Revista de Ciencias del Mar y Acuicultura “YAKU”: Vol. 7 (Núm. 12) (ene – jun 2024). ISSN: 2600-5824.
Research Article/Artículo de Investigación DOI: https://doi.org/10.56124/yaku.v7i12.002
14
BIOLOGICAL AND FISHERY ASPECTS OF HAKE (MERLUCCIUS
GAYI, GUICHENOT, 1848) CAUGHT BY TRAWL NETS IN THE GULF
OF GUAYAQUIL, ECUADOR
ASPECTOS BIOLÓGICOS Y PESQUEROS DE LA MERLUZA
(MERLUCCIUS GAYI, GUICHENOT, 1848) CAPTURADA CON RED DE
ARRASTRE EN EL GOLFO DE GUAYAQUIL, ECUADOR
José Washington Toledo Delgado
1,*
1
Facultad de Ciencias Naturales, Universidad de Guayaquil, Ecuador
*
Autor correspondencia: josetol33@hotmail.com
Abstract
Resumen
Fishery resources face challenges such as
overexploitation, data scarcity, and climate change,
highlighting the need to implement research strategies for
effective management. Hake is crucial among Ecuador's
fishery resources, thus periodic assessments of its status
are essential. The size composition of Merluccius gayi
caught with trawl nets in the industrial fishery was
analyzed, as well as the capture size and its relationship
with the size at sexual maturity, to provide a baseline for
future studies and applications in the management of this
fishery. Samples were obtained from landings in Puerto
Bolívar, Province of El Oro, Ecuador, during November
2014 to March 2015. A total of 574 individuals were
analyzed, with average capture size of 34.93 and 38.92 cm
LT for males and females, respectively. The size-weight
relationship showed a negative allometric growth for
males and females, with exponent (b) of 2.30 and 2.55,
respectively. It was observed that, with an 8.9 cm mesh
size in the codend, the males’ Lr50 was 34.35 cm LT,
which was less than the ASM of 34.75 cm LT. For
females, the Lr50 (37.97 cm) was greater than the ASM
of 37.28 cm. This shows the importance of analyzing
gender information separately during the evaluation of
fishing gear.
Key words: Gulf of Guayaquil, mesh size, trawl fishing,
average size at maturity.
Los recursos pesqueros enfrentan desafíos tales como la
sobreexplotación, la escasez de datos y el cambio climático, lo
cual enfatiza la necesidad de implementar estrategias de
investigación para una gestión efectiva. La merluza es crucial
dentro de los recursos pesqueros de Ecuador, por lo tanto, es
fundamental realizar evaluaciones periódicas de su estado. Se
analizó la composición de tallas de Merluccius gayi, capturada
con redes de arrastre en la pesquería industrial, así como la talla
de captura y su relación con la talla de madurez sexual, para
proporcionar una línea base para futuros estudios y aplicaciones
en la gestión de esta pesquería. Las muestras fueron obtenidas
de los desembarques realizados en Puerto Bolívar, Provincia de
El Oro, Ecuador, durante noviembre 2014 a marzo del 2015. Se
analizaron un total de 574 individuos, con talla media de
captura de 34.93 y 38.92 cm de LT para machos y hembras,
respectivamente. La relación talla-peso mostro un crecimiento
alométrico negativo para machos y hembras, con exponente (b)
de 2.30 y 2.55, respectivamente. Se observó que, con una luz
de malla de 8,9 cm en el copo de la red, la Lr50 de machos fue
34,35 cm LT, la cual resultó menor a la Talla Media de Madurez
(TMM) de 34,75 cm LT. Para las hembras, la Lr50 (37,97 cm)
fue mayor a la TMM 37,28 cm. Esto evidencia la importancia
de analizar por separado la información por sexos durante la
evaluación de artes de pesca.
Palabras clave: Golfo de Guayaquil, luz de malla, pesca de
arrastre, talla media de madurez.
Recibido: 2024-05-23 Aceptado: 2024-06-18 Publicado: 2024-06-27
Revista de Ciencias del Mar y Acuicultura “YAKU”: Vol. 7 (Núm. 12)
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1. Introduction
Merluccius gayi (Guichenot, 1848) is a species in
the family Merlucciidae that inhabits coastal and
oceanic areas, as well as epipelagic and
mesopelagic regions, at depths of 50 to 614 m. It
forms dense shoals from Ecuador to Peru,
including the Galapagos Islands (Hernández-
Téllez et al., 2024).
