Using otoliths to estimate age and growth of a large Australian endemic monocanthid, Nelusetta ayraudi (Quoy and Gaimard, 1824)

Abstract

Nelusetta ayraudi (the ocean leatherjacket) is an endemic Australian monacanthid species distributed from North West Cape (Western Australia) south to southern Queensland. The commercial and recreational fisheries targeting Nelusetta ayraudi have expanded substantially along the coast of New South Wales (NSW) in recent years but there exists little biological information on which to base effective management of this growing fishery. World-wide, only a few studies have aged monacanthids. Of these, researchers have interpreted periodic increments in bony structures such as vertebrae and anterior dorsal spines in preference to those found in otoliths. In this study we estimated age of N. ayraudi by counting growth increments in sectioned otoliths. The periodicity of increment formation was validated using a vital stain, (oxy-tetracycline), injected into young-of-the-year fish. Growth was rapid especially as juveniles with N. ayraudi attaining approximately 220 mm after 1 year and 340 mm after 2 years. No differences in growth rates were detected between sexes or between fish captured at different latitudes (zones). The largest male (605 mm, Total Length—TL) and female (656 mm, TL) were both recorded from northern NSW, with both sexes attaining the maximum age of 6+ years from northern and southern NSW. The von Bertalanffy parameters describing growth for N. ayraudi were \( {L_\infty } \) = 591 mm (TL), k = 0.377 year−1 and t
o = −0.247 years.

Full text

Using otoliths to estimate age and growth of a large
Australian endemic monocanthid, Nelusetta ayraudi
(Quoy and Gaimard, 1824)
Marcus E. Miller & John Stewart & Ron J. West
Received: 17 July 2009 /Accepted: 15 February 2010 /Published online: 20 March 2010
#
Springer Science+Business Media B.V. 2010
Abstract Nelusetta ayraudi (the ocean leatherjacket)
is an endemic Australian monacanthid species distrib-
uted from North West Cape (Western Australia) south
to southern Queensland. The commercial and recrea-
tional fisheries targeting Nelusetta ayraudi have
expanded substantially along the coast of New South
Wales (NSW) in recent years but there exists little
biological information on which to base effective
management of this growing fish ery. World-wide,
only a few studies have aged monacanthids. Of these,
researchers have interpreted periodic increments in
bony structures such as vertebrae and anterior dorsal
spines in preference to those found in otoliths. In this
study we estimated age of N. ayraudi by counting
growth increments in sectioned otoliths. The periodic-
ity of increment formation was validated using a vital
stain, (oxy-tetracycline), injected into young-of-the-
year fish. Growth was rapid especially as juveniles
with N. ayraudi attaining approximately 220 mm after
1 year and 340 mm after 2 years. No differences in
growth rates were detected between sexes or between
fish captured at different latitudes (zones). The largest
male (605 mm, Total Length—TL) and female
(656 mm, TL) were both recorded from northern
NSW, with both sexes attaining the maximum age of
6+ years from northern and southern NSW. The von
Bertalanffy parameters describing growth for N.
ayraudi were L
1
=591 mm (TL), k=0.377 year
−1
and
t
o
=−0.247 years.
Keywords Ageing
.
Otolith
.
Validation
.
Growth
.
Nelusetta ayraudi
.
Monacanthid
Introduction
Leatherjackets or filefish of the family Monacanthidae
belong to the highly modified and advanced group of
fish which form the order Tetraodontiformes. Mon-
acanthids are well represented throughout the world’s
oceans with 102 species being recorded (Nelson
2006). The highest monacanthid diversity is found
in Australian waters with a total of 60 species being
recorded, 22 of which are only found in the southern
half of the continent (<30°S), in cooler temperate
waters (Hutchins 2000; Allen et al. 2006). Of the
many monacanthids inhabiting these waters, the
ocean leatherjacket (Nelusetta ayraudi), also known
as the chinaman or sand leatherjacket, is one of
largest monacanthids in the world and the most
Environ Biol Fish (2010) 88:263–271
DOI 10.1007/s10641-010-9639-4
M. E. Miller (*)
:
J. Stewart
NSW Department of Primary Industries,
Cronulla Fisheries Research Centre of Excellence,
PO Box 21, Cronulla, NSW 2230, Australia
e-mail: marcus.miller@dpi.nsw.gov.au
R. J. West
ANCORS, University of Wollongong,
Wollongong, NSW 2522, Australia

