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 Standard Nordi-mesh Entanglement – gill nets Considerations: HABITAT!!!, DEPTH, MESH SIZE
Freshwater Equivalent= Passive Gear Entanglement -Longlining Considerations: Habitat, by-catch, hook size, type of bait, set time, predation, finding the gear 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 Plastic style Glass style
Passive Gear Angling – sort of a weird mix between active/passive
Active gear - Common Drag/Tow – trawling
Active gear - Common Standing Wave Drag/Tow – larval fish sampling – Bongo nets, Miller sampler Considerations: depth, size of larvae, other stuff in water Reduced Opening
Active gear - Common Encircling – Purse seine and beach seine
Active gear - Common Stream electrofishing- backpack, 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
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!
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 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. Ecosystem effects: Bear and tree populations cycle based on salmon runs, stream invertebrate abundance then influences birds and spiders
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,