6.2.5.1.1. Sexuality
The sexes are separate. Female gonads have a weight slightly higher than that of male gonads.
6.2.5.1.2. Gonad maturation
In Senegal, the period of maturity extends from April to October; the GSR is equal or above two. Frade and Postel (1955) have shown that during maturation, the ovocytes around 280 μ in March reach 600 μ in June when they are ripe. In males, spermatogenesis begins and becomes widespread starting in April, the seminal vesicles are filled with spermatozoids in June.
6.2.5.1.3. Size at first maturity
Postel (1955) defined size at first maturity as the smallest specimen where the gonad weight represents 2% of the body weight. He found it is 448 mm for males and 454 mm for females.
6.2.5.1.4. Reproductive periods and zones
Postel (1955) and Frade and Postel (1955) note that spawning in Senegal starts in April-May, has its maximum in June, and terminates in September-October. Conand (1970) has shown that the species reproduces in August. Marchal observed males and females in reproduction in October off Guinea. Zhudova (1969) collected larvae off Abidjan and Monrovia in September, December, February and March. Spanish mackerel reproduce throughout their range when waters are warm.
6.2.5.1.5. Fecundity
Postel (1955) found that the maximum fecundity of a female of 95 cm is around 1 million eggs. This value corresponds to the individual relative fecundity. The number of egg releases is unknown.
6.2.5.1.6. Sex-ratio
The number of females is much higher than the number of males. Postel (1955) and Diouf (1980) have shown from samples collected in Senegal that the sex-ratio is over 2. For females, size varies from 402 to 975 mm, for males, from 427 to 835 mm. The proportion of females increases with size (Postel, 1955).
6.2.5.2.1. Growth in length
Growth in length of Spanish mackerel has been studied by Postel (1955) from the analysis of size frequency distributions of 812 individuals caught in Senegal. He notes that the size of juveniles of undetermined sex is 12 cm at the end of August and goes to 25 cm in October then to 35 cm in November, that is a growth rate of around 25 cm in 3 months. From the frequency distribution of adults fished in the same zone, Postel (1955) estimated the growth of males and females:
| Fork Length (cm) | ||
Age | Males | Females |
<1 year | < 50 cm | < 55 cm |
1 – 2 years | 50 – 60 cm | 55 – 65 cm |
2 – 3 years | 60 – 70 cm | 65 – 75 cm |
3 – 4 years | > 70 cm | 75 – 85 cm |
> 4 years | > 70 cm | > 85 cm |
Females, in their first year, reach a size superior to males, an advantage that they keep afterwards in a constant way. This dimorphism in growth between males and females has also been observed for S. Cavalla (Johnson et al., 1980).
6.2.5.2.2. Longevity
The largest specimen found in the eastern tropical Atlantic has a fork length of 100 cm (Diouf, 1980). Postel (1955) estimates that fish over 85 cm in the zone are more than 4 years old. In the absence of precise studies on the age of S. tritor in the east Atlantic and taking into account the conclusions above and maximum size observed, Spanish mackerel seem to have a longevity of at least 5 years.
Spanish mackerel caught in Senegal are grouped in schools often associated with other species; in the warm season, they are caught at the same time as spotted tunny, but also with mackerels and horse mackerels which are theri prey. Off Mauritania, the species is associated with the plain bonito (Orcynopsis unicolor). No study on school size and the determinants of school formation has been done in the study zone.
S. tritor feeds essentially on clupeids (sardinellas), mullets (Mugil sp.), carangids and ammodytids (Postel, 1955). Fagade and Olaniyan (1974) note that the species feeds abundantly on Ethmalosa fimbriata in the Lagos Lagoon.
No information is available for the zone but large pelagic species and sharks would be predators of S. tritor.
Postel (1955) found on 286 Spanish mackerel caught off Dakar, plerocercus larvae Callitetrahyncus gracilis (Rudolphi) localised in the general cavity of individuals examined.
In this chapter, species for which very little information is available in the study zone are combined. The results presented are essentially preliminary, but constitute references for those interested in the subjects discussed.
Reproduction: In Senegal spawning takes place starting in May (Frade and Postel, 1954; Postel 1956), near the coasts. The fecundity is around 600,000 eggs for a female of 6 kg. (Postel, 1956). Spawning is fractional.
