5. Results of the fish survey work

5.1 The echo recordings and their interpretation
5.2 The estimates of total fish biomass
5.3 Fish distribution on the Arakan Coast
5.4 Fish distribution in the Delta area
5.5 Fish distribution on the Tenasserim Coast
5.6 The distribution by depth of bottom trawl catches
5.7 The Deep Sea Shrimp Trawling Ground
5.8 Biomass estimates based on catch rates in the bottom trawl
5.9 Analysis of catches of shallow water shrimp

5.1 The echo recordings and their interpretation

Assessment of the abundance of fish resources based on acoustic observations combined with experimental fishing is a method which especially lends itself to fish found in schools or other aggregations in mid-water. This is, however, a type of behaviour which characterizes a considerable number of the fish species found in Burmese waters. But there ate also notable exceptions, e.g. surface schooling tunas and tuna-like species and strictly bottom dwelling fish such as rays and flounders. Any fish found very close to the bottom (½-1 m) or in the very surface layer will escape echo sounder detection. For navigational reasons the work with the R/V "Dr. Fridtjof Nansen" is limited to waters deeper than about 15 m. The extreme inshore waters of the northern Arakan coast, the eastern Gulf of Martaban and the mid part of the Tenasserim Coast could thus not be covered.

Because of differences in behaviour and size, different species or groups of fish species may give rise to different types of echo-recording. Small-sized pelagic fish are for instance often found in well-defined schools, the recordings of which can be distinguished from those of the often looser aggregation in which semi-demersal larger fish are often found. Such classification of the echo recordings is of considerable assistance in interpreting the acoustic observations, but a positive identification by fishing operations is still indispensable and also provides the only means of sampling fish in this type of combined survey.

Based on previous experience and on identification by fishing, the fish recordings from the Burmese waters were classified as follows:

(i) Recordings of true larger schools or dense layers mostly in upper water, Figure 11. These will most often derive from pelagic schooling fish usually of smaller size e.g. clupeiods, scads. This type was the most common in the coastal areas.

(ii) All other fish recordings which especially comprised looser agreegations of smaller and larger fish near the bottom and in mid-water. These are ascribed to demersal or semi-demersal fish such as croakers grunts, breams, snappers, sharks, ponyfish etc. This type of recording was also common, and examples are shown in Figure 12. In this group was also included single fish traces or small schools of bigger fish closer to the surface waters. These recordings are thought to derive from tunas and tuna-like fish. They were less common and probably often "lost" in dense plankton recordings near the surface.

Figure 11. Echo diagrams of recordings of small pelagic fish showing fish in: dense layer (upper), in small schools (middle) and in transition from dense to disperse distributions (lower)

Figure 12. Echo diagrams of recordings of "other fish" showing demersal fish, semi-demersal fish (upper and middle) and single fish traces at low speed (lower).

A third category of fish traces, i.e. from mesopelagic fish species is usually also recorded in this type of survey work. This consists of lantern fish and other small-sized related species. While found in high abundance off the shelf in the north-western Arabian Sea this type proved, however, to be relatively scarce in Burmese waters, except in a limited part of the Delta region.

The acoustic observations relating to the two categories of fish described above were recorded continuously along all survey tracks, and they form the basis for the preparation of charts of distributions of fish. The unit of measurements of fish abundance in these charts relates to the acoustic echo received from the fish and they are therefore termed echo-intensity-charts and show the relative abundance and distribution of fish. They are transferred into estimates of absolute abundance of fish biomass measured e.g. in tonnes/n.m². by help of a conversion factor which must be adjusted to the settings and performance of the instruments and to the size of the fish in the area. The basis for this conversion is explained in Annex II to this report.

In the further descriptions of this; report the information on the distribution and behaviour of the fish obtained from the acoustic systems will be presented in the form of charts of echo-intensity distribution and will thus only show relative values. For each sub-area and category of resources a conversion to estimates of total fish biomass will be made. In addition come the catch rates and catch compositions from the fishing operations which will be used to identify, interpret and supplement the acoustic survey data.

5.2 The estimates of total fish biomass

On the basis of the charts of echo-intensity distribution the total echo- abundance for each area and type of fish was calculated by a planimetric integration. Table 2 shows the results. The table also presents the parts of the areas in which relatively dense concentrations were found. It is evident that there is a higher tendency for the small pelagic fish to be concentred in areas of higher abundance, than for the demersal and semi- demersal fish.

Table 2. Acoustic indices of abundance

SMALL PELAGIC FISH:
Indices			Dense concentrations* as % of total
	Oct.-Nov.	March-April	Oct.-Nov.	March-April
Arakan coast	59.100	57.500	88	63
Delta area	103.800	219.600	50	49
Tennasserim coast	19.400	176.200	30	81
Total	182.300	453.300	60	63

OTHER FISH
Indices			Dense concentrations* as % of total
	Oct.-Nov.	March-April	Oct.-Nov.	March-April
Arakan coast	21.500	19.900	32	20
Delta area	39.900	122.100	0	39
Tennasserim coast	18.400	21.900	0	0
Total	78.800	163.900	9	31

*Mean integrator values >20/n.m.