commonly captured species from Australian waters
(Miller 2007). Thought to be endemic to Australian
waters, N. ayraudi are distributed from North West
Cape in Western Australia around the south of the
continent to Cape Morton in Queensland (Kailola et
al. 1993). In New South Wales (NSW) wat ers, annual
commercial landings of N. ayraudi have increased
rapidly from 134 to 430 tonnes between 2000–2001
and 2006–2007 (Miller and Stewart 2009). Despite
the rapidly expanding commercial fishery, there exists
almost no information on the biology of N. ayraudi
on which to base the management of this species.
Ageing monacanthids has proven to be difficult
and the available literat ure indicates a lack of studies
using otoliths to estimat e age. The few studies that
have used otoliths to estimate age have examined
daily incremental development and growth of embry-
onic and pre-larval settling juveniles using whole
sagittal otolit hs (Kingsford and Milicich 1987;
Kawase and Nakazono 1994; Rogers et al. 2001;
Ben-David and Kritizer 2005). The lack of studies
using otoliths to estimate age in post-larval monacan-
thids is curious given that otoliths are recognized as
being the most widely used and reliable structure for
estimating age in bony fish (Campana 2001). One
reason may be that monacanthids have very small and
fragile otoliths which consequently can be difficult to
process and interpret successfully (Grove-Jones and
Burnell 1991; Man cera-Rodriguez and Cas tro-
Hernandez 2004 ). This difficulty, coupled wi th the
fact that few monacanthid fisheries are of sufficient
economic v alue to warrant subs tantial research,
appears to have hampered age estimation in this
group of fish. Studies that have reported estimates of
age and growth in monacanthids have used vertebrae
(Shiqin and Yachu 1980;Park1985; Grove-Jones and
Burnell 1991), anterior dorsal spines (Johnson and
Saloman 1984; Manooch and Drennon 1987;
Mancera-Rodrig uez and Castro-Hernand ez 2004)
and length frequency analyses (Peristiwady and
Geistdoerfer 1991). Validation of the accuracy and
precision of these alternative methods of estimating
age and growth is limited.
In this paper we describe the use of otoliths to
estimate the age of N. ayraudi. Age was esti mated by
counting opaque zones in sectioned sagittal otoliths
from wild caught fish and the method was validated
by using a vital stain (oxy-tetracycline—OTC)
injected into young-of-the-year-fish. Estimates of
size-at-age were used to model rates of growth, which
were compared between sexes and between latitudes
(zones) in eastern Australia.
Materials and methods
N. ayraudi were collected from commercial catches
from two zones along the coast of NSW. The northern
zone was described as the area of co astline stretching
from Forster/Tuncurry (32°11′.00 S, 152°31 ′.00 E) to
the border of NSW and Queensland (28°10
′.02 S,
153°33′.03 E). The southern zone was described as
the region stretching from Kiama (34°40′.20 S, 150
51′.54 E) to the Victorian border (37°31′.50 S, 149°
58′.70 E) (Fig. 1). Twenty fish per month were
collected from each zone between March 2003 and
March 2004. Due to a limited number of large (older)
fish in these monthly samples, a further 19 large fish
were collected from commercial catches at Iluka and
Ballina (northern zone) during September 2005.
Sagittal otoliths were removed from these fish for
age estimation. Juvenile N. ayraudi were also sam-
pled each month from the Port Hacking River (34°
47′.50 S, 151°08′.00 E) (Fig. 1), between December
2002 and April 2003 and their total lengths (TL, mm)
recorded to estimate monthly growth of the cohort.
Oxy-tetracycline was used to stain the otoliths of
wild-caught young-of-the-year (0+) captive re ared
fish. During December 2002, juvenile N. ayraudi
were collected from the Port Hacking River using
small opera house traps covered with 12 mm mesh set
on a seagrass (Zostera capricorni and Posidonia
australis)/sand bottom. Fish were placed into aerated
5,000 L tanks with flow through ambient seawater
and maintained prior to injection with OTC in March
of 2003. Prior to injection the fish were sedated with
50 mL of benzocaine solution (ethyl-p-amino benzoate
dissolved in 100% ethanol at 100 g·1,000 mL
−1
),
weighed(g),measured(TL,mm)andgivenan
intraperitoneal injection of tetracycline (Engemycin
100—oxytetracycline hydrochloride at 5 mg·mL
−1
)at
adoseof50mg·kg
−1
body weight (McFarlane and
Beamish 1987). Any leatherjacket louse (Ourozeuktes
owenii) found attached to the fish was removed at this
time. Between 2002 and 2004, fish were sampled
intermittently and their otoliths removed for examina-
tion. Sagittal otoliths were removed by cutting hori-
zontally above the eyes of the fish, exposing the brain
264 Environ Biol Fish (2010) 88:263–271

