Fish Kills Flashcards
(21 cards)
Discuss 3 reasons it is important to investigate and diagnosis fish kills
Indicator of environmental change,
potential risk to humans, may
predict downstream events.
Legal obligations – Companies may
or may not be authorized to kill fish.
Fish kills may end up in court.
Fisheries management – fish kills
may influence how a population is
managed
True or False: Fish kills can occur naturally
True
Winter Kill - When biological oxygen demand (BOD)
exceeds what is available, fish may die due to
lack of oxygen
What fish symptoms, and environmental conditions are typically associated with a winter kill (oxygen related)
Fish Symptoms:
Lethargy - Reduced activity and sluggish behavior.
Gasping - Fish may be seen gasping for air at the surface
or near ice holes.
Mortality - Large numbers of fish may die, often observed after ice-out in spring.
Environmental Conditions:
1.) Ice Cover - Prevents oxygen exchange between water
and air.
2.) Lack of Light - Reduces photosynthesis, further
limiting oxygen production.
3.) Spring Melt - Oxygen levels typically replenish during
spring melt and turnover.
Fish Mortality: Larger fish tend to die first due to their body size to gill ratio, although some species are better adapted to low oxygen conditions.
Visibility: Fish kills may not be noticeable until spring when large volumes of dead fish are washed ashore.
What fish symptoms, and environmental conditions are typically associated with a summer kill (oxygen related)
Environmental Conditions:
- Summer kill can be caused by heat, DO depletion, and/or algal toxins.
- Associated with lakes with abundant rooted vegetation, heavy algal blooms, or high concentrations of decaying organic matter
- Eutrophic lakes more prone to summer kill – higher nutrient loads (more algal growth & warmer)
Fish Symptoms:
Lethargy
Gasping
Mortality
Why might we see die offs of Walleye, Northern Pike, and other spring spawners during the spring?
Rapid Temperature Changes: Sudden fluctuations in temperature can stress fish, leading to die-offs.
Stranding: Fish that have moved upstream to spawn may become stranded when water levels recede, causing temperature or oxygen stress.
Disease and Parasite Transmission: Crowding during spawning increases susceptibility to diseases and parasites.
Exhaustion: Fish may be in weak condition after a long winter and further exhausted from spawning, leading to mortality.
Why might oxygen become limited in the winter and summer in a stratified lake?
Winter:
1.) Ice Cover: Prevents the exchange of oxygen between
the water and the atmosphere.
2.) Reduced Light: Limits photosynthesis by aquatic plants
and algae, reducing oxygen production.
3.) Decomposition: Organic matter continues to
decompose, consuming oxygen.
4.) Stratification: Cold water at the surface and slightly
warmer water below create layers that do not mix,
trapping oxygen-depleted water at the bottom.
Summer:
1.) Thermal Stratification: Warm surface water and
cooler bottom water create distinct
layers that do not mix.
2.) Decomposition: Increased biological activity and
decomposition of organic matter
consume oxygen in the bottom layer.
3.) Algal Blooms: Can lead to rapid oxygen depletion
when algae die and decompose.
4.) Calm Weather: Reduces mixing of water layers,
exacerbating oxygen depletion in the bottom layer.
Can an oxygen kill occur during fall or spring turnover? Why?
Yes, an oxygen kill can occur during fall or spring.
Mixing - Spring turnover mixes water layers, causing
temporarily low dissolved oxygen (DO)
throughout the water column.
Decomposition - Organic matter from the bottom rises,
consuming oxygen.
Stress - Rapid changes in oxygen levels stress fish.
Mortality - Fish may die due to low oxygen.
Why might oxygen become limited after a big algal bloom?
Increase in BOD: Decaying algae increase Biological Oxygen Demand (BOD), rapidly depleting oxygen levels.
True or False : toxin related kills are more gradual than oxygen related kills
False.
Toxin-related kills are generally more gradual than oxygen-related kills. Oxygen depletion can cause rapid fish die-offs, often within hours, while toxin-related kills may take longer as the toxins accumulate and affect the organisms over time.
True or False: sudden changes in temperature can cause a fish kill?
True.
Sudden changes in temperature can cause a fish kill. Rapid temperature fluctuations can stress fish, disrupt their metabolism, and reduce the dissolved oxygen levels in the water, leading to mortality.
True or False: fish are immune to algal toxins
False.
Fish are not immune to algal toxins. While they may be more tolerant than humans or other animals, algal toxins can still affect fish, causing health issues and potentially leading to mortality.
True or False: Algal toxins are more likely to peak during the night period
False.
Algal toxins are more likely to peak during the day, particularly late in the morning to midday, when algae have access to sunlight and their growth is at its highest
True or False: Toxins tend to kill large fish, while DO depletion impacts large fish
False.
Both toxins and dissolved oxygen (DO) depletion can impact fish of all sizes, but the effects can vary:
Toxins: While fish are generally more tolerant of algal toxins than humans, toxins can still affect fish of all sizes. The impact may not be size-specific.
DO Depletion: Large fish are often more affected by DO depletion due to their higher oxygen requirements relative to their body size.
True or False: Neonicotinoids is a type of herbicide that can kill fish and other aquatic animals
False.
Neonicotinoids are a type of insecticide, not herbicide, and they can indeed harm fish and other aquatic animals
True or False: Fertilizers typically lead to an influx of Nitrogen and Ammonia in the water
True.
Fertilizers typically lead to an influx of nitrogen and ammonia in the water, which can contribute to nutrient pollution and eutrophication.
True or False: Acid waste from mining can mobilize heavy metals into the environment
True.
Acid waste from mining can mobilize heavy metals into the environment, leading to contamination of water sources and harm to aquatic life and ecosystems.
True or False: Septic systems can cause toxic levels of ammonia in downstream waterbodies
True.
Septic systems can cause toxic levels of ammonia in downstream waterbodies, especially if they are not properly maintained or if they fail, leading to contamination of water sources.
Why might we see fish kills after a heavy rain?
1.) Runoff: Heavy rain can cause runoff from urban,
agricultural, and industrial areas, carrying
pollutants like fertilizers, pesticides, and other
chemicals into water bodies.
2.) Nutrient Overload: Excess nutrients (nitrogen and
phosphorus) from fertilizers can lead to algal
blooms. When algae die and decompose,
they consume oxygen, leading to oxygen
depletion.
3.) Sediment: Increased sediment can cloud the
water, reducing light penetration and
affecting photosynthesis, which can lead to
oxygen depletion.
4.) Temperature Changes: Sudden influx of rainwater
can cause rapid temperature
changes, stressing fish.
Where do heavy metals typically accumulate in fish?
Metals can accumulate in liver and fats, and then
become toxic when fish use those fat reserves.
Heavy metal testing is usually done on the blood, brain and liver.
Explain the difference between impingement and entrainment?
- Impingement -
Impingement occurs when fish and other aquatic organisms are trapped against intake screens of water intake systems, such as those at power generating stations (hydro, nuclear) and various industrial facilities. This physical contact can cause injury or death as the organisms are unable to escape the force of the water. - Entrainment -
Entrainment involves small aquatic organisms, such as fish larvae and eggs, being drawn into water intake systems and becoming stuck within pipes or facilities. These organisms are carried through pumps and machinery, often resulting in injury or death. Entrainment can occur at power generating stations and other industries with water intake pipes.
“Branding” is a symptom of what type of fish kill?
“Branding” is often associated with fish kills caused by toxic algal blooms.
