Last updated on 10 March 2014
The two main target species of red snappers caught in Aru, Arafura and Timor Seas are identified as Malabar blood snapper (Lutjanus malabaricus), and Scarlet snapper (Lutjanus erythropterus). A stock assessment of these two species was conducted during the joint research on shared stocks of red snappers by Australia and Indonesia in the Arafura and Timor Seas between 1999 and 2003. The objectives of this joint research were first, to describe the population dynamics, stock structure and biology of snappers (primarily L. malabaricus) relevant to the management of stocks shared between Australian and Indonesian fisheries; second, to characterize the social and financial structures of the Indonesian fishery so they could be taken into account in the development of management strategies; and third, to explore ways of developing complementary management for the long term sustainability of the snapper fisheries (Blaber et al., 2005).
Stock structure was evaluated by looking at the genetic population structure of these two species in both Australia and Indonesia by allozyme electrophoresis and sequence variation of mitochondria DNA. The analysis of the allozyme data on the genetic structures of the 2 species of red snappers (L malabaricus and L erythropterus) from central and eastern Indonesia including Arafura and Timor Seas indicated the existence of 6 discrete populations of L malabaricus, of which 5 of these are stocks in Arafura and Timor Seas (Kupang, Ambon, Tual, Aru and Merauke) (Fig 1). While L. Erythropterus showed genetic homogeneity covering a large area in Arafura and Timor Seas region (Salini et al, 2006)(Fig. 2).
Figure 1. Stock structure of L. malabaricus Source: Salini et al., 2006.
Figure 2. Stock structures of L. eryptropterus Source: Salini et al., 2006.
A more recent study (Prisantoso and Badrudin et al, 2010) indicates that there may be separate stocks in Indonesian and Australian waters.
Several workshops to focus on the stock assessment were conducted during the joint research project. Stock assessment of all red snappers was analyzed via a biomass dynamic model for the Arafura Sea, based on Australian and Indonesian catch data collected by the project enumarators, District Fisheries Government, research and survey data on trawls, transhipment data provided by commercial companies, harbourmaster data on landing, observer and biological data. All these data combined with the results of socioeconomic study provide inputs to stock assesssments and management. Recent Indonesian catch data presented a problem and had to be estimated, resulting in the modelling of two possible catch scenarios, and results were considered to be relative rather than absolute estimators of abundance (Blaber et al 2005).
Last updated on 10 March 2014
The joint research between Australia and Indonesia produced a list of management recommendations on shared snapper fisheries in Arafura and Timor Sea. The result of the stock structure analyses led to an assumption that Indonesia and Australia fish the same stocks of L malabaricus and L erythropterus, particularly for fishing grounds along the transboundary areas. Within this context, Australia suggesteda collaborative management plan for the shared stock of red snappers in Indonesian and Australian waters be developed. However, the results of a recent paper presented by Prisantoso and Badrudinet al (2010) that indicated that there are separate stocks in Indonesian and Australia waters were discussed during the workshops on red snappers in 2008 and 2009, and further discussion among two countries is planned to develop possible management options.
Table 1: Preliminary list of management options for snapper fisheries in the Timor and Arafura Seas and their potential applicability to each fishery sector of the conceptual model. Fishery sectors are described in Table 1. Y: yes (applicable); N: no (not applicable).
|Management Options||Timor Sea||Arafura Sea|
|Timor Barat||Sahul Bank Indonesia||Sahul Bank Australia||Maluku||Fish net Indonesia||Fish trawl Australia|
|Capacity controls:||Y short-term, N long-term||Y short-term, N long-term||Y short-term, N long-term||Y short-term, N long-term||Y short-term, N long-term||Y short-term, N long-term|
|a) Includes raise license fee/vessel size/gear type sk||Y short-term, Y long-term||Y short-term, N long-term||Y short-term, N long-term||Y short-term, N long-term||Y short-term, N long-term||Y short-term, N long-term|
|b) Min. legal size– on capture||N||N||N||N||N||N|
|c) Min legal size – gear||Y||Y||Y||Y||Y||Y|
|Effort Limits (eg seasons)||Y||Y||Y||Y||Y||Y|
|Multizone Management||In place||In place||Y||In place||In place||Y|
|Close the Fishery||Y||Y||Y||Y||Y||Y|
Source: Anon, 2003.
