4. BIOLOGY OF THE SARDINE

4.1 General
4.2 Number of vertebrae
4.3 Electrophoresis studies
4.4 Growth
4.5 Age composition of the catches
4.6 Length-weight relationships
4.7 Unit of length measurement
4.8 Spawning and maturity
4.9 Distribution and migration
4.10 Sardine on the Senegal coast
4.11 Conclusions on stock separation

4.1 General

The Group noted that little information is available on the sardine found north of Casablanca, and that around the Canary Islands. It is likely that these sardines belong to small, separate stocks and the Group decided to limit its studies to the major resources in the area between Casablanca and somewhat south of Cape Blanc.

4.2 Number of vertebrae

Whereas at the previous session no significant differences were found in vertebra numbers reported for the sardine caught between Casablanca and Cape Blanc, a paper submitted to the meeting of the Ad hoc Working Group on West African Coastal Pelagic Fish from Mauritania to Liberia, Dakar, 1978 (Domanevski and Barkova, 1979), distinguished two races of sardine, the "Moroccan" and the "Sahara" race, stating that these demonstrate a difference in number of vertebrae. The Soviet participants agreed to provide the CECAF Working Party on Resources Evaluation: with further details of the vertebrae numbers observed in the different parts of the area.

4.3 Electrophoresis studies

No new information from electrophoresis or other biochemical studies to identify sardine populations has become available.

4.4 Growth

Data on growth were presented by Morocco, Spain, Poland and USSR. Average values of length at each age are given in Table 1.

Fig. 1 Main fishing areas (Zones A, B and C) of the sardine fishery

Table 1

AVERAGE LENGTH BY AGE GROUP, IN THE CATCHES BY COUNTRY AND FISHING ZONE

Country	Fishing zone	Years of observation	Age
			I	II	III	IV	V	VI
Morocco	A	1973-1978	16.2	17.8	19.2	20.0	20.8
Spain	B	1975-1978	14.8	18.8	20.4	21.2	21.7	22.0
USSR1	C	1971-1977	12.1	11.8	20.7	22.1
Poland	C	1973-1976 (2nd quarter)	14.2	17.4	19.7	21.2	22.3	23.0

¹ Data converted from fork length to total length

Increases in growth rate of several age groups in Zone C from 1970 to 1975 have been reported in the paper by Domanevski and Barkova (1979). These growth rates appeared to coincide with variation in the upwelling, the stronger the upwelling the higher the growth rate.

The increase in these years is apparent in the Soviet and Polish data on length of age group I in Zone C (Table 2). The Spanish data on length at age in Zone B showed fluctuating values for the length of one-year - old fish with perhaps some tendency to increase in the period 1970-1975, and the Moroccan data for Zone A in 1973-1975 showed, if anything, a decrease (Appendixes 3, 4 and 8). However, the growth increments for older ages, calculated from the average length at each age reported by USSR for Zone C at this meeting (Appendix 8) and by Poland at the Dakar meeting, did not indicate a growth increase for the older ages (Tables 3 and 4). The data in Table 3, however, do suggest a marked decrease in growth from 1974/75 till 1976/77. Such a decrease is less obvious on Polish data. The USSR scientists agreed to bring further details of Domanevski and Barkova's growth data to the forthcoming meeting of the CECAF Working Party on Resource Evaluation in Dakar.

4.5 Age composition of the catches

The age composition in the catches of the various fleets have varied over the years. The major age groups in the catches are given in Table 5. (Data are taken from Appendixes 3, 4, 8 and from Krzeptowski (1975) unpublished mimeo.)

Whereas in Zones A and B relatively younger fish were caught in recent years, in Zone C the catches shifted towards the older fish. This apparently reflects the arrival of strong year classes at old ages, rather than an actual shift in fishing practices (see Section 7.3).

Table 2

LENGTH AT AGE I IN THE PERIOD 1970-1978 FOR ZONES A, B AND C

Zones		1970	1971	1972	1973	1974	1975	1976	1977	1978
Zone A
	Moroccan data				16.2	14.8	14.6	17.6	16.7	17.1
Zone B1
	Spanish data	14.0	14.8	14.3	14.1	14.5	15.1	14.9	14.5	16.4
Zone C2
	Soviet data		10.2	10.7	10.4	10.9	11.4	11.3	11.0
	Polish data				14.1	14.3	-	15.0	15.4

¹ Data obtained by backcalculating from rings in the scales
² Soviet data: fork length; all other: total length

Table 3

GROWTH INCREMENTS BY AGE AND CALENDAR YEAR INTERVAL OF SARDINE IN THE SOVIET CATCHES IN ZONE C

Year interval	Age
	I-II	II-III	III-IV
1971	6.1	1.7	1.8
1972	5.8	2.1	1.5
1973	6.3	2.0	1.4
1974	6.1	2.1	1.4
1975	5.8	1.9	1.3
1976	5.6	1.5	1.1

AVERAGE LENGTH AT AGE OF SARDINE DURING THE PERIOD 1973-1977 IN ZONE C (AFTER KRZEPTOWSKI, POLAND)

