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Evaluating estuarine nursery use and life history patterns of Pomatomus saltatrix in eastern Australia

Authors:
  • NSW DPI Fisheries
  • New South Wales Department of Primary Industries - Fisheries

Abstract and Figures

Estuaries provide important nursery habitats for juvenile fish, but many species move between estuarine and coastal habitats throughout their life. We used otolith chemistry to evaluate the use of estuaries and the coastal marine environment by juvenile Pomatomus saltatrix in eastern Australia. Otolith chemical signatures of juveniles from 12 estuaries, spanning 10° of latitude, were characterised using laser ablation-inductively coupled plasma-mass spectrometry. Based upon multivariate otolith elemental signatures, fish collected from most estuaries could not be successfully discriminated from one another. This was attributed to the varying influence of marine water on otolith elemental composition in fish from all estuaries. Using a reduced number of estuarine groups, the multivariate juvenile otolith elemental signatures and univariate Sr:Ca ratio suggest that between 24 and 52% of adult P. saltatrix had a juvenile period influenced by the marine environment. Elemental profiles across adult (age-1) otoliths highlighted a variety of life history patterns, not all consistent with a juvenile estuarine phase. Furthermore, the presence of age-0 juveniles in coastal waters was confirmed from historical length-frequency data from coastal trawls. Combining multiple lines of evidence suggests considerable plasticity in juvenile life history for P. saltatrix in eastern Australia through their utilisation of both estuarine and coastal nurseries. Knowledge of juvenile life history is important for the management of coastal species of commercial and recreational importance such as P. saltatrix.
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MARINE ECOLOGY PROGRESS SERIES
Mar Ecol Prog Ser
Vol. 598: 187–199, 2018
https://doi.org/10.3354/meps12495 Published June 28§
INTRODUCTION
Estuaries function as nursery grounds for juveniles
of many coastal fish species, providing refuge, food
and habitat (Beck et al. 2001, Able 2005). Many spe-
cies subsequently emigrate from estuaries to join
adult populations in coastal waters, with the duration
of the estuarine life history stage ranging from
months to years (Gillanders et al. 2003, Fodrie &
Herzka 2008). Assessing connectivity between estu-
arine and coastal environments is critical for the
management of coastal species, but is a complex
task, due to the constraints and logistical difficulties
of mark-recapture studies using juvenile fish. An
alternative approach is to use the elemental composi-
tion of fish otoliths or other calcified structures, which
allows insights into how species use estuarine and
coastal environments throughout their life history
(Gillanders et al. 2003, Brown 2006, Izzo et al. 2016).
In recent decades, otolith chemistry has become
an increasingly popular tool to investigate multiple
aspects of fish life history. As fish otoliths are biolog-
© The authors and UNSW Australia 2018. Open Access under
Creative Commons by Attribution Licence. Use, distribution and
reproduction are un restricted. Authors and original publication
must be credited. Publisher: Inter-Research · www.int-res.com
*Corresponding author: h.schilling@unsw.edu.au
§Advance View was available online April 17, 2018
Evaluating estuarine nursery use and life history
patterns of Pomatomus saltatrix in eastern Australia
H. T. Schilling1,2,*, P. Reis-Santos3,4, J. M. Hughes5, J. A. Smith1, 2, J. D. Everett1, 2,
J. Stewart5, B. M. Gillanders4, I. M. Suthers1, 2
1Evolution and Ecology Research Centre, University of New South Wales, Sydney, NSW 2052, Australia
2Sydney Institute of Marine Science, Building 19, Chowder Bay Road, Mosman, NSW 2088, Australia
3MARE − Marine and Environmental Sciences Centre, Faculdade de Ciências, Universidade de Lisboa,
1749-016 Campo Grande, Lisboa, Portugal
4Southern Seas Ecology Laboratories, School of Biological Sciences, The University of Adelaide, SA 5005, Australia
5New South Wales Department of Primary Industries, Chowder Bay Road, Mosman, NSW 2088, Australia
ABSTRACT: Estuaries provide important nursery habitats for juvenile fish, but many species
move between estuarine and coastal habitats throughout their life. We used otolith chemistry to
evaluate the use of estuaries and the coastal marine environment by juvenile Pomatomus saltatrix
in eastern Australia. Otolith chemical signatures of juveniles from 12 estuaries, spanning 10° of
latitude, were characterised using laser ablation-inductively coupled plasma-mass spectrometry.
Based upon multivariate otolith elemental signatures, fish collected from most estuaries could not
be successfully discriminated from one another. This was attributed to the varying influence of
marine water on otolith elemental composition in fish from all estuaries. Using a reduced number
of estuarine groups, the multivariate juvenile otolith elemental signatures and univariate Sr:Ca
ratio suggest that between 24 and 52% of adult P. saltatrix had a juvenile period influenced by the
marine environment. Elemental profiles across adult (age-1) otoliths highlighted a variety of life
history patterns, not all consistent with a juvenile estuarine phase. Furthermore, the presence of
age-0 juveniles in coastal waters was confirmed from historical length-frequency data from
coastal trawls. Combining multiple lines of evidence suggests considerable plasticity in juvenile
life history for P. saltatrix in eastern Australia through their utilisation of both estuarine and coastal
nurseries. Knowledge of juvenile life history is important for the management of coastal species of
commercial and recreational importance such as P. saltatrix.
KEY WORDS: Otolith chemistry · Elemental profiles · Bluefish · Tailor · Strontium · Barium
Contribution to the Theme Section ‘Innovative use of sclerochronology in marine resource management’
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Mar Ecol Prog Ser 598: 187– 199, 2018
ically inert and grow continuously, trace elements
from the surrounding environment are incorporated
on the growing surface of the otolith (Campana &
Thorrold 2001). Since water masses are known to
vary in their environmental conditions over time and
space, fish collected in different environments are
expected to have different otolith elemental composi-
tion (Campana et al. 2000). These elemental ‘signa-
tures’ or ‘fingerprints’ have been used to successfully
identify natal origins and nursery estuaries of adult
fish (Gillanders & Kingsford 1996, Gillanders 2002a,
Vasconcelos et al. 2011, Reis-Santos et al. 2013), dis-
criminate between populations (Rooker et al. 2001,
Tanner et al. 2016) and determine mixed stock com-
position (Munch & Clarke 2008, Geffen et al. 2011).
Otoliths are also used as environmental chronome-
ters of temporal variation in elemental concentra-
tions. Through analysis of elemental profiles from the
core to the edge of otoliths, a continuous record of
how elements change in concentration throughout
the life of a fish may be revealed (Campana & Thor-
rold 2001). In particular, profiles of strontium and
barium have been used successfully in reconstruct-
ing environmental and estuary−ocean migration his-
tories for individual fish (Elsdon & Gillanders 2005a,
Fowler et al. 2016), as concentrations of these ele-
ments are strongly influenced by salinity (Secor &
Rooker 2000, Walther & Limburg 2012). If fish move-
ment occurs over a large salinity gradient, it is more
likely to be detected, and hence most research has
focused on migrations between freshwater and mar-
ine environments. However, studies reconstructing
habitat use and environmental life histories along
narrow salinity gradients are becoming more com-
mon (Tanner et al. 2013, Williams et al. 2018).
Tailor or bluefish (Pomatomus saltatrix) is a glob-
ally distributed pelagic mesopredator that is fished
commercially and recreationally throughout its range.
Stark differences in life history patterns exist be -
tween populations (Juanes et al. 1996), particularly in
growth rates and average maximum size (L). For
example, Lin the west Atlantic Ocean is more than
double that in the Mediterranean (Ceyhan et al.
