NATIONAL FISHERIES AUTHORITY

PO Box 2016, Port Moresby, National Capital District, Papua New Guinea

Telephone: (675) 309 0444, Facsimile: (675) 3202061, Email: nfa@fisheries.gov.pg

Introduction

Prawn fishery has been in Papua New Guinea since the colonial era and is still in existence to date. The success of this long existence is a resultant of a well-structured management plan that governs the fishery, in particularly, the Gulf of Papua Prawn Fishery. This research involves scientists going out on surveys to collect penaeus merguiensis samples for analysis. The analysis and report is then translated into recommendations and laws to safe guard the fishery and the stakeholders that interacts with it. This particular concept was tried out in the formerly existing fishery: The Orangerie Bay Prawn fishery.

As such, the survey aim to quantify and to determine the catch quantity and quality of the penaeid species and to see if it be able to be reopened for commercial trawling operations. The primary objectives of the survey are to:

1. Calculate catch rates (CPUE) of prawns and bycatch,

2. Determine recruitment of P. merguiensis, and species structure

Background

The Orangerie Bay Prawn Fishery is located in Milne Bay Province, south-west of Alotau. It is a relatively small fishery compared to the Gulf of Papua prawn fishery, and has operated with only one or two smaller vessels since 1981. The bottom comprises rocky grounds, reefs and sand compared to the soft substrate, which forms the seabed of the Gulf of Papua. The principle industrial trawling grounds are located between Baibara Island and Saubina, from 2 to 10 m (approximately 1 to 5 fathoms) depth, but chiefly between Laimodo and Saubina. The seaward limit of the trawl grounds is the 5 fathom (10 m) depth contour. The south-easterly trade winds begin in April or May and blow steadily through to October. During these winds, the big seas affect the area west of Gadaisu. The ocean swells 1.8 m high may roll for long periods. Because of this reason, fishing is restricted to the sheltered water to the east, where under favourable conditions of rainfall and tide, good catches are made.

Similar to the Gulf of Papua Prawn Fishery, the Orangerie Bay Prawn Fishery had been in existence fishery since early 1980s. Following the years there after, the fishery had faced an annoyance of ownership rights issues between the locals and the fishing industry. Thus, led to disinterest from the industry and ultimately leading to the fore closure of the fishery in the late to mid-2000. The first trawl survey for stock assessment of offshore shrimp was conducted in 1987 and the results from these surveys are the base for establishing total allowable catch (TAC) in the offshore shrimp fishery.

After a period of more than 10 years since the closure, the National Fisheries Authority (NFA) has now conducted a biological survey to determine the viability of opening up the fishery again.

Materials and Methods

Study Site

The NFA sanctioned Orangerie Bay survey for 2016 was conducted from November 5^thth to November 7th, 2016 on board Fishing vessel Charisma; a Licenced GOPPF 26m quad-rigged bottom trawler. The survey covered 2 sites; 1: Laimodo and Bona. 2: Gadaisu, in the Suau area, South Cape, Milne bay Province.

Sampling Gear

A 26m beam trawler, fitted with a quad-rigged gear of 50mm mesh size nets for both the main net and the cod ends. Also, a try net (50mm mesh) was used to check availability of prawns in the water before and during the shot (winch up every 15 minutes).

Sampling Timing and Intervals

Due to the size of the fishing area, the sampling time was set for an hour. Basically, the nets are shot away for an hour and then are winched back up for sampling and processing. The method replicates for the shots hereon after.

Sample collection and sorting

Firstly, as the net comes up; the catch comprising of shrimps and by-catch are discharged into the holding tray and then shovelled onto the sorting conveyor for processing. The prawns are hand pick and placed onto the separate baskets. The prawns are then sorted out in different species furthermore, into grades of small, medium and large. Once this is done, the P. merguiensis species samples are randomly handpicked from their grading baskets/bin for carapace lengths recording whereas rest of the prawns are processed, packaged and stored for commercial purposes.

Carapace Data collection

Using the carapace standard measurement (minimum length of the carapace), each P merguiensis specimen is measured with a vernier calliper from the inside of the eye socket to the posterior margin (Cole H.A. and Mistakidis, M.N., 1953). The minimum sample size per shot for P merguiensis is set at 78 samples. In order to avoid bias selection in carapace length, the prawns are handpicked from each bin or bucket of different graded sizes and placed in one bucket and then tossed from side to side and top to bottom. The carapace length for the first 78 samples are measured and recorded.

By- catch Data collection

The bycatch are all weighed using nelly plastic bins (60cm×30cm×50cm). Bycatch weights are captured using a 50 Kg hanging scale and records are entered onto data sheets.

Data management

All survey data are written on paper based sheet and then brought back to the NFA office in Port Moresby, National Capital District. Then, the data are entered into MS Excel spreadsheet version. Once entry is completed, the data were analysed in pivot table and appropriate graphs are drawn.

Catch per Unit Effort was calculated as weight in kilogram (

) divided by effort as time in hours trawled (

), where weight is the total weight of prawns sampled and time in hours as number of shots per day= 6 (α) multiply by the 1 hour per trawling (β) multiply by 2 sites (

) by 3 days (

, where

Results

Overall species structure and CPUE

Total hours fished = 15 hours

Species	Total Weight (kg)	Overall CPUE (kg/hr)
White Banana	33	2.2
Black tiger	29	1.9
Red Endeavour	17	1.1
Brown tiger	10	0.7

Table 1. CPUE of prawn species harvested from Orangerie Bay in ascending order

Distribution of Carapace Length total of 15 shots were done. Of which, a sample size of n= 1, 246 P. merguiensis were harvested for this survey. The samples were classified into class size of carapace length (CL) for the length frequency analysis.