	Autumn 1979	Spring 1980
Arakan coast	1.20	1.20
Delta area	1.44	1.16
Tennasserim coast	1.37	1.18

Table 3 shows the estimates of the biomass for the total shelf area. There is a general tendency for much higher biomass values from the spring survey than that, from the autumn. For pelagic fish the ratio is about 2, while the "other fish" biomass is increased by about 80%. The most likely explanation of this seasonal change is that it is caused by a fluctuation in biological production. Many of the fish species in this area are small-sized and have a brief life-span only. Their main period of production is adjusted to favourable ecological conditions during certain parts of the year. Similar large-scale seasonal fluctuations of the biomass of shortlived species such as sardines and anchovies have been demonstrated in nearby and comparable areas such as the coast off Pakistan and the southwest coast of India.

Table 3. Estimated biomass for the total shelf areas (In 1 000 tonnes)

SMALL PELAGIC FISH:
Area:	Autumn 1979	Spring 1980
Arakan coast	180	170
Delta area	370	640
Tennasserim coast	70	520
Total	620	1330

OTHER FISH
Area:	Autumn 1979	Spring 1980
Arakan coast	130	120
Delta area	290	710
Tennasserim coast	120	130
Total	540	960

In the following we will now consider the distribution and composition of fish biomass through a discussion of the charts of echo-abundance and of the findings of the fishing operations.

5.3 Fish distribution on the Arakan Coast

5.2.1 The small pelagic fish, Arakan coast
5.3.2 Other fish, Arakan coast
5.3.3 Results of the fishing operations, Arakan coast

The total estimated biomasses found along this part of the coast were as mentioned above as follows (1000 tons):

	Autumn	Spring
Small pelagic fish	180	170
Other fish	130	120
Total	310	290

5.2.1 The small pelagic fish, Arakan coast

Figure 13 shows that the small pelagic fish are mainly distributed in the inshore areas of the coast south of Sandoway. This corresponds to the narrowest part of the shelf. Especially in the heavier concentrations the fish occuried in well defined schools during daytime as layers at night.

Aimed mid water trawling was conducted to identify these pelagic concentrations of fish.The locations of the fishing stations are shown in Figures 1-4 and the catches and their composition are recorded in Annex Table IV.The results for each of the seasons are summarized in Table 4. From this it appears that sardines and anchovies by far dominate in these catches in both seasons. In the autumn sardines occurred in 5 of 7 catches, in the spring in 7 out of 12 catches. The genera found were Sardinella, Dussumeria and Ilisha. The anchovies represented mostly by Stolephorus were almost as common as the sardines, while the remaining pelagic fish consisted of Carangids, Scomberomorus and Sphyraena. From the figures showing the mean part by weight of the catches of these various categories it is evident that the sardines anchovies and carangids generally make cut substantial parts of the catches while Scomberomorus and Sphyraena are by-catches.

(...)

Figure 13. Distribution of small "pelagic fish" on the Arakan Coast, Sep-Nov 1979 (loft), and March-April 1980 (right). For explanation of the codes for the fish names, see text.

The composition of the mid water hauls has also been used to indicate the locations of occurrence of the various types of fish in the distribution charts, Figure 13. It is, however, uncertain to which extent these indications of local occurrence provide a typical or general description of the distribution of the fish over a longer period of time.

List of codes used to indicate fish distribution in figure 13 - 18 and their corresponding fish species or group names.

Acrop	=	Acropoma japonicum
Arius	=	Arius sp.
Atrob	=	Atrobucca nibe
Car	=	Caranx sp.
Congr	=	Congresox sp.
Chrys	=	Chrysochir sp.
Decap	=	Decapterus sp.
Duss	=	Dussmeria sp.
Eng	=	Engraulis sp.
Gerr	=	Gerrus sp.
Harp	=	Harpodon sp.
Ilis	=	Ilisha
Lact	=	Lactarius lactarius
Lei	=	Leiognathus sp.
Lept	=	Lepturacanthus
Leth	=	Lethrinus sp.
Loligo	=	Loligo sp.
Nemi	=	Nemipterus
Otho	=	Otholithes sp.
Pamp	=	Pampus sp
Penna	=	Pennahia sp.
Pent	=	Pentaprion sp
Poly	=	Polynemus sp.
Pom	=	Pomadasys sp.
Rac	=	Rachycentron sp.
Rast	=	Rastrelliger sp.
Ray/ska	=	Rays and skates
Sard	=	Sardinella sp.
Saur	=	Saurida sp.
Scia	=	Scianeidae
Scomb	=	Scomberoides sp.
Selar	=	Selar sp.
Shar	=	Sharks
Shri	=	Shrimps
Sphy	=	Sphyraena sp.
Stol	=	Stolephorus sp.
Thrys	=	Thryssa sp.

The small pelagic fish also frequently occur close to the bottom especially in shallow water and are often caught in the ordinary bottom trawl. Another supplementary way then of identifying and assessing the composition of the pelagic biomass is the analysis of the occurrence of those types of fish which are known to belong to the pelagic community in all catches in the area whether from bottom or mid water trawl hauls. Table 5 shows the frequency of occurrence on the total of fishing stations for the relevant families and their proportion of the total catch of pelagic fish. The findings support those from the mid water hauls in showing the relative importance of clupeids, engraulids and carangids in a similar order. The ribbon fishes represented mainly by Lepturacanthus also make an important contribution to the pelagic biomass.

Table 5. Occurrence by families of pelagic fish on all fishing stations (bottom- and mid water trawl), and proportion by weight of total catch of pelagic fish.