2007, Robillard et al. 2009). In general, adult P. salta-
trix undertake annual migrations along the coast
before spawning at sea, with larvae that are then dis-
tributed by ocean currents to downstream areas
(Juanes et al. 1996). While larvae recruit to both estu-
arine and coastal areas in most global populations, in
eastern Australia, larvae have only been documented
to recruit to estuaries (Miskiewicz et al. 1996), where
they remain until they emigrate to coastal marine
waters at approximately 27 cm fork length (FL) (Mor-
ton et al. 1993, Zeller et al. 1996), corresponding to
approximately 1 yr of age (Dodt et al. 2006, H.T.S.
unpubl. data). This contrasts with the life history of
other populations, namely the eastern Indian Ocean
and western Atlantic Ocean populations, which have
both coastal and estuarine recruitment (Lenanton et
al. 1996, Able et al. 2003, Callihan et al. 2008). It is
likely that juvenile tailor in eastern Australia use
both estuarine and coastal habitat, and this discrep-
ancy in juvenile habitat use has previously been
identified as warranting further attention (Juanes et
al. 1996).
Otolith chemistry is an ideal tool with which to
investigate life history plasticity and the use of estu-
arine and coastal juvenile habitats by P. saltatrix. The
broad goal of this study was to use otolith chemistry
techniques to gain insight into the life history of P.
saltatrix in eastern Australia, specifically estuarine−
ocean movements, and to compare these to the life
history patterns exhibited by populations elsewhere.
Specifically, we tested whether: (1) otoliths of juve-
nile P. saltatrix from different estuaries had charac-
teristic elemental signatures; (2) adult P. saltatrix
could be assigned to juvenile habitats types based on
the elemental signatures from the juvenile area of
their otoliths; and (3) elemental profiles from the core
to the edge of adult P. saltatrix support movement
between estuarine and oceanic habitats.
MATERIALS AND METHODS
Fish collection
Juvenile Pomatomus saltatrix (n = 360, age-0) were
collected from 12 estuaries along the east coast of Aus-
tralia over 2 southern hemisphere summers (2014/15
and 2015/16; Fig. 1; see Table S1 in the Supplement
at www. int-res. com/ articles/ suppl/ m598 p187 _ supp.
pdf). Fish were collected from 2 haphazardly selected
sites at least 1 km apart within each estuary. As P.
saltatrix were not found in all estuaries in both years,
some estuaries only had fish collected from one sum-
mer. Fish were collected with baited handlines and
frozen prior to dissection in the laboratory.
Adult P. saltatrix (n = 121, age-1) were also col-
lected from both estuarine and coastal habitats along
the east coast of Australia during the 2015−2016
summer (to match the 2014−2015 juvenile cohort;
Table S1 in the supplement). These fish were col-
lected by commercial fishers or donated by recre-
ational fishers. All fish were frozen prior to dissec-
tion. To confirm fish were from the correct cohort, the
188
Schilling et al.: Pomatomus saltatrix juvenile life history
ages of all fish were estimated from whole otoliths
viewed using a light microscope under water with
reflected light. This estimated age was subsequently
confirmed after transverse sectioning for otolith
chemical analysis (see below) and viewing the sec-
tion under reflected light (H.T.S. unpubl. data, Robil-
lard et al. 2009). Only fish aged 1 yr were selected for
subsequent analysis. The age and size at sexual
maturity of P. saltatrix in eastern Australia are 1 yr
and approximately 27 cm FL, respectively (Bade
1977, H.T.S. unpubl. data).
Otolith element analysis
To characterise the elemental signatures of P. salta-
trix from each estuary, sagittal otoliths were embed-
ded in indium-spiked (115In) resin (~40 ppm) and
sectioned transversely. The sections were then pol-
ished using fine lapping paper and fixed to micro-
scope slides with 115In-spiked thermoplastic glue
(~200 ppm; Hughes et al. 2016), and subsequently
cleaned and sonicated with ultrapure water. Otolith
sections were analysed at Adelaide Microscopy (The
University of Adelaide) using a New Wave UP-213-
nm laser ablation system connected to an Agilent
7500cs inductively coupled plasma-mass spectrome-
ter (LA-ICP-MS). The laser was run using a spot size
of 30 µm, at a frequency of 5 Hz and fluence of 7 J
cm−2. A single spot was ablated on the outer edge of
each otolith along the proximal surface, beside the
sulcal groove. Spots at the outer edge of the juvenile
otoliths were used to characterise the elemental fin-
gerprint of each estuary (i.e. representative of collec-
tion site) as this is the material most recently incorpo-
rated into the otolith (Elsdon et al. 2008). An inner
spot was also ablated on otoliths of adult (age 1) fish
along the same axis as the outer spot, and corre-
sponded to ablation of material accreted when these
fish were juveniles. These inner spots were located
ca. 250 µm from the core, which was the average dis-
tance that the corresponding edge spots in juveniles
were from the core. The elemental signature of these
inner spots should be indicative of the habitat adult
fish used as juveniles. The element concentrations
measured (and their associated dwell times) were 7Li
(150 ms), 24Mg (100 ms), 43Ca (100 ms), 55Mn (150 ms),
63Cu (100 ms), 66Zn (100 ms), 88Sr (100 ms), 115In (10 ms),
138Ba (100 ms) and 208Pb (150 ms). 43Ca was used as
an internal standard and 115In was analysed solely to
detect any contamination by resin or thermoplastic
glue.
Otolith sections of 12 adult fish were randomly
selected for analysis of elemental profiles from the
core to the edge. The profiles were run at a scan
speed of 3 µm s−1 using the same instrument settings
described above but only for the elements 43Ca,
55Mn, 88Sr, 115In and 138Ba. There is no experimental
validation of the relationship between salinity and
otolith elemental concentrations for P. saltatrix, so it
was assumed that the element:Ca ratios on the edges
of otoliths represent capture environment, and the
average Sr:Ca ratios of the edges of otoliths from
adults collected from coastal marine waters were
used as reference criteria to characterise the estuar-
ine or coastal marine environments (Milton et al. 2008).
The resulting average Sr:Ca ratio from fish captured
in coastal marine environments was 2.18 mmol mol−1.
We therefore defined Sr:Ca ratios greater than this
value as representing coastal marine environments
and any value below this value as representing estu-
arine or brackish environments. Ba:Ca thresholds
were calculated in the same way, but there was no
difference between edge otolith Ba:Ca of fish from
estuarine and coastal collection areas (Welch two-
sample t-test: t28 = 1.42, p = 0.176); therefore, Ba:Ca
was not used to characterise environments fish had
spent time in.
189
155°150°145° E
30°
S
35°
200 km
Moruya River
Jervis Bay
Clarence
River
Clyde River
Wagonga Inlet
Hunter River
Hawkesbury River
Georges River
Port Hacking
Sydney Harbour
Port Stephens
Shoalhaven River
Fig. 1. Locations of the estuaries where juvenile Pomatomus
saltatrix were collected. The dashed lines represent the re-
gions where offshore trawl samples were conducted during
the 1990s. These trawls were conducted at 2 depths: 5−27 m
and 64−77 m (Graham et al. 1993a,b, Graham & Wood 1997).
Each black circle represents the capture location of a 1-yr-
old P. saltatrix used in the elemental profile analysis
Mar Ecol Prog Ser 598: 187– 199, 2018
Periodic ablations on certified reference materials
(glass standard NIST 612 and carbonate standard
MACS-3) were used to calibrate elemental concen-
trations, correct mass bias and instrument drift, and
assess external precision. Prior to data collection and
before each ablation, background concentrations of
elements within the sample chamber were measured
for 40 s. A washout delay of 30 s was used between
each ablation to allow the chamber to purge and pre-
vent samples from becoming cross-contaminated.
