Final Flashcards
name some examples of fishing effort for CPUE
- troller days
- seine sets
- gillnet hours
- demersal trawl hours
- skate sets
- trap or pole sets
demersal trawl hours, complications
the amount of time a trawler drags its net across the bottom, but it is complicated by factors such as the power of the fishing vessel, speed, etc
skate sets, complications
skates are long line, which have hooks distributed along them with various spacing
C: hook spacing.
trap or pole sets, complications
this is the catch in a passive fishing gear as is used for crabs, lobsters, prawns, and fish like black cods.
C: variation in spacing of the traps as competition btwn traps occur.
describe the varying degrees of refinement of CPUE
- # fishers using gill nets.
- kg of fish/fisher/month
- kg of fish/day (masks different fisher power)
- kg of fish/fisher/day/100m length of gill net. (most refined)
Describe Mortality Rate**, what two types are there,
what is the equation
the rate at which fish are lost from the population due to death.
-Fishing mortality: mortality caused by a fishery (F)
-Natural mortality: mortality due to natural causes
Z=F+M
Leslie Plot of Stock Depletion is used to calculate what?
catch per unit effort
fish abundance, catchability
Name the assumptions for CPUE
- no changes in fishing gear
- no changes in operating strategies
- no seasonal and daily weather affecting efficiency
- no immigration/emigration
- uniform fish distribution
- no recruitment
- no natural mortality
- no different gear types operating on a single fishery with different fishing power
- no catchability changes
what is the most important bias of all assumptions for CPUE? why?
Changes in gear
-as a fishery develops the gear develops as well, so a modern fishery may have the same numbers as a virgin fishery, even thought the modern fishery may have significantly reduced stocks.
in order to conduct 2 or 3 pass removals, how does the stream get divided?
into stratums, which may be riffle, glide, pool, or other. Then each stratum is randomly sampled to estimate the number of fish in it.
when electrofishing, how many passes should be made?
Ideally, what percentage of the population should be sampled in the first pass?
- 2, but 3 will give best results
- 80% on the first pass
name the 3 assumptions for removals method (EFing, etc)
- the population is closed
- the probability of capture (p’i’) in the ‘i’th samle is the same for each individual exposed to capture
- the probability of capture ‘p’ remains constant from sample to sample
why must the population be closed for the removals method?
because it depends on the decrease of the CPUE, so no immigrating/emigrating populations
what are two population data categories that serve to increase the biomass of a stock of fish as opposed to mortality which reduces biomass
growth of fish, recruitment
what is the difference between Linf and Lmax?
Linf is a size at which the increase in length is minimal (species)
Lmax is the measure of a specific stock
what is the equation for the weight/length relationship?
W=aL^b
W=weight
L=length
a and b= constants
when preserving fish, what happens when preserved in:
- alcohol/formalin?
- freezing?
- a/f=shortening
- f=lengthening
when would you use a condition factor?
when comparing different stocks of fish, or a stock at different times of the year/years.
what does a condition factor compare?
how heavy a fish is for its length
in the equation:
W=aL^b
which coefficient is the condition factor?
the intercept, a.
what are the four common units of growth?
which one is only used for selmelparous fish?
- absolute growth rate
- specific growth rate
- instantaneous growth rate
- von Bertalanffy growth coefficient
-instantaneous
what is the name of this equation?
W1-W0/t1-t0
absolute growth rate
what is the name of this equation?
W1-Q0)*100/W0(t1-t0
specific growth rate
the three main means to determine a fish’s size and age are:
- examination of hard parts such as otoliths
- mark, recapture studies
- size frequency distributions
name common hard parts for analysis
- otoliths
- scales
- vertebrae
- fin spines
- clithra
- shell marks in mollusks
- statoliths in cephalopods
- teeth in marine mammals
for hard part analysis, name three ways of obtaining time verification
- mark recapture
- otolith or scale marking with tetracycline
- shell notching
why use lea’s formula?
by using the space of a hard part between checks, it can determine the length of the actual fish.
why use the swept area method?
used to estimate the abundance of demersal species wit a uniform distribution within their habitat.
what is the swept area method?
a transect survey in which a trawl net is dragged along the bottom and the area covered by the trawl related to the amount of fish captures.
-measures abundance
what is the traditional vs modern means of conducting a swept area method?
trawl nets vs ROVs
how should the strata be divided for swept area method?
high, medium and low density, or sometimes just high and low.
the area swept by the trawl, for swept area method, are a function of:
- the velocity of the trawl
- the time of the trawl
- the size of the trawl opening
what factors must be taken into consideration for swept area method?
- which fish get caught compared to out swim
- different species are more or less vulnerable to trawl gear
- different sized fish
- duration of trawl (which fish get tired faster)
How do ROVs differ from trawl surveys for swept area method?
- ROV estimates are often higher with lower variability for fish that are associated with the bottom which trawls have a difficult time capturing
- ROV give lower abundance for patchy distributed fish
- ROV give higher abundance variance b/c they only sample a narrow path
MSY
maximum sustainable yield- made from trawl surveys
