Announcements and Such Limnology Hiring Fair Wednesday April 2 nd at 5pm in the Red Gym (check “today in the union” postins for exact location) Comments on the Midterm Assignment: Peer Review Draft

Outline for the Day How to Write a Scientific Paper Lecture (Reminders of Expectations) Reproduction and Early Life History 2 nd Half of Wisconsin Fishes

GOALS Background on an important part of fish ecology that is often overlooked Generalizations of early life history of fish Spawning strategies

Basic Background

What do you mean “larval fish”? Embryo/Egg Larvae Adult

Early Life History Stages Embryonic period Larval Period Juvenile Period

What do Fish Larvae Look Like?

Diversity of Larvae American Eel

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?

Answers Kornis Came Up With 1.Survivorship of young influence future generation’s abundance (year class strength) a. Majority of mortality occurs early in life 2.Survivorship is affected by spawning strategies a.Time of hatch b.Habitat selection c.Size of larvae at hatch

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 survival Spawning 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? Brandt et al. 1987

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 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!

Yolk Size and Larvae Survival Temperature and Development of Fish at Hatch Lake Trout (Coldwater) Pygmy Sunfish (Warm water) Temperature also effects how long egg stage lasts

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 –Major period of dispersal –Major period of mortality Lotic Fish often have benthic larvae –Avoid being swept away –Exist for short periods, under heavy cover

How often: Semelparous = once, Iteroparous = more then once Common Spawning Strategies

Life history strategies Multiple strategies: Bluegill – parental care or Cuckolder 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 sediment Bluegill nests associated with fine sediments

Gaurding, Nests – Holes and burrows Catfish and bullheads make burrows or use existing holes

Livebearers, (none native) Mosquitofish progeny per brood, born live, male has modified anal fin to impregnate female