Table Of ContentAge Determination and Growth in the Male South African Fur
Seal Arctocephaluspusillus pusillus (Pinnipedia: Otariidae)
Using External Body Measurements
C. L. Stewardson', T. Prvan-, M. A. Meyer^ and R. J. Ritchie''*
'Botany and Zoology, Australian National University, Canberra, ACT,Australia. (Present address. Fisheries
and Marine Sciences Program Bureau ofRural Sciences, The Department ofAgriculture, Fisheries and
CANBERRAACT
Forestry, 2601 Australia).
NSW
-Department ofStatistics, Macquarie University, 2109,Australia.
^Marine and Coastal Management (MCM), Rogge Bay, Cape Town, SouthAfrica.
NSW
''School ofBiological Sciences, The University ofSydney, 2006, Australia.
*CorrespondingAuthor ([email protected])
Stewardson, C.L., Prvan, T., Meyer, M.A. and Ritchie, R.J. (2009). Age determination and growth in the
male South African fur seal ArctocephahispiisiUiispiisiUiis (Pinnipedia: Otariidae) using external body
measurements. Proceedings oftheLinnean SocietyofNewSoiithWales 130, 219-244.
Morphology, relative size and growth of the South African fur seal or Cape fur seal, Arctocephahis
pusilhispiisilliis, from the coast ofsouthern Africa are described and comparisons made to data available
on the closely relatedAustralian fur seal (Arctocephaluspusillus doriferus) and the New Zealand fur seal
(Arctocephalusforsteri). Useful information can be gained from body measurements of seal carcasses
provided canine teeth are extracted for aging. External body measurements (12 linear variables) were
examined in relation to standard body length (SBL) and chronological age (y) using linearregression and
non-linearleastsquaresfittingasappropriate.Animalsrangedfrom< 1 monthto> 12y. Ofthe 149animals
in the study, 39 were animals of known-age based on tagging; 34 were aged from highly reproducible
counts ofincremental lines observed inthe dentine ofuppercanines (i.e., range 1-10y); 10were identified
as adults > 12 y (i.e., pulp cavity ofthe upper canine closed); and 66 were not aged. At birth, male South
African fiir seals are 35% (c. 69 cm) oftheir mean adult size. At puberty, they are 57% (c. 113 cm). The
foreflippersmeasure25-26%(c. 18 cm)ofstandardbodylength(SBL)inpups, and24%(c. 48 cm)ofSBL
in adults. The hind flippers are considerably shorter, measuring 19% (c. 13 cm) in pups, and 14.5% (c. 29
cm) in adults. Axillary girth is usually about 51-61% ofSBL. Growth ofSBL was rapid during the early
postnatalperiodwithasignificantgrowth spurtoccurringattheonsetofpuberty (2-3 y).Therateofgrowth
slowed significantly between 6 and 7 y. Social maturity was reached at about 9 to 10 y. Growth slowed
thereafter The mean SBL for aged males >10 y and unaged animals > 200 cm was 199 cm. Relative to
SBL, facial variables andthe fore/hindlimbs scaledwithnegative slope relativeto SBL orwerenegatively
allometric; dpofsnoutto genital opening scaledwithpositive slope; andtipofsnouttoanteriorinsertionof
the foreflipperwaspositively allometric. Relativeto age, bodyvariables scaledwere negatively allometric.
SBLwas foundtobea 'rough indicator'ofage andagegroup. Thegrowthkineticsofjuvenileandadultthe
SouthAfrican fur seal and theAustralian fur seal are best describedby the logistic and double exponential
(Gompertz) modelsratherthan the exponential von Bertalanffymodel.Australian furseals grow at a faster
rate butasymptotic maximum sizes are similarin SouthAfricanandAustralian fiirseals.
Manuscriptreceived21 May 2008, accepted forpublication 17 December2008.
Keywords: AUometry,Arctocephaluspusillus doriferus,Arctocephaluspusilluspusillus,Australian fur
seal, body, growth, growth curve modelling, pinnipeds. SouthAfrican furseal.
evolutionary links within andbetweenpopulations of
INTRODUCTION the same species and between species. Growth and
body-size estimates can be used for monitoring the
Data on the physical growth of pinnipeds is effects of population pressures and changes in the
important to understanding the biology, ecology and quality of the habitat of marine mammals (Bester
BODY MEASUPIEMENTS OF SOUTH AFRICAN FUR SEALS
and Van Jaarsveld, 1994). Within the Otariidae (fur McKenzie et al., 2007) and the subantarctic fur seal
seals and sea lions) quantitative descriptions of (Bester and Van Jaarsveld, 1994). Apart from studies
growth in body length based on animals aged from by Scheffer and Wilke (1953) and Payne (1979)
tooth structure, or on animals of known-age (i.e., information on the relative growth of external body
animals tagged or branded as pups), are available for measurements ofother fur seals is scant, e.g., axillary
several species offur seals and sea lions including the girth vs. standard body length, length of limbs vs.
Australian fur seal {Arctocephaliispusillus doriferus) standard body length.