The south Pacific hake M. gayi, is present in the
coast of Ecuador between latitudes 1° and 4° S, in
depths ranging from 30 to 614 m (García et al.,
2014). The species was first recorded in
Ecuadorian waters in March 1965 (Bourgois,
1966), but it was not exploited for several
decades, possibly because the different fishing
gears in use by that time did not reach the depths
where the resource was located. Starting in the
1990s, technical documents related to the local
hake fishery are published within the category of
Class C demersal fish, i.e. low commercial value,
categorization suggested by Contreras and Revelo
(1992).
Martínez and Madirolas (1991) conducted studies
in Ecuador on hake biomass in the Gulf of
Guayaquil and estimated it in 18 046 ton, as well
as a maximum precautious catch of 2000 t per
year. This allowed them to establish that the
potential catch did not justify the development of
an industrial fishery, but instead an artisanal one
for direct human consumption at the local and
national levels. Other authors who conducted
studies on hake were: Villón et al. (1992); Revelo
(1994, 1995); Herrera and Zambrano (1998);
Herrera et al. (1998); Peralta (1999); Herrera et al.
(2010); Coello et al. (2017).
These studies enabled the Undersecretariat of
Fishery Resources (SRP) in cooperation with the
Ministry of the Environment of Ecuador and the
Ministry of Marine Rural Environment of Spain,
to carry out three fishery research campaigns on
the Ecuadorian continental platform and slope,
from where a total biomass of 340 559 t of M. gayi
was estimated (INP 2018). And since 2013, it has
been industrially exploited as an alternative to
shrimp trawling and shallow water fishing
(García et al., 2014).
Knowledge of reproductive aspects, such as the
average size at sexual maturity, are topics relevant
to understand the basic biology of the resource,
and for the use of stock assessment methods
(Mawa et al., 2021; Parker 1985; Rahman &
Samat, 2021), allowing to determine the
reproductive potential and biological
characteristics of exploited populations (Williams
2007).
The efficiency of fishing gear in capturing fish
according to their size is crucial for implementing
effective management strategies in fisheries
(Sparre and Venema, 1997). It is essential to
assess whether a fish can escape through or
become trapped in a mesh of specific dimensions,
as the dimensions of the mesh opening play a
critical role in fishing gear design (Reeves et al.,
1992). The design of fishing nets can significantly
impact the effectiveness of size selection. Ideally,
the mesh size should allow the release of all fish
smaller than a certain size (FAO, 1995; Yu et al.,
2023).
In this sense, this study aims to provide
information on the most relevant biological and
fishery aspects of the fishery of M. gayi captured
by the industrial trawl fleet operating in the Gulf
of Guayaquil, and to supply a baseline for future
studies on this fishery and its sustainable
management.
2. Materials and Methods
The study area was located in Puerto Bolívar,
province of El Oro at southern Ecuador (Figure
1). Samples were obtained during landings from
the fishing vessel "Elaine" between November
2014 and March 2015. The vessel performed
fishing activities off 8 nm from shore at depths 28
- 48 m within the Gulf of Guayaquil, from Puntilla
de Santa Elena to the border with Peru (02° 10' S-
81° 00' W; 03° 23' S-81° 00' W).
Revista de Ciencias del Mar y Acuicultura “YAKU”: Vol. 7 (Núm. 12) (ene – jun 2024). ISSN: 2600-5824.
Toledo, 2024.: Fishery Biology of Hake in the Gulf of Guayaquil
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Figure 1. Landing area where the samples of M. gayi were obtained.
The collected samples were taken to the
laboratory for morphometric analysis and
characterization of the
gonadal developmental stages of the specimens.
The total (TL) and standard lengths (SL) were
estimated with a digital ichthiometer with
precision 1 mm; the total weight (W) and that of
the other structures were estimated with a digital
balance of 0.1 g precision. The sex was
determined by macroscopic observations of the
gonads.
To compare whether the size frequencies between
males and females could be worked together, the
Kolmogorov-Smirnov statistical test was
performed under the null hypothesis that the size
frequency was similar for males and females. Sex
ratio was evaluated under the null hypothesis of
equal proportion (1M:1F) using the chi-square
test (χ2).
