Abstract
The Gorean snapper, Lutanus goreensis is an important component of artisanal fisheries and trawl landings in the Gulf of Guinea. Despite its economic importance, there is a dearth of information on size structure and life history strategies of the species. Therefore, the objectives of this study were to provide baseline data on the life stages, exploitation status and habitat use for the species in Nigeria. Monthly samples were obtained from artisanal and trawl catches in Five Cowrie Creek and Lagos coastal waters between December 2008 and December 2010, respectively. Length-frequency distributions of the fishes caught were analysed to provide preliminary information on mean and modal lengths at capture and life-history strategies based on habitat use and estuarine-dependency for L. goreensis. A total of 822 specimens of L. goreensis were collected from Five Cowrie Creek while 377 specimens were collected from Lagos coastal waters. Total length varied between 7.90-34.90 cm for creek samples and from 21.90-56.10 cm for marine samples. Length-frequency histograms showed polymodal size distributions in creek and marine samples. Length-frequency distributions of L. goreensis showed a high abundance ofjuveniles (<20 cm) and sub-adults (20-35 cm) which accounted for 84.1% and 68.4% of creek and marine samples examined, respectively. For the creek samples, fish in modal length class of 13.00-13.99 cm were the most exploited while in the marine samples, length classes of 29.00-30.99 cm and 31.00-32.99cm constituted the most frequently exploited fishes. Increase in total lengths from the creek (mean +/- SD; 16.19 +/- 3.73 cm) to the marine habitat samples (32.89 +/- 6.14 cm) indicated ontogenetic shift in habitat use. Occurrence of a predominant juvenile population in Five Cowrie Creek by L. goreensis suggests estuarine-dependency and is indicative of a temporary juvenile habitat or a migratory corridor. In conclusion, data from the presently reported study and previous studies demonstrated that juvenile L. goreensis displays estuarine dependency and habitat flexibility. Hence, this underscores the importance of preserving estuarine environments as essential fish habitats to prevent overfishing. The study also concludes that the species is vulnerable to recruitment overfishing in the marine environment especially as a consequence of shrimping. Consequently, it advocates for ban on all fishing activities during peak spawning periods in breeding grounds and shrimp ground assemblage.
Highlights
2003) common to 50cm but capable of attaining maximum total length of 80cm (Allen, 1985)
Exploitation status of the snapper species is suggested to be over-exploited in Nigerian coastal waters (Amiengheme, 1997, 2001), there is a dearth of information on the size structure of L. goreensis
Total lengths of creek samples ranged from 7.90cm to 34.70cm and body weight ranged from 9.51g to 695.60g whereas composite ranges for marine samples varied between 21.90cm and 56.10cm total length and from 156g to 2 975g body weight
Summary
2003) common to 50cm but capable of attaining maximum total length of 80cm (Allen, 1985). Population structure of fish depicted in length-frequency distribution provides useful information that can aid fisheries management. Spatial separation of size-classes of fish species suggests movement from one habitat to another with ontogeny (Cocheret de la Moriniere, Pollux, Nagelkerken, & van der Velde, 2003). An estuarinedependent species is defined as one in which estuaries, or similar habitats, are the principal environments for at least part of the life cycle and without which a viable population would cease to exist (Nagelkerken, & van der Velde, 2002; Able, 2005).The concept of estuarine dependence is often related to nurseries and it has so far been tested by comparing presence/absence of juvenile and adult fishes in estuaries versus offshore habitats (Cocheret de la Moriniere, Pollux, Nagelkerken, & van der Velde, 2002 ; Nagelkerken, & van der Velde, 2002). Available data from previous studies of Fakoya, Abass, Owodeinde, Lawson, and Ojo (2010); Orhibhabor and Ogbeibu (2010) in estuarine habitats consist of low sample sizes
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