(Amould and Wameke, 2002) which is very closely Here we examine the body measurements of 149
related to the South African fur seal (Wynen et al., male South African fiir seals, Arctocephaluspusillus
2001); the New Zealand fur seal {Arctocephalus pusillus, from Southem Africa. Specific objectives
forsteri) (Dickie and Dawson, 2003; McKenzie et were to: (i) describe the general morphology of the
al., 2007), the subantarctic fur seal {Arctocephalus animal; (ii) quantify growth of body measurements
=
tropicalis) (Bester and Van Jaarsveld, 1994), the (12 variables) relative to standard body length {n
Antarctic fur seal {Arctocephalus gazella) (Payne, 134 animals) and chronological age {n = 83 animals),
1979; Krylov and Popov, 1980; McLaren, 1993), the (iii) determine if standard body length (SBL) is a
Northern fur seal {Callorhinus ursimis) (Scheffer and usefial indicator ofage, (iv) compare three commonly
Wilke, 1953; Bychkov, 1971; Bigg, 1979; Lander, used models for the growth kinetics ofSouthAfrican
1979; McLaren, 1993; Trites and Bigg, 1992, 1996) fursealscomparedtoAustralianfiarseals(exponential
and the sea lions, Eumetopiasjubatus, the Steller sea saturation curve or von Bertalanffy curve. Logistic
lion (Fiscus, 1961; Thorsteinson and Lensink, 1962; curve and the double exponential or Gompertz curve)
Calkins and Pitcher, 1983; Loughlin and Nelson, (Zullinger et al., 1984; Zeide, 1993).
1986; McLaren, 1993; Winship et al., 2001), and
Otaria byronia, the South American sea lion (Rosas
MATERIALS AND METHODS
etal., 1993).
PhysicalgrowthinthenorthernfiirsealandSteller
sea lion have been studied in the most detail and is Collection ofspecimens
based onthe largestnumberofanimals ofknown age. South African fur seals were collected along
The general growth curve for the Northern fur seal the Eastem Cape coast of South Africa between
and the Steller sea lion is presumably representative Plettenberg Bay (34° 03'S, 23° 24'E) and East
of all highly polygynous male otariids. Male pups London (33° 03'S, 27° 54'E), from August 1978
ofNorthern sea lions measure c. 66 cm at birth and to December 1995, and accessioned at the Port
grow at a steady rate (Scheffer and Wilke, 1953; Elizabeth Museum (PEM). From this collection, 110
Trites and Bigg, 1992, 1996). Growth is claimed to males were selected for examination. Apart from
increase suddenly at 3^ y (puberty) and slows soon specimens collected before May 1992 {n = 38), all
after attainment of social maturity (McLaren, 1993). specimens were collected by the first author. PEM
Estimated asymptotic length is about 189 cm for animals were aged based on dentition (n = 32), some
males >4 y, and is reachedby c. 12 y in most animals PEM animals were agedusing dentition growthrings,
(McLaren, 1993). Growth curves of the Steller sea animals designated >12 y (n = 10) were animals with
lion are basically similar in shape and also claimed 12 growth rings in their teeth but their pulp cavities
to best fit a logistic ratherthan exponential saturation were closed and so no more growth rings could be
curve (Winship et al., 2001). Asymptotic maximum deposited and so were at least 12 y oldbut could have
size of the Steller sea lion is much larger than fur been older. One animal (PEM2238) was collectedNE
seals: maximum size ofmales is about 3 m and 700 ofthe study area, at Durban.
kg at about 12 y. Measurements from 39 males from Marine
The limited information on growth in body and Coastal Management (MCM), Department
size available for South African fur seals was based of Environment Affairs and Tourism, Cape Town
on measurements that were aged physiologically were also available. These measurements were
(cranial suture age) rather than chronologically (y) from animals that had been tagged as pups, and
MCM
(Rand, 1956). Unfortunately, in South African fur were therefore of known-age (1-13 y). seal
MCM
seals cranial sutures are not a very reliable guide to specimens are accessioned as followed by a
age (Stewardson, 2001; Stewardson et al., 2008). number. The accession numbers of all the animals
Comparisons will be made to data available on the used in the present study are listed in Appendix 1.
Australian fur seal (Amould and Wameke, 2002), The full data set is accessible in the public domain
theNew Zealand fur seal (Dickie and Dawson, 2003; (Stewardson, 2001).
