2. RESULTS FROM THE ACOUSTIC SURVEYS.

2.1 The Acoustic Method and its Limitations.
2.2 The Small Pelagic Fish Resources.
2.3. Acoustic Estimates of the Demersal Resources During the 1983-84 Surveys

Acoustic surveys combined with trawling for identification of the acoustic registrations provide data on distribution, abundance and species composition of the small pelagic resources. For the surveys in Oman, it is assumed that the survey grid totally encompasses the pelagic stocks in the area. Furthermore, no serious loss of acoustic data due to poor weather conditions has occurred. However, although the frame conditions were most favourable for acoustic surveys, the estimates are still vulnerable to sampling errors and random statistic variance.

Acoustic surveys are less suitable for the evaluation of demersal species This is mainly because the density level of the demersal stocks is much lower than the small pelagic stocks, making the relative sampling error and variance much higher. Therefore, less emphasis is put on the acoustic results concerning demersal stocks. They will be more thoroughly covered in the trawl-survey section.

2.1 The Acoustic Method and its Limitations.

Acoustic abundance estimation of fish is based on the principle that the intensity of the echoes reflected from the fish in the sea is linearly proportional to the density of fish in situ. By an electronic instrument, called echo integrator, the echoes received over fixed intervals of the vessels survey track are made representative for indices of fish abundance within these intervals. Apart from being density dependent, these indices are also dependent of the type of species and the size of the fish. To convert these indices of density into absolute densities one has therefore to apply both species dependent and size dependent correction factors. Information on these factors is usually aquired through calibration procedures on fish in situ or from experimental setups with fish in cages. Absolute densities are converted into absolute abundances by multiplying the densities of fish by the area of the fish distribution.

In spite of its relatively simple basic principles, the acoustic method has several limitations which always should be kept in mind when interpreting the results from acoustic surveys and applying them for fishery development purposes. Of the limiting factors the main are:

a) Underrepresentation of bottom dwelling fishes. Fish that stay close to the bottom, especially rays and flat fishes, are detected as part of the bottom and will not be distinguished by the echo integrator. In addition, due to a so called dead-zone, the fish immediately off the bottom are not fully represented in the estimates. All this leads to a certain underrepresentation of demersal fish, especially those living very close to the bottom.

b) Screening effect from plankton. Plankton is also detected by the acoustic system, and it is the task of the scientist on basis of the characters of the echo-traces and composition in the trawl catches to separate the density indices into plankton and fish. Various methods are available, both special acoustic/electronic setups and procedures for reading the echo-traces. But in areas with dense concentrations of plankton combined with scattered and low densities of fish, a correct separation of the echo-indices into fish and plankton is difficult. In such cases the plankton can represent up to several hundred times the amount of fish recordings, and assessing the fish abundance has more the character of qualified guesses than estimates. This factor does not seriously affect the total estimates if it concerns small areas only, but it might be significant in those regions where low-densities are found over large areas and will thus sum up to considerable total abundances.

c) Disproportional sampling in multispecies fish communities. Ideally, when several species are present in the same area one should distribute the indices of total density recorded by the acoustic system into indices of species densities and convert these indices into absolute abundance estimates by applying species and size dependent conversion factors on the indices. When the behavioural pattern of the mixing species (i.e. schooling pattern, depth preferences, day/night behaviour etc.) are quite similar, it is an ardous, if not impossible task to separate the species on basis of the echo traces. The species composition in the trawl catches are used as assistance in splitting the total estimates down to species or species group levels. But the catchability of the trawl is highly species and size dependent, and the distribution in the catches are not directely representative of the distribution in situ. In areas where the fish biomass is mainly made up of some few dominating species or species groups, the estimation of abundance is less complicated than in cases where a multitude of species contribute to the total abundance. In the last case the estimates suffer from low precision, both on the total and on the group/species level.

In acoustic surveys, separate estimates of pelagic and demersal fish are usually made to provide useful information to two different fisheries, the demersal and the small pelagic fishery. A total estimate is less useful. The separation into these two categories is usually relatively easy, based on the echotraces and the information from the trawl catches. The smallpelagic fish usually form distinct aggregations which can be easily separated. At times, however, the same species can be present in high abundances both in the pelagic and in the demersal community. In such cases even the separation into pelagic and demersal becomes difficult.

d) Lack of information on the acoustic properties of tropical fish species. As already mentioned, the conversion factor applied on the indices of abundance, to convert them into absolute abundances, are species dependent. Aquisition of the basic information leading to these factors is an ardous task, and for most tropical species this work is at present in its most initial phase or not really started at all. In lack of detailed information on the dominating species, one often has to apply values from similar and better known species from temperate waters. In addition, when dealing with multispecies occurrences of fish, it is almost impossible to calculate the various conversion factors to use in the estimates and a rough effective overall factor has to be applied.

