L1 Intro to fisheries/L2 types of fisheries & fish capture methods
L2 types of fisheries & fish capture methods
L3: Calculating statistics for stock
assessment
assessment
L3: Calculating statistics for stock
assessment/L4: Introduction to Stock Assessment
assessment/L4: Introduction to Stock Assessment
L4: Introduction to Stock Assessment/L5: Data collection for stock assessment
L5: Data collection for stock assessment
L5: Data collection for stock assessment/L6 Salmon Stock Assessment
L6 Salmon Stock Assessment
L6 Salmon Stock Assessment/ L7 Fish Stocking
L7 Fish Stocking
L7 Fish Stocking (cont)
L7 Fish Stocking (cont)
100
Define a sustainable fishery (4)
1. Fish population large and stable
2. Harvesting methods do not destroy habitat
3. Fisheries have low by-catch
4. Low environmental impact, including carbon footprint.
100
Advantages and disadvantages of gill nets
Advantages
- low effort, especially if left in the water for a long time
- Not a lot of skill/experience required
- Can be size selective based off mesh sizes
Disadvantages
But also size biased
• Very dependent upon fish activity/location
• Can damage fish (may not be appropriate for certain markets) •
Not species selective
100
Measures of body condition (4)
1. Fultons condition factor
2. Relative weight (Wr) condition factor
3. Regression of length-weight data
4. Physiological measures
100
Explain proportional stock density (PSD)
- Stock density indices are also used to assess size structure
PSD = number of fish >= quality length x 100
Quality length = length preferred (by anglers)
Stock length = minimum size at which anglers catch fish (either legal, or possible)
100
How to use the MSY curve
1. As development proceeds you monitor fishing effort as it increases slowly and gradually, while monitoring yield so you can plot the catch curve
2. Once the fishery has reached the top of the curve (and yield begins to drop), you have found the MSY
100
Effort
number caught per unit effort (CPUE) is a relative abundance index
• Absolute abundance is desirable but costly (OR IMPOSSIBLE)
100
Pros and cons of aerial surveys
Pros
- Sample entire lake, can get an idea of where people prefer to be (popular fishing holes)
Cons
- rental cost of plane (gas)
- bad weather prevents flights
100
Pre-season forecasts of salmon returns are based on biological and/or statistically based models
Variables typically used in the production of stock forecasts (4)
1. Historic trends in escapements and total returns
2. returns of sibling age classes
3. Returns and escapement of the brood (parental) year
4. environmental conditions (just recently)
100
Mark recapture programs
• A statistically based enumeration method which provides a population estimate rather than an absolute count
100
Effectiveness problems
- often found to be ineffective or even detrimental to wild populations
- stocked fish may merely compete with wild fish (system is unable to support any more individuals) = replacing natural populations, not supplementing them
100
Fall fry (<5 g)
appropriate for remote access (most fish per volume) in a productive monoculture environment (i.e., no competition or predation), cost-efficiency (lowest cost per fish), and to reduce the incidence of early maturation under some conditions.
100
Fraser Valley 3N
200
Types of Fisheries (3)
1.Commercial
2. Subsistence/traditional
3. Recreational
200
Advantages and disadvantages of hoop nets
Advantages
- Fish usually not harmed (drawstring at cod end)
- Highly selective
Disavantages
- highly selective, depends on management objective and hypothesis
- Can fill up with fish, they thrash around and can hurt each other, can become full which makes population estimates difficult.
200
Fish weight tends to increase with the cube of length, what is the condition factor index equation
W= aLb
W = Weight
L = Length
a and b are population specific constants
b = 3 when fish growth is isometric but can range from 2.5 - 4.0
200
Explain productivity indices
•the capacity of a lake/stream to support fish populations is very important to the fishery manager
•therefore have research into predicting fish standing stock and yield given some parameters of a water body
•earlier, used lake surface area and depth, then added nutrients to mode
200
Negatives of the MSY curve
• Unfortunately, you cannot find the top of the curve until you have gone “over the top”
• The more “noise” in your data, the further over the top you have to go
200
Number caught per length interval
Gives:
- length-frequency distribution
- age structure of population (look for weak age classes)
- growth
200
Mail and telephone surveys
• collect data on earlier trips
• sample population comes from list of names from fishing licenses, boat registration, etc.
