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Age Determination and Validation in Chondrichthyan Fishes

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1 Age Determination and Validation in Chondrichthyan Fishes
Presented by Kara Baca and Sharon Homer-Drummond

2 Methodology Age determination process: Collection of hard part samples
Preparation of the hard parts Examination (age reading) Assessment of validity and reliability Interpretation (modeling growth)

3 Hard parts used Vertebral centra Dorsal fin spines Neural arches
Caudal thorns

4 Vertebral Centra Larger, more anterior centra should be used
Whole or sectioned Vertebrae should be sectioned sagittally (longitudinally)

5 Dorsal Fin Spines Used particularly in dogfish sharks
Spines from second dorsal fin are preferred Used whole or longitudinally cut

6 Neural Arches May be useful for species that have poorly calcified vertebral centra Preliminary studies with sixgill sharks

7 Caudal Thorns and Other Structures
Serra-Pereria et al., 2005 Caudal Thorns and Other Structures Caudal thorns used with vertebral centra to determine age in bathyrajid species Evidence for growth bands found in upper jaw of the wobbegong Orectolobus japonicus

8 Preparation of Samples (Centra)
Thaw (if frozen) or wash (if preserved in alcohol) Clean excess tissue and separate into individual centra Sectioning typically done with low-speed diamond-bladed saw After mounting sections to slides, sand with wet fine-grit sandpaper to approximately 0.3 to 0.5 mm and air-dry Binocular dissecting microscope is generally used for analysis

9 Age Determination View wide bands (opaque) separated by distinct narrow bands (translucent) Tend to occur in summer (wide) and winter (narrow) Each pair of wide/narrow bands considered to represent an annual growth cycle Validity must be tested Age determination for spines are nearly identical

10

11 Dorsal fin spines

12 Banding in Neural Arches
Distinct bands in sixgill sharks Potential use in age determination

13 Staining & imagery Imagery & enhancement Staining Histology
scanning EM (atypical) steromicroscopy binocular light microscopy X-radiograophy (atypical) X-ray spectrometry Graphite microtopography Staining silver nitrate (McFarlane et al., 2002) cobalt nitrate (Hoenig and Brown, 1998) ammonium sulfide (Hoenig and Brown, 1988) haemotoxylin cedar wood oil, alizarin red, crystal violet, salts (Cu, Fe, & lead) Histology Goldman, 2004

14 Evaluating Precision Average percent error (APE)
May serve as good relative indicator of precision within and between readers However, tells which reader was less variable, not which was better or if either was biased Goldman’s approach to estimating precision: Calculate percent reader agreement (=[No. agreed/No. read] x 100) within and between readers for all samples Calculate percent agreement plus or minus one year Calculate percent agreement with individuals divided into appropriate length or disk width groups Test for bias Criticism: varies widely among species and ages within a species

15 Tests for Bias Age bias plot- graphing one reader vs. the other and referencing equivalence line of the 2 readers (45° line through the origin) Chi-square tests of symmetry, such as Bowker’s Evans-Hoenig test

16 Back-Calculation Method for describing the growth history of each individual sampled Numerous methods – formulas that follow hard part or body proportion hypothesis are recommended Proportional relationship between animal length or disk width and radius of vertebral centrum or distance from focus to each annulus within a given centrum

17 Verification & Validation
Confirmation of age determination by indeterminate and determinate methods

18 Why validation & verification? Caillet, 1990
Apex Predators website: “Sharks are long-lived animals that grow very slowly and do not produce many young. In many parts of the world, sharks are fished commercially, thus, in order to ensure proper management of the stocks, age and growth data must be obtained. With this data, we can determine the longevity of the species as well as maximum age, age at maturity, growth rate, and differences in growth between males and females.” The process of evaluating growth zone deposition in fishes can be divided into verification and validation. Verification: “… conforming an age estimate by comparison with other indeterminate methods” Validation: “… proving the accuracy of age estimates by comparison with a determinate age”

19 Some methods of validation
Some methods of verification Chemical tagging of wild fish Mark-recapture of known-age fish* Bomb carbon dating* Growth ring frequency distinction between absolute age (*) & periodicity Centrum age analysis Relative marginal increment analysis

20 And now ... on to aging and analysis!
Size mode analysis Primarily a verification tool Progression of discrete length modes over time Size modes taken from a random sample of all size classes from a population Mean or median sizes in age classes assessed by other means (e.g.: age classes predicted by von Bertalanffy growth function applied to physical assessment) Random sample size modes and mean or median sizes at age compared Coincidence supports assumption of age classes Monitor discrete length modes across a given time period at discrete intervals And now ... on to aging and analysis!

