Download Fish Pop. Biol.

Life History of Aquatic Organisms
 Life History = “birth,” growth, reproduction, &
death of an organism --- Trade Offs
 Life history characteristics vary.
Rate of growth (How long to sexual maturity?)
Number of offspring
Frequency of reproduction
Number, size,
and sex
ratio of
offspring
Age of death
Salmon Life History
Life History
 Reproductive Value = the average number of
offspring in a population that remain to be
born to individuals of a certain age.
immediately before
first reproduction
reproductive
value
age
 Fecudity = # of ova produced by a female.
 Fertility = # of offspring produced by a female.
Fecundity ≠ Fertility
Fertility ≤ Fecundity
Fish Fecundity with Age
= expected if directly proportional
= observed
FECUNDITY
Difference
invested in
growth etc.
AGE
sexual maturity
Iteroparity & Semelparity
 Iteroparity = individuals
may reproduce in >1
reproductive season during
its life. (most organisms)
 Semelparity = individuals
may reproduce in 1
reproductive season during
its life.
“BIG BANG” reproduction;
all energy to repro. (squid,
octopus, some Pacific salmon)
Parental Care
 Broadcast Spawning = buoyant eggs externally
fert.; no parental care; many small eggs.
 Egg Scattering = non-buoyant, non-adhesive eggs
externally fert.; no parental care; many small eggs.
 Shelter Spawning = non-buoyant, adhesive eggs
laid in existing shelter; parental care via guarding &
egg care in many.
 Nest Building = non-buoyant, eggs laid in created
shelters; parental care in nest construction, many
guard & clean eggs.
 Brooding/Bearing = non-buoyant, adhesive eggs
externally fert. & laid on a parent; care extensive.
 Livebearing = eggs fertilized inside female and
develop there; female parental care extensive.
Parental Care (or lack thereof)
Growth of Individuals
 Fishes are said to have indeterminate (never
ending) growth. However, growth does
plateau.
Fish
SIZE
Crustacean
SIZE
AGE
AGE
Populations in Fisheries Context
 Population = individuals of one species that
simultaneously occupy a defined area
 Deme = individuals of one species that form a
distinct reproductive community
 (Fisheries) Stock = individuals of one species
that share common production characteristics
and support the same basic fisheries.
 Year Class (Cohort) = All the individuals in a
population born/hatched in a single “year”
 Year Class Strength = the number of
individuals in a year class
Size of Individuals in a Pop.
 Older individuals (esp. fish) usually are larger.
 Year class structure can often be seen in the
size distribution of individuals in a population.
Individuals in a Seasonally Reproducing Population
#
SIZE
Survivorship & Mortality
 Survivorship = percent / proportion of the
initial year class that survives
 Mortality = percent / proportion of the year
class that dies over a given time period
 Most commercial species exhibit high
mortality when young,
AND with great year to year mortality
variation due to climate.
This is associated with
HIGH FECUNDITY.
Why?
Population/Stock Change
 Population size = (births + immigration) (deaths + emigration)
 Stock size = (recruitment + immigration) (harvest + predation + emigration)
 Recruit = individual enters the catchable
population.
 Recruitment = number of recruits that enter
a stock over a given time period.
Year classes may all recruit around the
same time if size variation is low.
Population Growth
 Logistic growth
 rmax = rate of increase, N = pop. size
 K = carrying capacity
 dN/dt =
K
rmax N [(K-N)/K]
A “bad year”
can lower K
& a “good year”
can elevate K.
N
1/2 K
t
Population Growth
 Logistic growth
 rmax = rate of increase, N = pop. size
 K = carrying capacity
 dN/dt =
K
rmax N [(K-N)/K]
N
1/2 K
higher fecundity
lower fecundity
t
Population Growth
 Logistic growth
 rmax = rate of increase, N = pop. size
 K = carrying capacity
 dN/dt =
rmax N [(K-N)/K]
1/2 K
dN/dt
Would higher
or lower fecundity
affect this?
N
K
Predation
 Interspecific Predation = Consumption of
an individual of one species by another
 Cannibalism (Intraspecific Predation) =
consumption of an individual by a member of
the same species (includes egg cannibalism)
Density Dependent - increases with density
 Predation direct effects = death or injury
 Predation indirect effects =
predation avoidance  reduced movement,
reduced feeding, &/or reduced breeding 
reduced individual condition &/or pop. size
Density & Predation Risk
 Density Independent Predation =
predation risk per individual is
independent of prey density
 Direct Density Dependent Predation =
predation risk increases with prey
density
 Inverse Density Dependent Predation
(Depensatory) = predation risk
decreases with prey density (swamping)
Competition
 Intraspecific Competition usually more
significant than interspecific
competition.
 Effects density dependent and usually
indirect (less to go around).
 When two species are using the same
resource…
1. they are competing… or
2. the resource is not limiting (e.g.,
seasonally abundant).
Lepomis Competition
snails & benthic inverts.
Lepomis gibbosus
zooplankton
Lepomis macrochirus
small fish, surface insects, & macrophytic inverts.