Raw count data for the spot analyses were processed
using the GLITTER software program (Griffin et al.
2008). Profile data reductions were performed manu-
ally using spreadsheet software (Microsoft Excel). All
elemental data were expressed as ratios to 43Ca (in
mmol mol−1) to account for fluctuations in the abla-
tion yield (Munro et al. 2008). In the few cases where
data fell below the limit of detection, the raw data
were used because substituting values with an arbi-
trary number has been shown to bias data owing to
non-random patterns in the distribution of small val-
ues (Helsel 2006, Schaffler et al. 2014, Lazartigues et
al. 2016).
Statistical analysis
PERMANOVA and canonical analysis of principal
coordinates (CAP) were used to analyse the elemen-
tal data, using PERMANOVA+ for PRIMER software
(Anderson et al. 2008). Prior to analysis, the elemen-
tal variables in each dataset were normalised and
assumptions were checked using shade plots, which
confirmed the equal spread of variance within each
dataset (Clarke et al. 2014).
The factors in the PERMANOVA analysis were ‘estu-
ary’ (fixed), ‘year’ (fixed) and ‘site’ (random, nested
within estuary), and ‘fork length’ was in cluded as a
covariate because otolith chemistry can vary with
ontogeny (Beer et al. 2011). Euclidean distances were
used to calculate the resemblance matrix. Type I sum
of squares was used in the analysis so that the factor
‘estuary’ was fitted to the data after the covariate.
Permutations were conducted on residuals under a
reduced model, rather than on raw data, to avoid
inflated Type 1 error rates associated with covariates
in multivariate analyses (Anderson et al. 2008). P-val-
ues were generated using 9999 permutations. This
PERMANOVA analysis was performed on the multi-
variate (elemental ‘signature’) data as well as uni-
variate element data.
CAP was used to visualise multivariate differences
in otolith elemental signatures between estuaries,
and to determine how accurately juvenile individuals
could be allocated to their collection estuary. The
goal of this was to assign juveniles of known estuar-
ies back to the area of collection; therefore a full
baseline of all estuaries in which tailor may be found
was unnecessary. Following initial analysis, which
found that most estuaries could not be discriminated
accurately (see ‘Results’ for details), 3 groups were
formed to improve discrimination accuracy. These
groups represent the most marine-dominated estu-
ary in NSW (highest salinity; Jervis Bay; mean = 35.0,
min = 32.5, max = 36.0, SD = 0.7; CSIRO 1994), the
estuary with the largest freshwater input in NSW
(lowest salinity; Clarence River; mean = 22.7, min =
5.4, max = 35.7, SD = 9.2; NSW Office of Environment
and Heritage 2012) and ‘Other estuaries’, which
were a mix of smaller estuaries of variable freshwater
input and size (mean = 30.8, min = 6.4, max = 35.7,
SD = 3.7; NSW Office of Environment and Heritage
2012). These 3 groups were selected as a parsimo-
nious representation of the potential types of estuar-
ine habitat used by juvenile P. saltatrix. CAP allows
additional samples to be placed onto the canonical
axes of an existing CAP model and thereby classifies
each of the new unknown origin samples to an exist-
ing group. Using this procedure, the elemental sig-
natures from the juvenile section of otoliths of 121
adult fish were added onto the existing CAP model to
identify the most likely nursery origins of the adult
fish [i.e. whether they had a marine influenced signa-
ture (Jervis Bay) or an estuarine influenced signature
(Clarence River or ‘Other estuaries’)]. Fish that had
signatures that placed them outside the boundaries
of the current CAP analysis were removed (n = 3), as
this suggests that they came from areas that were not
characterised in our analysis.
As an additional concurrent univariate analysis,
the Sr:Ca values from the spot analyses of the juve-
nile section of adult otoliths were arranged to visu-
alise the spectrum of Sr:Ca values observed within
juvenile regions, aiming at representing sites used by
juveniles relative to the 2.18 mmol mol−1 Sr:Ca break
between coastal marine and estuarine environments.
Otolith elemental profile data from age-1 tailor
were smoothed with a 7-point moving average and
plotted relative to distance from the primordium.
Fish with similar profiles of both Sr:Ca and Ba:Ca
were considered to be representative of different
P. saltatrix life histories. Despite no difference in
Ba:Ca being observed in our saline estuarine and
coastal samples described above, high Ba:Ca values
were still interpreted as indicative of high fresh-
water influence.
190
Schilling et al.: Pomatomus saltatrix juvenile life history
Historical offshore length frequency analysis
To provide additional support for the findings from
the otolith chemistry analyses regarding habitat use
and life history patterns, a re-analysis of historical
trawl data was undertaken. Length-frequency and
abundance data for P. saltatrix were compiled from a
multi-species dataset from 2 sets of research voyages
conducted by the RV ‘Kapala’ between 1990−1992
and 1995−1996. The original aim of the research voy-
ages was to determine the relative abundances and
size composition of prawns and associated bycatch
species on trawling grounds in the Newcastle and
Clarence River regions (Graham et al. 1993a,b, Gra-
ham & Wood 1997). The trawls were conducted in
coastal waters of 2 regions, near the Clarence River
(northern NSW; 28.5−29.5° S; Fig. 1) and near
Newcastle/ Tuncurry (central NSW; 32− 33° S; Fig. 1).
Within these regions, both inshore (5−27 m depth)
and offshore (64−77 m depth) trawl transects were
conducted. The trawling was conducted with three
22 m head line Florida Flyer prawn nets towed in a
triple-rig ar rangement. Fish were measured onboard
the RV ‘Kapala’ for fork length.
RESULTS
Juvenile elemental signatures by estuary
Variations in juvenile otolith element: Ca ratios
among estuaries were evident (Fig. 2). For instance,
higher Ba: Ca and Mn:Ca ratios were found in otoliths
from Clarence River than from the other estuaries
sampled. Using multivariate PERMANOVA, signifi-
cant differences were found between estuaries as
well as between sites (nested within estuary; Table 1).
Fork length as a covariate was also significant. Pair-
wise tests of estuaries re vealed that only some estu-
aries were significantly different to each other (Table
S2 in the Supplement). The significant effects of estu-
ary and site show that variation in otolith chemistry
of Pomatomus saltatrix could be used for discrimina-
tion of groups in some situations. Overall, univariate
PERMA NOVAs found a significant effect of estuary
for Mg, significant site (nested within estuary) effects
for Mn, Sr and Ba, and a significant estuary × year
interaction for Sr (see Table S3 in the Supplement for
full univariate PERMANOVA results).
This study was unable to successfully classify fish
to estuaries of capture based on their multivariate
otolith elemental signatures (with only 31% of indi-
viduals correctly classified), but classification suc-
cess varied greatly among estuaries (Table 2). Clas-
sification accuracies for Jervis Bay, Wagonga Inlet
and Clarence River were the highest (68.4, 52.0 and
50.0% accuracy respectively), and as Jervis Bay and
Clarence River correspond to estuaries with differ-
ent freshwater flow (highest and lowest salinity),
further classification analysis was undertaken (see
‘Mat erials and methods’ for full justification). Classi-
fication analysis using only 3 groups (Jervis Bay,
Cla rence River and ‘Other estuaries’) had an im -
proved overall classification rate of 86%. Individual
classification success for each group was 73% for
Jervis Bay, 62% for Clarence River and 89% for
‘Other estuaries’. While the overall classification ac -
curacy for both the CAP analysis with 12 groups and
the CAP analysis with 3 groups was approximately
3 times better than random, the higher allocation
191
df MS Pseudo-Fp(perm)
Fork length 1 106.46 8.2391 0.0001
Estuary 11 26.595 1.6642 0.0479
Year 1 18.699 2.6345 0.1735
Site(Estuary) 14 13.174 1.9321 0.0012
Estuary × Year 3 10.657 2.3534 0.2458
Year × Site(Estuary) 2 4.159 0.60998 0.6741
Residuals 327 6.8183
Total 359
Table 1. Summary of PERMANOVA results for the multi-
variate analysis of edge otolith elemental compositions of
juvenile Pomatomus saltatrix collected in different estuaries.
