Jason Link

The effect of light on Lake Herring (coregonus artedi) reactive volume

The lake herring (Coregonus artedi) is an important coldwater planktivore in the Laurentian Great Lakes and in smaller inland lakes in portions of Canada and the northern United States. Lake herring cruise the pelagia and feed selectively in both gulping and particulate modes. They are visual predators in environments with adequate illumination. Visual predation by fish consists of a series of discrete steps. We studied the first step in the predation sequence, reaction to prey, at light intensities of 2–1500 Lx in a simulated pelagic environment at 10–13°C. We measured lake herring reactive distances, the distance at which a prey item will be detected and attacked, to live Limnocalanus macrurus, a natural prey of lake herring in Lake Superior. We used the reactive distances and associated angles of bearing and elevation, which described the location of the prey relative to the lake herring, to calculate reactive volume. This reactive volume can be envisioned as an irregular sphere surrounding the fish, within which prey are detected and attacked. All of the attacks on prey occurred in the anterior portions of the sagittal and lateral planes of the lake herring, as would be expected for a pelagic, cruising fish. The reactive volume surrounding the lake herring was generally spherical, but was more irregular than the simple spheres, hemispheres, cylinders, cones or other geometries assumed in previous studies. The reactive distances and the reactive volume changed with light intensity and were significantly smaller at 2–10 Lx than at 40–1500 Lx. At 40–1500 Lx, the reactive volume was expanded over that observed at 2–10 Lx laterally and caudally. Collectively our results indicate that lake herring can visually forage most effectively in environments with light levels >10 Lx.

Capture Probabilities of Lake Superior Zooplankton by an Obligate Planktivorous Fish—The Lake Herring

Abstract –Lake herring Coregonus artedi were videotaped while feeding separately on seven different zooplankton taxa. If a fish reacted to a prey item, I observed whether the prey item entered the buccal cavity of the fish. Copepods were captured at a lower percentage of the time (mean = 48.9%) than were cladocerans (mean = 86.7%). Limnocalanus macrurus, a large copepod, was captured less frequently (30%) than smaller copepods such as Diaptomus sicilis (42.5%), Cyclops vernalis (57.5%), and diaptomid copepodids (65%). Daphnia galeata mendotae were captured less frequently (80%) than smaller cladocerans such as juvenile daphnids (87.5%) or Bosmina longirostris (92.5%). The differences between copepods and cladocerans and sizes of each likely result from differential swimming strengths and behaviors of these various taxa. These results confirm observations from other planktivores that the evasive ability of zooplankton greatly reduces the successful completion of the planktivory process (encounter, attack, ...

Relationships of Lake Herring (Coregonus artedi) Gill Raker Characteristics to Retention Probabilities of Zooplankton Prey

Abstract We measured morphometric and meristic parameters of gill rakers from the first gill arch of 36 adult lake herring (Coregonus artedi) from Lake Superior that ranged in length from 283–504 mm. These data, coupled with the mean of the smallest two body dimensions (length, width, or breadth) of various zooplankton prey, allowed us to calculate retention probabilities for zooplankton taxa that are common in Lake Superior. The mean of the smallest two body dimensions was positively correlated with body length for cladocerans and copepods. The large cladoceran, Daphnia g. mendotae, is estimated to be retained at a greater probability (74%) than smaller cladocerans (18%-38%). The same is true for the large copepod, Limnocalanus macrurus (60%), when compared to smaller copepods (6–38%). Copepods have a lower probability of being retained than cladocerans of similar length. Lake herring gill rakers and total filtering area are also positively correlated with fish total length. These data provide further ev...

A General Model of Selectivity for Fish Feeding: A Rank Proportion Algorithm

Abstract Given that various prey are available to fish in a particular ecosystem, by default fish feed selectively. Studies of fish feeding ecology have provided key insights into the dynamics of aquatic ecosystems, yet prey selectivity is the least addressed component of these studies. This may be due to the higher level of effort associated with examining both the stomach contents and ambient prey abundance, the assumption that a determined diet composition is static, or the lack of a predictive protocol for a priori estimates of prey selectivity and diet composition. Here I present a rank proportion algorithm (RPA) model that predicts prey preference from first principles of predation that, when coupled with ambient prey concentrations, can predict prey utilization (i.e., diet composition). I applied the model to benthivore, planktivore, and piscivore examples from lentic, lotic, estuarine, and marine ecosystems. Compared with observed stomach contents, the RPA models predictions of diet composition e...

