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JIPK. Volume 13 No 2. November 2021
Sinta 2 (Decree No: 10/E/KPT/2018) Available online at https://e-journal.unair.ac.id/JIPK/index
Research Article
Population Dynamics of Bullet Tuna (Auxis rochei Risso 1881) from the In-
dian Ocean, West Nusa Tenggara, Indonesia
Evron Asrial1,* , Fathurriadi1, Yasir Arapat1, Usma Kurniawan Hadi2, Lalu Achmad Tan Tilar
Wangsajati Sukmaring Kalih1, Lalu Samsul Rizal1, Mita Ayu Liliyanti2, Erwin Rosadi3, Ruly Isfatul
Khasanah4, Daduk Setyohadi5, Muhammad Junaidi6, and Ishani Nelunika Rathnayake7
1 Department of Fisheries Resources Utilization, Faculty of Fishery, University of 45 Mataram, Mataram, West Nusa Tenggara, 83239. Indonesia
3 Department of Capture Fisheries, Faculty of Fishery and Marine, University of Lambung Mangkurat, Banjarbaru, South Kalimantan. Indonesia
4 Marine Science Program, Faculty of Science and Technology, State Islamic University of Sunan Ampel, Surabaya, East Java, 60237. Indonesia
5 Department of Fisheries Resources Utilization and Marine, Faculty of Fishery and Marine Science, University of Brawijaya, Malang, East
Java, 65145. Indonesia
6 Department of Aquaculture, Faculty of Agriculture, University of Mataram, Mataram, West Nusa Tenggara, 83115. Indonesia
7Department of Fisheries and Aquaculture, Faculty of Fisheries & Marine Sciences and Technology, University of Ruhuna, Matara. Sri Lanka
ARTICLE INFO
*) Corresponding author:
E-mail:evronasrial81@gmail.com
Keywords:
Adolescence
BLT
Mesomorph
Neritic
Abstract
The bullet tuna (Auxis rochei), BLT or tongkol lisong (Indonesian) is a species of
neritic tuna which is one of the target sh for small scale shers. The problem of
bullet tuna sheries was that it has reached over exploitation and the immature
bullet tuna are still caught.This study aimed to assess the population dynamics
of the BLT and its size composition caught by small scale shers in the Indian
Ocean, West Nusa Tenggara. The location of this research was in Bangko-Bangko
(West Lombok), Cemplung Beach (South Sumbawa) and Tanjung Luar Fishing
Port (East Lombok) between July 2019 and June 2020. The data was derived from
the measurement and weighing results of 1,217 BLT collected from the respec-
tive collector traders at each sampling location. The growth pattern of BLT was
Cite this as: Asrial, E., Fathurriadi, Arapat, Y., Hadi, U. K., Kalih, L. A. T. T. W. S., Rizal, L. S., Liliyanti, M. A., Rosadi, E.,
Khasanah, R. I., Setyohadi, D., Junaidi, M., & Rathnayake, I. N. (2021). Population Dynamics of Bullet Tuna (Auxis rochei Risso
1881) from the Indian Ocean, West Nusa Tenggara, Indonesia. Jurnal Ilmiah Perikanan dan Kelautan, 13(2):116–123. http://doi.
JIPK
(JURNAL ILMIAH PERIKANAN DAN KELAUTAN)
Scientic Journal of Fisherie s and Marine
Department of Aquaculture, Faculty of Fishery, University of 45 Mataram, Mataram, West Nusa Tenggara, 83239. Indonesia
Received: March 19, 2021
Accepted: June 10, 2021
This is an open access article under
the CC BY-NC-SA license (http://
creativecommons.org/license/by-n
org/10.20473/jipk.v13i2.26017
e-ISSN:2528-0759; p-ISSN:2085-5842
DOI=10.20473/jipk.v13i2.26017
isometric (b= 2.99) which meant the ideal body shape (mesomorph) and length at
first maturity (FLm) was 31.11 cm. The length-weight relationship curve showed
that BLT was in an immature age group (adolescent fish). Meanwhile, the comp-
osition of BLT is worth selling (Condition Factor>1.00), fit for catch (FLc / FLm
> 1.00), and worthy of maturity (FLc > FLm), respectively 99.92%, 0.82% and
0.00%. The BLT fish composition indicates that the stocks of resources and pop-
ulations do not support current sustainable fisheries management.
Copyright ©2021 Faculty of Fisheries and Marine Universitas Airlangga 144
2
c-sa/4.0/)
13(2):144-155. http://doi.
