Geology topics

Daniel L. Yule

Publications and source records attributed to Daniel L. Yule.

At least 55 records · Page 3Linked to original sources

USGS2016

Ciscoes ( Coregonus , subgenus Leucichthys ) of the Laurentian Great Lakes and Lake Nipigon

This study of the ciscoes ( Coregonus , subgenus Leucichthys ) of the Great Lakes and Lake Nipigon represents a furtherance through 2015 of field research initiated by Walter Koelz in 1917 and continued by Stanford Smith in the mid-1900s—a period spanning nearly a century. Like Koelz’s study, this work contains information on taxonomy, geographical distribution, ecology, and status of species (here considered forms). Of the seven currently recognized forms ( C. artedi , C. hoyi , C. johannae , C. kiyi , C. nigripinnis , C. reighardi , and C. zenithicus ) described by Koelz as major in his 1929 monograph, two ( C. johannae and C. reighardi ) are extinct. In addition, C. alpenae , described by Koelz but subsequently synonymized with C. zenithicus , although extinct, is recognized as valid making a total of eight major forms. Six of these forms, all but C. artedi and C. hoyi , have been lost from Lake Michigan, and seven have been lost from Lake Huron, leaving in Lake Huron only C. artedi and an introgressed deepwater form that we term a hybrid swarm. C. artedi appears, like its sister form C. alpenae , to have been lost from Lake Erie. Only C. artedi remains extant in Lake Ontario, its three sister forms ( C. hoyi , C. kiyi , and C. reighardi ) having disappeared long ago. Lakes Superior and Nipigon have retained their original species flocks consisting of four forms each: C. artedi , C. hoyi , and C. zenithicus in both lakes; C. kiyi in Lake Superior; and C. nigripinnis in Lake Nipigon. Morphological deviations from the morphotypes described by Koelz have been modest in contemporary samples. Overall, C. kiyi and C. artedi were the most morphologically stable forms while C. hoyi , C. nigripinnis , and C. zenithicus were the least stable. Although contemporary populations of C. artedi from Lakes Michigan and Huron are highly diverged from the morphotypes described by Koelz, the contemporary samples were of undescribed deep-bodied forms unlikely to have been sampled by Koelz because of their association with bays. Of the two intact species flocks, Lake Nipigon’s was much less stable morphologically than Lake Superior’s even though Lake Nipigon is far less disturbed. Two priorities for research are determining the role of developmental plasticity in morphological divergence, especially within C. zenithicus of Lake Superior, and the basis for morphological divergence in C. artedi .

Lake Nipigon, Laurentian Great Lakes↗

USGS2015

Spatial synchrony in cisco recruitment

We examined the spatial scale of recruitment variability for disparate cisco ( Coregonus artedi ) populations in the Great Lakes ( n = 8) and Minnesota inland lakes ( n = 4). We found that the scale of synchrony was approximately 400 km when all available data were utilized; much greater than the 50-km scale suggested for freshwater fish populations in an earlier global analysis. The presence of recruitment synchrony between Great Lakes and inland lake cisco populations supports the hypothesis that synchronicity is driven by climate and not dispersal. We also found synchrony in larval densities among three Lake Superior populations separated by 25–275 km, which further supports the hypothesis that broad-scale climatic factors are the cause of spatial synchrony. Among several candidate climate variables measured during the period of larval cisco emergence, maximum wind speeds exhibited the most similar spatial scale of synchrony to that observed for cisco. Other factors, such as average water temperatures, exhibited synchrony on broader spatial scales, which suggests they could also be contributing to recruitment synchrony. Our results provide evidence that abiotic factors can induce synchronous patterns of recruitment for populations of cisco inhabiting waters across a broad geographic range, and show that broad-scale synchrony of recruitment can occur in freshwater fish populations as well as those from marine systems.

