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Fisheries techniques:
Passive vs active gear
Gear vulnerability (can you catch them)
Biases-season, depth, location, temperature (if they are there will you catch them)
Fish in an ecosystem context:
Nutrient movers
salmon in the PNW , but also suckers in Lake Superior
inshore offshore: bluegills in a pond, alewife in LS
Nutrient resuspension
bottom feeders Flecker's fish in Adean streams
Destructive
carp pull up weeds
Fish biocontaminants
Mercury moving up to humans
PCB's, birds, Botulism
Biocontrol
Mosquito fish
Considerations:
What factors have we discussed:
What factors have we discussed:
Two types of methods:
Active or Passive
Passive Gear
Entanglement – gill nets
Considerations: HABITAT!!!, DEPTH,
MESH SIZE
Standard
Nordi-mesh
Passive Gear
Entanglement -Longlining
Considerations: Habitat, by-catch, hook size,
type of bait, set time, predation, finding the
gear
Freshwater Equivalent=
Pelagic
Bottom
Passive Gear
Considerations: location,
mesh size, funnel diameter
Entrapment- trap nets, know the parts!
Wings
Pot or Car
Funnel
Wings
Lead
Trap nets, Lots of variety
Fyke Net
Pound Net
River Trap Net
PA style trap Net
Hoop Net - river
Passive Gear
Minnow trap – can mean anything
Considerations: location, mesh size, funnel
diameter, trap fullness = more or less caught,
predation
Gee style
B style
square
Glass style
Plastic style
Passive Gear
Angling – sort of a weird mix between active/passive
Active gear - Common
Drag/Tow – trawling
Active gear - Common
Drag/Tow – larval fish sampling – Bongo nets, Miller sampler
Considerations: depth,
size of larvae, other stuff
in water
Reduced Opening
Standing Wave
Active gear - Common
Encircling – Purse seine and beach seine
Active gear - Common
Stream
electrofishingbackpack, tow
boat, bank based,
electric seine
Considerations: safety –
fish and researchers,
Active gear Boat Electrofishing
Considerations: depth,
safety again
Active gear - Common
Toxicants – rotenone, lampricides
Considerations: Selective, ease of
application, health concerns, turning the
piscicide off
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Gear bias – this is the official term (as in use it on the exam) when you discuss why certain species, sizes, or
habitats would not be caught in the gear relative to you the population. Every gear has bias, I’ll say again, EVERY
GEAR HAS SOME BIAS, none are perfect.
This is important. Say for instance you knew there were exactly 25 individuals of 4 different species in a blocked
section of stream or a pond. You deployed your sampling gear and caught the following:
Species ASpecies BSpecies CSpecies D5766
We would say that this gear had little bias for describing the community composition because it caught all of the
species, roughly in the same proportion to what they were in the pond or stream. If instead our sample looked like
this we would know that our gear was biased.
Species ASpecies BSpecies CSpecies D102001
The same goes for size, if you only catch one size of fish, there are 2 reasons for that:
That is a true representative sample of the population, the population is all one size
Your gear was biased for only catching one size of the population
Think of how this changes the conclusions you make about the ecology of a fish in a given water. This is really
important to understand that the goal of fisheries sampling is to provide the least biased sample possible! All
gears have bias, how do you get around this problem, use multiple gears. You can never be sure that you have a
population of fish perfectly sampled, but you know with some extra effort and experience you have a high degree
of confidence that you have adequately represented a fish community with your sample. For example, if the
minnow traps in Kitchell’s pond caught 0 minnows, does that mean there aren’t any there, what if it catches 2
minnows, did they still not work or are there very few minnows in the pond, such that you caught a representative
sample. The only way you can get at this is with repetition and multiple gears!
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Direct Observation: This can either be from a camera or in person. Examples include SCUBA or
snorkeling, towing cameras or setting stationary cameras, counting windows in fishways where
people watch/count fish that swim by.