Published: September 28, 2021
145
Jurnal Ilmiah Perikanan dan Kelautan
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1. Introduction
Most of the neritic tuna caught by fishers are
sold to retailers on landings site. The remaining fish
caught by the fishers are sold to fish collectors around
the coun- tries. The role of the neritic tuna fisheries in
WNTs is important as it provides economic benefits
for coastal communities and an inexpensive source of
protein for the community.
Neritic tuna resources caught by Indonesian
fishers in the national fisheries management area of the
Republic of Indonesia (WPPN RI) were 573 species
including little tuna (Euthynnus affinis Cantor, 1849),
frigate tuna (Auxis thazard Lacepede 1800), long tail
tuna (Thunnus tonggol Bleeker, 1851), and bullet tuna
(Auxis rochei Risso 1810). The neritic tuna is one of the
pelagic fish group that is highly valued by international
consumers, national consumers, and West Nusa Tengga-
ra (WNT) residents. The Indian Ocean in the South of
West Nusa Tenggara Province is a potential habitat for
four species of neritic tuna that have landed in Bang-
ko-Bangko (West Lombok), Cemplung Beach (South
Sumbawa), and Tanjung Luar Fishing Port (East Lom-
bok). Furthermore, its exploitation uses surface long-
lines for 12 months a year. All types of fishing gear used
in the coastal waters are classified as environmentally
friendly fishing gears (Asrial et al., 2020).
The utilization of bullet tuna in the Indian Ocean
South Sumbawa Island has reached fully exploited sta-
tus (Asrial et al., 2020). This condition is not good for
the security of resource reserves and the population of
bullet tuna. It was reported that the fork length of BLT
(FLc) caught was shorter than the fork length of BLT at
first maturity (FLm) with a value of less than 1.00 (FLc
< FLm; FLc / FLm <1.00) (Asrial et al., 2020). This
condition affects the ongoing decline of the BLT fish
population. Currently, conditions status of fish popula-
tion is an important issue in sustainable BLT fisheries
management in the coastal waters of the Indian Ocean.
According to IOTC (2019), BLT fisheries man-
agement in the Indian Ocean is not supported by data
to estimate BLT resources stocks, so that the status of
BLT stocks in the Indian Ocean is unknown (IOTC,
2019a; IOTC, 2019b; IOTC, 2020). Utilization of BLT
resources in Indian waters has been reported to reach an
overexploited status (E = 80.0%) (Jasmine et al., 2013;
Rohit et al., 2014). Sri Lanka faces a similar problem,
namely limited data relating to distribution and migra-
tion of BLT fish (Dalpathadu et al., 2019). Currently,
there is no information regarding the status of BLT
resource stocks in Southeast Asian waters (Kaewnu-
ratchadasorn et al., 2020). Thus, the Indian Ocean Tuna
Council (IOTC) pays special attention to BLT species
in the Indian Ocean within the territory of Indonesia
(Fahmi et al., 2019). BLT fish caught in the waters of
the Indian Ocean in the southern part of Java Island and
Lombok Island were dominated by the immature fish
size population (Setyadji et al., 2013; Tampubolon et
al., 2015). Based on the author’s knowledge, the avail-
ability of data on BLT fish from coastal waters areas of
NTB is very limited.
Research on the resources and population of A.
rochei (Risso, 1881) in the TNB area, particularly in the
waters of the Indian Ocean, are limited and was car-
ried out by Asrial et al. (2020) and Tampubolon et al.
(2015). For this reason, it is necessary to study more
deeply about the resources and population of BLT orig-
inating from the Indian Ocean in the southern part of
the WNT.
The present study aimed to determine the eli-
gibility status and size composition of BLT resources
and population for the sake of implementing sustainable
fisheries management policies in Indonesia.
2. Materials and Methods
2.1
Study Area
This research was carried out from July 2019 to June
2020. Samples of BLT were obtained from fish landing
centers, namely Bangko-bangko (Lombok Barat Dis-
trict), Tanjung Luar Fishing Port (Lombok Timur Dis-
trict), and Cemplung Beach – Labangka (Sumbawa Dis-
trict) (Figure 1).
Figure 1
. Map of sampling location of BLT fish
2.2
Procedures
A descriptive dependent survey method was
used for the data collection in which the authors rely
heavily on other parties to obtain samples and data as
well as other information about the phenomena occur-
ring. The data collection techniques consisted of sam-
pling, observation, interviews, and documentation. The
main material for this study was the BLT samples caught
by fishers, obtained from fish collector trader that were
Asrial et al. / JIPK, 13(2):144
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50
residents of each study location. Fishers caught the BLT
in the coastal waters of the Indian Ocean using surface
longlines and motorboats as means of transportation to
the fishing ground.