Growth: No data, but Postel's (1956) observations seem to show a difference in growth between males and females.
Longevity: No data, but the largest individual measured at Dakar is 107 cm (FL) for a weight of 12.4 kg (Postel, 1956); it may reach 130 cm (Seret and Opic, 1981).
Sex-ratio: Postel (1956) from 189 individuals examined has shown that the sex-ratio is 1. Males have sizes that vary from 67 to 104 cm, females from 72 to 107 cm. Under 40 cm, all are immature.
Nutrition and feeding behavior: In 189 stomachs examined, Postel (1950) has shown that bonito feed on small coastal pelagics (anchovies, sardinellas, carangids …). Bonito feed on the surface, the peak of the first dorsal fin sticks out of the water like a shark fin.
Parasites: Bonito in Senegal is parasitized by nematode larvae, by copepods, and by trematodes localised in the body cavity, the liver and on the pinnules (Postel, 1956).
Reproduction: reproduction may occur in warm waters. It begins in May and extends to August (Frade and Postel, 1954). Marchal (1961) collected larvae in October in the Gulf of Guinea.
Nutrition and feeding behavior: Wahoo feeds principally on pelagic species.
In this section we will limit ourselves to giving the most common and most recent biometric relations concerning the principal tuna species approached in this synthesis. These relations are on one hand those that link size and weight of each species, and on the other hand, for yellowfin and bigeye, those that link predorsal length and size, as well as those linking the weight before and after evisceration of the two species.
Weight: total weight of entire fish
Eviscerated weight: weight of the fish measured after cleaning and removal of gills.
Fork length (FL): the vertically projected distance between the anterior extremity of the upper jaw and the posterior extremity of the shortest caudal ray, measured at the trough (fork) of the caudal fin.
Predorsal length (DL1): the rectilinear distance between the anterior extremity of the upper jaw and the anterior base of the first dorsal fin (figure 6.44).
- Yellowfin
This relation has been calculated by Caveriviere (1976) from data taken from frozen, refrigerated, or fresh yellowfin caught throughout the study zone. This author points out that he did not attempt to analyze the data according to the location of catch of the individuals or their mode of presrvation, and mentions that preliminary observations indicated that the variations due to these factors are negligible.
This relation is written as:
Figure 6.44 Methods of measurement of tunas: FL = fork length; LD1 predorsal length.
P = 2.1527 × 10-5×FL2.976 with: number of observations, n = 6487.
Size range of individuals measured: 32 to 172 cm (FL)
r = 0.99
P = total weight in kg
FL = fork length in cm
The length-weight key calculated from this relation is given in table 6.19.
- Bigeye
This relation has been calculated by Parks et al., (1982) from samples coming from all of the zone covered by this synthesis and catches by different fishing gear. Despite the analyses of covariance pursued and the demonstration of point differences, no variation as a function of location or time of catch of the samples has been demonstrated. The global relation (all data mixed) between length and weight is written as:
P = 2.396 × 10-5 × FL 2.9774 with n = 3186
Size range of individuals sampled: 37–210 cm (FL)
P = total weight in kg
FL = fork length in cm
The correspondence key between length and weight calculated from this relation is given in table 6.19.
Table 6.19 Table of correspondence between length (fork length, FL) and weight (W) of yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) in the Atlantic. This table was established from the relations calculated by Caverivière (1976) for yellowfin and by Parks, Cayré, Kume and Santos (1982) for bigeye.
