International Journal of
Fisheries and Aquaculture

  • Abbreviation: Int. J. Fish. Aquac.
  • Language: English
  • ISSN: 2006-9839
  • DOI: 10.5897/IJFA
  • Start Year: 2010
  • Published Articles: 223

Full Length Research Paper

Age, growth and mortality rates of round sardinella, Sardinella aurita (Valenciennes, 1810) from the Senegalese coasts (West Africa)

Alassane Sarr
  • Alassane Sarr
  • Institut Universitaire de Pêche et d’Aquaculture (IUPA), UCAD II Bâtiment Pédagogie/Rez-de-Chaussée Université Cheikh Anta Diop de Dakar (UCAD), Sénégal.
  • Google Scholar
Ismaïla Ndiaye
  • Ismaïla Ndiaye
  • Service Régional des Pêches de Kolda, Sénégal.
  • Google Scholar
Waly Ndiaye
  • Waly Ndiaye
  • Institut Universitaire de Pêche et d’Aquaculture (IUPA), UCAD II Bâtiment Pédagogie/Rez-de-Chaussée Université Cheikh Anta Diop de Dakar (UCAD), Sénégal.
  • Google Scholar
Alioune Faye
  • Alioune Faye
  • Institut Universitaire de Pêche et d’Aquaculture (IUPA), UCAD II Bâtiment Pédagogie/Rez-de-Chaussée Université Cheikh Anta Diop de Dakar (UCAD), Sénégal.
  • Google Scholar
Malick Diouf
  • Malick Diouf
  • Institut Universitaire de Pêche et d’Aquaculture (IUPA), UCAD II Bâtiment Pédagogie/Rez-de-Chaussée Université Cheikh Anta Diop de Dakar (UCAD), Sénégal.
  • Google Scholar


  •  Received: 14 November 2018
  •  Accepted: 23 January 2019
  •  Published: 28 February 2019

 ABSTRACT

Sardinella aurita is the main species exploited by small-scale fisheries in Senegal and represents an important source of low cost protein in the Senegalese market. The objective of this study was to determine the age, growth and mortality parameters of S. aurita obtained from the Senegalese coastal waters. Age, growth parameters and mortality rates of this species were estimated using FiSAT II (FAO–ICLARM Stock Assessment Tools) software. A total of 5104 specimens of S. aurita were collected monthly between March 2012 and February 2013 from commercial landings in three sites of Senegalese coasts (Joal, Mbour and Kayar). Mean growth parameters for the entire period were estimated as L∞= 32.82 cm, K= 1.10 year-1 and t0 = -0.14 year. Instantaneous total mortality (Z = 2.77 year-1) coefficients per year were estimated using catch curves and methods based on the mean length of the fish caught. Natural mortality (M = 1.49 year-1) was estimated using the Pauly’s empirical equation and fishing mortality (F = 1.28 year-1) by the difference between total and natural mortality values. The exploitation rate (E) of 0.46 indicated no over-fishing on this species.

Key words: Round sardinella, age, growth, mortality, Senegalese coast.

 


 INTRODUCTION

Senegal has one of the most productive fishery resources along the West African coast. The EEZ is famous being among the full of fish zones in West Africa.

Clupeiform fishes are important because of their high biomass and their role in marine ecosystems. Sardinella aurita (Valenciennes, 1810) was selected for the present study. It is a small pelagic fish that lives in tropical and subtropical  waters of  the  western  and  eastern  Atlantic Ocean, the Pacific Ocean, the Mediterranean and, occasionally, the Black Sea (Sabate et al., 2006). According to the Department of Maritime Fisheries the round sardinella, S. aurita dominates the fish captures with nearly 38% of the unloading in 2011. The round sardinella is a mid-sized pelagic fish that represents one of the most important commercial fishery resources in the Senegalese coasts.

