Maturity and growth of Paralonchurus brasiliensis females in

J. Appl. Ichthyol. 21 (2005), 94–100
2005 Blackwell Verlag, Berlin
ISSN 0175–8659
Received: May 2, 2004
Accepted: September 26, 2004
Maturity and growth of Paralonchurus brasiliensis females in southern Brazil
(Teleostei, Perciformes, Sciaenidae)
By D. dos S. Lewis1 and N. F. Fontoura2
1
Pós-Graduação em Zoologia, UFPA, Curitiba; 2Laboratório de Dinâmica Populacional Aplicada a Ecossistemas Aquáticos,
PUCRS, Porto Alegre, Brazil
Summary
Samples of Paralonchurus brasiliensis Steindachner, 1875 (627
females; no males) were taken monthly from June 1997 to May
1998 at the fishing pier of Cidreira – Rio Grande do Sul
(3008¢S; 5011¢W) in southern Brazil. The fish were captured
by sport fishermen using different sizes of hook-and-line. The
reproductive period of P. brasiliensis extends from August to
March, presenting greater activity from October to February.
Females reach first maturation at 15.4 cm total length (TL). Of
the 466 scales analyzed, one to six annuli were found. Growth
annuli are formed between June and August, corresponding to
the winter period (southern hemisphere), with the first visible
annulus being formed when the fish are 1.5 years old. The
length growth curve for P. brasiliensis females is described as:
Lt ¼ 20.0 (1 ) e)0.564·t), TL in centimeters and age in years.
The undersize asymptotic length may be a result of excessive
fishing mortality on the studied population.
Introduction
Paralonchurus brasiliensis Steindachner, 1875 is a very common species along the Brazilian coast (distribution recorded
from Panamá to Argentina). It is a coastal species, often found
up to 100 m depth in sand or mud (Menezes and Figueiredo,
1980). According to Haimovici et al. (1996), P. brasiliensis is
captured in 94% of all trawling along the Rio Grande do Sul
coast up to 20 m depth, and in 76% of the trawling from 20 to
40 m depth. The species is captured throughout the year,
although less frequently in winter.
Distribution patterns of fish species along the Brazilian
coast, mainly in the southern region, have been systematically
studied over the past few years. The presence of different
populations along the Brazilian coast has been suggested
(Vazzoler, 1971; Vargas, 1976; Yamaguti, 1979). Two populations of P. brasiliensis were identified and named São Paulo
(SP) and Rio Grande do Sul (RS), located north and south of
29S, respectively. During the winter when colder waters reach
northern latitudes there is a spatial overlap between the RS
and SP populations (Vargas, 1976; Paiva Filho and ZaniTeixeira, 1980).
The reproductive period of the northern (SP) population of
P. brasiliensis extends from August to December (Paiva Filho
and Rossi, 1980). In the southern population (RS), a reproductive period from September to March has been recorded
(Oliveira and Haimovici, 2001). The presence of mature
ovaries over several months and a large range of egg diameters
in a same individual point to P. brasiliensis as a partially
multiple-spawning species (Paiva Filho and Rossi, 1980;
U.S. Copyright Clearance Centre Code Statement:
Oliveira and Haimovici, 2001). On larval surveys in Rio
Grande do Sul, P. brasiliensis was the second most abundant
species, representing 28.5% of all captured larvae. Larvae
smaller than 3 mm were found from spring to autumn (Ibagy
and Sinque, 1995). Size estimates at first maturation ranged
from 14.8 to 18.0 cm (Vazzoler et al., 1973; Paiva Filho et al.,
1976; Oliveira and Haimovici, 2001).
Maximum recorded total lengths (TL) are 29 and 30 cm for
P. brasiliensis (Menezes and Figueiredo, 1980; Kotas, 1998).
Captures of P. brasiliensis ranging from 7.0 to 23.0 cm were
made in the northern (SP) population, with a sex ratio
displaced to female dominance (Vazzoler et al., 1973). Up to
six growth annuli were observed in scales (Yamaguti et al.,
1973). Braga (1990) estimated the asymptotic length (Linf) for
the species (SP population) as 26.3 cm and the instantaneous
growth rate (k) as 0.2736.
