age determination and validation in chondrichthyan fishes presented by kara baca and sharon...
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Age Determination and Age Determination and Validation in Validation in
Chondrichthyan FishesChondrichthyan Fishes
Presented by Kara Baca Presented by Kara Baca
and Sharon Homer-and Sharon Homer-DrummondDrummond
MethodologyMethodology
Age determination process:Age determination process: Collection of hard part samplesCollection of hard part samples Preparation of the hard partsPreparation of the hard parts Examination (age reading)Examination (age reading) Assessment of validity and Assessment of validity and
reliabilityreliability Interpretation (modeling growth)Interpretation (modeling growth)
Hard parts usedHard parts used
Vertebral centra Vertebral centra Dorsal fin spinesDorsal fin spines Neural archesNeural arches Caudal thornsCaudal thorns
Vertebral CentraVertebral Centra Larger, more Larger, more
anterior centra anterior centra should be should be usedused
Whole or Whole or sectionedsectioned Vertebrae Vertebrae
should be should be sectioned sectioned sagittally sagittally (longitudinally)(longitudinally)
Dorsal Fin SpinesDorsal Fin Spines Used Used
particularly in particularly in dogfish sharksdogfish sharks
Spines from Spines from second dorsal second dorsal fin are fin are preferredpreferred
Used whole or Used whole or longitudinally longitudinally cutcut
Neural ArchesNeural Arches
May be useful for species that have May be useful for species that have poorly calcified vertebral centrapoorly calcified vertebral centra
Preliminary studies with sixgill Preliminary studies with sixgill sharkssharks
Caudal Thorns and Other Caudal Thorns and Other StructuresStructures
Caudal thorns used Caudal thorns used with vertebral with vertebral centra to determine centra to determine age in bathyrajid age in bathyrajid speciesspecies
Evidence for growth Evidence for growth bands found in bands found in upper jaw of the upper jaw of the wobbegong wobbegong Orectolobus Orectolobus japonicusjaponicusSerra-Pereria et al., 2005
Preparation of Samples Preparation of Samples (Centra)(Centra) Thaw (if frozen) or wash (if Thaw (if frozen) or wash (if
preserved in alcohol)preserved in alcohol) Clean excess tissue and Clean excess tissue and
separate into individual separate into individual centracentra
Sectioning typically done Sectioning typically done with low-speed diamond-with low-speed diamond-bladed sawbladed saw
After mounting sections to After mounting sections to slides, sand with wet fine-slides, sand with wet fine-grit sandpaper to grit sandpaper to approximately 0.3 to 0.5 approximately 0.3 to 0.5 mm and air-drymm and air-dry
Binocular dissecting Binocular dissecting microscope is generally microscope is generally used for analysisused for analysis
Age DeterminationAge Determination View wide bands View wide bands
(opaque) separated by (opaque) separated by distinct narrow bands distinct narrow bands (translucent)(translucent)
Tend to occur in Tend to occur in summer (wide) and summer (wide) and winter (narrow)winter (narrow)
Each pair of Each pair of wide/narrow bands wide/narrow bands considered to considered to represent an annual represent an annual growth cyclegrowth cycle
Validity must be testedValidity must be tested Age determination for Age determination for
spines are nearly spines are nearly identicalidentical
Banding in Neural ArchesBanding in Neural Arches
Distinct bands in Distinct bands in sixgill sharkssixgill sharks
Potential use in Potential use in age age determinationdetermination
Staining & imageryStaining & imagery Imagery & enhancementImagery & enhancement
scanning EM (atypical)scanning EM (atypical) steromicroscopysteromicroscopy binocular light microscopybinocular light microscopy X-radiograophy (atypical)X-radiograophy (atypical) X-ray spectrometryX-ray spectrometry Graphite microtopographyGraphite microtopography
StainingStaining silver nitrate (McFarlane et silver nitrate (McFarlane et
al., 2002)al., 2002) cobalt nitrate (Hoenig and cobalt nitrate (Hoenig and
Brown, 1998)Brown, 1998) ammonium sulfide (Hoenig ammonium sulfide (Hoenig
and Brown, 1988)and Brown, 1988) haemotoxylinhaemotoxylin cedar wood oil, alizarin red, cedar wood oil, alizarin red,
crystal violet, salts (Cu, Fe, crystal violet, salts (Cu, Fe, & lead)& lead)
HistologyHistologyGoldman, 2004
Evaluating Precision Evaluating Precision Average percent error (APE)Average percent error (APE)
May serve as good relative indicator of precision May serve as good relative indicator of precision within and between readerswithin and between readers
However, tells which reader was less variable, not However, tells which reader was less variable, not which was better or if either was biasedwhich was better or if either was biased
Goldman’s approach to estimating precision:Goldman’s approach to estimating precision: Calculate percent reader agreement (=[No. Calculate percent reader agreement (=[No.