This species is of paramount economic interest in the national economy. The exploitation of this stock generates employment, incomes, foreign currencies, and contributes to the population’s food safety. The round sardinella is a marine pelagic fish that is widely distributed throughout the tropical and subtropical seas of the world, including the entire Mediterranean and the Black Sea (Froese and Pauly, 2003). It is a key species inhabiting the ecosystem of the northwest African upwelling region (Bard and Koranteg, 1995). It is intensively exploited and crucial to the economies of the West African countries. Indeed, this fish is the primary species fished in Senegal, and the second in Mauritania, with total landings exceeding 500,000 tons per year (Corten et al., 2012; FAO, 2013). According to Fréon (1998), the Senegalese-Mauritanian stock which extends from Mauritania (26°N) to Guinea (10°N) is most important in West Africa. In Senegal, very few data exist on its biology in general and its growth in particular. Indeed, data related to the growth parameters of S. aurita in Senegal were obtained by Boely et al. (1982), Boely (1983), Camarena-Luhrs (1986) and Fréon (1998). The methods used to determine  the  growth  were  subjective (method of Petersen) or unsuited to the tropical medium. Thus, it seemed important to bring up to date the principal growth parameters of this species with the aim of improving comprehension of their biological cycles, and of contributing to the evaluation of stocks and their management.

Moreover, scientific studies on sardinella in the North East Atlantic are considered insufficient and a lack of biological monitoring for several years has been reported (CSRP, 2012). Therefore, it appears difficult to make a good stock assessment to estimate the recruitment and identify different segments of the exploited stock. All these lacks make it necessary to conduct additional research.

The present study aims to determine age, growth and mortality parameters of S. aurita obtained from the Senegalese coastal waters.

 


 MATERIALS AND METHODS

Study area

The study was carried out in Senegalese coasts. Fishes were collected from commercial landings in three sites of Senegalese coasts: Joal (14.10°N; 16.51°W); Mbour (14.24°N; 16.58°W) and Kayar (14.55°N; 17.07°W) (Figure 1). The hydrology of the Senegalese coast is characterized by seasonal upwelling. This phenomenon supports the phytoplankton development, which forms the base of the food chain.

 

 

Sampling strategy

A total of 5104specimens were collected from March 2012 to February 2013 by monthly random sampling of artisanal purse seine nets catches in three landing sites: Kayar, Mbour and Joal. The artisanal purse seine is an active net in which the fish is captured by surrounding.

For each sampled fish, the total weight (TW) was recorded to the nearest 0.1 g and the fork length (LF) was measured to the nearest cm. The length data were analyzed to study the age and the growth. The monthly length frequencies were grouped into classes of 1 cm interval and were laid out sequentially over one year to estimate the growth.

Age and growth parameters

To estimate the age and growth parameters from length frequency data, monthly length frequency distribution was constructed. The Data were analyzed using FiSAT II (FAO–ICLARM Stock Assessment Tools) software.

The routine incorporated in the FISAT II software (Gayanilo et al., 1994), assumes that a seasonally oscillating version of the von Bertalanffy equation is used to describe the growth in length of the fish studied; specifically, it uses Somers’ (1988) modification of the seasonal growth model of Pauly and Gaschiitz (1979):

Where, L, is the length at age t, L∞, the mean length of the fish would reach if they were to grow indefinitely, K is the von Bertalanffy  curvature  parameter,  to  the  theoretical  age  at which length is zero, where St = (CK/2π)sin2π(t-ts), St0 = (CK/2π)sin2π(t0-ts), and C and ts describe the amplitude and timing, respectively, of the seasonal growth oscillations. This equation reduces to the standard von Bertalanffy model, Lt = L∞ [1-e-k(t-t0)], when C=0. C can take values generally ranging from zero (in tropical fishes) to unity (in temperate fishes) (Gaschütz et al., 1980). The seasonal parameters (C) and (WP) were used for a better adjustment of the growth curves. C indicated the amplitude of oscillations of the growth speed and (WP) the year time during which the growth is minimal.

In the present study, C was fixed at 0.1 and WP at 0.15,and ts = WP-0.5.

The growth curves index of adjustment (Rn) identifies the growth curve which was adjusted best with the whole size frequencies data. Rn varied between 0 and 1 and its maximum value corresponds to the best combination between L∞ and K.

ELEFAN estimates only two of the three growth parameters (L and K). The   theoretical  age  at  birth (t0)  was calculated using the empirical formula:

The theoretical age at birth (t0) was calculated using the empirical formula:

The growth index performance (ɸ') of S. aurita was calculated from the equation:

Mortality rates

The annual instantaneous rate of mortality (Z) was estimated by the average of length-converted catch curve method as implemented in FiSAT II (Pauly and Munro, 1984). Natural mortality rate (M) was estimated using Pauly’s empirical relationship, with a mean surface temperature (T) of 25.5°C:

Where, M is the instantaneous natural mortality, L∞ is the asymptotic length, T is the mean surface temperature and K refers to the growth rate coefficient of the von Bertalanffy growth function.

