ORIGINAL ARTICLE European Journal of Environment and Earth Sciences www.ej-geo.org Growth, Mortality and Exploitation Levels of Sphyraena sphyraena (Pisces: Sphyraenidae) and Apsilus fuscus (Pisces: Lutjanidae) in Ghanaian Waters Joseph Aggrey-Fynn and Divine Worlanyo Hotor ABSTRACT Sphyraena sphyraena (Linnaeus, 1758) and Apsilus fuscus (Valenciennes, 1830) are commercially important fish species in Ghana. The stocks are Published Online: February 5, 2021 exploited mainly by the artisanal and semi-industrial fisheries. Growth and ISSN: 2684-446X mortality rates, and exploitation levels of the two stocks in inshore waters of Ghana were assessed as a contribution to fill the knowledge gap on the DOI :10.24018/ejgeo.2021.2.1.108 species. Samples were obtained from three landing sites along the coast of Ghana from February to July, 2017. Length-frequency data were used to J. Aggrey-Fynn* estimate growth, mortality and exploitation ratios. The modal class for S. Department of Fisheries and Aquatic sphyraena was 37.0–39.9 cm total length (TL) and 34.0–35.9 cm TL for A. Sciences, University of Cape Coast, Cape fuscus. The length and weight relationships established that growth in S. Coast, Ghana. (e-mail: jaggrey-fynn@ ucc.edu.gh) sphyraena was negative allometric, whereas that of A. fuscus was isometric. D. W. Hotor The estimated growth parameters from the length frequency data fitted Department of Fisheries and Aquatic with the von Bertalanffy growth function were asymptotic length (L∞) of Sciences, University of Cape Coast, Cape 69.9 cm TL for S. sphyraena and 53.5 cm TL for A. fuscus. The growth Coast, Ghana. constant (K) was calculated as 1.64 yr-1 for S. sphyraena and 0.50 yr-1 for A. (e-mail: hworlanyohotor gmail.com) fuscus. The mean length-at-first capture (Lc) was found to be lower than the *Corresponding Author mean length at sexual maturity (Lm) for both species. The sex ratio showed a dominance of females over males in S. sphyraena, and 1:1 for A. fuscus. The total mortality rate (Z) for S. sphyraena was more than for A. fuscus. The estimated natural mortality (M) was 1.88 yr-1 for S. sphyraena and 0.74 yr-1 for A. fuscus whilst fishing mortality (F) rate was 3.04 yr-1 for S. sphyraena and 0.93 yr-1 for A. fuscus. The exploitation ratio showed that both fish stocks were exploited over the optimum levels. The estimated population parameters of the species obtained from the study, therefore, might be useful for the sustainable management of the stocks. Keywords: Artisanal fisheries, Fish stock assessment, Growth and mortality parameters, Length-frequency distribution. African nations [7]-[10]. The African forktail snapper is a I. INTRODUCTION demersal species which inhabits rocky bottoms [11], deep Pelagic species make up majority of fish catches that are coral and rock reefs [12]. They are mostly caught in the landed which is about 80 % of the total fish catch, whilst commercial octopus fishery [13]. demersal species constitute 20% of total fish catch in Ghana Growth and mortality parameters as the biological [1]. Among other fisheries resources that are commercially characteristics of the fish species are important for baseline important in Ghanaian waters are Sphyraenidae and information to understand the population dynamics of fish Lutjanidae for which Sphyraena sphyraena (European stocks that are exploited by fishery. In [14], the population barracuda) and Apsilus fuscus (African forktail snapper) dynamics of obtuse barracuda, Sphyraena obtusata, were respectively belong [2], [3]. The high commercial value of studied in south-west coast of India to determine biological these fishes has resulted in low fish densities in catches due parameters of the fishery resource. In spite of the to fishing pressure [2], with evidence in poor fish landings commercial importance of these fisheries resource in which suggests that the Maximum Sustainable Yield (MSY) Ghanaian waters, few reports on the occurrence in artisanal may have been surpassed [4]. and transshipment landings [8], [15], relative abundance Sphyraena sphyraena is a tropical and subtropical fish and food preferences [5] of barracuda are known. Again, the species mostly occur in the Atlantic, Pacific and Indian literature on growth, mortality and exploitation ratios of Oceans. In West Africa, the distribution of the species these species are not available from Ghanaian waters. extends from Morocco to Angola. The species is caught Hence, this study aims at determining the growth and amongst schools of commercially-important small pelagics