There were > 9000 unique permutations for each term in the
model
Estuary % Allocated correctly
Clarence River (Cla) 50.0
Port Stephens (PS) 14.3
Hunter River (HR) 32.0
Hawkesbury River (HB) 31.0
Sydney Harbour (SH) 4.4
Georges River (GR) 36.7
Port Hacking (PH) 20.0
Shoalhaven River (SR) 4.8
Jervis Bay (JB) 68.4
Clyde River (Cly) 38.1
Moruya River (MR) 21.1
Wagonga Inlet (WI) 52.1
Table 2. Summary of total correct cross-validated individu-
als of juvenile Pomatomus saltatrix classified back to the
estuary in which they were caught, based upon otolith ele-
mental chemistry and canonical analysis of principal coordi-
nates (CAP). The % allocation to each estuary in a random
assignment would be ~8%
Mar Ecol Prog Ser 598: 187– 199, 2018
accuracies from the 3-group analysis allowed the
results to be interpreted in a more biologically
meaningful way.
Juvenile life period chemical signatures
from adult otoliths
Using the CAP analysis, the chemical composition
of the juvenile area of each adult’s otolith was used to
classify fish to the 3 major estuary groups (Jervis Bay,
Clarence River and ‘Other estuaries’). A random clas-
sification of fish would result in ~33% assigned to
each group. Assuming that most estuaries available
for P. saltatrix would have signatures similar to those
of the Clarence River (high freshwater) or ‘Other
estuaries’ groups, classification of fish from estuarine
nursery areas would likely result in more fish as -
signed to these 2 groups. However, the majority of
the adult fish were classified as having juvenile oto -
lith elemental ‘signatures’ most similar to those of the
Jervis Bay group, and thus most resembling the mar-
ine environment (51.6% Jervis Bay, 30.3% Clarence
River and 18.0% ‘Other estuaries’). This suggests
that both coastal and estuarine environments are
important juvenile habitats.
192
Cla
PS
HR
HB
SH
GR
PH
SR
JB
Cly
MR
WI
Cla
PS
HR
HB
SH
GR
PH
SR
JB
Cly
MR
WI
Cla
PS
HR
HB
SH
GR
PH
SR
JB
Cly
MR
WI
Cla
PS
HR
HB
SH
GR
PH
SR
JB
Cly
MR
WI
Cla
PS
HR
HB
SH
GR
PH
SR
JB
Cly
MR
WI
Cla
PS
HR
HB
SH
GR
PH
SR
JB
Cly
MR
WI
Cla
PS
HR
HB
SH
GR
PH
SR
JB
Cly
MR
WI
Cla
PS
HR
HB
SH
GR
PH
SR
JB
Cly
MR
WI
0.000
0.002
0.004
0.006
7Li
0.00
0.02
0.04
0.06
0.08
24
Mg
0.0000
0.0005
0.0010
0.0015
55
Mn
0.000
0.003
0.006
0.009
63
Cu
0.001
0.002
0.003
0.004
0.005
66
Zn
1.5
2.0
2.5
88
Sr
0.000
0.001
0.002
0.003
Estuary
Element:CA
138
Ba
0.0000
0.0005
0.0010
208
Pb
Fig. 2. Element:Ca ratios (mean ± 1 SE) from a spot analysis at the edge of otoliths from juvenile (age-0) Pomatomus saltatrix
collected in different estuaries. All units are in mmol mol−1. Estuaries are arranged by latitude; abbreviations are given in
Table 2. These otolith elemental ratios may represent contributions from a variety of sources, including the water, diet and
other physiological influences
Schilling et al.: Pomatomus saltatrix juvenile life history
The spot analysis of juvenile regions within the
adult otoliths revealed a range of Sr:Ca values (1.46−
2.84; Fig. 3). These spots provide a snapshot of the
juvenile phase of many fish and also suggest that
juvenile P. saltatrix utilise a wide range of salinity
environments. A total of 24% of the
spots from the juvenile section of the
adult otoliths were above the 2.18
mmol mol−1 ratio marine water thresh-
old for Sr: Ca. This was less than the
percentage of spots considered to have
a signature most similar to the marine
environment from the multivariate
analysis (52%), but it corroborates evi-
dence that a substantial proportion of
the fish sampled were in fluenced by
the marine environment during their
juvenile period.
Otolith elemental profiles
All elemental profiles of adult P.
saltatrix showed elevated levels of
manganese at the start (Fig. S1 in the
Supplement), indicating that the pro-
file started at the core of the otolith
(Brophy et al. 2004). Distinct shifts in elemental con-
centration were observed in the profiles of some
otoliths. Sr and Ba profiles showed variation between
individual fish, but 4 main patterns were evident
(Fig. 4). While over half of the profiles showed a pat-
193
0 20 40 60 80 100 120
1.6
1.8
2.0
2.2
2.4
2.6
2.8
Ranked Individual P. saltatrix
Sr:Ca (mmol mol–1)
Coastal
Estuarine
Fig. 3. A visual representation of the continuum of Sr:Ca (mmol mol−1) values
observed in the spot analyses of the juvenile section from adult otoliths. The
numbers on the x-axis indicate ranked individual Pomatomus saltatrix. The
dashed line shows the calculated threshold between estuarine and coastal waters
(2.18 mmol mol−1)
1.5
2.0
2.5
3.0
Sr:Ca (mmol mol–1)
Sr:Ca
Ba:Ca
0.0000
0.0025
0.0050
0.0075
0.0100
0 500 1000 1500
1.5
2.0
2.5
3.0
Distance (µm)
0 500 1000 1500
0.0000
0.0025
0.0050
0.0075
0.0100
Ba:Ca (mmol mol–1)
ab
cd
Fig. 4. Examples of profiles of Sr:Ca and Ba:Ca from 1-yr-old Pomatomus saltatrix from the core to the edge of otoliths, showing
different life history patterns. Profiles were created using a 7-point moving average. The dashed horizontal line represents the
calculated reference criteria for Sr:Ca in coastal environments based upon the end points of the profiles from adults caught in
coastal environments (2.18 mmol mol−1). These otolith elemental ratios may represent contributions from a variety of sources,
including the water, diet and other physiological influences
Mar Ecol Prog Ser 598: 187– 199, 2018
tern of initially high Ba concentration, which then
progressively declined along the profile until approx-
imately 350 µm from the otolith core (Fig. 4B,C),
other fish did not have this initial spike of Ba
(Fig. 4A,D; Fig. S2 in the Supplement). Sr concentra-
tions initially declined in all fish (until approximately
350 µm from the otolith core) before subsequently
increasing again once (Fig. 4B) or twice (Fig. 4A;
Fig. S2) throughout the life history at approximately
650 and 900−1000 µm from the core.
Historical coastal trawl data
The RV ‘Kapala’ voyages collected 3050 P. saltatrix.
The fish ranged in size from 9 to 37 cm FL, with the
majority being between 11 and 20 cm FL (Fig. 5),
smaller than the age-1 size of 27 cm at which fish
would emigrate from estuaries (Morton et al. 1993).