220 Proc. Linn. Soc. N.S.W., 130, 2009
C.L. STEWARDSON, T. PRVAN, M.A. MEYER AND R.J. RITCHIE
Body measurements Currently, examination of tooth stmcture is
Standardnecropsieswereperformedand biolog- the most precise method of age determination in
ical parameters recorded, based on recommendations pinnipeds (McCann, 1993), including South African
of the Committee on Marine Mammals, American fur seals (Oosthuizen, 1997; Oosthuizen and Bester,
SocietyofMammalogists (1967). Uppercanineswere 1997). However, this method can only be used in
collected forage determination. The skull is probably South African fur seals < 12 y. At about 12 y ofage,
the most usefiil part of a seal carcass to retain for closure of the pulp cavity terminates tooth growth
later study but it is not always possible to arrange and no fiirther growth rings are formed. Amould and
for the skull of a dead seal to be retained. Nuisance Wameke (2002) claim that growth rings could be
seals are sometimes culled to satisfy the concerns distinguished in male Australian fur seals up to 16 y
of aquaculture and fisheries interests. From humane and a similar upper limit ofabout 15 y was found in
considerations, permits for such culls usually specify the Antarctic fur seal by Payne (1978). Payne (1978,
that the animals are fatally shot in the head, which 1979) also found that usefijl ages could be estimated
ruins the skulls for morphological studies, but teeth from growth lines in the cementum of the teeth of
for aging can usually be retrieved (Thorsteinson and Antarctic fur seals {A. gazella) but this method was
Lensink, 1962; Pemperton etal., 1993; Winship et al., not attempted in the present study.
2001; Amould and Wameke, 2002; McKenzie et al., Ofthe 149animalsinthestudy:(i)39wereknown-
MCM
2007). Bodymeasurements ofseal carcasses are most age animals; (ii) 34 were aged from counts of
useful ifcanine teeth are extracted for aging. incremental lines observed in the dentine of upper
Measurements (12 variables) were taken to the canines, i.e., range 1-11 y; (iii) 10 were identified as
mm
nearest5 (0.5 cm)usingaflexibletapemeasureor adults > 12 y (pulp cavity ofthe uppercanine closed);
vernier callipers as appropriate (Figure 1). Although (iv) 66 were not aged but could be classified into
body weight and blubber thickness were recorded, subadults and adults based upon SBL; allowing for
these measurements were not included in the analysis (i), (ii) and the problem animals mentioned in (iii)
because they can vary according to physiological above, there was a total of73 animals ofknown age
condition, e.g., body condition is influenced by available for modelling ofgrowth vs. age.
seasonal fluctuations in food supply, illness or injury, For this study, the following age groups were
andbreeding condition. The blubber ofAustralian fur used: pup (< 1 month to 6 months); yearling (7
seals is known to vary seasonally with a maximum months to 1 y 6 months); subadult (1 y 7 months to
in late austral spring (Amould and Wameke, 2002). 7 y 6 months); and adult (> 7 y 7 months) (Table 1).
Apart from specimens collectedbefore May 1992, all Very old animals ofknown-agewerenot available for
PEM measurementswererecordedby thefirstauthor. examination. Estimated longevity is c. 20 y, based
MCM
The majority of measurements were recorded uponthelifespanofzooanimals andknownlife-spans
by the third author. ofotherfurseals (Wickens, 1993).Austrahanmalefiir
seals {A. pusillus doriferus) have a lifespan ofabout 20
Age determination years but femaleAustralian fiar seals are known to live
The age ofanimals was estimated from counts of to over 20 y (Amould and Wameke, 2002). The New
GrowthLayerGroups (GLGs) observedinthedentine Zealand fiar seal {A. forsteri) (McKenzie et al., 2007)
of thin tooth sections (Payne, 1978; Oosthuizen, and the Steller sea lion {Eiimetopiasjubatiis) (Winship
1997; OosthuizenandBester, 1997; Stewardson etal., et al, 2001) both have similar lifespans ofabout 20 y
2008). Upper canines were sectioned longitudinally formales andwell in excess of20 y for females.
using a circular diamond saw. Sections were ground
down to 280-320 p,m, dehydrated, embedded in resin Australian Material
and viewed under a stereomicroscope in polarised The South African fur seal data on SBL vs. age
light (Oosthuizen, 1997; Oosthuizen and Bester, were compared to published material from Amould
1997). Each section was read by one individual five and Wameke (2002) on Australian fur seals. Data
times, without knowledge ofwhich animal was being were read off the graphs in their published paper
examined (repeated blind counts) similar to Payne (AmouldandWameke, 2002) with an accuracy ofthe
(1978). Ages were rounded off to the nearest birth SBL readings ofabout± 1 cm. Fits oftheirdata were
date. The median date ofbirth was assumed to be 1 then compared to similar data for South African fur
December (Shaughnessy and Best, 1975), which is seals from the present study using the same statistical
similartothemeandate ofbirthforAntarctic furseals software.
(Payne, 1978). The median ofthe five readings was
used as an estimate of age. Outliers were discarded
as reading errors.
Proc. Linn. Soc. N.S.W., 130, 2009 221
BODY MEASUREMENTS OF SOUTH AFRICAN FUR SEALS
''^T^Tfmfm, j?^a^i«^ggjiflgrpT»aByH^^
•1
\
' _:• J
12
I
I
I
I
I
.J
Figure 1: Diagram ofa male South African Fur Seal showing how individual body measurements were
taken. All measurements were taken with the animal lying on its back.
