Diet and Prey Selection of Alewives in Lake Michigan: Seasonal, Depth, and Interannual Patterns

To evaluate the current diet of alewives Alosa pseudoharengus and interactions with their prey in light of recent changes in Lake Michigan, we determined the seasonal diet and prey selectivity of large (>100 mm total length) and small (<100 mm) alewives in southeastern Lake Michigan. Selectivity and diet were evaluated on a biomass basis for alewives collected near Muskegon, Michigan, during June, July−August, and October 1999–2001. Fish were sampled from three depth zones: shallow (15–25 m), transitional (35–55 m), and deep (65–90 m). Prey selectivity and diet patterns indicated that alewives had considerable flexibility in adjusting to prey availability, which varied by season, depth zone, and year. Although small copepods were an abundant prey item throughout the year and in all depth zones, they were mainly important in the diet (large and small alewives) in June and at the shallow stations, where many of the other prey types were not available. Despite declining numbers, Diporeia continued to be important for large alewives in spring, particularly at the transitional and deep stations, where their biomass was many times higher than that of other prey. During summer, large alewives selected either Bythotrephes longimanus or Mysis relicta in all depth zones and years. The diet of large alewives consisted mainly of Mysis in July 1999 and August 2001, whereas in August 2000 mainly Bosmina were eaten. During October, Mysis and Bythotrephes, along with large zooplankters (Daphnia spp. and large calanoid copepods), were selected and were most important in the diet of large alewives. In contrast, only the large zooplankton were selected and were important prey for the small alewives in fall. Annual, seasonal, and depth differences in prey biomass as well as differences in alewife size all influenced diet and selectivity patterns.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141716/1/tafs1068.pd

Effects of Activity and Energy Budget Balancing Algorithm on Laboratory Performance of a Fish Bioenergetics Model

We evaluated the performance of the Wisconsin bioenergetics model for lake trout Salvelinus namaycush that were fed ad libitum in laboratory tanks under regimes of low activity and high activity. In addition, we compared model performance under two different model algorithms: (1) balancing the lake trout energy budget on day t based on lake trout energy density on day t and (2) balancing the lake trout energy budget on day t based on lake trout energy density on day t + 1. Results indicated that the model significantly underestimated consumption for both inactive and active lake trout when algorithm 1 was used and that the degree of underestimation was similar for the two activity levels. In contrast, model performance substantially improved when using algorithm 2, as no detectable bias was found in model predictions of consumption for inactive fish and only a slight degree of overestimation was detected for active fish. The energy budget was accurately balanced by using algorithm 2 but not by using algorithm 1. Based on the results of this study, we recommend the use of algorithm 2 to estimate food consumption by fish in the field. Our study results highlight the importance of accurately accounting for changes in fish energy density when balancing the energy budget; furthermore, these results have implications for the science of evaluating fish bioenergetics model performance and for more accurate estimation of food consumption by fish in the field when fish energy density undergoes relatively rapid changes.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141002/1/tafs1328.pd

Changes in Diet and Body Condition of Lake Whitefish in Southern Lake Michigan Associated with Changes in Benthos

We evaluated the long‐term trends of the benthic macroinvertebrate community (1980–1999) and biological attributes of lake whitefish Coregonus clupeaformis (1985–1999) in southeastern Lake Michigan. We also determined what food types were important to lake whitefish in an area where the amphipod Diporeia had not yet declined in 1998 and how the diet of lake whitefish changed as Diporeia declined during 1999–2000. Zebra mussels Dreissena polymorpha invaded the study area in 1992; Diporeia began to decline in 1993 and was nearly absent by 1999. The body condition of lake whitefish decreased after 1993 and remained low thereafter. The length at age and weight at age of lake whitefish was lower in 1992–1999 than in 1985–1991. After declines of Diporeia off the city of Muskegon, Michigan, between 1998 and 1999–2000, the proportion of Diporeia in the diet by weight fell from 70% to 25% and the percent occurrence decreased from 81% to 45%. In contrast, the proportion of lake whitefish that ate other prey, such as Mysis relicta (an opossum shrimp), ostracods, oligochaetes, and zooplankton, increased in the same period. At sites south of Muskegon, where the density of Diporeia has been low since 1998, chironomids, zebra mussels, and fingernail clams (Shaeriidae family) were the most important diet items of lake whitefish. Decreases in body condition and growth are associated with the loss of the high‐energy prey resource Diporeia, the consumption of prey with lower energy content, such as zebra mussels, and possible density‐dependence. Commercial harvests of lake whitefish will probably decrease because of low body condition and growth. Future management may require changes in harvest quotas, size restrictions, and depth restrictions as zebra mussel‐related impacts spread northward in Lake Michigan.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142050/1/nafm0876.pd

Spatial distribution, biomass and population dynamics of Mysis relicta in Lake Michigan

The abundance, biomass, and life history traits of Mysis relicta were evaluated in the spring, summer, and autumn of 2000 at 8 nearshore (45 m) and 8 offshore (75–110 m) stations throughout central and southern Lake Michigan. Abundance was also evaluated on a smaller scale during June 2000 at 4 nearshore and 4 offshore stations in southeastern Lake Michigan. For large-scale sampling, the abundance of M. relicta did not differ among locations in the spring. In the summer and autumn the abundance of M. relicta was similar among offshore stations with the exception of one station each season; for nearshore stations, abundance was generally highest off Pentwater, Michigan. The abundance of mysids was not consistently high for central or southern basin sites, although overall biomass was higher in the southern basin each season. Abundance of Mysis was positively correlated with bottom depth, but not with bottom water temperature, surface water temperature, or mean chlorophyll concentration. Within the smaller region in southeast Lake Michigan, the abundance of M. relicta differed among locations for both nearshore and offshore stations. Brood size and size of reproductive females did not differ among lake wide locations, but the proportion of females with broods and the size distribution of M. relicta did.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42900/1/10750_2004_Article_5266883.pd