All these limitation factors, when applicable, lower the precision of the acoustic estimate.

The suitability of Omani waters for acoustic surveys.

The pelagic fish community in Omani waters is made up of relatively few species mainly concentrated in high densities. The demersal community is characterized by a multitude of species. The demersal biomass has a scattered distribution, with only very few dense patches. The occurrence of plankton did not constitute a serious problem. As a general conclusion, acoustic research can easily be applied to the stocks of small pelagic fish found in Omani waters, but this method does not suite as well the demersal stocks.

2.2 The Small Pelagic Fish Resources.

2.2.1 Distribution and Relative Abundance During the 1983-84 Surveys.
2.2.2 Biomass Estimates - Small Pelagic Fish
2.2.3 Results from Earlier Surveys Dr. Fridtjof Nansen.
2.2.4 Estimates of Yield of the Small Pelagic Resources.
2.2.5 Nursery Areas

The small pelagic resources in Oman waters consist mainly of Trachurus indicus, Sardinella longiceps and Sardinella gibbosa. Less dominating, but important, are Stolephorus punctifer, Dussumieria acuta, Decapterus russelli, Rastrelliger Kanagurta, Selar chrumenophthalmus and Etrumeus teres. While the stocks of Sardinella longiceps, occurring in shallower waters, have been exploited by the beach-seine fishery, the presence of much bigger stocks of Trachurus indicus, farther offshore, has been less known.

2.2.1 Distribution and Relative Abundance During the 1983-84 Surveys.

Figures 4-6 show the distributions of small pelagic fish from the three surveys. The distributions are given in four density levels: scattered, gathered, dense and very dense, which roughly correspond to 14- 140 tonnes/nm2, 140-280 t/nm2, 280-1400 t/nm2 and > 1400 t/nm2 respectively.

The dominant species in the different locations were identified by trawling.

Figure 4. Distribution of small pelagic fish during the first survey, based on acoustic registrations.

A. North of Ras al Hadd

In this area, small pelagic fish is nearly absent. During the two coverages made in this region, only very few scattered occurrences were located. These were mainly of Dussumieria acuta. This species was present in 6 out of 17 hauls, with an average catch of 115 kg/hour, all hauls included, representing 20 % of all fish caught in the area.

Figure 5. Distribution of small pelagic fish during the second survey, based on acoustic registrations.

Figure 6. Distribution of small pelagic fish during the third survey, based on acoustic registrations.

B. Ras al Hadd - Masirah Island

In the Ras al Hadd - Masirah Island area, scattered to dense occurrences of small pelagic fish were found during all three coverages. The main species were Trachurus indicus, Decapterus russelli, and Sardinella gibbosa in order of importance. Also present, but in lesser quantities, were Dussumieria acuta, Stolephorus sp. and Etrumeus teres. Information on the relative abundance of the most important pelagic species in the catches is given below:

Species	Bottom trawl		Pelagic trawl
	% of	% of	% of	% of
	pel. fish	all fish	pel. fish	all fish
T. indicus	60	16	62	41
D. russelli	27	7	16	11
S. gibbosa	-	-	7	5
D. acuta	-	-	8	5
Stolephorus spp.	-	-	4	3
E. teres	-	-	3	2
Other pelagic	13	3	-	-
Total pelagic	100	26	100	67
Number of hauls	28		9
Mean pelagic catch/hour	280		786

The main purpose of the trawling is to identify the acoustic registrations. In addition, many of the bottom hauls are carried out in a semi random trawl survey programme. The average catches thus do not reflect the catches to be expected in a commercial fishery, but can be used as a rough indication of the level of the resources in and between regions. Expected commercial catch rates will be discussed in section 3.3.

