BULLETIN OF MARINE SCIENCE, 69(3): 1109–1119, 2001
GROWTH AND MORTALITY OF THE BIGMOUTH SOLE,
HIPPOGLOSSINA STOMATA EIGENMANN & EIGENMANN 1890
(PISCES: PARALICHTHYIDAE), OFF THE WESTERN COAST OF
BAJA CALIFORNIA, MEXICO
Marco A. Martínez-Muñoz and A. A. Ortega-Salas
ABSTRACT
Data on growth and mortality were obtained for bigmouth sole, Hippoglossina stomata, collected with otter trawls during 10 cruises off the western coast of Baja California, Mexico, from April 1988 to December 1990. In all, 1115 bigmouth sole were caught
and, over the sampling period, in 298 specimens the male to female ratio was 1:1.03. The
relationship between weight and length is described for females by W = 0.00000538
SL3.21054 and for males by W = 0.0001963 SL2.48525. Age-groups were estimated from length
frequency data, von Bertalanffy growth parameters for all fish combined were the following: L• = 341.34 mm SL, k = 0.1757, t0 = -0.9835; for males, L• = 308.53 mm SL, k
= 0.205, t0 = -0.6812, annually; and for females, L• = 359.43 mm SL, k = 0.1924, t0 = 0.769, annually. Males were smaller than females. The age groups allowed to determine
a total mortality (Z) rate of 0.69, and estimate the fishing mortality (F) of 0.52 and natural
mortality (M) of 0.17. Although the bigmouth sole is not a target species of commercial
fisheries, it suffers high mortality as part of the bycatch in the shrimp fishery.
Off the western coast of Baja California, flatfishes are the most abundant soft-bottom
fishes caught in otter trawls (Martínez-Muñoz and Ramírez-Cruz, 1992). They are an
important component of the shrimp fishery bycatch and constitute an important fisheries
resource (Castro-Aguirre et al., 1992; Balart, 1996).
The bigmouth sole, Hippoglossina stomata (Family Paralichthydae) is one of the more
common species, it lives on sandy substrata from Monterey Bay, California, to the northern Gulf of California (Allen and Herbinson, 1991; Hensley et al., 1995). It is usually
found in depths of 30 to 237 m (Martínez-Muñoz and Ramírez-Cruz, 1992). Bigmouth
sole are relatively small, reaching a maximum total length of 40 cm (Eschmeyer et al.,
1983) although fish longer than 35 cm are rare. Larger bigmouth soles could be of commercial importance due to the excellent quality of their meat (Balart, 1996).
Bigmouth sole first mature at about 162 mm total length. It is a summer-fall spawner.
This species preys on mysids and gammaridean amphipods (Allen, 1982) as well as pelagic red crab, Pleuroncodes planipes (Ramírez-Murillo et al., 1998).
Ramírez-Murillo (1995) estimated age and growth parameters for bigmouth sole off
the West coast of Baja California, and presented an otolith reading interpretation by the
marginal-increment analysis. No data on mortality were available.
The purpose of this paper is to provide information on the growth and mortality of
bigmouth sole populations in the Mexican Pacific Ocean at Baja California, Mexico, for
use in managing this species as a fishery resource.
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MATERIALS AND METHODS
Fishes were collected from April 1988 to December 1990 from 165 otter trawls conducted during the course of 10 cruises aboard the BO EL PUMA and BI MARSEP XVI.
The 34 sampling stations were located off the West coast of Baja California, from Boca del
Carrizal (23∞00'N) to Sebastian Vizcaino Bay (28∞51'N) in depths of 10 and 250 m (Fig. 1). The
bottom temperature varied between 11 to 19oC. All fish were collected using an otter trawl that
measured 20 m wide and 9 m high at the mouth, 24 m in length, with a stretched mesh size of 3 cm
and code mesh of 1.5 cm.
Trawling time and speed were recorded to estimate the area swept by the net. Trawling speed
ranged between 1.1 and 1.5 m s–1. Trawls were towed for 30 min along isobaths (10 to 250 m).