Corrigendum to “Recent changes in primary production and phytoplankton in the offshore region of southeastern Lake Michigan” [J. Great Lakes Res. 36 (Supplement 3) (2010) 20–29]

The authors regret that there is an error on the labels of two figures that were published in the paper referenced above. For Figs. 5b, c, and d and 7b and c the y-axes have the wrong labels. The following are the correct y-axis labels: Fig. 5b — the y-axis should range from 0 to 5, Fig. 5c — the y-axis should range from 0 to 2, Fig. 5d — the y-axis label should range from 0 to 3, Fig. 7b — the y-axis should range from 0 to 40, and for Fig. 7c — the y-axis should range from 0 to 50

Corrigendum to “Recent changes in primary production and phytoplankton in the offshore region of southeastern Lake Michigan” [J. Great Lakes Res. 36 (Supplement 3) (2010) 20–29]

The authors regret that there is an error on the labels of two figures that were published in the paper referenced above. For Figs. 5b, c, and d and 7b and c the y-axes have the wrong labels. The following are the correct y-axis labels: Fig. 5b — the y-axis should range from 0 to 5, Fig. 5c — the y-axis should range from 0 to 2, Fig. 5d — the y-axis label should range from 0 to 3, Fig. 7b — the y-axis should range from 0 to 40, and for Fig. 7c — the y-axis should range from 0 to 50

Alewife planktivory controls the abundance of two invasive predatory cladocerans in Lake Michigan

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74873/1/j.1365-2427.2007.01728.x.pd

Effects of Hypoxia on Consumption, Growth, and RNA:DNA Ratios of Young Yellow Perch

As in various freshwater and coastal marine ecosystems worldwide, seasonal bottom water hypoxia is a recurring phenomenon in Lake Erie’s central basin. While bottom hypoxia can strongly affect sessile benthic animals, its effects on mobile organisms such as fish are less understood. We evaluated the potential for bottom hypoxia to affect the growth rates of yellow perch Perca flavescens, a species of ecological and economic importance in the lake. To this end, we (1) conducted laboratory experiments to quantify the effects of reduced dissolved oxygen on consumption, somatic growth, and RNA : DNA ratios (an index of short‐term growth) of young yellow perch and (2) explored the effects of bottom hypoxia on young yellow perch growth in Lake Erie’s central basin by collecting individuals in hypoxicand normoxic regions of the lake and quantifying their RNA : DNA ratios. Yellow perch consumption and growth in our experiments declined under hypoxic conditions (≤2 mg O2/L). While yellow perch RNA : DNA ratios responded strongly to experimental temperature, nucleic acid ratios were not significantly affected by dissolved oxygen or feeding ration. We did, however, observe a positive correlation between yellow perch growth and RNA : DNA ratios at low temperatures (11°C). The nucleic acid ratios of yellow perch collected in Lake Erie varied spatiotemporally, but their patterns were not consistent with hypoxia. In short, while yellow perch consumption and growth rates respond directly and negatively to low oxygen conditions, these responses are not necessarily reflected in RNA : DNA ratios. Moreover, in central Lake Erie, where yellow perch can behaviorally avoid hypoxic areas, the RNA : DNA ratios of yellow perch do not respond strongly to bottom hypoxia. Thus, this study suggests that there is no strong negative effect of bottom hypoxia on the growth of young yellow perch in Lake Erie.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141858/1/tafs1574.pd

Influence of invasive quagga mussels, phosphorus loads, and climate on spatial and temporal patterns of productivity in Lake Michigan: A biophysical modeling study

We applied a three‐dimensional biophysical model to Lake Michigan for the years 2000, 2005, and 2010 to consider the mechanisms controlling spatial and temporal patterns of phytoplankton abundance (chlorophyll a) and lake‐wide productivity. Model skill was assessed by comparison to satellite‐derived Chl a and field‐measured water quality variables. We evaluated model sensitivity to scenarios of varying mussel filter feeding intensity, tributary phosphorus loads, and warm vs. cool winter‐spring climate scenarios. During the winter‐spring phytoplankton bloom, spatial patterns of Chl a were controlled by variables that influenced surface mixed layer depth: deep mixing reduced net phytoplankton growth through light limitation and by exposing the full water column to mussel filter feeding. Onset of summer and winter stratification promoted higher surface Chl a initially by increasing mean light exposure and by separating the euphotic zone from mussels. During the summer stratified period, areas of relatively high Chl a were associated with coastal plumes influenced by tributary‐derived nutrients and coastal upwelling‐downwelling. While mussels influenced spatial and temporal distribution of Chl a, lake‐wide, annual mean primary production was more sensitive to phosphorus and warm/cool meteorology scenarios than to mussel filter feeding scenarios. Although Chl a and primary production declined over the quagga mussel invasion, our results suggest that increased nutrient loads would increase lake‐wide productivity even in the presence of mussels; however, altered spatial and temporal patterns of productivity caused by mussel filter feeding would likely persist.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/139984/1/lno10595-sup-0001-suppinfo.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139984/2/lno10595.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139984/3/lno10595_am.pd