Dynamics of lake herring (Coregonus artedi) reactive volume for different crustacean zooplankton

Lake herring (Coregonus artedi) can drastically alter the zooplankton community of a lake through size-selective predation. I studied the first step in the predation sequence, reaction to prey, for different zooplankton taxa by lake herring. Reactive distance was significantly shorter for smaller zooplankton taxa (p < 0.0001). Reactive volume was calculated from measured distances and angles of elevation and bearing. This volume augments the reactive distance data and showed a three dimensional geometry, roughly analogous to a deflated basketball, that is amenable to a cruising style of planktivory. Reactive volume is dynamic with respect to variations in prey size (p < 0.001). Reactive volume is a refined measure of a ‘reaction’ by fish to a prey item than are simple, linear distances or other, assumed shapes. Thus, for a cruising planktivore, three dimensions need to be considered.

Winter Diet of Lake Herring (Coregonus artedi) in Western Lake Superior

Lake herring (Coregonus artedi) and zooplankton samples were simultaneously collected through the ice in the Apostle Islands region of western Lake Superior to provide information on the winter feeding ecology of lake herring. Zooplankton constituted the entire diet of the 38 lake herring collected for this study. We found no evidence of piscivory, although it has been reported by anglers. Diet selectivities were calculated using a Wilcoxon signed-ranks test and showed a preference of lake herring for larger zooplankton, especially Diaptomus sicilis, whereas the smaller copepod, Cyclops bicuspidatus thomasi, and immature copepod stages were selected against. These data document that overwintering copepods are food for a broad size range of lake herring in winter.

Changes in the Lake Superior Crustacean Zooplankton Community

We examined crustacean zooplankton densities at five locations in two regions of Lake Superior during a time period that spanned two decades, for three years in the early 1970s and again for three years in the early 1990s. We used coupled multivariate and univariate analyses to find whether the zooplankton community had changed over these decades, and to determine if such changes had occurred consistently across all stations. Seasonal variation was also examined. We found that the structure of the zooplankton community changed in directions predicted by the concurrent increase in the abundance of a major endemic planktivore, the lake herring (Coregonus artedi). The presence and abundance of various species in different habitats also varied within a year, between years, and between decades. The spatiotemporal scale of this study confirms that size-selective planktivory may produce community-wide effects in large lakes.

A model of salmonid planktivory: field test of a mechanistic approach to size-selection

A mechanistic model was developed to simulate the planktivory process for the pelagic lake herring (Coregonus artedi) on common crustacean zooplankton of Lake Superior. The model was constructed as a product of probabilities associated with detection, attack, capture and retention. Sensitivity analysis showed that these coefficients were robust and that initial zooplankton density affected the model behavior more than altering the coefficients. The model output provides percent composition of adult lake herring stomach contents. Zooplankton communities from several stations and seasons in Lake Superior were sampled to provide an initializing zooplankton community for the model. Model output was then contrasted with simultaneously field caught lake herring stomachs. The model predictions agreed with the observed stomach contents at an average accuracy of 80%. The overall agreement of the predictions with observed stomach contents is suggestive that the mechanisms modeled track planktivore feeding dynamics adequately.

Piscivory by Lake Superior lake herring (Coregonus artedi) on rainbow smelt (Osmerus mordax) in winter, 1993-1995

The stomach contents of 31 lake herring (Coregonus artedi), captured by anglers from western Lake Superior in the winters of 1993–1995, were examined to determine if predation on rainbow smelt (Osmerus mordax) was occurring as indicated by anglers. Twenty-six (84%) of the stomachs contained rainbow smelt, with an average of 7.0 rainbow smelt/stomach. This was the first documentation of piscivory by lake herring on rainbow smelt in the Great Lakes.

Benthic Nepheloid Layers in Central and Western Lake Superior

Abstract Data were collected monthly on the occurrence and intensity of the Benthic Nepheloid Layer (BNL) during the ice free period of 1992 at several sites in Lake Superior. Light transmission profiles at an offshore, deep station did not vary with depth. Profiles at shallower stations closer to shore exhibited decreases in transmission typical of BNLs. The BNL is not ubiquitous in Lake Superior and appears to be a nearshore and shallow water phenomenon. The term “Benthic Nepheloid Layer” should be used with caution.