Specimens of bigmouth sole were measured, to the nearest millimeter standard length (SL),
weighed to the nearest gram and sexed visually immediately after being caught. The gonads were
examined macroscopically using the staging criteria of Nikolsky (1963). These data were used to
calculate length-weight relationships, varying the logarithmic form of the equation: W = aLb for
each sex, where W is weight in grams, a is the y-intercept, SL is standard length in millimeters, and
b is the slope calculated with FISAT software (Gayanilo et al., 1994).
Length frequency histograms of bigmouth sole were used to find the age-groups by the modal
progression of Petersen (1939) method to start with, then the FISAT software was used to accurate
Figure 1. Trawl stations sampled off Baja California, Mexico, 1988–1990, at depths of 10 to 250 m.
MARTÍNEZ AND ORTEGA: GROWTH AND MORTALITY OF THE BIGMOUTH SOLE
1111
Figure 2. Length frequency distributions showing population structure of bigmouth sole,
Hippoglossina stomata, during 1988–1990.
the age-groups from the length frequency scattergram as seen in Fig. 5. Mean lengths for age
groups were fitted using the von Bertalanffy (1938) equation Lt = L•(1-exp-k (t-to)); Ford (1933) and
Walford (1949) methods by FISAT software were used to describe theoretical growth and growth
parameters where Lt = standard length of fish at t years, L• = theoretical asymptotic length, k =
growth coefficient rate of approach to L•, t0 = theoretical age at which Lt = 0. LFDA (Length
Frequency Distribution Analysis ver 3.1), Holden and Bravington (1992), and Ortega-Salas (1981)
basic programs were also used.
Estimation of the instantaneous total mortality rate (Z) was calculated by the Beverton and Holt
(1959) catch curve method described in Ricker (1975) using the FISAT software, based on all
fishes ≥3 yrs of age. The difference between the total mortality coefficient (Z), which includes
migration, and the natural mortality coefficient (M) gave an estimate of fishing mortality (F): F =
Z-M. Although bigmouth sole is considered an exploitable species, its natural mortality (M) was
estimated as an index from the rate of growth (k) as described by Beverton and Holt (1959).
RESULTS
Fishes from all trawls were combined, so that 1115 bigmouth soles, ranging in size
from 55 to 290 mm SL and weights from 2.9 to 429 g were registered. From 298 fishes,
145 (48.65%) were females, 137 (45.97%) were males, and the sex of 16 (5.36%) was
undetermined; hence, the female to male ratio was 1:1.03. A chi square test showed no
seasonal difference in numbers of females relative to males (c2 = 0.2268; df = 1; P < 0.01).
As with most flatfish, females were considerably larger in length and weight relative to
males (Figs. 2,3). The largest female measured 290 mm SL and weighed 429 g, compared
with 223 mm and 189 g, respectively, for the largest male. The mean values for females
were 160.5 mm SL ± 42.6 SD and 80.7 g ± 63.9 SD weight, and males 142.7 mm SL ±
35.3 SD and 55.1 g ± 41.5 SD, respectively (Table 1). Use of a t-test and mean differences
revealed no significant difference between sexes according to the mean length was 17.78;
confidence interval (CI) was 95%; df = 280; t = 3.80; and significance level = 1.76 ¥ 10-4 at
P< 0.05, not even mean weight revealed significant differences between sexes was 25.65;
CI = 95%; df = 280; t = 3.96; and significance level = 9.15 ¥ 10-5.
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BULLETIN OF MARINE SCIENCE, VOL. 69, NO. 3, 2001
Figure 3. Weight frequency distributions showing population structure of bigmouth sole,
Hippoglossina stomata, during 1988–1990.
Length and weight were closely correlated with the determination coefficients ranging
from 0.96 in females to 0.74 in males (Fig. 4). The slope shows that females are heavier
than males for the same length.
Age-groups were estimated from the length frequency scattergram of the bigmouth
sole and the von Bertalanffy parameters calculated are the following: L• = 341.34 mm
SL, k = 0.1757, t0 = -0.9835 as shown in Figure 5.
Theoretical growth of males and females of the bigmouth sole is shown in Figures 6
and 7. After age 3 (210 mm), females were consistently longer and heavier than males
due to differences in reproductive condition or general robustness of fish, although the
rate of growth (k) for the two sexes was similar. Females attained an older age and longer
length than males.
