The estimation of bigeye tuna (Thunnus obesus, (Lowe, 1839 ... · The catch in Benoa Port mainly...

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( Received 30 October 2018; Accepted 18 November 2018; Date of Publication 30 November 2018 )

WSN 115 (2019) 1-14 EISSN 2392-2192

The estimation of bigeye tuna (Thunnus obesus, (Lowe, 1839)) fishing season in the East Indies

Ocean which is disembarked in Benoa Port, Bali

Arsa Dipanoto*, Mega L. Syamsuddin, Zuzy Anna, Izza Mahdiana A.

Faculty of Fisheries and Marine Sciences, Universitas Padjadjaran, Indonesia

*E-mail address: [email protected]

ABSTRACT

Prediction about fishing season is needed for fishing operation, so it can help fisherman to catch

a big number of fish with effective and efficient. This study was started on May – June 2018. This study

aimed to analize fishing season pattern of big eye tuna in Indian Ocean. Historical data about fish

production and fishing effort of long line vessel for 5 years (2013-2017) collected from Indonesia Tuna

Longline Asociation (ATLI) in Benoa Port, was used to calculate monthly CPUEs which were then

analyzed using average percentage methods to obtain fishing season index for each month and sea

surface temperature (SST) data collected from satellite. The result shows that big eye tuna can be caught

along the year, but there was a pattern that fishing season occurs from June – September, December,

and April with the peak season in east season. Optimum distribution of sea surface temperature base on

big eye tuna’s fishing ground ranged from 27-27.5 °C.

Keywords: Bigeye Tuna, Fishing Season, SST, Indian Ocean, Thunnus obesus

1. INTRODUCTION

Indonesian waters, particularly the Indies ocean, have great potential because of its vast

oceanic wealth, especially with its big pelagic fishes (Amandè et al., 2012). Benoa Port is the

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biggest port in Bali province, which is directly connected to the Indies Ocean. Benoa Port has

fishing areas which is also a place for tuna debarkation in Indonesia.

Tuna, specifically the bigeye tuna, is a big pelagic species commercial target and a

valuable species in the longline tuna fishing that operates in the Eastern Indies Ocean (ISSF

2012 in Nurdin 2012). Indonesia’s Bigeye tuna production reached 34,259 tons in 2013 (Indies

Ocean Tuna Commission, 2015). The bigeye tuna deployment follows the fish migration path,

one of which is affected by temperature. The migration path that is based on the temperature

includes South Sumatera waters, Southern Java, Bali, Nusa Tenggara, and Banda Ocean.

Bigeye tuna fishing rate is still below the amount of the allowed potential. Therefore, it

is necessary to increase effort so that the fishing rate will increase. The knowledge of fishing

season patterns is needed in order to increase bigeye tuna productivity. This is also a way in an

effort of sustained fishing so that the bigeye tuna potential lasts and its utilization will not

exceed the allowed fishing rate. Information about bigeye tuna fishing season is not common

in research. Therefore, it is deemed necessary to estimate the bigeye tuna fishing season in the

Eastern Indies Ocean based on the amount of catch that is disembarked in Benoa Port and ocean

surface temperature distribution.

Photo 1. Thunnus obesus (Lowe, 1839)

2. MATERIALS AND METHODS

This research was conducted in the waters of Indian Ocean with fishing base in Benoa

Port, Bali which will be carried out in April – May 2018. Benoa port is a location to take

production of big eye tuna and catching effort data. This research is conducted in 2 phases,

which is data gathering and data processing, respectively. This research used survey with

descriptive analysis which includes direct data gathering (in-situ) and visual analysis of satellite

images (ex-situ). The in-situ data includes the bigeye tuna fishing rate and the fishing trip rate

of Benoa port, while the ex-situ data includes the image of ocean surface temperature (OST)

from MODIS image detection satellite using Aqua sensor (MODIS-Aqua)

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Figure 1. The Research Site Map

The obtained data was analyzed using the catch per unit effort (CPUE) (Gulland, 1983,

in Edmond, 2017), and the fishing season patterns. The fishing pattern is obtained by calculating

the average percentage based on the time series analysis (Spiegel, 2016), and both of the

analysis are connected. According to Purwasasmita (1983), the fishing season analysis used the

following procedure:

1. Calculate the CPUE value per month

CPUEi = 𝐶(𝑖)

𝑓(𝑖)

2. Calculate the monthly average of CPUE in a year

m

i

iUm

U1

1

where: Ū = CPUE monthly average in a year

Ui = CPUE per month (ton/trip)

m = 12 (the number of months in a year)


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3. Calculate the ratio of Ui to Ū

U

UU i

p × 100%

where: Up = Ratio of Ui to Ū

4. Calculate the season index

IMi =

t

i

pUt 1

1

where: IMi = ith Season Index

t = the sum of year from the data

5. If the IMi is not 1200% (12 month × 100%), then an adjustment is required by using

the following formula:

IMSi =

m

i

iIM1

1200× IM

where: IMSi = The Adjusted ith Season Index

6. While calculating, if the Up has an extreme value, then the Up value is discarded from

the Season Index (IM) calculation, and the IM median (Md) will be used as a substitute. If the

Md is not 1200%, then an adjustment is required by using the following formula:

IMMdSi =

m

i

iMd1

1200 × Mdi

where: IMMdSi = The Adjusted ith Season Index median

7. If the IM is more than 1 (>100%) or greater than the average value, then it is fish season,

and if the IM is less than 1(<100), then it is not. Lastly, If the IM is equal to 1

(= 100%), then it is in a normal or balanced state.

