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PNW Fishes Midterm
Terms in this set (37)
Describe the difference between stormflow and baseflow. Which streamflow generation processes generate stormflow, and which ones generate baseflow?
What is the dominant source of primary production in Pacific Northwest streams?
Periphyton (stuff attached to rocks, slimy). This includes unicellular green algae (diatoms) and cyanobacteria (multicellular)
Also has vascular macrophytes, bryophytes, and phytoplankton.
Why are headwater streams more likely to be dominated by shredders rather than scrapers?
There's a higher input of allochthonous input (i.e. leaf litter). At the headwaters there is more shading, so scrapers will not do well because they mainly graze on periphyton, who are primary producers and rely on sunlight.
List three common adaptations of riparian trees and describe how these traits might be particularly advantageous in floodplain environments.
Adaptations common to opportunistic colonizers in frequently disturbed habitats--light tolerance, fast growth, N-fixation, and small, easily dispersed seeds.
Adaptations specific to riverine habitats--moisture tolerance, resilient roots, asexual reproduction, and hydrochory.
Why are riparian zones in the Pacific Northwest typically dominated by deciduous trees?
What are the advantages and disadvantages of anadromy as a life history strategy for Pacific Northwest fishes?
Access to productive N. Pacific Ocean (greater body size, fecundity)
Disadvantages: Arduous migrations (high mortality rate, heavy metabolic costs)
Juveniles avoid marine predators
Why are there several anadromous fishes but no catadromous fishes in Pacific Northwest rivers?
There aren't any catadromous fish because of the lower food availability in rivers vs oceans and the lack of predators in the rivers in the PNW.
What are the three components of the "Triangle of Habitat" for stream-dwelling fishes? Give an example of each type of habitat for a coho salmon.
Fry typically rear in lakes
Kokanee (sockeye, until maturity), Rainbow (FW steelhead resident, to maturity), and FW resident cutthroat (to maturity).
Fry typically rear in streams for 1-2 years, needs refuge from high flows in winter
Coho (o. kisutch)
Spawns in spring, iteroparous, hardiest of the Pacific salmon
Cutthroat (o. clarki)
Largest of the Pacific salmon, has spring and fall spawning runs
Chinook (o. tshawytscha)
Migrates to sea soon after emergence, known as "dog" salmon
Chum (o. keta)
Migrates to sea directly after emergence, has distinct even- and odd-year spawning runs
Pink (o. gorbuscha)
Spawns in spring, has winter and summer spawning runs
Steelhead (o. mykiss)
What are the key differences between ocean-type and stream-type chinook salmon?
Ocean-type chinook do not rear, they head to the sea soon after emergence (similar to pinks). Stream-type chinook rear 1-2 years in streams (similar to lake- and stream-sockeye and coho).
What are the key differences between spring (i.e., early) and fall (i.e., late) chinook? Which is more vulnerable to the effects of warm summer temperatures?
Spring/early chinook return to FW in the spring and summer, while fall/late chinook return in fall. Early chinook are more vulnerable to the effects of warm summer temperatures.
What are the key differences between summer and winter steelhead?
Describe how ocean-type and river-type sockeye differ from most other populations of sockeye salmon.
Consider the phenomenon of homing in Pacific salmon. What are the evolutionary implications of homing with respect to local adaptations and the development of genetically distinct populations (i.e., ecotypes)? Why does straying persist?
Homing creates reproductive isolation that leads to genetically distinct populations of salmon that allow for unique local adaptations to become present. A relatively large genome size allows for rapid evolution providing a buffer from inbreeding depression.
Strays persist because it allows for genetic diversity and allows for salmon to colonize new habitats after disturbance.
Consider the typical size difference between sockeye and kokanee. What does this tell us about the advantages of anadromy? What are the disadvantages?
Kokanee are landlocked, non anadromous sockeye populations that are usually adfluvial. Compared to anadromous sockeye salmon. The ocean entails increased growth, so the sockeye are generally much larger than the kokanee. This shows that the pros to anadromy are that there is access to productive north pacific ocean which allows for a larger body size and fecundity while still allowing juveniles to avoid marine predators. The cons to anadromy are that the migrations are arduous and have high mortality risk and heavy metabolic costs.
Why are jacks smaller than other spawners of the same species? Given the selective pressures favouring larger-bodied salmon on the spawning grounds, how does this life history strategy persist? Why are there no female jacks (i.e., "jills")?
Jacks are smaller because they are sexually mature, precocious males returning to spawn at an early age. This life history persists because there is a decreased chance of predators and a decreased chance of dying at sea. The strategy persists on a density dependent frequency, because if there are a lot of big males it's advantageous to be a jack but if there aren't than it's not worth it.
There are so few jills because eggs are very energetically costly and it is hard to be successful with fewer eggs because of a smaller body to produce them with. The bigger females are the better for eggs.
What is the difference between a residual salmon and a landlocked salmon such as kokanee or rainbow trout? Which species are known to have residuals?
Residual salmon are males of otherwise anadromous populations that never migrate out to sea, but mature and spawn entirely in freshwater. They are generally the progeny of anadromous fish. Compared to landlocked salmon that are generally reproductively separate from the anadromous fish.
They are seen in chinook, sockeye, and coho but are NOT seen in pink or chum.
What are the selective pressures that favour the development of kypes in male salmon?
Males most often experience a more intense intra (within) specific competition because it's less costly to produce milt, so they have more energy, they can stay longer, and can fertilize more than one redd. Therefore, there are generally more males than females so they have to fight for fertilization and they do so in direct contest competition which puts a selective pressure to develop more intense sexual dimorphism like kypes.
