AGE DETERMINATION OF FISHES: CONCEPTS AND HANDS-ON TECHNIQUES GRADUATE MODULE by Steven E. Campana Marine Fish Division Bedford Institute of Oceanography Dartmouth, 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

l Periodic features are ubiquitous l Several scales of variability

PERIODIC STRUCTURES l Types: scales, bones, otoliths, spines, rays, teeth l Preferred structure varies with animal l 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 (CaCO 3 vs organic) asymmetric growth false checks (cause and criteria)

WHOLE OTOLITH

CRACK AND BURN

SECTION

OTOLITH REMOVAL AND PREPARATION l Composition affects storage and degradation l Removal can be done in several ways l Storage of otoliths and other structures

READINGS 1) Beamish and McFarlane (1983) 2) Blacker (1974) 3) Campana (2001) 4) Natanson et al. (2001)

Lab l 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) l Remove scales from each fish l Read all whole sagittae (put drop of water on it before reading) l Read all scales l Read blue shark vertebrae (keep dry) l Crack and read cod sagittae (water on broken surface) l Read top row on plate of cod otolith sections l Examine dogfish spine, tarpon scale, seal tooth section, clam section

Day 2

SOME TERMS l Ageing error –Random versus biased –Accuracy versus precision l 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 l Release of known-age and marked fish into the wild l Bomb radiocarbon

Delta C-14 in Atlantic Ocean YEARCLASS D E L T A C Florida coral Bermuda coral Georges bivalve Haddock otoliths

AGE VALIDATION METHODS l Mark-recapture of chemically-tagged wild fish

AGE VALIDATION METHODS l Radiochemical dating l Marginal increment analysis

AGE VALIDATION METHODS l Rearing in captivity

CORROBORATION TECHNIQUES l Tag recapture analysis l Length frequency analysis

CORROBORATION TECHNIQUES l Progression of strong year-classes

METHODS WHICH ARE NEITHER VALIDATION NOR CORROBORATION l Back-calculated lengths l 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 l Entrained by a 24 hr light-dark cycle acting on an endogenous circadian rhythm of endocrine secretion l Once entrained, daily increment formation continues in the absence of a normal photoperiod l Fluctuations in temperature, feeding and metabolic rate can ‘mask’ the endogenous rhythm, and produce additional increments

DAILY INCREMENT FORMATION l Subdaily increments are formed by masking agents such as temperature l Daily increments appear more regular than subdaily increments, since the endogenous rhythm forms increments at a constant frequency l Daily increments accurately reflect age in young, growing fish

WHEN NOT TO USE DAILY INCREMENTS l Increments often cease with older age or spawning l Narrow increments can go unresolved, particularly around core l Validation more important to confirm your interpretitive ability

CHECKS l Caused by stress or growth interruptions l Will often see lunar checks in marine fishes l Hatch check is useful landmark

OTOLITH MICROSTRUCTURE APPLICATIONS l Age determination; especially useful in Age 0 and tropical fishes l Growth rate

LIFE HISTORY TRANSITIONS l Freshwater to saltwater migrations l metamorphosis

RECRUITMENT l Hatch date distributions l Total mortality l Size-selective mortality Cod

ELEMENTAL ANALYSIS AND MASS MARKING

READINGS l Campana and Neilson (1985) l Methot (1983) l Campana and Thorrold (2001) l Campana (1996) Lectures on Students page of Otolith web site mpo.gc.ca/science/mfd/otolith/english/gra duate.htm

DAY 2 - LAB l Crack and burn both halves of cod sagittae (put oil on burnt surface) l Crack and burn both halves of redfish sagittae l Remove sagittae from 1 YOY smelt and 1 YOY grayling; remove tissue and dry on slide IN PAIRS l Section cod sagittae and read l Section blue shark vertebra and read