Michigan Bound

This week, LJ Rogers and I went to Michigan for the annual Midwest Fish and Wildlife Conference to present our work on the scotopic visual sensitivity of walleye.

LJ and I at poster presentation night

Sander Award

We also attended the walleye technical committee where we got to talk about the future of walleye research and explain the work we are doing at UMD.

Near-Shore vs. Off-shore Predators: Morphotypical Variation in Vision?

Within Lake Superior there are currently 4 different morphotypes of Lake Trout identified (Figure 1); morphotypes are the same species, but show phenotypic and genotypic variation. We wanted to investigate whether the 2 morphotypes, Siscowet and Lean Lake Trout, had adapted different visual properties owing to their different habitats (Figure 2).  The Lean Lake Trout is a littoral or near-shore morphotype that occupies water less than 80 meters deep and historically has less body fat.  In contrast, the Siscowet Lake Trout is a pelagic (off-shore) morphotype that occupies waters greater than 80 meters and can have up to 70% body fat. Both are apex predators within their respected zones.

Figure 1.  The 4 morphotypes of Lake Trout within Lake Superior

The two morphotypes also display different behavior.  Lean Lake Trout perform Diel Bank Migration (DBM) where they move into shallower, near shore waters in the evening, while Siscowet perform Diel Vertical Migration (DVM) characterized by moving higher in the water column at night (Figure 3).

Figure 2. Characteristics of Lean vs. Siscowet Lake Trout

With the help of data published in a previous study entitled Visual Sensitivity of Deepwater Fishes in Lake Superior by a former lab mate, Kelly Harrington (photo), we were able to compare the visual properties of Siscowet Lake Trout to the data we collected on Lean Lake Trout.  Additionally, L.J. Rogers collected Lean Lake Trout with the help of the DNR (photo), helped analyze and collect the data and was able to complete a UROP project (Undergraduate Research Opportunities Program).

Figure 3. Diel (Daily) migration patterns for Lean and Siscowet Lake Trout within Lake Superior. A, Day; B, Night.

For this study we wanted to determine which colors of light Lean Lake Trout see and at what intensities. To do this, we conduct electroretinography, or ERG, for short.  These ERG's essentially tell us when neurons are firing in response to a color and intensity of light; we can then quantify based on the response.  The ERG setup is outlined below (Figure 4 and in short, involves flashing monochromatic (one color) light at different intensities and recording the neural response.

Figure 4: Schematic drawing of electroretinography setup. From left to right: (A) Constant current power supply, (B) electric shutter, (C) quartz-tungsten halogen lamp, (D) neutral density filters, (E) monochromator, (F) Faraday cage, (G) fiber optic light pipe, (H) recording electrodes, (I) signal amplifier (G-I within circular enlargement), (J) PowerLab, (K) personal computer, (L) chilled water lines.

Left: L.J Rogers holds a Lean Lake Trout he collected this past fall with the help of the MN DNR. Right: L.J. Rogers, Kelly Harrington and myself taking a break from conducting ERG trials.


When we analyzed our Lean Lake Trout data and compared to Siscowet data in Harrington et al. (2015), we see that there are some differences in visual sensitivity between the two morphotypes. Lean Lake Trout have peak sensitivity at 550 nm (green) while Siscowet have peak sensitivity at 525 nm (blue-green) (Figure 5).  We also see that Leans have green-shifted vision with higher sensitivity to the upper wavelengths.  In contrast, Siscowet are blue-shifted and show higher sensitivity to the blue range of wavelengths.

As blue green wavelenths penetrate deepest in freshwater, this supports the sensitivity hypothesis that a fish will be most sensitive to the light available in its environment. The siscowet is most sensitive to 525 nm blue-green light which is the only light available at depth.  In shallower waters, the green wavelengths have yet to attenuate and can be sued by a visual predator like the Lean Lake Trout. Green wavelengths also penetrate furthest in turbid waters and may aid Leans in shallower, wave agitated areas.

Figure 5.Visual sensitivity of Lean and Siscowet Lake Trout.

By determining the lowest intensity light each morphotype can detect, we can equate this to what depth a fish might be able to see.  We determined that Siscowet and Lean Lake Trout have the same depth profiles for vision and both are able to detect light ~350 m within Lake Superior in the summer.  In fall, with an increase in lake turbidity, vision is limited to ~100 m.  This data suggests that while Siscowet and Leans have evolved different sensitivities to different wavelengths, they have yet to develop absolute sensitivity differences.

LJ received an award this spring at MN AFS for the above work

American Fisheries Society Student Subunit at the University of MInnesota, Duluth

In May of 2015, we established the first American Fisheries Student Subunit at the University of Minnesota, Duluth.

We have 25 active members and are comprised of both undergraduate and graduate students.

We have bi-weekly meetings and our scheduled activities revolve around conservation and fisheries education.



Mission Statement :  A club for students interested in strengthening their fisheries knowledge, advancing fisheries science, and conserving fisheries resources and aquatic systems within Minnesota.

