Quiz 10 Flashcards
(26 cards)
What is special about watersheds in the Pacific Northwest?
They are intimately linked by nutrients provided by salmon, as they’re a keystone species
Why are salmon referred to as an Anadromous Nutrient Pump? (2)
They “pump” nutrients uphill against the force of gravity
They carry about the perfect 10:1 N:P ratio (3%N and 0.3%P)
How do scientists trace salmon nutrients? (2)
Salmon nutrients can be traced using stable isotopes of carbon 13 and nitrogen 15
This is because lighter isotopes are excreted, creating a heavier presence of C13 and N15
What are the pathways of influence on stream food webs? (2)
Salmon carcasses have nutrients and dissolved organic carbon in their biofilm which is eaten directly by invertebrates then by predators
Or nutrients, dissolved organic carbon, and particulate organic carbon are consumed by predators directly
What are some of the stable isotope studies that can be used to trace salmon nutrients, and what do they do? (4)
Sediment cores from sockeye lakes
Tree rings from riparian zones
Stream food web analysis
-all indicate that salmon nutrients strongly influence productivity and biodiversity of coastal and interior PNW
How do isotopes get into salmon?
Phytoplankton take up C13 and N15, which are then taken up by zooplankton, which are eaten by fish - all the while lighter isotopes such as C12 and N14 are excreted
Benefits of adding carcasses to the ecosystem (3)
Increase in biofilm
Increase in macroinvertebrates
Increase in size of juvenile coho
What is the evidence of nutrient loss in the Pacific Northwest? (5)
Only 5-7% of historical pre-European nutrients was reaching PNW prior to 2001
Watershed P and salmon landings have decreased markedly in the last 50 years
Impoundment effects are increasing
Prior to European arrival, aboriginal use of salmonids was in balance with production, and the majority of nutrients were recycled in the watershed
Now they aren’t because industrialized fishing increased in the 1880s with canning improvements
What are the compounding effects leading to salmon and nutrient loss in the Pacific Northwest? (6)
Deleterious effects of past forest harvesting practices
Extensive hydroelectric development
Urbanization and habitat loss
Climate change
Dramatic changes in ocean survival due to open net pen aquaculture
Increased marine mammal predation
Paradox between water quality and salmon (4)
Too few nutrients in upper watersheds and too many in lower watershed
Too much nutrients causes pollution
Too few causes depressed salmon stocks
Need to manage for both
What are some non-responses that have been observed with lake fertilization? (3)
Some non-responses have been observed in sockeye due to:
N:P imbalances
Non-target species responses
Light limitations reducing productivity (in glacial lakes)
History of Kootenay Lake
Nutrients were stripped from the some areas and pooled in some areas due to the trapping of nutrients behind two dams: the Duncan Dam and the Libby Dam
River impoundment response (3)
right after a dam is put in, the flooding causes a sudden increase in nutrients and productivity
Production then decreases and “busts” and continues very low in an ultra-oligotrophic phase
In Kootenay Lake, p loading decreased below historical loading after 1973 when the dams were put in and a fertilizer plant in Kimberley was closed down
What was another reason for Kootenay Lake’s low productivity?
Mysid shrimp additions in 1949 and 1950 which became invasive as they couldn’t be eaten due to their transparency so it made things worse by competing with Kokanee for nutrients
As the Kokanee collapsed, so did the Gerrard Rainbow Trout as they are “oblique piscivores”
This was compounded with predation from bass
What did Carl Walters argue? (2)
Fertilization may not be affective as increasing nutrients may just increase mysid, and remove more plankton
But he also recommended an experiment and fertilize it very carefully - worth a try
What was the experimental design of the Kootenay Lake fertilization experiment? (3)
7 sampling stations were set up throughout the lake
Nutrient loading was seasonally adjusted for adaptive management - fertilizer was reduced 40% from 1997-2000
All monitored for adaptive management: Total Dissolved Phosphorus Algal biomass Mysid density Kokanee Gerrards
Knowledge gaps in lake fertilization (5)
Main areas of uncertainty involve:
Understanding the implications of seasonal nitrogen limitation
Fine tuning of nutrient application (loading, P:N ratio, timing and dispersal method) to avoid large inedible algae
Relationship between Kokanee density, fecundity, and creation of cyclic dominance
Algal nutrients, fatty acids (EPA, DHA), and algal food quality
Long term responses of predators and/or competitors
What happened after lake fertilization? (3)
Lake initially recovered and Kokanee and predator abundance increased
However, from 2011 to 2015, kokanee abundance decreased rapidly and fish size increased, which was a sign of low population sizes
Potential egg deposition in Kootenay Lake also decreased rapidly
What happened from 2011 to 2015? (7)
There was a mass decrease in Kokanee
An increase in Gerrard from 2009 to 2012 which compounded bull trout predation
There was an increase in N and P nutrients
An increase in Secchi Depth (transparency)
An increase in edible algae
A decrease in mysids
BUT a mass increase in daphnia due to cloning and a lack of predators to the point where daphnia biomass > Kokanee biomass
Why did Kokanee decrease from 2011 to 2015? (2)
Because the fertilization program worked to increase daphnia, but the increase in Kokanee combined with a tightening of angling regulations led to a Gerrard rainbow trout outburst in 2009
Unusual fall abundance’s of daphnia since 2012 was an indicator of a major daphnia-Kokanee biomass imbalance
What were the three valid early warning signals on the dashboard from 2009 to 2013?
Gerrard increase in 2009
Low Kokanee numbers in 2013 (when it dropped below historical numbers)
Increase in daphnia in 2012
What was the PR model for nerkids? (4)
Model developed by Alaskan fisheries limnology staff to predict:
Optimal escapement of adult sockeye to spawn
Maximum number of smolts (usually 2 to 4 grams)
Maximum smolt biomass (kg)
What was the original model? (6)
Was called the Alaskan EV Model
Was a rearing capacity model using the average euphoric zone depth of the lake to predict sockeye rearing capacity
1 EV unit = 10^6 m3 of euphotic volume
EV units = EZDx (Area) / 10^6
Where:
EZDx = seasonal average euphotic zone depth (m) Area = lake surface area (m2)
What was the new model? (5)
DFO scientists refined the model by using actual primary production measurements in the lakes using 14C
PR unit estimated by actual 14C field measurements
PR unit = (0.0583 PRx + 3.25)Area/10^6
Where:
PRx = seasonal average daily PR (mgC/m2/d) Area = lake surface area (m2)