ARAKAN COAST
Total no. of stations	Sept.- Nov.		March - April
	56		49
	No. of stations occurring	% of total catch	No. of stations occurring	% of total catch
Clupeidae	30	38	21	52
Engraulidae	22	28	12	25
Trichiuridae	20	21	14	4
Carangidae	19	3	19	16
Sphyrenidae	21	9	11	2
Scombridae	15	1	9	1

5.3.2 Other fish, Arakan coast

As shown in Figure 14 the distribution of demersal and semi-demersal fish as indicated by the acoustic data is also confined to the shelf with the centres of higher concentration well inside the shelf edge. In the March-April survey there is a tendency for this type of fish to be found even further inshore and in shallower waters than in September-October. This may be related to the lifting of the oxygen-deficient layer from autumn till spring as discussed under 4 above. An inshore movement of bottom fish may also explain the lower biomass estimate for the spring survey, a greater part of these fish is then found in the extreme inshore shallow waters which could not be covered by the survey.

Table 6 shows the occurrence of the most common families of demersal- and semi-demersal fish in the catches on the Arakan coast during the two main survey periods. Ponyfishes (Leiognatidae), croakers (Sciaenidae) and grunts (Pomadaridae) were both widespread and made out the greatest part of the catches, but also lizard fishes(Synodontidae) and catfishes (Ariidae) were common. Squids and shrimp were widespread although contributing little to the total weight of the catches in contrast to sharks and rays which made out a significant part of the catch on relatively few stations.

In the distribution maps fishes predominant in the bottom trawl hauls in the various regions have been recorded approximately where caught. In the extreme north rays and skates were found together with ponyfish, Pomadasys and Saurida. From Sandoway southwards the dominating forms are again Pomadasys and Leiognatus with Saurida, Lutjanus and Nemipterus spp.

Figure 14. Distribution of other fish on the Arakan Coast, Sep-Nov 1979 (left)and March-April 1980 (right). For explanation of the codes for the fish names, see text.

Table 6 Occurrence by families of "other fish" on all fishing stations, and their proportion by weight of total catch of "other fish".

ARAKAN COAST
Total no of stations	Sept - Nov		March-Apr
Ariidae	56	8.4	49	3.0
Carangidae	18	1.4	12	1.4
Gerridae	20	0.8	16	17.2
Lactaridae	17	5.8	10	2.1
Leiognatidae	17	7.5	9	19.0
Lutjanidae	39	1.9	19	0.6
Mullidae	14	1.1	8	2.8
Muraenesocidae	24	0.9	16	1.2
Nemipteridae	9	0.8	7	4.8
Pomadasidae	24	21.4	18	10.4
Sciaenidae	29	33.4	22	4.5
Scombridae	21	2.1	17	1.1
Synodontidae	21	1.8	13	6.2
Sharks and rays	27	3.3	26	9.6
Squids	16	0.5	8	0.8
Shrimp	28	1.4	17	2.6
Miscellaneous*	28	6.5	18	12.7

*Includes about 17 families of fish occurring in few catches, and with less than 1 % of catch and non-fish catches such as Jelly fish.

5.3.3 Results of the fishing operations, Arakan coast

A summary of all fishing activities in this area during the two periods is as follows:

	BOTTOM TRAWL		PELAGIC TRAWL
	Oct - Nov /79	Mar - Apr /80	Oct - Nov /79	Mar - Apr /80
Number of stations	45	28	11	22
Total catch (kg/hour units)	27420	35976	1455	5242
Mean total catch per hour kg	609	1285	132	238
Max. catch rates kg	6390	5250	380	680

The maximum catch rates shown above represent the means of the 3 highest catches.

The detailed data for each station are recorded in Annex Table IV. The average catch rate in bottom trawl in March-April/80 is about twice that in Oct-Nov/79. This should not be interpreted directly as indicating a higher abundance, since a considerable part of the autumn fishing relates to a special shrimp survey near Sandoway. Also pelagic trawling yielded somewhat higher catches during the spring survey. This may in a general way indicate a higher availability of pelagic schooling fish, but in our survey system fishing with mid-water trawl is conducted for the purpose of identifying the various types of echo-recordings of fish and for sampling and this type of operation does not provide much information of interest for assessment of fish abundance or catchability.

Bottom trawl fishing provides more comprehensive data, both with regard to the availability of the demersal stocks and the composition of the catches. One should, however, note that exploratory fishing conducted as in this survey will not simulate a commercial fishery. One important difference is that commercial fishing will be concentrated in areas with high abundance of desired species whereas the exploratory fishing will cover a wider range of fish densities. The average catch rates in this survey would thus be expected to be lower than those of a commercial fishery. There is on the other hand an effect which will act in the opposite way when the survey is conducted in an unfished virgin area. A commercial fishery will after having been established reduce the standing biomass and result in a decline of catch rates. One should keep these reservations in mind when considering the following analysis of the bottom trawl results.

Tables 7 and 8 show the distribution of the various most common forms of fish on catch groups and the mean catch. The fish forms are ranged in the order in which they contribute to the total catch. It appears that in the autumn croakers made out about 1/4 of the total catch in the area, followed by grunts and clupeoids. These three groups contributed nearly half the catch. The catch rates (standardized to one hour hauls) for each form of fish were mostly lower than 50 kg/h, but with a fair part between 50-199 kg/h and a few above 500 kg/h.

The fewer hauls in the spring were dominated by anchovies, ponyfish, mojarras and grunts with a fair number of catch rates exceeding 500 kg/h. The commercial value of the different types of fish differs considerably. To enable an evaluation on the basis of this criterion the various fish species were allocated on 4 economic classes (Appendix Table III). An analysis of the bottom trawl catches according to their composition of fish of different commercial value is shown in Table 9. It appears that more than 80% of the total catch are fish in economic class 2 and 3. The catch rates of these classes of fish (considered as a whole) are fairly high - frequently exceeding 200. kg/h and often also 500 kg/h.