Minnesota↗

USGS2015

Evaluating the importance of abiotic and biotic drivers on Bythotrephes biomass in Lakes Superior and Michigan

The ability of planktivorous fishes to exert top-down control on Bythotrephes potentially has far-reaching impacts on aquatic food-webs, given previously described effects of Bythotrephes on zooplankton communities. We estimated consumption of Bythotrephes by planktivorous and benthivorous fishes, using bioenergetics and daily ration models at nearshore (18 m), intermediate (46 m), and offshore (110 m) depths along one western Lake Superior transect (April, and September-November) and two northern Lake Michigan transects (April, July, September). In Lake Superior, consumption (primarily by cisco Coregonus artedi) exceeded Bythotrephes production at all offshore sites in September-November (up to 396% of production consumed) and at the intermediate site in November (842%) with no evidence of consumption nearshore. By comparing Bythotrephes biomass following months of excessive consumption, we conservatively concluded that top-down control was evident only at the offshore site during September-October. In Lake Michigan, consumption by fishes (primarily alewife Alosa pseudoharengus) exceeded production at nearshore sites (up to 178%), but not in deeper sites (< 15%). Evidence for top-down control in the nearshore was not supported, however, as Bythotrephes never subsequently declined. Using generalized additive models, temperature, and not fish consumption, not zooplankton prey density, best explained variability in Bythotrephes biomass. The non-linear pattern revealed Bythotrephes to increase with temperature up to 16 °C, and then decline between 16 and 23 °C. We discuss how temperature likely has direct negative impacts on Bythotrephes when temperatures near 23 °C, but speculate that predation also contributes to declining biomass when temperatures exceed 16 °C.

Wisconsin and Michigan↗

USGS2015

Impact of fishing and stocking practices on Coregonid diversity

Fish species diversity can be lost through interacting stressors including habitat loss, stocking and overfishing. Although a multitude of stressors have played a role in the global decline of coregonid (Coregonus spp.) diversity, a number of contemporary studies have identified habitat loss stemming from eutrophication as the primary cause. Unfortunately, reconstructing the role of fishing and stocking practices can be difficult, because these records are incomplete or appear only in hard-to-access historic grey literature. Based on an illustrative set of historic and contemporary studies, we describe how fisheries management practices may have contributed to coregonid diversity loss in European and North American lakes. We provide case studies examining how fishing and stocking may reduce coregonid diversity through demographic decline and introgressive hybridization. In some lakes, fisheries management practices may have led to a loss of coregonid diversity well before issues with habitat degradation manifested. Our review suggests that fish conservation policies could beneficially consider the relative importance of all stressors, including management practices, as potential drivers of diversity loss.

Great Lakes, Lake Constance, Lake Geneva, Lake Gre↗

USGS2015

Status and trends in the Lake Superior fish community, 2014

In 2014, the Lake Superior fish community was sampled with daytime bottom trawls at 73 nearshore and 30 offshore stations. Spring and summer water temperatures were the coldest measured for the period of records for the surveys. In the nearshore zone, a total of 15,372 individuals from 28 species or morphotypes were collected. Nearshore lakewide mean biomass was 6.9 kg/ha, which was higher than that observed in the past few years, but below the long-term average of 9.2 kg/ha. In the offshore zone, a total 12,462 individuals from 11 species were collected lakewide. Offshore lakewide mean biomass was 6.6 kg/ha. The mean of the three previous years was 8.6 kg/ha. We collected larval Coregonus in surface trawls at 94 locations and estimated a lakewide average density of 577 fish/ha with a total lakewide population estimate of 14.2 billion (standard error + 30 million).

Lake Superior↗

USGS2014

Depth gradients in food-web processes linking habitats in large lakes: Lake Superior as an exemplar ecosystem

In large lakes around the world, depth-based changes in the abundance and distribution of invertebrate and fish species suggest that there may be concomitant changes in patterns of resource allocation. Using Lake Superior of the Laurentian Great Lakes as an example, we explored this idea through stable isotope analyses of 13 major fish taxa. Patterns in carbon and nitrogen isotope ratios revealed use of both littoral and profundal benthos among populations of most taxa analysed regardless of the depth of their habitat, providing evidence of nearshore–offshore trophic linkages in the largest freshwater lake by area in the world. Isotope-mixing model results indicated that the overall importance of benthic food-web pathways to fish was highest in nearshore species, whereas the importance of planktonic pathways increased in offshore species. These characteristics, shared with the Great Lakes of Africa, Russia and Japan, appear to be governed by two key processes: high benthic production in nearshore waters and the prevalence of diel vertical migration (DVM) among offshore invertebrate and fish taxa. DVM facilitates use of pelagic food resources by deep-water biota and represents an important process of trophic linkage among habitats in large lakes. Support of whole-lake food webs through trophic linkages among pelagic, profundal and littoral habitats appears to be integral to the functioning of large lakes. These linkages can be disrupted though ecosystem disturbance such as eutrophication or the effects of invasive species and should be considered in native species restoration efforts.