BLT samples were measured and weighed for
a total of 1217 individuals. The data from the sampling
results, which have been recorded, were tabulated in
excel format to be processed quantitatively using sev-
eral equations. Furthermore, the results of analyzed data
processing are used according to the needs and objec-
tives of this study.
2.3
Data Processing and Analysis
The data processing was carried out to estimate
the eligibility status of the resources and the population
dynamics of the BLT fish in the Indian Ocean coastal
waters. The eligibility consists of the composition of the
number of fish worth selling, worth catching and worth
spawning, as well as growth patterns and fish age
groups. For fish population dynamics study, the length
of infinity, growth rate, mortality, exploitation rate,
maximum length, recruitment, growth, and composition
of fish age group members were calculated.
2.3.1
Growth pattern and the model
The growth pattern is the growth rate of the length
and weight of the fish at the same time, which is mea-
sured simultaneously. The value was obtained by an-
alyzing the length of the fish and weight data using a
simple regression method designed to estimate the body
shape of the fish. In this case, the data used were the
FL and BW size of the BLT sample. Since fish are liv-
ing organisms that grow, move, and regenerate in free
water (wild), first the data was converted into natural
logarithms (ln). The output of data processing follows
a mathematical model:
model: ln BW =
𝑎
+ ln FL
,
where:
𝑎
= intercept coefficient and b= coefficient of
FL variable. The next step was to perform a t-test
following the steps described in section “Worth
catching”. The status of growth patterns and body
shape, represented by the value b, consists of: (a) b <
3.0 (minor allometric) = thin (ectomorph), (b) b = 3.0
(isometric) = slim / streamlined (mesomorph), and (c)
b > 3.0 (major allometric) = fat (endomorph).
2.3.2
Length at first maturity (Lm)
The size of the fish for the initial gonad matu-
rity (Lm) is the range of length of fish when 50% of
the gonad has matured. The fish with gonads maturity
level (GML) I and GML II are classified as immature
while GML III and IV are classified as mature. The size
estimation of first time gonad matured fish (Lm = L
50
)
length of the fish under 50% maturity conditions was
carried out using a logistic curve approach (Sparre and
Venema, 1998). The equation is Q = 1/ 1 – e
-a (FL-FL )
}
where Q = fraction of fork length class maturing gonads
(GML III and IV), 1 = 100% ripe gonads, e = 2.718, a =
constant, FL = mean class of fish fork length, and FL
50
=
fork length of fish at 50% maturity of gonads.
Furthermore, the equation is converted into linear form:
ln(Q/1-Q) = aFL
50
- aFL. By using linear regression, it was
obtained that the length of the fish when the gonad has
matured was FL
50
= aFL / a where aL = intercept and a =
slope.
2.3.3
Fish age group
The results of the fork length to body weight
(LWR) analysis were used in estimating the age group of
the fish. Based on LWR = BW/
𝑎
FL
b
(Ndimele et al.,
2010; Kurniawan et al., 2019) where: BW = body
weight (g), FL = fork length (cm),
𝑎
= intercept, and b =
growth exponent. The data for LWR analysis were FL
and BW, which were not converted in any form, also
known as “raw data”. The graph used was an
exponential curve that can provide a phenomenon for
the age group of fish by observing the trend in the
direction of the graph line.
Fish growth is described in the form of a curve
that relates length and weight to time or age. The shape
of the fish growth curve resembles the letter S in such a
way that it is said to be a sigmoid curve (S curve). In
order to estimate this, the LWR diagram must be com-
pared with the fish growth curve (S-curve). The S-curve
divides the age group of the fish into three age groups
(a)
childhood and adolescence fish (immature) on the lag
phase, (b) adulthood fish (mature & high productivi- ty) on
the exponential phase, and (c) old age fish (mature & low
productivity) on the stationary phase (Figure 2).
Figure 2
. Sigmoid curve (S curve)
2.3.4
Worth selling
The marketability of fish for sale (worth selling)
was estimated using the condition factor (CF) approach,
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based on body weight (BW) and fork length (FL) data.
According to Effendie (2002), condition factor (CF) is
estimated based on an economic approach in order to
determine if the fish have reached the status of “worth
selling” (Effendie, 2002). In order to generate the CF
values, data processing uses the equation: CF = 10
2
BW
/ FL
3
, where: CF = condition factor, BW = body weight
(g), FL = fork length (cm), a = intercept, and b =
coefficient (Effendie, 2002). The equation is used when
the growth pattern is isometric (b = 3.0).
