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Determination of Age and Growth

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Age refers to a description of how long an organism. has lived. Growth refers to a ... fin rays, cleithera, vertebrae, operculum bones, and. dentary bones. ... – PowerPoint PPT presentation

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Title: Determination of Age and Growth


1
Determination of Age and Growth
  • DeVries and Frie
  • Chapter 16

2
Age and Growth-- Age refers to a description of
how long an organism has lived. Growth refers
to a change in some metric of fish size (e.g.
mass, length) between two points in time. Both
Age Growth can be described over a range
of temporal scales from hours to days to years.
3
Why do we care about age and growth? Growth
provides an integrated measure of the
environmental (e.g. Temperature), water
chemistry, and endogenous conditions (e.g.
genetics) affecting a fish. Growth can therefore
be used to assess quality and quantity of
habitat, food availability, or the need for or
influence of management activities. For
Example (If stunted bluegill are a problem in a
lake, thinning of the BG population might be
accomplished by addition of shallow
water predators like Musky. Results of the
management action could be evaluated by checking
the growth rates of BG before and after stocking).
4
16.2 Approaches to Aging Fish The three most
common approaches are 1. Direct Observation
of Individuals 2. Use of Length/Frequency
Analyses 3. Use of Hard Parts
5
Conventions for Age Designations (Box 16.1)
There is a great deal of confusion about
nomenclature used to describe fish ages. Both
Roman and Arabic numerals have been used. Also
use plus or standard numeral designation (e.g.
Age-0 vs. Age-0). Due to differences in
species and regions in the timing of laying down
annulus, AFS suggests use of JAN 01 and JULY 01
in the northern and southern hemispheres, respect
ively to represent growth in the current year of
life.
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16.2.1 Direct Observations of Individuals
Most direct and accurate of methods for
quantifying the fish age. Usually direct
observations of individuals in confinement.
(Tanks with eggs gt larvae of known days
post-hatch). Can be marked and released into
natural environment and recaptured later with
time between capture and recapture used to
quantify/verify age. Often used to verify or
validate other methods like hard-part
analysis. (Do annuli or daily rings
correlate with known age specimens?)
8
16.2.2 Length-Frequency Analysis
Length-frequency analysis can sometimes be used
to separate age-groups. method assumes
that fish length within each division is
normally or unimodally distributed. For some
species, e.g. tropical fishes, without a distinct
period of slow/no growth, aging with hard
parts may be impossible and L/F analysis may
be the only way to age them.
9
Peterson Method. The Peterson Method involves
collection of a sample of fish by some method
without bias of fish age or size. Then, the
frequency of individuals is plotted as a
function of fish length. After plotting, each
peak is assigned an age beginning with the
youngest and smallest.
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The Petersen Method seems simple, but can be
difficult if the peaks of multiple ages overlap
(B) or if age-classes are absent (A).
1
0
1
2
0
2
? ? ?
0
1
A
B
12
The overlap depicted in example B is more
common among older fish because they increase
in length more slowly with size/age. This
tends to restrict the usefulness of this
technique to younger age-classes.
Variation in growth rates either among
individuals or between sexes OR different
hatch dates can confound the use of this
method.
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Note scientific articles generally require the
use of aging methods such as validated,
hard-parts for most papers involving aging of
fish. Choice of method will affect aging
results without validation Text reports that
Crumpton (1988) found 8 age-classes with
otoliths, but only 2 groups with L/F analysis
for crappies.
15
Circumstances Where Peterson Method Might Prove
Reliable for Aging 1. Large samples with
accurate representation of lengths of fish
present in the population to be aged. 2.
Relatively short spawning period. 3. Relatively
rapid growth that is relatively uniform
among individuals within the same age-groups.
16
Points on the Peterson Method (contd.)
Originally age-groups were distinguished by
modes in L/F visually. Now, oftentimes
statistical methods are used (Maximum
likelihood estimation). Peterson does provide
a low-cost method even though the applications
may be limited.
17
16.2.3 Use of Hard Parts in Aging - This
is the most often used method of aging fish.
- Parts used include scales, otoliths, fin
spines, fin rays, cleithera, vertebrae,
operculum bones, and dentary bones. -
Aging is based on the appearance of marks on the
part that correspond with annular (years) or
daily growth. (Often referred to as like rings
on a tree.
18
16.2.3 Use of Hard Parts in Aging - Annual
marks are related to seasonal changes in growth
such as slowing and stopping during winter
followed by a rapid acceleration in growth
following spring. - daily increments are
