Studies of Indonesian tuna fisheries, Part 2: Changes in yellowfin abundance in the Gulf of Tomini and North Sulawesi¹

¹The original paper presented at the Shimizu meeting ("The interaction between the artisanal and industrial tuna fisheries in the eastern Indonesia with special reference to Sulawesi Sea" by N. Naamin) has been revised extensively based on reviewers' comments. The present paper represents one segment of the original paper.

C.P. Mathews
Central Institute for Fisheries Investigations, and
Marine Coastal Ecosystems and Processes Project, Jakarta, Indonesia

D. Monintja
Fakultas Perikanan, Institute Pertanian, Bogor, and
Marine Coastal Ecosystems and Processes Project, Jakarta, Indonesia

Nurzali Naamin
Research Institute for Marine Fisheries
Komplek Pelabuhan Perikanan Samudera
J1. Muara Baru Ujung
Jakarta 14440 Indonesia

ABSTRACT

Yellowfin tuna are taken on four Tomini Gulf (North Sulawesi) fishing grounds around "rakit"(small shallow-water fish aggregating devices) targeted towards scads and small yellowfin and around "rumpon" (larger deep-water fish aggregating devices) targeted towards medium-sized yellowfin. In Gorontalo, yellowfin landings increased from 1988 to a peak of more than 1,500 mt in 1990; the landings then declined steadily until 1995. Landings in Tilamuta, Paguat and Marisa fluctuated, but tended to peak between 100 and 200 mt around 1990. The CPUE at Gorontalo peaked in 1990 and fell markedly from 1990 onwards in all four fisheries; in 1995 the CPUE fell to about 30% of 1990 level in Gorontalo and to less than 10% of the 1990 levels at Tilamuta, Paguat, and Marisa. The sharp decline in CPUEs coincided with the extension of intensive offshore fishing by tuna longliners (mostly from Taiwan) and with the introduction of large-scale offshore industrial purse seining (which targets skipjack but also takes substantial amounts of yellowfin) by Philippine boats around North Sulawesi in 1990. The marked decline in yellowfin abundance suggests that offshore fishing impacted the Tomini Gulf fisheries.

1. INTRODUCTION

Naamin et al. (1996, Part 1 of this study) assessed the effects of industrial fishing on the coastal tuna fisheries in Manado and especially in Bitung (North Sulawesi), giving special attention to the skipjack fishery centered in these ports. They noted several data problems, but concluded that foreign rumpon (FADs or fish aggregating devices) placed in Indonesian waters around 12-50 nm (nautical miles) from the coast, impacted the important coastal pole-and-line fisheries for skipjack in Bitung and Manado. They were, however, unable to provide useful effort data for the coastal yellowfin fisheries based around Bitung and Manado. During surveys carried out in many smaller North Sulawesi fishing ports in the Gulf of Tomini (described by Naamin et al., 1996, Part 1 of this study) reliable data on yellowfin catch and effort were obtained. The object of this paper is to use these new data to estimate changes in yellowfin abundance after the introduction of rumpon into Indonesian waters in 1990.

2. DATA AND METHODS

Localities and data collection methods have been described by Naamin et al. (1996, Part 1 of this study). Data on gear, landings, and species composition were obtained through the cooperation of the Provincial Fisheries Service (Tingkat I, Manado), the Gorontalo City Fisheries Office and the Gorontalo County Fisheries Office also located in the city of Gorontalo. These organizations developed and executed regular landings and effort surveys for Tilamuta, Marisa, and Paguat since the mid-1980s. The fisheries in these areas are characterised by the presence of FADs used to attract tuna and scad. Detailed records of the number of FADs deployed were not kept in all study areas. Nevertheless, records on the number of handlines ("pancing ulur") and troll lines ("pancing tonda") deployed on each fishing ground are available and were used to estimate effort.

3. RESULTS AND DISCUSSION

The two kinds of FADs deployed in the Gulf of Tomini tuna fishing grounds include "rakit" and "rumpon".

3.1 Rakit

Rakit are small FADs usually made of traditional materials. They are located in shallow waters (50-200 m deep at most) within 5-10 nm (9-18 km) of the coast, usually no more than 10-20 nm (35 km) from the nearest fishing port. Rakit have been used in Indonesia since time immemorial (Monintja, 1993) and are know to have been used for more than 30 years in many areas around Sulawesi Island, especially North Sulawesi. New rakit exploitation areas have also been established more recently (Mathews and Monintja, 1996). Rakit attract three commercially important species:

1. Small yellowfin, mostly juveniles, are attracted in large numbers and are taken by small handline boats (5-10 m, 45-100 hp outboard engines).