Direct observation is an active gear, it is especially useful for describing presence absence and
community composition, but because you don’t handle the fish it is difficult to quantify other
metrics about the fish you observe. Direct observation can help determine more detailed habitat
choice of fish because you can observe them in the exact spot within a given location. It is
frequently used in rivers and in lakes. Data is kept on tablet or communicated through a snorkel
to a recorder. Fishways that allow movement around a dam often have counting windows to
identify and count fish. Fish that swim away or are attracted to divers can bias this method.
Water clarity also causes an issue. Length can be estimated from direct observation, usually to
the nearest 25 or 50mm size class.
Fish Weirs: these are the stream versions of trapnets. Weirs can face
either upstream or downstream, and can include a fence that blocks
passage through a stream area. This makes fish enter the trap
location. Most weirs also concentrate water flow into the funnel area to
help fish “find” the trap. You can tell from the pictures below that these
can be some huge pieces of gear. Many of the fences or grates are
built so that they can be pulled when the weir is not being fish. These
are not necessarily big river techniques either, they have been
effectively used in small headwater streams to catch out migrating
salmon smolts.
Hydroacoustics: means the study of sound in water, but in our case we refer to the use of sound to locate fish. The general
principal includes sending sound wave out from a “transducer” then collecting the sounds that bounce back off of fish and other
objects. For fish the swimbladder is what the sound bounces off of. Generally, the larger the fish, the larger the swimbladder, the
larger the “target strength”, this is the term used for how strong the signal is that bounces back. Hydroacoustics is usually performed
from a moving boat, with the expensive $200,000-$500,000 transducers attached to a tow body. Different transducers have different
sound frequencies to penetrate deeper depths or be more accurate with certain sizes of target strengths. Fish that are close to the
bottom are difficult to distinguish from the sound bouncing off the bottom, therefore the technique is often used to survey the
abundance of pelagic fishes. Of course keeping track of the distance or time that you sample is important in order to get a relative
measure of fish abundance. Acoustics can also be stationary, that is the fish move through the “cone”, that is the area in which the
sound can be heard if it bounces back. Data look like the figure below. Note the scale on the right which measures the target
strength (fish size). In order to calculate how many fish there are and what size you need to know the amount of area scanned and
what target strength = what size fish. It is basically impossible to tell the difference between different species that are the same size.
Others
push nets, lift nets, pop nets, dip nets, fish wheels,
cast nets, drop nets, spears, detonating cord
Nutrient movers
salmon in the PNW , but also suckers in Lake Superior
inshore offshore: bluegills in a pond, alewife in LS
Nutrient resuspension
bottom feeders Flecker's fish in Adean streams
Destructive
carp pull up weeds
Fish biocontaminants
Mercury moving up to humans
PCB's, birds, Botulism
Biocontrol
Mosquito fish
Fish Ecology @ an Ecosystem Scale
What do we mean by that…
Those cases where fish or their behavior create an
effect that influences multiple trophic levels or is
critical for other ecosystem to functions.
Other names:
Keystone species
Integrator species
Move nutrients
Ecosystem effects:
Bear and tree
populations cycle
based on salmon
runs, stream
invertebrate
abundance then
influences birds and
spiders
Classic example: Pacific Salmon
move out of streams weighing a few
grams, gain 1-30kg at sea, then
move back into headwater rivers
and streams to spawn, die.
Move nutrients
Other example: Littoral-Pelagic Coupling
Littoral fish move into the pelagic at night, feed
on invertebrates, move back to littoral zone, fertilize
littoral zone with pelagic nutrients. Can be multiple
kilometer movements
Ecosystem effects:
Increased algal
production,
increased benthic
invertebrate
production, higher
predator fish
biomass
Move nutrients
Other example: Bioaccumulation
Mercury is well known
contaminant. Accumulates in
tissue that doesn’t turn over
often (fatty tissues)
Unique Human – Fish – Human
Linkage
Nutrient resuspension/destruction
Other example: Salmon, White suckers, Carp
Ecosystem effects: Increased turbidity,
reduced algal production,