Table 2: Advantages and limitations of the potential management options for snapper fisheries in the Timor and Arafura Seas listed in Table 1.Y: yes; N: no.
|Management Options||Selective gear||Non -Selective gear||Advantages||Limitations|
|MPAs/closure||Y||Y||Protects range of species and/or habitat; good in data poor area; limits harvest||May re-distribute effort so higher pressure outside; needs to be big enough; social displacement; inefficiency; bilateral agreement needed|
|Limited entry||Y||Y||Limits effort and/or yield; avoid over-capacity; capitalization; ownership||Allocation problems; displacement of effort; needs licence system|
|Capacity controls –||Y short-term, N long-term||Y short-term, N long-term||Limits effort and/or yield; avoid over-capacity; capitalization||Regulation|
|a) Includes raise license fee/vessel size/gear type sk||Y short-term, Y long-term||same||May increase government revenue|
|b) Min. legal size– on capture||N||N|
|c) Min legal size – gear||Y||Y||Protects juveniles; improves catch value||Only protects juveniles; difficult for mixed species fisheries; not suitable for small targets; survival rate of escapees|
|Effort Limits (eg seasons)||Y||Y||Protect spawners and/or juveniles; limit catch and harvest||Difficult to apply in high seas; shift effort to alternate fisheries|
|Catch limits||Y||Y||Direct control||Need good statistics; high grading|
|Multizone Management||Y||Y||Preserves catch niche for smaller operators; reduces sector conflict; protect habitat||Local, regional, national policy agreement|
|Habitat Protection||Y||Y||Shifts effort||Displace effort|
|Stock Enhancement||Not viable for these fisheries|
|Close the Fishery||May save resources||Drastic displacement|
|Restrict trade||Prevent destructive practices thus protect habitat; cheaper than controlling catchers||International cooperation|
Last updated on 10 Mar 2014
The stock assessment workshop in 2003 determined Maximum Sustainable Yield (MSY) and associated reference points but, given the associated uncertainty in the model, used them only as relative measures. The authors decided to reference the biomass in 1990 as the limit under which the biomass should not be allowed to fall. This biomass level (6,500 tons) was chosen as it represents the year that the biomass was slightly above the biomass at MSY (Blaber et al 2005).
Last updated on 10 March 2014
To accommodate the lack of information, the joint Indonesian/Australian study examined two catch history options: the pessimistic one assumed a maximum catch in year 2002 of 4,000 tonnes. For the optimistic scenario, the 2002 catch was assumed to be 2,000 tonnes. In both cases, catches for the intervening years were estimated by linear interpolation. In addition to that, due to the data-poor situation, the status of the fishery relative to sustainable yields was investigated. The biomass at 1990 has been chosen as the limit under which the biomass should not be allowed to fall (i.e. the target is that for the fishery to return above the limit, and that may be sustainable in the long term). This year was chosen as it represents the year that the biomass was slightly above the biomass at the Maximum Sustainable Yield (Blaber et al 2005).
The report illustrated two options (pessimistic and optimistic) using biomass at 1990 as a reference point. For the pessimistic scenario where the catch in the year 2002 was at its higher estimate, 2002 biomass levels were estimated at 11% of the limit reference point (biomass in 1990). Recovery of the stock would be protracted even under an assumption of zero future catch, with only partial recovery in 2010 to 30% of the limit reference point (Figure 3). Under the more optimistic assumption – the 2002 catch is 2,000 tons – the 2002 biomass is at 31% of limit reference levels. If the future catch is kept at 2002 levels the resource will continue to slowly deteriorate to a 2010 biomass merely 23% of limit reference levels (Figure 4).