mortality parameters, and exploitation pattern of S. [5], [6]. Apsilus fuscus is also distributed along West sphyraena and A. fuscus caught by traditional fisheries African coast, from Congo to Ghana; and it is exploited by along Ghanaian coast in the Gulf of Guinea. artisanal, recreational and industrial fisheries in many West DOI: http://dx.doi.org/10.24018/ejgeo.2021.2.1.108 Vol 2 | Issue 1 | February 2021 16 ORIGINAL ARTICLE European Journal of Environment and Earth Sciences www.ej-geo.org II. MATERIALS AND METHODS A Chi-square (χ2) test was undertaken to compare the male-female ratios per month with the hypothesized sex- A. Study Area ratio of 1:1. This study was conducted along the coast of Ghana, The estimates of growth parameters were obtained by specifically in Sekondi, Elmina, and Tema fish landing sites procedures of [20] as incorporated in FiSAT. And the total (Fig. 1). The Tema Fishing Harbour (5.6413° N, 0.0154° E) mortality (Z) parameters were estimated from procedures in the Greater Accra Region is the largest fishing harbour in outlined in [21], [22]. The natural mortality (M) was the country, followed by Albert Bosomtwi-Sam Fishing. estimated from the empirical formula as: Log (M) = - 0.0066 – 0.279log (L∞) + 0.6543 log (K) + 0.463 log (T) [23] where M is the natural mortality, K and L∞ are growth parameters of the von Bertallanfy growth function and T (°C) is the annual mean sea surface temperature of the study area. The level of exploitation (E) of the fish stocks were calculated from the equation: 퐹 퐸 = [24] 푍 Fig. 1. Map of study area showing sampling sites. where E is the exploitation ratio, F the fishing mortality [22] and Z the total mortality. Harbour (ABS) in Sekondi (04°55′00ʺN, 01°46′00ʺW) in the Western Region, and the Elmina fish landing site (5°5′0ʺN, 1°21′0ʺW) in the Central Region. These landing III. RESULTS sites were chosen because of their major contribution to A total of 420 specimens of S. sphyraena were examined. fisheries in Ghana. Traditional canoes of all sizes and The length measurements were grouped in a pooled sample inshore trawlers in all the three landing sites exploit into 3 cm class intervals and size groups ranging from 10.0– commercially important fishes including S. sphyraena and 12.9 cm to 64.0–66.9 cm TL (Fig. 2 a). The pooled samples A. fuscus. Purse seine, hook and line and bottom trawl gears showed a unimodal length-frequency distribution with a are employed in the exploitation of the fisheries resources modal length class of 37.0–39.9 cm TL. [16]. Fig. 2(b) shows a length-frequency distribution of overall B. Methods specimens of 423 of A. fuscus that were obtained. The lengthWorking classesTitle: ranged from 20.0–21.9 cm to 50.0–51.9 cm Fish samples were collected monthly from February 2017 Growth, Mortality and Exploitation of Sphyraena sphyraena (Pisces: Sphyraenidae) and to July 2017. The sampling sites were visited once every TL.Apsil usThe fuscu s pooled(Pisces: L utsamplesjanidae) in Gshowedhanaian wa tears unimodal frequency distribution with a modal length of 34.0–35.9 cm TL. month where specimens of varied sizes were randomly RE-PLOTTED FIGURES obtained directly from the fishermen. Specimens were then (a) preserved on ice and transported to the laboratory. Fish 30.0 y c n = 420 identification was done using identification keys [11], [17]. n 25.0 e u q 20.0 e Total length (TL) were measured to the nearest 0.1 cm r F e 15.0 g using the fish measuring board, and the body weight of each a t n 10.0 e c specimen was weighed to the nearest 0.01 g using the r e 5.0 P Ohaus Ranger 7000 model electronic balance. Specimens 0.0 were dissected and the sex of each fish was identified by .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 66 0- 3- 6- 9- 2- 5- 8- 1- 4- 7- 0- 3- 6- 9- 2- 5- 8- 4- visual examination of gonads. 1 1 1 1 2 2 2 3 3 3 4 4 4 4 5 5 5 6 Total length, TL (cm) Total lengths were used to determine the length- frequency distributions; and the relationship between total (b) length and body weight was expressed by: 30.0 y c 25.0 n = 423 n e u 20.0 b q e BW = aTL [18], [19] r F 15.0 e g a t 10.0 n e c where BW (g) is fish body weight, TL (cm) the total length, r e 5.0 P ‘a’ intercept and ‘b’ the slope. The condition factor (K) of 0.0 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 the fish was determined from the relationship: 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 0- 2- 4- 6- 8- 0- 2- 4- 6- 8- 0- 2- 4- 6- 8- 0- 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 5 퐵푊 Total length, TL (cm) K = ×100 [18] 푇퐿ᵌ Fig.