• sample randomly from list
200
In-season activities; Often, the ocean fisheries in which returns are first detected are on mixed stocks, and mechanisms to differentiate stocks must be in place.
Techniques to differentiate stocks (3)
1. DNA analysis
2. scale analysis
3. Coded wire tags (CWT) from hatchery produced fish
200
Assumptions of mark recapture programs (8)
1. All salmon have equal probability of being caught (application) and recaught (recovery)
8. All tagged salmon are recognised and reported on recovery
200
Stocking objective; restoring fish stocks
- restoring fish stocks which had been eliminated or severely reduced in abundance
- stocking is a much easier technique than enhancing critical fish habitat, or reducing harvesting levels (e.g. Coho salmon)
200
Fingerling (5-9 g):
appropriate for remote access, cost-efficiency, some adaptive advantage associated with less time spent in hatchery.
200
Horsefly River
300
Define a commercial fishery, explain small scale vs large scale
Commercial: Any fishery that harvests and sells fish (or invertebrates) for profit.
Small scale: Usually labour-intensive (low CPUE - catch per unit effort) with relatively small boats and low fuel consumption. Often family owned. (e.g., artisanal, independent salmon fisheries)
Industrial: Fisheries with high production capacity and CPUE. Capital-intensive, highly mechanized with high fuel consumption. (e.g., Many shrimp, tuna, herring and anchovy fisheries)
300
Advantages of fyke nets
- Good for species that are mobile and like to seek cover eg pike and bass
- Can also be used for migratory species that are known to cruise shorelines (e.g. salmon)
300
Explain the fulton's condition factor (k) and provide the equation
First index used to describe fish condition (1950’s)
• Assumes isometric growth (fish shape does not change with growth, b = 3)
K = (w/L3)(x)
k= condition factor
W = weight
x = Scaling constant usually applied to get integer value (100,000 for salmonids using g and mm) ]
L = Length
300
Define MEI and the equation
Morphoedaphic Index (MEI) of Ryder et al. 1965 (Canadians, eh! ) used internationally to assess potential fish yield in lakes based on physical constraints on productivity
MEI =
conc. of total dissolved solids (TDS)/ mean depth
300
Explain the demise of msy
up to the 1980’s, MSY was considered the ideal target reference point for determining catch levels
• *Larkin argued that MSY is problematic for many reasons but most importantly it does not account for environmental variation!
• MSY still used as a reference point BUT now viewed as the upper limit of catch that should be avoided!
300
Habitat caught
location gives spatial distribution
• E.g., young vs. old fish have different preferred habitats, so use fishing regulations to protect weak age classes
300
Pros and cons of mail and telephone surveys
Pros:
• inexpensive, good response rate
Cons:
- biased (not all anglers have boats, for example)
- people's memory may not be accurate
300
In season activities; Catch monitoring First Nations fisheries (4)
• Most major First Nations salmon fisheries, including the Fraser River fisheries, are monitored and sampled and regular reports are produced
• Some First Nations fisheries that involve pilot sales have mandatory landing programs
• Other fisheries are monitored through catch and effort sampling programs and census data
• Most monitored by First Nations' technical staff
300
Mark recapture recovery data formula for total population
Peterson formula
300
restoring fish stocks
Shortcomings (2)
i. since lost or endangered, number of suitable adults available for brood stock is very low
ii. Doesn’t address what caused the decline in the first place (e.g., excessive fishing, habitat damage, blocked access to spawning area)
300
Yearling (10-25 g)
better survival especially where other species occur (competition/predation pressure), some cost-efficiency (compared to catchables), slight adaptive advantage over catchables
300
Types of hatcheries (3)
i. Production Hatchery - Produce large numbers of fish (to support stockingdependent fisheries)
ii. Supplementation Hatchery - Utilize wild-caught broodstock with sophisticated breeding programs - Produce fish that will spawn naturally (but still focused on production!)
iii) Conservation Hatchery - Focus is gene pool preservation - Population recovery (e.g., restore or rebuild spawning runs) - E.g., White Sturgeon recovery (Nechako, Columbia hatcheries), Lake char
400
Define Subsistence/traditional, give an example
Subsistence/traditional: Fish are caught and consumed directly by fishing families or communities.
• Pure subsistence fisheries are rare as fish are often exchanged for goods/services!
