6. OTHER SMALL PELAGIC FISH

Catch composition

Only catches from bottom hauls were considered in this analysis. As in the previous surveys conducted by “Pantikapey” and “S. Rybak” the area covered was divided into the following subareas: Machese, Beira, Quelimane I, Quelimane II and Angoche + Moebase.

Several families are included in the group (Table 1). Families Clupeidae, Engraulidae, Leiognathidae and Sphyraenidae were the most representative in the catches. They were mainly caught, at depths shallower than 25 meters where total catch amounted to about 6.5 tons. The best catch rates were obtained in the sub-areas Beira and Quelimane I at depths shallower and deeper than 25 meters, respectively, where the family Clupeidae dominated the catches. In subareas north of Zambezi river, Angoche + Moebase and Quelimane II, families Clupeidae and Carangidae were the most important in the catches.

Detailed information on sardines and ponyfishes is presented in the next chapters. The information concerning the other small pelagic fish is found in Annex 3.

Catch rates, distribution and biology of the main families

Sardines

In this group two families were included, Clupeidae and Engraulidae, excluding Stolephorus sp. which was considered in the group of anchovies as in the previous reports on surveys with the R/V Dr. Fr. Nansen.

A. Family Clupeidae

a) Catch rates and distribution

The most representative species of the family Clupeidae is Pellona ditchela. It was found in the whole surveyed area at depths from 6 to 36 meters. The highest catch rates were obtained at depths above 20 meters although in one single haul at 23-26 meters depth a catch of 516 kg was recorded (Fig. 14, Table 2).

Table 1. Composition of small pelagic fish catches (kg/h) by subarea and depth interval (meters).

Table 2. Catch rates of the main species of the family Clupeidae by depth and subarea.

	B. + Machese		Quel. I		Quel. II		Ang. + Moeb.		Total
	<20	21-45	<20	21-45	<20	21-45	<20	21-45	<20	21-45
P. ditchela	162.7	1.2	53.3	206.4	78.9	0.04	8.0		96.6	86.21
H. kelee	-	-	0.4	-	0.04	-	-	-	0.1	-
Sardinella spp.	33.0	-	12.2		0.4	10.5	0.4	-	17.0	3.5
Total (all species)	196.8	20.6	66.7	206.4	79.7	24.9	15.7	-	115.7	97.7
Hours of hauling	7.00	1.00	3.42	2.50	2.75	2.00	3.00	.50	16.17	6.00

Fig. 14. Catch rates of P. ditchela and length composition by subarea.

The remaining species of this family, namely Hilsa kelee, Dussumieria acuta, Sardinella gibbosa, Sardinella sp., appeared in the catches in very low quantities. They were mainly found at depths above 20 meters.

This distribution is in good accordance with the results of the previous surveys.

b) size composition of P. ditchela

The length distributions in each subarea were combined. For each haul the number of individuals measured was extended to the total catch in numbers per hour of trawling and the average catch in numbers per hour calculated for each length class. The percentage obtained in each class is represented in Fig. 14.

Small individuals were caught in the subarea Angoche + Moebase and Machese + Beira and the large ones between Quelimane II and Machese + Beira.

During the last “Fr. Nansen” survey, in September 1982 small fish were found in the subareas Quelimane I and II.

c) Growth curve of P. ditchela

A total of 55 otoliths were used for age readings by counting the number of daily growth rings.

The von Bertalanffy growth equation was fitted to the data and the following equation was obtained:

L_t = 24.0 (1 - e^{-0.88 (t-0.23)})

Fig. 15 shows the growth curve of P. ditchela.

Fig. 15. Growth curve of P. ditchela.

d) Gonad development of P. ditchela

A total of 1027 gonads were examined and the maturity stages analysed (Table 3). Most of gonads were immature (stage II) or preparing for spawning (stages III and IV).

Fish smaller than 15 cm were mainly immature. Females in spawning were caught at nearly all stations where this species was present but the higher concentrations were found between Zambezi river and Quelimane (Fig. 16). Most of them were of sizes larger than 15 cm.

Fig. 16. Occurrence of females of P. ditchela in spawning.

Table 3. Relative percentage of maturity stages of P. ditchela by sex.

FEMALES						MALES
I	II	III-IV	V	VI	n	I	II	III-IV	V	VI	n
-	31.9	30.4	30.4	7.3	533	-	15.8	17.6	59.5	7.1	494

Gonadasomatic index (gonad weight/total weight × 100) was estimated for each sex.

