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23 Cards in this Set
- Front
- Back
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What's absolute |
Actual number of fish in a population or particular age class at a specific time
As its impossible to collect all fish in a stock in one place to be counted |
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What' s relative |
A statistics that reflects the changes in the number of fish without an exact count |
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Absolute or direct abundance estimates |
Usually made when there are aggregations of the entire populations for a particular purpose
Most anadromous fish__alewifes
Lake dwellers---walleye
River dwellers--salmon and diadromous fish |
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Pelagic fish |
May aggregate in particular spawning sites--known and unknown--herring |
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Anadromous fish 1. Run tracking |
1. Vessels use sonar to estimate density and size of passing schools 2. Verify sonar estimates with test fisheries to calibrate sonar scans 3. Obtain absolute number of fish along with samples to identify the SPECIES+STOCK 4. Sample include scales, tissue, parasites, otoliths |
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Run tracking Absolute abundance estimates |
1. Are used to confirm the predictions that were made by modeling before the run actually started 2. Are used for in season catch allocations and management decisions-not used for forecasting future runs |
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In river-hydroacoustic estimates |
1. Sonar based 2. Ex Didson-dual frequency identification sonar a. Counts fish passing a point in the rover to gave absolute abundance estimates b. Provides size, species, fry/adults c. Can be mounted on vessels for transact work |
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Anadromous fish Counting fences |
Set up on many river systems and take various forms to make fish visible to observation technicians on an overhead platform |
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Anadromous fish In rivet surveys |
Employ a variety of techniques that make individual fish mountable 1. River walks(pole counts) 2. Scuba surveys 3. Aerial overflight Issue: observer experience differ per group so true numbers may vary Observation are combined with statistical methods |
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Dead pitch counts |
Issue: counts are biased by fish which wash down stream after death or consumed by scavengers
Remove tail or head to prevent double counting |
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Sessile fish Transacts |
A straight line of narrow section the earths surface, along which observations are made or measurements taken
Used to reduce the number of fish that need to be counted to reduce costs$$$ |
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transacts issues |
1. Observer error 2. Accurate species identification 3. Incorrect identification of strata categories 4. Variation observation due to visibility |
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Quadrat counts |
1.similar to transacts except that rather than counting in straight line, squares of specific size (quadrats) are used 2. Quadrats place randomly in different strata 3. All animals in the quadrat ate counted and identified |
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Mark and recapture population estimates |
Have long history and mathematical calculation that accompany them have become increasingly complex as the techniques have developed |
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MR estimates give |
1. Estimate of number of animals in a population 2. Mortality rate 3. Population geographical range 4.individual growth rates 5. Range of recruitment 6.ageing validation of species 7. Migration patterns |
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MR population estimates |
1.Sample of individuals from the population are marked a d released back into the population 2. A second or more samples are taken and the RATIO of marked unmarked recorded 3. Many different types of tags or marks available for fishery biologist 4. Each tab has advantages and disadvantages specific to the species being markes , the snapping gear and the environment |
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MR recapture external tags Tag come in several formats such as |
--Spaghetti --disc tags --peterson disc --streamers --harpoon Internal anchor |
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Advantages of MR recapture extern tags |
1. Cheap and can be individually markes or numbered 2. Rapid application(+\anesthesia) 3. Used on wide variety of fish size 4. Easily recognized on fish in water 5. Good retention depending on species |
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Disadvantage of MR external |
1. Hard on smal fish 2. Loss of tage- intraspecific aggression 3. Affect fish behavior 4 affect survival- attracts predators 5. Unreadable with age, abroskon and sun exposure 6. Can affect catchability |
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MR internal body tags |
Advantage 1. Excellent retention 2. Little effect on fish health 3.tag rotten information does not fade 4. Can be metallic or magnetic permit easy recovery at processing plants
Disadvantage 1. Fish must be anesthetized 2. Move complex than external tagging 3. Tags not seen in water 4. Fisherman do not find tag when filleting fish 5. Must kill fish to recover 6. Cost increases |
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MR calcein scale tagging |
Impregnates calcium concentration within scales and rays-- observed with UV light |
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Advantage and disadvantage of MR CALCEIN SCALE TAGGING |
advantage 1 good for marking very small fish 2. Simple to mark large numbers in a short period of time 3. Mark is permanent and can be recovered non lethally
Disadvantages 1. Cannot be seen on fish while in water 2. Requires specialized fluorescent light for detection 3. Marks may become obscured when fish grow to a large size |
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MR other tagging system |
1. Freeze and heat branding 2. Fin clipping Disadvantage 1. Don't allow the identification of individual fish 2. Can't be observed easily underwater 3. Can cause behavioral issue 4. Significant mortality effects |
