A Review on the Research and Fisheries of Barramundi, Reef Fish, Dugongs, Turtles and Spanish Mackerel in the Papua New Guinea Side of the Torres Strait
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SPC/Inshore Fish. Mgmt./BP 27 1 June 1995 ORIGINAL : ENGLISH SOUTH PACTFIC COMMISSION JOINT FFA/SPC WORKSHOP ON THE MANAGEMENT OF SOUTH PACIFIC INSHORE FISHERIES (Noumea, New Caledonia, 26 June - 7 July 1995) A REVIEW ON THE RESEARCH AND FISHERIES OF BARRAMUNDI, REEF FISH, DUGONGS, TURTLES AND SPANISH MACKEREL IN THE PAPUA NEW GUINEA SIDE OF THE TORRES STRAIT by B.D. Kare Dept. of Fisheries & Marine Resources Port Moresby, Papua New Guinea A Review on the Research and Fisheries of Barramundi, Reef fish, Dugongs, Turtles and Spanish mackerel in Papua New Guinea side of the Torres Strait. Barre D.Kare Department of Fisheries and Marine Resources Research and Surveys Branch Kanudi Fisheries Research Station P. 0. Box 165, Konedobu, Papua New Guinea. Introduction The Torres Strait Treaty between Australia and Papua New Guinea was signed on 18 December 1978. The Treaty establishes the Protected Zone within which both countries have rights and responsibilities. The main purpose of the Protected Zone is to protect the traditional way of life and livelihood of the traditional inhabitants, including traditional fishing. Several marine species in the area are common to both Papua New Guinea and Australia. Barramundi are fished throughout northern Australia and southern Papua New Guinea. Prawn stock occur within the area and extent into the Gulf of Papua arid the Gulf of Carpentaria. The migration of tropical rock lobsters provides an example of a common stock that must be fished and shared. Dugongs and turtles occur throughout the area and these are important to the traditional way of life of the inhabitants. The purpose of this review is to update our understanding on the current status of the commonly used or shared resources of the Torres Strait from the PNG side of that region and to brief on this to the Australian and PNG scientists and officials in a technical meeting scheduled to review the Torres Strait Region fisheries in the later part of 1995. The review concentrates on the five fisheries (barramundi, reef fishes, dugongs, turtles and Spanish mackerel) that are currently been exploited by the local fishermen. Barramundi (Lates calcarifer) Research and Fishery Past history - Research The early history and development of the barramundi research andfishery has been described by Dunstan (1961, 1962) ; Reynolds and Moore (1973, 1982); Moore (1982) Anon (1979, 1980) and Opnai VOL 1/630 2 1 and Tenakanai (1987). These studies were conducted to understand the biology and ecology of the species as a result of a major i commercial enterprise in Western Papua. i When the Division of Fisheries was established in 1954, under the then Department of Agriculture, Stock and Fisheries, a series of | surveys were undertaken to estimate the density of the population : (Dunstan 1961, 19S2) . After 1961, further surveys were conducted I in the area to further gain information on the commercial quantities. The results of these have not been published, due to ' incomplete records and in many cases the information gathered was lost. In 1970, detailed investigation commenced and considerations were given to such factors as movements, growth, mortality, reproduction, commercial yields, economic viability and conservation measures (Reynolds and Moore, 1973; and Anon, 1979 and 1980) . The aspects of the fishery has been reviewed by Opnai and Tenakanai (1987). Distribution and Abundance The species distribution and abundance is confined to the southern part of the country's coast and has been described by Dunstan (1961 and 1962); Reynolds (1972, 1978) and Moore (1980). It ranges from the Mullins Bay in the east to the Irian Jaya border in the west. It is most abundant in rivers with substantial lake and swamp systems and with extensive deltas. A high concentration of the population exists in the Gulf of Papua, with it's deltaic system to the Fly, Kikori and Purari Rivers. It is less abundant on the east coast which lacks extensive swamps or deltaic systems. The eastern rivers are short and fast flowing. Age and growth Reynolds and Moore (1982) used length frequency analysis and I length increment data from tagging to determine growth rate of ; barramundi. They seined extensively in the coastal waters of western Papua New Guinea (P.N.G).Such an extensive seining has , , provided the unbiased length frequency distributions needed to determine year classes from modal progression. From their data analysis, they calculated mean lengths at age 1, 2, 3, 4 and 5 (years)of barramundi in Papua New Guinea to be 328, 454, 566, 663 and 750 mm respectively and suggested that this represents the whole population. The life history of this fish is complex and the growth rates vary considerably between age