agreed/No. read] x 100) within and between agreed/No. read] x 100) within and between readers for all samplesreaders for all samples
Calculate percent agreement plus or minus one Calculate percent agreement plus or minus one yearyear
Calculate percent agreement with individuals Calculate percent agreement with individuals divided into appropriate length or disk width divided into appropriate length or disk width groupsgroups
Test for biasTest for bias Criticism: varies widely among species and ages Criticism: varies widely among species and ages
within a specieswithin a species
Tests for BiasTests for Bias Age bias plot- Age bias plot-
graphing one graphing one reader vs. the reader vs. the other and other and referencing referencing equivalence line of equivalence line of the 2 readers (45° the 2 readers (45° line through the line through the origin)origin)
Chi-square tests of Chi-square tests of symmetry, such as symmetry, such as Bowker’sBowker’s
Evans-Hoenig testEvans-Hoenig test
Back-CalculationBack-Calculation
Method for describing the growth Method for describing the growth history of each individual sampledhistory of each individual sampled
Numerous methods – formulas that Numerous methods – formulas that follow hard part or body proportion follow hard part or body proportion hypothesis are recommendedhypothesis are recommended Proportional relationship between animal Proportional relationship between animal
length or disk width and radius of length or disk width and radius of vertebral centrum or distance from focus vertebral centrum or distance from focus to each annulus within a given centrumto each annulus within a given centrum
Verification & Verification & ValidationValidation
Confirmation of age Confirmation of age determination by determination by
indeterminate and indeterminate and determinate methodsdeterminate methods
Why validation & Why validation & verification?verification?Caillet, 1990Caillet, 1990
Apex Predators website: Apex Predators website: “Sharks are long-lived “Sharks are long-lived animals that grow very slowly and do not produce animals that grow very slowly and do not produce many young. In many parts of the world, sharks many young. In many parts of the world, sharks are fished commercially, thus, in order to ensure are fished commercially, thus, in order to ensure proper management of the stocks, age and growth proper management of the stocks, age and growth data must be obtained. With this data, we can data must be obtained. With this data, we can determine the longevity of the species as well as determine the longevity of the species as well as maximum age, age at maturity, growth rate, and maximum age, age at maturity, growth rate, and differences in growth between males and females.”differences in growth between males and females.”
The process of evaluating growth zone The process of evaluating growth zone deposition deposition in fishes can be divided into in fishes can be divided into verification and validation.verification and validation.