The length - weight ratio was established using
the allometric function (Ricker 1975):
(1)
where: W-total weight in g, TL-total length in cm,
a and b are regression constants. The values of a
and b were obtained by adjusting the linearized
equation as log10(W) = log10(a) + b log10(TL)
using the least squares method (Munro & Pauly,
1983). The value of the slope was contrasted with
3 using a Student’s t-test (Zar 2014), to establish
the type of growth of the species as: isometric
(b=3), negative allometric (b < 3) or positive
allometric (b > 3).
In order to calculate the retention length and
selection range (RS), the following equations
were used:
(2)
(3)
Where P is the percentage retained of each fish
size, a is the intercept, b is the slope, L the length
class and RS is the interval over which the fishing
gear makes selection.
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The ratio (1-P) / P is associated to the size or
length in which the fish have the same opportunity
to escape or be retained in the gear (50% chance
or Lr50), so that:
(4)
In order to calculate the selection factor (SF), the
following equation was used:
(5)
Where SF is the factor that describes the ability of
the fish to escape through the mesh, Lr50 is the
retention length of 50% and MS is the mesh size
(8.89 cm in the codend).
To obtain the selection curve, the models were
adjusted separately according to the sex to
compensate for the differences in composition by
size, as proposed by Queirolo et al. (2013).
The determination of the Mean Size at Sexual
Maturity (MSM) was made by macroscopic
cataloguing of the validated gonadal maturity
scale for hake (Merluccius gayi) (Perea et al.
1997). For estimating the MSM, a logistic
function was adjusted to the proportion of mature
individuals per size class, considering the
maturity stages III, IV and V, using the equation
proposed by King (1995):
(6)
Where P is the proportion of mature individuals
in each size Interval (L), L50 is the length at which
50% of individuals reach sexual maturity and r is
a constant.
3. Results
A total of 574 individuals were sampled, showing
a sex ratio of 1.65M:1H, with a significant
predominance of males (p < 0.001). Male sizes
ranged from 26 to 48 cm TL, and female sizes
ranged from 28 to 72 cm TL, with an average size
of 36.21 cm TL for combined sexes (Table 1). The
size structure differed significantly between the
sexes (Kolmogorov-Smirnov test; p < 0.05), so the
analyses that follow were processed separately by
sex (Figure 2).
Table 1. Statistical briefing of size frequency of M. gayi landed in Puerto Bolivar, El Oro Province,
Ecuador, between November 2014 and March 2015.
Sex
N
Min
Max
Average
SD
p
Males
358
26
48
34.93
3.65
<0,001
Females
216
28
72
38.32
6.05
<0,002
Sexes combined
574
26
72
36.21
4.98
<0,003
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Toledo, 2024.: Fishery Biology of Hake in the Gulf of Guayaquil
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Figure 2. Size frequency distribution of male and female M. gayi captured using codends with 8.9 cm
mesh size.
Length – weight relationship.
The length – weight relationship for males was W
= 0.084 TL 2.3018, r
2
= 0.79 (Figure. 3A), and for
females W = 0,035 TL2.5588, r
2
= 0.88 (Figure.
3B). The b exponents differed significantly
between sexes and were smaller than 3 (Student’s
t test, p < 0.05), so the growth of the species was
considered to be negative allometric.
Size at sexual maturity.
For estimating MSM, the gonads of 378
specimens were analyzed corresponding to 229
males and 149 females of M. gayi. For males, the
MSM was estimated in 34.75 cm TL, while for
females the MSM was 37.28 cm TL (Figure. 4)
and an average MSM of 36.02 cm TL for sexes
combined.
Selectivity of the trawl net.
To obtain the selectivity curve of the trawl, 574
size data were used, of which 358 corresponded
to males and 216 to females.From the male data,
the parameters obtained were a= 17.884, b=-
0.521, and a Pearson correlation coefficient (r) of
0.995 (p < 0.001). The catch size at which 50% of
the males were retained in the gear was Lr50 =
34.35 cm LT, with a selection range of 4.22 and a
net selection factor SF = 3.86.
For females, the estimated parameters were: a =
7.380, b = -0.194, Pearson correlation coefficient
r = 0.939 (p < 0.05), capture size Lr50 = 37.97 cm
LT, a selection range of 11.31 and a net selection
factor of SF = 4.27. For sexes combined, the
estimated parameters were a = 7.880; b = 0.220,
Pearson correlation coefficient r = 0.933 (p <
0.001), capture size Lr50 = 35.84 cm LT, a
selection range of 9.98 and a net selection factor
SF = 4.03 (Figure. 5).