formed by differential deposition of CaCO3
protein over a 24-h period perhaps related
to Circadian Rhythms.
19
16.2.3 Choice of Hard Parts Scales -
Scales have historically been the most often used
(for those fish having scales). - Advantage
of removal without sacrifice of the fish. - BUT,
scales may not have marks (annuli) due to
overall slow growth (due to temp extremes,
food limitation) or scales can be re-absorbed
in severe stress (Crighton effect).
20
16.2.3 Choice of Hard Parts (continued)
Scales - Slow growth, resorption of scales, or
scale loss and regeneration of scales can all
lead to errors in aging. - Also may have
spawning checks or other checks associated
with summer temps or food limitation that may
appear to be annuli.
21
Scales are removed from different areas on a fish
for different species. This is due to studies
showing certain areas were more readable or
reliable than others.
22
Otoliths Do require sacrifice of the fish,
but are not re-sorbed Continue to form
increments or annuli despite growth. In
comparison, often times otoliths are more
precise than those from scales.
23
Otoliths (continued)
24
There are 3 prs. Of otoliths in a fishs
head. The saggital are the largest.
Saggital Otoliths
Brain
Generalized location of saggital otoliths in fish
25
16.2.3.2 Techniques for Using Hard
Parts SCALES popular because they dont req.
sacrifice of fish. To sample 1. wipe away
mucous 2. Keep scales clean 3. Remove scales
with knife/scalpel/forceps 4. Place scales
into labeled coin envelope. 5. Sample should be
5-10 scales 6. Try to avoid regenerated
scales or ones from the lateral line area.
26
16.2.3.2 Techniques for Using Hard Parts To
View Scales - Usually we take impressions of
scales in acetate slides or you can mount them
between 2 microscope slides. - Can use a
microfiche or dissecting scope or
specialize scale projector.
27
16.2.3.2 Techniques for Using Hard Parts
28
16.2.3.2 Techniques for Using Hard
Parts Features of Scales
29
16.2.3.2 Techniques for Using Hard
Parts Scales
30
16.2.3.2 Techniques for Using Hard Parts
31
16.2.3.2 Techniques for Using Hard
Parts Otoliths - Fish must be sacrificed to
obtain. - To remove one must cut through the
head. - once exposed, remove otoliths with
forceps. - once removed they can be stored in
coin envelopes (dry) or stored in vial with
water, ethanol, or a 5050 mix of water and
glycerine.
32
16.2.3.2 Techniques for Using Hard
Parts Features of Otoliths
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Some actual otoliths..
35
Aging With Spines - some fish like catfish
lack scales and otoliths are difficult to
retrieve due to small size of otoliths and
thick skulls. - In these cases we may use
cross-sections of spines or rays to age. -
Catfish spines may be de-calcified in 5 aq.
Nitric acid to make sectioning easy.
36
Location to take cross-sections of spines rays
37
So, you know how to age fishnow what can you do
with it? - determination of size at age
(importance to mgt.) - back-calculation of
size-at-age. - determination of size-specific
mortality (e.g. Lees) - estimation of hatch
dates and survivorship attributes (primarily
for larvae).
38
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39
Back-calculating size-at-age Because hard-part
growth may be linearly related to body (length)
growth, we may be able to back-calculate size at
age for a fish from fish length and increments
measured along the hard-part. Direct Proportion
Method Li Si / Sc Lc Li back-calc length
of fish when ith increment formed. Lc length of
fish at capture. Sc radius of hard part at
capture. Si radius of hard part at the ith
increment
40
Back-calculating size-at-age (continued) Fraser-L
ee Method used when relationship between fish
length and hard-part radius is not at the
origin. Li (( Lc - a ) / Sc )) Si a a
the intercept parameter from a plot of scale
radius (X) and body length (Y-axis). Li
back-calc length of fish when ith increment
formed. Lc length of fish at capture. Sc
radius of hard part at capture. Si radius of
hard part at the ith increment
41
Source of the intercept value for Fraser-Lee.
42
What is Lees Phenomena? This occurs when the
back-calculated lengths at age are smaller for
older fish than for younger fish in the sample.
43
Why Does Lees Phenomena Occur? (1) Older fish
had decreased vulnerability to fishing M or
predation because they are slower growing. (2)
Sampling gear is selective for faster-growing
individuals of the youngest age classes. (3)
Aging technique is faulty. (4) Bias exists in the
intercept parameter (5) Ratio of fish length to
hard part radius varies systematically with fish
growth rate.
44
Length at age von Bertalanffy Model
45
To get K and Lmax Ford-Walford Plot

46
To get to Beverton Linearization
a intercept b slope To -(a/b)
Ln(Lmax-Lt)/Lmax
Age
47
Aging of fish is an important aspect of
fisheries management. One that is probably
under-emphasized by colleges and
universities. Aging is also an art (as you will
see). When starting to age fish you will want to
look at small individuals first to get an idea of
what age-0s look like. Look at several scales
per individual. You will want to review your age
estimation after the first 100 fish or so and
probably have a 2nd reader.
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