Early Life and Spawning

GOALS

Background on an important part of fish ecology that is often overlooked

Generalizations of early life history of fish

Spawning strategies

Basic Background

Life History

Embryo/Egg

Larvae

Adult

Early Life History Stages

• Embryonic period

• Larval Period

• Juvenile Period

What do Fish Larvae Look Like?

Diversity of Larvae

Lake Sturgeon

Yellow Perch

Lake Trout

Diversity of Larvae

Brown Bullhead

Northern Pike

Largemouth Bass

How we sample larvae

Bongo Nets

Opening Discussion

Why are early life histories important to fish ecology?

Key Reason

1. Survivorship of young influence future generation’s abundance (year class strength)

a. Majority of mortality occurs early in life

b. Boatloads of things affect early survivorship

Factors that influence early life survival

Temperature-How quickly adult fish mature and spawn-How quickly eggs hatch-Growth rate of larvae and YOY

Factors that influence early life survival

Food availability-Is the right food available once yolk sac is used up?

-As they grow does the food out grow them? Do they outgrow the food?

Factors that influence early life survivalSpawning Site -Water Level: Eggs can be left high and dry or smothered?

-Refugia: Egg survival can depend on size of substrate or degree to which they are hidden

-Flow: Too fast and eggs are swept away. Too slow and not enough oxygen

Factors that influence early life survival

Predation-Do larvae face a predator gauntlet?

Predation

Lake trout eat alewives…right?

What about larval lake trout?

Great lakes LT spawning reefs

Must fill swim bladder at surface (physoclistous )

Strength of Year Class

• Match/Mismatch Hypothesis– Food and other conditions are good for

survival = strong year class• Food is abundant• Predators are not abundant• Temperature is appropriate

– Cues for Spawning– Several factors can disrupt matching and

result in weak year classes

Match/Mismatch Hypothesis

Yellow perch hatch

Yellow perch hatch

Eat small copepods, then switch to Daphnia

Eat small copepods but Daphnia show up too late

Conditions match what is needed

Conditions don’t match what is needed

Timing is everything…Figure from Cargnelli and Gross 1996

Evolution at work!

Egg Size (r vs K strategist)

• Larger eggs more developed at hatching

Herring: eggs, newly hatched, and 7-10 months

Newly Hatched Steelhead

Altricial: Mouths just formed at yolk depletion (Long Larvae)

Precocial: Good predators at yolk depletion (Short Larvae)

Yolk Size of Various Fishes

Fish evolve to spawn in different locations

Temiscamie – strain

Tributary spawner

Assinica- strain

Outlet spawner

Little Tupper strain

Shoal spawner

Why...think about the emerged fry!

Lentic vs. Lotic Patterns

• Lentic Fish often have pelagic larvae

• Lotic Fish often have benthic larvae

How often: Semelparous = once, Iteroparous = more then once

Common Spawning Strategies

Life history strategies

Multiple strategies: Bluegill – parental care or Cuckolder

http://publish.uwo.ca/~bneff/research_beea.htm

Female mimic

Common Spawning Strategies

Non-guarding vs. guarding

Pelagic vs. Benthic

Fine vs. Coarse substrate

Vegetation

Livebearers

Non-gaurding , Pelagic

Alewife - inshore waters, eggs settle

Gizzard shad - Often move up rivers, eggs drift down

High fecundity

High early stage mortality

Non-gaurding , Pelagic

Freshwater drum eggs float on surface until hatch

Paddlefish eggs are sticky when fertilized, adhere to the first thing they touch

Non-gaurding , Benthic – fine substrate

Spottail shiners spawn on gravel and silt substrates

Non-gaurding , Benthic - Crevice

Spotfin shiners use rock crevices to hold eggs

Non-gaurding , Benthic – stream

Pacific salmon and brown trout dig redds – clean gravel where stream water upwells

Non-gaurding , Benthic –vegetation

Northern pike prefer flooded vegetation in backwaters

Sticklebacks make nests of algae and macrophytes and then lay eggs inside the nests

Guarding , Nests – nests of plants

Guarding means higher survival

Gaurding , Benthic – Underside of rocks

Both round gobies and Johnny darters spawn under rocks, attaching the eggs to the underside of the rocks

Aggressive defense can incur high costs to parents or death

Gaurding , Nests – gravel

Common in centrachids also lamprey, nests are often fanned to increase water flow and remove sediments

Smallmouth bass

American brook lamprey

Gaurding , Nest – fine sedimentBluegill nests associated with fine sediments

Gaurding , Nests – Holes and burrows

Catfish and bullheads make burrows or use existing holes

Livebearers , (none native) Mosquitofish

60 -100 progeny per brood, born live, male has modified anal fin to impregnate female