These juvenile fish were only caught in the nearshore
coastal trawls and not the deeper offshore trawls.
DISCUSSION
Pomatomus saltatrix in eastern Australia show
greater life history plasticity than previously hypothe-
sised. Otolith chemistry analysis of both ju veniles and
adults revealed a more complex and variable life his-
tory than expected, which highlights the use of both
coastal and estuarine environments during the juve-
nile phase of P. saltatrix in this re gion. The multiple
lines of evidence, in cluding the better than random
as signment of fish to estuary of capture, the range of
Sr:Ca values in the juvenile region of adult oto liths,
the evidence of estuary−coast movement in some
profiles, and the presence of juvenile tailor in offshore
trawls, show that P. sal tatrix use a mix of estuarine
and coastal areas during their juvenile stage, with
some individuals potentially only using coastal habi-
tats, as seen in other P. saltatrix populations globally
(Lenanton et al. 1996, Callihan et al. 2008). This
further highlights the importance of both estu aries
and coastal regions as habitats for juvenile fish (Able
2005, Nagelkerken et al. 2015, Sheaves et al. 2015).
Juvenile otolith chemistry differences
The elemental signatures in P. saltatrix otoliths dif-
fered significantly among estuaries and among sites
within estuaries, indicating that there are inter-
individual patterns in habitat use at various spatial
scales. The lack of consistent differences between
all estuaries concurs with previous research in the
region (including for the same set of estuaries), which
found differences in the otolith chemistry of Pagrus
auratus and Pelates sexlineatus from some but not
all estuaries (Gillanders 2002a, Sanchez-Jerez et al.
2002). Estuaries are variable environments, influ-
enced by both terrestrial and marine inputs (Roy
et al. 2001), and the consequent variation in water
chemistry is often reflected in otolith chemistry (Els-
don & Gillanders 2003, 2004). Water quality and
chemistry within an estuary can vary temporally and
spatially, and this variability influences the estuarine
signatures from the otoliths. Nonetheless, it is not
uncommon for otoliths from some estuaries to have
similar elemental signatures, particularly in studies
with larger numbers of source sites (Gillanders
2002a, Marriott et al. 2016). It is possible that the lack
of distinct otolith chemistry signatures between estu-
aries found in this study is due to P. saltatrix visiting
multiple source estuaries. While this study suggests
movement of juveniles between estuarine and coastal
habitats, previous tag-recapture work suggests there
is no evidence for movements between estuaries
(Morton et al. 1993). Recapture studies are often
biased by high sampling effort in close proximity to
release locations (Gillanders et al. 2001). However
due to the high popularity of P. saltatrix with fishers,
fishing effort in this region is uniformly high, and no
tag was returned from an estuary other than the estu-
194
0 5 10 15 20 25 30 35 40
0
5
10
15
20
Fork length (cm)
Frequency(%)
Central NSW
Northern NSW
Fig. 5. Compiled length-frequency data of Pomatomus salta-
trix in coastal trawls from surveys conducted by the RV ‘Ka-
pala’ in central NSW (dashed line; n = 1533) and northern
NSW (solid line; n = 1517) during 1990−1992 and 1995−1996
(Graham et al. 1993a,b, Graham & Wood 1997). The vertical
dotted line represents size at age-1, when P. saltatrix were
previously assumed to emigrate to coastal marine waters
(Morton et al. 1993, Zeller et al. 1996)
Schilling et al.: Pomatomus saltatrix juvenile life history
ary in which a fish was tagged. It is thus considered
unlikely that the otolith elemental signature of juve-
nile P. saltatrix is being influenced by individuals
spending time in multiple estuaries.
It is noted that Jervis Bay, the most marine-domi-
nated estuary, had the lowest average Sr:Ca ratio in
the juvenile otoliths. While there was no significant
effect of fish length found in the univariate Sr PERM-
ANOVA (Table S3), the fish from Jervis Bay were,
on average, the smallest (Table S1) and there were
therefore possibly some size-related intrinsic effects
on otolith chemistry here such as ontogenetic changes
in diet (Buckel et al. 2004, Engstedt et al. 2012) or
differing physiology in small P.saltatrix (Grammer et
al. 2017). Indeed, decreases in Ba:Ca and Sr:Ca ratios
have previously been demonstrated in P. saltatrix
when switching diet from prawns to fish (Buckel et al.
2004). Fish from Clarence River may have had a
higher proportion of crustaceans in their diet (due to
their small size) than the fish from some of the other
estuaries (Schilling et al. 2017), and this may have
been reflected by the high Ba:Ca ratios found for this
group. However, this pattern was not seen in similarly
small fish collected from Jervis Bay, suggesting, con-
versely, that diet had a limited impact on Ba:Ca ratios
in this group (Izzo et al. 2018). Nevertheless, these
patterns could simply reflect the higher freshwater
input in Clarence River compared with in Jervis Bay.
Due to the large variation in the otolith chemistry of
individual P. saltatrix within all the estuaries sam-
pled, it was not possible to link P. saltatrix individuals
to a particular source estuary, and we rejected our
initial hypothesis that P. saltatrix otoliths have estu-
ary-specific elemental signatures.
Within-estuary variation has previously been ob -
served in multiple estuaries (Dorval et al. 2005), in -
cluding some of the same estuaries sampled in this
study (Gillanders 2002b, Sanchez-Jerez et al. 2002).
There are 2 possible explanations for the within-estu-
ary (site) differences observed in the present study.
First, perhaps the highly mobile nature of P. saltatrix
may result in groups of individuals spending enough
time in different areas within an estuary to pick up
different chemical signatures. Alternatively, it is pos-
sible that there are multiple distinct P. saltatrix
schools within an estuary which do not mix with one
another and thus pick up different chemical signa-
tures. Al though juvenile P. saltatrix are pelagic pred-
ators (Schilling et al. 2017), and are known to roam
widely around estuaries (Morton et al. 1993), differ-
ences in chemical composition resulting from pollu-
tants have been observed in P. saltatrix at various
sites within a single estuary (Sydney Harbour; Man-
ning et al. 2017). These spatial differences support
the idea that juvenile P. saltatrix are resident enough
that the bioaccumulation of chemicals is different
between areas within a single estuary and thus intra-
estuary differences in otolith chemistry could be
observed in some circumstances.
Assigning adults to estuaries
The ability to assign individual fish back to specific
juvenile sites requires a site-specific baseline of
elemental fingerprints. To subsequently discern the
contribution of individual nursery habitats to adult
populations would require a library of otolith chem-
istry signatures of all potential source sites (Elsdon et
al. 2008). While this study did not have such a library,
we were able to test the ability to discriminate P. salta-
trix source sites using our sampled sites. Al though the
ability to discriminate individual estuaries based upon
juvenile P. saltatrix otolith elemental signatures was
generally poor, it was still possible to distinguish be-
tween 3 main groups: Jervis Bay (the most ‘marine’
estuary), Clarence River (the estuary with the largest
freshwater input) and ‘Other estuaries’ (other estuar-
ies influenced by variable freshwater flows and mar-
ine influences). The allocation of signatures from the
juvenile section of adult otoliths back to these groups
showed that more than half of these fish had juvenile
life stage signatures most similar to the Jervis Bay
group (51.6%). This indicates that a large proportion
of adult P. saltatrix have multi-elemental signatures in
the juvenile section of their otoliths that are most simi-
lar to those found in juveniles from a marine-domi-
nated estuary. The 3 fish that were unable to be allo-
cated to any of our 3 groups may indicate that there
was a missing juvenile habitat not sampled; if so, it is
likely to be another coastal marine group (possibly a
northern group) as our estuary groups encompassed
many types of estuaries. We believe it is unlikely that
there is another marine group, as a previous study
showed that the eastern Australian population is a
well-mixed stock along the coast (Nurthen et al.