Bl, Circumference ofhead at canine; B2, circumference ofhead ateye; B3, tip ofsnoutto centre
ofeye; B4, tip ofsnoutto centre ofear; B5, tip ofsnoutto angle ofgape; B6, standard body length orSBL
(straight line from tip ofsnout to tip oftail with animal lying on its back); B7, ventral curvilinear length
(tip ofsnout to tip oftail overbody curve); B8, tip ofsnoutto genital opening; B9, tip ofsnoutto anterior
insertion ofthe foreflipper; BIO, length offoreflipper(anteriorinsertion to tip offirst claw); Bll, axillary
girth; and B12, length ofhind flipper(anteriorinsertion to tip offirst claw).All body measurements were
made in cm.
222 Proc. Linn. Soc. N.S.W., 130, 2009
C.L. STEWARDSON, T. PRVAN, M.A. MEYER AND R.J. RITCHIE
Table 1: The age distribution of Male South Af- calculated using the Spearman rank-order correlation
rican Fur Seals. Pups were defined as animals < coefficient.
MCM
1 month old. Animals 1-10 y: 37 animals Linear discriminant analysis can be used to
PEM
were of known-age; 34 animals were aged classify individual seals into mutually exclusive age
from counts of incremental lines observed in the groups based on seal body length. The dependent
MCM
dentine ofupper canines. Animals > 12 y: 2 variable (v) is the age group and the independent
animals were 13 y; 10 PEM males were > 12 y, i.e., variable seal body length (x) is the feature that might
the pulp cavity ofthe upper canine was closed. describe the age group. For each age group we can
determine the mean ofseal body length (jc ) and for
each seal we compute the Mahalanobis distances of
Age the body length (x) to the mean seal body length of
Age(y) Frequency Percentage
group age group
/:
Pup 3 3.6
EQUATION
1
Yearling 1 10 12.0
Subadult 2 5 6.0
Df(x) = -2[xi^S"'x-jx,''S-'x.]+x^S^'x
3 4 4.8
4 7 8.4
where, S is the pooled sample variance matrix. Since
5 6 7.2 we are dealingwith univariate datawehavex- = x.
6 6 7.2 , x' = X and S being the pooled sample covariance.
The term in square brackets is the linear discriminant
7 15 18.1 function. We allocate an observation (x) to the age
Adult 8 4 4.8 group (pup, yearling, sub adult, adult), which gives
the smallest calculated Mahalanobis distance. This
9 4 4.8 is equivalent to allocating the observation (x) to the
age group which has the largest linear discriminant
10 6 7.2
function value (Anderson, 1984).
12 1 1.2
Growth Models
13 2 2.4
The most commonly used growth models (SBL
>12 10 12.0 vs. age) for post-natal growth of marine mammals
are the exponential saturation curve, known as the
Total 83 100
von Bertalanffy model, the logistic 'curve and the
double exponential or Gompertz model (Zullinger et
Statistical analysis al., 1984; Trites and Bigg, 1992, 1996; Zeide, 1993;
Body variable expressed in relation to standard body Winship et al., 2001; Amould and Wameke, 2002;
length McKenzie et al, 2007). In most cases where these
Growthinbodymeasurement,relativetostandard equations have been used, a time base adjustment
body length (SBL), was calculated as follows: (moving the x-axis) has been used to optimise the
fit but this is not a good statistical procedure. No
body measurement (cm)/SBL (cm) x 100% attempt is usually made to estimate the errors ofthe
fitted parameters. In the present study, the models
As the variance ofthe ratio estimate is difficult have been expressed in forms where the unknowns
to validly estimate, particularly on small samples, were the asymptotic maximum size, the apparent pup
percentages must be interpreted with caution, i.e., size (P) and an exponential constant. Models are for
both y and x vary from sample to sample (Cochran, post-natal growth; they are not intended to model the
1977, p. 153). growth ofsucklingpups andthe apparentpup size (P)
does notnecessarily reflectthe actual birth size:
Body length as an indicator ofage
The degree of linear relationship between log
body measurement (log SBL) and age (y) was
Proc. Linn. Soc. N.S.W., 130, 2009 223
,
BODY MEASUREMENTS OF SOUTH AFRICAN FUR SEALS
EXPONENTIAL SATURATION ORVON
The growth ofsuckling pups would be expected
BERTALANFFY CURVE
to be governed by a different growth curve and so
EQUATION
2
the apparent pup size (P) is an abstraction. There are
Y= (E„-P).(l-e^)+P
also statistical limitations of the models. Three (3)
Y = E^-E„e^ + unknowns have to be fitted. It is much more difficult
or Pe'^
to fit an equation with 3 unknowns than one with 2
where,E^^ is the asymptotic maximum size, unknowns. The characteristics of the underlying
function can also give rise to difficulties; the logistic
P is the apparent pup size,
equation, in particular, is notoriously difficult to fit
kis an exponential growth constant (Zullinger et al., 1984). The equations cannot be
adequately fitted if there is an insufficient amount
t IS tim e. of data to clearly indicate curvature towards an
asymptotic maximum.
