Ichthyology Final Exam - fisheries

how do you calculate the length of a fish at different years?

Ln = a + (L-a)(Vn)/ Vr

What do all the variables mean in the length equation?

L= length of fish at present day in cm

a = length of fish when scales first form in cm (standard set for species)

Vn = length of scale at annulus in cm (use annulus that matches with the year you are calculating for)

Vr = length of scale at edge of scale in cm

how to calculate plumpness factor/ condition factor

K = weight (grams) * 100 / Lcm3

how many oz in 1 pound?

16 oz

how many grams in one pound?

454 grams

How do you tell a male Salmon from a female?

Males have a hooked lower jaw called a kype

Salmon lifecycle: Egg house

Eggs are placed in a tray where water upwells through them. Tanks covered, lights on the tanks are red. Eyeup stage is around January

Salmon lifecycle: How are unfertilized/ not viable eggs identified?

Shocking

dropping eggs from a high to low space (6-12in) and turns not viable eggs white and the “bad” eggs are picked out

What is the eyeup stage?

when you can see the eyes forming through the egg membrane

Salmon lifecycle: What stages do the salmon go through in the egg house?

sacfry, two more weeks and they hatch and begin to swim as fry

what is the sacfry stage?

first larval stage: from hatching out of egg membrane to completely reabsorbing yolk sac

what is the fry stage?

second larval stage: starts when they start feeding until the axial skeleton is complete. (This stage has many names. Black Fry in Bass, Alevins in Salmonids, Elvers in eels.)

When do fry get taken out of the egg house? what is this dependent on?

They remain in the egg house until they are large enough to move to raceways around early June.

This is dependent on the temperature of the water.

what stage occurs after fry?

the first juvenile stage: parr

what is the parr stage?

begins when all fins have formed. It is often marked by vertical bars. In salmonids it ends as the fish becomes silvery and in searun fish is moving into salt water. 

what is the second juvenile stage occurring in winter and early spring called?

smolt

what is the smolt stage?

for salmonids is the later juvenile stage which ends as the fish becomes sexually mature.

what is the definition of a pond in Maine?

a water <10 acres

what is a fish population?

a group of interbreeding fish in a body of water

what is a fishery?

the population of fish that is harvested

why do fisheries biologists lay burlap bags in rivers in march/early april?

they lay the bags where fish (rainbow smelt) usually spawn to collect eggs

why are the pectoral fins not clipped in river species?

pectoral fins are needed for stability so they are very important in fast moving water like a river.

what is the preferred method for stocking fish?

trucks with tanks that are aerated drive to the lake, transfer to aerated barrels in a small boat and released into the middle of the lake to ensure the fish reach appropriate depths.

how are fish stocked if the lake is remote?

they may fly them inside aerated pontoon tanks and dump them in

or they may backpack them in inside aerated backpacks

what are the three methods used for bass census?

1. rod and reel: wearing polarized glasses can see males defending nests. they catch them and take measurements (length, weight, take scales for aging)

2. scuba diver pulled around lake by boat. Males are counted and estimated sizes are recorded by others on boat

3. electrofishing

what are the two types of Creel censusing?

1. frequent fishers keep log books and record name of water, amount of time fishing, gear used, number caught, species caught, lengths, weights, fin clips

2. biologists visit waters and ask fishers to take measurements of fish they have in their creel (and note any fin clips)

What is gill netting?

People deploy a long mesh net in shallow water, leave it overnight, and pull it up to catch fish as they seek inshore areas for nesting. They also take standard measurements of the target fish.

what is the advantage and disadvantage of gill netting?

advantage: quick way of getting a sample of a target species

disadvantage: lethal

what does YOY mean?

young of the year

what are the two methods of electrofishing?

1. in streams looking for YOY in summer or fall. backpack generator, anode in water that sends out current. cathode distance away, fish muscles contract causing them to swim to the anode where they are netted and species and measurements taken

2. the state of Maine have several boats. used to look for a variety of species and age, classes even invasive species

pond and lake surveys

updating a variety of physical measurments: map of water, temp ranges, depth, species in water, fishing regulations.

seasonal changes in lake that stratify

what is most important for the number of fish that can be stocked in a lake?

water temperature and dissolved oxygen levels

what is trap netting?

used to catch lake trout, brown trout, etc. as the adults travel into the shallows looking for cobble for their nests.

what do biologists do when when they believe there is too much competition in a water for the preferred species.

1. set large bag limits for certain species and sizes

2. have derbies to fish out some species or sozes

Barriers to fish movement: hanging culverts

replace them with large natural bottom or ridged bottom, large culverts

fishways: single shot

single vertical slot between each pair of pools, which creates a high-velocity jet. 

Fish can swim through the slot at any depth, and the low-velocity areas on the sides of the pool allow for resting

Fish movement can be slower than in other fishways

fishway: double vertical shot

two vertical slots between each pair of pools, typically spaced symmetrically. 

The flow is split between two slots, potentially resulting in lower flow velocities and a more gentle transition between pools

The dual slots may create more diverse flow conditions, allowing for a greater range of fish behaviors

fishway: denil

series of baffles within a channel to allow fish to swim upstream

create low-velocity zones where fish can rest and ascend, making it easier for them to navigate the channel. Denil fishways are particularly useful on steeper slopes.

reclamation of big reed pond

someone introduced rainbow smelt and they reproduced and ate arctic charr (endangered in Maine)

reclaiming: trap out as many charr as possible and put in hatchery, pump into the hypolimnion rotenone, in the spring after insects have returned to the lake they reintroduce the charr

what is rotenone?

a chemical that blocks the uptake of oxygen in the gills, very expensive process

what damage does running a skidder through a stream do?

causes siltation downstream, covers fish nests and eggs don’t develop

what species does family Salmonidae - salvelinus include?

brook trout, lake trout, arctic charr

physical characteristics of all salvelinus

creamy white spots, white lead edge to pectorals and pelvics

Salvelinus fontinalis

brook trout, also called squaretails

look for wormy pattern on black and red pots with blue halos

sea run brook trout are silvery

Salvelinus namaycush

lake trout, also known as a togue

lack vermiculation

deeply forked tail and big teeth

Salvelinus alpinus

arctic charr

some males are orange

no vermiculation, tail slightly forked

Salmo salar

Landlocked salmon

deeply forked tail but can square off as adults

few teeth on roof of mouth

Salmo trutta

square tails

two strong rows of teeth on roof of mouth

large and often orange adipose, black spots

what is a tiger trout?

male brook trout and female brown trout

what is a splake?

male brook trout and female lake trout, characteristics highly variable

they grow large and are much better competitors than brooks so they can be stocked in waters which have too much competition.