C. Masirah Bank

From the southern tip of Masirah Island to Ras al Madraka, also referred to as the Masirah Bank region, the small pelagic resources consisted mainly of Trachurus indicus, Sardinella gibbosa, Sardinella longiceps and Decapterus russelli, with very small fractions of anchovies (Thryssa sp. and Stolephorus sp.). The pelagic fish distribution in the catches was as follows:

	Bottom trawl		Pelagic trawl
	% of	% of	% of	% of
	pel. fish	all fish	pel fish	all fish
Trachurus indicus	93	60	93	88
Sardinella gibbosa	-	-	3	3
Sardinella longiceps	-	-	1	1
Decapterus russelli	7	4	2	2
Total pelagic	26	100	67	100
Number of hauls	34		20
Mean pelagic catch/hour	1728 Kg		2550 Kg

Trachurus indicus (the Indian horse mackerel) has its distributional center of gravity in this area. The greatest concentrations were found close to the shelf edge during all three surveys, with mean lengths of 16cm, 24cm and 24cm respectively. During the second survey (November), younger specimens, around 10 cm mean length were located closer to the shore, at around 20-25 m depth. These probably recruited to the main stock at the shelf edge in the following spring, thus lowering its average length.

During the two surveys in spring (survey I and III) the highest catches of Indian horse mackerel were obtained in the 90-100 m bottom depth zone. 90% of the total catch of Trachurus indicus came from this area. In November (survey II) the maximum catches were obtained in the 130-140m bottom depth zone.

Sardinella gibbosa and S. longiceps have their centre of distribution on the Masirah Bank, in the shallow waters between 20 and 30 m bottom depth, S. gibbosa also occurring in shallower waters, to 14 m bottom depth. The mean length from the samples varies between 14 and 17 cm total length (TL), with no clear seasonal variation. The highest catches were obtained where the two species co-occurred, S. gibbosa being slightly dominating.

Decapterus russelli is distributed from 14 to 100 m bottom depth. The highest catches occurred from 20 to 50 m bottom during the first two surveys, while during the third survey this species seemed to concentrate between 75 and 100 m depth. The mean lenth from the samples collected in the course of the three surveys is 17 cm TL.

D. Sauquara region

The region from Ras al Madraka to Ras Marbat, including Sauquara Bank and the shelf north of Kuria Muria Islands, is in this report referred to as the Sauquara region. The small pelagic resources in this area consisted of Trachurus indicus, Sardinella longiceps, Etrumeus teres and Decapterus russelli. The pelagic fish distribution in the catches is given below:

	Bottom trawl		Pelagic trawl
	% of pel	% of all	% of pel	% of all
Trachurus indicus	73	58	12	6
Sardinella longiceps	16	13	75	40
Decapterus russelli	11	9	-	-
Etrumeus teres	-	-	13	7
Total pelagic	100	80	100	53

Trachurus indicus was located in scattered occurrences in a band off the shelf edge (150 m bottom depth) and slightly outwards. During the second coverage, the Indian horse mackerel was almost absent, the few catches below 3 kg/hour. During the third survey (May 1984), good catches of this species were obtained from the 50-80 m bottom depth zone. The mean lengths found in this region are the same as in the Masirah Bank.

Sardinella longiceps was located from about 20 m bottom depth to beyond the continental slope, with highest concentrations in bottom depths less than 60 m. Scattered, off-shelf occurrences were observed during the first two surveys and consisted of larger fish (range 20-24 cm) than in the shallow waters (range 14-17 cm). During the third survey, all sardinella caught was within the 20-24 cm size range.

Decapterus russelli was located from 70 m bottom depth to beyond the shelf edge. Best catches were obtained between 70 and 120 m bottom depth during the first two surveys. During the third survey, this species was virtually absent, with few and small catches close to the shore. Size ranged between 12 and 19 cm TL during the first survey, and between 19 and 30 during the second survey.

Etrumeus teres was caught from 20 m bottom depth to beyond the shelf edge (pelagic). Young specimens in the 7-14 cm range were found in the shallow waters, while from 70 m and outwards the range was 15-20 cm. The catches were not substantial and of the 8 catches only one exceeded 100 kg/hour. The off-shelf catches were on scattered registrations and were less than 3 kg/hour.

A special phenomenon in this area is the co-occurrence of Trachurus indicus, Sardinella longiceps and Etrumeus teres in the pelagic waters immediately off the shelf edge. These species formed a scattered longitudinal band of registrations along the continental slope during the first two surveys. This indicates that the hydrographic conditions of this area could favour plankton production above the average. It would be interesting to investigate, in the course of future research, the migration of this fish in relation to the strength of the upwelling. Our data are unfortunately too limited to allow such a study.