cavity. The otolith sacculus, extending downwards on
either side of the forefront of the brain cavity, were
extracted, otoliths removed and allowed to dry for a
short period of time before being set in resin blocks. A
single bladed low speed diamond saw was used to cut
athin(∼0.5 mm) cross-section from the dorsal to
ventral margins through each otolith core (primordium).
These otolith sections were mounted on a glass slide and
viewed under reflected light against a black background
with 4× magnification. Counts of opaque zones were
made along a radius from the core to the outer edge of
the ventral lobe of the otolith using a microscope
Forster / Tuncurry
Ballina
Iluka
Crowdy Head
Jervis Bay
Sydney
N
Kiama
Coffs Harbour
Laurieton
Cronulla Fisheries Research Centre
Northern Zone
Southern Zone
Port Macquarie
Forster / Tuncurry
Ballina
Iluka
Crowdy Head
Jervis Bay
Sydney
Kiama
Coffs Harbour
Laurieton
Cronulla Fisheries Research Centre
Northern Zone
Southern Zone
Port Macquarie
Forster / Tuncurry
Ballina
Iluka
Crowdy Head
Jervis Bay
Sydney
100 km
Kiama
Coffs Harbour
Laurieton
Cronulla Fisheries Research Centre
Northern Zone
Southern Zone
Port Macquarie
Pacific Ocean
Fig. 1 Study locations
along the coast of New
South Wales, Australia,
showing sampling zones
Environ Biol Fish (2010) 88:263–271 265

mounted video camera interfaced with a computer,
running ‘Image Pro Plus’ image analysis software
(Version 4.5.1, media Cybernetics Inc, Bethesda, MD).
The otoliths from fish that were injected with OTC were
observed under reflected light and opaque zones
counted and measured. Observations were then made
using ultraviolet (UV) light to identify the marked area
of OTC on the otolith. Each otolith was measured from
the core to the OTC mark and to the outside edge of
the otolith. All otoliths were re-read to examine the
precision of estimates of counts of opaque zones. The
coefficient of variation (CV) for the two readings for
each otolith was calculated and averaged across all
otoliths (Campana 2001).
A birth date of 1st August was assigned to all fish
based on the peak in the spawning season (Miller
2007). Age was calculated as the number of opaque
zones plus the proportion of the year following this
date that the fish was sampled. N. ayraudi have a
short winter spawning period (Mil ler 20 07)and
therefore errors in under-estimating or over-estimating
the absolute age of fish born slightly earlier or later
than 1st August will be minor. The von Bertalanffy
growth function (VBGF) was fitted to the size-at-age
data for wild caught ocean leatherjackets, using solver
in Microsoft Excel 2003 to minimise the sum of
squares. An analysis of residual sums of squares
(ARSS) (Chen et al. 1992) was used to compare the
VBGFs between: (1) sexes from each latitudinal zone,
and; (2) latitudinal zones.
Results
Otoliths from N. ayraudi are typical of those
described for other monacanthids (Furlani et al.
2007) in being very small, hour-glass shaped, the
dorsal margin flat and slightly irregular and the
ventral margin rounded and irregular (Fig. 2a). They
had a diameter from the posterior to anterior margins
of between 0.5 mm in younger fish to around 3 mm in
older fish and were very fragile. When sectioned, the
internal structure of all otoliths appeared complex.
The core was densely opaque with a larger translucent
zone surrounding it with scattered finer streaks of
opaque markings throughout. This zone represented
the rapid growth fish experience while juveni le. This
structure was followed by a more definite opaque
zone that was scored as the first annulus. The mean
(± SE) distance (mm) from the core to the outside
edge of the first annulus in the 585 wild fish
examined was 0.345 mm±0.002 mm. Annuli beyond
the first opaque zone were charact erized by reason-
ably well defined alternating opaque and translucent
zones (Fig. 2b).
The young-of-the-year N. ayraudi that were
injected with OTC an d maintained in the aquaria
ranged between 97 and 193 mm TL. The otoliths of
sampled fish all had clearly visible OTC marks when
viewed under UV light (Fig. 2c, d). Thirty were
sampled before they formed thei r first annulus, 21
were sampled when 1+ years and 7 were sampled
when 2+ years (Fig. 3). Otolith growth from the OTC
mark to the edge of the otolith indicated that the
otoliths increased in diameter approximately linearly
during the 26 months of the validation experiment
(Fig. 3). The mean (± SE) distance from the core to
the outside edge of the first opaque zone in these
otoliths was 0.325 mm±0.006 mm which was similar
to fish from the wild (see above). The OTC mark,
administered during March, was always present
within the translucent zone prior to the first opaque
zone, indicating that the opaque zone was probably
formed sometime during the winter period. The first
opaque zone was scored as completed in 1 of 4 fish
during July and in all fish by August.
Estimates of age were assigned to the 585 otoliths
examined from both the northern and southern zones.
Of the otoliths re-examined, 80.5% were not different
from the original readings, 18.8% differed by ± 1 year
and 0.7% differed by ± 2 years. The coefficient of
variation (CV), averaged across all ages, was 0.066.
Six age classes (1 to 6 years) were recorded from the
585 wild caught fish sampled fr om commercial
landings. Only two fish, one male and one female
were estimated as being 6+ years old. The largest
recorded fish was a female from the northern zone
which measured 656 mm (TL) and was estimated at
5.8 years. The largest male (605 mm TL) was also
from the northern zone and was estimated to be
5.2 years old. The largest fish from the southern zone
was a female (596 mm TL) estimated at 3.8 years old
and the largest mal e from the southern zone (583 mm
TL) was estimated to be 4.2 years old.
Comparisons of rates of growth between sexes
from each zone revealed no significant differences
(ARSS northern zone, f
(3,312)
=0.55, P=0.64 and
southern zone, f
(3, 261)
=1.38, P=0.25). Similarly,
266 Environ Biol Fish (2010) 88:263–271