Lake Superior↗

USGS2014

Habitat coupling in a large lake system: delivery of an energy subsidy by an offshore planktivore to the nearshore zone of Lake Superior

1. We hypothesised that the autumn spawning migration of Lake Superior cisco ( Coregonus artedi ) provides a resource subsidy, in the form of energy-rich cisco eggs, from the offshore pelagic to the nearshore benthic community over winter, when alternate prey production is likely to be low. 2. We tested this hypothesis using fish and macroinvertebrate surveys, fish population demographics, diet and stable isotope analyses, and bioenergetics modelling. 3. The benthic, congeneric lake whitefish ( C. clupeaformis ) was a clear beneficiary of cisco spawning. Cisco eggs represented 16% of lake whitefish annual consumption in terms of biomass, but 34% of energy (because of their high energy density: >10 kJ g wet mass −1 ). Stable isotope analyses were consistent with these results and suggest that other nearshore fish species may also rely on cisco eggs. 4. The lipid content of lake whitefish liver almost doubled from 26 to 49% between November and March, while that of muscle increased from 14 to 26% over the same period, suggesting lake whitefish were building, rather than depleting, lipid reserves during winter. 5. In the other Laurentian Great Lakes, where cisco populations remain very low and rehabilitation efforts are underway, the offshore-to-nearshore ecological link apparent in Lake Superior has been replaced by non-native planktivorous species. These non-native species spawn in spring have smaller eggs and shorter incubation periods. The rehabilitation of cisco in these systems should reinstate the onshore subsidy as it has in Lake Superior.

Wisconsin↗

USGS2014

Foraging and predation risk for larval cisco (Coregonus artedi) in Lake Superior: A modelling synthesis of empirical survey data

The relative importance of predation and food availability as contributors to larval cisco ( Coregonus artedi ) mortality in Lake Superior were investigated using a visual foraging model to evaluate potential predation pressure by rainbow smelt ( Osmerus mordax ) and a bioenergetic model to evaluate potential starvation risk. The models were informed by observations of rainbow smelt, larval cisco, and zooplankton abundance at three Lake Superior locations during the period of spring larval cisco emergence and surface-oriented foraging. Predation risk was highest at Black Bay, ON, where average rainbow smelt densities in the uppermost 10 m of the water column were >1000 ha −1 . Turbid conditions at the Twin Ports, WI-MN, affected larval cisco predation risk because rainbow smelt remained suspended in the upper water column during daylight, placing them alongside larval cisco during both day and night hours. Predation risk was low at Cornucopia, WI, owing to low smelt densities (<400 ha −1 ) and deep light penetration, which kept rainbow smelt near the lakebed and far from larvae during daylight. In situ zooplankton density estimates were low compared to the values used to develop the larval coregonid bioenergetics model, leading to predictions of negative growth rates for 10 mm larvae at all three locations. The model predicted that 15 mm larvae were capable of attaining positive growth at Cornucopia and the Twin Ports where low water temperatures (2–6 °C) decreased their metabolic costs. Larval prey resources were highest at Black Bay but warmer water temperatures there offset the benefit of increased prey availability. A sensitivity analysis performed on the rainbow smelt visual foraging model showed that it was relatively insensitive, while the coregonid bioenergetics model showed that the absolute growth rate predictions were highly sensitive to input parameters (i.e., 20% parameter perturbation led to order of magnitude differences in model estimates). Our modelling indicated that rainbow smelt predation may limit larval cisco survival at Black Bay and to a lesser extent at Twin Ports, and that starvation may be a major source of mortality at all three locations. The framework we describe has the potential to further our understanding of the relative importance of starvation and predation on larval fish survivorship, provided information on prey resources available to larvae are measured at sufficiently fine spatial scales and the models provide a realistic depiction of the dynamic processes that the larvae experience.

