3.7 The Gulf of Venezuela

3.7.1 Small pelagic fish
3.7.2 Demersal resources
3.7.3 Overview and discussion of survey results

As shown in Figure 3.6.1 the Gulf was extensively covered in all of the surveys except for the inner part in survey 3. The number of successful trawl hauls were 45, 34, 36 and 28 for surveys 1 through 4 respectively.

3.7.1 Small pelagic fish

Fish distribution

Figure 3.6.2 which derives from the acoustic observations shows that aggregations of pelagic fish are found on the outer half of the Gulf in all seasons while no records were made in the inner part on June and only scarce traces in February. Areas with high densities are very restricted and most consistently found close to the west coast of the Paraguana Peninsula. The schooling behaviour was different from that found in the Oriente with numerous smaller schools distributed in patches over the various parts of the Gulf.

Catch compositions

Engraulids, clupeids and carangids were the dominating groups of pelagic fish in the catches with variable presence of the predators scombrids and barracudas. The catch data are summarized in Table 3.7.1. One should keep in mind the varying catchability of different types and sizes of fish which reduces the value of these data for describing the composition in the sea. Anchovy gave some high catches in February consisting of Engraulis eurystole, and again in September when Anchoa species dominated. Clupeids and carangids gave relatively high catches in the first part of the year, and for the sardines also in September, while catches in the last survey were low as for all the other groups.

Table 3.7.1 Gulf of Venezuela. Pelagic fish. Catch rates in kg/hour by main groups by surveys. Mean rate, three highest rates and rate of occurrence. All hauls.

Survey		Mean rate	Highest rates			Rate of occurrence
	ANCHOVIES
1 February		43	733,	571,	320	27/45
2 June		6	68,	29,	22	15/34
3 September		26	387,	193,	81	16/36
4 November		2	30,	5,	1	8/28
	CLUPEIDS
1 February		40	978,	178,	156	33/45
2 June		42	212,	137,	108	30/34
3 September		54	325,	224,	202	31/36
4 November		19	147,	83,	58	17/28
	CARANGIDS
1 February		34	51,	50,	43	40/45
2 June		86	399,	384,	352	33/34
3 September		28	139,	132,	130	31/36
4 November		22	222,	99,	53	25/28
	SCOMBRIDS
1 February		10	95,	76,	52	36/45
2 June		6	42,	36,	23	24/34
3 September		6	44,	22,	22	23/36
4 November		3	20,	17,	11	12/28
	BARRACUDAS
1 February		2	32,	17,	7	16/45
2 June		20	286,	79,	70	20/34
3 September		18	374,	32,	31	26/36
4 November		1	6,	4,	3	13/28
	HAIRTAILS
1 February		5	55,	36,	31	23/45
2 June		52	987,	301,	89	18/34
3 September		8	178,	30,	28	12/36
4 November		13	308,	28,	6	11/28

The species compositions for the sardines and the carangids are shown in Table 3.7.2, (which, however, include only the more abundant species). The thread herring is the most abundant clupeid and common at all seasons. The dogtooth herring was abundant in June and September and round herring only in February. The bumper dominate the carangids in all surveys with smaller contributions from the rough scad, lookdowns and a few scads.

Table 3.7.2 Gulf of Venezuela. Species distribution by families of small pelagic fish. Catch by weight of species by surveys as per cent of total catch of family. Most abundant species only.

Survey:		1	2	3	4	Mean
	CLUPEIDS
Mean catch, kg/hour		40	42	54	19
Opisthonema oglinum		26	31	47	67	43
Sardinella aurita		12	35	10	6	13
Chirocentrodon bleekerianus		6	33	34	27	19
Etrumeus teres		66	1	8	0	19
	CARANGIDS
Mean catch, kg/hour		34	86	28	22
Chloroscombrus chrysurus		90	80	78	87	84
Selene spp.		3	3	14	10	7
Trachurus lathami		6	16	7	3	8
Decapterus spp.		1	1	1		1

The catches of scombrids consisted of about 1/3 of each of the species chub mackerel, king and serra Spanish mackerels.

The southern sennet Sphyraena picudilla represented 80% of the catches of barracudas.

The general picture is of an assemblage of small pelagic fish consisting of a number of species, partly appearing in fluctuating abundance.