E. Salalah region

The region from Ras Marbat and eastward to the PDR-Yemen-border, is referred to, in this report, as the Salalah region. This area lies in the outskirts of the upwelling zone and this is reflected both in the lower primary production as well as in the lower fish densities. Only 5 trawl hauls were carried out in this region and small pelagic species were caught only. once. Among these, Sardinella gibbosa, S. longiceps, Trachurus indicus and Decapterus russelli. Only S. gibbosa exceeded 100 kg/hour. The area is thus not considered as promising for commercial pelagic fisheries after our investigations.

2.2.2 Biomass Estimates - Small Pelagic Fish

Table 2 shows the provisional biomass estimates of small pelagic fish from the survey reports. Through a second critical evaluation of the source data, some of the biomass figures have been revised. This mainly because the average fish size, in areas of very high fish densities, was found to be lower than the average for the region. As the calibration coefficient applied in the biomass calculations is fish-size dependent, this affects the estimates. Furthermore, the size of the areas represented by high densities have been slightly modified. Table 3 shows the revised and final estimates of the small pelagic fish in Oman waters. The same results are visualized in Figure 7.

Figure 7. The estimates of small pelagic fish, and their regional distribution.

The estimates of the total biomass of small pelagic fish from the three surveys ranges between 1 and 1.3 million tonnes (av. 1.2 million tonnes). The first survey was carried out with analog integrators with some saturation problems on very high fish densities. This does not apply for the second and third surveys where new digital integrators were used. Probably, the lower density levels recorded during the first survey can be explained with the loss of information due to the above mentioned saturation problem of the analog integrator. Therefore, we do not consider the difference in total biomass obtained from the surveys as evidence of any real difference. We consider 1.2 million tonnes as a reasonable figure to reflect the size of the standing stock of small pelagic fish in Oman waters, practically all of which is found between Ras al Hadd and Ras al Marbat. The main resources are found on the Masirah Bank, average 600 thousand tonnes and 60% of the total. Of the remaining 40 %, 10% is allocated to the region Ras al Hadd - Masirah and 30% to the Sauquara Bank. The seasonal fluctuations in biomass within regions are mainly caused by migration between regions. The Ras al Hadd - Masirah Island region is relatively stable in terms of fish resources. Some migration of Trachurus indicus between this region and Masirah bank can be inferred from the catch records. The main regional fluctuations are caused by migration of Trachurus trecae and, partly, Sardinella gibbosa and S. longiceps between Masirah and Sauquara Bank.

Table 2 Provisional biomass estimates from the survey reports. Small pelagic fish. Rounded figures, thousand tonnes.

Region	SURVEY I Mar-Apr '83	SURVEY II Nov-Dec '83	SURVEY III May '84
A North of Ras al Hadd	N.S.	10	0
B Ras al Hadd - Masira	150	100	75
C Masira Bank	600	850	1100
D Sauquara & Kuria Muria Banks	250	400	500
E Salalah region	0	50	5
Total	1000	1400	1680

NS = not surveyed

Table 3 Revised biomass estimates. Small pelagic fish. Rounded figures, thousand tonnes

Region	SURVEY I Mar-Apr '83	SURVEY II Nov-Dec '83	SURVEY III May '84	AVERAGE	AVERAGE REGIONAL DISTR. (%)	MAXIMUM FLUCTUATION (%)
A North of Ras al Hadd	N.S.	10	0	0	0	0
B Ras al Hadd - Masira	150	100	120	125	10	50
C Masira Bank	600	750	700	680	60	25
D Sauquara & Kuria Muria Banks	250	400	400	350	30	60
E Salalah region	0	50	5	-	-	-
Total	1000	1300	1225	1175	100	30

NS = not surveyed

A North of Ras al Hadd	0
B Ras al Hadd - Masira	55
C Masira Bank	225
D Sauquara & Kuria Muria Banks	60
E Salalah region	0
B-D Ras al Hadd - Ras al Marbat	100

The following list gives, for comparison, densities from other regions surveyed by the R/V Dr. F. Nansen with the same method:

t/nm2
100 - 110:	West Sahara, Senegal, Guinea
90:	Northeast Somalia
75:	Mauritania
60 - 80:	Ivory Coast, Ghana
30 - 40:	Tanzania, Mozambique
25:	Burma, Bangladesh
18:	Kenya, Thailand, Malaysia

The shelf south of Ras al Hadd, and especially the Masirah Bank, thus stands out as one of the worlds richest in terms of fish densities. However, fish densities do not directly reflect the production level and expected yield from an area. Therefore, comparison between the above areas and Oman should take into account that most of those areas are heavily exploited while Oman waters are virtually virgin.