List or Describe four ways in which riparian vegetation enhances habitat for salmonid fishes.
Helps regulate stream temperature. This helps salmon because they need an optimal temperature to execute standard and active metabolism (if it's too hot or too cold, salmon will start "shutting down" and cannot function properly). It also controls autotrophic production.
Leaf litter provides OM, which is a basis for heterotrophic food webs.
Sediment and nutrient filtration-
Biological uptake of dissolved nutrients in SS flow. Denitrification. Mechanical (?) interception of suspended solids in surface runoff. Filtration will be less effective where surface runoff occurs in rills or gullies or where tile drainage systems circumvent root zones.
Root systems anchor soil, minimize bank erosion, siltation. Undercut banks are when roots keep topsoil in place while deeper soils erode.
Cover for fish-
Undercut banks and overhanging roots.
Floodplain as reservior for high flows-
Minimizes volume and velocity of water carried downstream. Moderates pulse of stormflow.
Source of large woody debris (LWD)-
LWD provides so much; some examples are flow impediment, flow deflection, and cover.
List or describe four functions by which large woody debris (LWD) enhances habitat for salmonid fishes.
Increased retention leads to decreased peak flow, erosion and siltation making the river habitat
survivable for salmon in many ways; allowing the salmon to rest and allowing for clear waters for photosynthesis.
Creates pools (dam, plunge, backwater scour) for habitat complexity, provides places for salmon to rest away from the flows.
Bank and be armouring-
Leads to decreased erosion and siltation, provides refuge for salmon in deep pools that are hidden from predators.
Nurse logs for other trees providing shade/temperature refuge and eventually nutrients from leaf litter.
Keeps salmon safe from predators (and potentially from natural events like an increase in speed flow) and decreases temperature.
Source of OM, nutrients-
Slowly releases CPOM, FPOM, and DOM
Describe the process by which large woody debris (LWD) creates scour pools in streams. Describe two benefits of LWD-formed pools for Pacific salmon. Which species or life history stages are most likely to be affected?
Pools are formed from LWD because it deflects the oncoming water back, which scours the bottom and creates pools. Pools provide essential habitat as velocity cover (can hang out in the pools will little energy cost and provides access to food carried in the drift), thermal refuge (deep pools have greater thermal inertia relative to riffles, LWD pools provide shade), and cover from predators. LWD pools are good for fry and mature salmon.
Describe the process by which large woody debris (LWD) creates off-channel habitat in streams. Why is this beneficial for Pacific salmon? Which species and life history stages are most likely to benefit?
LWD can create off-channel habitat taht resulted from the formation of channel islands. A channel island is formed when LWD and large grains pile up (creating an isalnd) and forces the water flow to around, creating off-channels. These off-channels are esentially for overwintering coho fry, who need refuge from high flows.
What is siltation and how does it influence egg-to-fry survival in Pacific salmon?
Siltation influences egg-to-fry survival because it stops water flow from going into the redds
where the eggs are buried. This flow is important because it delivers dissolved oxygen and removes
Describe three ways in which siltation affects the growth and survival of Pacific salmon
Define off-channel habitat and provide an example. Why is off-channel habitat important to Pacific salmon? Which species are most likely to require off-channel habitat?
Describe one habitat feature that provides refuge from high flows in winter, and one habitat feature that provides refuge from high temperatures in summer. What species and life history stages of Pacific salmon are most likely to use each of these habitat features?
Winter- Side channels used to allow rest from heavy flow coming from floods. Used for coho?
Summer- Deep pools allow for cooler temperature refuge.
Describe two factors or stresses that influence egg-to-fry survival in Pacific salmon. (Extra: What exacerbating factors or considerations make eggs more or less vulnerable to these stresses?)
Temperature impacts the rate of development and the timing of emergence which impacts the amount of degree days (TU = 1 day x 1 C) the fish has accumulated. These impact when the fish emerges which can be an issue if it's too early or too late because there will be less food available and could be some temperature issues. Can be exacerbated by shading of the river or
Redd superimposition influences survival because sometimes redds can get dug up if they are made too early and shallow by bigger salmon if there is not enough space for the amount of salmon that return to spawn. This is a density dependent factor so eggs can be more or less vulnerable based on how many fish there are.
Describe two factors or stresses that influence fry-to-smolt survival in Pacific salmon. (Extra: What exacerbating factors or considerations make eggs more or less vulnerable to these stresses?)
Food availability from small invertebrates (exacerbated by photosynthesis levels and primary productivity) and predation from resident FW fishes like sculpin and trout (exacerbated by the availability of refuge like LWD, undercut banks, and roots).
What is the difference between density-dependent and density-independent factors affecting salmon populations? Give an example of each.
Density dependent factors are factors that are made more intense by the number of salmon that exhibit that factor. An example is success of jacks, the more jacks there are the less successful they will be.
A density independent factor is a factor that is not impacted by the amount of salmon there are, an example could be
Describe three selective pressures favouring larger-bodied salmon and one selective pressure favouring smaller-bodied salmon.
Three pressures favoring large salmon are the ability to build deeper redds, are better at competing (males) and can carry more eggs (females).
One selective pressure favoring smaller salmon is that they are less likely to be eaten by bears.
Describe an example of an interactive effect whereby two or more stresses combine to exert a greater influence on salmon survival rates than either stress would individually. Be sure to describe the effects of each stress individually as well as how one might exacerbate the effects of another
An example is physical barriers in the river combined with predators. Barriers are often very energetically costly and can make it impossible for some salmon to pass either at the time or all together. Adding in predators like bears makes it even harder to survive past the barrier.
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