Abstract and Figures

About half of the extant shark species occur only in deep waters (defined as.200mdepth), yet few published studies on sharks include these taxa. As fisheries worldwide enter deeper waters, the provision of biological data for these little-known taxa is critical to management and conservation. The shortspine spurdog, Squalus cf. mitsukurii, is an abundant shark on the insular slopes of the Hawaiian Islands. We assigned ages by counting growth bands on the enamel caps of both dorsal fin spines. Age estimates ranged from 3 to 26 years for females and from 6 to 23 years for males. Growth was modelled with multiple length-at-age models, fitted using maximum likelihood estimation and nonlinear least-squares methods. For female data, the logistic model yielded the most biologically cogent parameter estimates (LN ¼126 cm (total length, TL) and k¼0.080 year �1). The two-parameter von Bertalanffy Growth Model yielded optimal model fit and realistic parameter estimates for males (LN ¼72 cm (TL) and k¼0.080 year �1). Maturity ogives suggested that females and males mature at 64-cm TL (15 years) and 47-cm TL (8.5 years), respectively. Fecundity ranged from 3 to 10 embryos; mating appeared to be aseasonal. We reveal a conservative life history, common among deep-water elasmobranchs, and provide further evidence of geographic variation in reproductive and growth parameters in this nominal species.
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Age, growth and reproduction of a common deep-water
shark, shortspine spurdog (Squalus cf. mitsukurii),
from Hawaiian waters
Charles F. Cotton
A
,
D
,R. Dean Grubbs
B
,Toby S. Daly-Engel
C
,Patrick D. Lynch
A
and John A. Musick
A
A
Department of Fisheries Science, Virginia Institute of Marine Science, College of William
and Mary, P.O. Box 1346, Gloucester Point, VA 23062, USA.
B
Florida State University Coastal and Marine Laboratory, 3618 Highway 98, St. Teresa,
FL 32358, USA.
C
University of Arizona, 1140 E. South Campus Dr Forbes 410, Tucson, AZ 85721, USA.
D
Corresponding author. Email: chip@vims.edu
Abstract. About half of the extant shark species occur only in deep waters (defined as .200 m depth), yet few published
studies on sharks include these taxa. As fisheries worldwide enter deeper waters, the provision of biological data for
these little-known taxa is critical to management and conservation. The shortspine spurdog, Squalus cf. mitsukurii,isan
abundant shark on the insular slopes of the Hawaiian Islands. We assigned ages by counting growth bands on the enamel
caps of both dorsal fin spines. Age estimates ranged from 3 to 26 years for females and from 6 to 23 years for males. Growth
was modelled with multiple length-at-age models, fitted using maximum likelihood estimation and nonlinear least-squares
methods. For female data, the logistic model yielded the most biologically cogent parameter estimates (L
N
¼126 cm (total
length, TL) and k¼0.080 year
1
). The two-parameter von Bertalanffy Growth Model yielded optimal model fit and
realistic parameter estimates for males (L
N
¼72 cm (TL) and k¼0.080 year
1
). Maturity ogives suggested that females
and males mature at 64-cm TL (15 years) and 47-cm TL (8.5 years), respectively. Fecundity ranged from 3 to 10 embryos;
mating appeared to be aseasonal. We reveal a conservative life history, common among deep-water elasmobranchs, and
provide further evidence of geographic variation in reproductive and growth parameters in this nominal species.
Additional keywords: fecundity, geographic variation, growth models, squaloid, von Bertalanffy.
Introduction
The global harvest of deep-water sharks has increased, primarily
owing to collapses in some near-shore fisheries, the advent of
more efficient fishing technology and the increased ex-vessel
price of shark flesh and liver oil (Irvine 2004; Kyne and
Simpfendorfer 2007). This recent increase in fishing effort
comes in spite of a considerable body of literature indicating that
sharks, particularly deep-water sharks, are highly ‘K-selected’
(MacArthur and Wilson 1967; Musick 1999), characterised by
slow growth, high longevity, late maturity and low fecundity
(Hoenig and Gruber 1990; Musick 1999; Kyne and Simpfendorfer
2007). As a result of this type of life history, these deep-water
species are prone to overexploitation and localised depletion
(Musick et al. 2000; Stevens et al. 2000; Morato et al. 2006). To
properly manage long-lived animals, such as deep-water sharks,
managers need basic taxonomic information, relative species
abundances and species-specific information on critical habi-
tats, reproduction, age structure and growth rates (Camhi et al.
1998). The dearth of information available for most deep-water
shark species precludes formulation of proper management
plans, potentially exacerbating the long-term effects of exploi-
tation at current levels of fishing.
The shortspine spurdog, Squalus mitsukurii, is a medium-
sized dogfish with a cosmopolitan, but patchy distribution
throughout warm waters (Last and Stevens 1994; Compagno
et al. 2005). This dogfish inhabits continental and insular
shelves and upper slopes, as well as seamounts and ridges,
usually in depths 100–500 m. The shortspine spurdog is a high-
trophic-level predator, feeding primarily on cephalopods, tele-
osts and caridean shrimp (Ebert et al. 1992; Corte´s 1999;
R. Grubbs, unpubl. data). As with many of the deep-water fishes,
little is known about the biology of this species, but a few studies
of age, growth and reproduction are reported in the literature
(e.g. Litvinov 1990; Wilson and Seki 1994; Fischer et al. 2006).
Based on morphometric, meristic and molecular data, previ-
ous authors have claimed that the taxon S. mitsukurii represents
a species complex (Last and Stevens 1994; Compagno et al.
2005; Last et al. 2007b; White et al. 2007). Taxonomic investi-
gation of this species is ongoing and the identifications of
specimens collected for this study remain unverified. As
CSIRO PUBLISHING
www.publish.csiro.au/journals/mfr Marine and Freshwater Research, 2011, 62, 811–822
ÓCSIRO 2011 10.1071/MF10307 1323-1650/11/070811
specimens collected for the present study differ in several
characters (e.g. head length, interdorsal length; R. Grubbs,
unpubl. data) from published morphometric data from the
holotype (Last et al. 2007a), we refer to the specimens investi-
gated in the present study as Squalus cf. mitsukurii.
Squalus cf. mitsukurii is abundant around the Hawaiian
Islands and is taken as by-catch in the lutjanid bottomfish fishery
around the main Hawaiian Islands (Daly-Engel et al. 2010).
However, these sharks are not harvested and resultant mortality
is likely minimal. During 1967–1984, Japanese and Soviet
fishing fleets developed an intense trawl fishery for slender
armorhead (Pseudopentaceros wheeleri) around the junction of
the Emperor Seamount Chain and the Hawaiian Ridge Sea-
mount Chain (Uchida and Tagami 1984; Wilson and Seki 1994).
Surveys of the armorhead stock showed that S. mitsukurii was
taken as by-catch in the armorhead trawl fishery (Uchida and
Tagami 1984). The armorhead fishery ceased more than two
decades ago, and that fishery never extended eastward into the
main Hawaiian Islands. For these reasons, we assume the
population around Oahu has likely undergone minimal histori-
cal exploitation.
Landings data for S. mitsukurii worldwide are sparse. Last
and Stevens (1994) state that ‘small quantities’ of S. mitsukurii
are sold in the fish markets of Australia; however, Graham et al.
(2001) showed a precipitous decline of this species between
1976–77 and 1996–97 in Australian waters, largely a result of
unreported by-catch in other deep-water fisheries in the area.
Elsewhere globally, fishing effort for S. mitsukurii is likely to be
minimal, but possibly underestimated owing to unreported
by-catch and/or misidentification (Cavanagh and Lisney 2003).
Accurate information about population age structure and
individual growth rate is necessary to understand fish life history
and provide data for fisheries management (e.g. growth models,
yield per recruit models and stock assessment models). In this
study, age estimates were obtained from dorsal fin spines to
model the growth dynamics of S. cf. mitsukurii. The technique of
ageing squaliform sharks by counting enamel growth bands on
dorsal fin spines has been well-documented in several studies
of a congener, S. acanthias (Kaganovskaia 1933; Holden and
Meadows 1962; Nammack et al. 1985; Tribuzio et al. 2010).
Formation of these enamel cap growth bands is caused by
alternating periods of fast and slow growth coincident with
seasonal fluctuations in water temperature, photoperiod and/or
food availability (Goldman 2005).
Knowledge of reproductive biology, specifically size and age
at maturity, fecundity and reproductive seasonality and period-
icity, is especially important for the proper management of
sharks (Camhi et al. 1998). In the present study, we reported
size and age at maturity, apparent periodicity of spawning and
fecundity. These parameters were also compared with published
data for this species.
By determining the growth and reproductive parameters of
S. cf. mitsukurii, we can assess whether this species exhibits
conservative life history characteristics consistent with other
deep-water sharks. Additionally we compared S. cf. mitsukurii
life history parameters from Oahu, Hawaii to those reported in
the literature from other locales. Such information may be useful
in establishing regional management plans, as well as in
determining whether the reported variability in life history
parameters is locally mediated (e.g. differences in productivity
or thermocline depth) or attributable to different species within a
species complex.
Methods
We collected most specimens by demersal trotlines set on the
insular slope around the Hawaiian island of Oahu (Fig. 1). We
fished 24 trotline sets between 250- and 450-m depth from
180°175°170°165°160°
Johnston Atoll
Maro Reef
Kure Atoll
Midway Atoll
Pearl and Hermes Atoll
0 200
Kilometres
Lisianski
(n 4) Raita Bank
(n 1)
Hawaii
Maui
Kauai
Penguin Bank
(n 8)
Oahu
(n 138)
Nihoa
(n 2)
Gardner Pinnacles
(n 1)
400
155°
20°
25°
30°
Papahanaumokuakea Marine National Monument
Fig. 1. Map of the Hawaiian archipelago showing locations of Squalus cf. mitsukurii collections and the number of
specimens collected at each location (n). Image adapted from Daly-Engel et al. (2010), used with permission.
