3.3 VENEZUELA ORINOCO

3.3.1 Small pelagic fish
3.3.2 Demersal resources
3.3.3 Overview and discussion of survey results

Figure 3.1.1 shows the course tracks and fishing stations in the area.

Introduction

There is a widening of the shelf as its edge turns northwards off the east coast of Trinidad. Soft mud is prevalent over the inner and mid shelf and a main feature of the inshore hydrography is the discharges of the Orinoco with its seasonal maximum in late autumn. The Guiana Current causes upwelling along the shelf edge, but it seems doubtful whether this reaches the surface and affects the productivity in the inner shelf area.

3.3.1 Small pelagic fish

Fish distribution

In surveys 1, 2 and 4 a narrow belt of fish aggregations was located inshore, see Figure 3.1.2. Very little fish was recorded offshore in any of the surveys. The inshore fauna consisted of anchovies, sardines and carangids with some Spanish mackerel and hairtails. The areas of aggregations were restricted and the densities were not very high.

Catch compositions

Table 3.3.1 shows the mean and the highest catch rates and the incidence of occurrence by families and surveys.

Table 3.3.1 Venezuela, Orinoco. Pelagic fish. Catch rates in kg/hour by main groups by surveys. Mean rate, three highest rates and rate of occurrence.

Survey	Mean rate	Highest rates			Rate of occurrence
ENGRAULIDS
1 February	56	308,	212,	180	11/16
2 May	12	116,	44,	43	8/22
3 August	1	3,	3,	0	2/10
4 November	72	674,	291,	24	6/14
CLUPEIDS
1 February	30	114,	78,	58	14/16
2 May	57	1063,	59,	55	12/22
3 August	7	35,	14,	11	6/10
4 November	52	336	158	127	7/14
CARANGIDS
1 February	12	70,	61,	18	12/16
2 May	39	434,	184,	66	18/22
3 August	7	24,	15,	11	5/10
4 November	18	132,	49,	38	10/14
SCOMBRIDS
1 February	2	12,	10,	9	6/16
2 May	7	40,	29,	22	12/22
3 August	2	11,	3,	3	4/10
4 November	15	104,	83,	14	6/14
HAIRTAILS
1 February	50	226,	168,	96	13/16
2 May	30	252,	158,	121	10/22
3 August	9	32,	26,	16	7/10
4 November	12	46,	30,	14	9/14

The catch rates for anchovies and sardines are similar to those obtained in Guyana, but the rates for carangids and scombrids are lower. The hairtail Trichiurus lepturus seems to be a characteristic species off the Orinoco. There is a marked decline in catch rates for the August survey demonstrating the same phenomenon of low availability at this season as further east along the Guianas. The species compositions of the various groups, see Table 3.3.2 show some features differing from those of Suriname and Guyana. The anchovies are dominated by anchoviella species, thread herring and sardinella are scarce and the carangids are represented nearly only by the genera Selene, Caranx and Trachinotus.

Table 3.3.2 Orinoco. Species distribution by families of small pelagic fish. Catch by weight of species by surveys as per cent of total catch of family.

Survey:	1	2	4	Mean
ENGRAULIDS
Mean catch, kg/hour	56	12	72
Anchoa species	38	15	11	21
Anchoviella species	57	68	88	71
CLUPEIDS
Mean catch, kg/hour	30	57	52
Opisthonema oglinum	5	6	5	5
Sardinella aurita	9	22		10
Pellona harroweri	20	17	39	25
Chirocentrodon bleekerianus	24	33	10	22
Harengula jaguana	42	23	25	30
Odontognathus spp.			22	7
CARANGIDS
Mean catch, kg/hour	12	39	18
Selene spp.	70	70	79	73
Caranx sp.	16	16	14	15
Trachinotus sp.	14	5	13	11

Biomass estimates.

Table 3.3.3 shows the acoustic estimates of the stock biomasses. The levels are very low for the August survey as found in the other parts of the Guianas, but also the estimates from survey 4 are low. Using the means of surveys 1, 2 and 4 gives a total stock biomass of 70 000 tonnes of small pelagic fish with 40 000 tonnes anchovies and sardines and 30 000 tonnes carangids etc.

Table 3.3.3 Orinoco. Estimates of standing biomass of pelagic fish by surveys and groups. 1 000 tonnes.

Survey	Pelagic 1	Pelagic 2	Total
1 February	55	37	92
2 May	46	33	79
3 August	7	1	8
4 November	16	11	27

A further rough breakdown using the proportion of total catches by families gives:

Anchovies	15 000	tonnes
Sardines	25 000	tonnes
Carangids	14 000	tonnes
Hairtails	14 000	tonnes
Scombrids	2 000	tonnes

3.3.2 Demersal resources

For the Orinoco region the data for the swept area analysis constitute 12, 21, 14 and 13 trawl stations from the respective four surveys. In the analysis the data have been stratified by two bottom depth strata, 0-50 m and 50-120 m termed the inner and outer shelf respectively. Only the highlights of the results from the analysis will be commented upon in the text. The complete results are presented in tables in Annex 7 of the DATA FILE.

