CATCH AND SIZE OF BULLET AND FRIGATE TUNA CAUGHT BY USING DRIFTING GILLNET IN INDIAN OCEAN OF INDONESIA BASED AT CILACAP FISHING PORT

Pelagic fishes such as bullet and frigate tuna in the Indian Ocean were caught in Indian Ocean of Indonesian jurisdiction using various fishing gears including, drifting gillnet and landed in various fishing port in along coastal of west Sumatera (Banda Aceh, Pariaman, Bungus/Padang and Painan) as well as south Java, Bali and Nusatenggara (Muarabaru/Jakarta, Pelabuhanratu, Cilacap, Kedonganan, Benoa). In Cilacap, tuna drifting gillnet fishery is fishing bullet and frigate tuna as by product. The current work describes the catch and size distribution of bullet tuna (Auxis rochei Risso, 1810) and frigate tuna (Auxis thazard Lacepède, 1800) caught by drifting gillnet based at Cilacap Fishing Port. Data and information obtained through catch monitoring, port sampling and landing report of Cilacap Fishing Port 2011 as well as from Capture Fisheries Statistics of Indonesia 2010. The catch estimation of bullet and frigate tuna on drifting gillnet fishery is about 3.220 and 47.346 tons respectively. The catch rate of drifting gillnets on the frigate tuna was 0.364 mt/trip in 2006 decreased to 0.054 mt/trip in 2011 (decreased average 17% per year). The catch rate of drifting gillnets on the bullet tuna was also decreased from 0.178 mt/trip in 2006 to 0.013 mt/ trip in 2011. The FL of bullet and frigate tuna ranged respectively between 16-39cm and 25-46cm. Both species were mostly caught by drifting gillnet in adult size condition. KEYWORD: Catch and size distribution, bullet and frigate tuna, drifting gillnet, Indian Ocean, Cilacap fishing port.


INTRODUCTION
Drifting gillnet was developed in Cilacap (Southern coastal of central Java) since ten years ago.The fishing ground of drifting gillnet based at Cilacap is in Indian Ocean.The main target of this fishing gear is tuna and tuna like including neritic tuna and sheerfish.Based on the 'Cilacap Fishing Port Annual Report of 2011', the number of drifting gillnetter based at Cilacap Fishing Port is 205 fleets.This number has increased significantly compared to that in 2010 when it was 165 fleets.The drifting gillnet was nylon multifilament with mesh size 5 inch and operated by wooden boat 20-30 GT.Each boat operates about 50-60 piece of drifting gillnet.
There are 4 species of neritic tuna and 2 species sheerfish under IOTC management i.e. longtail tuna (Thunnus tonggol), frigate tuna (Auxis thazard), bullet tuna (Auxis rochei), kawakawa (Euthynnus affinis), narrow-barred Spanish mackerel (Scomberomorus commerson) and Indo-Pacific king mackerel (Scomberomorus guttatus) (Herrera, at al., 2009).National Fisheries Statistic of Indonesia (DGCF, 2011) noted that the six species were caught in Western Sumatera and Southern Java Indian Ocean.Generally neritic tuna and sheerfish are part of the catch of purse seine, drifting gillnet, hand lining and trolling lines gear.Cilacap Fishing Port (2012) reported that mostly of bullet tuna (Auxis rochei Risso, 1810) and frigate tuna (Auxis thazard Lacepède, 1800) caught by drifting gillnet.Total production of the drifting gillnets fisheries landed in Cilacap Fishing Port on 2012 reached 101 mt and 6 mt for bullet and frigate tuna respectively.The production drifting gillnet contributed about 0.20% and 0.26% of total catch of bullet and frigate tuna from Indian Ocean West of Sumatera and South Java, Bali and Nusa Tenggara.

Statistic of Marine Fisheries of
Availability the information of catch by species, gear and fishing ground as well as the size of fish was important aspects in the fish stock assessment work.This paper describes the catch and size distribution of bullet tuna (Auxis rochei Risso, 1810) and frigate tuna (Auxis thazard Lacepède, 1800) caught by drifting gillnet in the Indian Ocean based at Cilacap Fishing Port, Central Java.

MATERIALS AND METHODS
The primary data were gathered in 2010 from catch monitoring and landing report of drifting gillnetters operated in Indian Ocean based at Cilacap Fishing Port where the field survey was conducted in 2011.The data covered fishery and fish biology aspects.Fishery data consisted of fishing operational and catch (effort data and trip catch, the biological data consisted of species and size (fork length-FL).The samplings were conducted in April, August and December, it was done by two enumerators.
The enumerator did the record of data/information including vessel name, number of piece of net, trip duration, main fishing ground) and total catch (weight) for all drifting gillnetter arriving in port after fishing.Those data and were information obtained from the skippers through interview and available log book.The biological aspects of data were obtained through the random sampling of catch.Number of sample was three boxes (about 30-50 kg/box) taken on the beginning, middle and the end times of catch unloading.The secondary data were noted from National Fisheries Statistics 2005-2010 published by DGCF and Annual Report of Cilacap Fishing Port for the period of 2005-2011.