812 Marine and Freshwater Research C. F. Cotton et al.
January 2005 to November 2008. Lines were fished for 12–14 h,
and usually set at dusk and hauled at dawn. Commercial fish-
ermen also provided specimens collected near Oahu and the
North-west Hawaiian Islands (NWHI). In total, 124 female and
30 male S. cf. mitsukurii were collected, measured for precaudal,
fork and ‘stretched’ total lengths (PCL, FL, and TL, respec-
tively), weighed and dissected. We also removed reproductive
tracts, collected vertebrae and intact first (D1) and second (D2)
dorsal fin spines and weighed the livers. For male specimens, we
measured inner and outer clasper lengths and inspected the vas
deferens for coiling. For females, we measured the diameter
of the largest oocyte, noted maternity status and counted and
measured any visible embryos. Embryos not clearly visible upon
inspection (,0–10-mm TL) were assigned a size of 0 mm.
Maturity designation in males was determined by the presence
of a fully coiled vas deferens and fully calcified, elongated
claspers. Maturity designation in females was usually noted by
the presence of embryos, but in a few cases by the presence of a
stretched (postpartum) uterus or fully enlarged oocytes and
oviducal glands.
Cleaned vertebral centra were inspected for the presence
of growth bands, but visibility was too poor to discern
banding in either whole or sectioned centra. Staining verte-
bral centra with a solution of saturated alizarin red in 1%
potassium hydroxide (1 : 9, v/v) did not improve band clarity.
Therefore age estimates were obtained solely from dorsal fin
spines. Spines were collected and cleaned using trypsin and
hot water (,40 g L
1
) as described in Cotton (2010). Two
readers independently assigned ages by counting growth
bands on the enamel caps of each cleaned fin spine. Spines
were viewed under a low-power dissecting microscope with a
bifurcated, episcopic, fibre-optic light source. Any spine
yielding an age estimate that differed by more than 2 years
was re-examined by both readers jointly, and age was
assigned by consensus between both readers. For those age
estimates that differed by 2 years or less, the mean value of
the two estimates was assigned and used in growth models.
Notations were made for damaged or eroded spines.
Heterogeneous variability in the weight–length relationship
indicated multiplicative error structure and was accounted for
using a log-transformed version of the weight–length model
(sensu Quinn and Deriso 1999):
ln Wi
ðÞ¼ln aðÞþbln Li
ðÞþei;ð1Þ
where W
i
is weight, ais condition factor, brepresents the cur-
vature of the relationship, L
i
is length and e
i
is a random error
term. Akaike’s Information Criterion (AIC) was used to evalu-
ate whether growth was isometric (W¼aL
3
) or allometric
(W¼aL
b
,b3). Hepatosomatic index (HSI ¼liver weight/
bodyweight) was calculated and compared by maturity stage
using a t-test.
An age bias plot was constructed using the means and 95%
confidence intervals of reader estimates per age class (Campana
et al. 1995). A chi-square test of symmetry was used to look for
evidence of systematic disagreement between readers (Hoenig
et al. 1995; Campana 2001).
As recommended by Cailliet et al. (2006), we fitted multiple
growth models to the length-at-age data. Three forms of the
von Bertalanffy Growth Function were used: the original form
(VBGF; von Bertalanffy 1938; Cailliet et al. 2006):
Lt¼L1ðL1L0Þekt ;ð2Þ
where L
t
is the predicted length at age t,L
N
is the asymptotic or
theoretical maximum mean length (t¼N), L
0
is length-at-
birth (t¼0) and kis the rate constant; a modified (conven-
tional) form (VBGF
mod
: Beverton and Holt 1957; Cailliet et al.
2006):
Lt¼L11ekðtt0Þ
 ð3Þ
where t
0
¼theoretical age when length equals zero; and a two-
parameter form with fixed length-at-birth (VBGF
2par
):
Lt¼L1ðL123:3Þekt ;ð4Þ
where the L
0
term from the VBGF has been replaced by 23.3 cm,
the mean length of term embryos observed in this study. Other
growth models included a form of the Gompertz model (Ricker
1975; Mollet et al. 2002; Carlson and Baremore 2005):
Lt¼L0eG1ekt

;ð5Þ
where G¼ln(L
N
/L
0
); and the logistic function (Ricker 1979;
Carlson and Baremore 2005):
Lt¼L1=1þekðtaÞ

;ð6Þ
where arepresents the inflection point of the curve (expressed as
t
0
in Ricker 1979).
Growth models were fitted using both nonlinear least-
squares (LS) and maximum likelihood estimation (ML) using
R software (R Development Core Team 2009). Growth model
selection was based on AIC. For ML-fitted models, we used a
variant of AIC (AICc) developed for small-sample bias adjust-
ment (Burnham and Anderson 2002):
AICc ¼2lnðLð
^
yÞÞ þ 2kþð2kðkþ1ÞÞ=ðnk1Þ;ð7Þ
where
^
yÞrepresents the likelihood estimate, kis the number of
model parameters and nis the sample size. For LS-fitted models,
we used a variant of AIC developed for nonlinear least-squares
methods (Kimura 2008), with the small-sample bias adjustment
term from the previous equation:
AICc ¼n1þln 2pRSS=n
ðÞðÞ
þ2k
þ2kkþ1ðÞðÞ=nk1ðÞ;ð8Þ
where RSS is the residual sum of squares of the model. Con-
cordance of model parameter estimates with empirical evidence
was also considered for model selection.
Maturity and maternity ogives were constructed with Sigma-
Plot 2000 using logistic regression with male data binned in
2-cm size class intervals and female data binned in 5-cm size
class intervals. Male clasper lengths were also fitted with
logistic regression using SigmaPlot 2000. The inflection points
of the curves were determined visually from each plot.
Shortspine spurdog age, growth and reproduction Marine and Freshwater Research 813
Results
Somatic growth
Length relationships (PCL, FL and TL, Table 1) of S. cf.
mitsukurii were nearly identical for both sexes, indicating no
sexual dimorphism in the caudal region (see Accessory Pub-
lications A, B). Bodyweight of male and female S. cf. mitsukurii
followed similar, approximately cubic relationships with length
(Table 1 and Accessory Publications C, D).
Mature females exhibited a significantly lower HSI than
immature females (t
95
¼3.2725, P¼0.0015). Similarly, the
slope of the regression of bodyweight and liver weight was
0.049 (95% confidence interval (CI) ¼0.033–0.066) for mature
females and 0.106 (95% CI ¼0.096–0.116) for immature
females, indicating that the proportional mass of the liver
decreased significantly after reaching maturity (Fig. 2). Owing
to the small sample size of immature males (n¼4), no test was
conducted to determine differences in HSI for males. However,
the four values of liver weights for immature males closely align
with the regression for mature males, suggesting that differences
in HSI between mature and immature males is not likely to be
significant (Fig. 3).
Age determination
Overall readability was similar between fin spines for both sexes.
Sexual dimorphism of fin spines was observed, with mature male
fin spines bearing a proximal constriction of the enamel cap on
the anterior surface of each spine (Fig. 4). For this reason, mature
male spines were more difficult to interpret. Immature male fin
spines resembled female fin spines. Eroded and broken fin spines
did not present problems in ageing, as has been found in
S. acanthias (Nammack et al. 1985). Erosion, when present, was
usually confined within the first annulus and therefore did not
require a correction factor for age assignment. The incidence of
broken spine tips was low in both sexes, and usually occurred so
far distally that age determination was not affected in most cases.
Of the total number of female fin spines aged (n¼244), 31 spines
were broken (D1 ¼16, D2 ¼15) and for males (n¼60 spines
aged) 7 spines were broken (D1 ¼5, D2 ¼2).
Age estimates ranged from 3 to 26 years for females and 6 to
23 years for males (Fig. 5). Reader agreement was 0–2 years
for 255 of 303 (84.2%) spines (Table 2), and for 48 spines
(15.8%), reader agreement was .3 years; none of these came
from sharks younger than 10 years. For most age classes, Reader 1
recorded age estimates higher than Reader 2, resulting in a
slight nonlinear bias in the inter-reader agreement (Table 2,
Fig. 6). We rejected the hypothesis of symmetry between ages
assigned by both readers (x
2
¼112.66, P,0.001, d.f. ¼61),
indicating that disagreement between readers was systematic
and not owing to random error.
Growth models
Growth models were fitted to length-at-age data for each sex
independently (Fig. 5). For females, the LS-fitted VBGF and
VBGF
mod
models did not converge. Otherwise, parameter
estimates were generally similar among models (Tables 3, 4),
Table 1. Equations for length and weight relationships in Squalus cf.
mitsukurii
Length was expressed as total length (TL), fork length (FL) and precaudal
length (PCL) and measured in cm. Bodyweight (W) was also calculated in
terms of TL and measured in g
Conversion type Sex Variable Equation r
2
Length conversions Female TL 1.2160(PCL) þ2.2200 0.9972
FL 1.0930(PCL) þ0.7688 0.9987
TL 1.1116(FL) þ1.4150 0.9969
Male TL 1.2132(PCL) þ2.0997 0.9908
FL 1.0974(PCL) þ0.4536 0.9961
TL 1.1050(FL) þ1.6250 0.9937
Weight conversions Female W0.0007 TL
3.45
0.9750
Male W0.0022 TL
3.13
0.9369
Bodyweight (g)
0 1000 2000 3000 4000 5000
Liver weight (g)
50
0
50
100
150
200
250
300
Fig. 2. Relationship of liver weight to total weight for female Squalus cf.
mitsukurii collected around Oahu, Hawaii. Measurements for immature and
gravid females are represented by closed and open circles, respectively. Data
for five mature, non-gravid females are indicated by inverted triangles and
were not used to generate either regression.
Bodyweight (g)
0 200 400 600 800 1000 1200 1400 1600
Liver weight (g)
0
10
20
30
40
50
60
70
80
90
Fig. 3. Relationship of liver weight to total weight in male Squalus cf.
mitsukurii collected around Oahu, Hawaii. Measurements for immature and
mature males are represented by closed and open circles, respectively. Since
data were available for only four immature individuals, no regression was
generated for those data.
814 Marine and Freshwater Research C. F. Cotton et al.
with the exception of L
N
, which varied considerably among
models and with respect to method of model fitting. For males,
both methods of model fitting (LS and ML) yielded similar
estimates of growth parameters with all models. Analysis of
residuals verified the assumption of a normal error structure and
homoscedasticity for length-at-age data of both sexes. The AICc
for females varied considerably with the ML-fitted Gompertz
model and the LS-fitted VBGF
2par
yielding the lowest AICc
values for each method of model fitting. However, for males,
AICc values were generally similar for all growth models,
irrespective of method of model fitting, with the logistic model
yielding the lowest AICc value. All growth model estimates of
length at birth (L
0
) for both sexes were similar to the observed
mean size of term embryos (23.3 cm). Growth model parameters
estimated in the present study were compared with those pub-
lished in the literature for this species (Table 5).