Although Braga (1990) suggests a low fishing mortality of
P. brasiliensis because of a non-directed fishing effort, important by-catch mortalities are reported for the southern population. Bottom-trawling fisheries directed toward the shrimp
Xiphopenaeus kroyeri (Coelho et al., 1993) are responsible for
teleost discards, mainly Sciaenids, of up to 95% (85.2% on
average), with P. brasiliensis catch of up to 643 individuals h)1
(Kotas, 1998).
In this paper, estimates of the reproductive period, size, and
age at first maturation and growth curves are made for
P. brasiliensis females in the southern distribution range.
Comparisons with available growth information are made to
assess if the population structure is being changed by the nondirected fishery effort.
Material and methods
Samples of P. brasiliensis (627 females; no males) were taken
monthly from June 1997 to May 1998 from the fishing pier of
Cidreira – RS (3008¢S; 5011¢W). The fish were captured by
sport-fishermen using hook-and-line of different sizes and
employing different bait (mainly Annelida: cf. Diopatra;
Mollusca: Mesodesma mactroides; Crustacea: Emerita brasiliensis, Sergio mirim, Farfantepenaeus paulensis, Artemesia
longinaris).
Once captured, each fish was measured (TL; ±1 mm) and
weighed (mechanical balance, ±0.1 g). Gonads were weighed
in the laboratory on an analytical balance (±0.01 g). The
ovaries were classified macroscopically as immature, maturing,
mature, spent, or at rest. Size at first maturation was obtained
through the relative frequency of adult females (maturating,
mature, and spent) by size class as follows:
0175–8659/2005/2102–0094$15.00/0
www.blackwell-synergy.com
Maturity and growth of Paralonchurus brasiliensis
F ¼ 1=ð1 þ eaþbL Þ
95
ð1Þ
where, F ¼ frequency of adult females for each length class
interval; L ¼ pivotal point of each length class interval; a and
b are parameters.
The parameters a and b were estimated by least squares of
the linearized form of the previous function:
ln½ð1=F Þ 1 ¼ a þ b L
ð2Þ
The size at first maturation (L50) as the length in which 50%
of the individuals joined the reproductive population was
estimated as:
L50 ¼ a=b
ð3Þ
where, a and b are the same parameters of the previous
equation (2).
The reproductive period was graphically determined by the
variation of individual and mean values of the gonadosomatic
index (GSI):
GSI ¼ ðWg =W Þ 100
ð4Þ
where, Wg ¼ gonad weight (g); W ¼ total weight (g).
For analysis of the P. brasiliensis growth pattern, trials were
made to identify growth annuli in otoliths and scales. As
growth annuli were easily identified on scales without any
special treatment, this structure was used for further analysis.
Four to five scales from around the pectoral fin area as well as
the ovaries were stored in plastic bags with 4% formaldehyde.
The scales were permanently mounted on microscope glass
slides. Scale reading was performed using a microfile machine
(IEC MICROstar F 285). Measurements of the TL of each
scale from the center to the left edge and from the focus to
each opaque growth annulus were recorded. The morphometrical relationship between the fish total length (L, cm) and
the scale total length (D, mm) was adjusted by a power
function:
L ¼ a Db
ð5Þ
where, a and b are the coefficients of the function.
The function parameters ÔaÕ and ÔbÕ were estimated with logtransformation by least squares. The parameters were then
used to estimate the corresponding fish total length (Li, cm) at
the moment of each annulus formation (Di, mm):
Li ¼ a Dbi
ð6Þ
For a range of Linf- and tf-values within acceptable
biologically limits, the growth parameter k was estimated
through the following equation:
X
k¼
f ln½1 ðLt =Linf Þ=ðti 1 þ tf Þg=n
ð9Þ
where, Lt ¼ estimated total length (cm) of each individual
when forming scale annuli is related to age ti ) 1 + tf (years);
n ¼ number of length to age data pairs.
The best fit of the VBGF was then obtained with Linf- and
tf-values that minimize the residual variance (S2):
X
½fLinf ð1 ekðti 1þtf Þ Þ Lt g2 =ðn 1Þ
ð10Þ
S2 ¼
By log-transformation and least-squares method, parameters of the length/weight relationship were adjusted and
applied on the length growth curve to estimate the weight
growth curve.