The monthly sea surface temperature data that has the same period with the bigeye tuna

fishing period is obtained from MODIS Aqua sensor with a spatial resolution of 4 km. The data

are then combined (overlay) with the fishing ground coordinates from the fishing logbook. The

results of the data are analyzed descriptively to identify the correlation between temperature

distribution with bigeye tuna productivity in the Eastern Indies Ocean.


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3. RESULTS

3. 1. Temperature Distribution Analysis in The Indies Ocean

Temperature is an oceanographic factor that affects fishing rate. Weilan (2013) stated that

a low or high temperature will affect the fishing productivity. Every fish will adjust with the

temperature that is ideal to its metabolism.

In this research, the temperature distribution is divided into each season, this is done to

identify the best season that has the ideal temperature to fish bigeye tuna. Indonesian waters are

highly related with ENSO and affected by the west monsoon or wet season which occur from

December to February, followed by the transitional season I from March to May, whilst the east

monsoon or dry season occur from June to August followed by the transitional season II from

September to November (McBride and Nicholls 1983; Haylock and McBride 2003; Hendon

2003).

Overall, the temperature distribution of Indies Ocean surface is within the range of 24-30

°C. In the east monsoon (June-August) from 2013 to 2017, the temperature is relatively warm

in the western offshore ranging between 28-29 °C. Upwelling occurs at the coastal area in east

monsoon, such as the one that occurred in 2015. Therefore, the temperature tends to be colder

and ranging between 24-25 °C (Pictured in Figure 2). East monsoon has a colder Ocean Surface

Temperature (OST), this is due to the water current from Eastern Australian waters flows into

Indonesian waters. Based on these, the season indicates that it is the ideal season for tuna

distribution because of the temperature distribution that tends to be low offshore.

The OST in the early transitional season II is seen to be affected by the east monsoon,

and as the transitional season II approaches the end (November), the temperature gradually

increases. The warm temperature in transitional season II ranges between 29-31 °C, which

generally distributed in the eastern offshore (Pictured in Figure 3), and in coastal area, it tends

to be colder with the temperature ranging between 25-28 °C. This is due to the upwelling, as

stated in a research by Goela (2016), that is, upwelling causes the ocean surface having lower

temperature.

In the west monsoon from 2013 to 2017, the OST in Indies Ocean ranges between 24-35

°C. The OST distribution of west monsoon is relatively warmer. This warmer temperature

spreads across the eastern offshore and ranging between 28-32 °C, and the lower temperature

spreads across the western waters and ranging between 25-27 °C (Pictured in Figure 4). The

warmer OST in the western season could be caused by the effect of the west monsoon which

moves to southeast and bringing warmer current temperature. The uneven low temperature is

affected by the South Equatorial Current (SEC) which then causes upwelling.

Entering the transitional season I, that is the transition from west monsoon to east

monsoon, causes the OST starting to decrease. The current moving from the west near the

equator, that occurred in this season, causes the water temperature to be warm although the

degree keeps decreasing.

The temperature in this season ranges between 26-34 °C (pictured in Figure 5). The warm

temperature in this season spreads more on the eastern offshore (28-30 °C), and colder

temperature spreads on the western waters, with the exception in May of 2005 and 2017 which

is indicated to have upwelling in the coastal area.


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Figure 2. The Ocean Surface Temperature (OST) Distribution in East Monsoon in 2013-2017


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Figure 3. The Ocean Surface Temperature (OST) Distribution in Transitional Season II

in 2013-2017


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Figure 4. The Ocean Surface Temperature (OST) Distribution in West Monsoon

in 2013-2017


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Figure 5. The Ocean Surface Temperature (OST) Distribution in Transitional Season I

in 2013-2017


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3. 2. Bigeye Tuna Production Analysis in Benoa Port, Bali

The catch in Benoa Port mainly consists of tuna, one of which is the bigeye tuna.

swordfish, cakalang (skipjack tuna), escolar and squid are other types of catch in Benoa Port.

The catch of bigeye tuna in Benoa Port for 5 year period (2013-2017) based on the data below

showed a fluctuating result every month (Pictured Below).

Figure 6. The Fluctuating Pattern of Monthly Bigeye Tuna Catch from 2013-2017

in Benoa Port

The highest bigeye tuna catch is in July 2013, with the total of 318 tons, whilst December

2017 has the least bigeye tuna catch with the total of 31 tons. Syamsuddin (2016) stated that

the highest fishing rate occurred between June – August, which meant that the catch rate is also

the highest in those months. The fluctuation of the bigeye tuna production is caused by a few

factor which include the fish availability, the fishing effort, the fishing success rate, the number

of manpower, the duration of fishing, and climate changes (Cheung 2010). The bigeye tuna

production tends to be higher at mid-year (east monsoon), this indicates that the mid-year has

suitable temperature for the tuna’s metabolism.