LOGISTIC EQUATION
EQUATION The errors of the fitted parameters can be
3
estimated using matrix inversion methods (Johnson
Y= and Faunt, 1992). However, most attempts to use
'^
\ such growth curves on mammals and growth oftrees
+
1 e have not used enough data points, resulting in the
P
asymptotic errors being so large that the estimates of
where,E^, is the asymptotic maximum size. the fitted parameters are not useful (Zullinger et al.,
1984;Zeide, 1993).
Most previous attempts to fit various types
IS a scaling constant.
of exponential saturation curves have used data
where the equations have been simplified by using
P IS the apparent pup size, a fixed estimate of the inifial condition at t = (the
kis an exponential constant, apparent pup size), hence simplifying the equations
to equations with only two unknowns (Australian fiir
tis time. seals - Amould and Wameke, 2002; New Zealand
DOUBLE EXPONENTIAL OR GOMPERTZ fur seals - McKenzie et al., 2007; Steller sea Hon
-Winshipetal., 2001).
EQUATION - EQUATION 4
Least squares fitting routines assume that
Y= E the error in the dependent variable is normally
e^^''^"^^-''**
distributed and independent of the magnitude ofthe
where,E^ 1s the asyrnptotic maj:imum size independent variable. In many biological situations
this assumpfion is not valid because the error of
[Ln(P) - Ln(E^)] IS a scaling constant
the dependent variable increases with increasing
P IS the apparent pup size, magnitude of the independent variable. A constant
relative error is often a more realistic assumption
kis an exponential constant,
to make for biological data. The usual procedure to
tis time. deal with situations is to log/log transform the data
and then use a least squares fitting procedure on the
transformed data. In the present study, we found
ForEquations 2, 3 and4 the incremental component
no great improvement in the curve fits (in terms of
ofgrowth(E^^^^,Jis;
correlation r) using log/log transformed data. Plots
EQUATION of residuals vs. predicted Y-values did not indicate
5
a svstematic increase in the size of the residuals as
the predicted Y-value increased. No log/log
gfWSftl 'if transform was needed.
The approximateerrorforE^^^. (^E^^. )is.
gmrth "^ g-cwfti'
Bivariate allometric regression
AE^owa.«V(^Ej'+(AP)' The relationship between value of body
where,AE^, is the error of the ma^dmum body SIZe' mweaassiunrveemsetingtateadndu:si(nig) tShBeLlogaanrdith(miii)ca(gbease(ye)),
AP IS the error of the ^iparent pup size. transformation ofthe allometric equation,
224 Proc. Linn. Soc. N.S.W., 130, 2009
C.L. STEWARDSON, T. PRVAN, M.A. MEYERAND R.J. RITCHIE
y = ax*, which may equivalently be written as log 1999, 12.23), Microsoft Excel 97 (Microsoft Corp.,
y = log a + b log x. 'Robust' regression (Huber M- Seattle, 1997) and S-PLUS (MathSoft, Inc., Seattle,
Regression) was used to fit straight lines to the 1999, 5.1). The EXCEL 97 routines for non-linear
transformed data. The degree of linear relationship least squares fits and calculation of the asymptotic
between the variables was calculated using the errors ofthe fittedparameters forthe von Bertalanffy,
Spearman rank-order correlation coefficient, r Logistic and Gompertz equations (Equations 2, 3 and
(Gibbons and Chakraborti, 1992). This is a non- 4) are available from DrR.J. Ritchie (rrit3143@usyd.
parametric procedure. Since the log-transformation is edu.au) upon request.
monotonicyougetthesamevalueforrontransformed
oruntransformed data. It is important to note that the Terminology
regression equations relating to overall growth are A juvenile is a weaned pup that has not yet
notusedonbodymeasurementsthatare likelyto vary achievedadultsize. Pubertyiswhenreproductionfirst
with seasonal variations in body condition that are becomes possible (production of sperm in quantity),
known to occur in this species (e.g. Rand, 1956). For and social maturity is the age when the animal
example,bodygirthorweightwouldbe inappropriate reaches fiall reproductive capacity (physically able to
parameters to use in such analyses. establish andmaintain a harem). Sexual development
Statistical tests of hypotheses about model ofmale SouthAfricanfurseals isdiscussedelsewhere
parametersareonlyvalidifthemodelassumptionshold (Stewardson et al., 1998).
(i.e.,errorsareindependentlyandidenticallynormally
distributed, with zero mean and with a variance (a-)
(Weisberg, 1985, p. 24, 156). The standard approach RESULTS
is to first examine the residual values versus fitted
plot. Ifthis is a random scatter about zero then it is Age determination based on dentition (intra-
valid to assume the model is adequate and proceedto observer variability)
check the normality assumption. In the present study, Counts ofGLGs (growth layer groups) in canine
the following tests for checking for normality were teeth were found to be highly reproducible. Of the
used: (i) Anderson-Darling, (ii) Ryan-Joiner and (iii) 34 PEM animals for which GLGs were counted, 14
Kolmogorov-Smimov (Cochran, 1977). (41%) had all five readings equal; 16 (47%) had one
We used the following test statistic to test one of reading outof5 different fromthemode; and4 (12%)
the hypotheses given below about the slopes of the had 2 readings out of5 different from the mode.