Longevity (A0.95), as defined by Taylor (1962), is the time for
reaching 95% of the maximum average length (Linf), and
estimated as follows:
A0:95 ¼ 0:996=k
ð11Þ
Results
The seasonal pattern of the GSI (Fig. 1) for P. brasiliensis
females shows a long reproductive period. The median GSI in
June and July represents only 1% of total body weight,
beginning a process of gradual increase from August onward.
From October to January the median ovary weight attains
more than 4% of total body weight, indicating a period of
greater reproductive activity. For the following months a
falling pattern is observed until May, when average IGS
reaches its minimal annual value.
The maximum individual GSI was observed in November
when the ovarian weight of one female reached 8.25% of the
total weight. From August to March, females presenting GSI
values >4% can be observed, which is the average GSI value
for peak reproductive months and may be a possible criteria to
define the limits of the reproductive period. Nevertheless, two
females captured in June with GSI >4% suggests that some
individuals may present an off-season reproduction.
The smallest P. brasiliensis female accepted as an adult
(maturing, mature, or spent) was a 14.5 cm individual. From
16.5 cm upwards, all females captured during reproductive
months were recognized as adults. The mean length at first
The growth curve length was adjusted following the von
Bertalanffy (1938) model (VBGF):
Lt ¼ Linf ð1 ekðtto Þ Þ
ð7Þ
kðti 1þtf Þ
Lt ¼ Linf ð1 e
Individual IGS
8.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
1
Þ
ð8Þ
where, ti ¼ number of scale annuli; tf ¼ time interval
between Lt ¼ 0 to the first annulus formation.
Median IGS
7.00
GSI (%)
where, Lt ¼ mean total length (cm) at age t (years);
Linf ¼ average maximum total length (cm); k ¼ instantaneous growth rate; to ¼ time parameter-related length at birth
or recruitment.
Linf- and k-values were estimated using the minimal residual
variance method following Gonçalves and Fontoura (1999)
and the MINIVAR file for Microsoft Excel (N. F. Fontoura,
2002, unpubl. data). To incorporate the age at first annuli
formation, the von Bertalanffy (1938) formula was rewritten
as:
9.00
2
3
4
5
6
7
8
9
10
11
12
Months
Fig. 1. Gonadosomatic index (GSI) of Paralonchurus brasiliensis
females captured at Cidreira fishing pier, Rio Grande do Sul, Brazil,
between June 1997 and May 1998
96
D. dos S. Lewis and N. F. Fontoura
45
0.9
40
n = 151
0.8
Average distance from each
annulus to the scale edge (mm)
Frequency of adult females
1.0
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
12.5
13.5
14.5
15.5
16.5
17.5
18.5
Table 1
Number of captured Paralonchurus brasiliensis females showing one to
six scale annuli by total length size-classes (hook-and-line capture at
Cidreira fishing pier, southern Brazil)
0
0
0
0
0
1
0
2
2
8
17
13
9
4
56
19.36
20
15
10
Jun
0
0
0
0
0
0
0
0
0
2
3
4
6
3
18
19.88
0
0
0
0
0
0
0
0
0
0
0
1
3
1
5
20.52
maturation (L50, equation 10) for P. brasiliensis was estimated
as 15.4 cm (Fig. 2).
Scales from 466 females ranging from 12.4 to 23.6 cm TL
were analyzed and measured. Up to six annuli (five individuals) were found, while the great majority presented two or
three annuli. Table 1 shows the size frequency distribution of
females presenting one to six annuli. An unusual growth data
series can be observed, with animals with just one annuli
attaining 16.6 cm and then growing almost linearly at rates
ranging from 0.53 to 1.31 cm year)1 (average 0.78), with no
age reduction pattern. A large overlap of the size range of
females with different numbers of growth annuli is also clear.
Even considering scale misreadings, the data set suggests great
growth plasticity for individuals of the same age. Thus, when
ÔagedÕ females did not fit the von Bertalanffy growth model,
back-calculation trials were then made.
Considering a seasonal growth cycle, new annuli are formed
during periods of reduced growth. At that time, the average
distance from the last annuli to the edge of the scale is reduced,
since a new ring appears just within the external border of the
scale. For P. brasiliensis, the mean distance from the last
annulus to the edge of the scale for individuals with the same
number of annuli indicates the period of opaque annulus
Jul
Aug
Sept
Oct
Nov
Feb
Mar
Apr
May
formation from June to August (Fig. 3). Annulus formation
has an annual periodicity in all age-classes, although it is more
evident in animals with just one annulus.