2. Scad (Decapterus spp., called "layang" or "malalugis" in North Sulawesi). Scad are captured around rakit by small purse seiners, locally called "mini-purse seiners" or "pajeko". Pajeko are usually 10-15 m long boats carrying outboard engines of 45-120 hp, and laying nets less than 200 m long.

3. Small amounts of skipjack are taken by the pajeko as an interesting, but not very important scad bycatch; skipjack are marketed separately.

3.2 Rumpon

Rumpon are larger FADs which are placed on deeper waters (usually 400-4,000 m) and located up to 50 nm from the coast; exceptions are in North Sulawesi where rumpon are usually located within 10-20 nm of the coast. Many rumpon are located in territorial or archipelagic waters (Mathews and Monintja, 1996). Fishing around rumpon is targeted towards tuna, mainly skipjack and yellowfin. The effects of rumpon on tuna fisheries have been studies in detail by Monintja (1993) and Monintja and Mathews (1995). In the Gulf of Tomini, rumpon occur only in the Gorontalo yellowfin fishery.

Although scad, and small amounts of small skipjack, are produced in the Gulf of Tomini fisheries, yellowfin is usually the prime target species. This is particularly the case for the Gorontalo yellowfin fishery where one company (PT Usaha Mina) uses high technology fish processing methods and targets the Tokyo fresh fish market. About 50 mt of fresh sashimi-quality yellowfin chunks are exported monthly; exports are made on Friday afternoon, arriving in Tokyo on Sunday morning in time for consumption at Sunday lunch. Prices obtained range from US$10-12/kg.

3.3 Effort Standardisation

Yellowfin are caught around rakit or rumpon principally from small boats with handlines. In some areas troll lines are also deployed and take small amounts of yellowfin. A standard handliner carries five handlines, each handline with at least five hooks of different size. Boats that troll usually carry around four troll lines. Based on experience and interviews with county and city fisheries service staff and fishermen, a conversion factor of four troll line boats to one handline boat was used. Therefore, the standard handline boat had a fishing power equal to 16 troll lines or five handlines. Available data on the catch and he number of handlines and troll lines were used to estimate effort in numbers of standard handline boats (Tables 1 and 2).

Table 1. Gorontalo yellowfin tuna fishery.

	Catch (mt)	Effort (HLyr)*	CPUE (mt/HLyr)
1988	1,282	574	2.23
1989	1,366	579	2.36
1990	1,593	501	3.18
1991	1,416	825	1.72
1992	1,388	1,235	1.12
1993	1,120	1,295	0.86
1994	854	1,293	0.66
1995	811	n/a	n/a

* HL = standard handline boat (see text)

LANDINGS (T), TILAMUTA Yellowfin Tuna FISHERY

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Total Catch	Total effort	CPUE	Effort
																Headlines	Troll Lines
1985	18.0	249	21.2	325	19.0	10.9	144	14.6	138	184	226	171	2274
1986	179	87	141	228	19.7	16.5	191	197	377	307	302	31 3	268.4
1987	46	4.9	348	86	100	76	6.3	57	41	51	67	76	106.0
1988	18.1	30.1	233	262	293	221	8.5	32	86	88	76	116	1974
1989	8.9	17.9	135	20.2	13.7	99	88	107	85	12.1	15.3	182	157.7
1990	10.1	62	14.7	9.7	15.6	176	186	154	10.6	209	19.3	12.6	171.3	21.88	7.83	105	14
1991	11.1	13.8	173	13.1	8.2	55	158	107	197	237	271	181	1841	24.88	740	120	14
1992	00	0.0	00	10.8	84	58	158	11.3	11.4	13.2	7.7	11.3	96,7	34.63	2.77	165	26
1993	5.5	5.5	14	9.4	7.5	100	2.5	3.9	2.7	5.7	4.2	37	620	40.81	1 52	195	29
1994	26	1.4	45	4.5	4.6	24	1.3	4.5	2.2	47	6.5	4.1	43.3	41.88	1 03	200	30
1995	1.5	24	17	3.7	8.9	4.8	1.4	0.6	1.7	1.1	0.6	1.3	297	47.19	0.63	225	35
TOM	98.3	1158	146.5	1615	144.9	113.1	112.5	100.3	1211	144.4	1478	136.9	1543.1
%	6.37	750	9.49	10-47	9.39	7.33	7.29	5.03	7.85	936	9.58	8.87	100.00