fitted lines:
Age determination (variability between known-
age and canine aged animals)
EQUATION 6 Standard body length (SBL) was selected to
MCM
investigate whether (animals of known-age)
and PEM (canine aged animals) animals were similar
b-1 with respect to age. When comparing the (robust)
MCM
T = regressionlineforSBL onagefor animalswith
SE(b) SBL on age for PEM animals, partial t-tests indicate
that age is important (/ = 7.07,p < 0.001), even after
adjusting for group and age-group interaction; but
where, b is our estimate ofthe slope using robust they provide little information on group (/ = -0.82,p
regression and SE ( b) is the standard error = 0.42) and age group interaction (t= 0.87,/? = 0.58),
of b Under the null hypothesis the test statistic hence one straight line canbe fittedto the data. These
.
T has a t distribution with n - 2 degrees offreedom statistical conclusions were verified by examining
graphical displays of fitted values and residuals.
(df).
The following hypotheses were tested: Thus PEM and MCM animals were not significantly
H^: b= 1 (isometric)versusH,: b7^ 1 (eitherpositively differentwith respect to age distribution.
or negatively allometric); Hj: b > 1 (positively This conclusion is supported by the sequential F
allometric); H,: b < 1 (negatively allometric). test,providedthesequenceofternisaddedsequenfially
(first to last) was: (i) none (i.e., fitting a line parallel
Statistical Software to the X axis); (ii) age (F = 817.69, p < 0.001) (one
MCM
Statistical analysis and graphics were straight line); (iii) museum (i.e., and PEM) (F
implemented in Mmitab (Minitab Inc., State College, = 0.0659,p = 0.7984) (two parallel lines); (iv) age x
Proc. Linn. Soc. N.S.W., 130, 2009 225
BODY MEASUREMENTS OF SOUTH AFRICAN FUR SEALS
museum interaction (F = 0.1883, p 0.6661) (two was variable relative to age, r = 0.59 (Appendix 4).
lines not necessarily parallel). Overall growth expressednegative allometry relative
to SBL and age (Appendix 3, 4), increasing by 57%
Bivariate allometric regression at 10 y relative to pups (RTP) (Table 2). Growth
Regression statistics for body measurements on increment decreased with increasing SBL until about
SBL and age (1-10 y) are given in Appendix 3 and 7 y (c. 15% ofSBL) (Table 3). The mean Bl ofmales
4. Overall, correlation coefficients were moderately > 10 y (including unaged animals > 200 cm and of
to strongly positive, i.e., most points on the scatter indeterminate age > 12 y) was 31.8 ± 1.2 cm (« = 5).
plot approximated a straight line with positive The maximum-recorded value was 35.0 cm (animal
slope, r > 0.70. Exceptions included tip of snout to MCM3017, SBL 209 cm, 12 y 11 months).
centre of eye (B3) with age and SBL (r = -0.008
and r = 0.15 respectively); tip of snout to angle of Circumference ofhead at eye (B2)
gape (B5) with age {r = 0.56); circumference of Growthofcircumference ofheadateye (B2) was
head at canine (Bl) with age (r = 0.59). Although rapid during the early postnatal period and continued
correlation coefficients indicate that linearity was to increase until at least 13 y. Overall growth
reasonably well approximated for most variables expressed negative allometry relative to SBL and
by log-log transformations, a linear relationship did scaled with negative slope relative to age {h = 0.12)
not necessarily best describe the relationship. In the (Figures 2a, b; Appendix 3, 4), increasing by 65%) at
present study, we have attempted to fit more complex 10 y (RTP) (Table 3). Growth increment decreased
models in the case of SBL vs. age with the specific with increasing SBLuntil about 7 y (c. 22%o ofSBL)
aim ofcomparing ourgrowth curves with those found (Table2). MeanB2 ofmales> 10y(includingunaged
for the Australian fur seal (Amould and Wameke, animals > 200 cm and of indeterminate age > 12 y)
2002)(see below). was 45.8 ± 1.8 cm (n = 6). Maximum recorded value
was 53.0 cm (animal PEM676, SBL 197 cm).
Growth ofbody variables
Most variables were significantly positively Tip ofsnout to centre ofeye (B3)
correlated with each other, r > 0.68 (Appendix 2). Growth oftip ofsnout to centre ofeye (B3) was
Exceptions were: (i) tip ofsnout to centre ofeye (B3) highlyvariablerelativetoage,r=-0.008,andSBL,r=
with all variables; (ii) circumference of head at eye 0.15 (Appendix 3, 4). Growth increment decreased
(B2) withtip ofsnoutto angle ofgape (B5) (r=0.61); with increasing SBL until about 9 y (c. 5% ofSBL)
and(iii) circumference ofheadatcanine (Bl) withtip (Table 2). Mean B3 of all males > 10 y (including
ofsnout to angle ofgape (B5) (r= 0.63). unaged animals > 200 cm and ofindeterminate age >
12 y) was 10.4 ± 0.6 cm {n = 10). Maximum recorded
Circumference ofhead at canine (Bl) value was 14.4 cm (animal PEM2194, SBL 194 cm).