Table 7. Distribution of the catches by families In 45 bottom trawl hauls on the Arakan coast Oct/Nov 1979.

Catch grouping	>10 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	>500 kg/h	% incidence in total no. of hauls	Mean catch	% of total catch
FAMILY:
Sciaenidae	5	8	3	0	2	40	145	24
Pomadasyidae	5	12	9	2	1	64	93	15
Clupeidae	9	9	3	0	1	49	46	8
Ariidae	9	2	1	0	1	29	37	6
Engraulidae	7	1	0	0	1	20	36	6
Trichiuridae	8	5	1	0	1	33	35	6
Leiognathidae	7	12	5	3	0	60	32	5
Lactaridae	8	6	1	0	1	36	25	4
Mesopelagic fish	0	0	1	1	0	4	12	2
Carangidae	15	8	2	0	0	56	11	2
Rays	4	1	2	1	0	18	11	2
Sphyraenidae	6	6	0	1	0	29	10	2
Scombridae	11	7	2	0	0	44	10	2
Synodontidae	13	9	1	0	0	51	8	1
Shrimps	13	7	1	0	0	47	6	1
Lutjanidae	4	7	2	0	0	29	6	1
Lobsters	3	0	1	0	0	9	3	-
Squids	14	2	0	0	0	36	2	-
Other fish							80	13
TOTAL							608	100

Table 8. Distribution of the catches by families in 28 bottom trawl hauls on the Arakan coast March/April 1980

Catch grouping	>10 kg/h		50-199 kg/h	200-499 kg/h	>500 kg/h	% incidence in total no. of hauls	Mean catch	% of total catch
FAMILY
Engraulidae	0	2	1	0	1	14	199	17
Leiognathidae	1	1	3	2	5	43	175	15
Gerridae	1	2	2	1	1	25	160	13
Pomadasyidae	3	4	8	2	1	64	95	8
Rays	3	0	2	0	2	25	89	7
Clupeidae	0	3	2	4	1	36	81	7
Synodontidae	4	7	6	0	1	64	55	5
Nemipteridae	5	6	5	0	1	61	45	4
Sciaenidae	2	7	1	3	0	46	42	4
Carangidae	2	10	2	0	1	54	37	3
Ariidae	4	2	3	1	0	36	27	2
Mullidae	6	3	4	1	0	50	26	2
Shrimps	4	8	2	1	0	54	24	2
Lactaridae	0	4	2	1	0	25	19	2
Lohsters	3	0	0	0	0	11	0.5	-
Squids	5	4	1	0	0	36	6	-
Other Fish							107	9
TOTAL							1187	100

Table 9. Distribution of the catches by economic classes in the bottom trawl on the Arakan coast.

October-November 1979

Class:	<10 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	>500 kg/h	% incidence in total no hauls	Mean catch	% of total catch
Economic class 1	11	21	10	2	1	84	86	14
Economic class 2	12	5	19	7	2	82	311	51
Economic class 3	11	17	11	5	1	87	193	32
Economic class 4	37	4	4	0	0	44	16	3

Birch-April 1980

Class:	<10 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	>500 kg/h	% incidence in total no hauls	Mean catch	% of total catch
Economic class 1	7	6	12	2	1	82	104	9
Economic class 2	5	0	8	7	8	89	494	42
Economic class 3	8	3	5	4	8	86	548	46
Economic class 4	10	10	8	0	0	79	42	3

5.4 Fish distribution in the Delta area

5.4.1 The small pelagic fish, Delta Area
5.4.2 Other fish, Delta Area
5.4.3 Results of the fishing operations, Delta area

It seems pertinent to stress that the extreme inshore parts of the Delta area particularly those of the eastern Gulf could not be covered for navigational reasons.

The total estimated biomasses during the two surveys were (in 1000 tons):

	Autumn	Spring
Small pelagic fish	370	640
Other fish	290	710
Total	660	1350

5.4.1 The small pelagic fish, Delta Area

Figure 15 shows the distributions of the biomass at the two seasons. The main concentrations are found in a belt not more than about 60 n.m. wide roughly covering the bottom depth countours from about 15 to about 60-70 m.

Figure 15. Distribution of pelagic fish on the Delta Area Sep-Nov 1979) (upper) and March-April 1980 (lower), For explanations of the codes for the fish names, see text.

The biomass during the second survey (March-April) is nearly 2 times higher than that of the first, but the composition seems largely to be the same. As shown in Table 10 the most common fish in the mid water hauls were sardines, anchovies and ribbon fish. Scombrids and carangids were also relatively common. In parts of the area small pelagic shrimp (Acetes) could be found in abundance in mid water as well as on the bottom. Leiognathus, Harpodon, squid and fish larvae were also frequently found in the mid water catches.

Table 10. Identification of small pelagic fish by aimed mid water trawling. Frequency of occurrence (when being more than 10% of catch by weight) and mean part of weight of catch (%).

