What can parameters about a fish can we measure that relate to feeding?

What environmental factors influence fish feeding?

What biotic factors influence fish feeding?

Group discussion questions

DiscussionWhat parameters about a fish can we measure that relate to feeding?

Lists: -At distance react food

-measure stomach contents (counts, weight, volumetric

-Gape

-how long it takes for a fish to swallow prey

-rates, number per time

- attempts per diet item

- angle of attack

- are there other fish around

DiscussionWhat environmental factors influence fish

feeding?Lists:

pH

temp

Time of day

season

light level

DO

Substrate

Fishing pressure

Lists:

pollution

reproductive cycle

nest guarding

Flow velocity

turbidity

Physical Habitat

Salinity

DiscussionWhat biotic factors influence fish feedingLists: Prey abundance

Size of prey

Size of predator

Competition

Gill rakers, mouth placement, and other morphology

Indirect competition (common predator)

Level of production

Specialist or generalist or omnivore

Experience

Maturity

Gender

Vegetation

Lists:

Community Composition

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Example:

General factor: Turbidity

Assumptions?: For all visual feeders

Water Clarity or TurbidityDis

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I think the darker the water gets the harder it will be to find food, and the relationship should be linear!

No way, fish don't care if it gets a little muddy, up to a point, then they can't see anything!

You are both crazy, think about when it gets foggy, you can't see crap, little increases in turbidity have a way bigger effect, but then once it gets cloudy fish just use other senses!

Electivity: what's the proportion of item an in the environment compared to the proportion in the stomach?

If an items is rare in the environment but prevalent in diets, it is selected for.

How do we measure that....well for a lot of organisms we take invertebrates samples and then pick them.......lets practice!

How does a fish decide what to eat?

Samples are from Big Spring Creek?

DAM

Big Spring Creek StoryBig Spring Creek is located just west of Lake Mason. The watershed is full of agriculture but the stream has lots of springs flowing into it.. There is a dam that separates 2 very different fish communities: the downstream community that is connected to Lake Mason includes largemouth bass, white suckers, yellow perch, bluegill, and a few mottled sculpin. No fish can ascend the dam, above the dam the community contains mottled sculpin, central mudminnows, creek chubs, brook sticklebacks, and brook trout in the headwaters The dam is being removed and there is a suggestion that this stream will become a brook trout stream....but with all those predators and competitors below the dam there could be some interesting ecology happening when the dam comes out.

We're interested in what fish are consuming above and below the dam, not just from the fish perspective, but from the invertebrate community perspective. If we quantify the types and numbers of invertebrates in the creek (above and below dam) we can discuss the potential impact the different fish communities are having on these invertebrates and we can understand one piece of the fish diet electivity equation.

First we picked bugs from Hess samples of Big Spring Creek.  A Hess sampler samples all the invertebrates in a .3m diameter ring.

Difference in invertebrate abundance were quite obvious with more and larger invertebrates upstream and smaller invertebrates down stream. We suspect this is due to the presence of better insect feeding fish below ( white suckers, perch, and bluegill). Upstream invertevores are mostly sit and wait predators (Mudminnows and sculpin).  Additionally the largemouth bass predation likely keeps sculpin and mudminnow abundance low in below the dam.

We'd expect the change in dam, to change the abundance of inverts. This could have an effect on the stream primary production (algae) or alternatively, the change in the number of invertebrates hatching from the stream could reduce the amount of food for insectivorous brids in riparian areas. 

We also discussed electivity  So say there are 3 bugs all equal proportion in the stream, in the trout they are 90%, 10%, 0%.  Fish are highly selective on first species.  The only way you know this is if you quantify how many bugs are in the stream to do that, you have to pick a lot of samples.  Everyone got to pick a lot of samples, so they knew what it was like to do consumption and electivity ecology.

Trout stomachs: lots and lots of caddisflies, some sculpin, a bunch of amphipods.   Talked about the difference in eating one sculpin vs how many caddisflies or amphipods.  Lot more energy, maybe less work, maybe more work.

Data Online.

Samples are from Big Spring Creek?

Samples are pink because I added rose bengal: it dyes biological material but not sediment

Bugs are Pink Dirt is not

Pick the bugs into the ice cube trays

Sort them based on how they look

Do one upstream and one downstream sample....lets see how different they are

While picking, think about how the fish that are in the creek would consume invertebrates, who would get picked off first, why?

How

Samples are pink because I added rose bengal: it dyes biological material but not sediment

Bugs are Pink Dirt is not

Pick the bugs into the ice cube trays

Sort them based on how they look

Do one upstream and one downstream sample....lets see how different they are

While picking, think about how the fish that are in the creek would consume invertebrates, who would get picked off first, why?

• Holling Processes of predation– Search– Encounter– Pursuit– Capture– Handling

C.S. Buzz Hollingaka "the man"

Functional response was developed based in a 1959 paper

These eating These

Sometimes called the disk equation cause this is how he taught it to students

Review

Trichoptera (Caddisfly)

Ephemeroptera (Mayfly)

Diptera (Flies)

Non-biting Midges Black Flies Crane Flies

Amphipods

Isopod