| FL (cm) | WEIGHT | FL (cm) | WEIGHT | FL (cm) | WEIGHT | |||
| YELLOWFIN | BIGEYE | YELLOWFIN | BIGEYE | YELLOWFIN | BIGEYE | |||
| 30 | 0.54 | 0.60 | 68 | 6.1 | 6.8 | 136 | 48.1 | 53.9 |
| 31 | 0.59 | 0.67 | 70 | 6.7 | 7.5 | 138 | 50.3 | 56.3 |
| 32 | 0.65 | 0.73 | 72 | 7.3 | 8.1 | 140 | 52.5 | 58.8 |
| 33 | 0.71 | 0.80 | 74 | 7.9 | 8.8 | 142 | 54.7 | 61.3 |
| 34 | 0.78 | 0.87 | 76 | 8.5 | 9.5 | 144 | 57.1 | 63.9 |
| 35 | 0.85 | 0.85 | 78 | 9.2 | 10.3 | 146 | 59.4 | 66.6 |
| 36 | 0.92 | 1.0 | 80 | 9.9 | 11.1 | 148 | 61.9 | 69.4 |
| 37 | 1.0 | 1.1 | 82 | 10.7 | 12.0 | 150 | 64.4 | 72.2 |
| 38 | 1.1 | 1.2 | 84 | 11.5 | 12.8 | 152 | 67.0 | 75.1 |
| 39 | 1.2 | 1.3 | 86 | 12.3 | 13.8 | 154 | 69.7 | 78.1 |
| 40 | 1.3 | 1.4 | 88 | 13.2 | 14.8 | 156 | 72.4 | 81.2 |
| 41 | 1.4 | 1.5 | 90 | 14.1 | 15.8 | 158 | 75.2 | 84.3 |
| 42 | 1.5 | 1.6 | 92 | 15.0 | 16.8 | 160 | 78.1 | 87.5 |
| 43 | 1.6 | 1.7 | 94 | 16.0 | 18.0 | 162 | 81.0 | 90.8 |
| 44 | 1.7 | 1.9 | 96 | 17.1 | 19.1 | 164 | 84.0 | 94.2 |
| 45 | 1.8 | 2.0 | 98 | 18.1 | 20.3 | 166 | 87.1 | 97.6 |
| 46 | 1.9 | 2.1 | 100 | 19.3 | 21.6 | 168 | 90.3 | 101.2 |
| 47 | 2.0 | 2.3 | 102 | 20.4 | 22.9 | 170 | 93.5 | 104.8 |
| 48 | 2.2 | 2.4 | 104 | 21.7 | 24.3 | 172 | 96.8 | 108.5 |
| 49 | 2.3 | 2.6 | 106 | 22.9 | 25.7 | 174 | 100.2 | 112.3 |
| 50 | 2.4 | 2.7 | 108 | 24.2 | 27.2 | 176 | 103.7 | 116.2 |
| 51 | 2.6 | 2.9 | 110 | 25.6 | 28.7 | 178 | 107.2 | 120.2 |
| 52 | 2.8 | 3.1 | 112 | 27.0 | 30.3 | 180 | 110.8 | 124.3 |
| 53 | 2.9 | 3.3 | 114 | 28.5 | 31.9 | 182 | 114.5 | 128.4 |
| 54 | 3.1 | 3.4 | 116 | 30.0 | 33.6 | 184 | 118.3 | 132.7 |
| 55 | 3.3 | 3.6 | 118 | 31.5 | 35.3 | 186 | 122.2 | 137.0 |
| 56 | 3.4 | 3.8 | 120 | 33.2 | 37.2 | 188 | 126.1 | 141.4 |
| 57 | 3.6 | 4.0 | 122 | 34.8 | 39.0 | 190 | 130.2 | 146.0 |
| 58 | 3.8 | 4.3 | 124 | 36.6 | 41.0 | 192 | 134.3 | 150.6 |
| 59 | 4.0 | 4.5 | 126 | 38.3 | 43.0 | 194 | 138.5 | 155.3 |
| 60 | 4.2 | 4.7 | 128 | 40.2 | 45.0 | 196 | 142.8 | 160.1 |
| 62 | 4.6 | 5.2 | 130 | 42.1 | 47.2 | 198 | 147.2 | 165.0 |
| 64 | 5.1 | 5.7 | 132 | 44.0 | 49.3 | 200 | 151.7 | 170.0 |
| 66 | 5.6 | 6.3 | 134 | 46.1 | 51.6 | |||
For yellowfin and bigeye the measurement of predorsal length is often preferred to that of fork length as these two species can reach large sizes and the measurement of total length is difficult or imprecise as:
individuals are often deformed or damaged by freezing and the different handling to which they are subjected
large individuals are difficult to handle.
yellowfin and bigeye tails are sometimes cut to faciltate storage.
It is therefore very standard procedure to take predorsal length measurements, these are next converted to fork length with the help of the following relations:
- Yellowfin
The relation established by Caverivière (1976) from yellowfin caught in all of the zone covered by this synthesis:
FL = 1.9011 ×DL1.177 1 with n = 3139
Range of predorsal length (DL1) of observed individuals: 10–50 cm (DL1).
r = 0.99
DL1 = predorsal length in cm
FL = fork length in cm
The correspondence key calculated from this relation is given in table 6.20.