21 Tag-recapture Initial in field:
Measure Weigh Tag Release Recapture and assess for growth in length and/or weight Compared to von Bertalanffy growth functions, TET, oxytetracycline (OTC) or other methods, based on size changes between tagging and recapture

22 file:///D:/age%20validation/Tetracycline%20or%20OTC_files/age1.jpg

23 Simpfendorder, 2000: dusky sharks

24 Chemical marking, tag-recapture & lab
Validation of absolute age focuses on validating “temporal periodicity of … growth increment formation” Tetracycline (TET): standard for marking free-swimming animals OTC: marks by binding to Ca2+ & depositing to active calcification sites 25mg/kg bw IM + external tag highly visible marks in vetebral centra & dorsal fin spines under UV use body growth & calcification changes to compare ‘time at liberty’ [release] w/growth band deposition (# rings in vetra centra or spine post-injection = time hacks) lab or captivity Tag-recapture + marking tag + OTC followed by recapture tag + TET followed by recapture Other tags Fluorescein (not well-evaluated in elasmo.; 5-10mg/kg bw, higher=mortality) Calcein (not well-evaluated in elasmo. .; 5-10mg/kg bw, higher=mortality) Define age & indiv. growth characteristics Combining information from mark w/observed growth changes

25 Tetracycline group Broad spectrum Ab’s that block bacterial protein synthesis by inhibition of aminoacyl-t-RNA binding to the rRNA A site. TET = tetracycline higher water solubility at pH = 7, than other Ab’s in same group OTC = oxytetracycline Inject TET or OTC at capture while tagging 25 mg/kg absorbed & deposited at growth sites only mark glows under UV pairs > mark = growth over time

26 Centrum edge analysis Centrum edge analysis:
Compares opacity (width) &/or translucency (density) of centrum edge over time measure or grade edge compare to time of year or season detail: analyze Ca2+ & PO4 – at edge by x-ray or electron microprobe spectrometry not used much yet: recaptured nurse sharks marked with TET (Carrier and Radtke, 1988) 4 ray species in the Irish Sea marked with TET (Gallagher et al., 2004) tiger sharks (Winter and Dudley, 2000) Winter and Dudley, 2000

27 Relative marginal increment analysis
RMI = MIR (ratio): (VR-Rn)/(Rn-Rn-1) Parameters MIR – marginal increment ratio VR = vetebral radius Rn = distance from center to outer edge of last complete band Rn-1 = distance from center to outer edge of next-to-last complete band Direct: plot against month to find band formation trend line Assess seasonal band &/or ring deposition measure margin (growth) area of centrum from last growth ring to centrum edge divide by width of last fully formed annulus (none for age 0) plot values against month of capture determine periodicity of band formation Poss. combine w/stable isotope analysis fish work no elasmo. work yet proved viable in other chondrichthyans

28 Carlson and Baremore, 2004

29 Neer et al., 2005: Bull shark growth

30 Captive rearing Laboratory or aquaria growth
Particularly useful if poor ring formation, calcification, etc. Morphometric data reveals age and growth Periodicity of growth zone formation in vetebral centra Difficult to determine true baseline & captivity effects

31 Bomb carbon (radiocarbon) aging
Tied to global oceanic rise in 14C following cold war atomic testing Synchronous uptake in marine carbonates Dated marker of calcified structures allowing growth band dating Born < 1956: low Born : higher Born > 1965: declining Regional identification Validation of annulus formation & absolute age

32 Campana et al., 2002

33 Campana et al., 2002

34 Current status of studies
Caillet, 1995 was last major review 115 publications listed in chapter since then (several not included in chapter that were published late 2004 – mid-2005) 68 newly studied spp. among those Methods: most studies combine (mult. validation & mult. verification) most use structure calcification 1°ly vetebral centra (70% of studies reviewed in chap.) dorsal spines (7%) neural arches (1 study) & jaws (1 study) captive growth (9%) tag-recapture (7%) embryonic growth (4%) precision analyses: several growth parameter values 1° reviewed methods = MIR or ratio (50%) + centrum edge modal analysis (25 studies, 22 spp.) tag-recapture (20 studies, 19 spp.; many combined w/OTC marking) lab growth (21 studies; 18 of which used OTC marking) bomb carbon study (Natanson et al., 2002, validated pobeagle growth & indicated shortfin mako growth of 1 ring/yr.) combined w/tag-recapture & OTC Combining validation & verification seems to be the most robust means

35 Growth models von Bertalanffy (VBGF): fish growth
size at a given point in time depends on anabolism & catabolism identification of the growth coefficients are dependent on the given study easy population comparisons fitting allows for fine-tuning problems: small sample size: poor parameter estimation t0 (theoretical size) should be replaced by L0 (length at birth) as 3rd parameter (more to come) Gompertz: larval & early growth S-shaped model function (like Ricker logistic function) also can fit to fine-tune for a given study growth rate = log of asymptotic disk width or length - actual asymptotic disk width or length most commonly used for skates & rays possibly most appropriate for ovoparous spp. possibly most appropriate for spp. that grow in V more than weight or L possibly better estimate captive growth (slowed or atypical growth due to stress) Best fit functions: choice of model based on length-at-age or weight-at-age nonlinear least-squares regression analysis maximum likelihood function

