Studies of Indonesian Tuna Fisheries [2]

CHANGES IN YELLOWFIN ABUNDANCE IN THE GULF OF TOMINI AND NORTH SULAWESI

C.P. Mathews, D. Monintja, Nurzali Naamin

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.(fulltext ..>>)

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Environmental Changes on the Coasts of Indonesia [2]

THE CHANGING COASTLINES OF INDONESIA


Eric C. F. Bird and Otto S. R. Ongkosongo

Although there has been geomorphological research on several parts of the Indonesian coastline, the coastal features of Indonesia have not Yet been well documented. The following account-based on studies of maps and charts, air photographs (including satellite photographs), reviews of the published literature, and our own traverses during recent years-is a necessary basis for dealing with environmental changes on the coasts of Indonesia. Coastal features will be described in a counter-clockwise sequence around Sumatra, Java, Kalimantan, Sulawesi, Bali and the eastern islands, and Irian Jaya. Inevitably, the account is more detailed for the coasts of Java and Sumatra, which are better mapped and have been more thoroughly documented than other parts of Indonesia. In the course of description, reference is made to evidence of changes that have taken place, or are still in progress.

Measurements of shoreline advance or retreat have been recorded by various authors, summarized and tabulated by Tjia et al. (1968). Particular attention has been given to changes on deltaic coasts, especially in northern Java (e.g, Hollerwoger 1964), but there is very little information on rates of recession of cliffed coasts. Measurements are generally reported in terms of linear advance or retreat at selected localities, either over stated periods of time or as annual averages, but these can be misleading because of lateral variations along the coast and because of fluctuations in the extent of change from year to year.

Our preference is for areal measurements of land gained or lost or, better still, sequential maps showing the patterns of coastal change over specified periods. We have collected and collated sequential maps of selected sites and brought them up-to-date where possible.

Coastal changes can be measured with reference to the alignments of earlier shoreline features, such as beach ridges or old cliff lines stranded inland behind coastal plains. In Sumatra, beach ridges are found up to 150 kilometres inland. The longest time scale of practical value is the past 6,000 years, the period since the Holocene marine transgression brought the sea up to its present level. Radiocarbon dating can establish the age of shoreline features that developed within this period, and changes during the past few centuries can be traced from historical evidence on maps and nautical charts of various dates.

These have become increasingly reliable over the past century, and can be supplemented by outlines shown on air photographs taken at various times since 1940. Some sectors have shown a consistent advance, and others a consistent retreat; some have alternated. A shoreline sector should only be termed "advancing" if there is evidence of continuing gains by deposition and/or emergence, and "retreating" if erosion and/or submergence are still demonstrably in progress.

Coastal changes may be natural, or they may be due, at least in part, to the direct or indirect effects of Man's activities in the coastal zone and in the hinterland. Direct effects include the building of sea walls, groynes, and breakwaters, the advancement of the shoreline artificially by land reclamation, and the removal of beach material or coral from the coastline. Indirect effects include changes in water and sediment yield from river systems following the clearance of vegetation or a modification of land use within the catchments, or the construction of dams to impound reservoirs that intercept some of the sediment flow. There are many examples of such man-induced changes on the coasts of Indonesia.

Reference will also be made to ecological changes that accompany gains or losses of coastal terrain, and to some associated features that result from man's responses to changes in the coastal environment. (full text)

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Studies of Indonesian Tuna Fisheries [1]

INTERACTIONS BETWEEN COASTAL AND OFFSHORE TUNA FISHERIES
IN MANADO AND BITUNG, NORTH SULAWESI

Nurzali Naamin, C.P. Mathews, D. Monintja


ABSTRACT

Since 1990 an important offshore industrial tuna fishery has been established in northern Indonesian waters. This fishery is theoretically confined to the EEZ, but in practice it occupies large areas of territorial and archipelagic waters. Fishing is carried out by "sets" or groups of boats based on a single purse seiner, supported by carrier and smaller patrol boats. These groups fish around rumpon (FADs) deployed in waters from 200-4,000 m deep, and take substantial catches, most of which is landed directly into General Santos City and other southern Philippine ports. The offshore fishery lands more than 50,00 mt per year from waters around North Sulawesi and northern Irian Jaya. Coastal fishing is carried out for skipjack by two kinds of small pole-and-line vessels ("funai": 5-15 GT; "huhate": 20-30 GT) in North Sulawesi. The coastal fishery landed less than 9,000 mt of skipjack in 1989, the last year before large scale offshore fishing commenced. Data for Manado and Bitung (North Sulawesi) were analysed to determine the effects of the offshore fishery on the skipjack and yellowfin fisheries based in these cities. Skipjack CPUE fell in Manado (from 50-70 mt/boat/year in 1980 to less than 20 mt/boat/year in 1992) and Bitung (from more than 100 mt/boat/year in 1980 to about 60 mt/boat/year in 1990). Effort on skipjack in Bitung rose slowly from approximately 40 boats in 1986 to more than 100 boats in 1991, and then fell to under 35 boats in 1995; the decline was probably due to competition with the industrial fishery. Industrial CPUE fell from 0.69 mt of tuna/GT of effort/year in 1993 to 0.37 mt/GT in 1995. Available data are insufficient for a complete analysis of offshore-onshore tuna fishery interactions. Nevertheless it is likely that industrial, offshore tuna fishing impacted the coastal fisheries in Manado and Bitung by reducing the amount of skipjack and yellowfin available to the coastal fishery.(full text)

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