Biomass estimates

The estimates of biomass based on the acoustic observations are shown in Table 3.7.3. There is great variations between surveys which is mainly caused by the* appearance of high biomasses offish in the inner part of the Gulf in the February and September surveys. The catches in these parts consisted mainly of a mixture of engraulids and clupeids as described in the catch compositions. The estimates of fish biomass for the outer shelf is seen to vary much less and it represents on the average only about 36% of the totals. The biomass variations could also reflect production cycles in the various stocks or movements in and out of the surveyed area, but with the high number of species it is difficult to demonstrate such phenomena. The best available estimate is probably the simple mean of all the surveys.

Table 3.7.3 Gulf of Venezuela. Estimates of standing biomass of pelagic fish by surveys and groups and for outer part of the gulf separately. 1 000 tonnes.

Survey	Pelagic 1		Pelagic 2		Total
	Total	Outer	Total	Outer	Total	Outer
1 February	208	56	27	5	235	61
2 June	55	32	13	13	68	45
3 September	148	64	93	40	241	104
4 November	93	29	24	4	117	33

The stock biomasses for the Gulf of Venezuela can thus be assessed at:

Clupeids and anchovies	126 000	tonnes
Carangids	21 000	tonnes
Scombrids	3 000	tonnes
Barracudas	5 000	tonnes
Hairtails	9 000	tonnes

A swept area estimate of the barracudas gives close to 3 000 tonnes and for hairtails 5 000 tonnes.

3.7.2 Demersal resources

Demersal fish

The data on demersal fish in the Gulf have been analysed by two bottom depth strata, 0-50 m and 50-100 m, mainly corresponding to the inner Gulf and its mouth respectively. The data input is from 89 random trawl-hauls, with 18, 30, 25 and 16 hauls from the four surveys. The demersal fish fauna is mainly composed of croakers inside the Gulf and snappers in the deeper waters of the mouth. The dominating species are whitemouth croaker, American harvestfish and lane snapper in the inner part of the Gulf and Atlantic bigeye, mutton snapper and dwarf goatfish in the deeper waters in the mouth. The mean catch of the dominating species together with their catch distribution by size classes are shown in Table 3.7.4. Table 3.7.5 show the mean catches summed by main species groups. The croakers, the dominating group in the Gulf, consisted of a multitude of species, of which the whitemouth croaker was the most abundant. All croakers give a mean catch rate of 25 kg/hour of which the whitemouth constitutes 10 kg/hour. The remaining 15 kg/hour is from species not exceeding 1.5 kg/hour each. The snappers in the mouth of the Gulf give a mean catch of 30 kg/h.

Table 3.7.4 Gulf of Venezuela. Mean catch rates and catch distribution by size classes for all swept-area hauls carried out.

Species		Mean rate	Number of hauls in catch groups.						Rate of occurrence*
		kg/hour	1-30 kg	30-100 kg	0.1-03 t	0.3-1 t	1-3 t	>3 t
INNER PART 0-50 m
	Whitemouth croaker	10	30	4	1				35/89
	American harvestfish	8	33	3	1				34/89
	Lane snapper	4	35	3					38/89
OUTER PART >50 m
	Atlantic bigeye	14	33	5					38/89
	Mutton snapper	14	16	1	1				18/89
	Dwarf goatfish	10	33	3					36/89

* Calculated on basis all hauls total gulf.

Family	INNER PART	OUTER PART
Snappers	7	30
Groupers	0	4
Croakers	25	0
Grunts	2	4
Seabreams	2	2

Biomass estimates

Annex 7 of the DATA FILES gives the estimates of fish density by depth strata. By multiplying these densities with the area of the shelf, 4 000 nm² and 1 850 nm² for the Gulf and its mouth respectively, estimates of standing biomass are obtained by surveys and species or species groups. Such estimates are presented in Table 3.7.6 summarized for the main species groups.

The table shows a considerable variation between the surveys. Especially the last survey stands out with its low estimate of croakers in the shallow waters and may point to an atypical situation during this survey. A mean figure of 4 100 tonnes of croakers, based on the three first surveys is perhaps more representative for the size of the stock in the Gulf. The snappers in the deeper waters have two low estimates, both around 500 tonnes and two higher of around 2 000 and 3 000 tonnes, of which the highest is strongly influenced by two abnormally high catches. The low estimate in survey 4 coincides with an observed increased availability of snappers on the western side of the Guajira Peninsula in Colombia at this time.