Verification: Verification: “… conforming an age estimate by “… conforming an age estimate by comparison with other indeterminate methods”comparison with other indeterminate methods”
Validation: Validation: “… proving the accuracy of age “… proving the accuracy of age estimates by comparison with a determinate age”estimates by comparison with a determinate age”
Some methods Some methods of validationof validation
Chemical tagging of Chemical tagging of wild fishwild fish
Mark-recapture of Mark-recapture of known-age fish*known-age fish*
Bomb carbon Bomb carbon dating*dating*
Growth ring Growth ring frequencyfrequency distinction between distinction between
absolute age (*) & absolute age (*) & periodicityperiodicity
Centrum age Centrum age analysisanalysis
Relative marginal Relative marginal increment analysisincrement analysis
Some methods Some methods of verificationof verification
Size mode analysisSize mode analysis Primarily a Primarily a verificationverification tool tool Progression of discrete Progression of discrete
length modes over timelength modes over time Size modes taken from a Size modes taken from a
random sample of all size random sample of all size classes from a populationclasses from a population
Mean or median sizes in age Mean or median sizes in age classes assessed by other classes assessed by other means (e.g.: age classes means (e.g.: age classes predicted by von Bertalanffy predicted by von Bertalanffy growth function applied to growth function applied to physical assessment)physical assessment)
Random sample size modes Random sample size modes and mean or median sizes at and mean or median sizes at age comparedage compared
Coincidence supports Coincidence supports assumption of age classesassumption of age classes
Monitor discrete length Monitor discrete length modes across a given time modes across a given time period at discrete intervalsperiod at discrete intervals
Tag-recaptureTag-recapture Initial in field:Initial in field:
CaptureCapture MeasureMeasure WeighWeigh TagTag ReleaseRelease
Recapture and assess for Recapture and assess for growth in length and/or growth in length and/or weightweight
Compared to von Compared to von Bertalanffy growth Bertalanffy growth functions, TET, functions, TET, oxytetracycline (OTC) or oxytetracycline (OTC) or other methods, based on other methods, based on size changes between size changes between tagging and recapturetagging and recapture
Chemical marking, tag-recapture Chemical marking, tag-recapture & lab& lab
Validation of absolute age focuses on validating “temporal Validation of absolute age focuses on validating “temporal periodicity of … growth increment formation”periodicity of … growth increment formation”
Tetracycline (TET): standard for marking free-swimming animalsTetracycline (TET): standard for marking free-swimming animals OTC: marks by binding to CaOTC: marks by binding to Ca2+2+ & depositing to active & depositing to active
calcification sitescalcification sites• 25mg/kg bw IM25mg/kg bw IM• + external tag+ external tag• highly visible marks in vetebral centra & dorsal fin spines under UVhighly visible marks in vetebral centra & dorsal fin spines under UV• use body growth & calcification changes to compare ‘time at liberty’ use body growth & calcification changes to compare ‘time at liberty’
[release] w/growth band deposition (# rings in vetra centra or spine [release] w/growth band deposition (# rings in vetra centra or spine post-injection = time hacks)post-injection = time hacks)
• lab or captivitylab or captivity Tag-recapture + markingTag-recapture + marking
• tag + OTC followed by recapturetag + OTC followed by recapture• tag + TET followed by recapturetag + TET followed by recapture
Other tagsOther tags• Fluorescein (not well-evaluated in elasmo.; 5-10mg/kg bw, Fluorescein (not well-evaluated in elasmo.; 5-10mg/kg bw,
higher=mortality)higher=mortality)• Calcein (not well-evaluated in elasmo. .; 5-10mg/kg bw, Calcein (not well-evaluated in elasmo. .; 5-10mg/kg bw,
higher=mortality)higher=mortality) Define age Define age && indiv. growth characteristics indiv. growth characteristics Combining information from mark w/observed growth Combining information from mark w/observed growth
changeschanges
Tetracycline groupTetracycline group
Broad spectrum Ab’s that block bacterial Broad spectrum Ab’s that block bacterial protein synthesis by inhibition of aminoacyl-protein synthesis by inhibition of aminoacyl-t-RNA binding to the rRNA A site.t-RNA binding to the rRNA A site.