Fishery (Fleet, Gear and Season)
Mostly drifting gillnet fleets based at Cilacap Fishing Port are fishing in Indian Ocean within Indonesian Fisheries Management Area-FMA 573.The number of registered fishing fleet based at Cilacap Fishing Port in 2011 was 892 with detail of 299 tuna longliners, 138 set gillnetters, 205 drifting gillnetters, 181 trammel netters, 98 monofilament gillnetters, 42 bottom Danish seiners, 7 pelagic Danish seiners, 7 portable trappers and 3 lift netters (Table 1).The 205 drifting gillnetter were 23% of total fleet and only 127 active gillnetters noted in 2011.In general the number of gillnetter increased every year about 5.7% in average.
Drifting gillnet fleets were wooden boat size 10-30 GT with the main engine 120-160 HP and generator engine 24-30 HP.Fish hold of the boats is not equipped with refrigeration machine, the freshness of catch is preserved with the ice.Drifting gillnet fleets are generally equipped by compass and GPS for the navigation purpose and SSB radio for communication.Number of crew each boat about 12-14 persons.Fishing trip duration is 18-22 days per trip with the effective days 16-20.Figure 1   The drifting gillnet is a wall of fine, large-meshed synthetic netting with a series of floats attached in the corks line at the top and a series of weights (leads or concrete) at the bottom to maintain it vertical in midwater, in general, not far below the surface.It is normally set at dusk and hauled at dawn or in the morning.The length of drifting gillnets deployed by fishermen targeting tuna or other large pelagic fish such as swordfish, is commonly several kilometers whereas the height ranges from 18 to 30 m. Widodo (2011) noted that one piece of drifting gillnet in Cilacap has length 38-40 m and height 18-20 m.Webbing material is nylon multifilament type d-21 and mesh size 5 inch.Floats are synthetic rubber type Y-15 as much as 6 floats and 4 weights from concrete 0.5 kg each weight per piece of drifting gillnet.Each piece of gillnet is equipped 2 plastic buoy Ø 30 cm and buoy line 6 m in length for keeping the position of gillnet about 5-6 m below the sea surface.Generally, a drifting gillnet fleet operates 50-60 piece gillnets or about 1.5-2.5 kilometer in total length.
The fishing season represented by number of fish landing, the number of bullet and frigate landing in 2011 fluctuated between months, with the highest landing was experienced in December (Figure 3).During this month drifting gillnet was mostly fished in offshore waters where sea condition was very calm.

Catch
In Indonesian Fisheries National Statistic is reported that annual catch of the two main species of neritic tuna such as bullet and frigate tuna from Indian Ocean which composed of Western Sumatera, Southern Java and Southern Bali-NTT.The catch in 2010 is estimated 2,445 and 47,113 mt for bullet and frigate tuna respectively as described in Table 2. Compared to the previous year annual catch, annual catch of bullet in 2010 has experienced significant increasing.Since the past six years, the average annual catch of frigate tuna annual catch increased about 76% per year.While the average of bullet tuna annual catches was experienced steady decreasing reaching about 34% per year.The catch of frigate tuna from Indonesian Indian Ocean shared about 35% to the national level of frigate tuna total catch estimation (132,772 mt).Whilst the catch of bullet tuna contributed about 66% to the national level of bullet tuna total catch estimation (3,696 mt) as described in Table 3.
The catch per unit effort (CPUE) of drifting gillnets on frigate and bullet tuna based at Cilacap Fishing Port is represented by its catch rate.Result of catch monitoring during six past year (2006)(2007)(2008)(2009)(2010)(2011) shows that the catch rate of drifting gillnets on both species frigate and bullet tuna decreased year by year.As described in Table 4 that the catch rate of drifting gillnets on the frigate tuna was 0.364 mt/trip in 2006, this value decreased to 0.054 mt/trip in 2011 (decreasing average of 17% per year).The situation on the resource of bullet tuna is also similar to the frigate tuna.The catch rate of drifting gillnets on the bullet tuna was also decreased from 0.178 mt/trip in 2006 to 0.013 mt/trip in 2011.
In term of catch composition, drifting gillnet fish landing is dominated by skipjack tuna i.e. 68.5% from total 3358.878mt, whilst frigate and bullet tuna were only 1.6% and 0.4% respectively (Figure 3) and the detail of species caught by drifting gillnet is presented in Table 5 which was at least 50 species identified during catch monitoring in 2011.