there were no significant differences observed in rates
of growth when the two sexes were combined
between each zone (ARSS f
(3, 579)
=1.34, P=0.26).
As there were no significance differences in the rates
of growth between sexes and zones, growth data for
all fish were pooled to provide a general VBGF for
N. ayraudi. The VBGF parameters (±SE) estimated
were k=0.377 year
−1
(±0.0224) t
o
=− 0.247 ye ar
(±0.032), and L
1
=591 mm (±15.90) (Fig. 4). The
relationship between TL and body weight for all fish
sampled was described by a power relationship: Body
weight (g) = 0.00003 × TL
2.808
.
Sampling of young-of-the-year N. ayraudi between
December and April indicated rapid growth during
this period (Table 1). The mean length of juvenile N.
ayraudi samp led during April was 176 mm TL and,
based on a birthday of 1st August, these fish were
approximately 9 months old.
Discussion
This study has demonstrated that the technique of
using sectioned otolith s to estimate the age of fish
Fig. 2 a Whole otolith,
scale: 0.5 mm; b thin-
sectioned otolith viewed
under reflected light against
a black background. The
estimated age and size of
this fish was 4+ years and
551 mm, Scale: 0.5 mm; c a
captive reared 2+ year old
sectioned otolith under
reflected light, Scale:
0.25 mm; and, d the same
captive reared 2+ year old
sectioned otolith under ultra
violet light displaying the
oxy-tetracycline (OTC)
mark, Scale: 0.25 mm
0
0.05
0.1
0.15
0.2
0.25
0.3
Mar-03 Jun-03 Oct-03 Jan-04 Apr-04 Aug-04 Nov-04 Feb-05 May-05 Sep-05
0+ Year
1+ Year
2+ Year
0
0.05
0.1
0.15
0.2
0.25
0.3
Mar-03 Jun-03 Oct-03 Jan-04 Apr-04 Aug-04 Nov-04 Feb-05 May-05 Sep-05
Month -Year
Otolith Growth (mm)
0+ Year
1+ Year
2+ Year
Fig. 3 Sagittal otolith
growth after the
oxy-tetracycline (OTC)
mark in February 2003
(n=58)
Environ Biol Fish (2010) 88:263–271 267