TET = tetracyclineTET = tetracycline higher water solubility at pH = 7, than other Ab’s higher water solubility at pH = 7, than other Ab’s
in same groupin same group OTC = oxytetracyclineOTC = oxytetracycline Inject TET or OTC at capture while taggingInject TET or OTC at capture while tagging
25 mg/kg25 mg/kg absorbed & deposited at growth sitesabsorbed & deposited at growth sites only mark glows under UVonly mark glows under UV pairs > mark = growth over timepairs > mark = growth over time
Centrum edge analysisCentrum edge analysis Centrum edge analysis:Centrum edge analysis:
Compares opacity (width) &/or translucency Compares opacity (width) &/or translucency (density) of centrum edge over time(density) of centrum edge over time
• measure or grade edgemeasure or grade edge• compare to time of year or seasoncompare to time of year or season• detail: analyze Cadetail: analyze Ca2+2+ & PO & PO4 4
–– at edge by x-ray or at edge by x-ray or electron microprobe spectrometryelectron microprobe spectrometry
• not used much yet:not used much yet: recaptured nurse sharks marked with TET (Carrier recaptured nurse sharks marked with TET (Carrier
and Radtke, 1988)and Radtke, 1988) 4 ray species in the Irish Sea marked with TET 4 ray species in the Irish Sea marked with TET
(Gallagher et al., 2004)(Gallagher et al., 2004) tiger sharks (Winter and Dudley, 2000)tiger sharks (Winter and Dudley, 2000)
http://journal.nafo.int/35/10-gallagher.html
Winter and Dudley, 2000
Relative marginal increment Relative marginal increment analysisanalysis
RMI = MIR (ratio): (VR-RRMI = MIR (ratio): (VR-Rnn)/(R)/(Rnn-R-Rn-1n-1)) ParametersParameters
• MIR – marginal increment ratioMIR – marginal increment ratio• VR = vetebral radiusVR = vetebral radius• RRnn = distance from center to outer edge of last complete = distance from center to outer edge of last complete
bandband• RRn-1n-1 = distance from center to outer edge of next-to-last = distance from center to outer edge of next-to-last
complete bandcomplete band Direct: plot against month to find band formation trend Direct: plot against month to find band formation trend
lineline Assess seasonal band &/or ring depositionAssess seasonal band &/or ring deposition
• measure margin (growth) area of centrum from last growth measure margin (growth) area of centrum from last growth ring to centrum edgering to centrum edge
• divide by width of last fully formed annulus (none for age 0)divide by width of last fully formed annulus (none for age 0)• plot values against month of captureplot values against month of capture• determine periodicity of band formationdetermine periodicity of band formation
Poss. combine w/stable isotope analysisPoss. combine w/stable isotope analysis• fish workfish work• no elasmo. work yetno elasmo. work yet• proved viable in other chondrichthyansproved viable in other chondrichthyans
Captive rearingCaptive rearing Laboratory or Laboratory or
aquaria growthaquaria growth Particularly useful if Particularly useful if
poor ring formation, poor ring formation, calcification, etc.calcification, etc.
Morphometric data Morphometric data reveals age and reveals age and growthgrowth
Periodicity of growth Periodicity of growth zone formation in zone formation in vetebral centravetebral centra
Difficult to determine Difficult to determine true baseline & true baseline & captivity effectscaptivity effects
www.pac.dfo-mpo.gc.ca
Bomb carbon (radiocarbon) Bomb carbon (radiocarbon) agingaging
Tied to global oceanic rise in Tied to global oceanic rise in 1414C following C following cold war atomic testingcold war atomic testing
Synchronous uptake in marine Synchronous uptake in marine carbonatescarbonates
Dated marker of calcified structures Dated marker of calcified structures allowing growth band datingallowing growth band dating Born < 1956: lowBorn < 1956: low Born 1956-1965: higherBorn 1956-1965: higher Born > 1965: decliningBorn > 1965: declining
Regional identificationRegional identification Validation of annulus formation & Validation of annulus formation &
absolute ageabsolute age
Current status of studiesCurrent status of studies Caillet, 1995 was last major reviewCaillet, 1995 was last major review
115 publications listed in chapter since then (several not included in 115 publications listed in chapter since then (several not included in chapter that were published late 2004 – mid-2005)chapter that were published late 2004 – mid-2005)
68 newly studied spp. among those68 newly studied spp. among those Methods: most studies combine (mult. validation & mult. Methods: most studies combine (mult. validation & mult.