Reproduction
Elongation of male claspers slowed considerably after the onset
of maturity at ,50-cm TL (Fig. 7c). This corroborates the male
maturity ogive, which shows that 50% of the males sampled
were mature at 47 cm (Fig. 7a). The estimate of size-at-maturity
is tentative owing to the small number of males encountered in
the present study (4 immature, 25 mature). Approximately 50%
of females sampled were mature at 64 cm, with size-at-maturity
spanning 56–75 cm (Fig. 7a). Approximately 50% of females
sampled were pregnant at 70.5 cm, and 100% of females sam-
pled were pregnant at sizes .80 cm, suggesting a continuous
reproductive cycle (Fig. 7b). Oocyte diameter in pregnant
females increased throughout embryonic development until
parturition, further indicating that the reproductive cycle is
continuous in this species (Fig. 7d). The largest oocyte observed
in a mature, non-gravid female was 40.5 mm, approximately the
same size observed in females with near-term embryos. There
was no relationship between embryo size and month of capture,
indicating an asynchronous reproductive cycle (see Accessory
Publication E). There was a positive relationship between
maternal size (TL) and fecundity, with an apparent maximum
fecundity of 10 embryos (Fig. 8).
Discussion
Somatic growth
The relationship of weight to length was nearly cubic for both
sexes, similar to most other fishes (Helfman et al. 2009). Data
for immature females fit the regression very closely, but preg-
nant females exhibited more variability, owing to variation in
fecundity and stages of embryonic development. The allometric
model (AIC ¼165.02) yielded a better fit than an isometric
model (AIC ¼107.23) with cubic growth. For males, AIC
values indicated substantial support for either the allometric
(AIC ¼43.82) or isometric model (AIC ¼45.07) with cubic
growth.
Changes in liver weights (HSI) of mature females can reflect
the large energy demands of pregnancy. In this study, we found a
significant decrease in HSI after females reached maturity.
Walker (2005) reported a different trend for Galeorhinus galeus,
D1
D2
D1
D2
(a)
(b)
Fig. 4. Dorsal fin spines of (a) mature female and (b) mature male Squalus cf. mitsukurii. Black arrows represent
annual growth bands on the spines of this 12-year-old female and 15-year-old male. Growth bands are evident as
faint smudges on the surface of the enamel cap. The bases of both female spines were damaged during sampling,
hence the diagonal shape of the D2 base and shorter TSL of both spines. Scale bar, 10 mm.
Shortspine spurdog age, growth and reproduction Marine and Freshwater Research 815
in which liver weight increased concurrently with vitellogenesis.
This is likely because G. galeus and S. cf. mitsukurii have
different reproductive cycles. The ovarian cycle in G. galeus is
triennial, with vitellogenesis occurring mainly in the absence of
embryonic development. Therefore, females of that species are
able to sequester large energy reserves in the liver after parturition
to support vitellogenesis. However, in S. cf. mitsukurii,the
reproductive cycle is continuous and the entire ovarian cycle
occurs while the female is carrying embryos in utero. Therefore,
females of this species do not have the opportunity to build
energy reserves in the liver after parturition because vitellogene-
sis is essentially a continuous, energy-taxing process (Fig. 7d).
How this HSI reduction in mature females affects buoyancy
remains unclear. The net effect of numerous large, positively
buoyant ovarian oocytes, along with numerous embryonic livers,
may compensate any loss in buoyancy caused by the decreased
HSI in gravid females. For males, there was no apparent reduc-
tion in HSI observed after maturity, likely because males do not
undergo a similarly energy-taxing process as female pregnancy.
Age determination
Both readers had prior experience in ageing confamilial species
(i.e. S. acanthias and Cirrhigaleus asper), but found S. cf. mit-
sukurii fin spines to be considerably more difficult to read. Thus,
age determination required a great deal of effort to examine each
spine at many angles, under varying degrees of light intensity.
Age estimates obtained from the two fin spines (D1 and D2)
were similar for males, but females often yielded higher age
estimates on the first dorsal fin spine (Cotton 2010). This is
because the enamel cap of the first dorsal fin spine is longer and
wider in older females, offering a greater surface area for band
visualisation. The spines of mature males presented difficulties
in reading owing to the proximal constriction of the enamel cap
on the anterior surface of the spine. Growth bands deposited on
the small, constricted surface of the enamel cap after maturation
were tightly spaced and often difficult to discern. Of the 48
spines with the largest age discrepancies (.2 years), 18 were
from mature males (30% of 60 male spines examined) and 30
were from females (12% of 243 female spines examined). Thus,
males were disproportionately represented, owing to the diffi-
culty in interpreting growth bands on mature male spines.
Though reader bias was evident, it is likely that it did not pose
a problem in the present study. Most of the discrepancies in age
were limited to 1- or 2-year differences, and because mean age
estimates were used in these instances, the final effects of such
differences were likely to be negligible (0.5–1 year). In cases
of larger age discrepancies, the readers reviewed the spines
together and reached a consensus on age assignment.
Growth models
Overall, growth models showed that males grow faster, mature
earlier and reach a smaller maximum size than females, a
common pattern in elasmobranchs. Cailliet et al. (2006)
recommended fitting age data to multiple growth models, so we
used five common models, with two different techniques of
model fitting (LS and ML). Overall model fit was better for male
size-at-age data than for female data, as shown by the lower RSS
(LS) and s(ML) values.
In the case of female size-at-age data, optimisation was more
efficient using maximum likelihood estimation than least-
squares, possibly owing to limitations posed by the lack of an
asymptote in the curve. Two of the LS-fitted models did not
converge and only the LS-fitted logistic model yielded plausible
parameter estimates for female S. cf. mitsukurii. Estimates of
female L
N
(both LS and ML-fitted) were unrealistically high
in most models, probably owing to a lack of older individuals
being sampled (Cailliet and Tanaka 1990). Wilson and Seki
(1994) found only two individuals older than 20 years around
Hancock Seamount and attributed the lack of older individuals
to extensive harvest that occurred before their collections in
1986. This explanation is unlikely in the present study as
Hancock Seamount is .2500 km from Oahu, Hawaii.
The differences in growth and reproductive parameters
suggest that individuals from Oahu and Hancock Seamount
02468101214161820222426
0
20
30
40
TL (cm) TL (cm)
50
60
70
20
40
60
80
100
(a)
(b)
24681012
A
g
e (years)
14 16 18 20 22 24 26
VBGF
Gompertz
Logistic
VBGFmod
VBGF2par
Fig. 5. Growth models fitted to size-at-age data for (a) female and (b) male
Squalus cf. mitsukurii collected around Oahu, Hawaii.
816 Marine and Freshwater Research C. F. Cotton et al.
are isolated, with independent, site-specific life history para-
meters. Taniuchi et al. (1993) and Taniuchi and Tachikawa
(1999) showed a high degree of intraspecific variability in
biological parameters of this species (or possibly species com-
plex) across the north-central and north-western Pacific Ocean.
A few specimens in the present study (n¼8), including the
largest female, were from commercial fishermen operating
around the NWHI (Fig. 1). Although no genetic differences
exist between individuals from Oahu and the NWHI (Daly-
Engel et al. 2010), individuals from the NWHI may have
slightly different, locally influenced growth parameters com-
pared with those taken around Oahu.
Both methods of model fitting (LS and ML) performed
comparably with the male size-at-age data. All models (LS
and ML) that included an L
0
term yielded estimates that were
near the observed size at birth (23.3 cm) for both sexes. These
results suggest that when size-at-age data yield a good model fit,
either method of model fitting (LS or ML) generates similar
parameter estimates. However, when size-at-age data are limited
(e.g. lacking an asymptote), maximum likelihood estimation
may provide more robust parameter estimates.
Model selection was based on the lowest DAICc value, while
factoring the agreement of model parameter estimates with
observed values of maximum size and size-at-birth. For females,
the logistic model was selected as the best model because the
DAICc values were low for each method of model fitting and the
estimates of L
N
were closest to the observed maximum size of
101-cm TL. The maximum size reportedfor this species is 125 cm
and only one species (S. acanthias) in the family Squalidae
exceeds 125-cm TL (Compagno et al. 2005). The logistic model
estimate of L
N
(126 cm) therefore provided a more reasonable
estimate than all the other models. Model parameter estimates for
males were nearly identical across models, irrespective of method
of model fitting (LS or ML), and the VBGF
2par
was selecte d as the
best model. Although the AIC
c
value for the logistic model was
lowest for males, this model was rejected because the estimate
of L
N
(64.81 cm) was lower than the maximum size (67 cm)
observed in the present study. The parameter t
0
has no biological
meaning when modelling age and growth of elasmobranchs
(Cailliet et al. 2006) and other species with large offspring, and
therefore will not be discussed here.
Comparing model parameter estimates from this study with
those of previous studies of S. cf. mitsukurii is not straightfor-
ward, given the variety of models used in the present study, the
problematic estimates of female L
N
generated by our models,
and the possibility that multiple populations or species were
involved in these studies. Hancock Seamount is geographically
closer to Oahu than the other sampling sites listed in Table 5, yet
the growth parameters (particularly k) reported from that region
are quite different to those of our study, suggesting these studies
involved a different species to that used in the present study.