**Total Effort in number of standard handline boats = (Handlines/5)+(Troll lines/4x4). The same conversation was used for Paguat and Tilamuta

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Total	Effort
														Tom Effort	CPUE	Handlines	Troll Lines
1985
1986
1987
1988	0.0	0.0	12:1	79	49	1.3	2.6	7.5	7.9	16	106	3.8	602
1989	3.4	19.0	20.8	80	70	16.0	9.9	51	6.5	68	51	22	1098
1990	0.5	0.0	8.0	4.1	11 3	6.6	1.9	1.2	2.6	7.1	9.1	3.6	56.0	48.35	1.16	83	508
1991	1.8	4.5	5.4	9.9	1.3	0.0	1.8	0.0	0.0	0.0	00	0.0	24.7	67.16	0.43	98	601
1992	08	00	00	0.4	0.7	0.2	0.1	1.3	0.0	0.2	01	0.1	3.9	59.09	0.07	102	619
1993	0.0	70	1.2	3.8	20	0.9	01	0.1	0.2	0.1	0.0	0.0	154	61.66	0.25	114	620
1994	0.0	2.0	1.8	2.9	4.1	2.0	3.5	2.4	3.0	6,3	9.0	31	401	80.34	0.50	202	639
1995	0.3	0.7	0.7	0.3	1.3	1.6	1.4	1.4	0.9	1.6	0.2	04	10.8	87.33	0.12	236	642
Total	6.8	33.2	50.0	37.3	326	28.6	21.3	19.0	21 1	23.7	34.1	13.2	320.9
%	212	10.35	15.58	11.62	10.16	8.91	6.64	0.95	6.58	7.39	10.63	4.11	100.00

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Total	Tom Effort	CPUE	Effort
																Handlines	Troll Lines
1987	38	18	4.7	8.8	5.4	4.5	42	38	24	2.3	5.0	2.8	49.5
1988	00	0.0	12.1	7.9	4.9	1.3	2.6	7.5	7.9	1.6	10.6	3.8	60.2
1989	3.4	19.0	20.8	8.0	7.0	16.0	9.9	5.1	6.5	6.8	5.1	2.2	109.8
1990	0.5	0.0	80	4.1	11.3	6.6	1.9	1.2	2.6	7.1	9.1	3.6	56.0	15.60	3.59	78
1991	18	4.5	54	9.9	1.3	0.0	1.8	0.0	0.0	0.0	0.0	0.0	24.7	98.00	0.25	98
1992	0.8	0.0	0.0	04	0.7	0.2	0.1	1.3	0.0	0.2	0.1	0.1	3.9	118.00	0.03	118
1993	0.0	7.0	1.2	3.8	2.0	0.9	0.1	0.1	0.2	01	0.0	0.0	15.4	143.00	0.11	143
1994	0.0	2.0	1.8	2.9	4.1	2.0	3.5	2.4	3.0	6.3	9.0	3.1	40.1	176.00	0.23	176
1996	0.3	0.7	0.7	0.3	1.3	16	14	1.4	0.9	1.6	0.2	0.4	10.8	193.00	0.06	193
Total	18.3	51.5	74.6	56.8	62.9	45.5	38.6	36.9	37.8	42.2	52.8	29.9	547.8
%	3.34	9.40	13.62	10.37	11.48	8.31	7.05	1.86	6.90	7.70	9.64	5.46	100.00

3.4 Catch, Effort and CPUE in the Gulf of Tomini Yellowfin Fisheries

Certain features are common to all four of the fisheries operating in the Gulf of Tomini:

1. Effort increased about two-fold between 1990 and 1995 for the Tilamuta and Paguat fisheries (Figures 1 and 2) and more than three-fold for the Marisa and Gorontalo fisheries (Figures 3 and 4).

2. Landings peaked at Gorontalo in 1990 (more than 1,500 mt; Figure 4), at Paguat and Marisa in 1989 (about 120 mt; Figures 2 and 3, respectively); and at Tilamuta from 1988-91 (about 200 mt/year; Figure 1).

