John M. Dettmers

Food Consumption by Larval Gizzard Shad: Zooplankton Effects and Implications for Reservoir Communities

Abstract Because peak abundance of larval gizzard shad Dorosoma cepedianum occurs simultaneously with the midsummer decline of macrozooplankton in Ohio reservoirs, we hypothesized that zooplanktivory by larval gizzard shad caused this decline. To test this hypothesis, we compared larval food consumption with zooplankton productivity in two reservoirs. Larval gizzard shad began to influence zooplankton production in a reservoir with high zooplankton productivity (exceeding 125 mg·m−3·d−1) only after peak zooplankton biomass occurred, even at high larval densities (38 shad·m−3). However, consumption by early juvenile (25−30-mm) gizzard shad severely reduced zooplankton in this reservoir. Conversely, relatively low densities of larval gizzard shad (3–7 shad·m−3) had variable effects on zooplankton in a reservoir with low zooplankton productivity (at most 4 mg·m−3·d−1). Depending on larval gizzard shad density and zooplankton production, larval gizzard shad alone or in conjunction with early juveniles may con...

Fish Size and Prey Availability Affect Growth, Survival, Prey Selection, and Foraging Behavior of Larval Yellow Perch

Abstract Zooplankton availability is strongly linked with the growth, survival, and ultimately recruitment of fish during their early life history. We examined how different types of zooplankton affected the growth, survival, and prey selection of larval yellow perch Perca flavescens in a series of laboratory experiments. The growth and survival of newly hatched (5–7-mm) to 12-mm yellow perch larvae was greatest when feeding on adult copepods and copepod nauplii. The growth and survival of yellow perch larvae longer than 12 mm was greatest when feeding on adult copepods and small cladocerans. Prey selection patterns closely followed trends in growth and survival; smaller larvae positively selected adult and naupliar copepods, whereas larger larvae selected adult copepods and small cladocerans. Foraging behavior experiments conducted with larvae longer than 12 mm revealed that these fish derived similar energetic gains when feeding solely on adult copepods and small cladocerans. The pathway to this energet...

Life in the fast lane: fish and foodweb structure in the main channel of large rivers

We studied the main channel of the lower Illinois River and of the Mississippi River just upstream and downstream of its confluence with the Illinois River to describe the abundance, composition, and/or seasonal appearance of components of the main-channel community. Abundance of fishes in the main channel was high, especially adults. Most adult fishes were present in the main channel for either 3 or 4 seasons/y, indicating that fishes regularly reside in the main channel. We documented abundant zooplankton and benthic invertebrates in the main channel, and the presence of these food types in the diets of channel catfish and freshwater drum. All trophic levels were well represented in the main channel, indicating that the main channel supports a unique food web. The main channel also serves as an important energetic link with other riverine habitats (e.g., floodplains, secondary channels, backwater lakes) because of the mobility of resident fishes and because of the varied energy sources supplying this food web. It may be more realistic to view energy flow in large-river systems as a combination of 3 existing concepts, the river continuum concept (downstream transport), the flood pulse concept (lateral transport to the floodplain), and the riverine productivity model (autochthonous production). We urge additional research to quantify the links between the main channel and other habitat types in large rivers because of the apparent importance of main-channel processes in the overall structure and function of large-river ecosystems.

Exploring Zooplankton Changes in Southern Lake Michigan: Implications for Yellow Perch Recruitment

Abstract Recruitment of fishes frequently depends in part on availability of appropriate densities and sizes of zooplankton prey. In Lake Michigan, yellow perch ( Perca flavescens ) have experienced poor recruitment since 1989, although the mechanisms driving this poor recruitment have not been identified. To explore the possible influence of zooplankton density available for yellow perch larvae shortly after hatching on eventual recruitment success of age-0 yellow perch, we examined patterns of nearshore zooplankton and age-0 yellow perch relative abundance in southwestern Lake Michigan during June 1988-1990 and 1996-1998. Zooplankton density, mean size, and biomass that were available to newly hatched yellow perch larvae in June declined from the late 1980s to the late 1990s, suggesting that one or more of these declines may contribute to the current reduced rate of yellow perch recruitment seen in southwestern Lake Michigan. A strong positive linear relationship existed between the density of zooplankton present during June, the time when first-feeding larvae appear, and CPUE of age-0 yellow perch in a given year. A laboratory experiment revealed that more zooplankton does increase larval yellow perch survival, supporting the field pattern. Therefore, zooplankton availability for larvae can be an important determinant of yellow perch recruitment success in Lake Michigan and should be considered in addition to other mechanisms when evaluating the factors regulating recruitment of this species.

Biophysical Model of Larval Yellow Perch Advection and Settlement in Lake Michigan

ABSTRACT Potential for large-scale physical transport processes to affect recruitment of Lake Michigan yellow perch (Perca flavescens) was studied by examining the variation in larval distribution, growth rate, and settlement during June–August 1998–2003 using a 3D particle transport model linked with an individual-based bioenergetics growth model. In all years, virtual larvae were released nearshore in southwestern Lake Michigan, a known and important spawning region for yellow perch. For any given year, the same circulation pattern and water temperature either promoted or reduced yellow perch settlement depending on the consumption rates and settlement size chosen in the growth model. Increased consumption increased the number of settled larvae and expanded the total area where larvae settled, whereas increased settlement size reduced the number of settled larvae and reduced the overall settlement area. Interannual variability in circulation patterns and water temperature also resulted in contrasting larval settlement rates, settlement locations, and size of settlement areas between years. Model predictions were most consistent with field observations of age-0 yellow perch from Illinois and Michigan waters when settlement was assumed to occur at 50 mm. Moreover, our model suggests that larvae originating from southwestern Lake Michigan can recruit anywhere within the southern basin and even in the northern basin. Future model improvement will require information on the relative contribution of various sectors to the larval pool, their distribution with reference to the hydrodynamic landscape, the feeding and growth of yellow perch during their pelagic phase, and the size at transition to demersal stage.