0
20
40
60
80
100
120
140
160
180
27,5 31,5 35,5 39,5 43,5 47,5 51,5 55,5 59,5 63,5 67,5 71,5
Frecuency
Total length (cm)
Female
Male
n= 574
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Figure 3. Length – weight relationship of M. gayi landed in Puerto Bolivar, El Oro Province, Ecuador, from November 2014
to March 2015. A. Males. B. Females.
Figure 4. Mean size at sexual maturity (MSM) of M. gayi by sex, applying the logistic
model to the proportion of males and females by size. The intersections of vertical lines
with the abscissa axis show the MSM.
Considering the recommended mesh size (MS) in
the codend for the capture of M. gayi, values of
8.99 cm for males and 8.72 cm for females were
obtained, while for the combined sexes it was 8.93
cm (Table 2).
The capture size Lr50 34.35 cm TL for males
(Table 2), was less than the MSM (34.75 cm LT),
while the Lr50 of 37.97 cm TL for females (Table
2), was larger than their MSM (37.28 cm LT).
W = 0.0846Tl
2.3018
R² = 0.82
n= 358
0
100
200
300
400
500
600
700
800
900
- 10,0 20,0 30,0 40,0 50,0 60,0
Weigth (g)
Total length (cm)
A
W = 0.0353Tl
2.5588
R² = 0.90
n= 216
0
500
1000
1500
2000
2500
- 20,0 40,0 60,0 80,0
Weigth (g)
Total length (cm)
B
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Figure 5. Selectivity for size of males and females of M. gayi retained in the codend with
mesh size 8,9 cm. The intersections of vertical lines with the abscissa axis represent the
optimal capture lengths (L
50
).
Table 2. Selectivity parameters for males, females and sexes combined. L50 (length of first capture), SR (selection
range), SF (selection factor of net), a (y-axis intercept), b (slope), and MS (recommended mesh size, cm).
Group evaluated
a
b
L25
L50
L75
SR
SF
MS
Males
17.88
0.52
32.24
34.35
36.46
4.22
3.86
8.99
Females
7.38
0.19
32.35
37.97
43.66
11.31
4.27
8.72
Sexes combined
7.88
0.22
30.81
35.84
40.79
9.98
4.03
8.93
4. Discussion
The sex ratio observed in this study, 1.65M: 1H
(
2 p < 0.05), differed from the one reported by
Instituto Nacional de Pesca (2014), 1,25M:1H,
although both show the male predominance in the
population of M. gayi in Ecuadorian waters.
However, larger sizes were recorded among
females, coinciding with what was stated by
Iwamoto et al. (2010), who show that females
grow faster and reach a much larger size than
males. Determining the sex ratio is important to
have a full knowledge of the general biology of an
exploited population and is part of its fundamental
assessment (Holden and Raitt, 1975).
Size frequencies for combined sexes were in the
range 26-72 cm TL, with an average size of 36.21
cm. These values resembled those found in the
coast of mainland Ecuador by García et al. (2014)
who report hake sizes in the range 17-81 cm TL.
However, the values found in this study differed
significantly from the size intervals of 14-71 and
15-77 cm TL reported in 2009 and 2010,
respectively, for Ecuadorian coastal waters by
MAGAP (2009; 2010). Variations compared to
previous studies underscore the importance of
maintaining continuous monitoring of
populations, while similarities with other regions
highlight the need for international cooperation to
promote long-term sustainability (Mytilineou et
al., 2020).
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The study of length-to-weight relationships in fish
provides indirect information on growth,
maturity, reproduction, nutrition and therefore the
health status of populations. This allows
interpopulation comparative studies to be carried
out (Lorencio 1996). The results obtained in the
current study indicated that the type of growth of
M. gayi can be considered negative allometric,
which coincides with what is described in the
oceanographic campaigns of MAGAP (2008;
2009) in coastal waters of Ecuador, when values
of exponent b were 2.98 and 2.83, respectively.
Based on this, it is suggested that M. gayi
preferentially increases its relative length more
than its weight.
In the present study, the Mean Size at Maturity
(MSM) for males was established at 34.8 cm TL,
while for females it was 37.3 cm TL and an
average MSM of 36.0 cm LT for sexes combined.