1992). It is likely that these 3 fish (< 2% of analysed
fish) were outliers in the LA-ICP-MS analysis. The
univariate analysis of Sr:Ca ratios from the spots in the
juvenile section of adult otoliths suggested that 24%
of the sampled fish had a significant marine influence
in their juvenile life history stage. Combined, the uni-
variate (Sr) and multi-element analysis of the spots
suggest that a large proportion (24−52 %) of fish were
subject to high marine influence at the time that por-
tion of the otolith was being laid down.
195
Mar Ecol Prog Ser 598: 187– 199, 2018
The sizes of P. saltatrix collected by the RV ‘Kapala’
from coastal marine waters confirm that juvenile
(age-0, <27 cm) P. saltatrix inhabit coastal marine en -
vironments, providing the first documented evidence
of juveniles in coastal environments. The presence of
juveniles in the coastal marine environment is also
consistent with the strong marine-influenced signa-
ture in P. saltatrix otoliths demonstrated by the spot
analyses in their juvenile section. This re-affirms the
suggestion that a large portion of juvenile P. saltatrix
spend sufficient time in marine-dominated waters to
possess a marine-influenced signature, either in
coastal waters or near the entrances to estuaries
where coastal water is present. This is particularly
clear in the wide range of Sr:Ca ratios observed in
the juvenile section of adult otoliths. These findings
conform with the life history patterns observed in
other populations of P. saltatrix worldwide that indi-
cate the use of both estuarine and coastal nursery
habitats (Lenanton et al. 1996, Able et al. 2003, Calli-
han et al. 2008), and are further supported by our
elemental profile analyses.
Elemental profiles
Our exploratory analysis to determine the suita -
bility of elemental profiles on P. saltatrix otoliths
revealed multiple patterns in 1-yr-old fish. Assuming
the general relationship of increasing Sr and de -
creasing Ba with salinity (Campana 1999, Elsdon et
al. 2008), some of the observed patterns correspond
to the previously documented life history of P. salta-
trix in eastern Australia: that they spawn in marine
environments (high Sr and low Ba) before recruiting
to estuaries (lower Sr and higher Ba) and then, after
a period of time, return to the marine environment
(rising Sr and lower Ba; Bade 1977, Morton et al.
1993, Zeller et al. 1996). Only 58% of the fish showed
Ba rising to a high level initially, while the remaining
42% only showed a small or negligible rise, suggest-
ing some fish may never enter the less saline regions
of estuaries. While the Ba peaks only encompassed a
short time period, indicating that lower-salinity estu-
arine use is limited, the higher Ba concentrations are
similar to those recorded in previous research on
estuarine fish (Milton et al. 2008, Macdonald & Crook
2010). The Sr profiles show numerous spikes during
the juvenile phase, which suggests movement be -
tween estuarine/brackish waters and the coastal
marine environments. Overall, results indicate that
while some juvenile P. saltatrix recruit to estuarine
or more freshwater environments, others do not, and
they may stay in waters of approximately marine
salinity or move between estuaries and the coastal
marine environment. This is consistent with the re -
sults from the spot analyses and historical trawl sam-
ples discussed above, which showed that juveniles
are not restricted to estuarine environments. All fish
except one (fish 3; Fig. S2) were caught in coastal
environments, and as such, the end point of the pro-
files should represent a marine environment.
Low Ba concentrations at the end of the profile,
reflecting the marine environment when the fish was
caught, would be expected, and this pattern was ob -
served. Conversely, high Sr concentrations would be
expected at the end point of the profiles, and was
observed, although there were exceptions. As there
is a lag between otolith chemistry and fish movement
as new otolith material forms, these 2 exceptions may
be due to recent movement be tween estuarine and
coastal environments (Elsdon et al. 2008). The lag in
incorporating elements such as Sr into the otolith can
be over 20 d in some species (Elsdon & Gillanders
2005b, Engstedt et al. 2012), which makes it possible
that short temporal scales or recent movements be -
tween different environments are missed or not fully
represented in the elemental profiles.
It is increasingly being shown that otolith chem-
istry is influenced by numerous intrinsic (e.g. growth
and diet) and extrinsic (e.g. temperature, salinity)
factors in addition to a simple relationship with water
chemistry (Sturrock et al. 2014, 2015, Grammer et al.
2017). A recent meta-analysis highlighted this by
demonstrating that whilst salinity was the primary
driver of both Ba and Sr, Sr was also influenced by
factors including the ecological niche, condition, diet
and ontogeny of individual species (Izzo et al. 2018).
As such, it is important to note that factors such as
diet may be influencing the Sr:Ca profiles presented
here (Engstedt et al. 2012). While experimental vali-
dation of the variation in otolith Sr and Ba concentra-
tions is important in order to determine the resolution
at which movement between the coast and estuaries
(or even within estuaries) can be effectively deter-
mined, it is possible to use wild-caught fish from
known environments to define reference chemical
composition thresholds, assuming the otolith edge is
representative of capture location. Sr:Ca ratios of P.
saltatrix from both estuarine and coastal environ-
ments have previously been used to generate refer-
ence criteria representative of estuarine (3−12 salinity;
1.68 mmol mol−1) and coastal environments (~35 salin-
ity; 2.2 mmol mol−1) around Chesapeake Bay, USA
(Takata 2004). The coastal reference value from that
study was similar to that in ours, and suggests that a
196
Schilling et al.: Pomatomus saltatrix juvenile life history
Sr:Ca ratio of ~2.2 mmol mol−1 is an appropriate ref-
erence level for coastal environments. Sr:Ca ratios
lower than 1.68 mmol mol−1 were rarely ob served in
our study, probably because the salinity in the estuar-
ies sampled in the present study (NSW Office of
Environment and Heritage 2012) is rarely as low as
that observed in Chesapeake Bay (Takata 2004). The
lack of difference in Ba concentrations between the
coastal- and estuarine-caught fish in the present study
is possibly because the estuarine re gions where P.
saltatrix were collected were higher in salinity (> 25)
than regions where salinity is low enough to produce
the high Ba:Ca signal commonly observed in other
studies (Macdonald & Crook 2010). Overall, analysis
of otolith Sr:Ca and Ba:Ca profiles can be used to
trace estuarine−ocean movement in P. saltatrix, and
concur with both the spot analyses and re-analysis of
historical coastal length frequencies to indicate that
the life history of P. saltatrix in eastern Australia is
more facultative than previously thought, a finding
shared with several studies that have investigated
life history patterns in fish (Milton et al. 2008, Gillan-
ders et al. 2015, Condini et al. 2016).
Conclusions
Analysis of the otolith chemistry of Pomatomus
saltatrix from eastern Australia revealed a more plas-
tic life history than previously hypothesised. Due to
the weight of evidence from the otolith chemistry
analysis, we rejected our initial hypothesis that the
juvenile life history region of adult otoliths would
have characteristic estuarine signatures. The present
study has shown that P. saltatrix in eastern Australia
use both estuarine and coastal habitats as part of
their juvenile development. Furthermore, the use of
coastal habitats by juvenile P. saltatrix was supported
by both otolith elemental profiles and historical
length frequencies. These findings further corrobo-
rate the applicability of otolith chemistry to evaluate
life history patterns and confirm previously undocu-
mented complexity within fish species life histories.