36 VBGF Traditional: Lt = L∞(1-e-k(t-t0)) Modifications
substitute Lo and L for t and t0 Modifications Neer et al., 2005 (following Fabens, 1965) to estimate bull shark growth (modified to fit observed size-at-age data) Lt = L∞(1-be-k(t-t0)) = predicted length at time t b = L∞ = theoretical asymptotic length k = growth coefficient L0 = length at birth compared to fitted models to sex-specific size-at-age data w/traditional VBGF model theoretical longevity estimated at 95% L∞ (5x ln2 k-1) growth model parameters derived from least-squares regression

37 Neer et al., 2005

38 VBGF growth coefficients (k)
k = average rate to reach maximal length or size from length at birth Studies fitted to VBGF allow estimates of L∞ (asymptotic size), k, & Lo or to high k = fast growth rate (0 – 1) Large variance among spp. & studies k in chimaera: 0.05 – 0.47 k in sawfish: 0.07 – 0.08 k in guitarfish, torpedo rays & stingrays: 0.2 – 0.5 k in skates: 0.05 – 0.5 k in whale shark: 0.03 – 0.05 affected by: sample size, aging methods, verification, validation, & growth and model fitting

39 Estimating maturity & lifespan
Tmat estimated by various means & shows great variance among spp. & studies (sex, spp., method, study) chimaeras: 2.9 – 6.0 years C. monstrosa: 11.2 – 13.4 years sawfish: 10 years guitarfish, torpedo rays, stingrays: 1 – 9 years skates: 4 – 13 years angel shark: 11 years sixgill shark: 5 – 21 years carpet sharks: 16 – 25 years dog sharks: 4 – 45 years Related to longevity estimates (5x ln2 k-1) ( well duh!) chimaeras: years C. monstrosa: 29 years sawfish: years skates: years angel shark: 35 years carpet sharks: 9-35 years dog sharks: years

40 Back to why Better knowledge = better estimation of growth potential
Better estimation of growth potential = better management strategies Real consequences mean that precise, careful, redundant work is needed

41 Key references and citations
Goldman, K.J Chapter 6: Age and growth of elasmobranch fishes. unidentified book. Serra-Pereira, B., Figueiredo, I., Bordalo-Machado, P., Farias, I., Moura, T. and Gordo, L.S Age and growth of Raja clavata Linnaeus, 1758 – evaluation of ageing precision using different types of caudal denticles. Elasmobranch Fish. Sci. ICES CM. N-17:1-10. Gallagher, M.J., Nolan, C.P. and Jeal, F Age, growth and maturity of the commercially important ray species from the Irish Sea. e-journal NW Atl. Fish. Sci. V35(art.10):http://journal.nafo.int/35/10-gallagher.html. Carlson, J.K. and Baremore, I.E Growth dynamics of the spinner shark (Carcharhinus brevipinna) off the United States southeast and Gulf of Mexico coasts: a comparison of methods. Fish. Bull. 103: Natason, L.J., Casey, J.G. and Kohler, N.E Growth of the tiger shark, Galeocerdo cuvier, in the western North Atlantic based on tag returns and length frequencies; and a note on the effects of tagging. Fish. Bull. 97: McFarlane, G.A., King, J.R. and Sauders, M.W Preliminary study on the use of neural arches in the age determination of bluntnose sixgill sharks (Hexanchus griseus) Fish. Bull. 100: Gburski, C.M Ageing procedures for the big skate (Raja binoculata), longnose skate (Raja rhina), Alaska skate (Bathyraja parmifera), Aleutian skate (Bathyraja aleutica) and Berring skate (Bathyraja interrupta) at the Alaska Fisheries Science Center. In submission. Calis, E., Jackson, E.H., Nolan, C.P. and Jeal, F Preliminary age and growth estimates of the rabbitfish, Chimaera monstrosa, with implications for future resource management. e-journal NW Atl. Fish. Sci. V35(art.21):http://journal.nafo.int/35/21-calis.html Simpfendorfer, C.A Growth rates of juvenile dusky sharks, Carcharhinus obscurus (Lesueur, 1818), from southwestern Australia estimated from tag-recapture data. Fish. Bull. 98: Wintner, S.P. and Dudley, S.F.J Age and growth estimates for the tiger shark, Galeocerdo cuvier, from the east coast of South Africa. Mar. Freshwater Res. 51:43-53. Neer, J.A., Thompson, B.A. and Carlson, J.K Age and growth of the Carcharhinus leucas in the northern Gulf of Mexico: incorporating variability in size at birth. J. Fish. Biol. 67: , Campana, S.E., Natanson, L.J. and Myklevoll, S Bomb dating and age determination of large pelagic sharks. Can. J. Fish. Aquat. Sci. 59: Conrath, C.L., Gelsleichter, J. and Musick, J.A Age and growth of the smooth dogfish (Mustelus canis) in the northwest Atlantic Ocean. Fish. Bull. 100: Age determination of elasmobranchs. Age growth and demographic studies. Pacific shark research center. Moss Landing Marine Laboratories. Apex predators: age and growth in sharks. Questions, comments or snide remarks?


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