• Traditional fisheries or often tied to religious practices or cultural value; many crossover into commercial fisheries.
e.g., Eulachon dip-net fishing by First Nations – coastal BC
400
Advantages of trap nets
- good for trapping migratory species that follow a known route (historically used for salmon in BC)
400
Problems with K
• cannot compare different species or between different age groups (because b does not equal exactly 3!)
• *Using K has serious size bias*
• To use K correctly, it should be tested within length range you are applying
400
What is a fish "stock"?
A “stock” is generally a subpopulation that is isolated from other members of the same species either by space or time (often genetically distinct)
400
Best practice as an alternative to MSY
Ecosystem based fishery management
400
Age, maturity
Gives population structure, age-specific mortality
• Age related to length also gives growth
400
Citizen science databases
e.g., iBobber Fish Deeper Smarter MyCatch
-iBobber data complements creel survey data for fisheries management/ invasive species management
-study by Friske et al. 2020 used iBobber data to show that many fishing trips had travel between lakes within time frames that allow invasives to survive the trip
400
In season activities; Catch monitoring Recreational fisheries
Most major in tidal and non tidal sport fisheries (3)
1. Creel surveys
2. Vessel counts (via aircraft overflights)
3. Logbook programs (fishing lodges and charter operator)
*creel surveys tend to operate during peak fishing times only
400
Explain the variables in the Peterson formula
N = population estimate
C = number of fish tagged
M = total number of carcasses recovered
R = number of tagged carcasses recovered
400
Stocking objective;
Establish fisheries in newly created habitats
• when first filled or established there is no natural fish population
• thus, a fishery (usually sport) can be created without impacting natural fish populations (beyond the impact of the dam, that is)
400
Catchable
-appropriate in urban setting or high creel areas, immediately available to fishery, most expensive to raise
400
Production Hatchery
- Produce large numbers of fish (to support stockingdependent fisheries)
500
Define Recreational Fishing
• Recreational Fishing: Fishing for recreational purposes (leisure, challenge) and personal use. Does not include sale or trade.
• Federal survey in 2010 showed Anglers contributed a total of $8.3 billion to Canadian economy.
500
Why did K’ómoks First Nation fishers stop using these fish traps? (3)
1. Smallpox epidemic of 1862 reduced the population size (think Thanos), requiring fewer fish, and killing knowledge keepers
2. The Canadian government then banned trap nets (and actually destroyed them), preferring to have commercial fishers catch salmon for canning
3. The Residential school system, which prevented the passing on of knowledge of this traditional fishing technique
500
If you were wanting to compare among populations better to use what condition factor?
What is the eqauation?
Relative weight condition factor (Wr)
Wr = (W/Ws) x 100
Wr = Relative weight (expected range 95-105%)
W = weight
Ws = standard weight for specimen of measured length
500
What is stock assessment?
"involves the use of various statistical and mathematical calculations to make quantitative predictions about the reactions of fish populations to alternative management choices
• stock assessment forms the foundation of decision making for fisheries managers
500
Genetics
• Until recently, genetic analysis too expensive
• Used for fishes with high commercial or conservation value
500
Considerations for all methods of sport fishery sampling (5)
- problem here is that you get a biased sample, in terms of size of fish, species caught
• you will want to use proper biological sampling (netting, etc) to correlate angler catch with what's in lake
• basic unit of fishing effort is the angler-hour (one hour of active angling by one angler) (also have angler-days, boat-trips, etc.) For all of these methods: 30
• want to assess number, or biomass of fish caught
• also may want to measure other, non-stock assessment data such as angler satisfaction, and economic benefit, at the same time
500
In season activities; Catch monitoring Commercial fisheries (3)
- harvesters are now required to fill out logbooks of all catches and participate in various hail-in programs
- in some cases, independent observers are a mandatory requirement to verify catch data to managers
- mandatory landing slips (official records of salmon sold), also provide catch information
500
Independent measures of stock size (6)
1. Egg and larval surveys
2. Juvenile fish surveys (e.g., Inclined plane and rotary screw traps)
3. Tagging
4. Acoustic surveys, including DIDSON, ARIS
5. Use of drones (adults, redds)
6. Resistivity counter
500
Establish fisheries in newly created habitats
Local example, concern and solution
• when a natural pond did not pre-date the mine; (e.g., Trojan Pond at Highland Valley Copper)
• concern regards the possibility of the new fish escaping the new habitat and invading adjacent waters which do already contain these fish
Solution?