The closeness of the relationship between the
two variables can be confirmed by the value of b by per-
forming a t-test (Effendie, 2002). The hypothesis con-
sists of: (1) H
0
= isometric when the value of b = 3.00
and (2) H
1
= allometric when the value of b> 3.00 or b
<3.00. Next was to perform the t-test using the equation:
t – stat = (3 – b) / Sb,
where: b = the calculated value of
the FL and BW ratio of fish and Sb = standard
deviation of b. The next step was to compare the t-stat
value with the t-table value. The decision follows the
following conditions:
value of t-stat > t-table: H0 is rejected and H1 is
accepted, so the growth pattern is allometric (𝑏 ≠
3.0)
value of t-stat < t-table: H0 is accepted and H1 is
rejected, so the growth pattern is isometric (𝑏 = 3.0).
Marketable BLT status, developed and modi-
fied from the classification compiled by Fathurriadi et al.
(2020). The conditions are as follows: (1) CF < 1.00: the
body of the fish is slightly shallow and not yet fleshy,
therefore it has little economic value, immature age
group, it is not worth catching and selling, and it can
also become a broodstock candidates, (2) CF = 1.00
-
3.00: the body of the fish is flat and fleshy, therefore it
has a high economic value, mature age group, and it can
be caught and sold (marketable), and as potential
broodstock candidates, and (3) CF > 3.00: fish body is
less flattened and thick fleshy, it has highest economic
value, mature age group, and it is very suitable to be
caught and sold (marketable), but not suitable to be used
as broodstock because their productivity has decreased.
The value of CF also describes the fertility of the waters
related to the availability and adequacy of feed. The cat-
egories are as follows: (1) CF > 1.0: the feed available in
the wa- ters is very sufficient to support activities,
growth, and reproduction, (2) CF = 1.0: the availability
of feed in the waters is only enough for movement and
body growth, and (3) CF < 1.0: the feed available in the
waters is sufficient to survive.
2.3.5 Worth catching
The worth catching status of BLT was estima-
ted
using the fork length (FLc) data, which was com-
pared with the fork length at first maturity (FLm),
using equations: FLc / FLm. When the value is FLc /
FLm > 1.00, the fish is classified as “worth catching”
which means that BLT fish caught have spawned and
released their eggs into the waters. In this study, if the
value of FLc / FLm < 1.00, it was agreed that the BLT
was immature gonads, and therefore it was “unworthy to
catch”. The category for determining the worth catching
fish status consists of: (1) Damage (
𝐹𝐿𝑐
/
𝐹𝐿𝑚
< 1,0),
(2) Inadequate (
𝐹𝐿𝑐
/
𝐹𝐿𝑚
= 1,0), and (3) Eligible (
𝐹𝐿𝑐
/
𝐹𝐿𝑚 > 1,0) (Fathurriadi et al., 2020). The categories
are prepared on the basis of the precautionary principle
in accordance with recommendations for responsible
and sustainable fisheries resource management.
2.3.6 Worth spawning
BLT wish suitable for spawning are
discovered in adult fish especially those that have
reached the size for the first time experiencing gonad
maturation. The estimation of the spawning fish
follows the fork length equation, which is longer than
the length at the first maturity of the gonads
(FLc>FLm). In order to estimate the composition of
the number of BLT fish suitable for spawning, FL
data from the BLT sample and FLm data from BLT
in other waters areas in the Indian Ocean were
estimated.
The number of fish suitable for spawning was
obtained from the number of fish samples that have a
value of FLc > FLm. The authors decided that in the
interests of sustainable BLT fisheries resource manage-
ment and the safety of the BLT fish resource reserves,
the standard population of adult BLT fish is at least 12%
of its population. This value is estimated based on the
following technical assumptions: (1) fecundity = 36,480
eggs/ind. (Hadi, 2020), (2) the survival rate of larval to
post larva size = 5.00%, (3) the survival rate of post
larvae to adult fish size is at least 5.00%, and (4) the
number of eggs that hatch until it reaches adult fish is at
least 53.73%.
3. Results and Discussion
3.1
Results
3.1.1
Size composition
The tuna neritic fishing activities at the study
location were carried out by fishers using surface long-
lines and motorboats to catch fish in coastal waters (0-
12 nautical miles) of the Indian Ocean. The bullet tuna
species (A. rochei) dominates the catches and very few
little tunas (E. affinis) landed in Cemplung Beach -
Sumbawa (Asrial et al., 2020).