Figure 3. Estimated catch levels (tons) by year since 1971 for the Arafura Sea snapper fisheries, biomass levels as a proportion of 1990 biomass (%) and biomass at Maximum Sustainable Yield (%) under the pessimistic option projecting catches similar to 2002.
Source: Blaber et al (2005)
Figure 4. Estimated catch levels (t) by year since 1971 for the Arafura Sea snapper fisheries, biomass levels as a proportion of 1990 biomass (%) and biomass at Maximum Sustainable Yield (%) under the optimistic option projecting catches similar to 2002.
Source: Blaber et al (2005)
Given the potential inaccuracies in the model, the assessment was treated as a relative measure rather than an absolute estimator of abundance. Moreover, due to the paucity of current data and the simple assumptions of the population model, it is clear that the model should be used to investigate policy options rather than for quantitative prediction (Blaber et al 2005).
More recently, Indonesia’s Commission for Stock Assessment 2010 report classifies many of the Arafura and Timor Seas fisheries as fully exploited or over exploited (Anon. 2010 in ATSEA 2012).
The snapper fishery in Aru, Arafura and Timor Sea is targeted by semi-industrial and industrial operations using bottom longline and fish net/fish trawls. The traditional fishery uses dropline/handline, and bottom longline. The semi industrial bottom longline fishery targets larger fish for export purposes, where most of the vessels originate from Tanjung Balai Karimun in Sumatera, witha sub-base in Kupang, where catches are transported by carrier vessels from Probolinggo (East Java).
There have been observed changes in the catch composition of snapper fisheries in the region, based on catch data analysed from 1977 bottom longline and trap vessels from 2005 to 2007. The catch share of Malabar blood snapper declined from 42.1 % (2005) to 30.8 % (2006) and then 24.7% (2007). Another change was in size distribution, using the parameter of length at first capture. Studies show a decline in snapper size structure, for Malabar blood snapper from 50.7 cm and 67.3 cm (2000/2002) to 41cm (2007), and for Scarlet snapper from 59 cm (2000/2002) to 39 cm (2007) (Nuraini and Ernawati 2009). It is likely that the snappers landed were immature and yound broodstocks , compared to the sizes landed during the period of 1999-2002, which was generally longer than 60 cm in total length (Badrudin et al 2004) . These changes in catch composition and size structure can be an indication of unsustainable fishing (table 3).
Table 3. Changes of catch composition. Source: Nuraini and Ernawati 2009
Last updated on 10 Mar 2014
Eastern Timor, Aru and Arafura Seas are the major fishing grounds for red snappers, contributing to more than 30% (35,112 tons in 2007 and 27,012 in 2008) of the total catch in Indonesia (116,994 tons in 2007 115,523 tons in 2009), (MMAF 2009, 2010). Red snappers stated in government statistic data may consists of several species of Lutjanidae. The limited available catch data of snappers (likely L malabaricus and L erythropterus) collected from Tanjung Balai Karimun bottom longline vessels sub-base Kupang (west Timor) and Probolinggo (east Java) was 1,673.5 tons (2007), 1,678.2 tons (2008) and 1,523.3tons (January to August 2009)(table 4) (Badrudin and Aisyah 2009).
Table 4. Catch landings. Source: Badrudin and Aisyah (2009)
Figure 5. Aru, Arafura and East Timor Seas are part of Fishery Management Area number XI, with total landing of 30%
Source: Processed from Capture Fisheries Statistics of Indonesia in MMAF (2009)
Information on Catch Per Unit Effort (CPUE) of red snappers in Aru Arafura and Timor Seas is not available. It is likely caused by the paucity of data on the number of vessels, carrier ships and fishing trips.
The increase of fuel price in 2007 decreased the number of vessels (bottom longline) operating in Arafura and Timor Seas from 217 to 187.