Use sterile stocks or stocks from similar habitat within region
500
Non-reproductive strains (3)
i. triploid
ii. all female
iii. triploid all female
500
Supplementation Hatchery
- Utilize wild-caught broodstock with sophisticated breeding programs
- Produce fish that will spawn naturally (but still focused on production!)
600
Types of fish capture methods (2)
Passive and active capture
600
Best use of weirs and fish fences and there problems
Best use
- Especially good for migratory salmon and trout (used as counting stations in bc)
Problems
- Vulnerable to high flows and may log up with debris so must be maintained
- Chinook salmon tend to avoid them
600
What does the relative weight provide?
- get standard weights from weight-length relationship published for the species
- Useful because it allows you to make direct comparisons of different sizes and species of fish and provides a benchmark for evaluating the health of a population
600
Reasons why quantitative data is necessary in stock assessment (3)
1. Forecast future abundance
2. Set (or adjust) harvest rates
3. Assess health of stocks
600
Take home message when it comes to the role of a stock assessment
provide an estimate of the amount of natural variability, and to help design a management plan that takes this variability into account.
Political and biological forces surrounding commercial fisheries often lead to depletion, collapse or extinction of fish populations (Ludwig et al. 1993) – best to use precautionary principle!
600
Angler satisfaction
E.g trophy fish vs "kid fishery"
600
Sampling commercial considerations (3)
• information needed: catch, effort, biological characteristics of the exploited stock, and economic information
• Important to use combination of fishery-dependent and fishery-independent data
• Procedures for commercial catch sampling developed by region and often for specific fisheries (refer to DFO website)
600
In season activities; escapement surveys
(reminder: escapement is the number of salmon that reach the spawning grounds after "escaping" the fisheries)
• done with a range of partners, including First Nations and local community organizations
600
DIDSON sonar for salmon enumeration
Sonar mounted on a bracket by the river shore, takes snap shots 4x/second, it then stores these snapshots in 20 minute segments, with 4800 frames per segment, and 72 segments per day.
• watch the previous’ day footage at about 60 frames/second and thus can watch a 24 hour period in a couple hours
600
Stocking objective; Creating stocking-dependent fisheries
Objectives of creating stocking-dependent fisheries (4)
1. Provide “catchable” fish in marginal habitats unsuited for long-term survival, growth, and reproduction. (e.g., stock lakes for spring fishing, where the lakes are too warm in the summer to support fish) 19
2. Provide fishing near large population centers. Such waters are often not suited to natural production of desirable gamefishes, or natural production is insufficient to satisfy angler demand
3. Divert fishing pressure away from wild populations onto stocked fish
4. Improve the ability of weak fishers to catch fish (and thus enjoy the experience of fishing, since stocked fishes are often perceived to be more easily caught than wild ones)
600
Triploid (3N) fish
-technique results in the retention of the second polar body normally extruded shortly after fertilization, creating three sets of chromosomes instead of the usual two sets
600
Conservation Hatchery
- Focus is gene pool preservation
- Population recovery (e.g., restore or rebuild spawning runs)
- E.g., White Sturgeon recovery (Nechako, Columbia hatcheries), Lake char
700
Define Passive fish capture
The fish or invertebrate is captured by a stationary net or device
700
Uses for pots and there problems
Uses
• containers for crabs, lobster, etc.
• usually baited
• includes Gee traps (minnow traps)
• highly selective
• can release unharmed if monitored properly
Problems
- Traps may fill with crabs and can lead to underestimates of population size.
700
Limitations of the Relative weight condition factor (Wr)
- Although single growth equations for species are generally used, this does not account for differences in body forms between habitat types (e.g., lentic and lotic)
- Many different approaches to determining Ws (standard weight) criticized for lack of standardization.