verification)verification) most use structure calcificationmost use structure calcification
• 1°1°lyly vetebral centra (70% of studies reviewed in chap.) vetebral centra (70% of studies reviewed in chap.)• dorsal spines (7%)dorsal spines (7%)• neural arches (1 study) & jaws (1 study)neural arches (1 study) & jaws (1 study)
captive growth (9%)captive growth (9%) tag-recapture (7%)tag-recapture (7%) embryonic growth (4%)embryonic growth (4%) precision analyses: several growth parameter valuesprecision analyses: several growth parameter values
1° reviewed methods = MIR or ratio (50%) + centrum edge1° reviewed methods = MIR or ratio (50%) + centrum edge modal analysis (25 studies, 22 spp.)modal analysis (25 studies, 22 spp.) tag-recapture (20 studies, 19 spp.; many combined w/OTC marking)tag-recapture (20 studies, 19 spp.; many combined w/OTC marking) lab growth (21 studies; 18 of which used OTC marking)lab growth (21 studies; 18 of which used OTC marking) bomb carbon study (Natanson et al., 2002, validated pobeagle growth bomb carbon study (Natanson et al., 2002, validated pobeagle growth
& indicated shortfin mako growth of 1 ring/yr.)& indicated shortfin mako growth of 1 ring/yr.)• combined w/tag-recapture & OTCcombined w/tag-recapture & OTC
Combining validation & verification seems to be the most robust Combining validation & verification seems to be the most robust meansmeans
Growth modelsGrowth models von Bertalanffy (VBGF): fish growthvon Bertalanffy (VBGF): fish growth
size at a given point in time depends on anabolism & catabolismsize at a given point in time depends on anabolism & catabolism identification of the growth coefficients are dependent on the given identification of the growth coefficients are dependent on the given
studystudy easy population comparisonseasy population comparisons fitting allows for fine-tuningfitting allows for fine-tuning problems:problems:
• small sample size: poor parameter estimationsmall sample size: poor parameter estimation• tt00 (theoretical size) should be replaced by L (theoretical size) should be replaced by L00 (length at birth) as 3 (length at birth) as 3rdrd
parameter (more to come)parameter (more to come) Gompertz: larval & early growthGompertz: larval & early growth
S-shaped model function (like Ricker logistic function)S-shaped model function (like Ricker logistic function) also can fit to fine-tune for a given studyalso can fit to fine-tune for a given study growth rate = log of asymptotic disk width or length - actual growth rate = log of asymptotic disk width or length - actual
asymptotic disk width or lengthasymptotic disk width or length most commonly used for skates & raysmost commonly used for skates & rays possibly most appropriate for ovoparous spp.possibly most appropriate for ovoparous spp. possibly most appropriate for spp. that grow in V more than weight or possibly most appropriate for spp. that grow in V more than weight or
LL possibly better estimate captive growth (slowed or atypical growth possibly better estimate captive growth (slowed or atypical growth
due to stress)due to stress) Best fit functions: choice of model based on length-at-age or Best fit functions: choice of model based on length-at-age or
weight-at-ageweight-at-age nonlinear least-squares regression analysisnonlinear least-squares regression analysis maximum likelihood functionmaximum likelihood function
VBGFVBGF Traditional: LTraditional: Ltt = L = L∞∞(1-e(1-e-k(t-t-k(t-t
00))))
substitutesubstitute LLo o and L for t and tand L for t and t00
ModificationsModifications Neer et al., 2005 (following Fabens, 1965) to Neer et al., 2005 (following Fabens, 1965) to
estimate bull shark growth (modified to fit observed estimate bull shark growth (modified to fit observed size-at-age data)size-at-age data)• LLtt = L = L∞∞(1-be(1-be-k(t-t-k(t-t
00))) = predicted length at time t) = predicted length at time t
• b = b =
• LL∞∞ = theoretical asymptotic length = theoretical asymptotic length
• k = growth coefficientk = growth coefficient
• LL00 = length at birth = length at birth
compared to fitted models to sex-specific size-at-age compared to fitted models to sex-specific size-at-age data w/traditional VBGF modeldata w/traditional VBGF model• theoretical longevity estimated at 95% Ltheoretical longevity estimated at 95% L∞∞ (5x ln2 k (5x ln2 k-1-1))
• growth model parameters derived from least-squares growth model parameters derived from least-squares regressionregression
VBGF growth coefficients VBGF growth coefficients (k)(k)