- Bigeye
The DL1 - FL relation was established by Champagnat and Pianet (1974), from samples of bigeye caught by surface fisheries (pole and line boats and purse seiners) in the region from Senegal to Angola:
predorsal length range (DL1) of observed individuals: 13–48 cm
r = 0.99
DL1 = predorsal length in cm
FL = fork length in cm
The correspondence table between predorsal length (DL1) and fork length (FL) calculated from this relation is given in table 6.20.
It is common in certain fisheries, notably in longline fisheries, to clean the fish and remove their gills before storage (freezing). When the boats return to unload their catch, the weight of these fish corresponds to eviscerated weight. It is therefore necessary, in order to harmonize the statistical catch data, to express these weights as live weight before evisceration. Relations between eviscerated weight (EW) and live weight (W) of eastern tropical Atlantic yellowfin and bigeye have been calculated by Woo Il Choo (1976) from fish caught in the Gulf of Guinea:
Table 6.20 Table of correspondence between predorsal length (LD1) and fork length (FL) for yellowfin and bigeye in the Atlantic. This table was established from the relations calculated by Caverivière (1976) for yellowfin and Champagnat and Pianet (1974) for bigeye.
| LD1 (cm) | FORK LENGTH (cm) | |
| YELLOWFIN | BIGEYE | |
| 10 | 28.6 | 35.4 |
| 11 | 32.0 | 37.7 |
| 12 | 35.4 | 40.0 |
| 13 | 38.9 | 42.5 |
| 14 | 42.5 | 45.0 |
| 15 | 46.1 | 47.5 |
| 16 | 49.7 | 50.2 |
| 17 | 53.4 | 52.9 |
| 18 | 57.1 | 55.7 |
| 19 | 60.8 | 58.5 |
| 20 | 64.6 | 61.5 |
| 21 | 68.4 | 64.5 |
| 22 | 72.3 | 67.5 |
| 23 | 76.2 | 70.7 |
| 24 | 80.1 | 73.9 |
| 25 | 84.0 | 77.2 |
| 26 | 88.0 | 80.5 |
| 27 | 92.0 | 84.0 |
| 28 | 96.0 | 87.5 |
| 29 | 100.1 | 91.0 |
| 30 | 104.1 | 94.7 |
| 31 | 108.2 | 98.4 |
| 32 | 112.3 | 102.2 |
| 33 | 116.5 | 106.0 |
| 34 | 120.7 | 110.0 |
| 35 | 124.8 | 114.0 |
| 36 | 129.1 | 118.1 |
| 37 | 133.3 | 122.2 |
| 38 | 137.5 | 126.4 |
| 39 | 141.8 | 130.7 |
| 40 | 146.1 | 135.1 |
| 41 | 150.4 | 139.5 |
| 42 | 154.7 | 144.0 |
| 43 | 159.1 | 148.6 |
| 44 | 163.4 | 153.2 |
| 45 | 167.8 | 157.9 |
| 46 | 172.2 | 162.7 |
| 47 | 176.6 | 167.6 |
| 48 | 181.1 | 172.5 |
| 49 | 185.5 | 177.5 |
| 50 | 190.0 | 182.6 |
| 51 | 194.5 | 187.7 |
| 52 | 198.9 | 193.0 |
| 53 | 203.5 | 198.3 |
| 54 | 208.0 | 203.6 |
| 55 | 212.5 | 209.1 |
Table 6.21 Table of correspondence between fork length and weight of skipjack (Katsuwonus pelamis) in the Atlantic. This table was calculated the using relation calculated by Cayré and Laloë (1986).