700
Basic population growth metrics in stock assessment (3)
1. Growth
2. Mortality
3. Recruitment (most variable factor affecting dynamics, is the number of fish entering the fishery)
700
Considerations for Sampling (3)
1. Bias and Precision:
2. Standardized sampling
3. Sampling Design
700
Sampling the sport fishery (6)
1. Creel survey
2. Angler diaries
3. Fishing tournaments
4. Aerial surveys
5. Mail and telephone
6. Citizen science database
700
Sampling the commercial fishery:
Catch generally divided into 2 parts:
1. Part of catch kept for its commercial value
2. Part of catch discarded either at sea, or at dock
*Note: Bycatch particularly difficult to quantify!*
700
Escapement survey techniques (3)
1. Counting fences (mostly sockeye & coho, not chinook)
2. visual surveys (bridge counts, aerial surveys, stream walks and tower/dam counts) - drones to become more common
3. Mark recapture program *(gold standard)*
700
Management objectives of stocking (4)
1. Supplement wild populations
2. Restoring fish stocks
3. Establish fisheries in newly created habitats
4. Creating stocking-dependent fisheries
700
trout very common (Why?)
• grow well at low temps, can be reared all year long in hatcheries; warm-water species would stop growing in the winter)
700
Benefits of triploid (3N) fish
- increased size due to the fact that energy usually diverted into reproductive development can go to somatic (body) growth
- fish are unable to reproduce or mate with other hatchery or wild individuals (avoids hybrids with other salmonid species, or mixing genes of same species)
700
something you should never do
Never stock a non-native species into an existing water body with fish
800
Define active fish capture
The fish or invertebrate is captured by a mobile net or device
800
Best use for longlining and its problem
Best use
Used for halibut black cod and dogfish (BC)
Problem
- Non-selective, bycatch rate is usually very high
800
Accepted form of regression
-Although non-linear regression can be used to estimate b, ordinary least squares regression on transformed data is much easier (accepted method)
- Body form can change with increasing length (allometric growth, b is not always 3!
800
Explain fishery dependent surveys
involves collecting/analyzing statistics from the commercial or sport fishers - the fishery itself is seen as the best way to gather information about the stock
• data usually involves the total catch and an indication of fishing effort (may also include spatial mapping of fish abundances, size and age composition)
• the catch per unit effort (CPUE) is assumed to be proportional to the actual stock size
800
Bias and precision how to mitigate it? (2)
1. need to catch a sample that is representative of the population e.g., is net selective for certain size categories of fish?
2. Can use 2 or more sampling methods to look for biases in your data
- Lack of precision can result from small sample size more intensive sampling may increase precision & reduce bias
800
Creel survey
• surveyor goes person to person asking about catch statistics
• note that creel survey is better term than creel census, which implies a complete enumeration of the entire angling population
800
General, considerations with sampling of commercial fisheries (6)
- commercial fishers often lump several species into one market category (e.g., a can of ‘sardines’ could contain many species under this category)
• landings usually done by weight, not number of fish (e.g., global catch = 90 MT)
• Independent sampling often done at the dock to obtain other information (length, age, DNA etc.) = port sampling or dockside monitoring General notes on estimating catches: 34 Where and when fish caught:
• where a fish is caught is important b/c management often done at level of unit stock (can now be confirmed with genetic testing - used to combat fisheries fraud!)
• timing important to partitioning of fishing effort (e.g., may be needed to resolve gear conflicts)
800
Define test fishing
the act of fishing with a specified gear type (gill net, seine etc) in order to catch a representative sample of fish in an area (cant be bias)
800
Supplement of wild populations
• theory/concept is to produce more individuals than nature can produce by itself (a “value-added” or “enhanced” fishery)
800
Two major ways of supporting stocking-dependent fisheries
i) put-and-take fisheries
ii) put-grow-and-take
800
Further effects of triploiding fish
Females
-hormonally and functionally sterile (i.e., no ovary development or behaviour changes)
900
Types of passive fish capture (3)
1. Entanglement
2. Entrapment
3. hooks
900
Pole and line best use/advantage and problem
Best use
Tuna
Advantage highly selective (only keep target species)
Problem
- Operators concentrate tuna using boat as an aggregating device.
900
Explain the single regression equation wrt fisheries
Explain the ln (W) equation
• Single regression equation describes entire population (using slope or intercept of line as an estimate of c.f.)
• Good for comparing same population over time (but limited to outside comparisons)
Differences in regression lines can be statistically compared - Confidence intervals, overlap or use ancova
900
Problems with fishery dependent surveys (2)
1. Fishers are not random - good fishers go to places where the fish are concentrated, so CPUE remains high even while the stock is being depleted.