The fishing mortality (F) was calculated as F =Z – M in order to estimate the exploitation rate (E) by the equation E =F/Z.

 

 

 


 RESULTS

Age and growth parameters

The average values of von Bertallanfy growth function plot and length frequency estimated the asymptotic length (L) value at 32.82 cm and the growth constant (K) at 1.10 year-1 (Figure 2). The t0 value calculated using Pauly’s formula was -0.14 year. The alignment of points on the straight line was quite satisfactory with a higher coefficient of correlation (0.99). Using the growth parameters (L, K and t0), the von Bertalanffy growth function for length at time (t) was expressed as (Figure 3):

 

 

Figure 4 shows the restructured length frequency with superimposed growth curves with bimodal population structure, indicating probably the existence of four cohorts within the population. On these graphs, the number of lines represents the cohorts.

 

 

The round sardinella growth was very fast at the first year, it reached 22 cm. At the second year the growth slowed down and at the end of the third year it reached its maximum size 31 cm with a longevity, which exceeded 5 years (Figure 5).

 

 

The growth performance index value (ɸ') was estimated at 3.01 for S. aurita in Senegalese waters.

The amplitude of oscillation (C) for the first troop was 0.1, the winter  point (WP) was 0.15 and the adjustment index (Rn) was 0.19 (Table 1). The largest class was 32.5 cm.

 

 

Mortality rates

The calculated mortalities from FiSAT II output of the length converted catch curve are shown Figure 2.The total mortality coefficient (Z) of round sardinella was relatively high estimated as 2.77 year-1 based on the average of length-converted catch curve method (Figure 2). The natural mortality (M) was calculated as 1.49 year-1 by using Pauly’s method. Then, the fishing mortality (F) was obtained as 1.28 year-1. The exploitation rate (E) was found to be 0.46.

 

 

 

 

 

 

 


 DISCUSSION

The length frequency analysis (LFA) was used in the present study to estimate age and growth of S. aurita. In the present investigation, the growth constant (K) was estimated at 1.10 year-1, the asymptotic length (L) as 32.82 cm (FL) and t0 value was -0.14 year. The LFA showed that species might live for 5 years of life, whereas the age below two years dominated the catches. The data presented here confirmed that S. aurita is a fast-growing species (K = 1.1; ɸ' =3.07).

Growth parameters obtained in this study were compared with those found in tropical Atlantic and in Mediterranean  (Table  2).  Pham  and    Szypula   (1973) found a high asymptotic length (34.6 cm) in Mauritania and a very low growth coefficient (0.33 year-1). Samba (2011) found in Senegal starting from otoliths a very high growth constant (K=1.7 year-1) and a very weak asymptotic length (L=26.7 cm). This is explained partly by a number of much reduced sample. The growth parameters reported in Mediterranean coast of Sinai by Salem et al. (2010) (L=25.83 cm, K=0.299 year-1 and t0 =-0.87 year) were lower than those obtained in this study. However, results of Boely et al. (1982) (L=30.63 cm; K=-1.2 year-1 and t0=0.062 year) corroborated those found in this study. Nabil et al. (2012) obtained L=28.37 cm, K=0.23 year-1 and t0=-0.98 year. In Mediterranean Sea, Bouaziz et al. (1998) obtained L=34.96 cm, K=0.236 year-1and t0=0.71 year in Algerian coast and Gaamour et al. (2001) obtained L=31.32 cm; K=0.24 year-1 and t0=0.87 year in Tunisian coast. Differences in results between authors can come from the number of examined individuals, of the interpretation of the scratches of growth or the size of the individuals considered. It is observed that the maximum size and the speed of sardinella growth in Senegal-Mauritania zone were higher than those of the other areas. That could be explained by an unfavorable environment and less food in other areas (Boely et al., 1982). S. aurita has a fast growth, the individuals reach 22 cm (FL) in one year, and three years a size close to the average maximum size of 31 cm. Longevity is relatively short, approximately 5 years. These results are confirmed by the studies carried out by Postel (1955), Rossignol (1955), Boely et al. (1982) and Fréon (1998),  which  estimate  longevity beyond 5 years. The value of the parameter C (0.62) found in this study answers the biological character of the species. Indeed, according to Boely (1983), the adult individuals migrate and meet in a range of temperature of relatively narrow water (15 and 20°C).