| FL (cm) | WEIGHT (kg) | FL (cm) | WEIGHT (kg) |
| 30 | 0.48 | 66 | 6.2 |
| 31 | 0.53 | 67 | 6.5 |
| 32 | 0.59 | 68 | 6.8 |
| 33 | 0.65 | 69 | 7.2 |
| 34 | 0.72 | 70 | 7.5 |
| 35 | 0.79 | 71 | 7.9 |
| 36 | 0.86 | 72 | 8.2 |
| 37 | 0.94 | 73 | 8.6 |
| 38 | 1.0 | 74 | 9.0 |
| 39 | 1.1 | 75 | 9.4 |
| 40 | 1.2 | 76 | 9.8 |
| 41 | 1.3 | 77 | 10.2 |
| 42 | 1.4 | 78 | 10.7 |
| 43 | 1.5 | 79 | 11.1 |
| 44 | 1.7 | 80 | 11.6 |
| 45 | 1.8 | 81 | 12.1 |
| 46 | 1.9 | 82 | 12.6 |
| 47 | 2.1 | 83 | 13.1 |
| 48 | 2.2 | 84 | 13.6 |
| 49 | 2.4 | 85 | 14.1 |
| 50 | 2.5 | 86 | 14.7 |
| 51 | 2.7 | 87 | 15.2 |
| 52 | 2.9 | 88 | 15.8 |
| 53 | 3.0 | 89 | 16.4 |
| 54 | 3.2 | 90 | 17.0 |
| 55 | 3.4 | 91 | 17.6 |
| 56 | 3.6 | 92 | 18.3 |
| 57 | 3.8 | 93 | 18.9 |
| 58 | 4.1 | 94 | 19.6 |
| 59 | 4.3 | 95 | 20.3 |
| 60 | 4.5 | 96 | 21.0 |
| 61 | 4.8 | 97 | 21.7 |
| 62 | 5.1 | 98 | 22.4 |
| 63 | 5.3 | 99 | 23.2 |
| 64 | 5.6 | 100 | 23.9 |
| 65 | 5.9 |
- Yellowfin
W = 1.0837 EW + 1.4827 with n = 79
Size range of individuals observed: 104–163 cm (FL), (W is 22 to 83 kg)
r = 0.99
W = total weight of individuals in kg
EW = weight of individuals after evisceration and removal of gills (in kg)
- Bigeye
W = 1.1097 EW + 1.0352 with n = 39
Size range of individuals observed: 86 – 179 cm (FL) (W from 14 to 123 kg)
r = 0.99
W = total weight in kg
EW = eviscerated weight, gills removed, in kg.
A correspondence table summary between live weight (W) and eviscerated weight (EW), calculated from these relations is given by Woo Il Choo (1976):
| Evicerated Weight (kg) | 10 | 30 | 50 | 70 | 90 | 110 | 120 | 150 | |
| Live Weight (kg) Yellowfin | 12.3 | 34.0 | 55.7 | 77.3 | 99.0 | 120.7 | 142.4 | 164.0 | |
| Bigeye | 12.1 | 34.3 | 56.5 | 78.7 | 100.9 | 123.1 | 145.3 | 167.5 | |
In order to convert all eviscerated weights to live weights corresponding to the catch of several fish where individual weights are not known, the following rates (Woo Il Choo, 1976) can be used:
Yellowfin: W = 1.128 EW
Big eye: W = 1.130EW
with W = weight of entire individuals in kg
EW = weight of eviscerated individuals without gills in kg
This relation has been calculated by Cayre and Laloe from a very large sample of individuals (n = 14,140) coming from different zones of the east and west Atlantic largely including all of the zone covered by this synthesis. From various analyses and comparisons made by Cayre and Laloe, it is concluded that there is no difference in length-weight relation between the sexes (with exception of immature individuals); on the other hand if differences between zones have been demonstrated they are difficult to interpret, which has lead authors to adopt a single length-weight relation for all Atlantic skipjack. This relation is written as:
P = 7.480 × 10-6×FL3.2526 with n = 14,140
Size range of individuals sampled: 32 – 78 cm (FL)
r = 0.98
W = total weight of entire fish in kg
FL = fork length in cm
The correspondence table between length and weight of skipjack calculated from this relation is given in table 6.21.
This relation has been calculated by Diouf (1980) from samples coming essentially from the Senegalese region (13° N to 16° N):
W = 1.377 × 10-5×FL 3.035 with n = 1808
Size range of individuals sampled: 20 – 90 cm (FL)
r = 0.99
W = weight in kg
FL = fork length in cm
The correspondence table (length-weight) calculated from this relation is given in table 6.22.
The only available relation is the one calculated by Lenarz (1974) from a sample containing a mixture of Auxis thazard and Auxis rochei:
W = 2.80 × 10-7×FL 4.13514 with n = 50
Size range of individuals sampled: 30 – 45 cm (FL)
W = total weight in kg
FL = fork length in cm
The correspondence table (length-weight) calculated from this relation is given in table 6.22.