2. Honesty of the part of fishers - fishers may underreport catch or misidentify species.
900
How to standardize sampling
- Same timing (season), gear, sites, and effort to allow comparison of different samples over time
900
2 types of creel surveys
1. Roving
- talk to anglers onsite
- surveyor moves among anglers by boat or foot
- *very important to identify yourself as a data collector not law enforcement
2. Access point
- sample at boat launch, dock or pier.
900
2 factors important in estimating effort
1. type of Gear; motor & boat size (length or tonnage), number of units boats crab pots sonar, etc.
2. Time: hours gear in water
900
Purpose of test fishing
The purpose is to assess the fish stock from a specific location for a particular time.
Test fish information may indicate the stock abundance, fish behaviour, species composition, and provide biological samples (scales, tissue, fins, etc.)
900
Problems with supplementing wild populations (3)
1. Genetic effects
2. Increased catch of wild stocks
3. Effectiveness
900
Put-and-Take Fisheries
• fishes are stocked at a “catchable” size, and so are immediately available for harvest (sport fishing)
900
Males
- infertile, but still produce hormones that cause changes associated with maturation including deterioration of flesh quality, early mortality, development of testes, and secondary sex characteristics
- demonstrate “false” spawning behaviour, including migration and interactions with other fish on the spawning beds
1000
Types of active fish capture (5)
1. Trawl
2. Seine
3. Dredge
4. Troll
5. Other
1000
Trawl best use and problems
Best use
- Smaller pelagic open water species
Problems
- Non-selective (but recent modifications have improved selectivity for some fisheries)
- Habitat impacts
1000
Interpreting slope (b) as CF
Consider 3 as CF = or > or <3
CF = 3 ideal conditioned fish
CF > large fish lower stocking densities
CF < Skinny fish, higher stocking densities
1000
Explain fishery independent surveys and its problems
- Conducted by a management agency with its own vessel and crews
Problems
very expensive/limiting because can only have so many research boats out at one time (c.f. the commercial fleet)
1000
How would standardizing impact bias?
doesn't eliminate bias but holds it constant
1000
A good roving creel survey will (4)
1. cover entire lake
2. start at randomly chosen spot, random direction from here
3. travel at constant speed
4. if can't visit all anglers, systematically skip some (e.g., sample every 3rd angler)
1000
Problems in determining CPUE (3)
1. Trip limits (i.e. maximum catch allowed per trip)
2. New technology (fishers get more efficient)
3. Experience of fishers
1000
Most common test fishery Pacific region (BC)
Pacific salmon and herring
1000
Supplementing; genetic effects problems
Managers must limit the effects of (3)
1. Inbreeding
2. Genetic drift
3. Domestication
1000
When to use put-and-take (3)
And benefit cost
1 When self-sustaining population cannot be established
2 When survival of stocked fingerlings and fry is too low or uncertain to maintain a desirable fishery
3 When there will be only a short delay between stocking and fishing (want fisher's to catch soon after stocking or investment will be lost)
Benefit public is happy more cost to producing larger fish
1000
All-female (AF)
-production of all-female populations of fish is labour
-intensive -produced by crossing sex-reversed females with normal females
-to create sex reversed females, normal fry are exposed to testosterone derivatives to halt ovary development and produce normal testes
1100
Example of entanglement
- Fish entangled in mesh
Gill and trammel nets (can damage the fish)
1100
2 major types of seines
1. Beach seine
•small mesh size to avoid “gilling” fish •
small nets handled with poles, whereas large ones require spreaders
2. Purse seine
• net floats well above bottom
• a rope or wire cable is strung through rings along net bottom and is used to pull up the net like a purse-string
• targets schooling fish (e.g., sockeye, herring, tuna)
1100
Physiological measures of condition
Relates directly to composition of body tissues (e.g., evaluation of fat or protein content)
* gonado-somatic index (proportion of energy that goes to gonad production
liver somatic index (ratio of liver to body weight minus gonads)
% composition indices
• Can provide more precise measure of actual fitness in terms of stored energy
• Usually lethal sampling, more costly D) Physiological measures of condition: 20
• e.g., Bioelectrical Impedance Analysis (BIA): • electrical impedance correlated with fat content
1100
Potential solution to problems with fishery-dependent and independent surveys
Co-operative management
1100
What would sampling design entail? (3)
- Design should be appropriate for objectives
- Probability sampling (when all possible samples are included in the selection process – i.e., random sampling) is required to make inferences about entire population
- Nonrandom sampling commonly used in fish surveys!