Acknowledgements. We thank Ashley Fowler (NSW DPI) for
providing many helpful ideas during the data analysis pro-
cess, and Aoife Mcfadden for providing assistance with the
LA-ICP-MS. Many volunteers, including Chris Stanley,
Chris Setio, Matthew Hyatt, Alexandra Milne-Muller, Koren
Fang, Gareth Deacon, Chris Lawson, Aaron Puckeridge,
Georgia Brook, Dylan van der Meulen and Matthew Broad-
hurst, helped to collect the juvenile tailor. Many thanks to
the fishers who donated fish as part of the NSW Research
Angler Program, in particular Ben van der Woude and Aus-
tralian Surfcaster. We also thank the Fay family for looking
after H.T.S. in Adelaide. This research was supported by an
Australian Research Council Linkage Grant (LP150100923),
the NSW Recreational Fishing Trust, an Ecological Society
of Australia student research award and Hornsby Council.
H.T.S. was supported by a Research Training Scholarship.
P.R.S. was funded with a Fundação para a Ciência e Tec-
nologia (FCT) postdoctoral grant (SFRH/BPD/95784/2013).
Fish were collected under NSW DPI Scientific Collection
Permit no. P03/0086(F)-8.1 and the research was conducted
with approval from the NSW DPI Animal Care and Ethics
Committee (approval no. SIMS 14/14). This is contribution
no. 219 of the Sydney Institute of Marine Science. Thanks also
to the 3 anonymous reviewers, who provided many helpful
comments.
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199
Editorial responsibility: Stylianos Somarakis,
Heraklion, Greece
Submitted: June 19, 2017; Accepted: January 22, 2018
Proofs received from author(s): March 15, 2018
... Both otolith shape and otolith chemistry data are usually multivariate with hypothesis testing traditionally conducted using distance-based methods (eg. permutational multivariate analysis of variance (PER-MANOVA) 4,23,24 ) or model-based methods which assume a gaussian error distribution (eg. multivariate analysis of variance or linear discriminant analysis 25 ). ...
... We choose to use a common distance-based analysis, PERMANOVA with a nMDS ordination plot to visualise the differences. Using www.nature.com/scientificreports/ the 'vegan' R package 53 , we created a dissimilarity matrix using Euclidean distances as is common for otolith datasets using the 'vegdist()' function 23 . Distance based analyses such as PERMANOVA have an often untested assumption of homogeneity of variance between groups. ...
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... Otolith chemistry overcomes these limitations because all fish are 'tagged' from birth to death . In recent years, otolith chemistry has been used to examine stock structure, life-history patterns and adult movement patterns of wild fish (Crook et al., 2016;Fowler et al., 2016;Hamer et al., 2006;Miles et al., 2018;Schilling et al., 2018). Trace element concentrations vary among estuaries and coastal water masses, and fish otoliths have been shown to accrete these elements in proportion to the water concentrations in which growth occurred (Elsdon and Gillanders 2004; see also Izzo et al., 2018). ...
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... Conversely, most studies on otolith chemistry use Sr/Ca ratios as proxies for tracking fish migration along coastal systems (e.g. Schilling et al., 2018;Franco et al., 2019;Soeth et al., 2020;Avigliano et al., 2021). Two possible causes may explain the patterns observed herein. ...
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... It is generally assumed that ratios of trace elements to calcium (Ca), particularly strontium (Sr) and barium (Ba), are deposited chronologically into the otolith material consistently relative to ambient concentrations in the surrounding water (Izzo et al. 2018). Therefore, otolith Sr:Ca and Ba:Ca have been used as tracers of the past habitat use by estuarine fish (Gillanders and Kingsford 2000;Gillanders 2002a;Dorval et al. 2005b;Schilling et al. 2018). The predictive relationships between trace elements (i.e., Sr and Ba) and salinity where high Sr/low Ba associated with seawater, and low Sr/high Ba associated with freshwater habitats are often used to reconstruct fish life histories (Elsdon et al. 2008). ...
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Understanding the role different habitats play in the life histories of fishes is important for the development of holistic aquatic ecosystem management plans. We used otolith trace element analysis to reconstruct the life history of estuarine triplefin Forsterygion nigripenne and infer its habitat use. Analysis of otoliths using laser ablation inductively coupled plasma mass spectrometry showed an elemental profile without prominent changes in elemental concentration. The otolith elemental profiles were not indicative of movement between waters with substantial Sr:Ca and Ba:Ca differences. The Sr:Ca and Ba:Ca profiles were indicative of within—and near—estuary movements encompassing short time periods. Overall, the otolith microchemical profile was likely indicative of a life history closely associated with estuaries. However, it is difficult to rule out brief excursions to the marine environment given that may not have been of sufficient duration to be recorded in the elemental composition of the otolith. This suggests that F. nigripenne is the only species in southern New Zealand known to be closely associated with estuarine habitat for its entire life cycle.
... The analysis of otolith chemistry has been successfully used to reconstruct the life history of fish (e.g. Otake and Uchida, 1998;McCulloch et al., 2005;Tsunagawa and Arai, 2011;Schilling et al., 2018), and can be used to investigate estuarine dependency (Alburquerque et al., 2012). Otoliths are metabolically inert calcic structures that accrete relative to somatic growth, incorporating elements from the ambient water. ...
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... All scuta were washed in warm, soapy water to remove algae, membranes and other organic material, and bathed in 30% hydrogen peroxide for 72 h to remove any remaining traces of organic material. All specimens were then sonicated for 15 min in a Unisonic® ultrasonic cleaner (Unisonic, AU) using Milli-Q® water (MilliporeSigma, USA) to ensure surfaces were free of contamination (Schilling et al. 2018). For each specimen the scutum was hand-milled with a 399D Plus Como® Mini Drill with 2 mm drill bit (Como, UK) by shaving the uppermost growth band from its apex (estimated to represent the most recent week of growth) and collecting the calcite powder onto a piece of weigh paper. ...
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... In a recent study that included fish collected from the Georges River estuary, otolith chemistry and data from coastal trawls were used to show that juvenile tailor Pomatomus saltatrix move between lower estuarine and coastal nurseries in eastern Australia, although those using estuaries appear to have a home estuary, rather than moving between estuaries (Schilling et al., 2018). Thermal performance of ectotherms may shape biogeography/species distributions. ...
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... Противоречивые результаты классификации были получены при анализе выборок сеголеток снука Centropomus undecimalis п-ова Флорида: точность классификации особей, собранных в разное время в пределах одной эстуарной системы, составляла 57 % в одном случае и 98 % в другом, что продемонстрировало темпоральную вариабельность оседлости молоди вида среди обследованных районов нагула [Ley, Rolls, 2018]. Низкий уровень классификации был отмечен и при анализе выборок луфаря Pomatomus saltatrix, собранных в 12 эстуарных системах восточной Австралии [Schilling et al., 2018], что в комплексе с анализом исторических данных по размерному составу уловов подтвердило предположение о существенной пластичности молоди вида в использовании эстуарных и прибрежных зон нагула. ...
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Microchemical analysis of calcified structures of fish is a modern technique for determining the origin of fish species and ontogenetic reconstructions of their habitat that can be applied for such tasks as stocks separation in mixed samples, tracking of fish migrations, determining of spawning, feeding or wintering areas, differentiation of fish of artificial and natural origin, growth analysis, age evaluation, etc. The approach is based on analysis of trace elements concentration between the center and periphery of a calcified structure, or precise measurement of the elements and their isotopes concentration in certain sites of sample. The calcified structures most often used for analysis are otoliths, skeleton bones, scales, and also statoliths of lampreys or beaks and statoliths of cephalopods. Specifics of the method application are described with examples of its use for solving diverse tasks of fundamental and applied science, in particular in complex studies of biological resources in the Amur River basin.