This relation has been calculated for this synthesis with data collected by Diouf (1980) from samples coming essentially from the Senegalese zone (13°N to 16°N):
W = 9.337 × 10-6×FL 3.103 with n = 372
Size range of individuals sampled: 19 – 64 cm (FL)
r = 0.98
W = total weight in kg
FL = fork length in cm
The correspondence table (length-weight) calculated from this relation is given in table 6.22.
This relation has been calculated for this work from data collected by Diouf (1980) on samples coming from the Senegalese region (13°N - 16°N):
W = 1.170 × 10-5×FL 2.926 with n = 615
Size range of individuals observed: 6 – 79 cm (FL)
r = 0.99
W = total weight in kg
FL = fork length in cm
The correspondence table (length-weight) calculated from this relation is given in table 6.22.
Table 6.22 Table of correspondence between fork length and weight of 5 species of small tunas; the relations used to calculate this table were extracted from: Diouf (1980) for spotted tunny (Euthynnus alletteratus), from Lenarz (1974) for frigate tuna (Auxis thazard); the other relations are results of original calculations made for this paper.
| FL (cm) | WEIGHT (KG) | ||||
| TUNNY | AUXIDS | ATLANTIC BONITO | SPANISH MACKEREL | PLAIN BONITO | |
| 20 | 0.12 | 0.07 | 0.10 | 0.09 | 0.17 |
| 21 | 0.14 | 0.08 | 0.12 | 0.11 | 0.20 |
| 22 | 0.16 | 0.10 | 0.14 | 0.12 | 0.23 |
| 23 | 0.19 | 0.12 | 0.16 | 0.14 | 0.26 |
| 24 | 0.21 | 0.14 | 0.18 | 0.16 | 0.29 |
| 25 | 0.24 | 0.17 | 0.20 | 0.18 | 0.33 |
| 26 | 0.27 | 0.20 | 0.23 | 0.20 | 0.36 |
| 27 | 0.30 | 0.23 | 0.26 | 0.22 | 0.40 |
| 28 | 0.34 | 0.27 | 0.29 | 0.25 | 0.45 |
| 29 | 0.38 | 0.31 | 0.32 | 0.28 | 0.49 |
| 30 | 0.42 | 0.36 | 0.36 | 0.31 | 0.54 |
| 31 | 0.46 | 0.41 | 0.40 | 0.34 | 0.59 |
| 32 | 0.51 | 0.47 | 0.44 | 0.37 | 0.65 |
| 33 | 0.56 | 0.53 | 0.48 | 0.41 | 0.71 |
| 34 | 0.61 | 0.60 | 0.53 | 0.45 | 0.77 |
| 35 | 0.67 | 0.68 | 0.58 | 0.49 | 0.83 |
| 36 | 0.73 | 0.76 | 0.63 | 0.53 | 0.90 |
| 37 | 0.79 | 0.86 | 0.69 | 0.58 | 0.97 |
| 38 | 0.86 | 0.96 | 0.75 | 0.62 | 1.0 |
| 39 | 0.93 | 1.1 | 0.81 | 0.68 | 1.1 |
| 40 | 1.00 | 1.2 | 0.87 | 0.73 | 1.2 |
| 41 | 1.1 | 1.3 | 0.94 | 0.78 | 1.3 |
| 42 | 1.2 | 1.4 | 1.0 | 0.84 | 1.4 |
| 43 | 1.2 | 1.6 | 1.1 | 0.90 | 1.5 |
| 44 | 1.3 | 1.8 | 1.2 | 0.97 | 1.6 |
| 45 | 1.4 | 1.9 | 1.3 | 1.0 | 1.7 |
| 46 | 1.5 | 2.1 | 1.3 | 1.1 | 1.8 |
| 47 | 1.6 | 2.3 | 1.4 | 1.2 | 1.9 |