Table 2. Consistency in age estimates between readers of anterior (D1) and posterior (D2) dorsal fin spines of male and female Squalus cf. mitsukurii
The total number of spines aged was 303; three spines were missing, one spine was deemed unreadable by Reader 1 and one spine was deemed unreadable by
Reader 2
Consistency of age estimates D1 female D1 male D1 total D2 female D2 male D2 total Grand total
Reader 1 ¼Reader 2 36 (11.9%) 6 (2.0%) 42 (13.9%) 26 (8.6%) 5 (1.7%) 31 (10.2%) 73 (24.1%)
Reader 1 .Reader 2 – – – –
þ1 year 30 4 34 28 3 31 65
þ2 years 16 6 22 22 10 32 54
þ3 years 9 4 13 5 6 11 24
þ4 years 2 2 4 0 0 0 4
þ5 years 1 0 1 0 0 0 1
þ6 years 0 1 1 1 1 2 3
Total 58 (19.1%) 17 (5.6%) 75 (24.8%) 56 (18.5%) 20 (6.6%) 76 (25.1%) 151 (49.8%)
Reader 1 ,Reader 2 – – – –
1 year 14 4 18 19 3 22 40
2 years 10 1 11 12 0 12 23
3 years 1 1 2 3 2 5 7
4 years 2 0 2 4 0 4 6
5 years 1 1 2 1 0 1 3
Total 28 (9.2%) 7 (2.3%) 35 (11.6%) 39 (12.9%) 5 (1.7%) 44 (14.5%) 79 (26.1%)
Reader 2 a
g
e classes
0 5 10 15 20 25 30
Reader 1 mean ages
0
5
10
15
20
25
30
Fig. 6. Age bias plot showing means and 95% confidence intervals of age
estimates from Reader 1 for each age class determined by Reader 2.
Shortspine spurdog age, growth and reproduction Marine and Freshwater Research 817
Alternately, the apparent disparity in growth parameters could
be a result of differences in sampling. Taniuchi and Tachikawa
(1999) collected data in 1973, a period of intense harvest of
the pelagic armorhead (and by-catch of S. mitsukurii), whereas
Wilson and Seki (1994) collected data in 1985–88, after the
fishery had effectively ceased and a moratorium was in place.
Additionally, Taniuchi and Tachikawa (1999) may have experi-
enced data limitations, as the depth range they sampled around
Hancock Seamount was quite narrow (263–290 m). Furthermore,
growth parameters reported in the present study are as similar to
those from the Ogasawara Islands as they are to those from
Hancock Seamount (Taniuchi and Tachikawa 1999). Differences
in growth parameters between Oahu, where most samples in the
present study were collected, and Hancock Seamount could be
owing to latitudinal variation between Oahu (218270N) and
Hancock Seamount (308180N), or possibly to site-specific growth
rates controlled by the local productivity within these areas.
Differences in growth parameters in our study and those reported
from Japan (Choshi and Ogasawara: Taniuchi and Tachikawa
1999) and the South Pacific (Sala-y-Gomez seamounts: Litvinov
1990) might be a result of intraspecific geographic variation,
or more likely these studies involved a different species than the
present study. Another explanation for the observed differences
in growth model parameters could be that none of these prior
studies examined multiple growth models for parameter estima-
tion, which can vary substantially, as indicated by our results.
The rate constant kwas low for both sexes in all models. The
values of kestimated by the Gompertz and logistic models for
Table 3. Estimates of model parameters (6s.e.), standard deviation (r, for ML-fitted models), residual sum of squares (RSS, for LS-fitted models),
model likelihood values (2ln(L), for ML-fitted models), and model selection statistics (AICc and DAICc) for length-at-age data for female
Squalus cf. mitsukurii
Empirical mean length-at-birth (L
0
¼23.3 cm) was used in the VBGF
2par
model. The VBGF and VBGF
mod
models failed to converge using nonlinear least-
squares, as indicated by ‘–’
Model L
N
(cm TL) k(year
1
)L
0
(cm TL) t
0
(year) sRSS ln(L) AICc DAICc
Maximum likelihood estimation
VBGF 208.32 24.97 0.02 0.00 23.89 1.20 NA 4.70 0.29 388.60 785.51 2.98
VBGF
mod
164.59 13.25 0.02 0.00 NA 6.34 0.58 4.80 0.30 391.62 791.57 9.04
VBGF
2par
203.84 20.62 0.02 0.00 NA NA 4.73 0.29 388.92 784.03 1.50
Gompertz 150.71 22.41 0.04 0.01 27.71 1.36 NA 4.65 0.29 387.10 782.53 0.00
Logistic 126.16 12.36 0.08 0.01 NA 14.832.52
B
4.71 0.29 388.70 785.73 3.20
Least-squares
VBGF NA – – – –
VBGF
mod
––NA
VBGF
2par
318.69 120.13 0.01 0.00 NA NA 2850.81 – 781.45
A
0.00
Gompertz 170.50 31.80 0.04 0.01 27.82 1.37 NA 2827.70 – 782.51
A
1.06
Logistic 127.75 13.18 0.08 0.01 NA 15.16 2.68
B
2897.56 – 785.71
A
4.26
A
LS models used kþ1 parameters in the AICc calculation to standardise LS AICc and ML AICc, since ML models estimate one extra parameter (s).
B
This value represents the variable ‘a’ in the logistic equation, or the inflection point of the growth curve, not t
0
.
Table 4. Estimates of model parameters (6s.e.), standard deviation (r, for ML-fitted models), residual sum of squares (RSS, for LS-fitted models),
model likelihood values (2ln(L), for ML-fitted models), and model selection statistics (AICc and DAICc) for length-at-age data for male
Squalus cf. mitsukurii
Empirical length-at-birth (L
0
¼23.3 cm) was used in the VBGF
2par
model
Model L
N
(cm TL) k(year
1
)L
0
(cm TL) t
0
(year) sRSS ln(L) AICc DAICc
Maximum likelihood estimation
VBGF 71.92 4.49 0.08 0.01 23.08 1.10 NA 2.94 0.34 92.45 194.16 2.64
VBGF
mod
71.83 4.38 0.08 0.01 NA 4.75 0.64 2.94 0.34 92.46 194.16 2.64
VBGF
2par
72.13 4.52 0.08 0.01 NA NA 2.95 0.34 92.47 191.67 0.15
Gompertz 72.91 3.98 0.13 0.01 23.08 1.08 NA 2.89 0.34 91.71 192.67 1.15
Logistic 64.81 1.88 0.18 0.02 NA 3.25 0.50
B
2.84 0.33 91.14 191.52 0.00
Least-squares
VBGF 71.98 4.42 0.08 0.02 23.08 1.15 NA 320.73 – 194.16
A
2.64
VBGF
mod
71.97 4.92 0.08 0.02 NA 4.76 0.71 320.73 – 194.16
A
2.64
VBGF
2par
72.13 4.85 0.08 0.02 NA NA 321.06 – 191.67
A
0.15
Gompertz 67.33 2.86 0.13 0.02 23.09 1.12 NA 308.08 – 192.67
A
1.15
Logistic 64.81 2.01 0.18 0.02 NA 3.25 0.53
B
298.67 – 191.52
A
0.00
A
LS models used kþ1 parameters in the AICc calculation to standardise LS AICc and ML AICc, as ML models estimate one extra parameter (s).
B
This value represents the variable ‘a’ in the logistic equation, or the inflection point of the growth curve, not t
0
.
818 Marine and Freshwater Research C. F. Cotton et al.
females (0.04–0.08) are among the lowest reported growth
coefficients for any elasmobranch species (Cailliet and
Goldman 2004). With such slow growth rates, this species is
not resilient to extensive harvest and is therefore prone to
overexploitation and localised depletion in those areas where
harvested in abundance (Hoenig and Gruber 1990; Kyne and
Simpfendorfer 2007).
Age validation has been performed using multiple techni-
ques on a congeneric species, S. acanthias (Beamish and
McFarlane 1985; Tucker 1985; Campana et al. 2006). Although
we were unable to validate the periodicity of growth band
formation in this study, we assumed that S. cf. mitsukurii
deposits growth bands in the same manner and with the same
frequency as S. acanthias.Squalus acanthias is a high-latitude,
shallower-dwelling species that experiences more variation in
temperature seasonally. However, temperature is only one of
the major factors controlling growth, others being food quality
and abundance. Although S. cf. mitsukurii may not experience
similar magnitudes of seasonal temperature fluctuations, this
species probably experiences seasonal variation in food avail-
ability, as the food web responds to seasonal pulses of marine
snow (Billett et al. 1983; Karl et al. 1996). Ziemann (1975) also
noted seasonal changes in distribution of oplophorid shrimp, one
of the primary components of the diet of S. cf. mitsukurii
(R. Grubbs, unpubl. data). These seasonal changes in primary
production and prey availability could result in alternating
periods of fast and slow growth coincident with the formation
of growth bands on the dorsal fin spines (Goldman 2005).
Reproduction
According to the maturity ogives, females of this species reach
sexual maturity at ,64 cm, or 63% of the maximum observed
size (101-cm TL) and 15 years, or 58% of the maximum
observed age (26 years). Males mature at ,47 cm, or 70% of
their maximum observed size (67-cm TL) and 8.5 years, or
37% of their maximum observed age (23 years).
The maternity ogive was calculated using a slightly different
criterion than that which Walker (2005) used for Galeorhinus
galeus. Because reproduction is aseasonal and gestation period
is unknown for S. cf. mitsukurii, there was no way of predicting
time of parturition in postpartum females or females with term
embryos, as Walker (2005) did for G. galeus. Therefore, in the
present study, we used the term ‘maternal condition’ to denote
only pregnant females.
Fecundity ranged mostly from four to ten pups for S. cf.
mitsukurii. Although we observed three females with smaller
clutches, these small clutch sizes were likely the results of stress-
induced abortion. If this species undergoes a two-year repro-
ductive cycle, like S. acanthias, then females may carry only
three to seven clutches of pups in a lifetime. Given the maximum
observed age, the range of fecundity we present here, and a
continuous, asynchronous reproductive cycle, the species might
have lifetime fecundity as low as 12–70 pups. The difference in
age estimates for maturity and maternity ogives is three years,
suggesting that the reproductive cycle might be even longer than
that of S. acanthias, which would reduce these estimates of
lifetime fecundity.
Graham (2005) found a similar range of fecundity in Austra-
lian S. mitsukurii, although this study may have been conducted
on a different population or species than the present study.