Figure 1 Shows distribution of the carapace lengths recorded for P. merguiensis species

Statistical analysis

Mean = 33.4 mm

Variance = 20.7 mm

Standard dev = 4.6 mm

Max = 48.1 mm

Min = 24 mm

Range = 24.1 mm

Size class

Modal class = 30 – 34.9 mm

Min class = 20 – 24.9 mm

Max class = 45 – 49.9 mm

Catch Ratio

Prawn to Bycatch = 89 kg: 8,822 kg

= 1: 99

Ratio of female vs male

P.merguiensis = 379: 766

= 1: 2

Maturity stages of female P. merguiensis sampled.

Out of the total sample size of n = 379 females, a portion of the female species were sampled and recorded to get an indication of maturity stages which translates to future recruitment. The data collected shows that there are 12.60% of Zero stage, 22.83% of stage One, 35.96% of stage two and 28.61% of stage 3 or fully female.

The graph below summarizes the ratio between egg bearing and non- egg bearing females

Figure 2. Egg bearing vs non-egg bearing female P. merguiensis sampled during the survey

Discussion

The carapace length (CL) measurements were taken for P. merguiensis because it is the target species of prawns and is of higher value species, apart from P. monodon. Also this species (P .merguiensis) had its gender and gonad maturity study done to determine length-size at maturity and frequency of reproduction stages. Pre-season data collection of carapace lengths is vital to see the trend in which young recruits are coming out from the nursery grounds into the fishing grounds, and most importantly if there are a lot of egg bearing females that are first timers in the fishing ground, than they must be left alone to reproduce first before harvesting, i.e., egg bearing females must be protected/saved.

The current survey done in Milne Bay’s Orangerie Bay shows potential with the occurrence of two (2) major high value species P. merguiensis (banana prawn) and P.monodon. (Black-tiger prawn). These two high value species are recorded as the 2 most dominant with respective CPUE of 2.2kg and 1.9 kg/hr as shown in Table 1. The rest of the low value species show CPUE’s of 1.1kg and below.

At this stage most of the data collected and analyse is for the banana prawn as we were able to do sex identification and gonad maturity stage assessment.

The statistical analysis shows a mean carapace length (CL) of 33.4 mm and standard deviation of + or – 4.6 mm. Therefore usual catch in the area would have CL sizes between 28.8 mm and 38 mm, anything caught outside of these size range would be regarded as unusual clusters. In this case the area shows potential of harvesting large banana prawn size up to 48.1 mm and smaller sizes with CL of 24.1 mm. This is a normal population distribution size range where there are mixtures of sizes clusters in an area at a certain time with larger volume of population within 28.8mm – 38mm, and fewer below 28.8mm and above 38mm.

The histogram shows data that was collected from the November 2016 survey. The histogram for banana prawn species as shown in Figure 1 also shows a negative skew towards smaller/ juvenile size prawns. This clearly indicates healthy recruitment for the fishery even in the month of November where as in the Gulf of Papua the recruitment is only in the beginning of the year. This indicates a continuous or regular cycle of recruitment coming into the fishing grounds thereby supporting a healthy fishing stock.

Again, from this survey, it shows a ratio of 1 female to every 2 male. Although there are less females the vast majority more than 80% are egg bearing with gonad stages between 1 and 3 fully ripe.

Moreover, high number of mature prawns found in the fishery fishing zone could be a resultant of many driving factors. One factor that stands out the most, is the salinity tolerance level. Studies conducted in the past shows a good correlation between growth and salinity. This salinity tolerance level causes growing juveniles to migrate outward due to less salinity in the estuary (D.J Staples and D.J Vance, 1986). So when they grow older they tend to move outward into areas where there is high content of salinity which becomes conducive for them to breed.

This fact can also give rise to having higher number of juveniles in the fishing grounds during rainy season due to run off from nearby tributaries and estuaries which lowers the salinity in the fishing area.

Conclusion

The Orangerie Bay Fishery in Milne Bay Province even though small still shows potential for commercial prawn trawling. This is shown through the prawn catch structure with 2 high value species being the dominant harvest, white banana and black tiger. White banana showed the highest CPUE of 2.2kg/hr and black tiger with 1.9 kg/hr.

Current regular catch for the fishery stand between the ranges of 28.8 mm – 38 mm. Nevertheless the fishery also shows potential of catching prawn with CL of up to 48 mm for white banana prawn.

The Gulf of Papua Prawn Fishery also currently harvest similar modal size class for its fishery. Hence these further strengthens the commercial viability of this fishery.

However for Orangerie Bay trawling using smaller vessel (less than 14 metre total length) as stated in the Management Plan is still the best way forward. Not only is this an appropriate input control it also ensures sustainability and protects the fishery from over-exploitation

Recommendation

o A full scale survey should be done to fully capture sufficient biological data so that the fishery can be further assessed using inferential statistics giving greater precision in terms of analysis and forecasting the future of the fishery and also, identify appropriate areas for change or improvement in the current management plan.

o A more intense Socio-Economic study to be carried out around the fishery area and nearby villages. This will help capture the human elements or aspects of the fishery. This will also help understand how the immediate resource owners depend on this resource/fishery and benefit from it. That way when amendments need to be made to the existing plan we can also integrate the human aspects to capture a holistic approach to the management plan.

o Conduct a stakeholder workshop as a way forward to disseminate information and advice to the appropriate stakeholders and also gather views to amend and update the management plan. With the involvement of NFA’s Provincial Support and Industry Development (PSID) Unit, local resource owners will be able to understand and further develop their aspirations in becoming involved in Small to Medium Enterprise (SME) and also realistically understanding what some of the limitations are.

o A final recommendation for the fishery is the use of appropriate Bycatch Reduction Device (BRD) and fish eye to maximise its prawn harvest and reduce bycatch

References

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