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