age determination of fishes: concepts and hands-on techniques graduate module by steven e. campana...
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AGE DETERMINATION OF FISHES: CONCEPTS AND HANDS-ON TECHNIQUES
GRADUATE MODULE
bySteven E. CampanaMarine Fish Division
Bedford Institute of OceanographyDartmouth, Nova Scotia
PRINCIPLES
• generic to all animals
•3 methods:
•Direct (lab, marked)
•Statistical (length frequency)
•Single sample
•Modal analysis
•Sequential modal
•ELEFAN, MIX
•Assumes no size-selective mortality/emigration, point spawning, random sampling despite habitat changes with size/age
•However, easy to collect
Periodic features are ubiquitous
Several scales of variability
PERIODIC STRUCTURES Types: scales, bones, otoliths, spines,
rays, teeth Preferred structure varies with animal Why do they form?
– Analogous to trees– Temperature, photoperiod, sexual
maturation; seen in deepsea fishes– Correlated with somatic growth– Not always easily interpretable
SCALES
• Easy to collect and non-lethal
• Good for rapidly growing fish
• Problems: variability over body, age of formation, regeneration
• Biggest problem is that they stop forming annuli in old or slow-growing fish
VERTEBRAE
• Good for species with difficult otoliths (tuna) and those without otoliths (sharks)
•Problem: metabolically active, therefore not good for all fishes
•Can underestimate age in long-lived fishes
•Difficult to store
OTOLITHS
Advantages:
• acellular and metabolically inert
• grow from time of hatch throughout life of fish
• composition is ideal for other applications
ANNULI
• relative composition (CaCO3 vs organic)
• asymmetric growth
• false checks (cause and criteria)
WHOLE OTOLITH
CRACK AND BURN
SECTION
OTOLITH REMOVAL AND PREPARATION
Composition affects storage and degradation
Removal can be done in several ways
Storage of otoliths and other structures
READINGS
1) Beamish and McFarlane (1983)
2) Blacker (1974)3) Campana (2001)4) Natanson et al. (2001)
Lab Remove sagittae (large pair) from 1 fish of each species;
remove 2 small pairs if possible (but don’t spend more than 5 mins on it)
Remove scales from each fish
Read all whole sagittae (put drop of water on it before reading)
Read all scales Read blue shark vertebrae (keep dry) Crack and read cod sagittae (water on broken surface) Read top row on plate of cod otolith sections Examine dogfish spine, tarpon scale, seal tooth section,
clam section
Day 2
SOME TERMS Ageing error
– Random versus biased– Accuracy versus precision
Age validation– “The confirmation of the accuracy of an ageing method”– Applies to the frequency of formation and the definition
of the first increment– An absolute requirement, not an option (problems in
past)– May vary among populations, not just species
AGE VALIDATION METHODS
Release of known-age and marked fish into the wild
Bomb radiocarbon
Delta C-14 in Atlantic Ocean
YEARCLASS
19851975196519551945
DE
LTA
C-1
4
170
120
70
20
-30
-80
Florida coralBermuda coralGeorges bivalveHaddock otoliths
AGE VALIDATION METHODS
Mark-recapture of chemically-tagged wild fish
AGE VALIDATION METHODS
Radiochemical dating Marginal increment analysis
Month
14121086420
Pro
po
rtio
n o
f in
cre
me
nt
at
ed
ge
1.0
.8
.6
.4
.2
0.0
AGE VALIDATION METHODS
Rearing in captivity
CORROBORATION TECHNIQUES
Tag recapture analysis Length frequency analysis
70 90 110 130 150 170 190 210
Fork length (cm)
0
100
200
0
110
0
200
400
0
40
80
70 90 110 130 150 170 190 210
Fork length (cm)
0
50
0
8
16
0
10
20
0
20
40
CORROBORATION TECHNIQUES
Progression of strong year-classes
METHODS WHICH ARE NEITHER VALIDATION NOR CORROBORATION
Back-calculated lengths Comparison of multiple ageing
structures within a fish
VALIDATION OF THE FIRST GROWTH INCREMENT
OTOLITH MICROSTRUCTURE
• one of the most important methodological advances of fish ecology
• ubiquitous
• found in all environments
Chinook salmon
Leptocottus
DAILY INCREMENT FORMATION
Entrained by a 24 hr light-dark cycle acting on an endogenous circadian rhythm of endocrine secretion
Once entrained, daily increment formation continues in the absence of a normal photoperiod
Fluctuations in temperature, feeding and metabolic rate can ‘mask’ the endogenous rhythm, and produce additional increments
DAILY INCREMENT FORMATION
Subdaily increments are formed by masking agents such as temperature
Daily increments appear more regular than subdaily increments, since the endogenous rhythm forms increments at a constant frequency
Daily increments accurately reflect age in young, growing fish
WHEN NOT TO USE DAILY INCREMENTS
Increments often cease with older age or spawning
Narrow increments can go unresolved, particularly around core
Validation more important to confirm your interpretitive ability
CHECKS Caused by
stress or growth interruptions
Will often see lunar checks in marine fishes
Hatch check is useful landmark
Age (days)
3002001000
Fis
h le
ng
th (
mm
)
100
80
60
40
20
Age (days)
3002001000
Fis
h le
ng
th (
mm
)
100
80
60
40
20
OTOLITH MICROSTRUCTURE APPLICATIONS
Age determination; especially useful in Age 0 and tropical fishes
Growth rate
LIFE HISTORY TRANSITIONS
Freshwater to saltwater migrations
metamorphosis
RECRUITMENT
Hatch date distributions
Total mortality
Size-selective mortality
HATCH DAY OF YEAR
120100806040200-20-40
Nu
mb
er
70
60
50
40
30
20
10
0
Cod
ELEMENTAL ANALYSIS AND MASS MARKING
READINGS Campana and Neilson (1985) Methot (1983) Campana and Thorrold (2001) Campana (1996)
Lectures on Students page of Otolith web site
http://www.mar.dfo-mpo.gc.ca/science/mfd/otolith/english/graduate.htm
DAY 2 - LAB Crack and burn both halves of cod
sagittae (put oil on burnt surface) Crack and burn both halves of redfish
sagittae Remove sagittae from 1 YOY smelt and 1
YOY grayling; remove tissue and dry on slide
IN PAIRS Section cod sagittae and read Section blue shark vertebra and read