Year	Age
	I	II	III	IV	V	VI
1973	14.1	17.4	20.0	21.3	22.5	23.7
1974	14.3	17.4	19.8	21.6	22.7	-
1975	-	-	-	-	-	-
1976	15.0	17.2	19.4	20.8	22.0	22.8
1977	15.4	17.5	19.8	20.8	21.8	22.8

AGE GROUPS PREDOMINANT IN THE CATCHES

Year

Morocco (Zone A)

Spain (Zone B)

USSR (Zone C)

Poland (Zone C)

1972

II,

III

II,

III

1973

I,

II,

III

II,

III

II,

III

1974

II,

III

II,

III

II,

III

1975

II,

III

III,

IV

III,

IV

1976

I,

II

II,

III,

IV

III,

IV

III,

IV

1977

I,

II

II,

III

III,

IV

III,

IV

1978

I,

II

I,

II

4.6 Length-weight relationships

Mr M. Rami reported the following new length-weight relationship data to the meeting for Zone A.

1st quarter 1978:	W = 2.95 × 10-6 × L3.19 (n = 215)
2nd quarter 1978:	W = 2.26 × 10-6 × L3.25 (n = 441)
3rd quarter 1978:	W = 8.98 × 10-7 × L3.34 (n = 756)
4th quarter 1978:	W = 1.03 × 10-6 × L3.40 (n = 657)

W = weight in g; L = total length in mm; n = number of fishes measured

4.7 Unit of length measurement

It was reported that different standards are used for measuring sardine in the various countries, as follows:

Country	Dimension measured	Unit recorded for length frequency	Unit recorded for growth studies
Morocco	total length	1/2 cm, below	mm
Spain	total length	1/2 cm, below	mm
Poland	total length	nearest cm	nearest cm
USSR	fork length	nearest cm	nearest cm
Senegal	total length	1/2 cm, below	mm

(Total length is length with tail folded in the median line)

4.8 Spawning and maturity

Contrary to the observations in the first report which distinguished two spawning periods, the major one in winter and a secondary one in March-April, a paper by Siedletskaya (1979) indicated that in Zone C spawning takes place mainly between November and March, in the area between 22° and 29° N and no spawning was reported for April-May. Differences are observed in the area of major spawning concentrations in the various months, which in December, January and March were reported between 22° and 24° N and in February at about 26° N (data from 1952 to 1977).

According to Sedletskaia, the spawning takes place at depths between 110 and 300 m. The smallest fish observed in spawning condition was between 12 and 13.5 cm, the 50 percent point of the size at first maturity was 15.5 cm for males and 18 cm for females (fork length).

Rubies reported to the meeting that a spawning survey was conducted in April-May 1974 in the same area and period as the one conducted in 1973 and reported on at the previous meeting (Rubies and Palomera, in preparation). The 1973 survey showed the existence of two important sardine egg concentrations, one near Cape Bojador (between 25°30' N and 26°30' N) and the other, much less important, off Point Dunford (23°30' N to 24°30' N). The 1974 survey confirmed the existence of these two concentrations but they were located somewhat further south, between 24°30' and 25°30', and between 22° and 23° N, respectively. The abundance of the eggs and larvae was of the same order in both surveys. Spawning was found to take place above the shelf, mainly above depths between 25 and 150 m.

4.9 Distribution and migration

The meeting emphasized that the seasonal changes in the distribution and catch rates of the fishery described in the report of the first session can be taken to provide a good picture of the movements of the stocks.

Domanevski and Barkova (1979) reported on a substantial gradual shift in the southern boundary of the distribution of the sardine concentrations, from about 26° N in 1966 to about 19° N in 1974-1977, which coincided with an increase in the upwelling in that area.

Information on the Polish fishery (Appendix 7) showed that in recent years the fleet moved northward in summer from Zone C up to Zone B until September-October. During this period the fleet concentrated in two areas, 24°30' to 25°30' N and 26°30' to 27° N.

An acoustic and fishing survey carried out by USSR in Division 34.1.1 in December 1978 found sardine concentrations all along the coast from Zone A to Zone B.

4.10 Sardine on the Senegal coast

Fréon and Stéquert (in press) describe that since 1976 small quantities of sardines have been caught in warm waters along the Senegal coast. These fish showed a very high cephalic index (24.5 to 28.3 percent), and a low number of vertebrae (50.45). The length-weight relationship was: W = 5.6 × 10^-3 × L^3.21 (W is weight in g; L is total length in cm). These characteristics are substantially different from those of the fish further north.

4.11 Conclusions on stock separation

No new information has become available which enables more definite conclusions to be drawn on the existence of one or more sardine stocks in the major sardine fishing zones in the CECAF area.

The new observations on the continuous distribution of sardine from Zone A to Zone B during the December 1978 USSR survey, and on the northward extension until Zone B of the sardine distribution of Zone C during autumn, as reported by Poland, demonstrate that there exists no clear spatial separation between stocks. These observations, together with those described in section 4.7 of the report of the first session of the Ad hoc Group, suggest that Zone B is an area where fish from the three zones at least partly mix, and that the catches from Zone B cannot be considered as being obtained from a stock fully separate from those in Zones A and C.