Maturity ogives presented by Graham (2005) also indicated
larger sizes-at-maturity (female L
50% maturity
¼81 cm; male
L
50% maturity
¼63 cm) than those of our study. Likewise, Fischer
et al. (2006) reported similar fecundity estimates in Atlantic
S. mitsukurii from the north-east coast of Brazil, but the maturity
ogives also indicated larger sizes-at-maturity (female
L
50% maturity
¼78 cm; male L
50% maturity
¼65 cm) than those
reported in the present study. Lucifora et al. (1999) presented
Table 5. Comparisons of growth model parameters reported in various studies of Squalus cf. mitsukurii
The variables t
max
and t
mat
represent maximum observed age and observed age at maturity, respectively. All model parameters were estimated using the LS-
fitted VBGF
mod
(Eqn 3), except those labelled as ‘best growth models’
Location and source Sex L
N
(cm TL) k(year
1
)t
0
(year) t
max
(year) t
mat
(year)
Sala-y-Gomez (Litvinov 1990) ~104
A
15 6–15
B
#100
A
– 14 –
Hancock Seamount (Wilson and Seki 1994) ~107 0.041 10.09 27 15
#66 0.155 4.64 18 4
Hancock Seamount
C
(Taniuchi and Tachikawa 1999) ~83 0.103 2.94 17 14–16
#65 0.252 0.43
C
12 6–7
Ogasawara Islands, Japan (Taniuchi and Tachikawa 1999) ~111 0.051 5.12 27 15–17
C
#88 0.060 5.57
C
21 9–10
C
Choshi, Japan (Taniuchi and Tachikawa 1999) ~163 0.039 5.21 21 19–20
C
#109 0.066 5.03 20 10–11
Present study (VBGF
mod
)~165 0.020 6.34 26 15
#72 0.080 4.75 23 8.5
Present study (best growth models)
D
~126 0.080 14.83 26 15
#72 0.080 NA 23 8.5
A
Values are maximum observed length (L
max
), not L
N
.
B
Estimated from length-at-age curve.
C
Transcriptional and typographical errors were reported in Cailliet and Goldman (2004). Parameter estimates reported here are corrected. ‘SE Hancock
Seamount’ was referenced previously as ‘Japan, SE Harbor’.
D
Best model parameters: females, logistic model; males, VBGF
2par
model.
Shortspine spurdog age, growth and reproduction Marine and Freshwater Research 819
sizes at maturity from the Uruguayan–Argentine Common
Fishing Zone that closely agree with maturity ogives from the
present study. It is doubtful, however, that any of these studies
were conducted on the same population or species, as these
studies were conducted far from Hawaii and the taxon
S. mitsukurii comprises a species complex (Last and Stevens
1994; Compagno et al. 2005; Last et al. 2007b).
Conclusions
Squalus cf. mitsukurii exhibits a long-lived life history, char-
acterised by slow growth, high longevity, late maturity and low
fecundity (Musick 1999). The maximum age is at least 26 years
for females and 23 years for males, and sexual maturity is
reached at 58% and 37% (respectively) of the maximum
observedage in thisstudy. Estimates of the growth coefficient (k)
were very low, and lifetime fecundity is unknown for this species,
but conservatively estimated to be between 12 and 70 pups. With
such population characteristics and among the lowest genetic
diversity reported for any elasmobranch (Daly-Engel et al.
2010), which limits rebound potential, S. cf. mitsukurii cannot
40
0.0
0.2
0.4
0.6
Proportion mature
0.8
1.0
(a)
50 60 70
TL (cm)
80 90 100
40
0
10
20
30
Clasper length (mm)
40
50
60
(c)
45 50 55
TL (cm)
60 65 70 0
0
10
20
30
Oocyte diameter (mm)
40
50
(d)
50 100 150
Embr
y
o TL
200 250 300
40
0.0
0.2
0.4
0.6
Proportion mature
0.8
1.0
(b)
50 60 70
TL (cm)
80 90 100
Fig. 7. Reproductive biology of Squalus cf. mitsukurii collected around Oahu, Hawaii. (a) Length-based maturity ogives for females (open
circles) and males (closed circles). Size class intervals are 5 cm for females and 2 cm for males. Length at 50% maturity (L
50% maturity
) for
females corresponded to ,64 cm (,15.0 years) and the male L
50% maturity
was ,47 cm (,8.5 years). (b) Length-based maternity ogives
for females. Size class intervals are 5 cm. Length at which 50% of specimens examined were pregnant (L
50% maternal
) was ,70.5 cm
(,18 years). (c) Relationship of inner (closed circles) and outer clasper lengths (open circles) to length (TL) of males. Outer clasper lengths
were not recorded for four individuals. (d) Ovarian development concurrent with gestation in pregnant females. Embryos not clearly visible
upon inspection (,0–10 mm TL) were assigned a size of 0 mm. Mean observed TL of full-term pups was 233mm.
Maternal TL (cm)
60 65 70 75 80 85 90 95 100 105
Fecundity (# embryos)
0
2
4
6
8
10
12
Fig. 8. Fecundity versus length (TL) of pregnant female Squalus cf.
mitsukurii collected around Oahu, Hawaii.
820 Marine and Freshwater Research C. F. Cotton et al.
sustain high levels of fishing mortality. In areas currently
experiencing overfishing, this species will require a long
recovery time once proper management procedures are in place.
Elsewhere, if fisheries are to be developed, it would be advisable
to proceed conservatively.
The high degree of geographic variability in reproductive
and growth parameters reported in the literature for S. cf.
mitsukurii is either attributable to variability among isolated
populations of a single species that are influenced by local
conditions, or possibly a result of the sampling of multiple
species within a species complex. A recent taxonomic study in
Australia yielded six new species of Squalus, many of which
were previously cryptic (Last et al. 2007b). It is likely that
cryptic species exist globally within the taxon ‘Squalus mitsu-
kurii’, and these have all been historically identified as the same
species. Future taxonomic work is needed within this genus to
help resolve these uncertainties.
Acknowledgements
We thank Kim Holland, Dave Itano, Brian Bowen, Rob Toonen and
Michelle Gaither at the Hawaii Institute of Marine Biology for support and
assistance in collecting samples. Also, several fishermen (Timm Timoney,
Gary Dill, Leonard Yamada, Burt Kikkawa, K. Kawamoto and Stephen Lee)
and researchers (Bo Alexander, Chris Kelley) provided specimens for this
study. We thank Jason Romine and Henry Mollet for their assistance with
growth models, as well as Jose Castro, Tracy Sutton, Michael Vecchione and
two anonymous referees for valuable comments on the manuscript. Funding
was provided by the Evolution, Ecology, and Conservation Biology Program
at the University of Hawaii and the National Shark Research Consortium.
References
Beamish, R. J., and McFarlane, G. A. (1985). Annulus development on
the second dorsal spine of the spiny dogfish (Squalus acanthias) and
its validity for age determination. Canadian Journal of Fisheries and
Aquatic Sciences 42, 1799–1805. doi:10.1139/F85-225
Beverton, R. J. H., and Holt, S. J. (1957). ‘On the Dynamics of ExploitedFish
Populations: Fish and Fisheries Series11.’ (Chapman and Hall: London.)
Billett, D. S. M., Lampitt, R. S., Rice, A. L., and Mantoura, R. F. C. (1983).
Seasonal sedimentation of phytoplankton to the deep-sea benthos. Nature
302, 520–522. doi:10.1038/302520A0
Burnham, K. P., and Anderson, D. R. (2002). ‘Model Selection and Multi-
model Inference: A Practical Information-Theoretic Approach.’
2nd edn. (Springer–Verlag: New York.)
Cailliet, G. M., and Goldman, K. J. (2004). Age determination and validation
in chondrichthyan fishes. In ‘Biology of Sharks and Their Relatives’.
(Eds J. C. Carrier, J. A. Musick and M. R. Heithaus.) pp. 399–447. (CRC
Press: Boca Raton.)
Cailliet, G. M., and Tanaka, S. (1990). Recommendations for research
needed to better understand the age and growth of elasmobranchs. In
‘Elasmobranchs as Living Resources: Advances in the Biology, Ecolo-
gy, Systematics and the Status of the Fisheries. NOAA Technical Report
NMFS 90’. (Eds H. L. Pratt Jr., S. H. Gruber and T. Taniuchi.) pp. 505–
507. (U.S. Department of Commerce: Washington, DC.)
Cailliet, G. M., Smith, W. D., Mollet, H. F., and Goldman, K. J. (2006). Age
and growth studies of chondrichthyan fishes: the need for consistency
in terminology, verification, validation, and growth function fitting.
Environmental Biology of Fishes 77, 211–228. doi:10.1007/S10641-
006-9105-5
Camhi, M., Fowler, S., Musick, J., Brautigam, A., and Fordham, S. (1998).
Sharks and their relatives – ecology and conservation. Occasional Paper
of the IUCN Species Survival Commission 20, IUCN, Cambridge.
Campana, S. E. (2001). Accuracy, precision and quality control in age
determination, including a review of the use and abuse of age validation
methods. Journal of Fish Biology 59, 197–242. doi:10.1111/J.1095-
8649.2001.TB00127.X
Campana, S. E., Annand, M. C., and McMillan, J. I. (1995). Graphical and
statistical methods for determining the consistency of age determina-
tions. Transactions of the American Fisheries Society 124, 131–138.
doi:10.1577/1548-8659(1995)124,0131:GASMFD.2.3.CO;2
Campana, S. E., Jones, C., McFarlane, G. A., and Myklevoll, S. (2006).
Bomb dating and age validation using the spines of spiny dogfish
(Squalus acanthias). Environmental Biology of Fishes 77, 327–336.
doi:10.1007/S10641-006-9107-3
Carlson, J. K., and Baremore, I. E. (2005). Growth dynamics of the spinner
shark (Carcharhinus brevipinna) off the United States southeast and
Gulf of Mexico coasts: a comparison of methods. Fishery Bulletin 103,
280–291.
Cavanagh, R. D., and Lisney, T. J. (2003). Squalus mitsukurii. In ‘IUCN
2009. IUCN Red List of Threatened Species. (Version 2009.1)’. Avail-
able at http://www.iucnredlist.org [Verified 15 April 2011].
Compagno, L. J. V., Dando, M., and Fowler, S. (2005). ‘Sharks of the
World.’ (Princeton University Press: Princeton.)
Corte´s, E. (1999). Standardized diet compositions and trophic levels of
sharks. ICES Journal of Marine Science 56, 707–717. doi:10.1006/
JMSC.1999.0489
Cotton, C. F. (2010). Age, growth, and reproductive biology of deep-water
chondrichthyans. Ph.D. Dissertation, Virginia Institute of Marine
Science, College of William and Mary, Gloucester Point.
Daly-Engel, T. S., Grubbs, R. D., Feldheim, K. A., Bowen, B. W., and
Toonen, R. J. (2010). Is multiple mating beneficial or unavoidable?