3. The CPUEs fell markedly in 1995 to about one-tenth of the 1990 level at Tilamuta and Paguat (Figures 1 and 2, respectively) and to less than one-third of the 1990 level at Gorontalo; Figure 4). At Marisa (Figure 3) the CPUE in 1995 was very much lower than in any other fishery studied.

Table 3. CPUE (mt/HLyr) in some Tomini Gulf fisheries.

	Tilamuta	Paguat	Marisa	Gorontalo
1988	-	-	-	2.23
1989	-	-	-	2.36
1990	7.83	1.16	3.59	3.18
1991	7.40	0.43	0.25	1.72
1992	2.77	0.07	0.03	1.12
1993	1.52	0.25	0.11	0.86
1994	1.03	0.50	0.23	0.66
1995	0.63	0.12	0.06	-

3.5 Conditions on Other North Sulawesi Yellowfin Fisheries

No effort data for yellowfin landings are available for the Manado and Bitung fisheries. Yellowfin landings in Manado declined from more than 700 mt/year in 1987-88 to about 350 mt in 1995 (Naamin et al., 1996, Part 1 of this study, Table 3) and from 990 mt in 1989 to 234 mt in 1994 (Naamin et al., 1996, Part 1 of this study).

Provincial data for Bitung show that yellowfin landings increased from about 1986 onwards, contrary to observations in all other areas where landings decreased. The increase reported for Bitung (Naamin et al., 1996, Part 1 of this study) is probably an artifact arising from the inclusion in the Provincial (and local) data of substantial Taiwanese and other longliner landings from offshore waters. It is also likely that substantial yellowfin landings were reported for the Bitung area by the Philippine purse seiner fishery which started in Indonesian waters in 1990. Mathews and Monintja (1996) show that yellowfin provide about 30% of tuna catches made by ring netters and purse seiners around rumpon in both Philippine and Indonesian waters.

Reports from coastal fishermen at Kwandang, Inobonto, Tanawangko and Likupang on the north coast, and at Belang on the northeast coast (Naamin et al., 1996 Part 1 of this study, Figure 1) all indicate that yellowfin landings fell in recent years, while Bitung fishermen and managers also reported decreased coastal landings.

Figure 1. Catch, effort and CPUE in the Tilamuta yellowfin tuna fishery.

Figure 2. Catch, effort and CPUE in the Paguat yellowfin tuna fishery.

Figure 3. Catch, effort and CPUE in the Marisa yellowfin tuna fishery.

Figure 4. Catch, effort and CPUE in the Gorontalo yellowfin tuna fishery.

4. CONCLUSIONS

The sharp decline in CPUEs of the Tomini Gulf fisheries since 1990-91 coincided with and may have been caused by the sharp increase in effort expended on yellowfin by:

1) offshore industrial purse seiners from Philippines and other countries; and
2) increases in tuna longliners by Taiwanese and other vessels (Mathews and Monintja, 1996).

It is also possible that a combination of environmental and effort changes combined to impact the North Sulawesi coastal fisheries. In any case, concern about the current condition of the coastal yellowfin tuna fisheries in Indonesia is justified.

5. REFERENCES CITED

Mathews, C.P., and D.R. Monintja. 1996. Assessment of the role of foreign and industrial tuna fishing in Indonesia's EEZ, archipelagic and territorial waters. Report, PUSLITBANGKAN, Central Research Institute for Fisheries Research, Jakarta, Indonesia.

Monintja, D.R. 1993. Study on the development of rumpon as fish aggregating devices. Martek: Bulletin T.J.K. 3(3): 1-137.

Monintja, D.R., and C.P. Mathews. 1995. Fisheries and administrative management in the North Indonesian coastal zone. Report PUSLITBANGKAN, Central Research Institute for Fisheries Research, Jakarta, Indonesia.

Naamin, N., C.P. Mathews and D. Monintja. 1996. Studies of Indonesian tuna fisheries, Part 1: Interactions between coastal and offshore tuna fisheries in Manado and Bitung, North Sulawesi. In: Shomura, R.S., J. Majkowski and R.F. Harman (eds.). Scientific Papers from the Second FAO Expert Consultation on Interactions of Pacific Tuna Fisheries, 23-31 January 1995, Shimizu, Japan. [This volume]