140
120
100
80
60
40
20
0
0.0
Annulus 1
n = 130
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
3.0
3.5
4.0
3.5
4.0
3.5
4.0
120
Annulus 2
100
80
60
40
Number of measurements
0
0
0
0
0
2
6
11
19
34
25
20
13
6
136
18.05
25
Fig. 3. Monthly variation of the distance from the last annulus to the
scale edge of Paralonchurus brasiliensis females captured at Cidreira
fishing pier, Rio Grande do Sul, Brazil, between June 1997 and May
1998
1 annulus 2 annuli 3 annuli 4 annuli 5 annuli 6 annuli
0
0
0
0
0
8
11
28
59
61
38
18
8
3
234
17.32
More than 2 annulus
30
0
Fig. 2. Relative frequency of adult Paralonchurus brasiliensis females
(in maturation, mature, and spent) by total length classes. Reference
lines from the maturation curve indicate L50, defined as the size at
which 50% of the females attain sexual maturity. Fish captured at
Cidreira fishing pier, Rio Grande do Sul, Brazil, between June 1997
and May 1998
9
0
10
1
11
0
12
0
13
2
14
7
15
17
16
26
17
25
18
22
19
22
20
4
21
2
22
2
Total
130
Average Lt 16.63
Annulus 2
5
19.5
Total length (cm)
Lt (cm)
Annulus 1
35
n = 234
20
0
0.0
100
0.5
1.0
1.5
2.0
2.5
Annulus 3
80
60
40
20
n = 136
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
30
Annulus 4
25
20
15
10
n = 56
5
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
10
Annulus 5
8
6
4
n = 18
2
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Distance from the focus to the annulus (mm)
Fig. 4. Frequency distributions of distances from the scale focus to each
growth annuli of Paralonchurus brasiliensis females captured at Cidreira
fishing pier, Rio Grande do Sul, Brazil, between June 1997 and May 1998
Maturity and growth of Paralonchurus brasiliensis
97
26
Fish total length (cm)
24
n = 603
22
20
18
16
14
12
10
1
1.5
2
2.5
3
3.5
4
4.5
Distance from the scale focus to the scale border (mm)
Fig. 5. Relationship between fish total length and the distance from
the scale focus to the scale edge of Paralonchurus brasiliensis females
captured at Cidreira fishing pier, Rio Grande do Sul, Brazil, between
June 1997 and May 1998
To evaluate the effects of selective capture with hook-andline sport fishing, we compared the mean distance from the
focus to the first annulus in individuals with only one annulus
(D1 ¼ 1.97 mm) to that of individuals with two or more
annuli (D1 ¼ 1.38 mm). A significant difference was identified
(t ¼ 13.57; P < 0.001), suggesting selective capture or
selective mortality (Lee Phenomena). Working with the first
hypothesis (selective capture), only individuals with two or
more annuli were considered in back-calculation procedures.
Frequency distribution of the distance from the focus to
each scale annulus presents a mainly unimodal pattern
(Fig. 4), although polymodality (annulus 2) or asymmetry
(annuli 4 and 5) were also observed, suggesting interpretation
errors in reading scales. To minimize the effects of scale
misreading, we chose to use the pivotal point of the most
frequent class interval instead of employing the mean values of
all focus/annulus distances.
Figure 5 shows the relationship between TL (Lt) and the
distance from the focus to the edge of the scale (Dt). This
relationship is described by the equation: L ¼ 9.22 ·D0.633
(r ¼ 0.796; n ¼ 603), showing a negative allometric growth
of TL in relation to scales (or positive of the scales in relation
to TL) as the allometric coefficient is significantly smaller than
one (b ¼ 0.633 ± 0.0385).
Table 2 summarizes growth data from direct measurement
of females with ÔnÕ annuli and the estimated sizes from scale
data through back-calculation (Li ¼ 9.22 D0:633
). As can be
i
seen, very different growth stories can be told with different
data sets. A direct comparison with data from the northern
(SP) population (Yamaguti et al., 1973) suggests selective
capture by hook-and-line because of the larger size of animals
presenting one or two annuli. On the contrary, the compressed
Table 2
Number of scale annuli, scale length
and estimated total length (TL) of
Paralonchurus brasiliensis females in
southern Brazil
range of lengths by back-calculation points to selective size
mortality (Lee Phenomena).