Low multiple paternity and genetic diversity in the shortspine spurdog
(Squalus mitsukurii). Marine Ecology Progress Series 403, 255–267.
doi:10.3354/MEPS08417
Ebert, D. A., Compagno, L. J. V., and Cowley, P. D. (1992). A preliminary
investigation of the feeding ecology of squaloid sharks off the west coast
of southern Africa. South African Journal of Marine Science 12, 601–
609. doi:10.2989/02577619209504727
Fischer, A. F., Veras, D. P., Hazin, F. H. V., Broadhurst, M. K., Burgess,
G. H., et al. (2006). Maturation of Squalus mitsukurii and Cirrhigaleus
asper (Squalidae, Squaliformes) in the southwestern equatorial Atlantic
Ocean. Journal of Applied Ichthyology 22, 495–501. doi:10.1111/
J.1439-0426.2006.00749.X
Goldman, K. G. (2005). Age and growth of elasmobranch fishes. In
‘Management Techniques for Elasmobranch Fisheries. FAO Fisheries
Technical Paper Number 474’. (Eds J. A. Musick and R. Bonfil.)
pp. 76–102. (FAO: Rome.)
Graham, K. J. (2005). Distribution, population structure and biological
aspects of Squalus spp. (Chondrichthyes : Squaliformes) from New
South Wales and adjacent Australian waters. Marine and Freshwater
Research 56, 405–416. doi:10.1071/MF04275
Graham, K. J., Andrew, N. L., and Hodgson, K. E. (2001). Changes in
relative abundance of sharks and rays on Australian South East Fishery
trawl grounds after twenty years of fishing. Marine and Freshwater
Research 52, 549–561. doi:10.1071/MF99174
Helfman, G. S., Collette, B. B., Facey, D. E., and Bowen, B. W. (2009). ‘The
Diversity of Fishes: Biology, Evolution, and Ecology.’ 2nd edn. (Wiley–
Blackwell: West Sussex.)
Hoenig, J. M., and Gruber, S. H. (1990). Life-history patterns in the
elasmobranchs: implications for fisheries management. In ‘Elasmo-
branchs as Living Resources: Advances in the Biology, Ecology,
Systematics and the Status of the Fisheries. NOAA Technical Report
NMFS 90’. (Eds H. L. Pratt Jr., S. H. Gruber and T. Taniuchi.) pp. 1–16.
(U.S. Department of Commerce: Washington, DC.)
Hoenig, J. M., Morgan, M. J., and Brown, C. A. (1995). Analysing
differences between two age determination methods by tests of
Shortspine spurdog age, growth and reproduction Marine and Freshwater Research 821
symmetry. Canadian Journal of Fisheries and Aquatic Sciences 52,
364–368. doi:10.1139/F95-038
Holden, M. J., and Meadows, P. S. (1962). The structure of the spine of the
spur dogfish (Squalus acanthias L.) and its use for age determination.
Journal of the Marine Biological Association of the United Kingdom 42,
179–197. doi:10.1017/S0025315400001302
Irvine, S. B. (2004). Age, growth and reproduction of deepwater dog-
fishes from southeastern Australia. Ph.D. Thesis, Deakin University,
Warrnambool, Australia.
Kaganovskaia, S. (1933). A method for determining the age and composition
of the catches of the spiny dogfish (Squalus acanthias L.). Bulletin of
the Far East Branch of the Academy of Sciences (USSR) 1–3,
139–141.
Karl, D. M., Christian, J. R., Dore, J. E., Hebel, D. V., Letelier, R. M., et al.
(1996). Seasonal and interannual variability in primary production and
particle flux at Station ALOHA. Deep-Sea Research. Part II, Topical
Studies in Oceanography 43, 539–568. doi:10.1016/0967-0645(96)
00002-1
Kimura, D. K. (2008). Extending the von Bertalanffy growth model using
explanatory variables. Canadian Journal of Fisheries and Aquatic
Sciences 65, 1879–1891. doi:10.1139/F08-091
Kyne, P. M., and Simpfendorfer, C. A. (2007). A collation and summariza-
tion of available data on deepwater chondrichthyans: biodiversity, life
history and fisheries. A report prepared by the IUCN SSC Shark
Specialist Group for the Marine Conservation Biology Institute,
Cambridge.
Last, P. R., and Stevens, J. D. (1994). ‘Sharks and Rays of Australia.’
(CSIRO: Hobart.)
Last, P. R., White, W. T., and Motomura, H. (2007a). Part 6 – Description of
Squalus chloroculus sp. nov., a new spurdog from southern Australia,
and the resurrection of S. montalbani Whitley. In ‘Descriptions of New
Dogfishes of the Genus Squalus (Squaloidea : Squalidae). CSIRO
Marine and Atmospheric Research Paper 014’. (Eds P. R. Last, W. T.
White and J. J. Pogonoski.) pp. 55–69. (CSIRO: Hobart.)
Last, P. R., White, W. T., and Pogonoski, J. J. (2007b). ‘Descriptions of New
Dogfishes of the Genus Squalus (Squaloidea : Squalidae). CSIRO
Marine and Atmospheric Research Paper 014.’ (CSIRO: Hobart.)
Litvinov, F. F. (1990). Ecological characteristics of the dogfish, Squalus
mitsukurii, from the Sala-y-Gomez seamounts. Journal of Ichthyology
30, 104–115.
Lucifora, L. O., Valero, J. L., and Garcia, V. B. (1999).Length at maturity of
the greeneye spurdog shark, Squalus mitsukurii (Elasmobranchii : Squa-
lidae), from the SW Atlantic, with comparisons with other regions.
Marine and Freshwater Research 50, 629–632. doi:10.1071/MF98167
MacArthur, R. H., and Wilson, E. O. (1967). ‘The Theory of Island
Biogeography.’ (Princeton University Press: Princeton.)
Mollet, H. F., Ezcurra, J. M., and O’Sullivan, J. B. (2002). Captive biology
of the pelagic stingray, Dasyatis violacea (Bonaparte, 1832). Marine and
Freshwater Research 53, 531–541. doi:10.1071/MF01074
Morato, T., Watson, R., Pitcher, T. J., and Pauly, D. (2006). Fishing down
the deep. Fish and Fisheries 7, 24–34. doi:10.1111/J.1467-2979.2006.
00205.X
Musick, J. A. (1999). Ecology and conservation of long-lived marine animals.
In ‘Life in the Slow Lane: Ecology and Conservation of Long-Lived
Marine Animals. American Fisheries Society Symposium 23’. (Ed. J. A.
Musick.) pp. 1–10. (American Fisheries Society: Bethesda.)
Musick, J. A., Burgess, G., Cailliet, G., Camhi, M., and Fordham, S. (2000).
Management of sharks and their relatives (Elasmobranchii). Fisheries
25, 9–13. doi:10.1577/1548-8446(2000)025,0009:MOSATR.2.0.CO;2
Nammack, M. F., Musick, J. A., and Colvocoresses, J. A. (1985). Life history
of spiny dogfish off the northeastern United States. Transactions of
the American Fisheries Society 114, 367–376. doi:10.1577/1548-8659
(1985)114,367:LHOSDO.2.0.CO;2
Quinn, T. J., and Deriso, R. B. (1999). ‘Quantitative Fish Dynamics.’
(Oxford University Press: New York.)
R Development Core Team (2009). ‘R: a language and environment for
statistical computing. R Foundation for Statistical Computing.’ ISBN
3-900051-07-0. Available at http://www.R-project.org [Verified 15
April 2011].
Ricker, W. E. (1975). Computation and interpretation of biological statistics
of fish populations. Bulletin of the Fisheries Research Board of Canada
191, 1–382.
Ricker, W. E. (1979). Growth Rates and Models. In ‘Fish Physiology
Volume VIII, Bioenergetics and Growth’. (Eds W. S. Hoar, D. J. Randall
and J. R. Brett.) pp. 677–743. (Academic Press: New York.)
Stevens, J. D., Bonfil, R., Dulvy, N. K., and Walker, P. A. (2000). The effects
of fishing on sharks, rays, and chimaeras (chondrichthyans), and the
implications for marine ecosystems. ICES Journal of Marine Science 57,
476–494. doi:10.1006/JMSC.2000.0724
Taniuchi, T., and Tachikawa, H. (1999). Geographic variation in age and
growth of Squalus mitsukurii (Elasmobranchii : Squalidae) in the North
Pacific. In ‘Proceedings of the 5th Indo-Pacific Fish Conference,
Noumea–New Caledonia, 3–8 November 1997’. (Eds B. Se´ret and
J. Y. Sire.) pp. 321–328. (Society of French Ichthyologists: Paris.)
Taniuchi, T., Tachikawa, H., Shimizu, M., and Nose, Y. (1993). Geographi-
cal variations in reproductive parameters of shortspine spurdog in the
North Pacific. Nippon Suisan Gakkai Shi 59, 45–51.
Tribuzio, C. A., Kruse, G. H., and Fujioka, J. T. (2010). Age and growth
of spiny dogfish (Squalus acanthias) in the Gulf of Alaska: analysis of
alternative growth models. Fishery Bulletin 108, 119–135.
Tucker, R. (1985). Age validation studies on the spines of the spurdog
(Squalus acanthias) using tetracycline. Journal of the Marine Biological
Association of the United Kingdom 65, 641–651. doi:10.1017/
S0025315400052486
Uchida, R. N., and Tagami, D. T. (1984). Groundfish fisheries and research
in the vicinity of seamounts in the North Pacific Ocean. Marine Fisheries
Review 46, 1–17.
von Bertalanffy, L. (1938). A quantitative theory of organic growth (inqui-
ries on growth laws II). Human Biology 10, 181–213.
Walker, T. I. (2005). Reproduction in fisheries science. In ‘Reproductive
Biology and Phylogeny of Chondrichthyes’. (Ed. W. C. Hamlett.)
pp. 81–127. (Science Publishers Inc.: Enfield.)
White, W. T., Last, P. R., and Stevens, J. D. (2007). Part 7 – Two new species
of Squalus of the ‘mitsukurii group’ from the Indo–Pacific. In ‘Descrip-
tions of New Dogfishes of the Genus Squalus (Squaloidea : Squalidae).
CSIRO Marine and Atmospheric Research Paper 014’. (Eds P. R. Last,
W. T. White and J. J. Pogonoski.) pp. 71–81. (CSIRO: Hobart.)
Wilson, C. D., and Seki, M. P. (1994). Biology and population character-
istics of Squalus mitsukurii from a seamount in the central North Pacific
Ocean. Fishery Bulletin 92, 851–864.
