Life History of Aquatic Organisms Life History = birth, growth, reproduction, & death of an organism --- Trade Offs Life history characteristics vary.

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 offspringFrequency of reproductionNumber, 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.

age

reproductivevalue

immediately beforefirst reproduction

Fecudity = # of ova produced by a female.

Fertility = # of offspring produced by a female.

Fecundity ≠ Fertility Fertility ≤ Fecundity

= expected if directly proportional

Fish Fecundity with Age

AGE

FECUNDITY

sexual maturity

= observed

Differenceinvested in growth etc.

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

AGE

SIZE

Fish

AGE

SIZE

Crustacean

Fishes are said to have indeterminate (never ending) growth. However, growth does plateau.

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

Older individuals (esp. fish) usually are larger.

Year class structure can often be seen in the size distribution of individuals in a population.

Size of Individuals in a Pop.

SIZE

#

Individuals in a Seasonally Reproducing Population

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 withHIGH 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 =

rmax N [(K-N)/K]

A “bad year”

can lower K

& a “good year”

can elevate K.

N

t

K

1/2 K

Population Growth

N

t

K

1/2 K

Logistic growth

rmax = rate of increase, N = pop. size

K = carrying capacity

dN/dt =

rmax N [(K-N)/K]

higher fecundity

lower fecundity

Population Growth

dN/dt

N

1/2 K K

Logistic growth

rmax = rate of increase, N = pop. size

K = carrying capacity

dN/dt =

rmax N [(K-N)/K]

Would higher

or lower fecundity

affect this?

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 RiskDensity 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… or2. the resource is not limiting (e.g., seasonally abundant).

Lepomis Competition

Lepomis cyanellus

Lepomis gibbosus Lepomis macrochirus

small fish, surface insects, & macrophytic inverts.

snails & benthic inverts.zooplankton

Population ManagementWhich 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

Stock Biomass

Recruit-mentBiomass

Stock Biomass

Recruit-mentBiomass

Beverton-Holt

Ricker

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 =

kB [(BΦ -B)/ BΦ]

B

t

BΦ

1/2 BΦ

Rate of Stock Growth Maintaining the stock at 1/2 BΦ

maintains the greatest yield.

Maximum Sustainable Yield (MSY)

dB/dt

B

BΦ1/2 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 ManagementPresidentt

Commercet OtherDepts.

Interiort

Fish & Wildlife Service(FWS)

Natl. OceanAtmos. Admin.

(NOAA)t

Natl. MarineFisheries Serv.

(NMFS)t

Enviro.Protect.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, 1973Endangered = 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

Percina tanasi(snail darter)vs.Tennessee ValleyAuthority

1976Based on ESASupreme Courtstops TellicoDam project

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.

TellicoDam

How are fisheries managed?

How should fisheries be managed?

Freshwater?

Marine?