The Codfish Strategy

Up to9,000,000 eggs/spawn

Cod Math• The volume of the earth's oceans is 1.35 X 109 cubic Km.• A typical 50 cm female cod lays 200,000 eggs/yr• A typical mature cod might weigh...10 kg • Assuming that the fish stack perfectly with no void spaces and that

the density of the cod is equal to the density of seawater, then a cubic Km of cod would weigh...

• (1 cubic km) X (1,000,000,000 cubic m/cubic km) X (1000 kg/cubic m) X 1.032 to correct for seawater density) = 1.32 X 1012 kg.

• If a cod weighs 10 kg, then we can calculate the cod fish per cubic km as (1.32 X 1012 kg) X (1 cod/10 kg) = 1.32 X 1011 cod per cubic km of ocean.

• Then the number of cod that it would take to fill the ocean is equal to (1.32 X 1011 cod/cubic km of ocean) X (1.35 X 109 cubic km of ocean) = 1.78 X 1020 codfish.

If we assume that the codfish take 5 years to reach their maximum size of 10 kg, that they start spawning at 5 years of age, that each female would lays 200,000 eggs per year once it is 5 years old, and that they live to be at least 25 years old…

• Year 1: 2 codfish spawn• Year 2: 2 + 200,000 codfish• Year 3: 2 + 2(200,000) • Year 4: 2 + 3(200,000)• Year 5: 2 + 4(200,000)• Year 6: 2+ 5 (200,000) + (100,000 X 200,000)• Year 7: 2 + 6(200,000) + 2(100,000 X 200,000) • Year 8: 2+ 7(200,000) + 3(100,000 X 200,000) • Year 9: 2 + 8(200,000) + 4(100,000 X 200,000) • Year 10: 2 + 9(200,000) + 5(100,000 X 200,000) +(100,000 X 100,000 X 200,000)• 2 + 1,800,000 + 100,000,000,000 + 2,000,000,000,000,000 = 2,000,100,001,800,000 or 2 X 1015

• Year 11: 2(100,000 X 100,000 X 200,000)• Year 12: 3(100,000 X 100,000 X 200,000)• Year 13: 4(100,000 X 100,000 X 200,000)• Year 14: 5(100,000 X 100,000 X 200,000) = 1 X 1016

• Year 15: 6(100,000 X X 100,000 X 200,000) + (100,000 X 100,000 X 100,000 X 200,000) = 2 X 1020

Just15

Years !

Mola

23,000,000 eggs(300,000,000 max!)

Over the entire lifetime of this mola pair, how many of their babies must survive in order to keep the population stable ?

23,000,000 eggsyear/mola

20 yearlifespan= 460,000,000 eggsX

Need to replace the male and female breeding molas, therefore we need 2 fish out of the 460 million eggs.

Mola egg survival to maintain population = 1 per 230,000,000

10,000 eggsyear/salmon

1 yearspawning

= 10,000 eggsX

Need to replace the male and female breeding salmon, therefore we need 2 fish out of the 10,000 eggs.

Salmon egg survival to maintain population = 1 per 5,000

Tiger Shark

1 baby2 years/shark

20 yearlifespan

= 10 baby sharksX

Need to replace the male and female breeding sharks, therefore we need 2 fish out of the 10 babies to survive.

Shark baby survival to maintain population = 1 per 5

Two strategies1. Make bazillions of “low cost”

disposable eggs and abandon them. Hardly any survive, but when you start with millions…

2. Make very few eggs with tons of energy and guard them. There aren’t many eggs, but when most are going to survive…

R-selectionIn unstable or unpredictable environments the ability to reproduce quickly is crucial, and there is little advantage in adaptations that permit successful competition with other organisms, because the environment is likely to change again.

R= high fecundity, small body size, short generation time, and the ability to disperse offspring widely.

R- Dandelions, mice, grass carp

K-selectionIn stable or predictable environments the ability to compete successfully for limited resources is crucial, and populations of K-selected organisms typically are very constant and close to the maximum that the environment can bear.

K= large body size, long life expectancy, and the production of fewer offspring that require extensive parental care until they mature.

K-elephants, whales, Arctic Terns, tiger sharks

R (many eggs): Unstable environments. Many years things go wrong and the population drops, but in good years fry survival is high and the fish population can explode.

K (few eggs): Stable environments. Many animals competing with each other for resources. Difficult to find an opportunity for a big population increase, and they would probably starve anyway.

RiverUnpredictable flowUnpredictable plankton bloomsUnpredictable water tempsUnpredictable oxygen levels!

Coral ReefStable temperaturesStable water qualityConsistent plankton populations

Shallow temperate seasUnpredictable plankton bloomsUnpredictable water temps

Deep SeaConstant water tempConstant water qualityStable food supply

Intermediate Strategies

KK

RR

Stable tropical seasLarge well-developed youngLive bearers

Unpredictable conditions for fryEgg broadcasters- huge numbers

?

Other strategies

for the Kish crowd

Kurtus gulliveri the Nursery Fish

Kurtus gulliveri the Nursery Fish

Males carry eggs in clusters or balls attached to a hook on the head. This may

be an adaptation to environments with low oxygen and high turbidity

Snailfish

Snail Fish Eggs

Bitterling

BitterlingsAt Work

Seahorses

K

Ratfish

EagleRay

Manta

Stingray

Torpedo

Chevy Stingray

Oviporous

Mating Strategies

Oviporous

Eggs

SkateEgg

Shark Egg

Mermaid’s Purse

Port Jackson Shark

Smooth Dogfish

Porbeagle Shark

Baby sharks swim in the mother and get nutrients by drinking the uterine fluids

Another OviviparousStrategy

Uterus Like Sac

Shark Embryos

Placenta like structures carrying blood

Shark embryos in eggs

The mother shark feeds unfertilized eggs to the babies.

The mother shark feeds unfertilized eggs to the babies.

Tiger Shark1 of 5 must survive

Two basic strategies1. Make bazillions of “low cost” disposable

eggs and abandon them. Hardly any survive, but when you start with millions…

2. Make very few eggs/babies with tons of energy and guard them. There aren’t many eggs, but when most are going to survive…

3. There are plenty of intermediate strategies

Many ApproachesMany Approaches• Oviparous: Egg layers

–Broadcasters–Parental care

• Oviviparous: Eggs hatch inside female

• Viviparous: Placenta-like arrangements

• Oviparous: Egg layers–Broadcasters–Parental care

• Oviviparous: Eggs hatch inside female

• Viviparous: Placenta-like arrangements