UMD AFS graduate students at MN AFS

To date, we have coordinated beach cleanups with MN Sea Grant, visited the Great Lakes aquarium, judged the regional science fair, volunteered at both the Boat show and Home show, written letters of support for Lake Superior Marine Sanctuary, designed the MN AFS T-shirt for the annual meeting, collected for the MN AFS annual meeting auction and gone smelting as a group.

Collected 55lbs of trash of the shore of Lake Superior on Mn Point

T-shirt design for the MN AFS annual meeting

UMD AFS volunteering at the Boat show with MN Sea Grant

Field trip learn about fish husbandry at the Great Lakes Aquarium

Using the seine net to capture smelt during our annual UMD AFS smelt event

New publication in Journal of Great Lakes Research

link to article

My master's work on the foraging characteristics of siscowet lake trout has just been published.

Collection of Deepwater Fishes: Dealing with Barotrauma

Part of my research involves the collection of deepwater fishes from the cold waters of Lake Superior.  With the help of Owen Gorman and the folks at the Ashland, USGS, we make sure we have numerous, healthy fish for our experiments.

Our fish are collected via deepwater trawls aboard the USGS research vessel, the KIYI.  The fish of interest are brought up from 120 meters (~400ft) and much like scuba divers, rising too quickly to the surface can cause problems. Boyle's law that states that the volume a of gas is inversely proportional to the pressure, meaning that the gasses within fish expand as they move shallower.  This internal damage is known as barotrauma (baro=pressure, trauma=damage), and is most apparent in the expansion of the swim bladder and bursting of capillaries within tissues.

With every 10 meters ascent, the volume of a gas doubles.  Here we see a lake trout moving from 20 meters to the surface exhibiting a tripling in the volume of the swim bladder.

A siscowet lake trout showing typical barotrauma

Collected fishes typically show multiple signs of barotrauma including: exopthalmia (bulging eyes), bloated bodies (swim bladder expansion) and tissue damage from ruptured capillaries. There is also internal damage that is less obvious such as the nephron of the kidney rupturing.

While siscowet are hardy and we have not had any mortalities associated with barotrauma, some fish, like deep water coregonines (Kiyi) do not survive once captured.

The graph on the left shows survival of collected fishes in days since captured.  Here we see siscowet (SIS) have 100% surival, deepwater sculpin (SCP), 50% and Kiyi (DWC) do not live past 5 days.

In an effort to help alleviate barotrauma, Owen Gorman with the USGS created a hyperbaric vessel to quickly repressurize fish once captured, and then slowly depressurize them.  I hleped test the efficacy of this apparatus, known as the HAfF (Hyperbaric Aperatus for Fishes) this fall on Lake Superior.

HAfF aboard the RV Kiyi

Checking the valves before pressurization

Decompressed vs. non-decompressed siscowet lake trout

Collected fishes are slightly anesthetized with MS222, and added to the HAfF (A above). Pressure and mixtures of gasses are monitored from inside the ship via a control panel (B above).  We can monitor fish activity with a cameras mounted inside the pressure chambers on the HAfF (C & D above).

Dr. Gorman and I are currently writing up a report for the Great Lakes Fisheries Commision. We have seen marked improvement in the condition of siscowet lake trout since implementing the HAfF. Siscowet that have been decompressed show less tissue damage (A & B right) and show increased activity and feeding sooner.  As a comparison, a non-decompressed siscowet lake trout (C & D right) shows  obvious signs of barotrauma.

Siscowet Lake Trout Foraging Trials

Below is actual footage from a few of our foraging trials that show Siscowet Lake Trout foraging for Golden Shiners.  We analyze the footage looking for a set of foraging parameters or behaviors to determine how Siscowet manage to forage for prey at varying light intensities.

Video 1 shows the initiation of a trial with the lifting of the foraging arena gate that separates predator and prey.  Trials last 10 mins or until prey is consumed.

Video 2 breaks down the foraging parameters that we look for while analyzing footage.  A couple parameters we examine are reaction distance and angle of attack, We also look at whether trout capture prey and the time to capture. 

Video 3 Siscowet lake trout are able to sense their prey via mechanosensory detection (lateral line) in the dark. This video shows how the trout are able to detect and follow their prey, but rarely capture prey in absolute darkness.

Video 4 The siscowet lake trout is able to detect prey movements within half the total length of its body.  We see here that the siscowet does not detect the prey until it is within half a body length, and then quickly loses the prey when out of range. Trial in absolute darkness (0 lux).

Sea Grant Radio Guest

Burbot Radioshow Link
http://www.seagrant.umn.edu/audio/2015.09.15_burbot.mp3

This week I was a guest on the Sea Grant Radio Show entitle Burbot and the lota lota.  I talked with Olivia Dehler about the Burbot's history in Lake Superior and their current state.

Aired September 15, 2015.








http://www.seagrant.umn.edu/audio/transcripts/2015.09.15_burbot.pdf