Growth ofcircumference ofhead at canine (Bl)
Table 2 (Pages 227-228): Summary statistics for body variables (B1-B12), according to age (y) and age
group ofmale SouthAfrican Fur seals.
Data presented as mean body measurement in cm ± S.E., followed by coefficient of variation in
round brackets, and body variable expressed as a percentage ofSBL. Maximum value ofeach variable
(males ofunknown-age) is also presented.
Variables: Bl, Circumference ofhead at canine; B2, circumference ofhead at eye; B3, tip ofsnoutto
centre ofeye; B4, tip ofsnoutto centre ofear; B5, tip ofsnoutto angle ofgape; B6, standard body length
(SBL); B7, ventral curvilinear length; B8, tip of snout to genital opening; B9, tip of snout to anterior
insertion of the foreflipper; BIO, length of foreflipper; Bll, axillary girth; B12, length of hind flipper.
Variable B3 was poorly correlated with body variables and age (Appendices 1, 2, 3 and 4), therefore has
been excluded from further analysis. B7 was shown to be a poor indicator ofSBL, therefore was exclud-
ed from further analysis. Bll may be influenced by seasonal change and illness, therefore was excluded
from further analysis. Sample size (n) is the number ofdentition-aged and known-age (tagged) animals.
Sample size given in square brackets where this does not equal total sample size. The data summary
includes calculations ofthe mean ofeach variable ± S.E. for the 7 largest males (> 200 cm) ofknown or
unknown-age; maximum value in square brackets, followed by sample size.
226 Proc. Linn. Soc. N.S.W., 130, 2009
—
', '' '- ' ' ' '.- - '' '-•'. '. --. '- ' i ''.' :' ''- ''
C.L. STEWARDSON, T. PRVAN, M.A. MEYER AND R.J. RITCHIE
00 21
o o O
'/-> rn '/"i t*^ a>
ro r.| ^O r-i ir<
^
0-0H ^I^ oo 00I fJ^li '— \'-o^H ^<-No 0\2-r0;H\ o<o^ m vo m „1 q3-H oron 0d-0H Oo-noH o-H r- rt----H' 5^ q-H qri
09 dKr--H~ v"d-d^^ dtm--H^ o5^—d? 0dt•-~*H0^ o^'—d odV-OdH r^-^^ OdOm-NNH oO^r~ov^ sNodr-~OdH 0<^-0o^ dd"-H Nq^t-O^ Odx-NHo -r^«—v^d Od<^^i ^r^-—!' Oodot-N^onH oO^^-O^ d"d^-"H 0oNT^0dOf ^dT-"Hf o5NN?OO >du^--n"H1 \siD?n Od-d^-NH ^^T^:-r^ ONNO rry^:l>
oa od^^-oH- HqS'^t—-^?^ rrd•-r-H*,; g1—Ou--^i odw---H\^i ^fwo^t---s\~^ dK—"•*+1_ 0(^l'i—i/0SsS omd»-dnH 05r^S^--0?:' oodO-donH r,r—<nS, mdOi4^)n q^o(^r«Nd^-i r^dcH^dl ^rr^'U—^^1 oqdr--dH1 fsNd,—^O? doOr-n-dH ^O(^r^n^N- d0d1l-^0OH1 q5O^o—i?N dqd(-NH SdO^^—NT NNd-OOH r^O^'—^N ddrm-^H qZ^N^lO^. 1^ OdiI--flnj^ c
dOn ;ori<^?^ d1rN-O1 o^ON Trfo Sdoo? '(SN- N^OOn din NSr~O?^ dr- NSNO?O 0io0n C^rn-)^ d1rN-O1 f^NNO Cdrr-^L ^rr~--^ dNO rsi-?n 1d2r-^1 N5^O? 1m^^1 (^iNn OO irsno? ^din rsi^?ni omj mcII
oa o--^H^ ,TNVl^O-^- om-dH (o^Nd —(d-HN ,iiCnnnI^ rd'-—f^l <CNNJ O—-NH fr—--J^" OO-^HN ^i-—ni ^d—i^ N2-—O Oo4N^ oN—dO O0+n10' oi—dn o0-H0d '<•—^^i o—-dH o^•—d iO-nnH' df^ —^--H ^i'—n O—-NH ^c^d rN^O o^—+1 *'oT
'o"-S^iH- SdV?- <rr-O-^-*H~N]^ idO^nS dN0m-O0H ^of"—-o"^ mrOd(--iHON] oSinmrd?n^ id(r^-<n^H^ '(O#N^O ^r^^040o') n0No^rn0O^' odr1+-o^1^ <iqsr-Nn?~' o'r-td^—-o-^^H^ f<<sr-NNN?^ 2r^id-^nH^ ooNCSndO?TI oroNi-^noOHd,^ sid(^,——?Nn r^q1+-n1^ 0N^irr0O)i odr0t---ooH~' O(srf--NN?^^ mt^i-rTHi Cir-N^n^J'• —om--n^H' Coi—NnJ• 0N0O -o•r-**)H ricIIln
oa oN-.-nHO— ^mT,,—f-, oON-nOH ?<M-fN)^ dtr(m-NNNHi 0^osr0<?'- r^Nd-NOHj ^^N^rO-.^ON^ -^^dor-H*) ^rOrS—-^N?^ ONdC^-NOHNJ ^0qt^r---0^^ 0d1nrr„—-<-0H-;i dsO,i——^?n d•(^rr-rNHnnf i^OrO^-Nn^n^ (iq^n•-Nn^H^ -0^NO^^0N"O tdCoNi-NHOnl m(^t5'—iNN? Nm^nn^--oOH'' ^-?Kr—4~^- ri—ri-nn^nH sim,——?n 'drr^^0—-^-^^Hi ^oi,^——n 0^0 do^'——-oH c
o
Q.