The estimates are thus subject to fluctuations from migration in addition to sampling error, the latter of uncertain effect. The estimate of about 1 900 tonnes from all surveys pooled can be concidered as a minimum value for the standing stock of snappers available in the deeper waters of the Gulf. There are then strong indications that this represents a shared stock with Colombia.

Table 3.7.6 Gulf of Venezuela. Estimates of biomass of demersal fish by main groups and surveys.

		Survey 1	Survey 2	Survey 3	Survey 4	All surveys
INNER PART 0-50 m
	Snappers	600	800	1 350	600	900
	Croakers	6 000	4 250	2 100	300	3 350
	Grunts	50	700	150	0	250
	Groupers	0	100	100	50	100
	Seabreams	1 200	50	400	150	3 400
	Other demersal	900	5 200	4 700	2 250	3 450
OUTER PART >50 m
	Snappers	450	2 900	2 100	500	1 850
	Croakers	40	40	40	0	0
	Grunts	20	250	500	0	250
	Groupers	0	350	200	40	200
	Seabreams	0	250	150	0	150
	Other demersal	1 900	2 500	4 200	5 000	3 000
	Total, main groups	8 360	9 690	7 090	1 640	10 450
	Total, other dem.	2 800	7 700	8 900	7 250	6 450

3.7.3 Overview and discussion of survey results

The following resources were identified and will be discussed:

Oriente

Small pelagic fish was found in aggregations over the inner and mid shelf in all surveys. Fish densities were high and the areas extensive with sardinella as the dominating species, but the assemblage included other clupeids, engraulids and carangids accompanied by larger sized predators, barracudas, scombrids and sharks in the pelagial. Pelagic fish formed an important component of the catches also in the bottom trawl hauls.

Demersal fish was investigated by the random trawl sampling programme. The most important commercial groups were snappers, grunts, croakers, seabreams and groupers. The shelf squids were found to have a seasonal abundance in the first part of the year. Deep sea shrimp was found with relatively low densities in the slope

The narrow shelf from Cabo Codera to the Paraguana Peninsula was found to contain only very sparse resources consisting of scattered small pelagic fish, mostly carangids and some snappers.

Small pelagic fish appeared in seasonally variable abundance especially in the inner part of the Gulf. Thread herring was the dominating clupeid and bumper the most common carangid. Croakers, snappers and seabreams were the most important commercial bottom fishes. Squid had also in this area the highest abundance in the first part of the year. Trawl survey data indicate the possible existence of migration pattern of snappers between the Gulf and Colombian waters west of the Guajira Peninsula.

Summary of biomass estimates

Table 3.7.8 summarizes the estimates of biomass by areas and stocks or resource groups. It is thought that the acoustic method used to assess the pelagic fish will tend to produce somewhat underestimated results. As regards the swept area assessments for the demersal fish a bias one way or the other will largely depend on the choice of catchability coefficient. With our use of q = 1 the most likely bias is also here towards an underestimate.

Table 3.7.8 Venezuela. Overview of estimates of biomasses by main groups. Tonnes.

		Oriente	W. Coast	Gulf	Total
Pelagic fish
	Sardinella	800 000			800 000
	Anch. & sard.	200 000	10 000	126 000	336 000
	Carangids	220 000	22 000	21 000	263 000
	Scombr. etc.	20 000	8 000	17 000	45 000
	Total	1 240 000	40 000	164 000	1 444 000
Demersal fish
	Croakers	6 900	100	3 400	10 400
	Snappers	19 500	6 700	2 800	29 000
	Groupers	3 100	200	300	3 600
	Grunts	14 300	500	500	15 300
	Seabreams	2 900	900	3 600	7 400
	Total commerc.	46 700	8 400	10 600	65 700
	Others	36 800	5 400	6 600	48 800
	Total	83 500	13 800	17 200	114 500
Sharks		1 400
Squid		8 000		2 500	10 500
Total		1 333 000	53 000	183 700	1 570 000

The estimated total biomass for all the three areas is thus close to 1.6 million tonnes with about 1.3 million tonnes for the Oriente, 54 000 tonnes for the western coast and 184 000 tonnes for the Gulf of Venezuela.