As an example of high densities of fish that can be met in Oman waters we will refer to an intensive mini-survey carried out on an extreme dense aggregation of Trachurus indicus at the shelf edge of Masirah Bank at the end of the second survey. The aggregation formed a band along the shelf edge, 60nm long and about 4 nm wide. The estimated abundance of this aggregation was 205 thousand tonnes, with the extremely high average density of 3100 tonnes per nm².

The density distribution pattern of the small pelagic fish is shown in Table 5. Only about 15 to 25 % of the total is found in “scattered” to “slightly gathered” concentrations. Consequently, 75 to 85% is- located in “dense” to “ very dense” aggregations, very vulnerable to commercial fishing.

Table 5 Distribution of biomass on density levels (% of total biomass)

Density	Equivalent range (t/nm2)	SURVEY I	SURVEY II	SURVEY III	AVERAGE
Scattered	3-150	20	14	22	18
Slightly gathered	150-300	3	3	5	4
Dense	300-1500	64	54	28	49
Very dense	>1500	13	29	45	29

Table 6 shows the tentative species distribution in the aggregations of small pelagic fish, by region and by survey. Trachurus indicus dominates the Masirah Bank during all surveys, the Ras al Hadd - Masirah Island region during the two last surveys and the Sauquara Bank during the last survey only. Second in importance is Decapterus russelli, closely followed by Sardinella gibbosa and S. longiceps. As average for all regions and all surveys the analysis indicates that Trachurus indicus makes up 48% of the biomass, Decapteraus russelli 24%, Sardinella longiceps 14% and Sardinella gibbosa 11%.

Table 6 Tentative species composition in dense and very dense registrations of small pelagic fish, expressed as % of the estimated biomass

Survey >	B				C			D					B - D
	Ras al Hadd-Masira				Masira Bank			Sauquara & Kuria Muria Banks					Ras al Hadd -Ras al Marbat
	I	II	III	Av.	I	II	III	Av	I	II	III	Av.	Av.
Species
Trachurus indicus	0	75	70	48	50	60	50	53	20	10	85	38	48
Sardinella gibbosa	25	0	0	8	20	15	15	17	0	5	0	2	11
Sardinella longiceps	5	0	0	2	10	10	15	12	25	35	10	23	14
Decapterus russelli	25	25	30	27	20	15	15	17	55	50	5	37	24
Others	45	0	0	15	0	0	5	2	0	0	0	0	3

* Dussumieria acuta, Etrumeus teres etc.

2.2.3 Results from Earlier Surveys Dr. Fridtjof Nansen.

The R.V. “Dr. Fridtjof Nansen” has carried out 5 acoustic surveys in Oman waters in the period 1975-76. The biomass estimates of small pelagic fish for the super-region Ras al Hadd to Ras al Marbat (B-D) were as follows (thousand tonnes):

Cruise 1 and 2	Apr-May '75:	80
Cruise 3	Oct-Nov '75:	820
Cruise 4	Feb-Mar '76:	570
Cruise 5	May-Jun '76:	480
Cruise 6	Aug-Sep '76:	530

The mean from all surveys is 500 thousand tonnes and the mean of the four most consistent estimates is 600 thousand tonnes.

The results from the Arabian Sea Survey Programme (1975-76) suffer from limitations due to the very extensive programme which envisaged a survey of the whole region from Pakistan to Somalia in five coverages. Sampling intensity, both acoustically and in terms of fishing stations, had to be sacrified to the wide area coverage. The average sampling intensity during the five coverages in Oman was 11.8 nm/100nm, compared to the 20.2 nm/100nm² for the 1983-83 surveys. If we consider the Masirah Bank area, the most important for Trachurus indicus, the differences become even greater: 10 nm/100 nm² to the recent 24.2 nm/100nm² average intensity from the latest surveys.

Due to the open sampling track in the 1975-76 surveys, which was laid out before the real importance of the region in terms of fishery resources was known, it is possible that aggregations which are limited in extent, but strong in density, have been missed by the sampling track. This is especially applicable for the stocks of Trachurus indicus in Oman, as this species frequently forms such schools in the area. The biomass in the Masirah Bank area may therefore have been underestimated during the 1975-76 surveys.