On the slope 15 stations were carried out, of which 8 were in the 500-800 m bottom depth range. These stations are too few to justify a separate biomass analysis.

Demersal fish

The shallow waters are mainly inhabited by croakers and some harvestfish Peprilus. The main scieanids are the king weakfish Macrodon ancylodon, Jamaica weakfish Cynoscion jamaicensis, green weakfish C. virescens and shortfin corvina Isopisthus parvipinnis. American harvestfish Peprilus paru and catfish Arius grandicassis were also common in the catches.

On the outer shelf the clearly dominating species was cardinal snapper Pristipomoides macrophthalmus. Occasionally some croakers were caught, but at low rates.

The fish distribution on the inner shelf shows a strong seasonality. Most of the croakers had moved out of the investigated area during the third survey (August), only Jamaica weakfish was still present at low catch rates together with barbel drum Ctenosciaena gracilicirrhus which previously was only found at the outer shelf.

Catch composition

Table 3.3.4 shows the mean catch rates in kg/hour and the catch distribution by size classes for the main species on the shelf, and Table 3.3.5 shows the mean catch rates summed for the main commercial species groups.

On basis of all four surveys the mean catch rate of croakers in the inner shelf waters is 113 kg/hour. This incorporates, however, the survey where most part of these species were absent from the investigated area. A mean from the three other surveys only is 145 kg/hour. Mean catch of snappers at the outer shelf is 22 kg/hour. During the first survey, croakers were also caught at the outer part of the shelf with a mean rate of 65 kg/hour. Other demersal fish, mostly non commercial, amounts to 60 and 35 kg/hour on the inner and outer shelf respectively, taken as yearly average.

Table 3.3.4 Orinoco. Mean catch rates and catch distribution by size classes for all swept-area hauls carried out on the shelf.

Species		Mean rate	Number of hauls in catch groups						Rate of occurrence *
		kg/hour	1-30 kg	30-100 kg	0.1-0.3 t	0.3-1 t	1-3 t	> 3 t
INNER SHELF
	King weakfish	41	12	5	2	2			21/60*
	Jamaica weakfish	17	23	3	2				28/60*
	Green weakfish	17	15	5	1				21/60*
	American harvestfish	15	32	6	1				39/60*
	Shortfin corvina	10	17	3					20/60*
OUTER SHELF
	Cardinal snapper	16	9	3	1				13/29

* Calculated on basis all hauls total shelf.

Family	INNER SHELF	OUTER SHELF
Snappers	.5	22
Groupers	0	2
Croakers	113	20
Grunts	1	0

Biomass estimates

In Annex 7 are given estimates of fish density by the two depth strata applied. By multiplying these densities with the area of the shelf, given in Table 2.3.1 estimates of standing biomass are obtained by surveys and species or species groups. These estimates are presented in Table 3.3.6.

Table 3.3.6 Orinoco. Estimates of biomass of demersal fish on the shelf by main groups and surveys.

		Survey 1	Survey 2	Survey 3	Survey 4	All surveys
INNER SHELF
	Snappers	200	0	0	200	50
	Croakers	16 500	11 000	4 000	16 500	11 500
	Grunts	500	0	0	200	100
	Groupers	50	0	0	0	0
	Other demersal	6 500	7 000	1 000	15 500	5 500
OUTER SHELF
	Snappers	300	3 000	1 000	1 500	1 500
	Croakers	5 000	1 000	500	200	1 500
	Grunts	0	0	0	50	0
	Groupers	0	200	0	200	100
	Other demersal	1 500	5 000	2 000	2 500	2 500
	Total, main groups	22 500	15 000	5 500	19 000	14 500
	Total, other dem.	8 000	12 000	3 000	18 000	8 000

The croakers are estimated to 13 000 tonnes when all surveys are pooled. Excluding the third survey, when freshwater outflow from the Orinoco was at its peak, gives an average biomass of 16 500 for the group. Snappers, mainly located at the outer shelf, are estimated to 1 500 tonnes as a yearly mean. The lowest estimate, 500 tonnes, was obtained in February, and the highest, 3 000 tonnes in May.

Sharks

Table 3.3.7 shows that catch rates for sharks were low off the Orinoco, perhaps reflecting the low availability of the important prey species, small pelagic fish in this area. A swept area estimate indicates a biomass of 1 700 tonnes.

Table 3.3.7 Orinoco. Sharks. Catch rates in kg/hour by main groups by surveys. Mean rate, three highest rates and rate of occurrence.

Survey	Mean rate	Highest rates			Rate of occurrence
1 February	8	18,	17,	13	11/14
2 May	15	141,	37,	34	16/22
3 August	3	6,	3,	3	5/10
4 November	10	60,	21,	17	11/13

Table 3.3.8 shows the composition by groups. In addition to the Caribbean sharpnose shark the small eye smooth-hound had a relatively high incidence. Both of these species occurred with small sized specimens.