1100
Pros and cons of roving creel survey
Pros:
- surveyor can ID fish, even if angler cannot
- immediate, so don't depend on fisher memory
Cons:
- high cost per interview
- limit to how many anglers you can contact
1100
DFO'S stock assessment process for salmon split up into 3 seasons/steps
1. Pre-season forecasts
2. In-season stock assessment and re-forecasting of run sizes
3. Post-season evaluations
1100
Inbreeding
-special care must be taken in hatcheries to avoid crossing closely-related broodstock. When offspring are produced from parents sharing one or more recent ancestors they may be subject to inbreeding depression (may result in reduced fitness)
1100
Put-grow-and-take fisheries
Fishes are stocked as fingerlings or fry, with the expectation that they will survive and grow to a size suitable for harvest
1100
Benefits of All-female (AF) fish (3)
-slower maturation in females compared to males, and therefore more time available to the fishery
-larger fish -no male drop-out from the fishery associated with precocious maturation (or “jacking”) and high post-maturation mortality.
-stocking of all-female progeny in the absence of males effectively creates a functionally non
-reproductive population Note: this won’t work if anglers transfer 2N males to the lake…
1200
Entrapment method examples (5)
1. Hoop nets
2. Fyke nets
3. Trap nets
4. Weirs and fences
5. Pot traps
1200
Dredges how they work and problem
• drag gear along bottom, targets benthic organisms (shellfish mostly)
• modern dredges:- use water jets to loosen the bottom in front of rakes (water pumped down from the boat in a large hose)
Problem
- Destruction of bottom habitat (can denude bottom complexities, affects benthic spawners)
1200
Explain Relative abundance
absolute abundance is hard to get (intensive netting, mark-recapture, etc.) so use relative abundance
• Reminder: CPUE is considered a relative abundance index
• good for making temporal or spatial comparisons
• if a high correlation exists between relative abundance and absolute abundance then the CPUE can be used to estimate actual stock size
1200
How could co-operative management work? (3)
1. Provide incentives for fishers to work with agency by spending part of their time fishing "for information", in a designated research design (e.g., fish along transect lines defined by agency)
2. Get to keep "research fish"
3. may get preferential access to the best fishing areas and times
Ultimately on board observer's could provide more accurate reporting
1200
Statistics collected from a simple survey (9)
1. Length and weight
2. Overall health/appearance
3. . Number and biomass
4. Effort
5. Number caught per length interval
6. Habitat caught
7. Age, maturity
8. Genetics
9. Angler satisfaction
1200
Pros and cons of access point creel surveys
Pros:
- fishing trip is completed, so get more complete info - get to talk to more anglers
Cons:
- there may be several access points to a lake
1200
Pre-season forecasts
used in pre-season planning and stock status reports to identify (3)
1. longer-term trends in stock abundance
2. key conservation concerns
3. outlooks for the future
1200
Genetic drift
changes in genes due to random events rather than from natural selective pressures – can result in loss of genetic diversity which can reduce the ability of population to cope with change
1200
When to use put-grow-and-take (3)
1. When survival of young fishes is consistent on a yearly basis
2. When immediate fishing after stocking is not a management goal (need time to grow)
3.Useful in heavily altered habitat or overfished areas where there will not be much competition with established individual's
1200
Strains of RB (4)
1. Wild Pennask and AF3N
2. Blackwater
3. Fraser Valley 3N (domesticated strain)
4. Horsefly (latest)
1300
Hooks methods examples (2)
1. Longlining
2. Pole and line
1300
Define trolling
• large number of hooks dragged behind a boat
• targets individuals, not schools
• e.g., chinook salmon in BC (usually ~40 hooks), albacore tuna
1300
CPUE is considered
a relative abundance index
1300
Long time fundamental tenet of traditional fisheries theory wrt fishing effort-average catch relationship
Repeatable relationship between fishing effort and average catch
1300
length-weight
• length-weight relationship shows overall health, growth (plumpness!)