Feeding Preferences of Omnivorous Gizzard Shad as Influenced by Fish Size and Zooplankton Density

Abstract In Ohio reservoirs, larval gizzard shad Dorosoma cepedianum less than 30 mm total length consume only zooplankton but frequently switch to detritus as they grow longer than 30 mm. However, in laboratory studies without detritus, gizzard shad longer than 30 mm consume crustacean zooplankton. To explore the composition of diets of omnivorous 30–100-mm gizzard shad, we completed 1-h laboratory feeding trials with different amounts of zooplankton and detritus and quantified the diets of gizzard shad in reservoirs. In both laboratory and field, gizzard shad ate primarily detritus but also ate zooplankton, consuming more as more became available, which demonstrates that this species is a facultative detritivore. In the field, zooplankton consumption declined as gizzard shad body size increased. We believe gizzard shad maximize growth by supplementing their low-protein detritus diet with more zooplankton as more becomes available. With this strategy, omnivorous gizzard shad may compromise the potential ...

Quantifying Linkages among Gizzard Shad, Zooplankton, and Phytoplankton in Reservoirs

Abstract Food webs in northern temperate lakes frequently exhibit tightly linked interactions between adjacent trophic levels that lead to top-down effects from piscivores to phytoplankton. To determine if these interactions occur in reservoirs dominated by an omnivorous planktivore, gizzard shad Dorosoma cepedianum, we experimentally quantified crustacean zooplankton and phytoplankton responses to age-0 gizzard shad (23–90 mm total length) at four gizzard shad densities across three reservoirs, each with a different level of crustacean zooplankton productivity. Age-0 gizzard shad exerted strong top-down effects on crustacean zooplankton, eliminating it from most enclosures within 2 weeks. This decline in crustacean zooplankton did not lead to increases in phytoplankton unless Daphnia spp. were initially abundant. As detritivores, gizzard shad can remain abundant when planktonic food resources are depleted. This trophic decoupling probably allows gizzard shad to structure reservoir food webs by overconsum...

Ontogenetic Changes in Prey Preference and Foraging Ability of Yellow Perch: Insights Based on Relative Energetic Return of Prey

Abstract Ontogenetic diet shifts are an important component of the early life history of many fishes. Successfully shifting diets affects not only individuals but also populations and communities. We experimentally quantified prey selection and feeding behavior of age-0 yellow perch Perca flavescens to determine the sizes at which diet shifts occur and identify potential mechanisms driving these shifts. Yellow perch were provided three prey types (zooplankton, benthic invertebrates, and fish) at high- and low-density combinations. Small yellow perch (20 mm total length [TL]) positively selected zooplankton, but intermediate-sized fish (40 and 60 mm TL) shifted to benthic invertebrates. At 80 mm TL, yellow perch positively selected benthic invertebrate and fish prey, indicating the onset of piscivory. Relative densities of prey items did not influence prey selection patterns. Diet shifts from zooplankton to benthic invertebrates to fish prey were supported by an increased energetic gain and decreased forag...

Effects of Turbidity and Cover on Prey Selectivity of Adult Smallmouth Bass

Abstract Environmental factors such as turbidity and habitat complexity affect many aspects of aquatic food webs, including predator–prey interactions. We examined the effects of turbidity (0, 5, 10, 20, 40 nephelometric turbidity units [NTU]) and cover (presence or absence) on prey selection by adult smallmouth bass Micropterus dolomieu (mean ± SD = 290 ± 41 mm total length) in laboratory pools. Individual predators were given a choice of five northern crayfish Orconectes virilis, five golden shiners Notemigonus crysoleucas (a pelagic fish), or five round goby Neogobius melanostomus (an invasive benthic fish). Smallmouth bass selected round goby at low turbidities (0 and 5 NTU) and golden shiners at the highest turbidity (40 NTU) in trials without cover. With cover, smallmouth bass increased selectivity for golden shiners, particularly at the turbidity extremes (0, 20, and 40 NTU). Northern crayfish were negatively or neutrally selected in all trials across both turbidity and cover treatments. Turbidity ...

Acoustic telemetry reveals large-scale migration patterns of walleye in Lake Huron

Fish migration in large freshwater lacustrine systems such as the Laurentian Great Lakes is not well understood. The walleye (Sander vitreus) is an economically and ecologically important native fish species throughout the Great Lakes. In Lake Huron walleye has recently undergone a population expansion as a result of recovery of the primary stock, stemming from changing food web dynamics. During 2011 and 2012, we used acoustic telemetry to document the timing and spatial scale of walleye migration in Lake Huron and Saginaw Bay. Spawning walleye (n = 199) collected from a tributary of Saginaw Bay were implanted with acoustic tags and their migrations were documented using acoustic receivers (n = 140) deployed throughout U.S. nearshore waters of Lake Huron. Three migration pathways were described using multistate mark-recapture models. Models were evaluated using the Akaike Information Criterion. Fish sex did not influence migratory behavior but did affect migration rate and walleye were detected on all acoustic receiver lines. Most (95%) tagged fish migrated downstream from the riverine tagging and release location to Saginaw Bay, and 37% of these fish emigrated from Saginaw Bay into Lake Huron. Remarkably, 8% of walleye that emigrated from Saginaw Bay were detected at the acoustic receiver line located farthest from the release location more than 350 km away. Most (64%) walleye returned to the Saginaw River in 2012, presumably for spawning. Our findings reveal that fish from this stock use virtually the entirety of U.S. nearshore waters of Lake Huron.