Lepomis cyanellus
Population Management
 Which populations can stand the
greatest harvest?
Ones with a high reproductive rate.
(usually have low early survivorship)
Have many offspring.
Reproduce frequently.
Mature quickly.
 Which individuals are harvested?
What is the reproductive value of
harvested individuals?
Population Management
Fisheries Recruitment Models
 Used to predict stock size to manage stocks.
How much, where, and when can we harvest?
 Beverton-Holt Model - Recruitment
increases with stock size but comes to an
asymptote at some level. (More adults = more
recruits but pre-recruits resource limited.)
 Ricker Model - Recruitment peaks at some
intermediate level of stock abundance and
declines at higher abundance. (More adults =
more cannibalism/competition & pre-recruits
resource limited.)
Recruitment Models
Beverton- Recruitment
Holt
Biomass
Stock Biomass
Ricker
Recruitment
Biomass
Stock Biomass
Beverton-Holt & Ricker Models
 Which model applies to which stock?
Pre-
recruit competition and cannibalsim?
 Used in the 1970s but abandoned in 1980s.
 Theory supported but most data didn’t really
support. Year to year variance very high.
 What other things do you think might affect
recruitment? (i.e. What caused the variance?)
Stock Growth
 k = intrinsic rate of stock increase ( rmax)
 B = stock biomass ( N)
 BΦ = unexploited stock size ( K)
 dB/dt =
B
Φ
kB [(BΦ -B)/ BΦ]
B
1/2 BΦ
t
Rate of Stock Growth
 Maintaining the stock at 1/2 BΦ
maintains the greatest yield.
 Maximum Sustainable Yield
(MSY)
1/2 BΦ
dB/dt
B
BΦ
Problems with MSY
 Only a few terms in the model (B, BΦ, k).
 Difficult to identify a discrete “stock.”
 Estimating stock biomass (B) and possible
intrinsic rate of stock increase (k) is difficult.
 Estimating maximum stock size (BΦ) is
incredibly difficult.
BΦ (like K) often varies from year to year.
MSY History
 MSY developed in 1930s.
 Becomes commonly used in the U.S. in
1950s & U.S. had MSY made the goal of
international fisheries management in 1955.
 Challenged by academics in the late 1970s.
 Only abandoned in govmt. in the mid-1990s
after the collapse of the Atlantic cod fishery.
-Peruvian anchovetta fishery in 1972
-Atlantic herring fishery in 1977
-Atlantic cod fishery collapse in 1993
MSwhY?
 Why was MSY used for so long and only
tweaked?
U.S. Fisheries Agencies Hist.
 1903 - Bureau of Fisheries (Dept. of Labor &
Commerce)
 1939 - Bureau of Fisheries subsumed into the
new Fish and Wildlife Service (FWS) (Dept.
of Interior) - Sport and Commercial fisheries
 1956 FWS internally split into “sport” &
“commercial” (MSY management) agencies
 1960s - Great Lakes fisheries collapse
 1970 - Fish and Wildlife Service (FWS)
(Dept. of Interior) for “sport”
& National
Marine Fisheries Service (NMFS) = for
“commercial” (NOAA, Dept. of Commerce)
U.S. Fisheries Management
Presidentt
Commercet
Interiort
Natl. Ocean Fish & Wildlife
Service
Atmos. Admin.
(FWS)
(NOAA)t
Natl. Marine
Fisheries Serv.
(NMFS)t
Enviro.
Other Protect.
Depts. Agency
(EPA)
Magnuson-Stevens Act, 1976
 Extended U.S. territorial limits to 200 miles
(most of the continental shelf) from 12 miles.
 Required re-negotiation of all fisheries
treaties in response to “foreign” fishing
 Required NMFS to manage fisheries for
optimal benefit to society (OSY) not just MSY.
American Fisheries Promotion Act, 1980
 Provided grants to the fishing industry and
boat loan default guarantees.
 Directed identification of “new” stocks
 Goal = increase U.S. fishing
Sustainable Fisheries Act, 1996
 Modified Magnuson-Stevens Act
 Emphasized ending “overfishing”
 OSY redefined as MSY as reduced by social,
economic or ecological factors.
 Required NMFS regulate to reduce bycatch.
Endangered Species Act, 1973
 Endangered = in danger of extinction in
all or a significant portion of its range
 Threatened = is likely to become
Endangered in the foreseeable future
 Provides protection from “harvest and
loss of critical habitat.” – NO EXCEPTIONS
1976
Based on ESA
Supreme Court
stops Tellico
Dam project
Percina tanasi
(snail darter)
vs.
Tennessee Valley
Authority
Endangered Species Act, 1978
 Congress amended the ESA to create an
Endangered Species Committee that
could give exemptions & required
economics be considered.
 1979 - the Endangered Species Committee
did NOT give a Tellico Dam exemption.
 1979 - Congress gave a specific exemption.
Tellico
Dam
How are fisheries managed?
How should fisheries be managed?
Freshwater?
Marine?