Lake Superior↗

USGS2014

Males exceed females in PCB concentrations of cisco ( Coregonus artedi ) from Lake Superior

We determined whole-fish polychlorinated biphenyl (PCB) concentrations of 25 male and 25 female age-7 ciscoes ( Coregonus artedi ) captured from a spawning aggregation in Thunder Bay, Lake Superior, during November 2010. We also determined PCB concentrations in the ovaries and somatic tissue of five additional female ciscoes (ages 5–22). All 55 of these ciscoes were in ripe or nearly ripe condition. Bioenergetics modeling was used to determine the contribution of the growth dilution effect toward a difference in PCB concentrations between the sexes, as females grew substantially faster than males. Results showed that the PCB concentration of males (mean = 141 ng/g) was 43% greater than that of females (mean = 98 ng/g), and this difference was highly significant (P < 0.0001). Mean PCB concentrations in the ovaries and the somatic tissue of the five females were 135 and 100 ng/g, respectively. Based on these PCB determinations for the ovaries and somatic tissue, we concluded that release of eggs by females at previous spawnings was not a contributing factor to the observed difference in PCB concentrations between the sexes. Bioenergetics modeling results indicated that the growth dilution effect could explain males being higher than females in PCB concentration by only 3–7%. We concluded that the higher PCB concentration in males was most likely due to higher rate of energy expenditure, originating from greater activity and a higher resting metabolic rate. Mean PCB concentration in the cisco eggs was well below the U. S. Food and Drug Administration and Ontario Ministry of Environment guidelines of 2000 and 844 ng/g, respectively, and this finding may have implications for the cisco roe fishery currently operating in Lake Superior.

Lake Superior;Thunder Bay↗

USGS2014

Status and trends in the Lake Superior fish community, 2013

In 2013, the Lake Superior fish community was sampled with daytime bottom trawls at 79 nearshore and 35 offshore locations. In the nearshore zone, a total of 23,432 individuals of 27 species or morphotypes were collected. Nearshore lakewide mean biomass was 5.5 kg ha-1, which was slightly higher than that observed in the past few years, but below the long-term average of 8.8 kg ha-1. In the offshore zone, a total 20,371 individuals of 13 species were collected lakewide. Offshore lakewide mean biomass was 8.9 kg ha-1, which was similar to that observed in previous years.

Lake Superior↗

USGS2014

A new look at the Lake Superior biomass size spectrum

We synthesized data from multiple sampling programs and years to describe the Lake Superior pelagic biomass size structure. Data consisted of Coulter counts for phytoplankton, optical plankton counts for zooplankton, and acoustic surveys for pelagic prey fish. The size spectrum was stable across two time periods separated by 5 years. The primary scaling or overall slope of the normalized biomass size spectra for the combined years was −1.113, consistent with a previous estimate for Lake Superior (−1.10). Periodic dome structures within the overall biomass size structure were fit to polynomial regressions based on the observed sub-domes within the classical taxonomic positions (algae, zooplankton, and fish). This interpretation of periodic dome delineation was aligned more closely with predator–prey size relationships that exist within the zooplankton (herbivorous, predacious) and fish (planktivorous, piscivorous) taxonomic positions. Domes were spaced approximately every 3.78 log10 units along the axis and with a decreasing peak magnitude of −4.1 log 10 units. The relative position of the algal and herbivorous zooplankton domes predicted well the subsequent biomass domes for larger predatory zooplankton and planktivorous prey fish.

Lake Superior↗

USGS2013

Comparing two fish sampling standards over time: largely congruent results but with caveats