| 48 | 1.7 | 2.5 | 1.5 | 1.3 | 2.0 |
| 49 | 1.9 | 2.7 | 1.6 | 1.3 | 2.1 |
| 50 | 2.0 | 3.0 | 1.7 | 1.4 | 2.2 |
| 51 | 2.1 | 3.2 | 1.9 | 1.5 | 2.4 |
| 52 | 2.2 | 3.5 | 2.0 | 1.6 | 2.5 |
| 53 | 2.4 | 3.8 | 2.1 | 1.7 | 2.6 |
| 54 | 2.5 | 4.1 | 2.2 | 1.8 | 2.8 |
| 55 | 2.6 | 4.4 | 2.3 | 1.9 | 2.9 |
| 56 | 2.8 | 4.7 | 2.5 | 2.0 | 3.1 |
| 57 | 2.9 | 5.1 | 2.6 | 2.1 | 3.2 |
| 58 | 3.1 | 5.5 | 2.8 | 2.2 | 3.4 |
| 59 | 3.3 | 5.9 | 2.9 | 2.3 | 3.6 |
| 60 | 3.4 | 6.3 | 3.1 | 2.5 | 3.7 |
| 61 | 3.6 | 6.8 | 3.2 | 2.6 | 3.9 |
| 62 | 3.8 | 7.2 | 3.4 | 2.7 | 4.1 |
| 63 | 4.0 | 7.7 | 3.6 | 2.8 | 4.3 |
| 64 | 4.2 | 8.2 | 3.8 | 3.0 | 4.5 |
| 65 | 4.4 | 8.8 | 3.9 | 3.1 | 4.7 |
| 66 | 4.6 | 9.4 | 4.1 | 3.3 | 4.9 |
| 67 | 4.8 | 10.0 | 4.3 | 3.4 | 5.1 |
| 68 | 5.0 | 10.6 | 4.5 | 3.6 | 5.3 |
| 69 | 5.2 | 11.2 | 4.7 | 3.7 | 5.5 |
| 70 | 5.5 | 11.9 | 5.0 | 3.9 | 5.7 |
| 71 | 5.7 | - | - | 4.1 | 6.0 |
| 72 | 6.0 | - | - | 4.2 | 6.2 |
| 73 | 6.2 | - | - | 4.4 | 6.5 |
| 74 | 6.5 | - | - | 4.6 | 6.7 |
| 75 | 6.8 | - | - | 4.8 | 7.0 |
| 76 | 7.0 | - | - | 5.0 | 7.2 |
| 77 | 7.3 | - | - | 5.2 | 7.5 |
| 78 | 7.6 | - | - | 5.4 | 7.8 |
| 79 | 7.9 | - | - | 5.6 | 8.1 |
| 80 | 8.2 | - | - | 5.8 | 8.3 |
| 81 | 8.5 | - | - | 6.0 | 8.6 |
| 82 | 8.9 | - | - | 6.2 | 8.9 |
| 83 | 9.2 | - | - | 6.5 | 9.2 |
| 84 | 9.5 | - | - | 6.7 | 9.6 |
| 85 | 9.9 | - | - | 7.0 | 9.9 |
| 86 | 10.2 | - | - | 7.2 | 10.2 |
| 87 | 10.6 | - | - | 7.5 | 10.5 |
| 88 | 11.0 | - | - | 7.7 | 10.9 |
| 89 | 11.4 | - | - | 8.0 | 11.2 |
| 90 | 11.8 | - | - | 8.2 | 11.6 |
| 91 | 12.2 | - | - | 8.5 | 12.0 |
| 92 | 12.6 | - | - | 8.8 | 12.3 |
| 93 | 13.0 | - | - | 9.1 | 12.7 |
| 94 | 13.4 | - | - | 9.4 | 13.1 |
| 95 | 13.8 | - | - | 9.7 | 13.5 |
| 96 | 14.3 | - | - | 10.0 | 13.9 |
| 97 | 14.7 | - | - | 10.3 | 14.3 |
| 98 | 15.2 | - | - | 10.6 | 14.7 |
| 99 | 15.7 | - | - | 11.0 | 15.1 |
| 100 | 16.2 | - | - | 11.3 | 15.5 |
This relation has been calculated for this synthesis from data published by Postel (1956); the individuals that were used to establish this relation come essentially from the Senegal Guinea region and the Islands of Cape Verde (10° N – 18° N, 24° W - 16° W):
W = 4.0978 × 10-5×FL 2.795 with n = 189
Size range of individuals observed: 29–107 cm (FL)
r = 0.99
W = weight in kg
The correspondence table (length-weight) calculated from this relation is given in table 6.22.