 

 

The index of growth performance (ɸ') is considered as a useful tool for comparing the growth curves of different populations of the same species and/or of different species belonging to the same family. In this study, the value of growth performance index was ɸ'=3.01. This growth index was largest than those obtained by Gaamour et al. (2001) in the Tunisian coast (ɸ' =2.27), by Salem et al. (2010) in the Mediterranean coast (ɸ'=2.27) and by Chesheva (1998) in the Mauritanian coast (ɸ'=2.66).The mean index of growth performance Mediterranean stocks was lower than for northwest African coast (Tsikliras et al., 2005). Differences in growth parameters may be due to genetic structure, temperature, food available and diseases (Tsikliras et al., 2005).

This study provides evidence of population parameters might be used significantly to evaluate the level of exploitation of round sardinella in Senegalese coast. In the present investigation suggested by length frequency distribution, the total mortality (Z), natural mortality (M) and fishing mortality (F) were estimated at 2.77 year-1, 1.49year-1and 1.28year-1respectively. The total mortality recorded was relatively high compared to those found in East Mediterranean Sea (North Sinai Coast) by Salem et al. (2010). He found a total mortality coefficient (Z=1.49 year-1),  a  natural  mortality  (M=0.73 year-1) and a fishing mortality (F=0.076 year-1).In this study, the natural mortality (M=1.49 year-1) was greater than the fishing mortality (F=1.28 year-1), contrary to estimations reported by Salem et al. (2010) from East Mediterranean Sea (M=0.73 year-1); F=0.76 year-1). This observation could be due to the fact that S. aurita stock in Senegalese coastal waters is more susceptible to natural mortality conditions than to fishing gears.

S. aurita is an important resource for Senegalese inhabitants and it is well distributed all along the coastal area. The abundance of round sardinella in Senegalese waters varies seasonally. In the present investigation, the management tools were identified as spawning season and exploitation rate. The present study showed that the current exploitation of round sardinella in Senegal is not being well exploited (E = 0.46). The following management plans were advised to be applied to obtain sustainability over time. The spawning peak, eggs, larva and feeding habitat should be monitored and protected. These concerned zones should be identified and the stock managed as these species highly migrate. It was suggested to develop a selectivity gear for round sardinella targeting the marketable or legal sizes rather than the small sizes. Finally,  management plans would help to improve exploitation and sustainability of round sardinella in Senegal in future.

 

 


 CONFLICT OF INTERESTS

The authors have not declared any conflict of interests.

 



 REFERENCES

Bard FX, Koranteg KA (1995). Dynamics and use of Sardinella resources from upwelling of Ghana and Ivory Coast. Eds. ORSTOM, Paris 438 p.

 

Boely T (1980). Biology of two species of Sardinella Sardinella aurita (Valenciennes, 1847) and Sardinella maderensis (Lowe 1841) from the Senegalese coast. Doctoral thesis of State, University of Paris VI: 286 p.

 

Boely T, Fréon P, Stequert B (1982). The growth of Sardinella aurita in Senegal. Tropical Oceanography 17(2):103-119.

 

Bouaziz A, Bennoui B, Brahmi B, Semroud R (2001). The estimation of the state's operating sardinella (Sardinella aurita Valenciennes, 1847) of the region center of the Algerian coast. Rapport International Commission for the Scientific Exploration of the Mediterranean Sea pp. 36-244.

 

Bouaziz A, Semroud R, Brahmi B, Cheniti S (1998). Estimation of the growth of Sardinella (Sardinella aurita Valenciennes, 1847) in the Algiers region by size frequency analysis. In: Lleonart J (Eds.). Dynamics of marine populations. Mediterranean Options Papers 35:43-49.

 

Camarena-Luhrs T (1986). The main coastal pelagic fish species in Senegal: biology and resource assessment. PhD Thesis, University of Western Brittany, Rennes 174 p.

