Lecture 7 - Recruitment Flashcards
Recruitment (definition)
The number of individuals entering the fished population
Year-class (definition)
A given year’s recruitment
How does variable recruitment impact the number of fish to be harvested?
Variable year class strengths results in variations in the amount of fish to be harvested
What controls recruitment?
1) spawner biomass or abundance
2) physical processes/currents mediated by larval behavior
3) timing and magnitude of food availability (Hjort and match-mismatch hypothesis)
4) timing and magnitude of predator outbreaks
5) sources of mortality at ALL stages of development
The Beverton-Holt Curve is ___
asymptotic
The Ricker Curve ___
quasi-parabolic (declines to the right)
Why does the Ricker Curve decline to the right?
1) competition
2) increased predation
In the lecture example with the salmon, 1)___ relate to spawners, but 2)__ fish do not
1) fry
2) returning
Early life history stages of fish
1) egg
2) yolk-sac larvae
3) preflexion
4) flexion
5) postflexion
6) juvenile
Egg life stage characteristics
embryos enclosed in a chorion
Yolk-salk larvae (characteristics)
endogenous feeding
Endogenous feeding (definition)
nutrition is derived from the yolk
Preflexion life stage characteristics
1) exogenous feeding
2) larval pigment pattern present
Flexion life stage characteristics
Upturning of notochord as hypural bones form (related to swimming ability)
Postflexion life stage characteristics
1) larvae are swimming well
2) fins are mostly formed
Juvenile life stage characteristics
1) fins formed (finfold gone)
2) scales may form
3) often resembles adult, but may have unique characters
Most fish spend 1)__ days as eggs, but hatching time can very from 2)___
1) 2 to 15
2) 1 to 250 days
The hatching time of eggs is related to 1)___ and inversely related to 2)___
1) egg size
2) temperature
Pelagic larval duration (PLD) typically lasts ___
2 weeks to 2 months
How is PLD determined?
Larvae have daily growth rings and often settlement marks in their otoliths
Hjort’s two hypotheses:
1) the right food in high concentrations, at the right time, is need for larvae to survive
2) ocean currents must enable larvae to be where that food is and to end up at the right nursery habitats as juveniles
What currents lead to good recruitment in the case study of Alaskan pollock?
Years when currents kept eggs and larvae in the straits. Good food supply and shallow water for settling to the bottom as juveniles.
What currents lead to poor recruitment in the case study of Alaskan pollock?
Years where currents moved eggs and larvae offshore. Poor food supply and deep water were not ideal for the youngest juveniles.
True or false. Larvae are passive drifters.
False. In some species, larvae can actively move between reefs when current speeds are low
What guides larval movement?
1) water chemistry
2) sounds
3) visual cues
Larvae have a very small 1)___, so effective feeding is dependent on 2)___ to increase searched volume
1) visual search volume
2) swimming
“Critical period” concept
After the yolk sac is absorbed, larvae must have a sufficient abundance of food and feed within a certain brief period. If they do not, the larva will pass the “point of return,” after which they will die of starvation regardless of food availability.
Cushing’s “Math/Mismatch” hypothesis (or Hjort-Cushing Hypothesis)
The timing of fish spawning combined with the timing of seasonal plankton blooms determines recruitment success
“Stage-Duration” hypothesis
States that mortality from any source (starvation, predation, advection) at any stage affects recruitment
Mortality is 1)___ related to time because of 2)___
1) conversely
2) duration of development
Mortality is 1)___ related to size because 2)___
1) conversely
2) swimming, feeding success, and predator avoidance increase with size
Shorter life stage duration leads to ___ recruitment
greater
What makes for a song year class?
When all factors influencing larval recruitment are optimal