Ziemann, D. A. (1975). Patterns of vertical distribution, vertical migration
and reproduction in the Hawaiian mesopelagic shrimp of the family
Oplophoridae. Ph.D. Dissertation, University of Hawaii, Manoa, USA.
Manuscript received 7 December 2010, accepted 4 April 2011
http://www.publish.csiro.au/journals/mfr
822 Marine and Freshwater Research C. F. Cotton et al.
... Use of a capital breeding strategy is common in elasmobranchs (e.g. Pierce et al., 2009;Lteif et al., 2016;Corsso et al., 2018), but there is also evidence of income breeding strategies (Castro, 2009;Cotton et al., 2011) and species that exhibit both (Hammerschlag et al., 2018). The relative energy requirements for capital or income breeding strategies may be important for continued reproductive success in species that experience changing environments (Hammerschlag et al., 2018). ...
... Jordan & Snyder 1903 generally have a lower HSI than immature females and follow an income breeding strategy (Cotton et al., 2011). This strategy is likely to be enabled by simultaneous vitellogenesis and gestation, and suitable resource availability to preclude the need for compiling plentiful energy reserves before gestation. ...
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Here we investigated measurements of energy density and bioenergetic modelling for a pelagic ray, Mobula eregoodoo, to estimate its relative allocation to various bodily processes, and especially reproduction. The data revealed M. eregoodoo uses up to 21.0 and 2.5% of its annual energy budget on growth and reproduction, respectively. During pregnancy, females depleted energy reserves in the liver which, along with their biennial reproductive cycle, aligns with general theory that ectotherms are capital breeders, and thus build energy reserves prior to reproduction. However, the reduction in energy reserves did not account for all reproductive costs, and hence gravid females supplement reproductive costs through energy derived from the diet; as per an income breeding strategy. These characteristics imply M. eregoodoo exhibits some flexibility in fuelling reproduction depending on energy availability throughout the reproductive cycle, which may be prevalent in other elasmobranchs. The data represent the first estimates of both the metabolic costs of gestation in elasmobranchs, and the relative cost of reproduction in rays. Energy costs and plasticity associated with highly variable reproductive strategies in elasmobranchs may influence long-term population viability under a rapidly changing environment. This article is protected by copyright. All rights reserved.
... 24/05/2020) Off Japan, Squalus spp are reported from depths between 100-500 m (Ziadi-Künzli et al. 2020). It is thought to reach a maximum size of 112 cm total length (TL) (Cotton et al. 2011). Nothing else is known of its biology. ...
... Nothing else is known of its biology. Female age-at-maturity is 15 years and maximum age is 26 years (Cotton et al. 2011), therefore generation length is 20.5 years. ...
... Liu 2006; Barnett et al. 2009). In oviparous species, the variation of HSI may reflect differences in the energy requirements of follicle maturation, vitellogenesis and egg-laying in females and maturation and mating in males (Walker 2005;Cotton et al. 2011). For that reason, we used only mature individuals in the analysis. ...
... The higher L m : L max ratios in our study may reflect the high fishing pressure that results in a paucity of larger individuals, whereas in Australia, there is no directed fishery for the species. The maximum length of females from the waters of Seribu Islands is likely to be greater than 890 mm TL and the true L max may not be attained, as indicated by the female ogive curve not reaching an asymptote (Cotton et al. 2011;Irvine et al. 2012). ...
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The brown-banded bamboo shark, Chiloscyllium punctatum, is one of the most common sharks caught in coastal fisheries across Southeast Asia; however, its small size and low economic value typically exclude it from the attention of fisheries managers. As part of an assessment of a potential role for this shark in improving the sustainability of coastal shark fisheries in Indonesia, we investigated its reproductive biology from waters around the Seribu Islands on the basis of monthly sampling from a fish landing in Tanjung Pasir, Banten. Females have fully functional uteri, but asymmetric ovaries, with only the right ovary being functional and the left ovary being atrophied. The species is reproductively active throughout the year, with the optimum period for males to copulate being from June to August, and the optimum period for egg-laying in females from July to January on the basis of their physiological condition. Females mature at a larger size than do males, 704- and 653-mm total length respectively. To allow a continuous recruitment flow to the population, and to facilitate compliance and monitoring, we recommend that fishers release all brown-banded bamboo sharks greater than 700 mm in total length.
... For most deep-water elasmobranchs, poor mineralisation of the vertebral centra results in low discernibility in the banding patterns and contributes to the lack of age information (Goldman et al. 2012;Cotton et al. 2014;Cailliet 2015). Thus, various different anatomical structures have been investigated, including dorsal fin spines (Irvine et al. 2006;Cotton et al. 2011), caudal thorns (Henderson et al. 2005;Gallagher et al. 2006) and eye lenses (Francis et al. 2018), and alternative ageing methods developed, such as using near-infrared spectroscopy (Rigby et al. 2014). With the expansion of fisheries into deep water, it is imperative to develop life history information for deep-water elasmobranchs and use ageing techniques to generate critical growth information (Kyne and Simpfendorfer 2010). ...
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Owing to poorly mineralising structures, ageing deep-water elasmobranchs requires unconventional techniques. The aim of the present study was to develop an ageing method for the goblin shark Mitsukurina owstoni (Jordan, 1898) using Alcian blue staining of the vertebral column. One vertebral centrum from a male individual measuring 315.2-cm total length (TL) was aged with a minimum age of 27 years. Using a Bayesian von Bertalanffy growth model informed by back-calculated length at age, a literature search of maximum male TL, the TL of the smallest free-swimming individuals and informative priors, we estimated males grow to 374 cm TL, mature at 16 years and live up to 60 years. Our results provide useful life history information, with the aim of elucidating the cryptic biology of this deep-water shark.
... Feeding, migration and photoperiod are among several proposed possibilities for changes in band pair deposition but no study to date has determined the mechanisms driving these changes (Cailliet and Goldman, 2004;Natanson et al., 2014;Wells et al., 2017). Furthermore, the reasons why some species, such as deep sea sharks, have vertebral band pairs with poor readability or complete absence is not well understood, though some hypotheses include mineralization or lack thereof in deep sea sharks (Cotton et al., 2011;Francis and Maolagáin, 2019;Irvine et al., 2006;Kyne and Simpfendorfer, 2010). Periodicity of band pair deposition has been validated in some species (Natanson et al., 2002;Smith et al., 2003;Wells et al., 2013) but is lacking for the majority of sharks (Harry, 2018). ...
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Populations of sharks are declining globally, largely due to fishing pressure. There is a lack of fisheries-independent data on the demographics of many species, particularly those inhabiting deeper waters. The common sawshark (Pristiophorus cirratus) is a benthic-associated shark endemic to southeastern Australia that has been fished for over 90 years. Despite regular landings, little is known about their lifespan. To assess the age of P. cirratus, we first assessed their vertebral morphology to determine the best method for band pair elucidation. Based on morphology, vertebrae located in the post-branchial region were identified as the largest and least variable for band pair analysis. A total of eight different age-determination methods were then applied to shark vertebrae from this region to test the viability of traditional and nontraditional techniques in elucidating band pairs. Band pairs were indeterminable across all treatments. This research calls for further work into age validation and development of novel techniques to accurately age sawsharks.
... Secara umum, kelompok ikan ini sangat rentan terhadap kondisi lebih tangkap (overfishing) karena karakteristik siklus hidupnya seperti laju pertumbuhan lambat (Cotton et al., 2011). Selain itu, spesies ini juga mencapai kondisi matang gonad dalam jangka waktu yang lama dengan tingkat fekunditas sangat rendah (Camhi, et al., 2009). ...
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Sharks are one of bycatch for tuna longline fishery in Indonesia. The objective of this study is to identify catch composition, CPUE and conservation status of shark in tuna longline fishery. Data collection process conducted from January 2013 to December 2016 on tuna longline fishery that landed their catch in Benoa Port, Bali. There was found seven species of shark with total production of 335,261 tons. Blue shark (Prionace glauca) was dominated the catch with production nearly 300 tons or around 86.4%. The highest catch occurred on September 2016 with production of 36.5 tons. While the highest CPUE occurred on December 2016 with nearly 1.4 tons/vessel. The conservation status of near threatened occurred to blue shark and mako shark. The conservation status of vulnerable occurred to ocean whitetip shark, snaggletooth shark, silky shark and thresher shark. While the conservation status of endangered occurred to hammerhead shark. The results from this study be able to give information to stakeholders to reduce the catch of shark especially for endangered species.
... Choshi, Masseiba, Ogasawara Islands, Hancock Seamount) has been attributed to intraspecific geographical variation (Taniuchi et al., 1993) (Taniuchi and Tachikawa, 1999). Cotton et al. (2011) investigated the life history of 'S. cf. ...
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Japan is known for its marine biodiversity and diverse ecosystem due to its unique geological composition and water currents creating suitable habitats for a wider range of marine species. A rich deep-sea shark community with high endemism occurs on the continental shelf. Yet, the deep-sea shark taxonomy is still under development and poorly documented. Here, a DNA barcoding technique was adopted using the mitochondrial cytochrome oxidase I (COI) and NADH2 genes of samples collected from Japan with additional samples from genetic databases to draft out a phylogenetic tree of the deep-sea shark genus Squalus (dogfishes). The morphological divergence of congeners was further examined. Bayesian and maximum-likelihood-based species-level phylogenetic analyses of mitochondrial COI, ND2 and combined sequences provided strong support for distinct clades corresponding to the parental species with substantial sequence divergence between parental species. The combined dataset of the COI and ND2 gene was most suitable for barcoding of Squalus dogfishes. A multivariate analysis of morphological traits was largely consistent with the genetic data showing small but discrete differences in phenotypic characteristics allowing to separate Squalus species. Genetic samples of the taxonomically problematic Shortspine spurdog ‘Squalus mitsukurii’ from the Atlantic Ocean and Taiwan did not match with the type material of S. mitsukurii Jordan and Snyder, 1903 from mainland Japan. Squalus mitsukurii once considered a globally distributed species is a single, unique spurdog restricted to temperate Japan and Korea and may present an endemic in the Northwestern Pacific. This study further resolved two genetically and phenotypically distinct species of Squalus dogfishes in Japan, one in sympatry with S. mitsukurii in mainland Japan and one in sympatry with subtropical waters associated congeners in the Ryukyu Archipelago. The occurrence of populations of the ‘high-fin’ Taiwan spurdog, Squalus formosus, in subtropical Japan is herein confirmed.