1. We sampled Lake Bourget (surface area = 44 km 2 ) using CEN standard gillnet and provisional standard acoustic survey methods over 3 years (2005, 2010 and 2011) as the fish community responded to re-oligotrophication. A total of 16 species were caught in benthic gillnets and three species in pelagic gillnets. 2. Lake Bourget results were consistent with a recent study (Emmrich et al., Freshwater Biology , 57, 2012, 2436) showing strong correspondence between average biomass-per-unit-effort (BPUE) in standard benthic gillnets and average acoustic volume backscattering when smaller lakes (0.25–5.45 km 2 ) were treated as sample units. 3. The BPUE of whitefish ( Coregonus lavaretus ), perch ( Perca fluviatilis ) and roach ( Rutilus rutilus ) measured by benthic gillnets all declined significantly with increasing bathymetric depth; 93% of nets set at depths >50 m caught zero fish. 4. Pelagic gillnetting indicated that small (<10 cm) perch and small (<12.5 cm) roach occupied the upper pelagic habitat (0–20 m depths) and that whitefish were predominant in deeper pelagic habitat. The acoustic sampling showed fish biomass in the upper pelagic habitat varied significantly by year. Biomass there was highest in 2010 when a strong perch year-class recruited and lowest in 2011 when recruitment levels of perch and roach were both weak. Whitefish biomass in deep pelagic habitat (>20 m) increased significantly after 2005. 5. Both surveys showed whitefish biomass increased significantly during the study, but whitefish ≥25 cm were poorly represented in benthic gillnet catches. Contrary to the acoustic findings, the BPUE of perch and roach in benthic gillnets did not vary significantly over time. This metric is insensitive to changes in size structure in that a high catch of small fish and a low catch of large fish in different years can provide similar average BPUE estimates. 6. We examined correlations between BPUE in benthic gillnets and acoustic methods at fine spatial scales by averaging acoustic backscattering measurements encompassed by buffers of varying size (250–2000 m) around individual gillnets and by averaging samples collected from lake quadrants. Correlations at fines scales were generally poor, and only in 1 year was the quadrant correlation significant. The lack of correlation can be explained, in part, by the two gears sampling different components of the fish community. Conversely, in pelagic habitat, where the fish community was simpler, we found BPUE in pelagic nets to be strongly correlated with acoustic backscattering. 7. With respect to large lakes like Lake Bourget, we hypothesise that the congruence in average biomass measurements provided by these two survey methods occurs because these different community components are responding similarly to a common driver like lake trophic status (or possibly multiple drivers operating in synergy).

Lake Bourget↗

USGS2013

Use of classification trees to apportion single echo detections to species: Application to the pelagic fish community of Lake Superior

Acoustic methods are used to estimate the density of pelagic fish in large lakes with results of midwater trawling used to assign species composition. Apportionment in lakes having mixed species can be challenging because only a small fraction of the water sampled acoustically is sampled with trawl gear. Here we describe a new method where single echo detections (SEDs) are assigned to species based on classification tree models developed from catch data that separate species based on fish size and the spatial habitats they occupy. During the summer of 2011, we conducted a spatially-balanced lake-wide acoustic and midwater trawl survey of Lake Superior. A total of 51 sites in four bathymetric depth strata (0–30 m, 30–100 m, 100–200 m, and >200 m) were sampled. We developed classification tree models for each stratum and found fish length was the most important variable for separating species. To apply these trees to the acoustic data, we needed to identify a target strength to length (TS-to-L) relationship appropriate for all abundant Lake Superior pelagic species. We tested performance of 7 general (i.e., multi-species) relationships derived from three published studies. The best-performing relationship was identified by comparing predicted and observed catch compositions using a second independent Lake Superior data set. Once identified, the relationship was used to predict lengths of SEDs from the lake-wide survey, and the classification tree models were used to assign each SED to a species. Exotic rainbow smelt (Osmerus mordax) were the most common species at bathymetric depths <100 m with their population estimated at 755 million (3.4 kt). Kiyi (Coregonus kiyi) were the most abundant species at depths >100 m (384 million; 6.0 kt). Cisco (Coregonus artedi) were widely distributed over all strata with their population estimated at 182 million (44 kt). The apportionment method we describe should be transferable to other large lakes provided fish are not tightly aggregated, and an appropriate TS-to-L relationship for abundant pelagic fish species can be determined.

Lake Superior↗

USGS2013

Sensitivity of fish density estimates to standard analytical procedures applied to Great Lakes hydroacoustic data

Standardized methods of data collection and analysis ensure quality and facilitate comparisons among systems. We evaluated the importance of three recommendations from the Standard Operating Procedure for hydroacoustics in the Laurentian Great Lakes (GLSOP) on density estimates of target species: noise subtraction; setting volume backscattering strength (S v ) thresholds from user-defined minimum target strength (TS) of interest (TS-based S v threshold); and calculations of an index for multiple targets (N v index) to identify and remove biased TS values. Eliminating noise had the predictable effect of decreasing density estimates in most lakes. Using the TS-based Sv threshold decreased fish densities in the middle and lower layers in the deepest lakes with abundant invertebrates (e.g., Mysis diluviana). Correcting for biased in situ TS increased measured density up to 86% in the shallower lakes, which had the highest fish densities. The current recommendations by the GLSOP significantly influence acoustic density estimates, but the degree of importance is lake dependent. Applying GLSOP recommendations, whether in the Laurentian Great Lakes or elsewhere, will improve our ability to compare results among lakes. We recommend further development of standards, including minimum TS and analytical cell size, for reducing the effect of biased in situ TS on density estimates.