DELTA AREA
		Sept. - Nov.	March - April
Total no. hauls		19	25
Clupeids		5 - 31 %	10 - 40 %
	Sardinella	2 16 %	4 - 44 %
	Ilisha	3 - 35 %	1 - 33 %
	Dussumeria	1 - 16 %	4 - 14 %
	Raconda		5 - 26 %
Engraulids		6 - 47 %	6 - 44 %
	Thryssa	2 - 36 %	2 - 28 %
	Stolephorus	4 - 53 %	4 - 43 %
	Carangids	1 - 59 %	3 - 40 %
	Decapterus	1 - 59 %	2 - 44 %
Scombrids		6 - 25 %	4 - 41 %
	Scomberomorus	4 - 27 %	3 - 36 %
	Rastrelliger	2 - 16 %
Trichiurids		8 - 28 %	12 - 26 %
	Lepturacanthus	6 - 25 %	12 - 26 %
Leiognatus		5 - 43 %	5 - 74 %
Shrimp		4 - 38 %	2 - 16 %
Miscellaneous		9 - 39 %	13 - 38 %

Judging from the occurrence in all catches with both mid water and bottom trawls, the ribbon fishes seem to have the widest and highest abundance followed by engraulids and clupeids, see Table 11. Carangids, scombrids and sphyraenids also occur frequently, but make out a much smaller part of the total catch of pelagic fish.

Table 11, Occurrence by families of pelagic fish on all fishing stations (bottom- and mid water trawl), and proportion by weight of total catch of pelagic fish.

DELTA AREA
Total no of stations	Sept - Nov		March - April
	70		95
	No of stations occurring	% of total catch	No if stations occurring	% of total catch
Clupeidae	31	11	33	24
Engraulidae	34	35	44	33
Trichiuridae	44	40	55	35
Carangidae	23	6	29	7
Sphyrenidae	12	7	10	1
Scombridae	12	2	5	1

5.4.2 Other fish, Delta Area

The oceanographical regime which no doubt governs the distribution of bottom fish in this area is related to the river outflows and there is as demonstrated in chapter 4 above a marked change in both salinity- and temperature conditions from September-November till March-April. The change in the distribution of the fish with considerably higher concentrations during the last cruise may well be related to the change of the environment.

In the central and eastern parts of the Delta area some difficulties of identification of the echo recordings were encountered with relation to the occurrence both in mid water and closer to the bottom of shrimp of the Genus Acetes which is of little or no commercial interest. Relatively heavy concentrations of mesopelagic fish located in the southern part of the central Delta area are not included in the fish distribution chart.

Table 12 shows the occurrence in the catches of the most common forms of fish during the two surveys. The relatively high abundance of croaker (Sciaenidae) and catfishes (Ariidae) is a common feature with the fauna of the Arakan coast, but otherwise the Delta fauna differs in several respects from those of the coastal regions to the north and south. Noteworthy is the regular presence of threadfins (Polynemidae), pike congers (Muraenesocidae;) and Bombay duck (Harpodontidae). Sharks and rays are (...) widespread and abundant, while ponyfish (Leiognathus) is far less common than in the other areas.

Figure 16. Distribution of other fish on the Delta Area Sep-Nov 1979 (upper) and March-April 1980 (lower). For explanation of the codes for the fish names, see text.

The prominent forms in the catches are roughly located in Figure 16. Rays and skates are common everywhere while Polynemus is found in the central and eastern parts. Harpodon is particularly dominant in the catches from the shallow eastern parts of the Delta. Saurida and Nemipterus are common in the southeast towards the Tenasserim coast.

Table 12. Ocurence by families of "other fish " on all fishing stations and their proportion by weight of the total catch of "other fish"

DELTA AREA
Total no of stations	Sept - Nov		March - Apr
	No of stations occurring	% of total catch	No of stations occurring	% of total catch
Ariidae	70	4.4	95	8.1
Carangidae	29	0.2	36	6.1
Gerridae	8	1.3	27	1.0
Harpadontidae	18	2.2	10	20.5
Lactaridae	8	2.1	18	1.6
Letognatidae	11	2.6	21	1.3
Lutjanidae	25	4.2	26	2.6
Mullidae	22	1.9	20	3.3
Muraenesocidae	24	5.6	23	1.4
Nemipteridae	20	2.6	19	2.9
Polynemidae	26	6.2	21	3.0
Pomadasidae	19	0.9	25	2.7
Sciaenidae	28	18.5	26	9.7
Scombridae	33	2.2	37	0.8
Synodontidae	16	2.8	20	2.4
Sharks and rays	20	18.3	24	13.9
Squids	53	0.8	52	0.6
Shrimp	23	11.6	27	6.9
Miscellaneous	40	11.2*	40	12.0

*include 12 families of the fish occurring in few catches and with less than of catch

5.4.3 Results of the fishing operations, Delta area

A summary of all fishing stations in this area during the two periods is as follows:

	BOTTOM TRAWL		PELAGIC TRAWL
	Sept - Nov /79 Mar - Apr / 80		Sept - Nov / 79 Mar - Apr / 80
Number of stations	44	57	26	39
Total catch (kg)	18280	29248	6021	21786
Mean total catch per hour (kg)	415	513	232	559
Max. catch rates (kg/h)	2260	1380	1140	5340

Some of the bottom trawling in the spring formed part of a special trawl survey of the eastern Delta to obtain an independent estimate of demersal fish and especially the stock of Bombay duck. The mid water hauls may be interpreted as an indication of increased availability from autumn to spring of small pelagic fish. The maximum catch rates represent the mean of the three highest catches.

Tables 13 and 14 show the distribution on catch groups and mean catch rates for the most common types of fish. The largest parts of the total catch were made out of few forms: croakers, rays, ponyfish, pike congers, threadfins, Bombay ducks and ribbonfish. These types also gave the highest catches although the overall means are only of the order of 30-70 kg/h. A special survey was as already mentioned made of the Bombay duck-distribution which accounts for the relatively high values in the spring.