P
1*1 ^*'
t^
-H :=r
r-
I
o
o
A j<:
00
^2
cd
E c
D. ^
§ BO
C ^
bfi
< 0Q3.. >-C"3" 0X3I0 a< f2
Proc. Linn. Soc. N.S.W., 130, 2009 227
' ^ 1 'I ''
BODY MEASUREMENTS OF SOUTHAFRICAN FUR SEALS
H
g 3 ^ §
S
e
a
r.1 r-^ I — O_'Q*^
^ .
3 KOH)-
II
Ui
^
o 4^ d ^-^J to -f^ '^J\ 0\ U4l^ •"---^ O^^ Ln (-n t-/i 00 L^j-^H/c/&^3
—o
H-
°° Q Vk)^to oK)<-^^yibopvlftyio?oboy>k)>o o o o — i^^;^
^,P,";M_ 'h- ' ''IT'h"--'~'h"-T°'°hV'-^'T'h'-^'V^hV-"-'*h^'-TI'h"~-J ' ' ' ' ' 'V|uH--V|uh-f
713
4^ ui ^- tyi
K)
—
'3II' LKH-j) ^oH:^'oi^,HJ^.-j0bio0^o^,i^^-,^L^h-0—-S0.J?,^H4--^"0v^0ao,\01H'N-^^^oboy-,olo,^HvP-^o^o-hso'^=^i>Lr.or4otio,^^.x'oHh=o-J:,-^,,J4jH:^-^ob4o-,^ot,H^s-t?00o0b,^>N,^>S^'?o-ooJH^—-Jo->oI£H>^4-^^oJ^^o^kH>)-J'otk^oo)HO:-^^
4^ v^W tJ yJ tJ ^J' ^w s?
4i^
4i.
^ c: S3 ^ £S yi 2^ 23^ £29 5^^ ^ ^ - i 2 i S ? t5^ ^? 5^ - i1S :^ g
— '-^K)Oo*'^^0
' "" r-t;>f-^K>w-iI^^«OJ'-^I?^°OOb-o<'^<-^iOsKj>-^tb^^K-)^;K:);-<4^^OpJr-fo^^4:^^t^ii^—---i~obo|^:^^:-^
J^-—-t,^^ ^vv^PP OO^^ vovP^^ xox^pp CC^^ oNN^pp OO -o-ss^pp oNN^pp OO OO^^ OO^^ o--^^^ O^
— — H-— H-—-H-toH--^H-^H-^H-toH-(oH---H-— H-toH-^H----lf
H-
— —
OS I I ji. I
o«u#e,( c;fb-^^^^O—,— ,SI[^rc^^t^^^"——cT:^y'-'[1^^'—,-—i~^3r^J^-o',—'Ns~O[:I^;'oOjo(.J1M'p^;OOO^po—r—o',o'^OjNr^^—>N.o-J"^-^^"bo(Ioof.-'if—O5Oi-o°M/—o°is'or^0P\-^^^'rU^.i-it;-^uo^"i;'of-~^^o\;l-ihJiy^JiIJ-U.1~^);^"bt^v>NjvO^s-rT-^)'^
— n-Qso\^0>.^0^^0'\^ —
'^~^ LL ^ ' 14- "^ u_ ^-^ '' ^"^ ' ' rr ^ ' hr ^—^ rr
Np sP o o T—n nP Tl °^ ® T—^ ° T—"? o c' nP nP sP
I—' 4^ I I -^ — I I I
'—o^oKJ;'_—^ ^tsjL'—j^ rKJ^'—-^ ^toP'—f' oK>^'—o" ^tok'—)^ ^NJa'—N^ ^KJi'—o^ -KJ^'—o^ 5I—•a'—N- I^—'^'—^^ I—o> 3-"-^^.^—' U-""^)I—r' oiTl
K-H-K-H-^H--^H---H-^H-^H-^H-^H~^H-^H-^H-.-H-^-H-
^J'j:^4^Lh;n;avP^U)Ooo^L^t^^^4^^wKJLhOboO
O^ ^^ CJ^ Np v,0 O^ vO "^^T-" * 'O' °^ '"—^ x^^* '"—^ ' o^ o^ o^ o^ o^
228 Proc. Linn. Soc. N.S.W., 130, 2009