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The BLT sample was measured and weighed by
no fewer than 1217 individuals. The fork lengths of BLT
caught by fishers ranged from 20.00-30.60 cm/ind. and
an average of 23.86 cm/ind. Out of the 11 classes of
fork length (FL) frequency of BLT (Figure 3), the dom-
inant size was class 22-23 cm of about 406 individuals
(33.36%), followed by the 23-24 cm class of about 211
individuals (17.34%), and the 21-22 cm class of 180 in-
dividuals (14.79%).
The body weight (BW) of 1,217 BLT sample
individuals from the study location was divided into 7
classes. The lightest was 95.00 g/ind., the heaviest was
about 415.00 g/ind., and the average weight was 193.03
g/ind. (Figure 4). The majority of BLT were in classes
154-185 g and 124-154 g, 446 individuals (36.65%) and
306 individuals (25.14).
Figure 3
. Fork Length of BLT from Indian Ocean, WNT
Processing of FL and BW data from BLT trans-
formed into logarithmic data (natural logarithm / ln) uses
a simple regression method. The choice of the natural
logarithmic (ln) aims to: (a) avoid heteroscedas- ticity,
(b) find out the coefficients that show elasticity, and (c)
make the data scale closer (Ghozali, 2011). The result is
the value of the variable that is used to test the feasibility
of the model as follows:
The correlation (r) = 97.61% means that there is a
very close relationship between the variable BW and
FL (r > 80%)
Determination (R
2
) = 95.28% means that the FL vari-
able is very strong in determining the BW variable
(R
2
> 80%), and the model suitable for forecasting
(R
2
> 60%)
The adjusted R Square (Adj. R2) = 95.27% can be
interpreted that the sample has a high ability to find
answers in its population (Adj. R2 > 50%)
Standard Error (SE) = 5.85% means the model de-
viations that occur can be tolerated/accepted (SE <
25%)
The value of variables indicates that the data
used are very eligible for further processing. Therefore,
the results of data processing can be used for decision
making.
Figure 4
. Body Weight of BLT from Indian Ocean,
WNT
The average FL of BLT fish from the study loca-
tion is longer than those that landed in Cemplung Beach -
Labangka, namely 23.49 cm/ind. (Asrial et al., 2020) and
Prigi Fishing Port, which is 20.22 cm (Agustina and
Rochman, 2019). Meanwhile, the average FL of BLT
fish from Tanjung Luar Fishing Port and the Indian Ocean
West of Sumatra, respectively was about 26.29 cm/ind.
(Arapat, 2020) and 25-26 cm (Noegroho and Chodrijah,
2015), which is longer than BLT from the Indian Ocean in
South of NTB.
3.1.2
Growth pattern and the model
The results of data processing show the value
of the growth pattern (coefficient b) = 2.994. The value
of the growth pattern is in the isometric category, with
the growth rate of fork length equal to that of growth.
Therefore, the body shape of BLT is ideal. As for the
growth pattern model is In BW = -4.263 + 2.994 In FL.
The model is classified as “positive equation”. The
meaning of this equation is that each additional 1.0 unit
of fork length (FL) increases the value of body weight
(BW) by 2.994 (coefficient value b).
3.1.3
Length at first maturity (Lm)
The number of BLT fish samples measured
was 1,217 individuals. There were 63 ind. (5,18%) of
the fish that had reached the mature stage of the gonads
and 1,154 ind. (94.82%) had not yet reached the mature
stage (Figure 5).
BLT fish samples have reached the gonadal ma-
turity phase at a fork length class size of 23-24 cm and
the highest distribution of fish with matured gonads is in
the length class interval size of 26-27 cm. The analysis
result shows that the fork length at first maturity (FLm)
is 31.11 cm.
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Figure 5
. Fork Length composition of BLT fish sam-
ples
3.1.4
Fish age group
The BLT age group was estimated through the
LWR graph using BW and FLm data. The LWR curve
derived from the equation BW = 4,479FL
0.319
(Figure
4). Based on the t-test with a confidence level of 95%,
the growth of bullet tuna was minor allometric. When
the LWR curve (Figure 6) was compared with the fish
growth curve (S curve), the sample fish are classified as
age group of immatures (adolescence fish).
According to Expósito (2015), the age group of
BLT fish can be estimated using FL data, namely the
immature group is equivalent to FL < FLm (31.11 cm).
Based on the FL size of all BLT fish samples, the BLT
fish population in the study location only consisted of
one group of fish age, namely the immature group (Fig-
ure 7).