Table 13. Distribution of the catches by families in 44 bottom trawl hauls in the Delta area Oct/Nov 1979

Catch grouping	>10 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	>500 kg/h	incidence in total no of hauls	Mean catch	% of total catch
FAMILY
Sciaenidae	17	10	15	1	1	68	71	18
Rays	25	8	8	2	1	52	47	12
Shrimps	19	16	7	2	0	70	37	9
Polynemidae	34	3	6	1	0	39	24	6
Muraenesocidae	26	11	7	0	0	43	22	6
Trichiuridae	36	14	3	1	0	43	22	5
Ariidae	25	15	4	0	0	66	17	4
Lutjanidae	32	10	1	1	0	43	16	4
Sharks	31	12	0	1	0	52	14	3
Synodontidae	2	11	0	1	0	41	11	3
Engraulidae	34	9	1	0	0	48	8	2
Nemipteridae	31	11	2	0	0	50	10	3
Sphyraenidae	40	1	0	1	0	14	7	2
Mullidae	34	9	1	0	0	48	7	2
Lactaridae	42	1	0	1	0	11	7	2
Leiognathidae	36	6	2	0	0	34	7	2
Harpadontidae	38	3	3	0	0	16	6	2
Carangidae	37	6	1	0	0	30	5	1
Gerreidae	36	7	0	0	0	36	5	1
Clupeidae	38	5	1	0	0	41	5	1
Other fish							50	12
TOTAL							398	100

Table 14. Distribution of the catches by families in 57 bottom trawl hauls on the Delta area March/April 1980

Catch grouping	>10 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	>500 kg/h	% incidence in total no of hauls	Mean catch	% of total catch
FAMILY
Harpadontidae	43	4	2	3	5	28	87	17
Rays	35	7	12	1	2	47	52	10
Scianidae	26	16	14	1	0	60	40	8
Leiognatidae	44	4	6	2	1	30	36	7
Ariidae	29	19	7	1	1	63	30	6
Engraulidae	40	7	8	2	0	54	26	5
Shrimps	45	10	2	0	0	40	25	5
Trichiuridae	36	13	7	1	0	60	22	4
Carangidae	42	10	4	1	0	42	17	3
Mullidae	44	10	2	1	0	35	14	3
Clupeidae	46	7	3	1	0	37	13	3
Nemipteridae	40	13	4	0	0	35	12	2
Polynemidae	47	7	2	1	0	39	12	2
Mesopelagic fish	56	0	0	0	1	2	12	2
Pomadasyidae	39	14	4	0	0	40	11	2
Synodontidae	42	13	2	0	0	33	10	2
Lutjanidae	50	6	0	1	0	30	8	2
Sharks	45	10	2	0	0	40	7	1
Lactaridae	53	2	2	0	0	18	6	1
Lethiridae	54	2	0	1	0	7	6	1
Serranidae	54	2	0	1	0	11	6	1
Muraenescidae	47	9	1	0	0	29	5	1
Acropomidae	55	1	0	1	0	7	5	1
Other fish							52	10
TOTAL						57	514	99

Table 15 Distribution of the catches by economic classes in, the bottom trawl on the Delta area.

October-November 1979
Class:	<10 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	>500 kg/h	% incidence in total no of hauls	Mean catch	% of total catch
Economic class 1	4	13	20	5	2	98	116	29
Economic class 2	2	12	25	4	1	100	120	30
Economic class 3	3	12	18	9	2	100	138	34
Economic class 4	20	18	5	1	0	86	26	7

March-April 1980
Class:	<10 kg/h	10-49 kg/h	50-199 kg/	200-499 kg/h	>500 kg/h	% incidence in total no of hauls	Mean catch	% of total catch
Economic class 1	7	20	23	6	1	98	94	18
Economic class 2	10	16	16	15	0	89	109	21
Economic class 3	9	4	20	12	12	95	272	53
Economic class 4	20	30	6	0	1	89	40	8

The analysis of the catches from a point of view of commercial value, Table 15 shows that the fish of the Delta area tends to be of higher economic value than was the case for the Arakan coast with 20-30% of the catch being referred to the highest value class. The mean catch rate in this class is of the order of 100 kg/h, but there are single catches exceeding 500 kg/h.

5.5 Fish distribution on the Tenasserim Coast

5.5.1 The small pelagic fish on the Tenasserim coast
5.5.2 Other fish on the Tennasserim coast
5.5.3 Results of the fishing operations, Tenasserim Coast

The total estimated biomasses were (1000 tons):

	Autumn	Spring
Small pelagic fish	70	520
Other fish	120	130
Total	190	650

The coverage during the second survey included more of the inshore waters of the southern archipelago, but this can not explain the great difference in the findings since most of the fish occurred in the areas covered by both surveys.

5.5.1 The small pelagic fish on the Tenasserim coast

The biomass of the second survey is some 7 times that of the first. The distributions are shown in Figure 17. From the mid water trawling it is evident that anchovies represented by far the most widely distributed and common fish, see Table 16. But also sardines were wide-spread, while scombrids and carangids were only found in 4 out of 20 hauls in the spring cruise.

The analysis of the total fishing stations, presented in Table 17, indicate a wide distribution by area of both anchovies and sardines, but a marked dominance in catches of anchovy. Also the other pelagic fish families are shown to have a relatively wide distribution, but with small total catches compared to that for anchovy.

The areas of high abundance during the second survey formed a belt some 20 n.m. wide in the waters of the archipelago. The boundaries of these fish areas towards the shallower inshore waters were located except in the region from abt. 11°50' to 12°30' LN where inshore navigation was not possible.