 

Chesheva ZA (1998). The method for determining age and growth rate of gilt sardines Sardinella aurita in the Senegal-Mauritania population. Journal of Ichthyology 38:4-817.

 

Corten A, Mendy AN, Diop H (2012). The sardinella of Northwest Africa: fisheries, stock assessment and management. Dakar: Sub-Regional Fisheries Commission (SRFC).

 

CSRP (2012). Rapport de l'atelier sous-régional sur les lacunes dans les connaissances sur les sardinelles. Dakar, du 19 au 21 juin 2012, 45 p.

 

EL-Maghraby AM, Botros GA, Soliman IAM (1970). Age and growth on Sardinella maderensis Lowe and Sardinella aurita Cuv. and Val: from the. mediterranean sea at Alexandria (U.A.R.). Bulletin of the National Institute of Oceanography and Fisheries Cairo 1:47-82.

 

FAO (2013). Food and Agriculture Organization of the United Nations. Report of the FAO Working Group on the Assessment of Small Pelagic Fish off Northwest Africa. Casablanca. Morocco, 24-28 May 2013, Rome : FAO, Fisheries and Aquaculture.

 

Fréon P (1998). Responses and adaptations of West African clupeid stocks to the variability of the environment and the exploitation: Analysis and reflection starting from the example of Senegal. PhD thesis, University of Aix-Marseille, 287 p.

 

Froese R, Pauly D (2003). FishBase. World Wide Web electronic publication. Version 02/2014. 

 

Gaamour A, Missaoui H, Ben Abdallah L (2001). Biological parameter of round sardinella (Sardinella aurita, Valenciennes, 1847) in the region of Cap Bon, (Canal Siculo-tunisien). GFCM. 26-30 March 2001. Kavala, Greece. pp 26-30.

 

Ghéno Y (1975). New study on the determination of age and growth of Sardinella aurita Val. in the region of Pointe-Noire. ORSTOM notebooks 13(3):251-262.

 

Nabil FAEH, Attaia AO, Mohsen SH (2012). Stock Assessment and Potential management of Sardinella aurita Fisheries in the East Mediterranean sea (North Sinai coast). Egyptian Journal Aquatic Biology and Fisheries 16(2):121-132.
Crossref

 

Pauly D, Munro J (1984). Once More on the Comparison of Growth in Fish and Invertebrates. ICLARM Fishbyte 2(21).

 

Pauly D, Gaschiltz G (1979). A simple method for fitting oscillating length growth data, with a program for pocket calculators. ICES CM 1979/6:24, 26 p.

 

Pham T, Szypula J (1973). Biological characteristics of Gilt sardine Sardinella aurita (Cuv. et Val. 1847) from northwest African coast. Acta Ichthyolica et Piscatoria 3(1):19-37.
Crossref

 

Postel E (1955). Résumé des connaissances acquises sur les clupéidés de l'ouest africain. Rapport du Conseil d'Exploration de la Mer 137:14-17.

 

Rossignol M (1955). Premières observations sur la biologie des sardineIles dans la région de Pointe Noire (Sardinella eba Val., S. aurita Val.). Rapport du Conseil d'Exploration de la Mer 137:17-21.

 

Sabate A, Martin P, Lloret J (2006). Sea warming and fish distribution: the case of the small pelagic fish, Sardinella aurita, in the western Mediterranean. Global Change Biology 12(11):2209-2219.
Crossref

 

Salem M, EL-Aiatt AA, Ameran M (2010). Age, growth, mortality and Exploitation rates of round Sardinella (Sardinella aurita) from the east Mediterranean Sea (north Sinai coast). Research Journal Fisheries of Hydrobiology 5(1):32-38.

 

Samba O (2011). New evaluation of the biological characteristics of Sardinella aurita (Valenciennes, 1847) and Sardinella maderensis (Lowe, 1841). Memory DEA, University Cheikh Anta Diop of Dakar, Senegal.

 

Somers I (1988). On a seasonally oscillating growth function. Fishbyte 6(1):8-11.

 

Tsikliras AC, Koutrakis ET, Stergiou KI (2005). Age and growth of Sardinella (Sardinella aurita) of the northeastern Mediterranean. Scientia Marina 69(2):231-240.
Crossref

 




          */?>