Females:

s = 1.36
n = 254

s = 4.95
n = 234

a) Catch rates and distribution

This family was mainly represented by Thryssa vitrirostris which appeared together with P. ditchela. The best catch rates were obtained at depths above 20 meters, between Beira + Machese and Quelimane II (Table 4, Fig. 17). However, only in one haul at 23-26 meters depth a catch of 104 kg was obtained.

Other species of this family were caught, namely T. setirostris.

Table 4. Catch rates of T. vitrirostris by depth and subarea.

	B. + Machese		Quel. I		Quel. II		Ang. + Moeb.		Total
	<20	21-45	<20	21-45	<20	21-45	<20	21-45	<20	21-45
T. vitrirostris	60.1	-	35.0	41.6	24.3	+	5.4	-	38.6	17.5
Total (all species)	62.9	61.5	41.6	42.1	24.8	7.9	7.0	-	41.6	30.4
Hours of hauling	7.00	1.00	3.42	2.50	2.75	2.00	3.00	.50	16.17	6.00

Fig. 17. Catch of T. vitrirostris and length composition by subarea.

b) Size composition of T. vitrirostris

Length samples were combined by three subareas and the percentage of catch in numbers per hour of trawling of each length class represented in Fig. 17. At least two modes are present in each distribution.

The juveniles seem to occur in the whole area surveyed. In the last survey by “Fr. Nansen” juveniles were mainly found in the subareas Quelimane I and Quelimane II.

c) Gonad development of T. vitrirostris

A total catch of 785 gonads were examined and the relative percentage of maturity stages by sex determined (Table 4). Most of the fish were immatures (stage II) or preparing for spawning (stages III and IV).

Table 5. Relative percentage of maturity stages by sex of T. vitrirostris.

FEMALES						MALES
I	II	III-IV	V	VI	n	I	II	III-IV	V	VI	n
-	48.3	32.0	16.6	3.1	416	-	39.0	26.0	33.1	1.9	369

The gonadosomatic index was estimated for males and females separately. The results were:

Females:

n = 221

s = 0.59

n = 195

s = 0.45

a) Catch rates and distributions

Two species of the family Leiognathidae were abundant in the catches: Leiognathus equulus and Secutor insidiator. The best catches were obtained at depths above 20 meters in the subarea Beira + Machese. Catch rates of S. insidiator were also high in Quelimane II and Angoche + Moebase, as was found in the previous surveys (Figs 18, 19, Table 6).

Table 6. Catch rates of the species of family Leiognathidae by depth and subarea.

	B + Machese		Quel. I		Quel. II		Ang. + Moeb.		Total
	<20	21-45	<20	21-45	<20	21-45	<20	21-45	<20	21-45
L. equulus	11.5	-	0.5	6.5	-	-	4.2	-	5.9	2.7
S. insidiator	26.0	0.9	0.6	14.5	10.8	0.2	25.5	-	18.0	6.3
G. minuta	1.5	-	1.5	0.2	0.3	-	4.2	-	1.7	+
Total (all species)	38.8	0.9	2.6	21.1	11.1	0.2	33.9	-	25.5	9.0
Hours of hauling	7.00	1.00	3.42	2.50	2.75	2.00	3.00	.50	16.17	6.00

Fig. 18. Catch rates of L. equulus by subarea.

Another species of this family, Gazza minuta was also caught but in very low quantities.

b) Size composition of L. equulus and S. insidiator

A few samples of L. equulus were collected in the subareas Angoche + Moebase and Beira + Machese (Annex 3).

The length samples of S. insidiator were combined by subareas and the percentage of catch in numbers per hour of each length class represented in Fig. 19.

Fig. 19. Catch rates of S. insidiator and length composition by subarea.

c) Gonad development of L. equulus

A few gonads were examined and the relative percentage of maturity stages by sex determined (Table 7). Most of the fish was immature (stage II).

Table 7. Relative percentage of maturity stages of L. equulus by sex.

FEMALES						MALES
I	II	III-IV	V	VI	n	I	II	III-IV	V	VI	n
-	73.6	19.1	7.3	-	110	-	72.0	22.0	6.1	-	82

Other small pelagic species

All collected data of other pelagic species are included in Annex 3.