Figure 17. Distribution of small pelagic fish on the Tennasserim coast Sep-Nov 1979 (left) and March-April 1930 (right). For explanation of the codes for the fish names, see text.

5.5.2 Other fish on the Tennasserim coast

The densities of demersal and semi-demersal fish are considerably lower on the Tenasserim coast than in the Delta area and also significantly below those of the Arakan coast which represent a much smaller shelf area. There are no marked differences in distributional features between the two surveys as seen in Figure 18.

Table16. Identifications of small pelagic fish by aimed mid water trawling. Frequency of occurrence (when more than 10 % by weight) and mean proportion of weight catch (%).

TENASSERIM COAST
		Sept.-Nov.	March - April
Total no. Hauls		4	20
Clupeids			7 - 33 %
	Ilisha	2 - 16 %	4 - 22 %
	Dussumeria		5 - 13 %
Engraulids		3 - 16 %
	Stolephorus	2 - 24 %	14 - 70 %
	Thryssa	1 - 11 %
Scombroids			4 - 36 %
	Scomberomorus		2 - 57 %
	Rastrelliger	1 31 %	2 - 15 %
Carangids			4 - 37 %
	Decapterus	1 - 10 %	2 - 46 %
	Selar		2 - 27 %
Trichiurids
	Lepturacanthus	1 - 16 %	2 - 34 %
Sphyrena		1 - 17 %	2 - 21 %
Leiognatus		1 - 25 %	2 - 24 %
Miscellaneous		1 - 78 %	3 - 25 %

Table 17. Occurrence by families of pelagic fish on all fishing stations (bottom- and mid water trawl), and proportion by weight of total catch of pelagic fish.

TENASSERIM COAST
Total no of stations	Sept. - Nov.		March - April
	23		57
	No. of stations occurring	% of total catch	No. of stations occurring	% of total catch
Clupeidae	8	1	26	14
Engraulidae	9	92	22	74
Trichiuridae	11	1	14	4
Carangidae	13	1	24	5
Sphyrenidae	7	3	15	1
Scombridae	4	1	15	1

Table 18 shows the occurence in the catches of the most common forms of fish. Ponyfishes (Leiognathidae), grunts (Pomadasyidae), lizardfishes (Synodontidae), and false trevallies (Lactarida) are widespread and relatively abundant. The high percentage of ponyfish in the March-April survey is caused by some exceptionally high catches in shallow waters. More characteristic for the area is perhaps the relatively frequent occurrence of threadfin breams (Nemipteridae) and goatfishes (Mullidae). Squids are widespread, but represent a small part of the catch, while sharks and rays are far less common than in the two northern areas.

Table 18. Occurrence by families of "other fish" on all fishing stations, and their proportion by weight of the total catch of "other fish"

TENNASSERIM COAST
Total no of stations	Sept - Nov		March - Apr
	No of stations occurring	% of total catch	No of stations occurring	% of total catch
Ariidae	23	2.7	57	5.4
Carangidae	8	2.1	12	2.3
Gerridae	6	2.1	15	1.3
Lactaridae	10	12.0	11	4.0
Leiognatidae	6	15.5	11	56.9
Lutjanidae	14	1.7	24	2.9
Mullidae	88	4.8	10	2.7
Muraenesocidae	10	3.5	22	0.5
Nemipteridae	8	4.7	5	2.0
Pomadasidae	11	6.4	21	6.5
Sciaenidae	9	12.7	18	0.9
Synodontidae	8	2.6	9	3.6
Sharks and rays	10	3.1	19	0.8
Squids	10	1.9	8	0.6
Shrimps	10	2.5	23	0.3
Miscellaneous	6	21.7	8	9.3

The forms dominating the catches in the various locations are shown in Figure 18. Leiognathus has generally the most inshore distribution while Nemipterus, Saurida, Atrobucca, Lutjanus and Loligo are prominent in the more offshore parts of the archipelago.

5.5.3 Results of the fishing operations, Tenasserim Coast

A summary of the fishing stations in this area during the two periods is as follows:

	BOTTOM TRAWL		PELAGIC TRAWL
	Sep - Nov /79 Mar - Apr /80		Sep - Nov / 79 Mar - Apr /80
Number of stations	16	26	7	30
Total catch (kg)	14308	27074	579	8923
Mean total catch per hour (kg)	894	1041	83	297
Max. catch rates (kg /h)	3930	5070	510	1060

Figure 18. Distribution of other fish on the Tennasserim Coast Sep-Nov 1979 (left) and March-April 1980 (right). For explanation of the codes for the fish names, see text.

The fishing was considerably less intensive than in the-two other areas. The higher catches in the pelagic trawl in the spring support the impression of a higher total biomass of small pelagic fish in this season.

Table 19. Distribution of the catches by families in 16 bottom trawl hauls on the Tennasserim coast Oct/Nov 1979

Catch grouping	>10 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	>500 kg/h	% incidence in total no of hauls	Mean catch	% of total catch
FAMILY
Engraulidae	13	1	1	0	1	19	577	68
Sciaenidae	12	0	4	0	0	44	33	4
Leiognathidae	7	5	4	0	0	63	32	4
Lactaridae	15	0	0	1	0	19	31	4
Pomadasyidae	9	6	1	0	0	56	17	2
Mullidae	13	4	1	0	0	56	12	1
Nemipteridae	10	5	1	0	0	63	12	1
Carangidae	9	7	0	0	0	63	12	1
Trichiuridae	12	3	1	0	0	50	9	1
Muraenesocidae	14	0	2	0	0	19	9	1
Clupeidae	14	1	1	0	0	25	9	1
Other fish							99	12
TOTAL							852	100

The catch distributions are shown in Tables 19 and 20. The dominance of anchovy in the autumn data is caused by one large catch. The spring survey probably gives a better picture of the composition of the bottom fish in the area and the catch rates for the various forms. Ponyfish contributed some high catches, but otherwise the mean catch rates of croakers, cat-fishes and carangids were about the same as in the Delta area.

