Age & Growth Flashcards
What is Somatic Growth?
The mechanism and results of fish adding weight
At the individual level: eating more food
Results in an increase in biomass of the stock
Links size and age
Length-Weight models assume growth…
is at least a 3-dimensional process
Length, width, and depth
What is the simplest assumption associated with length-weight models?
L, W, D change in proportion to one another = isometry
Isomatic Growth
the relative increase in all dimensions is the same as the organism grows
most species do not exhibit isometric growth
Allometric growth
the relative increase in one dimension is greater than others.
What type of data does Allometric Models fit well?
weight-at-length data
What is the most common length-at-age model applied?
von Bertalanffy Growth Model
Who introduced the von Bertalanffy Growth Model, and when?
von Bertalanffy described model in 1938; introduced by Beverton & Holt in 1957
Explain the von Bertalanffy Growth Model
Rate at which individuals approach L∞ is constant (k)
model fit to data of a long-lived species
When broad size ranges are considered, the allometric model slight, but consistently, overestimates ____________?
weight at length for fish at the extremes (small and large)
L∞
Fish have indeterminate growth (L infinity)
L infinity – is the point where they don’t grow much more.
t0
Sometimes called the ‘initial condition’ parameter, fish growth begins at hatching
von Bertalanffy Growth Model - High k
Shorter life span
Low age & size at maturity
High reproductive output
von Bertalanffy Growth Model - Low k
Longer life span
Greater age & size at maturity
Lower reproductive output
What is another common model used?
Gompertz Growth Model
Gompertz Growth Model weight at age mostly used for?
Used to model the growth of invertebrates, skates, rays & some sharks
Gompertz Growth Model Lenth at age model used for
Used to model the growth of young fish (within the first year)
Why do we want to know about age and growth?
Life history
Management application
Why is life history important?
Age at maturity
Birthdates
Spawning period
Survival
Growth rate
Habitat suitability
Why is age and growth important to management?
Catch- or size-at-age
Selectivity of gear types
Age-structured stock assessments
Recruitment/year class strength
How to measure growth
Length
Weight
What are the two zones used for aging hard parts?
Hyaline zone – translucent, protein-rich ring
Opaque zone – calcium-rich layer
What are the types of hard parts used for again?
scales, vertebrae, spines,
What are the caveats for using hard parts for aging?
Loss & regeneration (scales)
Resorption (fin spines)
Validate the frequency of rings
Scales used for aging
Non-lethal
Environmental and spawning marks
Regenerated
What is an otolith?
An organ in the inner ear (Ear stone)
What is the most common otolith used?
Sagittus because it often larger than the other two.
What are the benefits of using otoliths for aging?
Cannot be lost/regrown
No resorption or erosion
What are downfalls?
Terminal for the fish
How to prepare an Otolith:
Sectioning
Mounting
Grinding/polishing
Reading (image analysis)