Although, the reported MSM data were within the
range previously reported, these results differed
from what was described by Instituto Nacional de
Pesca (2014), who reports a MSM of 33.7 cm LT
for combined sexes in the industrial hake fleet.
Castro-Moreira et al. (2023) also report that in
bottom longline fishing in Ecuadorian waters,
females reach sexual maturity at a larger size than
males. Moreover, Cerna and Oyarzún (1998) in
Chile, for the same species, established the MSM
at 38.9 cm TL, which is larger than the one
described in this study. Subsequent studies are
necessary to determine whether these variations
are due to the samples belonging to different
populations or to a pattern of size variation due to
changes in latitude or fishing exploitation.
Although it has been demonstrated that the
decrease in maturity size may be associated with
environmental changes (Legaki et al., 2024).
The values obtained for Lr50, 34.35 and 37.97 cm
TL for males and females, respectively,
resembled what is described by Queirolo et al.
(2013), in a selectivity study conducted on the
coasts of Chile between 50 and 370 m deep, where
the selective effect of trawls was 30 and 36 cm TL
in the codend and cover bag, respectively. From a
perspective for the conservation of the resource,
the catch size (Lr50) is sought to be greater than
the MSM (Subsecretaría de Pesca-Chile, 2001).
This would imply a natural impact on the
capturable stock of males, while for females it
would confirm the efficiency of the selectivity of
the trawl gear in catching females of M. gayi, after
their contribution of new individuals to the
population.
The calculation of the recommended mesh size
for the codend of trawls based on the combined
sex data was established in this study at 8.93 cm.
This would be in accordance with Article 9.2 of
the 018 agreement of Ministerio de Agricultura,
Ganadería y Pesca (MAGAP 2013), where it is
established that the codend must have a mesh size
of 8.9 cm (3 1/2 inches). However, when
information is disaggregated by sex, it is evident
that this mesh opening would be functional for
females (8.72 cm of recommended mesh size), but
would be at the limit for males, where the
recommended mesh size was 8.99 cm. MAGAP
(2009), in its fisheries research campaign report,
states that "the distribution of hake sizes does not
vary substantially with latitude, but it does with
depth, with the size range being significantly
smaller and farther from the mean as the depth
increases". Thus, it is feasible to think that the
differences found in this study with the provisions
of the ministerial agreement, are due to the
different depth interval of the trawls performed in
this study, 28 – 48 m, while those of the reference
studies of that regulatory framework were 0-100
m. On the other hand, authors such as Gálvez and
Rebolledo (2005), recommend a mesh opening of
12.0 cm in the codend, to protect the spawning
fraction of the common hake and to maximize the
biomass of the cohorts.
The percentage of captured hake that did not reach
the MSM was 41.06 and 50.46% for males and
females, respectively, coinciding with Instituto
del Mar del Peru (1996), who shows that the
industrial trawl fleet exploits an available and
accessible resource, whose characteristic is the
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presence of young specimens, the vulnerability of
which is significantly increased by their
concentration and the operational characteristics
of the fleet. This proportion indicates that a
significant part of the captured hake consists of
young specimens that have not yet reached
reproductive age. This could affect the
population's ability to sustain and renew itself
naturally, increasing the pressure on the most
vulnerable segments (García-Fernández et al.,
2021).
Since selectivity studies are aimed at conserving
the reproductive potential of species (Pavéz,
1989), and it is necessary to look for mechanisms
that allow immature individuals not to be
susceptible to capture.
While the method proposed in this study is
sustainable, it is important to validate the obtained
results with experimental tests in the codend and
cover bag or the use of juvenile reduction devices,
such as those applied in neighboring countries
Peru and Chile with good results. Likewise, it is
necessary to continue the selectivity studies in
other landing ports with different fishing depths,
several seasons and atypical years.
5. Conclusions
The analysis of the information collected in this
case study shows that, with a mesh size of 8.9 cm
in the codend of the trawls, for males the Lr50 was
34.35 cm which was less than the MSM 34.75 cm,
while for females the Lr50 37.97 cm was greater
than the MSM 37.28 cm. In consequence, when
information is disaggregated by sex, it is evident
that this mesh size would be functional for
females, but it would be very tight for males.
However, network selectivity does not distinguish
sexes, so the selectivity response would be
decreased.
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