Figure 6
. LWR of BLT from Indian Ocean, WNT
Figure 7
. BLT age group from Indian Ocean, WNT
3.1.5
Worth selling
The processing results of FL and BW data of
BLT fish resulted in a condition factor (CF) value of
more than 1.00 (Figure 3). The resulting CF values con-
sist of CF
min,
CF
max,
and CF
average
are 0.82, 1.79 and 1.38
respectively. The CF
average
value indicates that the body
shape of the BLT is “flattened”, which means that it is
“fleshy” and therefore it has a high selling price. An-
other meaning is that the feed available in the waters
is very sufficient to support activities, growth, and re-
production. In study location is known that 1.2016 ind.
(99.92%) of the BLT are worth selling and only 1 ind.
(0.08%) of the BLT is not worth selling (Figure 8).
Figure 8
. The BLT worth selling from the Indian
Ocean, NTB
3.1.6
Worth catching
The worth catching estimation of BLT is the ra-
tio of FLc and FLm based on the standard FLm = 31.11
cm (this study). BLT fish is declared fit for catching if
FLc / FLm > 1.00, meaning that the fish caught have
spawned at least once.
The frequency of fork lengths of BLT caught
(FLc) in the study locations ranged from 20.0 cm to 30.6
cm and averaged 23.90 cm. Furthermore, with regards
to the FLm of BLT fish (31.11 cm), the composition of
Fork Length (cm)
Number of Fish (ind.)
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BLT from the study location that is not fit for catching is
about 1.207 ind. (99.18%) and fit to be caught is about
10 ind. (0.82%) (Figure 9). Therefore, for every 1 ind. of
the BLT that deserved to be closed, there were 120-121
ind. worthy of being caught. Based on the FLc average
value data, the FLc / FLm value = 23.86 cm / 31.11 cm
= 0.77 (FLc / FLm <1.00), which means that the BLT
fish resources from the study location are “not worth
catching” and the status is “damage”.
location ranged from 20.00 - 30.60 cm and the average
was 23.86 cm/ind.
Based on the FLm of BLT in the study
location, which is 31.11 cm, the composition of BLT
caught by fishers in the study location, 100.00% of the
samples were not worth spawning (FLc < FLm)
(Figure 7). This means, in the waters of the Indian Ocean
South of WNT, it is estimated that there are no potential
BLT brood- stock candidates in the population.
3.2
Discussion
Gonads, gonad maturity, and Lm of fish are im-
portant parts in the discussion of fish reproductive biol-
ogy. The factors that can affect gonad maturity in fish
include genetic factors (Kuparinen and Merila, 2007;
Olsen et al., 2004) and overfishing (Rochet and Trenkel,
2003).
Figure 9
. The BLT worth catching from the Indian
Ocean, WNT
Table 1.
The fork length (FL) frequency of the
BLT fish from Indian Ocean
3.1.7 Worth spawning
Based on several scientific information, it is known
that BLT reaches gonad maturity at different FLm. The
frequency of FL of BLT caught by fishers in the study
The FL size of BLT fish from the Indian Ocean in
the WNT region ranged from 20.00-30.60 cm and aver-
aged of 23.86 cm, which results from the measurements
of 1,217 samples. The FL size of BLT fish from other
regions in the Indian Ocean within the National Fish-
eries Management Territory (NFMT) of the Republic
of Indonesia varies widely, with a range of 11.0 – 42.0
(Table 1). The study location (WNT region) is at NFMT
573, which is very wide and covers the Indian Ocean
waters in the south of the region of Java Island, Bali Is-
land, WNT Province, and East Nusa Tenggara Province
(ENT).
Indian Ocean
Fishing Gears Type
Frequency
(cm)
Mo-
dus
(cm)
References
Indian Waters
Longline, surface gill net
14-40
22-26
Rohit et al. (2014)
Cilacap (Central Java)
Gillnet
20-45
40.00
Widodo et al. (2011)
Cilacap (Central Java)
Mini purse seine
23-32
30.00
Setyadji et al. (2013)
South of Sumba Island
Purse seine (industrial
scale)
20-28
20-22
Setyadji et al. (2013)
West of Sumatra
Purse seine, fish net, lift
net, troll line
11-42
25-26
Noegroho and Chodri-
jah (2015)
Sendang Biru (East Java)
Surface longline / rinta
18.5-32.0
23.55
Fitriah (2018)
North & West of Sumatra
Purse seine
19-38
-
Salmarika et al.