However, it is striking that no major catches of Trachurus indicus were made in the Masirah Bank area in 1975-76. Of the 22 fishing stations carried out in the Masirah bank during those surveys, Trachurus indicus was present in 5 hauls and only in very small fractions of the total catches. These findings indicate that a major ecological shift might have occurred in the region between the periods 1975-76 and 1983-84. Unfortunately, available data cannot form the basis for the analysis of the above hypothesis. If major concentrations have not consistently escaped detection due to the relatively open sampling track in 1975-76, our data point to a major increase in the total biomass and to the relative importance of Trachurus indicus in the area. If so, considerable fluctuations in total biomass in the region might also take place in the future. Until more data become available, we consider this as the most reasonable and safe conclusion.

2.2.4 Estimates of Yield of the Small Pelagic Resources.

Estimates of the maximum sustainable yield (MSY) have usually been calculated according to the simple formula:

MSY = 1/2 MB₀

Investigations from other areas of the Indian Ocean provide the following K values (Pauly, 1978):

Sardinella longiceps	0.4 - 0.6
Sardinella gibbosa	1.1
Decapterus russelli	1.1

K values for Trachurus indicus are not found in the literature, but rough calculations from the changes in modal length observed during the survey period, indicate a K value of about 0.7 in the SW monsoon and immediate post monsoon periods, dropping to 0.3 during the NE monsoon and up to the arrival of the new SW monsoon. The same growth pattern is believed to apply to the other pelagic species: high growth in the period May-November and low growth in the period November-May. A rough, all-year growth coefficient for all pelagic species could therefore be 0.5. The small pelagic species in Oman waters are relatively short lived with a longevity of about 4-5 years. The natural mortality coefficient for fishes of such a life span is usually within the range 0.8 to 1.0 in unexploited populations (Hoenig, 1984). Most of the young fish seems to recruit to the parent stock within one year. For a first rough assessment of the yield we therefore use M = 0.8, K = 0.5 and recruitment age = 1 year for the pelagic stocks in Oman. Applying this to the functions developed by Beddington and Cooke we come to an exploitation rate of 23% of the initial total biomass which is also, well below the critical value for recruitment (Beddington and. Cooke, 1983). Applying this exploitation level to our biomass estimates, we obtain the following yield-estimates (thousand tonnes):

Total yield	270
By species:
Trachurus indicus	130
Sardinella gibbosa	30
Sardinella longiceps	40
Decapterus russelli	60
Others	10

The yield by species is obtained by using data in Table 3, and should only be considered as tentative.

The above yields are based on the production level of 1983-84 and are valid only if the stocks maintain such production level. Variations in the ecological system may induce long term changes in the fish production and species composition. As already mentioned, the relatively low estimates from the 1975-76 surveys and the minor importance of Trachurus indicus might coincide with a low level in the natural fluctuations in the fish community. It is therefore of vital importance that the level of the pelagic stocks is monitored when under exploitation to ensure that the fisheries are regulated in accordance with the long-term natural fluctuations in the bioproductivity of the stocks. Given the production level of 1983-84, the above total yield should be within the safe limit to ensure recruitment.

2.2.5 Nursery Areas

Masirah Bank seems to be the main nursery area on the basis of the length distributions. The shallow waters of less than 50m bottom depth were found to be an important nursery ground for immature Trachurus indicus, Sardinella gibbosa and S. longiceps. This area is probably of vital importance for the regeneration of the small pelagic fish stocks, and should not been given access to by any industrial fisheries. For the same reason, the small scale artisanal beach-seine fisheries in the Masirah region should preferably be regulated in order to avoid fishing on the immature parts of the stock. Juvenile specimens of the small pelagic fish were also caught in the very shallow waters between Ras al Madrak and Salalah.

2.3. Acoustic Estimates of the Demersal Resources During the 1983-84 Surveys

The estimates of the demersal stocks, based on the information from the acoustic system, are given in Table 7, and Figures 8-10 show the distribution of demersal fish from the registrations by the same system.

In general, acoustic methods tend to underestimate the abundance of the demersal resources.

Table 7 Acoustic biomass estimates of the demersal resources. Rounded figures, thousand tonnes.

		SURVEY I Mar-Apr 83	SURVEY II Nov-Dec '83	SURVEY III May '84
A	North of Ras al Hadd	N.S.	15	10
B	Ras al Hadd - Masira	50	10	5
C	Masira Bank	25	10	10
D	Sauquara & Kuria Muria Banks	160	25	40
E	Salalah region	0	0	5
	Total	235	60	70

N.S.= Not surveyed