Great Lakes↗

USGS2013

Morphometric variation among spawning cisco aggregations in the Laurentian Great Lakes: are historic forms still present?

Cisco (Coregonus artedi Leseur, formerly lake herring Leucichthys artedi Leseur) populations in each of the Laurentian Great Lakes collapsed between the late 1920s and early 1960s following a multitude of stressors, and never recovered in Lakes Michigan, Erie and Ontario. Prior to their collapse, Koelz (1929) studied Leucichthys spp. in the Great Lakes basin and provided a description of their diversity. Three cisco morphotypes were described; a ‘slim terete’morphotype (L. artedi artedi), a ‘deep compressed’ morphotype (L. artedi albus), and a deep-bodied form resembling tullibee in western Canadian lakes (L. artedi manitoulinus). Based on body measurements of 159 individuals (Koelz 1929), we used discriminant function analysis (DFA) to discriminate historic morphotypes. Shapes of historic morphotypes were found to vary significantly (Pillai’s trace = 1.16, P < 0.0001). The final DFA model used nine body measurements and correctly classified 90% of the historic cisco. Important discriminating measurements included body depth, eye diameter, and dorsal fin base and height. Between October-November of 2007-2011, we sampled cisco from 16 Great Lakes sites collecting digital photographs of over 1, 700 individuals. We applied the DFA model to their body measurements and classified each individual to a morphotype. Contemporary cisco from Lakes Superior, Ontario and Michigan were predominantly classified as artedi, while the most common classifications from northern Lake Huron were albus and manitoulinus. Finding historic morphotypes is encouraging because it suggests that the morphological variation present prior to their collapse still exists. We conclude that contemporary cisco having shapes matching the missing historic morphotypes in the lower lakes warrant special consideration as potential donor populations in reestablishment efforts.

Lake Michigan;Lake Erie;Lake Ontario;Lake Huron;La↗

USGS2013

Evaluating analytical approaches for estimating pelagic fish biomass using simulated fish communities

Pelagic fish assessments often combine large amounts of acoustic-based fish density data and limited midwater trawl information to estimate species-specific biomass density. We compared the accuracy of five apportionment methods for estimating pelagic fish biomass density using simulated communities with known fish numbers that mimic Lakes Superior, Michigan, and Ontario, representing a range of fish community complexities. Across all apportionment methods, the error in the estimated biomass generally declined with increasing effort, but methods that accounted for community composition changes with water column depth performed best. Correlations between trawl catch and the true species composition were highest when more fish were caught, highlighting the benefits of targeted trawling in locations of high fish density. Pelagic fish surveys should incorporate geographic and water column depth stratification in the survey design, use apportionment methods that account for species-specific depth differences, target midwater trawling effort in areas of high fish density, and include at least 15 midwater trawls. With relatively basic biological information, simulations of fish communities and sampling programs can optimize effort allocation and reduce error in biomass estimates.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2012

Relationship between mid-water trawling effort and catch composition uncertainty in two large lakes (Huron and Michigan) dominated by alosines, osmerids, and coregonines