The growth rate of the different age-groups (4 yrs and older) declined with age. Assuming no size- or age-selective catchability, the mean annual total mortality was calculated
as Z = 0.69 and, apparently, constant for the age-groups considered (Fig. 8). Age-groups
0 to 2 were excluded because of poor efficiency of the sampling net for the smaller fishes.
Hence, the natural mortality coefficient (M) according to Beverton and Holt (1959) was
estimated as 0.17. The estimated mortality rates were the following: Z = 0.69; M = 0.17;
F = 0.52, where F = 0.52 is an estimate for fishing mortality.
Table 1. Weight and standard length data of bigmouth sole, Hippoglossina stomata, males and
females.
Sex
Females
Standard length (mm)
Weight (g)
Males
Standard length (mm)
Weight (g)
n
Minimum Maximum
Mean
SD
145
55
2.9
290
429
160.4
80.7
42.6
63.9
137
55
2.9
223
189
142.7
55.1
35.3
41.5
MARTÍNEZ AND ORTEGA: GROWTH AND MORTALITY OF THE BIGMOUTH SOLE
1113
Figure 4. Length-weight relationships of male and female bigmouth sole, Hippoglossina stomata,
from Baja California. Scatter of points are from 1115 fish.
Figure 5. Length frequency scattergram of the bigmouth sole, Hippoglossina stomata, to find the
age groups.
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Figure 6. Growth curve of female and male bigmouth sole, Hippoglossina stomata, in standard
length, showing standard dispersion error at 95% confidence.
Figure 7. Weight curve of female and male bigmouth sole, Hippoglossina stomata, showing the
standard dispersion error at 95% confidence.
MARTÍNEZ AND ORTEGA: GROWTH AND MORTALITY OF THE BIGMOUTH SOLE
1115
Figure 8. Catch curve for bigmouth sole, Hippoglossina stomata, caught off Baja California, Mexico.
The curve is slightly nonlinear but regression analysis suggests a value of Z = 0.69. The FISAT
program was used.
DISCUSSION
The sex ratio in the flatfish species is generally 1:1 (Kramer, 1991; Minami and Tanaka,
1992) as found in this paper.
Ramírez-Murillo (1995) calculated age in bigmouth sole by the Cassie method (1954)
and by reading otoliths (Table 2), which compared with the present results of L• = 341.34
mm SL, k = 0.1757, t0 = -0.9835, reveal a bigger L•, possibly because maximum lengths
were of 290 mm SL, compared with their measurement of 258 mm SL, although the rate
of growth (k) was similar; in both papers a maximum age of 9 to 10 yrs has been estimated.
Few previous studies on the biology of the bigmouth sole exist; hence, the growth and
mortality parameters estimated here can only be compared to those obtained from studies
made in other flatfish species (Tables 3,4).
Growth of the bigmouth sole shows the same features as other flatfishes: females growing
faster than males, adult females being heavier (La = 359.43 mm SL) than males for the
same length (La = 308.53 mm SL).
In comparison with other flatfish species for which growth data are available, the growth
rate of the bigmouth sole is comparatively high and the species attains a size large enough
for commercial exploitation at 3 yrs.
Table 2. Growth parameters of bigmouth sole, Hippoglossina stomata by Cassie method and by
reading otoliths in 1990. Taken from Ramí rez-Murillo (1995).
Growth
parameters
L•
k
t0
March
426.4
0.004
-3.91
Cassie method
September
392
0.004
-4.99
Otoliths reading
December
226
0.0009
-2.42
289.09
0.184
-0.209
Location
Baja California,
Mexico
Baja California,
Mexico
Diamond turbot, Hypsopsetta guttulata Anaheim Bay,
USA
Dover sole, Microstomus pacificus
Northern
California, USA
Pacific sanddab, Citharichthys sordidus Southern
California, USA
Starry flounder, Platichthys stellatus
Monterrey Bay,
USA
Bigmouth sole, Hippoglossina stomata Baja California,
Mexico
Bigmouth sole, Hippoglossina stomata
Species
Fantail sole, Xystreurys liolepis
L• (mm)
443.00 SL
354.85 SL
444.68 SL
289.09 SL
198.50 SL
431.49 LT
494.58 LT
294.80 LT
297.50 LT
443.44 SL
592.86 SL
341.34 SL
308.53 SL
359.43 SL
Sex
Combined
Male
Female
Combined
Combined
Male
Female
Male
Female
Male
Female
Combined
Male
Female
Table 3. Comparison of the von Bertalanffy parameters in seven different flatfish species.