(2018)
Prigi Bay (East Java)
Purse seine
13.3-26.0
20.22
Agustina and Roch-
man (2019)
Labangka (Sumbawa)
Surface longline / rinta
21.0-29.2
23.50
Asrial et al. (2020)
Research location
Surface longline / rinta
20.0-30.6
23.86
Present study
151
Jurnal Ilmiah Perikanan dan Kelautan
There are differences in the frequency of FL at
each BLT landing site, where these differences are
likely caused by differences in the types of gear used by
fishers and fishing grounds (Table 1) (Asrial et al.,
2020). The FL frequency of BLT fish caught by Sendang
Biru (East Java) fishers using rinta is longer than that
caught by Prigi Bay (East Java) fishers using a purse
seine, even though Prigi Bay is located close to
Sendang Biru. The FL size of BLT fish landed in
Sendang Biru (18.5-32.0 cm) was identical to the one
that landed in Labangka (21.0-29.2 cm) and the South
of WNT (20.0-30.6 cm), which was caught using rinta
fishing gear. Furthermore, rinta is a type of surface
longline operated by being pulled using a boat, such as
a troll line in such a way that the position of the rinta
rope becomes diagonal in the waters. Rinta fishing
gear, operated by fishers from Sendang Biru, Labangka,
and the South of WNT, is a fishing gear that is selective
to the size of the fish caught and is environmentally
friendly. Meanwhile, the purse seine fishing gear used
by Prigi Bay fishers is a type of fishing gear that is not
selective on the size of the fish. According to Sumardi
et al. (2014), the level of purse seine selectivity is low.
Naturally, mature fish groups are caught in coastal
waters and around small islands (Collette, 1995), and
more young fish groups swim in oceanic waters
(Collette and Aadland, 1996). In this study, the
difference in the size of BLT fish caught by fishers i n
WNT tends to be ca used by differ e nt types of
fishi n g ge a r.
Table 2
. Parameters of eligibility of BLT fish
The eligibility of fish can be evaluated usin
g
FL and BW data to determine the growth rate (b) status
of fish which ends by setting the status of the fish’s
body shape. Other eligibility estimated using that data
(FL and BW) are status of fit for sale (CF), fit to be
caught (Lc / Lm > 1.0), and worth spawning (Lc > Lm)
(Table 2).
The status of the BLT growth pattern at the
study location is isometric (b = 2.99), which indicates
that the body shape is slim / streamlined (mesomorph).
The growth pattern is identical to that of the BLT fish
that landed in Tanjung Luar (b = 2.99), but different from
BLT fish in Sumbawa (b = 3.22) and Sendang Biru -
East Java (b = 3.39) that has the major allometric status
indicates that the body shape is fat (endomorph). The
BLT fish that live in the waters of western Sumatra have
a minor allometric status ( and the body shape is thin
(ectomorph). Based on the status of growth patterns
(isometric), it can be concluded that the waters in the
study location (South of NTB) are sufficiently fertile to
meet the vital needs and growth of the BLT fishery
resources. This conclusion is in line with the statement
that fish plumpness is deter- mined by eating habits,
feed availability, growth period, and water fertility
(Liestiana et al., 2015; Sasmito et al., 2016). Other
factors that support the growth pattern are nutrition and
feed consumed by the fish (Sonnaria et al.,2015).
Indian Ocean
Growth
Pattern
Condition
Factor
(CF)
CF >
1.00
(%)
FLc /
FLm
FLc /
FLm
>1.0 (%)
FLc >
FLm
(%)
References
West of Sumatra
2.82
1.50
100.00
1.05
100.00
100.00
Kurniawan et al.
(2019)
Sendang Biru
(East Java)
3.39
-
-
1.04
-
-
Fitriah (2018)
North & West of
Sumatra
30.00
Salmarika et al.
(2018)
Prigi Bay (East
Java)
-
-
0.75
-
6.86
Agustina and Roch-
man (2019)
Labangka (Sum-
bawa)
3.22
1.44
100.00
1.26
100.00
100.00
Fathurriadi (2019)
Tanjung Luar
(Lombok)
2.97
1.25
49.11
1.06
95.15
76.02
Arapat (2020)
Study location
2.99
1.38
99.92
0.99
25.72
29.01
Present study
Asrial et al. / JIPK, 13(2):144-155
JIPK. Volume 13 No 2. November 2021 / Population Dynamics of Bullet Tuna (Auxis rochei Risso 1881) from....
152
The results of the condition factor (CF)
analysis showed that 99.82% of the BLT fish landed in
the study area were salable (CF = 1.38) (Table 2). The
BLT fish in the study locations have the same status
with the ones in the waters of Western Sumatra
(Kurniawan et al., 2019), Labangka - Sumbawa
(Fathurriadi, 2020), and Tanjung Luar - Lombok
(Arapat, 2020) are fit for sale (CF > 1.00) (Table 2).