k = average rate to reach maximal length k = average rate to reach maximal length or size from length at birthor size from length at birth
Studies fitted to VBGF allow estimates of LStudies fitted to VBGF allow estimates of L∞∞ (asymptotic size), k, & L(asymptotic size), k, & Loo or t or too high k = fast growth rate (0 – 1)high k = fast growth rate (0 – 1)
Large variance among spp. & studiesLarge variance among spp. & studies k in chimaera: 0.05 – 0.47k in chimaera: 0.05 – 0.47 k in sawfish: 0.07 – 0.08k in sawfish: 0.07 – 0.08 k in guitarfish, torpedo rays & stingrays: 0.2 – k in guitarfish, torpedo rays & stingrays: 0.2 –
0.50.5 k in skates: 0.05 – 0.5k in skates: 0.05 – 0.5 k in whale shark: 0.03 – 0.05k in whale shark: 0.03 – 0.05 affected by: sample size, aging methods, affected by: sample size, aging methods,
verification, validation, & growth and model verification, validation, & growth and model fittingfitting
Estimating maturity & Estimating maturity & lifespanlifespan
TTmatmat estimated by various means & shows great variance estimated by various means & shows great variance among spp. & studies (sex, spp., method, study)among spp. & studies (sex, spp., method, study)
chimaeras: 2.9 – 6.0 yearschimaeras: 2.9 – 6.0 years• CC.. monstrosa monstrosa: 11.2 – 13.4 years: 11.2 – 13.4 years
sawfish: 10 yearssawfish: 10 years guitarfish, torpedo rays, stingrays: 1 – 9 yearsguitarfish, torpedo rays, stingrays: 1 – 9 years skates: 4 – 13 yearsskates: 4 – 13 years angel shark: 11 yearsangel shark: 11 years sixgill shark: 5 – 21 yearssixgill shark: 5 – 21 years carpet sharks: 16 – 25 yearscarpet sharks: 16 – 25 years dog sharks: 4 – 45 yearsdog sharks: 4 – 45 years
Related to longevity estimates (5x ln2 kRelated to longevity estimates (5x ln2 k-1-1) ( well duh!)) ( well duh!) chimaeras: 5 - 10 yearschimaeras: 5 - 10 years
• CC.. monstrosa monstrosa: 29 years: 29 years sawfish: 30 - 44 yearssawfish: 30 - 44 years guitarfish, torpedo rays, stingrays: 1 – 9 yearsguitarfish, torpedo rays, stingrays: 1 – 9 years skates: 9 - 50 yearsskates: 9 - 50 years angel shark: 35 yearsangel shark: 35 years carpet sharks: 9-35 yearscarpet sharks: 9-35 years dog sharks: 12 - 70 yearsdog sharks: 12 - 70 years
Back to whyBack to why
Better knowledge = better Better knowledge = better estimation of growth potentialestimation of growth potential
Better estimation of growth Better estimation of growth potential = better management potential = better management strategiesstrategies
Real consequences mean that Real consequences mean that precise, careful, redundant work precise, careful, redundant work is neededis needed
Key references and citationsKey references and citations
Goldman, K.J. 2004. Chapter 6: Age and growth of elasmobranch fishes. unidentified book.Goldman, K.J. 2004. 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. 2005. Age Serra-Pereira, B., Figueiredo, I., Bordalo-Machado, P., Farias, I., Moura, T. and Gordo, L.S. 2005. Age
and growth of and growth of Raja clavataRaja clavata Linnaeus, 1758 – evaluation of ageing precision using different types of Linnaeus, 1758 – evaluation of ageing precision using different types of caudal denticles. Elasmobranch Fish. Sci. ICES CM. N-17:1-10.caudal denticles. Elasmobranch Fish. Sci. ICES CM. N-17:1-10.
Gallagher, M.J., Nolan, C.P. and Jeal, F. 2004. Age, growth and maturity of the commercially important Gallagher, M.J., Nolan, C.P. and Jeal, F. 2004. Age, growth and maturity of the commercially important ray species from the Irish Sea. e-journal NW Atl. Fish. Sci. V35(art.10):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. 2005. Growth dynamics of the spinner shark (Carlson, J.K. and Baremore, I.E. 2005. Growth dynamics of the spinner shark (Carcharhinus Carcharhinus brevipinnabrevipinna) off the United States southeast and Gulf of Mexico coasts: a comparison of methods. ) off the United States southeast and Gulf of Mexico coasts: a comparison of methods. Fish. Bull. 103:280-291.Fish. Bull. 103:280-291.
Natason, L.J., Casey, J.G. and Kohler, N.E. 1999. Growth of the tiger shark, Natason, L.J., Casey, J.G. and Kohler, N.E. 1999. Growth of the tiger shark, Galeocerdo cuvierGaleocerdo cuvier, in the , in the western North Atlantic based on tag returns and length frequencies; and a note on the effects of western North Atlantic based on tag returns and length frequencies; and a note on the effects of tagging. Fish. Bull. 97:944-953.tagging. Fish. Bull. 97:944-953.