Using back-calculation data, considering a spring/summer
reproduction and a winter annulus formation, different ages
(tf) were simulated as the age of first annulus formation
(Table 3). Best statistical results (little residual variance, S2,
equation 10) were obtained when the estimated age of first
annulus formation was 1.5 years. This result implies a lack of
visible annuli from the first winter of life.
Table 4 and Fig. 6 present the relationships between the
estimated growth constant (k, equation 5), residual variance
(S2, equation 6) and estimated longevity (A0.95, equation 7) for
different values of the asymptotic length (Linf).
It can be observed when the asymptotic length values
increase from 19.0 cm that the residual variance values show a
substantial decrease, reaching its minimum value (S2 ¼ 0.054)
at the asymptotic length of 20.0 cm. From 20.0 cm on, the
residual variance again has a relevant increase. Best fit is then
obtained with an asymptotic TL of 20 cm, resulting in a
growth constant (k) of 0.535 and a longevity (A0.95) of
5.6 years (67 months). Thus, the mathematical expression of
the length growth curve is (TL in cm, age in years; Fig. 7):
Lt ¼ 20.0(1 ) e)0.535·t). By using Yamaguti et al. (1973) data
for the northern (SP) population of P. brasiliensis (Table 2,
Fig. 7), best fit to the von Bertalanffy growth model
(S2 ¼ 0.114) was either obtained when the average age of
animals presenting just one annuli was 2 years old (first annuli
formation at 1.5 years), resulting in an asymptotic length (Linf)
estimate of 25.5 cm, growth constant (k) equal to 0.340 and
longevity (A0.95) of 8.8 years. For growth pattern comparison,
Fig. 7 also presents a plot of the von Bertalanffy growth curve
as estimated by Braga (1990).
The relationship between total weight (g) and TL (cm) is
described by the equation (Fig. 8): Wt ¼ 0.00224 L3:52
t
(r ¼ 0.98; n ¼ 627). According to the allometric coefficient
of the weight/length relationship (b ¼ 3.52 ± 0.055),
P. brasiliensis females present an allometrically positive
growth. Applying the weight/length relationship to the length
growth curve, the weight growth curve is then described by the
equation (weight in g, age in years): Wt ¼ 85.1(1)e)0.535·t)3.52.
Discussion
No P. brasiliensis male was captured on the Cidreira fishing
pier, suggesting a differential habitat occupation related to sex,
males not being present in shallow waters (or at least not
susceptible to hook-and-line). Haimovici (1998) pointed out
that P. brasiliensis capture on the Brazilian southern continental shelf takes place in depths of up to 50 m, although with
decreasing frequencies at trawling depths >20 m. Haimovici
Number of
scale annuli
Average distance
from scale
focus to each
annulus (mm)
Estimated TL by
back-calculation
at moment of annuli
formation (cm)
Average female
TL with ÔnÕ
annuli (cm)
Average female
TL with ÔnÕ annuli
(cm) according to
Yamaguti et al.
(1973), SP population
1
2
3
4
5
6
1.37
2.12
2.62
2.87
3.12
–
11.25
14.84
16.96
17.97
18.95
–
16.63
17.32
18.05
19.36
19.88
20.52
12.6
15.6–16.7
18.9–19.5
20.3–20.7
–
23.3
98
D. dos S. Lewis and N. F. Fontoura
Table 3
Parameters of von Bertalanffy growth formulae for Paralonchurus
brasiliensis females in southern Brazil and residual variance with
different simulated ages for first annulus formation
Linf (cm)
k
Residual
Variance
Longevity
(A0,95, years)
0.5
1.5
2.5
19
20
22.5
1.170
0.535
0.294
5.175
0.054
0.306
2.6
5.6
10.2
20
Total length (cm)
Age at first annulus
formation (tf, years)
25
Mean total length of aged
females according YAMAGUTI
et al. (1973), SP population.
Calculated length to age
according BRAGA (1990), SP
Population.
Mean total length (our data)
estimated by back-calculation at
the moment of annuli formation.
Estimated von Bertalanffy
growth curve from our data.
