AGE DETERMINATION OF FISHES: CONCEPTS AND HANDS-ON TECHNIQUES GRADUATE MODULE

1. 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

2. 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

3. Periodic features are ubiquitous • Several scales of variability

6. 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

7. 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

8. 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

9. OTOLITHS • Advantages: • acellular and metabolically inert • grow from time of hatch throughout life of fish • composition is ideal for other applications

10. ANNULI • relative composition (CaCO3 vs organic) • asymmetric growth • false checks (cause and criteria)

11. WHOLE OTOLITH

12. CRACK AND BURN

13. SECTION

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

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

16. 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

17. Day 2

18. 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

19. AGE VALIDATION METHODS • Release of known-age and marked fish into the wild • Bomb radiocarbon

20. Delta C-14 in Atlantic Ocean 1 7 0 F l o r i d a c o r a l B e r m u d a c o r a l 1 2 0 G e o r g e s b i v a l v e H a d d o c k o t o l i t h s 4 1 7 0 - C A T L 2 0 E D - 3 0 - 8 0 1 9 4 5 1 9 5 5 1 9 6 5 1 9 7 5 1 9 8 5 Y E A R C L A S S

21. AGE VALIDATION METHODS • Mark-recapture of chemically-tagged wild fish

23. AGE VALIDATION METHODS • Radiochemical dating • Marginal increment analysis

25. AGE VALIDATION METHODS • Rearing in captivity

26. CORROBORATION TECHNIQUES • Tag recapture analysis • Length frequency analysis

28. CORROBORATION TECHNIQUES • Progression of strong year-classes

29. METHODS WHICH ARE NEITHER VALIDATION NOR CORROBORATION • Back-calculated lengths • Comparison of multiple ageing structures within a fish

30. VALIDATION OF THE FIRST GROWTH INCREMENT

31. OTOLITH MICROSTRUCTURE • one of the most important methodological advances of fish ecology • ubiquitous • found in all environments

32. Chinook salmon

33. Leptocottus

34. 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

35. 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 DAILY INCREMENT FORMATION

36. 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

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

38. OTOLITH MICROSTRUCTURE APPLICATIONS • Age determination; especially useful in Age 0 and tropical fishes • Growth rate

39. LIFE HISTORY TRANSITIONS • Freshwater to saltwater migrations • metamorphosis

40. RECRUITMENT • Hatch date distributions • Total mortality • Size-selective mortality Cod

41. ELEMENTAL ANALYSIS AND MASS MARKING

42. 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

43. 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