McFarlane, G.A., King, J.R. and Sauders, M.W. 2002. Preliminary study on the use of neural arches in McFarlane, G.A., King, J.R. and Sauders, M.W. 2002. Preliminary study on the use of neural arches in the age determination of bluntnose sixgill sharks (the age determination of bluntnose sixgill sharks (Hexanchus griseusHexanchus griseus) Fish. Bull. 100:861-864.) Fish. Bull. 100:861-864.
Gburski, C.M. 2005. Ageing procedures for the big skate (Gburski, C.M. 2005. Ageing procedures for the big skate (Raja binoculataRaja binoculata), longnose skate (), longnose skate (Raja Raja rhinarhina), Alaska skate (), Alaska skate (Bathyraja parmiferaBathyraja parmifera), Aleutian skate (), Aleutian skate (Bathyraja aleuticaBathyraja aleutica) and Berring skate ) and Berring skate ((Bathyraja interruptaBathyraja interrupta) at the Alaska Fisheries Science Center. In submission.) at the Alaska Fisheries Science Center. In submission.
Calis, E., Jackson, E.H., Nolan, C.P. and Jeal, F. 2005. Preliminary age and growth estimates of the Calis, E., Jackson, E.H., Nolan, C.P. and Jeal, F. 2005. Preliminary age and growth estimates of the rabbitfish, rabbitfish, Chimaera monstrosaChimaera monstrosa, with implications for future resource management. e-journal NW Atl. , with implications for future resource management. e-journal NW Atl. Fish. Sci. V35(art.21):Fish. Sci. V35(art.21):http://journal.nafo.int/35/21-calis.html
Simpfendorfer, C.A. 2000. Growth rates of juvenile dusky sharks, Simpfendorfer, C.A. 2000. Growth rates of juvenile dusky sharks, Carcharhinus obscurusCarcharhinus obscurus (Lesueur, (Lesueur, 1818), from southwestern Australia estimated from tag-recapture data. Fish. Bull. 98:811-822.1818), from southwestern Australia estimated from tag-recapture data. Fish. Bull. 98:811-822.
Wintner, S.P. and Dudley, S.F.J. 2000. Age and growth estimates for the tiger shark, Wintner, S.P. and Dudley, S.F.J. 2000. Age and growth estimates for the tiger shark, Galeocerdo Galeocerdo cuviercuvier, from the east coast of South Africa. Mar. Freshwater Res. 51:43-53., from the east coast of South Africa. Mar. Freshwater Res. 51:43-53.
Neer, J.A., Thompson, B.A. and Carlson, J.K. 2005. Age and growth of the Neer, J.A., Thompson, B.A. and Carlson, J.K. 2005. Age and growth of the Carcharhinus leucasCarcharhinus leucas in the in the northern Gulf of Mexico: incorporating variability in size at birth. J. Fish. Biol. 67:370-383., northern Gulf of Mexico: incorporating variability in size at birth. J. Fish. Biol. 67:370-383.,
Campana, S.E., Natanson, L.J. and Myklevoll, S. 2002. Bomb dating and age determination of large Campana, S.E., Natanson, L.J. and Myklevoll, S. 2002. Bomb dating and age determination of large pelagic sharks. Can. J. Fish. Aquat. Sci. 59:450-455.pelagic sharks. Can. J. Fish. Aquat. Sci. 59:450-455.
Conrath, C.L., Gelsleichter, J. and Musick, J.A. 2002. Age and growth of the smooth dogfish (Conrath, C.L., Gelsleichter, J. and Musick, J.A. 2002. Age and growth of the smooth dogfish (Mustelus Mustelus caniscanis) in the northwest Atlantic Ocean. Fish. Bull. 100:674-682.) in the northwest Atlantic Ocean. Fish. Bull. 100:674-682.
www.pac.dfo.-mpo.gc.cawww.pac.dfo.-mpo.gc.ca. Age determination of elasmobranchs.. Age determination of elasmobranchs. www.psrc.mlml.calstate.eduwww.psrc.mlml.calstate.edu. Age growth and demographic studies.. Age growth and demographic studies. www.flmnh.ufl.eduwww.flmnh.ufl.edu. Pacific shark research center. Moss Landing Marine Laboratories.. Pacific shark research center. Moss Landing Marine Laboratories. www.na.nefsc.noaa.govwww.na.nefsc.noaa.gov. Apex predators: age and growth in sharks.. Apex predators: age and growth in sharks.