Using the shelf area to a depth of 200 m the measure of total standing stock per unit shelf area comes out as follows: for the Oriente 111 t/nm² which indicates a high productivity, for the west coast 10 t/nm², a very low figure and for the Gulf 24 t/nm² which indicates a modest level of production. A number of previous surveys and assessments of various kinds have been made of the Venezuelan marine fish resources. Most directly comparable with our present work are the programmes conducted by Fundacion La Salle de Ciencias Naturales in cooperation with ORSTOM, Office de la Recherche Scientifique et Technique Outre Mer.

From this programme Gerlotto and Gines (1988) reports on results from acoustic surveys during 1980-1985 with the research vessels “LA SALLE”, “CAPRICORN” and “NIZERY” in which use was made of much the same type of equipment and methods applied in the DR “FRIDTJOF NANSEN”-surveys. For the Oriente region where the most intensive investigations were made, the total pelagic fish biomass was assessed at 1 400 000 tonnes. Of this the sardinella was estimated to represent between 730 000 and 1 000 000 tonnes. This compares well with our estimate for the same region of a total biomass of 1 240 000 tonnes with sardinella representing about 800 000 tonnes.

In a report on the preliminary results of the Venezuelan survey programmes up to 1984 Gerlotto and Eleguezabal (1986) included findings also from other parts of the Venezuelan shelf. The biomass estimates were:

Gulf of Venezuela	500 000	tonnes
Central littoral	100 000	tonnes
Oriente	1 400 000	tonnes

Our acoustic estimates for the Gulf of Venezuela is 160 000 tonnes and for the western coast 40 000 tonnes. Our highest seasonal estimate for the Gulf was, however, 240 000 tonnes. Although our biomass estimates from 1988 for the two western regions are thus somewhat lower than those from the earlier surveys, there is a marked similarity in the variation found between the three regions.

In order to maintain the fish stocks as a lasting resource only a part of the standing stock can be fished. The proportion of this long term yield varies between types of fish, and existing fisheries must also be taken into account in calculating the total potentials. In the following we will indicate 30% as being a reasonable level for relatively short lived small pelagic fish and squid and 20% for demersal fish and the larger sized pelagics such as barracudas, Spanish mackerels and hairtails. These proportions are only very rough indications of the levels of the sustained yields and they are based on an assumption of a moderate current exploitation of the stocks. If the standing stock is already significantly affected by the exploitation the proportion should be increased.

The official fishery statistics for Venezuela for 1986 show the following landings for the species or groups for which the surveys provide stock biomass data:

Pelagic fish:
Sardinella	51 000	tonnes
Other chip. & anch.	3 400	tonnes
Carangids	7 040	tonnes
Spanish mackerels	2 600	tonnes
Chub mackerel	800	tonnes
Hairtails	1 400	tonnes
Barracudas	350	tonnes
Demersal resources:
Croakers	17 600	tonnes
Snappers	6 500	tonnes
Grunts	5 800	tonnes
Groupers	2 740	tonnes
Squid	2 000	tonnes

If we compare these levels with the estimated stock biomasses in Table 3.7.8 it is evident that our surveys cannot have covered the main stocks of croaker, perhaps mainly because Lake Maracaibo and the shallow inner parts of the Gulf were excluded. If statistics on landings are available by areas our survey data may still be used for evaluations of croaker stocks in the areas covered. Part of the landings of snappers and groupers are from distant water fisheries and the 29 000 tonnes snapper biomass may then indicate that the resource may allow some increase of exploitation. There is also an indication that the total catch of squid might be increased, at least by 50%. For the pelagic stocks the estimated stock biomasses indicate considerable potentials for increased yields. For these types of resources there is a special need for caution when increasing the rate of exploitation because of the natural fluctuations in stock size which often occur. Still the sardinella stock seems to be fished at a very safe level with yields at 50 000 tonnes and it would be safe to expand fisheries considerably on carangids, hairtails, barracudas and probably also the Spanish mackerels. A more exhaustive analysis of stock conditions and potentials should be made with more detailed landing statistics and making use of the extensive size data obtained through the surveys.