Fish Size
The size (fork length-FL) both species frigate and bullet tuna caught by gillnet mesh size 5 inch varied with month and fishing area as presented below:

a. Bullet Tuna
The size (FL) of bullet tuna caught on April, August and December 2011 ranged between 16-39 cm with mode at 36 cm, 36 cm and 35 cm respectively (Figure 4).It is compared to the result of onboard observation in 2008-2010 (Widodo et al., 2011) that the size of bullet tuna caught in 2011 was relative smaller.The smallest size of bullet tuna caught in 2008 was ranged 24-45 cm with mode at 42 cm.

b. Frigate Tuna
In April, August and December 2011 the size (fork length-FL) distribution of frigate tuna caught ranged 25-46 cm with the mode 32cm, 33cm and 33cm respectively (Figure 5).The size was smaller than the common size frigate tuna i.e. 60 cm that as mentioned by Figueiredo et al. (2002).

Table 2
The estimate of catch of neritic tuna and sheerfish landing in Western Sumatera, Southern Java and Southern Bali-Nusatenggara 2005-2010.

Catch
Frigate and bullet tuna was species that mostly spend in inshore water, but they are probably cosmopolitan in warm waters; it is an epipelagic, neritic as well as oceanic species (Anonymous., 2006).Drifting gillnet based at Cilacap targets tuna and tuna like, whereas neritic tuna (frigate and bullet tuna) caught as by product.Catch rate of the frigate tuna was 0.364 mt/trip in 2006, this value decreased to 0.054 mt/trip in 2011 (decreasing average of 17% per year).The situation on the resource of bullet tuna is also similar to the frigate tuna.The catch rate of drifting gillnets on the bullet tuna was also decreased from 0.178 mt/trip in 2006 to 0.013 mt/trip in 2011.
The result of research was in line with the behavior of bullet tuna.The bullet tuna is an epipelagic, neritic as well as oceanic species with strong schooling behavior.Widodo (2011) noted that based on onboard observation conducted in 2008, 2009 and 2010 the drifting gillnet fleets based at Cilacap have similar fishing ground pattern in those years.In April they operate in the offshore waters, whereas in July and October they operate in the inshore waters.In 2011, the situation was relatively similar with the previous year.The fishing position of drifting gillnets fleets in 2011 ranged 7.0 o -11.0 o S and 107.0 o -111.0 o E (Figure 2).Since 2010 drifting gillnets fisheries experienced fishing pressure by the operation of purse seiners that are fishing in the drifting gillnet fishing ground.The purse seiners deploy FADs in the conventional drifting gillnet fishing ground and since that time most drifting gillnet fleets move to the inshore waters.

Fish Size
The first maturity size has been stated as 35 cm (FL), when the fish is two years old (Rodriguez-Roda, 1983 in Kahraman, 2010) that was in line with result of the research by Kahraman et al. (2010) which determined that sexually mature bullet tuna specimens were always well over 35 cm FL.Adults are principally caught in coastal waters and around islands (Anonymous., 2006).Base on the information of maturity size as mentioned above, so that <50% of bullet tuna caught by drifting gillnet in April was juvenile fish, whilst in August and December mostly of bullet tuna caught at matured size.
Maximum length of frigate tuna (unsexed) reaches 65 cm (CayrP, 1993).According to Jude et al. (2002) that males and females frigate tuna were found to attain maturity at slightly different length.Males 73-79 attained maturity at slightly smaller length than females.Males attain maturity at 30.8 cm while females at 32.8 cm.If assumed that all frigate tunas catch were females with length at first matured (L m ) 32.8 cm, so that the number of matured frigate tuna caught by drifting gillnet was reached 61.3% in April, whilst in August and December were 69.6% and 74.6% respectively.It means that mostly of frigate tuna caught by drifting gillnet at matured size.

COUCLUSION
Bullet and frigate tuna caught by drifting gillnet in Indian Ocean based at Cilacap Fishing Port as byproduct, accounted 0.4% and 1.6% of the total catch.The catch fluctuated between months and peak season experienced on December.The catch rate of both species bullet and frigate tuna decreased year by year since six past years, in 2011 the catch rate of bullet tuna 0.013 mt/trip/vessel and frigate tuna was 0.054 mt/trip/vessel.Both of species bullet and frigate tuna caught by drifting gillnet mostly as adult fish.

Figure 3 .
Figure 3. Catch composition of drifting gillnets based at Cilacap Fishing Port.
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Table 3 .
The national level and in Indonesian Indian waters Ocean catch of frigate and bullet tuna 2010.

Table 4 .
Catch rate of drifting gillnets to frigate and bullet tuna base at Cilacap Fishing Port year 2006-2011.

Table 5 .
The catch compositions of drifting gillnet based at Cilacap Fishing Port.
Catch and Size of ….……..in Indian Ocean of Indonesia Based at Cilacap Fishing Port (Widodo, A A & F. Satria) Figure 5. Size (FL) distribution of frigate tuna caught by drifting gillnets based at Cilacap Fishing Port in 2011.