Only BLT fish from Tanjung Luar were fit for sale
(Arapat, 2020), the number (49.11%) is much less
than those from the study location. Meanwhile, the
number of BLT fish fit for sale from the Indian
Ocean West of Sumatra and Labangka is almost the
same as that of the study location. The BLT fish in
the study lo- cations were of high quality (CF = 1.38)
and almost all (99.92%) were worth selling at high /
expensive prices (IDR 30,000 / kg). The conclusion is
in line with the opinion of Effendie (2002), which
explains that the condition factor is an indication that
individual fish are already fleshy, that they are suitable
for sale (economy) and that fish are ready to spawn
(pregnant), and there- fore that they are fit to become
broodstock. According to Fathurriadi et al. (2020),
the value of CF = 1.0 - 2.0 indicates that the fish have
high economic value, can be caught, can be sold, and
have the potential to become BLT fish.
The fish to be caught, expressed as the value of
Lc in relation to Lm, must be greater than one (FLc / FLm
> 1.0). BLT fish in the study location have a value of
FLc / FLm = 0.99, which means that they are not suitable
to be caught because FLc / FLm < 1.00. However, about
25.72% of BLT fish from the study location were fit to be
caught. The number is higher than the number of fish
that can be caught in Prigi Bay
- East Java which only
reached 6.86% (Agustina and Rochman, 2019). The
size of the fish to be caught (catchable) is when the
body length of the caught fish (Lc = length caught) is
longer than the body length at gonadal maturation (Lm
= length at first maturation) or Lc> Lm.
BLT fish in the study location are fit for
spawn- ing and have the potential to become
productive brood- stock candidates whose FLc size is
longer than FLm (broodstock = FLc > FLm). About
29.01% of BLT fish from the study locations were
suitable groups for spawning. This number is almost the
same as the number of broodstock candidates of BLT
fish (30.00%) from the Indian Ocean waters of the
West and north of Sumatra (Salmarika et al., 2018).
4. Conclusion
The BLT fish caught by the fishers had a fork
length (FL) = 20.0-30.6 cm (average 23.86 cm), and
body weight (BW) = 95.00-415.00 (average 193.03 g).
The BLT growth pattern is isometric (the ideal body),
and has a single age group that is an immature. The BLT
is not eligible to be caught and is not yet eligible for
spawning. In contrast, almost all of the BLT were
“fleshy”. In order to conserve BLT resources and sus-
tain BLT fisheries management, fishers are advised to
increase the size of the rinta fishing gear.
Acknowledgements
This research activity started with the prepa-
ration of proposals through to the publication of re-
sults, assisted and supported by the parties. The authors
express profound gratitude to the Foundation of 45
Mataram (Yayasan 45 Mataram) and Fishery Faculty,
University of 45 Mataram for supporting this research
and publication. The authors are grateful to the fishers
and all parties in Labangka (Sumbaaw), Tanjung Luar
(East Lombok), and Bangko-Bangko (West Lombok)
that assisted the team in collecting and identifying the
fish samples. The authors are also grateful to Randi,
Andi Firmansyah Kaplale, Fauzah Andriani, Resty, and
Ridwan, students of the Fishery Faculty, University of
45 Mataram that helped with the identification of the
fish sample.
Author’s Contributions
The authors have contributed very well, from
designing the research to reviewing the final draft of the
manuscript before sending to the journal managers.
Evron Asrial; designed and carried out surveys, moni-
tored data processing and analysis activities, also wrote
research reports and scientific publication manuscripts.
Yasir Arapat and Usma Kurniawan Hadi; compiled,
tabulated, and separated the data, especially the bullet
tuna sampling results. Erwin Rosadi, Daduk Setyohadi
and Muhammad Junaidi; carried out quantitative data
processing and wrote down the resume. Ruly Isfatul
Khasanah; analyzed the results of data processing.
Meanwhile, Lalu A.T.T.W.S. Kalih, Lalu Samsul Rizal,
Ishani Nelunika Rathnayake and Mita Ayu Liliyanti;
revised and perfected sentences and vocabulary in the
publication manuscript.
Copyright ©2021 Faculty of Fisheries and Marine Universitas Airlangga
153
Jurnal Ilmiah Perikanan dan Kelautan
Conflict of Interest
The authors declare that there is no conflict
of interest or conflict of interest between them.
Funding Information
This research and publication was funded by
the Ministry of Research and Higher Education
through the “Bidikmisi Program” scholarship fund,
the Founda- tion of 45 Mataram, the University of 45
Mataram and the authors.
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