classes. Reynolds and Moore (1982) showed that growth is apparently slower between 3 February and September and varies considerably during different life stages. Fish in freshwater have a much higher condition factor than those in salt water and are thus likely to grow much faster. Mortality rates The population dynamics of barramundi was studied by Reynolds (1978). He estimated the mortality rate using the Ricker/Beverton Holt model and divided the population into four cohorts according to the biological stages. He suggested that the 4th cohort makes up the commercial fishery (fish > 55 cm fork length). However, he showed that the fishing mortality was highest in the first cohorts (i.e fish < 35 cm fork length). This is surprising, as this group does not feature in the commercial catches. The most likely reason that appear to contribute to such a high mortality (fishing mortality) in the first cohort (~ 1 year old fish) is the high exploitation of this size fish in the coastal waters by the local artisanal fishermen. Spawning migration The spawning migration from inland waters to the coastal waters (catadromous species) is from September to January, corresponding with the dry season in the area (Moore and Reynolds 1982). Most fish that take part in this spawning migration are 3-4 years old. Moore (1982) indicated that spawning migration is subject to substantial lowering of inland water level. Post-spawning migrations back to freshwater also occur and some fish may repeat the spawning cycle but not every year. The fish that move from inland waters to the coastal waters for spawning, do not become resident in the coastal waters, but return to the same general area from which they migrated. Reproduction Moore (1982) identified a major spawning site between Sigabaduru and Jarai with a minor one at the Kiwai Island. The species is a protandrous hermaphrodite, that is it matures first as male and later changes to a functional female. The fish becomes sexually mature in the 4th year (590 to 690 mm fork length), at this stage they are male and at the age of 8 to 9 years the majority become females. There are some primary females which mature at 73 cm or 6 years. Fecundity is high, increasing with fish size. Moore (1982) sampled from fish lengths of 110 cm and 115 cm (fork length) which gave an estimates of 10,000,000 and 32,200,000 VOL I / 632 4 respectively. Spawning occurs in the coastal waters, where the eggs hatch and the larvae (< 5 mm fork length ) move into neighbouring coastal swamps during the months of November to February with the floods and spring tides. The swamps begin to dry in June - July and by August - September they are completely dry. Most juvenile barramundi ( about 200 mm fork length) leave the swamps at this time and migrate to the coastal waters and move eastward stopping for periods around the mouths of creeks, but do not enter. By the end of the first year, some have entered the estuary of the Ply River. The recruitment to the freshwater regions is by 1 + year old fish. This recruitment is not uniform as some move into the freshwaters after 1 or 2 years later. Not all fish move into the inland waters as there seems to be aresident population of all ages that remains in the coastal waters. Recent history - Research The distribution, biology and ecology of this most valuable resource are reasonably well understood (Reynolds and Moore 1973 and 1982; Reynolds 1978; Moore 1979, 1980 and 1982; and Anon 1979 and 1980). No adequate information however, is available on the dynamics of the fishery and the total fishing effort involved in the fishery. During the period 1989 to 1990,two research projects were conducted, particularly to (1) . gain information on the total fishing effort involved in the fishery, both in the coastal and inland waters and (2) .estimate seasonal abundance of juvenile barramundi in the coastal water. The former project was completed in 1989 and this involved interviewing of individual fishermen in the inland and coastal fisheries (Mobiha and Murri 1993) . They estimated that a total of 200 fishermen are engaged in the coastal fishery and that each have approximately one barramundi gill net. The largest concentration of the fishermen and nets appear to be located at the Torro Pass, in the southern bank of the Fly estuary (Katatai and Sui villages). This narrow channel is believed to be the migration route for barramundi to and from the spawning ground. In the inland fishery, most of the barramundi fishing occurred in the lower Lake Murray villages (Mobiha and Murri 1993) . This is due to easy access for the fishermen to sell their catch to the freezer boats or to the land based fish factory at Boboa. The second study concentrated on the seasonal abundance of juvenile barramundi in the coastal water. Samplings were conducted by setting gill nets in the area west of Daru; from VOL 1/633 5 Daru island to the mouth of Binaturi River, to the west.