0.294
0.241
0.244
0.317
0.441
0.281
0.1757
0.205
0.192
0.10
0.16
0.151
0.163
0.1843
k
Source
Martí nez-Muñoz and Ortega-Salas (1999)
0.540
0.753
-0.98
-0.336
0.42
0.33
-0.983
-0.681
-0.769
0.31
Present Paper
Orcutt (1950)
Arora (1951)
Hagerman (1952)
Lane (1975)
-0.098
-0.918
-0.423
0.2096 Ramí rez-Murillo (1995)
t0
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MARTÍNEZ AND ORTEGA: GROWTH AND MORTALITY OF THE BIGMOUTH SOLE
1117
Table 4. Comparison of total mortality (Z) in five different flatfish species.
Species
Diamond turbot,
Hypsopsetta guttulata
Dab,
Limanda limanda
Lepidorhombus boscii
Fantail sole,
Xystreurys liolepis
Bigmouth sole,
Hippoglossina stomata
Location
Anaheim Bay,
USA
Isle of Man, UK
Portuguese Coast,
Portugal
Baja California,
Mexico
Baja California,
Mexico
Z
2.6
M: 1.39
F: 1.06
0.45
0.62
0.69
Source
Lane (1975)
Ortega-Salas (1981)
Santos (1994)
Martí nez-Muñoz and
Ortega-Salas (1999)
Present paper
The age composition for both sexes of the same stock are clearly different and males
generally have a shorter life span than females. Thus, whereas males dominate the younger
age-groups, females are more abundant in the older groups.
The values obtained for annual total mortality, Z = 0.69, natural mortality, M = 0.17,
and fishing mortality, F = 0.52, are first estimations for the bigmouth sole population
from the western coast of Baja California. In spite of the consistency among those age
classes included, the mortality should be further investigated, especially with respect to
the younger age classes and by using direct methods.
Off the western coast of Baja California, a high fishing mortality of flatfishes, including bigmouth sole, occurs resulting from intensive trawl fishing for shrimp according to
Ehrhardt et al., (1982); van der Heiden et al., (1985). Although bigmouth sole is not a
target species of commercial fisheries, the rate of fishing mortality is higher than natural
mortality, possibly due to the large bycatch of flatfishes, including California halibut
(Paralichthys californicus), Fantail sole (Xystreurys liolepis), Longfin sanddab
(Citharichthys xanthostigma), Fourspot sole (Hippoglossina tetrophthalma), Spotted turbot (Hypsopsetta guttulata) and California tonguefish (Symphurus atricauda), among
others, in the shrimp fishery.
The bigmouth sole is considered a potentially exploitable flatfish but needs to be managed as a fishery resource.
ACKNOWLEDGMENTS
This study was partially supported by the Consejo Nacional de Ciencia y Tecnología de México
(CONACyT), grant P22OCC0R880518, and the Universidad Nacional Autónoma de México, which
provided the BO EL PUMA from 1988 to 1991. We also thank the Instituto de Ciencias del Mar y
Limnología (UNAM) for analyzing the data and the Centro de Investigaciones Biológicas del
Noroeste for processing the raw material. And to A. Nuñez and R. Ramírez for their collaboration.
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DATE SUBMITTED: August 10, 2000.
DATE ACCEPTED: June 12, 2001.
ADDRESSES: (M.A.M.-M.) Unidad Profesional Interdisciplinaria de Ingeniería y Ciencias Sociales y
Administrativas, I.P.N. Hocaba esq. Hopelchen Manz-353 L-1. Torres de Padierna. C.P. 14200, Mexico,
D.F., Mexico. E-mail: <[email protected]>. CORRESPONDING AUTHOR: (A.A.O.-S.) Instituto
de Ciencias del Mar y Limnología, UNAM, Apdo.Postal 70-305, México 04510, D.F., Mexico. E-mail:
<[email protected]>.