Lecture 7 - Recruitment

Question 1

Recruitment (definition)

Answer 1

The number of individuals entering the fished population

Question 2

Year-class (definition)

Answer 2

A given year’s recruitment

Question 3

How does variable recruitment impact the number of fish to be harvested?

Answer 3

Variable year class strengths results in variations in the amount of fish to be harvested

Question 4

What controls recruitment?

Answer 4

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

Question 5

The Beverton-Holt Curve is ___

Answer 5

asymptotic

Question 6

The Ricker Curve ___

Answer 6

quasi-parabolic (declines to the right)

Question 7

Why does the Ricker Curve decline to the right?

Answer 7

1) competition

2) increased predation

Question 8

In the lecture example with the salmon, 1)___ relate to spawners, but 2)__ fish do not

Answer 8

1) fry

2) returning

Question 9

Early life history stages of fish

Answer 9

1) egg
2) yolk-sac larvae
3) preflexion
4) flexion
5) postflexion
6) juvenile

Question 10

Egg life stage characteristics

Answer 10

embryos enclosed in a chorion

Question 11

Yolk-salk larvae (characteristics)

Answer 11

endogenous feeding

Question 12

Endogenous feeding (definition)

Answer 12

nutrition is derived from the yolk

Question 13

Preflexion life stage characteristics

Answer 13

1) exogenous feeding

2) larval pigment pattern present

Question 14

Flexion life stage characteristics

Answer 14

Upturning of notochord as hypural bones form (related to swimming ability)

Question 15

Postflexion life stage characteristics

Answer 15

1) larvae are swimming well

2) fins are mostly formed

Question 16

Juvenile life stage characteristics

Answer 16

1) fins formed (finfold gone)
2) scales may form
3) often resembles adult, but may have unique characters

Question 17

Most fish spend 1)__ days as eggs, but hatching time can very from 2)___

Answer 17

1) 2 to 15

2) 1 to 250 days

Question 18

The hatching time of eggs is related to 1)___ and inversely related to 2)___

Answer 18

1) egg size

2) temperature

Question 19

Pelagic larval duration (PLD) typically lasts ___

Answer 19

2 weeks to 2 months

Question 20

How is PLD determined?

Answer 20

Larvae have daily growth rings and often settlement marks in their otoliths

Question 21

Hjort’s two hypotheses:

Answer 21

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

Question 22

What currents lead to good recruitment in the case study of Alaskan pollock?

Answer 22

Years when currents kept eggs and larvae in the straits. Good food supply and shallow water for settling to the bottom as juveniles.

Question 23

What currents lead to poor recruitment in the case study of Alaskan pollock?

Answer 23

Years where currents moved eggs and larvae offshore. Poor food supply and deep water were not ideal for the youngest juveniles.

Question 24

True or false. Larvae are passive drifters.

Answer 24

False. In some species, larvae can actively move between reefs when current speeds are low

Question 25

What guides larval movement?

Answer 25

1) water chemistry
2) sounds
3) visual cues

Question 26

Larvae have a very small 1)___, so effective feeding is dependent on 2)___ to increase searched volume

Answer 26

1) visual search volume

2) swimming

Question 27

“Critical period” concept

Answer 27

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.

Question 28

Cushing’s “Math/Mismatch” hypothesis (or Hjort-Cushing Hypothesis)

Answer 28

The timing of fish spawning combined with the timing of seasonal plankton blooms determines recruitment success

Question 29

“Stage-Duration” hypothesis

Answer 29

States that mortality from any source (starvation, predation, advection) at any stage affects recruitment

Question 30

Mortality is 1)___ related to time because of 2)___

Answer 30

1) conversely

2) duration of development

Question 31

Mortality is 1)___ related to size because 2)___

Answer 31

1) conversely

2) swimming, feeding success, and predator avoidance increase with size

Question 32

Shorter life stage duration leads to ___ recruitment

Answer 32

greater

Question 33

What makes for a song year class?

Answer 33

When all factors influencing larval recruitment are optimal