(Campana 2001) can be successfully applied to a
member of the family Monacanthidae. While the
otoliths of this diverse and abundant family of fish are
very small, fragile and irregular in shape (Furlani et
al. 2007), they display alternating opaque and
translucent zones that can be counted and used to
estimate age. A review of the literature on ageing
monacanthids, and the closely related family of
Balistidae, shows that our results in demonstrating
the utility of using sectioned otolith s to estimate age
could lead to improvements in future studies of age
and growth in these families of fish. In Korea (Park
1985), South Australia (Grove-Jones and Burnell
1991), and China (Shiqin and Yachu 1980), studies
have estimated the age of black filefish (Navodon
modestus), ocean leatherjackets (Nelusetta ayraudi)
and green filefish (Navodon septentrionalis) using
sectioned vertebrae. Anterior dorsal spines have been
used in other ageing studies for the plane-head filefish
(Stephanolepis hispidus) from the Canary Islands
(Mancera-Rodriguez and Castro-Hernandez 2004),
the closely related balistids, the gray triggerfish
(Balistes capriscus) in the north eastern gulf of
Mexico (Johnson and Saloman 1984), and the queen
triggerfish (Balistes vetula) from the U.S Virgin
Islands and Puerto Rico (Manooch and Drennon
1987). None of these studies made use of sectioned
otoliths, with an accompanyin g validation, which is
generally accepted as the best ageing technique for
the majority of fish species (Campana 2001). Rather,
researchers have interpreted the concentric bands in
vertebrae and dorsal spines when estimating annual
ages. These bony structures are not ideal for estimat-
ing age because skeletal growth can be variable and is
influenced by many internal and external factors.
Vertebrae continually resorb tissue which can destroy
periodic growth increments and the spines of older
fish can become hollow and lose record of younger
growth patterns (Panfi li et al. 2002). In addition, the
precision of readings from both vertebrae and spines
tend to be poor compared to those from otoliths and
validation of the ageing interpretations di fficult
(Campana 2001). The negative ramifications of using
incorrect age estimates in fishery management are
well documented (Campana 2001) and our findings
that sectioned otoliths can be used to age monacan-
thids and balistids will be of use to future studies of
these families of fish. Nelusetta ayraudi sagi ttal
otoliths were well stained by OTC at a dosage of
50 mg·kg
−1
body weight. The 58 otoliths examined as
part of the validation experiment had clearly visible
OTC marks when viewed under ultra-violet light.
0
100
200
300
400
500
600
700
345 76
T
L
(mm)
= 591
k
(year
-1
)
= 0.377
t
0
(years)
= -0.247
12
A
g
e (Years)
Total Length (mm)
L
(mm)
= (±15.9)
k
(year
-1
)
= 0.377 (± 0.02)
t
0
(years)
= -0.247 (± 0.03)
Fig. 4 Estimated length at
age plot for N. ayraudi. The
von Bertalanffy growth
function (VBGF) parameters
for all fish (including
juveniles) combined from
each of the two zones are
shown. Note: open squares =
fish aged from otoliths;
closed diamonds = juvenile
fish aged from the nominated
birth date
Month Number of fish Mean size (mm) (SE) Mean growth (mm)/month
Dec-02 60 108.15 (2.28) –
Jan-03 60 124.65 (2.42) 16.50
Feb-03 60 155.70 (1.68) 31.05
Mar-03 30 168.03 (2.70) 12.33
Apr-03 8 176.00 (4.3) 7.97
Table 1 Average juvenile
growth (SE) during the
summer months of
2002–2003
268 Environ Biol Fish (2010) 88:263–271

