The beach seine fishery at Anlo Beach in the Shama district of Ghana exploits several species of which the cassava croaker, Pseudotolithus senegalensis is the most important, economically. The close proximity of the stock to the River Pra estuary could be attributed to availability of its prey species, mainly fish and shrimps (Blay et al., 2006) in the nearshore waters. Furthermore, sciaenids are reported (Ssentongo and Ansa-Emmin, 1986) to commonly aggregate in coastal waters near estuaries. Information on the characteristics of the fisheries of croakers in other parts of West Africa is however scanty with only a brief mention of the existence of a small scale fishery of the species in Benin (Sossoukpe et al., 2013a).
The maximum observed length (Lmax) of 105.4 cm TL of the species from Anlo Beach was close to the maximum length (114 cm TL) reported in Fishbase (www.fishbase.org), but significantly longer than the maximum lengths of 47 cm TL to 66 cm TL found in the coastal waters of Côte d’Ivoire, Benin, Sierra Leone and Liberia (Sossoukpe et al., 2013a; Olapade and Tarawallie, 2014; Tia et al., 2017; Wehye et al., 2017). The length frequency data show the presence of an appreciable proportion of small fish (< 20 cm) in July-August, 2012, and the primary modal length of these samples increased progressively until January-March 2013.
Studies on the breeding periods of some populations of P. senegalensis in the Gulf of Guinea show that spawning occurs from March to June, and September to December (Anyanwu, 1990; Sossoukpe et al., 2013b; Olapade and Tarawallie, 2014; Sylla et al., 2016). Although the reproductive biology of the species was not investigated in the present study, the small fish encountered in the July-August 2012 samples may be juvenile recruits from the March-June spawning. It is however unclear whether the present population breeds in September-December as small fish were absent in the January, February and March samples. Specimens were not seen in catches from April to June, a situation that could be ascribed to migration of the fish into deeper waters.
Growth of the cassava croaker population in Ghana was isometric, similar to the populations in Benin (Sossoukpe et al., 2013a) and Côte d’Ivoire (Tia et al., 2017). The growth constant of the fish in the present study (K = 0.2 yr–1) was not remarkably different from values determined for the Benin (Sossoukpe et al., 2013a) and Liberia (Wehye, et al., 2017) populations which have K values of 0.24 yr−1 and 0.13 yr–1,respectively. These estimates were however slightly lower than the estimate (K = 0.4 yr−1) for the Côte d’Ivoire stock (Tia et al., 2017). Hence, in general growth of the species in the Gulf of Guinea is slow. The longer maximum theoretical length (L∞ = 110.3 cm TL) of the Ghana fish compared to specimens in Côte d’Ivoire (L∞ = 47.9 cm), Benin (L∞ = 51.4 cm) and Liberia (L∞ = 66.6 cm) might suggest exposure of the former to better environmental conditions for growth.
It would appear from the VBGF that the Anlo Beach fish would only attain the maximum theoretical length (L∞ = 110.3 cm) beyond 20 years of age. Individuals of the species growing to 100 cm have similarly been associated with long life spans up to 20 years (Nunoo and Nascimento, 2015). The slow growth rate of the croakers at Anlo Beach could also account for the longer period it takes to reach the maximum theoretical length, which suggests a K-selected life history (Pianka, 1970) for the population. Growth performance index of the Ghana stock (ɸˈ = 3.40) was also higher than the populations in Benin (ɸˈ = 2.75; Sossoukpe et al., 2013a), Côte d’Ivoire (ɸˈ = 2.97; Tia et al., 2017) and Liberia (ɸˈ = 2.76; Wehye et al., 2017) which may explain the larger maximum theoretical length in fish from Ghana.
Fishing mortality coefficient of the Anlo Beach stock (F = 0.26 yr–1) was lower than that of the populations in Liberia (0.56 yr–1, Wehye et al. (2017) and Benin (3.70 yr−1, Sossoukpe et al., 2013a) which might explain the lower exploitation ratio (E = 0.38) for the Ghana population compared to the Liberia (E = 0.60) and Benin (E = 0.84) stocks (ibid). Okyere (2015) estimated E as 0.42 for the large demersal fish community in the study area from ECOPATH with Ecosim analysis (Pauly et al., 2000), which supports the current low exploitation ratio of the P. senegalensis stock. This apparent low exploitation could be attributed to strict compliance of the local regulation whereby daily fishing is rotated among the thirty-one fishing companies which operate in the area.