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Download reproduction and early life 2008
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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 Lake Trout Yellow Perch 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 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? Predation Lake trout eat alewives…right? What about larval lake trout? Must fill swim bladder at surface (physoclistous ) Great lakes LT spawning reefs 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 Conditions match what is needed Yellow perch hatch Eat small copepods, then switch to Daphnia Conditions don’t match what is needed Yellow perch hatch Eat small copepods but Daphnia show up too late Timing is everything… Figure from Cargnelli and Gross 1996 Evolution at work! Egg Size (r vs K strategist) • Larger eggs hatching more developed at Herring: eggs, newly hatched, and 7-10 months Altricial: Mouths just formed at yolk depletion (Long Larvae) Newly Hatched Steelhead Precocial: Good predators at yolk depletion (Short Larvae) Yolk Size of Various Fishes Fish evolve to spawn in different locations Temiscamie – strain Little Tupper strain Tributary spawner Shoal spawner Assinica- strain Outlet spawner Why...think about the emerged fry! Lentic vs. Lotic Patterns • Lentic Fish often have pelagic larvae • Lotic Fish often have benthic larvae Common Spawning Strategies How often: Semelparous = once, Iteroparous = more then once Life history strategies Multiple strategies: Bluegill – parental care or Cuckolder Female mimic http://publish.uwo.ca/~bneff/research_beea.htm Common Spawning Strategies Non-guarding vs. guarding Pelagic vs. Benthic Fine vs. Coarse substrate Vegetation Livebearers Non-gaurding , Pelagic Alewife - inshore waters, eggs settle High fecundity High early stage mortality Gizzard shad - Often move up rivers, eggs drift down 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 Guarding , Nests – nests of plants Guarding means higher survival Sticklebacks make nests of algae and macrophytes and then lay eggs inside the nests 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 American brook lamprey Smallmouth bass 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 60 -100 progeny per brood, born live, male has modified anal fin to impregnate female