15
10
5
Longevity estimate defined as the time (years) to attain 95% of the
asymptotic length. Data that result in the best fit are printed in bold
italics.
0
0
1
2
3
4
5
6
7
8
Age (years)
Table 4
Parameters of von Bertalanffy growth formulae for Paralonchurus
brasiliensis females in southern Brazil and residual variance with
different simulated asymptotic lengths and first annulus formation at
age 1.5 years
Linf (cm)
k
Residual variance
Longevity (A0.95, years)
19
20
21
22
23
24
25
26
27
28
0.714
0.535
0.465
0.417
0.380
0.350
0.325
0.303
0.285
0.269
1.446
0.054
0.518
1.266
2.169
3.167
4.224
5.315
6.422
7.533
4.2
5.6
6.4
7.2
7.9
8.6
9.2
9.9
10.5
11.1
Fig. 7. Length growth curve of Paralonchurus brasiliensis females
captured at Cidreira fishing pier, Rio Grande do Sul, Brazil, between
June 1997 and May 1998. For comparison purposes, age to length data
available in the literature is also presented
180
Fish total weight (g)
160
140
n = 627
120
100
80
60
40
20
0
10
0.9
8
0.8
7
0.7
6
0.6
5
0.5
4
0.4
3
0.3
0.2
0.1
Variância residual
2
k (annual)
1
Longevity (A0.95)
k (annual) – Residual variance
Longevity estimate defined as the time (years) to attain 95% of the
asymptotic length. Data that result in the best fit are printed in bold
italics.
Longevidade (A0.95)
0
18.5
19.0
19.5
20.0
20.5
21.0
21.5
22.0
0
22.5
Asymptotic total length (cm)
Fig. 6. Estimated values of the growth constant (k), longevity (A0.95)
and residual variance in relation to simulated values of the asymptotic
lengths (Linf) of Paralonchurus brasiliensis females. Data from fish
captured at Cidreira fishing pier, Rio Grande do Sul, Brazil, between
June 1997 and May 1998. Parameters adjusted by MiniVar file
(Microsoft Excel, N. F. Fontoura, 2002, unpubl. data)
(1998) did not mention the species sexual proportion as a
function of depth levels, thus this aspect of P. brasiliensis
biology deserves further investigation.
An interesting pattern relative to the reproductive period of
P. brasiliensis came from a comparison of the present study
with previous studies. On northern populations (SP population), the estimated reproductive period of the species is from
July to September (Vazzoler et al., 1999) or from August to
December (Paiva Filho and Zani-Teixeira, 1980). For the
12
14
16
18
20
22
24
26
Fish total length (cm)
Fig. 8. Weight/length relationship of Paralonchurus brasiliensis
females captured at Cidreira fishing pier, Rio Grande do Sul, Brazil,
between June 1997 and May 1998
southern population (RS population) Oliveira and Haimovici
(2001) identified, by GSI monthly variation, a reproductive
period from September to March, very similar to the pattern of
the present work. Considering an annual cycle, populations
closer to the equator usually start to reproduce first; this may
also be the case with P. brasiliensis. Nevertheless, a longer
reproductive period for populations at higher latitudes is not
the usual pattern rule for species with extended latitudinal
ranges. A longer reproductive period in the southern population of P. brasiliensis is also corroborated by the presence of
larvae (<3 mm) in spring, summer, and autumn (Ibagy and
Sinque, 1995). These results indicate the necessity for new
comparative studies between northern (SP) and southern (RS)
populations of P. brasiliensis, as the selective forces driving the
reproductive biology of both populations are quite different.
Available information (Paiva Filho and Zani-Teixeira, 1980;
Vazzoler, 1999) indicate that P. brasiliensis start to reproduce
first in the northern population, possibly due to high water
temperatures. On the contrary, increased natural productivity
on the Rio Grande do Sul coast, because of subtropical
convergence and summer upwelling (Garcia, 1998), may be
contributing to an extended reproductive period of the
southern population.