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The Add-my-Pet (AmP) collection of data on energetics and Dynamic Energy Budget (DEB) parameters currently contains 200 out of over 1100 extant species of chondrichthyans. This milestone in the compilation of data for this group led us to investigate: (1) do the characteristics that we reported in 2014 for 20 chondrichthyan species, relative to other fish, still hold (2) are novel patterns in properties revealed given the additional data and (3) do the four chondrichthyan subgroups (galean, squaleans, rays and chimaeras) differ in properties? We argue that a better understanding of these properties is key to sustainable management of the rapidly dwindling populations worldwide. Most of the inter-specific scatter in ultimate reproduction rate as function of ultimate body weight stems from differences in the mass of neonates as fraction of that of the mother, which is very high in chondrichthyans. The ultimate neonate mass production is found to be proportional to the ultimate respiration rate, with proportionality factor of 10 g/mol. The lifespan is found to be inversely proportional to weight-specific respiration, with a proportionality factor of 0.1 mol/g. The ultimate weight equals the life-time cumulated neonate mass production. These relationships also apply, with more scatter, to all 3000 animal species in the AmP collection. Sharks and rays were found to be more demand-species, contrary to ray-finned fish and chimaeras, which are supply species. Chimaeras also have that smallest weight at birth and precociality coefficient, compared to sharks and rays. Galeans grow much slower than squaleans and rays, but the chimaeras grow even slower. The lifespan equals 25 times the incubation time for chondrichthyans, but they are rather unique in this respect. Last but not least, we discuss the odd implications of recently published data on the energetics of the Greenland shark.
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The reproductive biology of thresher shark species of the Ecuadorian Pacific was analysed based on 1236 specimens of Alopias pelagicus (711 females and 525 males) and 354 of A. superciliosus (164 females and 190 males) landed in “Playita Mía”, from January to December of 2019. The length of A. pelagicus females ranged between 67.2 and 184 cm PCL (precaudal length) and the males between 69.0 and 178.4 cm PCL, A. superciliosus registered a minimum and maximum size of 76.0 and 202.2 cm PCL for females and 94.0 and 204.8 cm PCL for males. The most frequently captured size class for A. pelagicus was 147.2−157.2 cm PCL and for A. superciliosus was 156.0-166.0 cm PCL. The sex ratio (F:M) for A. pelagicus and A. superciliosus was 1.35F:1M and 0.86F:1M respectively. For A. pelagicus males the inflection point of the clasper length adjustment, was 134.2 cm PCL and size at first sexual maturity (L 50 ) was estimated at 136.0 cm PCL. For A. superciliosus males the inflection point of the clasper length adjustment, was 136.8 cm PCL, and the first sexual maturity (L 50 ) was estimated at 138.7 cm PCL.
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A new species of deep-water dogfish shark, Squalus shiraii sp. nov., is described herein as endemic to the tropical waters off Southern Japan. This species has been largely misidentified with S. mitsukurii. However, morphological, meristic and morphometric evidence support it to be a separate and undescribed species. Squalus shiraii sp. nov. differs from this species by having body brown in colour dorsally, caudal fin with ventral and dorsal tips markedly tapered and broadly white, dermal denticles uniscuspidate and lanceolate and larger number of precaudal (91-94) and total vertebrae (120-123) (vs. body dark grey to black; caudal fin with ventral and dorsal tips rounded and not white in colour; denticles tricuspidate and rhomboid; 86-90 precaudal and 116-117 total vertebrae). Squalus shiraii sp. nov. is also clearly separated from other Japanese congeners which are herein revisited to include six species, based on the examination of over 150 specimens caught from Japanese waters that were available in ichthyological collections: S. mitsukurii, S. japonicus, S. acutirostris, S. brevirostris and S. suckleyi. Squalus mitsukurii, S. japonicus and S. brevirostris are re-described in detail and the neotype of S. japonicus is herein designated. Squalus acutirostris is treated as a valid species with occurrences in Japan, China and Taiwan and, thus, a provisional diagnosis is given, as well as an updated diagnosis of S. suckleyi. A key to Squalus species from the Northwestern Pacific Ocean is given and main morphological differences between S. shiraii sp. nov. and the closest related species are discussed.
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Annual marks were visible in three different areas of the dogfish (Squalus acanthias) spine. The annuli in the mantle, the stem base, and the inner dentine develop independently of each other. Annuli that formed on the mantle were readily identifiable externally, making them the most useful for age determination. The mantle annulus is an accumulation of pigment that appears to form because enamel deposition is not synchronous with the upward growth of the spine, resulting in the production of darkened bands that often form ridges. We validated our interpretation of annuli from fish aged 20–70 yr by tagging and recovering dogfish that were injected with oxytetracycline. Through validation we were able to demonstrate that some previous studies have underestimated age, resulting in a misunderstanding of important life history parameters.
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It is important to understand the ages, growth characteristics, maturation processes, and longevity of fishes to assess their current population status and to predict how their populations will change in time (Ricker, 1975; Cailliet et al., 1986b). Fishery biologists have used age, length, and weight data as important tools for their age-based population models. Especially important are details about growth and mortality rates, age at maturity, and life span (Ricker, 1975; Cortés, 1997). Over the past several decades, it has become obvious that fisheries for chondrichthyan fishes have not been easily sustainable. In 1974, Holden suggested that these fishes had life histories that made them vulnerable to overfishing. Included in the characteristics he cited were slow growth, late age at maturity, few offspring, and lengthy gestation periods. Since then, fishing pressure on elasmobranchs, both as directed and as bycatch fisheries (and discards) has increased (Bonfil, 1994; Casey and Myers, 1998; Stevens et al., 2000; Baum et al., 2003), stimulating many studies on many important aspects of their life histories, such as age, growth, and reproduction.
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Validated age and growth estimates are important for constructing age-structured population dynamic models of chondrichthyan fishes, especially those which are exploited. We review age and growth studies of chondrichthyan fishes, using 28 recent studies to identify areas where improvements can be made in describing the characteristics of ageing structures (both traditional and novel) utilized to estimate ages of sharks, rays, and chimaeras. The topics identified that need consistency include the: (1) terminology used to describe growth features; (2) methods used to both verify and validate age estimates from chondrichthyan calcified structures, especially edge and marginal increment analyses; and (3) the functions used to produce and describe growth parameters, stressing the incorporation of size at birth (L0) and multiple functions to characterize growth characteristics, age at maturity and longevity.
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Ten growth models were fitted to age and growth data for spiny dogfish (Squalus acanthias) in the Gulf of Alaska. Previous studies of spiny dogfish growth have all fitted the t 0 formulation of the von Bertalanffy model without examination of alternative models. Among the alternatives, we present a new two-phase von Bertalanffy growth model formulation with a logistically scaled k parameter and which estimates L 0. A total of 1602 dogfish were aged from opportunistic collections with longline, rod and reel, set net, and trawling gear in the eastern and central Gulf of Alaska between 2004 and 2007. Ages were estimated from the median band count of three independent readings of the second dorsal spine plus the estimated number of worn bands for worn spines. Owing to a lack of small dogfish in the samples, lengths at age of small individuals were back-calculated from a subsample of 153 dogfish with unworn spines. The von Bertalanffy, two-parameter von Bertalanffy, two-phase von Bertalanffy, Gompertz, two-parameter Gompertz, and logistic models were fitted to length-at-age data for each sex separately, both with and without back-calculated lengths at age. The two-phase von Bertalanffy growth model produced the statistically best fit for both sexes of Gulf of Alaska spiny dogfish, resulting in L ∞=87.2 and 102.5 cm and k=0.106 and 0.058 for males and females, respectively.
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The age and growth dynamics of the spinner shark (Carcharhinus brevipinna) in the northwest Atlantic Ocean off the southeast United States and in the Gulf of Mexico were examined and four growth models were used to examine variation in the ability to fit size-at-age data. The von Bertalanffy growth model, an alternative equation of the von Bertalanffy growth model with a size-at-birth intercept, the Gompertz growth model, and a logistic model were fitted to sex-specific observed size-at-age data. Considering the statistical criteria (e.g., lowest mean square error [MSE], high coefficient-of-determination, and greatest level of significance) we desired for this study, the logistic model provided the best overall fit to the size-at-age data, whereas the von Bertalanffy growth model gave the worst. For "biological validity," the von Bertalanffy model for female sharks provided estimates similar to those reported in other studies. However, the von Bertalanffy model was deemed inappropriate for describing the growth of male spinner sharks because estimates of theoretical maximum size (L∞) indicated a size much larger than that observed in the field. However, the growth coefficient (k = 0.14/yr) from the Gompertz model provided an estimate most similar to that reported for other large coastal species. The analysis of growth for spinner shark in the present study demonstrates the importance of fitting alternative models when standard models fit the data poorly or when growth estimates do not appear to be realistic.
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Data are presented on size and age composition, age at sexual maturity, and feeding characteristics. Occurrence of reproductively isolated subpopulations around individual seamounts or ranges is suggested. -from Journal summary
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Reproductive parameters of Squalus mitsukurii were compared for four localities in the North Pacific, i.e. off Choshi (app. 36°N, 141°E), Masseiba (app. 30°N, 139°E), Ogasawara Islands (app. 27°N, 142°E), and on the Hancock Seamount (app. 30°N, 180°E). The size at maturity and the maximum size for both sexes were larger in Choshi than in Ogasawara and Hancock by 160–280 mm. Sexual dimorphism in the two parameters was also found for each locality. Clasper lengths and testis weights showed a rapid increase with the onset of maturation. Fecundity expressed as litter and clutch sizes showed large differences among the Choshi, Masseiba, and Ogasawara specimens. Fecundity increased with latitude. Both litter and clutch sizes increased with the length of the parent and were described as regression lines for these three localities. As a result, we concluded that this shark has a common reproductive strategy but that each population manifests a fecundity schedule according to the local environmental conditions. The annual increment of growth was estimated to be 18 mm after maturation on the assumption that the shark produced pups every two years. © 1993, The Japanese Society of Fisheries Science. All rights reserved.