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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.
Table 3.7.5 Gulf of Venezuela. Mean catch rates (kg/hour) in all hauls by main commercial groups.

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 west coast
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.
The Gulf of Venezuela
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.
One should note that some areas of importance for small scale fisheries could not be covered by the surveys: the inner shallow parts of the Venezuelan Gulf and the Lake of Maracaibo and that the objectives of the surveys did not include the stocks of tuna which represent resources for important Venezuelan fisheries.

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.


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