Because it is not possible to identify species with echosounders alone, trawling is widely used as a method for collecting species and size composition data for allocating acoustic fish density estimates to species or size groups. In the Laurentian Great Lakes, data from midwater trawls are commonly used for such allocations. However, there are no rules for how much midwater trawling effort is required to adequately describe species and size composition of the pelagic fish communities in these lakes, so the balance between acoustic sampling effort and trawling effort has been unguided. We used midwater trawl data collected between 1986 and 2008 in lakes Michigan and Huron and a variety of analytical techniques to develop guidance for appropriate levels of trawl effort. We used multivariate regression trees and re-sampling techniques to i. identify factors that influence species and size composition of the pelagic fish communities in these lakes, ii. identify stratification schemes for the two lakes, iii. determine if there was a relationship between uncertainty in catch composition and the number of tows made, and iv. predict the number of tows required to reach desired uncertainty targets. We found that depth occupied by fish below the surface was the most influential explanatory variable. Catch composition varied between lakes at depths <38.5 m below the surface, but not at depths ≥38.5 m below the surface. Year, latitude, and bottom depth influenced catch composition in the near-surface waters of Lake Michigan, while only year was important for Lake Huron surface waters. There was an inverse relationship between RSE [relative standard error = 100 × (SE/mean)] and the number of tows made for the proportions of the different size and species groups. We found for the fifth (Lake Huron) and sixth (Lake Michigan) largest lakes in the world, 15–35 tows were adequate to achieve target RSEs (15% and 30%) for ubiquitous species, but rarer species required much higher, and at times, impractical effort levels to reach these targets.

Fisheries Research↗

USGS2012

Habitat use by fishes of Lake Superior. II. Consequences of diel habitat use for habitat linkages and habitat coupling in nearshore and offshore waters

Diel migration patterns of fishes in nearshore (15–80 m depth) and offshore (>80 m) waters of Lake Superior were examined to assess the potential for diel migration to link benthic and pelagic, and nearshore and offshore habitats. In our companion article, we described three types of diel migration: diel vertical migration (DVM), diel bank migration (DBM), and no diel migration. DVM was expressed by fishes migrating from benthopelagic to pelagic positions and DBM was expressed by fishes migrating horizontally from deep to shallow waters at night. Fishes not exhibiting diel migration typically showed increased activity by moving from benthic to benthopelagic positions within demersal habitat. The distribution and biomass of fishes in Lake Superior was characterized by examining 704 bottom trawl samples collected between 2001 and 2008 from four depth zones: ≤40, 41–80, 81–160, and >160 m. Diel migration behaviors of fishes described in our companion article were applied to estimates of areal biomass (kg ha −1 ) for each species by depth zone. The relative strength of diel migrations were assessed by applying lake area to areal biomass estimates for each species by depth zone to yield estimates of lake-wide biomass (metric tonnes). Overall, species expressing DVM accounted for 83%, DBM 6%, and non-migration 11% of the total lake-wide community biomass. In nearshore waters, species expressing DVM represented 74% of the biomass, DBM 25%, and non-migration 1%. In offshore waters, species expressing DVM represented 85%, DBM 1%, and non-migration 14% of the biomass. Of species expressing DVM, 83% of total biomass occurred in offshore waters. Similarly, 97% of biomass of non-migrators occurred in offshore waters while 83% of biomass of species expressing DBM occurred in nearshore waters. A high correlation (R 2 = 0.996) between lake area and community biomass by depth zone resulted in 81% of the lake-wide biomass occurring in offshore waters. Accentuating this nearshore-offshore trend was one of increasing estimated total areal biomass of the fish community with depth zone, which ranged from 13.71 kg ha −1 at depths ≤40 m to 18.81 kg ha −1 at depths >160 m, emphasizing the importance of the offshore fish community to the lake ecosystem. The prevalence of diel migration expressed by Lake Superior fishes increases the potential of fish to link benthic and pelagic and shallow and deepwater habitats. These linkages enhance the potential for habitat coupling, a condition where habitats become interconnected and interdependent through transfers of energy and nutrients. Habitat coupling facilitates energy and nutrient flow through a lake ecosystem, thereby increasing productivity, especially in large lakes where benthic and pelagic, and nearshore and offshore habitats are often well separated. We propose that the application of biomass estimates to patterns of diel migration in fishes can serve as a useful metric for assessing the potential for habitat linkages and habitat coupling in lake ecosystems, and provide an important indicator of ecosystem health and function. The decline of native Lake Trout and ciscoes and recent declines in exotic Alewife and Rainbow Smelt populations in other Great Lakes have likely reduced the capacity for benthic-pelagic coupling in these systems compared to Lake Superior. We recommend comparing the levels and temporal changes in diel migration in other Great Lakes as a means to assess changes in the relative health and function of these ecosystems.

Lake Superior↗