Thesis
Evaluating the importance of inshore coastal habitats for the maintenance of exploited coastal fish populations is key to delineate sustainable strategies for both fishery and ecosystem management. Jacks are highly prized tropical marine fishes. Most of them complete their whole life cycle at sea, but some use estuaries at the juvenile stage before moving back to coastal waters and joining offshore adult exploited stocks. This is the case of the horse-eye jack (Caranx latus), an exploited yet poorly studied species frequently found in estuaries in North-Eastern Brazil, at least at the juvenile stage. However, little was known on the species' ecology in these inshore habitats, nor on their importance for the maintenance of its local exploited stock. To start filling this knowledge gap, this thesis combined three complementary research axes. The first one investigated the local size-at-age and growth of C. latus using size data and otolith readings from 282 specimens captured both at Sea and in varied inshore habitats. This allowed to specify fish ages in all the environments colonised by the species in the area and to infer the growth parameters for its local exploited stock. The second axis investigated local variations in the diet and food resources of C. latus juveniles in estuaries and their causes, by a combined analysis of the stomach contents and stable isotopes (13C and 15N) signatures of 439 juveniles of both C. latus and another sympatric jack species (C. hippos), in three neighboring estuaries with contrasted morphological and biological features. It highlighted a plasticity in local resources use by juvenile jacks according to the estuarine environmental settings, allowing them to limit the trophic competition among them, with potential consequences on their respective sizes and abundances. Finally, the third research axis aimed to quantify the importance of local estuaries for sustaining the adult stock of C. latus exploited offshore, by analysing different chemical elements incorporated in the juvenile part of 183 otoliths of juveniles and adults captured in varied estuarine and marine habitats in this area. This revealed that 75% of the sub-adults and adults exploited by the fisheries off the coast of the Pernambuco state have spent their first year of life growing in local estuaries, particularly those under strong marine influence. These findings significantly advance previous knowledge on C. latus ecology and demonstrate that estuaries play a key role in the maintenance of the C. latus population in North-Eastern Brazil. Yet, local differences in the abiotic and biotic environmental conditions experienced by juvenile jacks during their estuarine stay strongly modulate the respective value of these inshore habitats for the renewal of the stock fished at Sea, with strong implications in terms of local fishery and ecosystem management.
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The effectiveness of marine conservation areas are influenced by the structure of the food webs they encompass, including the population dynamics of potentially important forage species that occupy trophic positions between those of zooplankton and higher trophic levels. Capelin is a key forage species for marine mammals, seabirds, and fish in the Saguenay-St. Lawrence Marine Park (SSLMP, Canada), yet knowledge on its population dynamics is incomplete. In particular, the natal sources sustaining this critical forage species within the conservation area remain unknown. Otolith microchemistry as an index of natal habitat was investigated, including measures of boron, barium, iron, magnesium, manganese, and strontium over the protracted spawning season of capelin. Otolith microchemistry indicated that the principal natal source of 1+ capelin found within the SSLMP was located in the St. Lawrence estuary, outside the conservation area boundaries. To ensure the sustainability key forage species within the conservation area, larger scale long-term management strategies are necessary to encompass ecological processes related to capelin that extend beyond the conservation area boundaries.
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Fish otoliths are widely used to answer biological and ecological questions related to movements and habitat use based on their chemical composition. Two fundamental assumptions underlie otoliths as environmental tracers and proxies for reconstructing exposure histories: (i) otolith chemistry reflects water chemistry, and (ii) ambient environmental conditions affect otolith element incorporation. Here, we test these assumptions for Sr and Ba through meta-analyses. Our first meta-analysis confirmed a correlation between concentrations of Sr:Ca and Ba:Ca in otoliths and the surrounding water, both elements displaying positive otolith–water correlations. The second meta-analysis examined the relative influences of salinity and temperature on otolith Sr and Ba partition coefficients (an index of otolith element regulation). Our environmental effects meta-analysis confirmed that otolith Sr and Ba are affected by temperature and salinity; however, study-level covariates (e.g., water chemical concentrations and species ecological niche) influenced otolith element incorporation, and this varied by element. These findings confirm that even though otolith chemistry and elemental incorporation are differentially affected by environmental conditions, other factors play a decisive role. While we focused on studies that directly linked water and otolith chemistry, systematic reviews are key to further demonstrate the link between otolith chemistry and extrinsic and intrinsic factors. Ultimately, disentangling the relative effects of multiple factors on otolith chemistry and a detailed understanding of biomineralization is critical to the continued use of otoliths as natural tags for tracing fish movements and habitat use.
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Otolith chemistry has been widely used as a natural tag for determining environmental histories of fish that migrate across large distances and environmental gradients. However, it is not as well established as to whether otolith chemistry can be a useful tool for determining fine-scale movement and dispersal patterns of fish, particularly larvae, within estuaries. In this study, we collected water samples and otoliths from larvae of black bream, Acanthopagrus butcheri, an estuarine resident fish, and analyzed each for a suite of trace elements to determine the degree of spatio-temporal variability in elemental composition and which elements were incorporated into otoliths in relation to their associated water chemistry. We found that there were three distinct water layer signatures based on their Me : Cawater (Me = each element): a freshwater signature, a halocline signature, and a marine signature. There were also significant spatio-temporal patterns in Me : Caotolith, most notably for Li : Ca, K : Ca, and Mn : Ca. This study provides encouraging evidence for the utility of intra-estuary otolith chemistry to reconstruct environmental histories during larval development. This application will enable a better understanding of the abundance, timing, and duration of residency in particular water masses and locations that are important larval nursery habitats for species that develop within estuaries.
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Biogeochemical tracers found in the hard parts of organisms are frequently used to answer key ecological questions by linking the organism with the environment. However, the biogeochemical relationship between the environment and the biogenic structure becomes less predictable in higher organisms as physiological processes become more complex. Here, we use the simultaneous combination of biogeochemical tracers and fish growth analyzed with a novel modeling framework to describe physiological and environmental controls on otolith chemistry in an upwelling zone. First, we develop increasingly complex univariate mixed models to describe and partition intrinsic (age effects) and extrinsic (environmental parameters) factors influencing fish growth and otolith element concentrations through time. Second, we use a multivariate mixed model to investigate the directionality and strength between element-to-element and growth relationships and test hypotheses regarding physiological and environmental controls on element assimilation in otoliths. We apply these models to continuous element (Na, Sr, Mg, Ba, Li) and growth increment profiles (monthly resolution over 17 years) derived from otoliths of reef ocean perch (Helicolenus percoides), a wild-caught, site-attached, fully marine fish. With a conceptual model, we hypothesize that otolith traits (elements and growth) driven by environmental conditions will correlate both within an otolith, reflecting the time dependency of growth and element assimilation, and among individuals that experience a similar set of external conditions. We found some elements (Sr:Ca and Na:Ca) are mainly controlled by physiological processes, while other elements (Ba:Ca and Li:Ca) are more environmentally influenced. Within an individual fish, the strength and direction of correlation varies among otolith traits, particularly those under environmental control. Correlations among physiologically regulated elements tend to be stronger than those primarily controlled by environmental drivers. Surprisingly, only Ba:Ca and growth are significantly correlated among individuals. Failure to appropriately account for intrinsic effects (e.g. age) led to inflated estimates of among individual correlations and a depression of within individual correlations. Together, the lack of among-individual correlations of otolith traits in properly formulated models and the biases that can be introduced by not including appropriate intrinsic covariates suggest that caution is needed when assuming multi-elemental signatures are reflective solely of shared environments. This article is protected by copyright. All rights reserved.
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