Opaque growth annuli in P. brasiliensis scales are formed in
the winter, between July and August. Such a pattern is
frequent for fish of temperate regions, being related to a
decrease in the growth rate because of low temperatures. The
von Bertalanffy growth function applied to aged animals
Maturity and growth of Paralonchurus brasiliensis
(Yamaguti et al., 1973) and back-calculation from scale annuli
(our data) of P. brasiliensis resulted in best fit (minimum
residual variance) when the age of the first annuli was
simulated at 1.5 years. For most of the temperate species,
annuli start to be formed in the first winter, although Lentsch
and Griffith (1987) had reported a lack of first-year annuli on
scales of salmonids.
The largest specimen of P. brasiliensis captured off the
Cidreira fishing pier was a female of 23.6 cm TL presenting
five annuli in the scales. Although 29 and 30 cm TL had been
recorded (Menezes and Figueiredo, 1980; Kotas, 1998),
according to Vazzoler et al. (1973) and Braga (1990) through
the analysis of commercial fishery data both from São Paulo
and Rio Grande do Sul populations, no individuals larger than
25 cm were captured.
Available literature points out that the estimated value of
20 cm for the asymptotic length is clearly undersized. This
pattern can result from back-calculation when there is size
selective mortality (Lee Phenomena), when due to natural
causes, or more frequently due to fishery, there is an increased
mortality of the larger fish of the same age-group. This may be
the case for the P. brasiliensis southern population as a result
from by-catch mortality as reported by Kotas (1998).
Estimates of size at first maturation were similar in several
papers: 15.7 (SP pop., Vazzoler et al., 1973); 14.8 (RS pop.,
Paiva Filho et al., 1976), 16.8 (RS pop., Oliveira and Haimovici, 2001), and 15.4 cm (present work). The largest discrepancy was obtained by Paiva Filho et al. (1976) for the northern
population, where females presented an estimated 18.0 cm
mean size at first maturation. Comparing size at first maturation with age and growth data (Table 2; Fig. 7), P. brasiliensis
starts reproduction in the spring when completing 3 years of
life (two growth annuli, estimated TL from 14.7 to 16.3 cm on
the three different growth curves). This pattern does not
apparently differ from other South Atlantic sciaenids, as
reported by Haimovici (1997); maximum sizes (inside parentheses) recorded by Menezes and Figueiredo, 1980: Micropogonias furnieri (60 cm) and Cynoscion striatus (50 cm), 3 years;
Umbrina canosai (40 cm), 2 years; and Macrodon ancylodon
(45 cm) at 1 or 2 years. The problem is that species that first
reproduce at 3 years are significantly larger than P. brasiliensis;
other larger species seem to reproduce even earlier. Furthermore, why start to reproduce at 3 years when maximum
recorded age is 6–7 years and longevity (A0.95) is estimated as
5.6 years? The explanation might be associated with a
remarkable fecundity increase related to female size, so that
delaying reproduction for 1 year can be overcompensated by
more egg production the following year. Paiva Filho and Rossi
(1980) reports the fecundity/length relationship for the species,
fecundity increasing at a power of 5.3. This figure suggests that
for P. brasiliensis it could be an advantage to reproduce later,
saving energy to grow and reducing mortality related to
reproductive stress, compensating delayed maturation by
increased egg production. This hypothesis nevertheless remains
to be confirmed, since a direct analysis of fecundity was not
done in the present work.
Paralonchurus brasiliensis presents a sexually related distribution pattern, with males not being captured near the
shoreline. The southern population has a long reproductive
period, from August to March, with greater activity from
October to February. Scale annuli formation is annual and
occurs during the winter, the first visible annuli being formed
at age 1.5 years. The estimated asymptotic length (Linf) as
20 cm and instantaneous growth rate (k) as 0.535 are probably
99
biased as a result of size-related fishing mortality (Lee
Phenomena). A maximum of six growth annuli was found
on scales; longevity A0.95 was estimated as 5.6 years. Females
reach first maturation with 15.4 cm, presenting two annuli on
the scales and a presumed age of 3 years.
Acknowledgements
The authors thank Dr Manuel Haimovici and Dr Jorge P.
Castello for their valuable suggestions to the present work.
Thanks also to the staff of the Cidreira fishing pier for their
cooperation and incentives during this research.
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Author’s address: Nelson Ferreira Fontoura, Laboratório de Dinâmica, Populacional Aplicada a Ecossistemas
Aquáticos, PUCRS – Av Ipiranga 6681, Porto
Alegre, RS, CEP 90619-900, Brazil.
E-mail: [email protected]