Table 3.3.8 Orinoco. Sharks. Proportion by weight in catch, range of sizes and percentage occurrence in all catches.

		Catch %	Range of size, kg.	Incidence %
Requiem sharks,	Carcharhinus spp.	14	1.5 - 2	2 - 5
Sharpnose sh.,	Rhizoprionodon spp.	45	0.5 - 0.7	2 - 47
Hammerheads,	Sphyrna spp.	7	1 - 5	8 - 9
Smooth-hounds,	Mustelus spp.	34	0.3 - 0.5	14 - 37

Shrimp

Shallow water shrimp. The catch data from the hauls in which shallow water shrimps were caught are shown in Table 3.3.9. Pink shrimp was overall the most common species with highest catches in the first and last survey. Modal sizes were lowest in February, but wide size ranges indicate a long period of recruitment. The pink shrimp showed about the same catch rate in day and night time perhaps an effect of more turbid water off the Orinoco. The brown shrimp showed highest rates in February and August as found in Guyana. The modal size was lowest in August. Data on the fish by-catches are available for analysis.

Table 3.3.9 Orinoco. Shallow water shrimps. Mean catch rates in hauls where present and highest rates by surveys, mean rates for all surveys and by day/night, kg/hour. Total catch adjusted to a standard survey effort for all surveys.

	Brown	Red spotted	White	Pink
1 February	4 (10)		2 (3)	18 (25)
2 May	2 (3)	3 (5)		3 (6)
3 August	5 (12)	1		2 (4)
4 November	2 (3)	1	2	5 (9)
All surveys	2	2	1	5
All surveys day	2.5	0	1.1	4.2
All surveys night	1.9	1.7	0.3	5.3
Adjusted catch	123 kg	72 kg		410 kgs

Deep water shrimp. In surveys 2, 3 and 4 some tests were made with bottom trawl for deep water shrimp outside the edge. The results are summarized in Table 3.3.10. In addition to the species assessed as being of commercial interest some catches were at times made with higher rates of non-commercial types such as Nematocarcinus and Glyphocrangon. The scarlet shrimp Plesiopenaeus edwardsianus and the royal red shrimp Pleoticus robustus were the most important species, the latter occurred jointly with some other Solenoceridae of commercial size. The density of the various species differed with depth and possibly also with season, but the data are too scanty to demonstrate such differences between surveys.

Table 3.3.10 Orinoco. Tests for deep water shrimp, 15 hauls 200-790 m. Catch rates in kg/hour and main dept

	Mean catch	Highest			Incidence	Depth
All commercial shrimp	5	13,	10,	8	14/15
Plesiopenaeus edwards.	2	7,	7,	4	10/15	600-700
Pleoticus robustus a.o.	2	8,	6,	5	8/15	300-500
Acanthephyra sp.	.3	3,	2,	1	3/15	700

3.3.3 Overview and discussion of survey results

The following groups of resources were identified and will be discussed:

Small pelagic fish was found in aggregations in a narrow inshore belt with largely moderate densities where catch compositions included anchovies, sardines, and carangids with some hairtails and Spanish mackerel.

Demersal fish was found mainly on the inner shelf with croakers as the main group and giving high catch rates. The distribution of croakers extended also out to the mid shelf region where cardinal snapper was the main species.

Sharks were caught in modest amounts mostly in depths less than 40 m.

Shrimp are described only with some data on catch compositions by species and surveys and with an account of some tests for deep sea shrimp.

Table 3.3.11 shows a summary of the assessments of the standing stock of the various groups. With a total biomass of about 100 000 tonnes and a shelf area to 100 m depth of 5 300 nm² the standing stock density is 19 t/nm² which is somewhat lower than off Guyana and indicates a moderate to low level of productivity. One problem in evaluating the findings of our work in this area is that the shallow inshore part of the shelf not covered by our survey is large and the application of the results from the outer area may introduce bias both as regards composition and abundance of the resources. Previous trawl surveys have covered this area, but results are not readily available. Data on fisheries are missing, but if ones assumes a moderate rate of exploitation including the effect of the by-catch in the shrimp fisheries, the potential long term yield of demersal fish, mostly croakers amounts to abot 4 000 tonnes. In addition comes a 5 000 tonnes yield of hairtails, Spanish mackerel and some carangids.

Table 3.3.11 Venezuela, Orinoco. Summary of estimates of standing stock biomass. Tonnes.

Pelagic fish Anchovies		15 000
	Sardines	25 000
	Carangids	14 000
	Hairtails	14 000
	Scombrids	2 000
	Total		70 000
Demersal fish
	Croakers	16 500
	Snappers	1 500
	Grunts	100
	Groupers	100
	Other demersal mostly non-com	8 000	26 200
Sharks			1 700
Shallow water shrimp
Deep water shrimp
Total			98 000