Marking these fish with OTC showed that opaque
zones were formed once per year during the winter.
Many other temperate species in Australian waters
have also been shown to form annual opaque zones
during the winter months (Stewart and Hughes 2007;
Morton et al. 2008). The finding that otolith growth
from the core to the first opaque zone of fish in
aquaria was similar to that of wild fish provided some
confidence that the captivity did not affect the
validation experiment.
The internal structure of otoliths from N. ayraudi
was complex and alternating opaque and translucent
zones were often diffuse. This pattern was interpreted
as being the result of a fast growth rate, particularly
during the early years. Variations in somatic growth
have been shown to effect the internal structural
development of otoliths (Fowler 1995), with fish
having faster growth rates being associated with less
distinct annuli (Esteves and Burnett 1993; Stewart and
Hughes 2007). Nevertheless, the overall precision from
ageing N. ayraudi (mean CVof 6.6%), was comparable
to those reported in other ageing studies (Campana
2001).
Growth of juvenile monacanthids has been poorly
documented for other species that are captured in
large commerci al fisheries around the world. Data
exist for the growth of the early stages of develop-
ment of several juvenile species such as Parika
scaber in New Zealand (Kingsford and Milicich
1987), Stephanolepis hispidus in the USA (Rogers et
al. 2001) Navodon modestus (Kakuda 1979)and
Rudarius ercodes and Paramonacanthus japonicus
in Japanese waters (Kawase and Nakazono 1994).
Ishida and Tanaka (1983 ) showed recruitment
and growth of juvenile small filefish (Rudarius
ercodes) in Odawa Bay Japan, while Peristiwady
and Geistdoerfer (1991) reported recruitment of
juvenile Monacanthus tomentosus in sheltered bays
and estuaries of West Seram, Moluccas, Indonesia. In
the present study, juvenile N. ayraudi exhibited rapid
growth during the summer months between Decem-
ber and April. A mean maximum monthly growth of
31 mm occurred during February. Pollard (1994)
noted that seagrass beds ( Zostera capricorni and
Posidonia australis) played an important role in the
early stages of growth for juvenile N. ayraudi and
suggested that the species migrated to deeper waters
as it grew larger. Gro ve-Jones and Burnell (1991) also
had the highest capture rates of juvenile N. ayraudi
from sheltered bays and estuaries, in the months of
February, with a decline in numbers in the months
that foll owed. Again, they assumed that these fish
were recruiting to the fishery offshore. They also
found that the mean growth rates were highest in
February and April (27 mm and 28 mm respectively).
N. ayraudi is a mongst the largest monacanthids in the
world, with a maximum recorded length of 700 mm
(Hutchins and Swainston 1986). The largest fish
sampled during the present study were substantially
smaller than this, suggesting that ocean leatherjackets
may attain ages considerably greater than 6+ years. A
summary of ageing studies done world-wide indicates
Table 2 A review of ageing studies of monacanthid and balistid species, summarising the maximum lengths and ages for sexes
Species Family Maximum length (mm) Maximum age (years) Reference
Nelusetta ayraudi Monacanthidae 656 ♀, 605 ♂ 6 ♀,6♂ 1
423 ♀, 393 ♂ 9 ♀,7♂ 2
Navodon modestus Monacanthidae 250 ♀, 260 ♂ 3 ♀, ♂ 3
320 ♀, ♂ 3 ♀, ♂ 4
340 8 5
Thamnaconus septentrionalis Monacanthidae 290 9, 7 6, 7
Balistes capriscus Balistidae 561 ♀, 544 ♂ 12 ♀,13♂ 8
Balistes vetula Balistidae 378 ♀, ♂ 7 ♀, ♂ 9
Monacanthus tomentosus Monacanthidae 117 ♀, ♂ 5 ♀, ♂ 10
Stephanolepis hispidus Monacanthidae 250 ♀, ♂ 3 ♀,2♂ 11
1) Present Study; 2) Grove-Jones and Burnell (1991); 3) Kakuda (1978); 4) Kakuda (1979); 5) Park (1985); 6) Shiqin and Yachu
(1980); 7) Chen et al. (1998); 8) Johnson and Saloman (1984); 9) Manooch and Drennon (1987
); 10) Peristiwady and Geistdoerfer
(1991); 11) Mancera-Rodriguez and Castro-Hernandez (2004)
Environ Biol Fish (2010) 88:263–271 269

that other species of monacanthids are relatively short
lived (<9 years) (Table 2). Nevertheless, our results
indicate very fast growth rates. No differences in growth
rates were found between males and females. The lack
of differences in growth rates with latitude may be a
result of migration between our sampling zones.
Commercial fishers in NSW have provided anec-
dotal evidence that commerci ally-sized fish undergo
large latitudinal movements seasonally, especially
during winter when fish are spawning. Although
these spawning migrations have no t been confirmed
in NSW, Lindholm (1984) reported that N. ayraudi in
South Australian waters were highly mobile and that
larger fish were captured from deeper waters. This
study has demonstrated that monacanthids can be
successfully aged using sectioned otoliths and recom-
mends that future studies on this and other closely
related families adopt our methods. We consider that
the improvements in accuracy and precision by using
sectioned otoliths in preference to the commonly used
vertebrae and dorsal spines outweigh the difficulties
in handling small, fragile otoliths. It would be useful
to use sectioned otoliths to age species that have
previously been studied using vertebrae and dorsal
spines. This new information on age and growth of N.
ayraudi in eastern Australia has provided the first
insight into how the stock may respond to the rapidly
increasing fishery. The relatively few age classes and
rapid growth rates suggest that N. ayraudi maybe
resilient to fishing; however further information on
the re productive biology, life-history, movements,
stock structure and fishery landings are still required
if informed management is to be implemented.
Acknowledgements This study could not have been possible
without the support and enthusiasm of the commercial fishermen
from the NSW ocean trap (fin-fish) and deep water lobster
fisheries. Thank you to Noel Gogerly, Phil Roach, Ray Blake,
and Steve Drake for their expertise in catching ocean leatherjackets.
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