Ontario, Canada. In the summer and fall of 2002, we used automated fish positioning systems to compare the behavior of lake trout during 1‐h disturbance periods (boat traffic or manual tracking) with behavior in the preceding 1‐h baseline periods (no disturbance). In addition, we compared behavioral differences of lake trout during disturbance and baseline periods (experimental trials) with a similar period of time when no boats were on the lake (control trials). This comparison allowed us to determine whether the observed changes in behavior during normal boat traffic or manual tracking were within the natural range of variation. Overall, we observed no effect of boat traffic or manual tracking on the depth, speed, and path predictability of lake trout. Similarly, the changes in lake trout behavior between the disturbance and baseline periods of the experimental trials were all within the natural range determined by control trials. The response of lake trout to manual tracking was not related to their proximity to the motorboat, both when lake trout were in deep water (6 m; summer) and when they were in shallow water (2 m; fall spawning season). The lack of significance of the relationship between patterns of fish behavior and manual tracking activity provides support for the continued use of this method in fisheries research.