• used to calculate condition factor
1300
Angler diaries
- ask certain anglers to keep a "log" of their fishing effort and harvest
1300
In-season stock assessment and re-forecasting, of run sizes is done using information gained from (3)
1. test fisheries
2. catch monitoring programs
3. escapement surveys
1300
Domestication
-results from selective forces of the hatchery environment (genetic) as well as behavioural (aversion to predators, feeding, increased aggression)
1300
Benefit (2) cost of put grow and take
1. Rearing fingerlings is less expensive than rearing larger fishes
2. After stocking, fingerlings adjust to natural habitats and behave more like wild fishes than do fish stocked as catchables (i.e., produces a more natural fishing experience)
Cost
•Size of fish stocked based on cost of rearing individuals to a particular size compared with the survival of fishes after stocking
1300
What strain to stock?
The strain of trout stocked depends on several factors (3)
Lake physical features include: -temperature, pH, winterkill, abundant shoals, depth, oxygen levels Lake
biological features include: -productivity, prey fish species, wild trout present, competition and predation
Management objectives: - catchability, family/trophy, catch and release mortality, remote low/high use, urban, priority lake
1400
Characteristics of a gill net
• vertical wall of net anchored in water
• bottom is weighed down, top has floats
• use various mesh sizes, depending on objectives
• can set at various depths
• place in location where fish are likely to be
• can use in lake or river
• often kills or maims fish (destructive technique)
• Can use under the ice in winter
1400
Other types of active capture
Fish wheels
• Electrofishing (boat or backpack)
• Diving or direct underwater observation (e.g., snorkel floats)
• Toxicants or explosives
•Traditional traps, fences, dip nets, etc.
- Spearfishing (selective harvesting of invasive species)
- Drones
DIDSON, ARIS, edna
1400
Explain population structure
•analysis of the various size classes in a fish sample gives an indication of the age structure of the population
•the age-frequency distribution of a population gives the structure of the successive cohorts in that population
* changes in the proportions of cohorts over time can indicate Age specific mortality , or a sudden increase in mortality in the habitat*
• looking at modes in the distribution is a population aging method that is easier than aging using hard body parts (e.g., scales or otoliths)
1400
What does the assumed relationship between fishing effort and average catch graph look like
1400
Overall health/appearance
Look for evidence of disease, sores, tumors, ectoparasites
1400
Fishing tournaments
- very cost effective, as have lots of fishers in concentrated area
- problem is have "experts", so CPUE will be biased
1400
In-season data, provides information on (4)
1. run timing
2. stock composition
3. stock abundance
4. age structure
1400
Approaches to limiting genetic effects (2)
1. Take genetic strain of fish from the local area (most similar to local strain)
2. Use a mixture of strains, so that resulting fish have a wide range of genetic material.
1400
Examples of stocked species in bc (6)
Rainbow trout
Cutthroat trout
Eastern brook trout
Kokanee
Steelhead
White sturgeon
1400
Wild Pennask
1500
How are fish caught in a gill net (3)
1. Mesh holds fish by body (wedged)
2. Held by mesh slipping behind operculum (gilled - most common method)
3. Held by body part (spine, teeth) in mesh (tangled)
1500
Problems with the use of age frequency distributions (3)
1. Modes more distinct for younger fish
2. prolonged or intermittent spawning will blur together modes
3. hard to separate modes if the difference between modes is less than twice the minimum standard deviation
1500
What is the MSY dogma
MSY - any species each year produces a harvestable surplus, and if you take that much and no more, you can go on getting it forever and ever...
1500
Number and biomass
- estimate fish density
- species composition: predation, competition, resource use etc.
1500
Aerial surveys
• count anglers from plane/helicopter
• count boats & people (or even rods) in water and shore
• hard to see shore due to riparian cover
• only get idea of effort, not yield
Drones
1500
Post-season evaluations
use estimates of (6)
1. total run size
2. harvest rates
3. catches
4. effort
5. escapement
6. other factors used to assess whether escapement goals and other management objectives have been met
1500
Supplementing; Increased catch of wild stocks
Problems
- hatcheries produce lots of fish
- because of this, more fish are caught in the commercial fishery due to increased fishing intensity
- this results in an increased capture of endangered stocks
1500
Age of released
Size/age released is determined considering both production aspects as well as ecological aspects of the receiving lake
Considerations (8)
- Distance/access from hatchery
• Season of release
• Limitations of hatchery
• Probability that lake will winterkill
• Presence of predators and competing fish
• Type of prey present (small fish in addition to inverts)
• Proximity of lake to a city or town
• Priority of the lake
1500
Blackwater