Table 20. Distribution of the catches by families in 26 bottom trawl hauls on the Tennasserim coast March - April 1980

Catch grouping	>10 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	>500 kg/h	% incidence in total no of hauls	Mean catch	% of total catch
FAMILY
Leiognathidae	13	1	3	3	6	58	510	49
Sciaenidae	18	3	2	2	1	35	81	8
Pomadasyidae	12	6	6	2	0	69	59	6
Ariidae	18	2	3	3	0	42	49	5
Carangidae	18	7	5	1	0	73	37	4
Lactaridae	17	4	4	1	0	38	36	3
Synodontidae	19	3	8	0	0	62	32	3
Clupeidae	18	6	3	1	0	50	31	3
Lutjanidae	20	3	2	1	0	31	25	2
Mullidae	16	5	5	0	0	73	24	2
Nemipteridae	16	13	3	0	0	73	18	2
Engraulidae	23	2	0	1	0	15	15	1
Gerreidae	23	2	0	1	0	35	11	1
Trichiuridae	22	2	2	0	´	19	11	1
Other fish							104	10
TOTAL							1048	100

The commercial value of the bottom fish on the Tennasserim coast appears, however, as seen in Table 21, to be much lower in general than that of the more northern parts with a dominance of fish of economic class 3.

Table 21 Distribution of the catches by economic classes in the bottom trawl on the Tennasserim coast

October -November 1979
	>10 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	>500 kg/h	% incidence in total no of hauls	Mean catch	% of total catch
Economic class 1	5	6	5	0	0	88	43	5
Economic class 2	5	2	8	1	0	88	95	11
Economic class 3	3	4	7	1	1	88	671	79
Economic class 4	9	2	4	1	0	81	44	5

March April 1980
	>10 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	>500 kg/h	% incidence in total no of hauls	Mean catch	% of total catch
Economic class 1	2	9	12	3	0	100	95	9
Economic class 2	2	6	8	6	4	96	270	26
Economic class 3	7	3	6	2	9	77	636	61
Economic class 4	8	12	5	1	0	96	43	4

5.6 The distribution by depth of bottom trawl catches

Table 22 shows an analysis of catch rates versus depth, and their composition by economic classes. On the Arakan coast the catch rates in the shallowest zone 10-24 m is clearly higher in the spring than in the autumn. This is probably related to the change in the oceanographical conditions between the two seasons as discussed in chapter 4. In the spring, water with low oxygen content, cover large areas of the shelf and will cause A shoreward movement of the demersal fish. Fishing at depths greater than 50 m gave low catch rates on the Arakan coast, but the economic value of the catch in deeper waters was relatively higher than at shallower depths.

In the Delta there is no clear seasonal difference in the depth distribution of the catches and the catch rates decline more slowly with depth although there is a clear tendency for highest rates in depths of less than 50 m. The value of the fish is relatively higher in the deeper strata. On the Tennasserim coast the relatively few hauls indicate high catch rates in the shallowest strata dominated by fish of economic class 3 (ponyfish), with lower catch rates but relatively more valuable fish in the deeper waters.

Table 22. Mean catch in bottom trawl by depth strata and by economic classes (kg/h).

ARAKAN COAST
	Dept in metres
SPRING	10-24	25-49	50-74	75-149
Economic class 1:	98	141	2	0
Economic class 2:	482	357	22	0
Economic class 3:	869	737	2	0
Economic class 4:	43	49	13	0
Economic class 1 - 4:	1492	1284	39	0
Number of hauls:	11	13	4	0
AUTUMN:
Economic class 1:	127	109	33	72
Economic class 2:	181	572	27	42
Economic class 3:	115	342	21	15
Economic class 4:	6	9	2	26
Economic class 1 - 4:	429	1032	83	155
Number of hauls:	8	21	5	5
DELTA AREA
SPRING:
Economic class 1:	93	77	137	27
Economic class 2:	84	231	49	46
Economic class 3:	329	308	37	3
Economic class 4:	24	15	146	34
Economic class 1 - 4:	530	631	369	110
Number of hauls:	35	12	8	3
AUTUMN:
Economic class 1:	219	101	144	34
Economic class 2:	135	187	65	43
Economic class 3:	177	212	83	35
Economic class 4:	34	10	11	16
Economic class 1 - 4:	565	510	303	128
Number of hauls:	7	17	10	7
TENNASSERIM COAST
SPRING:
Economic class 1:	102	92	41	135
Economic class 2:	359	360	124	10
Economic class 3:	851	907	185	7
Economic class 4:	39	59	54	11
Economic class 1 - 4:	1351	1417	404	163
Number of hauls:	10	8	4	4
AUTUMN:
Economic class 1:	83	40	33	30
Economic class 2:	144	75	107	100
Economic class 3:	3284	115	40	17
Economic class 4:	172	4	26	29
Economic class 1 - 4:	3681	234	206	176
Number of hauls:	3	6	4	2