From the data shown above, the year 2013 has the highest catch rate of 2,214,126 kg and

2017 has the lowest catch rate of 755,888 kg. This decreasing trend could be caused by the trip

rate that also decreases each year. This is because the fishing effort affects the results of catch

rate as stated before.

The bigeye tuna fishing effort by the fishermen in Benoa Area include using the ship with

an array of long line. The size of the ship used in Benoa is between 30 GT (Gross Tonage) to

200 GT. From 2013-2017, the total fishing effort in Benoa is 9097 trip. As the catch rate, the

highest fishing effort occurred in July 2013 with the total of 383 trips and the lowest fishing

effort occurred in December 2017 with the total trip of 29 trips.

The fishing effort fluctuation is affected by a few factor such as the increasingly further

fishing ground potential, and climate changes affected the fishermen decision to make a trip.

-

50 000

100 000

150 000

200 000

250 000

300 000

350 000

BIG

EYE

TU

NA

CA

TCH

(KG

)

2013 2014 2015 2016 2017


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In addition, according to The Association of Tuna Longline Indonesia (ATLI), the

number of longline fleet decreases each year in the 5-year period. This, in turn, also decreases

the fishermen fishing effort.

The bigeye tuna catch and effort catch data is used as the reference data to determine the

Catch Per Unit Effort (CPUE) per month (kg/trip) in the 5-year period. The CPUE Analysis

showed that there is a correlation between the increase and decrease of the catch with the fishing

effort. The highest CPUE is in April 2016 with the rate of 2013 kg/trip and the lowest is in

March 2014 with the rate of 441 kg/trip. This is because in 2016, the fishing effort rate tends to

be low which increases CPUE, and vice versa in 2014, which has a pretty high fishing effort

rate which decreases the catch per trip.

Potier and Boely (1990, in Apriliani, 2018) stated that fishing is affected by season and

the water environmental conditions. In this research, the highest CPUE occurred in eastern

season (east monsoon). This confirms by Rochman et al. (2017) that stated eastern season has

the highest CPUE for bigeye tuna because the climate changes causes relatively low tide and

currents, which in turn causes the longline fleet to operate more often.

3. 3. The Bigeye Tuna Fishing Season Pattern

The estimation of bigeye tuna fishing season in Eastern Indies waters was based on the

average of monthly fishing effort (2013-2017). The obtained season pattern will refer to the

catching season index (IMP) calculation. Based on the IMP, it can be seen that bigeye tuna

fishing can be done throughout the year. However, fishing season mostly occurred in eastern

season. The seasonal pattern can be seen in Figure 7.

Pictured below, the fishing season occurred in April, June, July, August, September, and

December. The non-fishing season, occurred when the IMP is less than 100%, is in January,

February, March, May, October, and November.

Figure 7. Bigeye Tuna Fishing Season Index Pattern in Indies Ocean Waters

The graph above indicates that the indices are higher in the eastern season, this confirms

Nurani et al. (2012) research that showed the tuna fishing season peak in the southern waters

106,77 107,22

114,8

107,58

115,45

107,22

80

90

100

110

120

1 2 3 4 5 6 7 8 9 10 11 12

SEA

SON

IND

EX

MONTH

THE FISHING SEASON INDEX

IMP IMP = 1


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of Indian Ocean occurred in June and July, which is in the eastern season as evidence by the

large number of catches. The results obtained from this research is consistent, this is shown by

the highest CPUE is in the eastern season and fishing season mostly occurred in the eastern

season, as well.

Based on the calculation of bigeye tuna catch data, fishing season mostly occurred in the

eastern season. The temperature distribution in said season is relatively low and ranging

between 24-30 °C. Based on the fishing location which are 30 coordinates obtained from the

fishing logbook, with August to November 2016 came from KM Surya Terbit – 169 and KM

Sari Dewata – 1 which is based in Benoa Port Bali (Pictured in Figure 8), the ideal temperature

distribution to fish bigeye tuna ranges between 27-27.5 °C. This temperature range confirms

Syamsuddin et al. (2013) research that showed bigeye tuna is mostly fished in waters with a

temperature between 24-27.5 °C (Pictured in Figure 9). The logbook data showed that the

bigeye tuna fishing are is wider in August with the average temperature distribution of 27 °C.

Figure 8. The Bigeye Tuna Fishing Map in August (a), September (b), October (c), and

November (d) 2016 in the Eastern Indies Ocean Waters


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Figure 9. The Ideal Temperature Distribution from August to November 2016 in the Eastern

Indies Ocean Waters

4. CONCLUSION

The bigeye tuna fishing activity in the Indies Ocean peaks at eastern season, specifically

in July and September. The ideal ocean surface temperature distribution in the Eastern Indies

Ocean based on the location of bigeye tuna fishing ranges between 27-28°C, this range is also

the temperature distribution in bigeye tuna fishing season.

ACKNOWLEDGEMENT

The authors would like to thank the NASA for the SST data and Benoa Port for catching of big eye tuna data.

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