APPENDIX 1 (CHAPTER 6)
MACROSCOPIC STAGES OF MATURITY
YELLOWFIN
(after Albaret, 1977)
Stage I.1 (Immature sex indeterminate): Gonads are reduced to a thin white or pink opalescent string several millimeters in size.
Stage I.2 (Immature sex determined): Males: gonads somewhat more developed, triangular or crescent shaped in section, whitish. Females: Ovaries pinkish white, round or oval in section. Albaret emphasizes that “at these two stages, whatever the sex, the gonads are firm and the superficial vascularization is not apparent”
Stage II (beginning of maturation): In females, the ovary is enlarged (20 to 30 cm in length), color wine pink to pale yellow, consistency soft to flexible but fairly firm, vascularization lightly developed
Stage III (maturation): Ovaries well developed, color yellow-orange, consistency soft. Vascularization quite extensive, ovocytes visible after cutting open the ovary.
Stage IV.1 (advanced maturation, prespawning): Ovaries occupy nearly all of the abdominal cavity, highly vascularized, color bright yellow-orange to orange-red, less soft than stage III; ovocytes are large and easily visible through the ovarian wall. In males, testes are very large and white, sperm runs at the slightest pressure on the gonads. Stage IV.2 (spawning); Stage very transient with characteristics similar to stage IV.1. A pressure on the ovaries or on the abdomen causes the expulsion of eggs.
Stage V (post-spawning): The yellow-orange or wine red ovary is soft or even flacid.
Stage VI (seasonal sexual resting): Ovaries reduced in size, flacid and soft, pale yellow-orange or still wine red.
SKIPJACK
(after Cayré, 1981; Cayré and Farrugio, 1986)
Stage 0: Immature - Gonads appear in the form of thin bands; sex is not identifiable with the naked eye.
Stage I: Sex identifiable despite the gonads being still very thin. Females: Gonads pale pink, translucent, elongated and subcylindrical in form. Males: Gonads very thin and flat in the form of a band, the testicular artery is nevertheless easily visible in the medial region.
Stage II:
Females: This stage include the very beginning of maturation and also the sexual resting stage. Gonads
are still of subcylindrical form and beige to pink in color. A light vascularization begins to be visible
at their surface. Ovocytes not visible through the ovary wall.
Males: The testicular artery is easily visible, gonads are thicker (crescent shaped in section), and
whitish in color.
Stage III:
Females: Ovocytes are visible through the ovarian wall. Gonads well developed, at this stage maturation
is well advanced; vascularization is extensive.
Males: Gonads well developed, whitish color, a light puncture in their thickest area, followed by pressure,
causes expulsion of some seminal fluid.
Stage IV:
Females: Last stage of maturity preceding spawning, even the spawning stage itself. Gonads have
their maximum size; ovocytes are very visible, translucent. Pressure on an ovary at this stage causes
expulsion of ovocytes from the ovary as occurs during spawning.
Males: Here also the gonads have attained their maximum size; red blotches perhaps visible at their
surface. A simple pressure causes seminal fluid to spurt out; this may occur by itself and can be
observed on fish prior to dissection.
Stage V:
Females: This stage follows spawning, gonads may have a variable aspect depending on whether spawning
has occurred recently (appearance of empty, highly vascularized, sacks), whether some time
has elapsed (appearance of stage III), or whether the fish has entered sexual resting (appearance of
stage II).
Males: Same remarks as for females; gonads are flacid and reddish, with a little unreleased seminal
fluid if spawning was very recent.
BIGEYE
(after Gaikov, 1983)
Stage I (juvenile): Gonads extremely thin in the form of bands. Sexes not determinable.
Stage I (immature): Gonads better developed but still flattened. Sex determinable by careful observation.
Stage II (beginning of maturation): Ovaries well developed, some ovocytes visible through ovarian wall. Testes of males triangular in section; no seminal fluid in sperm duct.
Stage III: (advanced maturation): Ovaries very developed, ovocytes clearly visible. Sperm runs if testes are punctured or pressed.
Stage IV (end of maturation, spawning): Ovaries have reached their maximum development; ovocytes easily detached from the follicles or present in the oviduct. Seminal fluid runs liberally from testes.
Stage V: (post-spawning): Ovaries contain residual ovocytes, wall still intact or in different stages of resorption. Testes are soft, streaked with blood, reddish or gray in color; sperm duct may still sometimes contain sperm.
