Composition and structure of the mangrove fish and crustacean communities of Vanga Bay, Kenya

Caroline Wanjiru,Mark Huxham,Sonja Rueckert

doi:10.4314/wiojms.v20i2.3

Abstract

Mangroves support coastal fisheries, particularly by providing nurseries for juvenile fish. However, much remains unknown about the fish and crustacean communities in mangroves and about the lifecycles and behaviours of individual species. This study is the first to describe the fish and crustacean communities in the Vanga mangrove ecosystem, the largest mangrove forest and the most important marine fisheries landing site in southern Kenya. Using fyke nets, 14 mangrove creek sites were sampled once every 3 months during spring tides, between September 2015 and September 2017. The sampling period covered the north east (NEM) and south east (SEM) monsoon seasons. A total of 1,879 fishes and 1,132 crustaceans were caught, represented by 59 and 16 species, respectively. Over 95 % of the fishes caught were juveniles with 50 % of both fish and crustacean species being of commercial importance. About 70 % of the catch was dominated by only 6 fish species with Yarica hyalosoma and Acropoma japonicum contributing 44 % of the total abundance. Penaeus semisulcatus and Penaeus indicus dominated the crustaceans. Fish abundances differed significantly between seasons, with the SEM catches almost three times higher than those in the NEM, while crustaceans displayed no clear seasonality. The study documents for the first time the fish and crustacean communities in Vanga mangroves and confirms their importance as juvenile habitat for commercial species. The importance of mangrove and near mangrove habitat as nursery habitat for both fish and crustaceans emphasizes the need for conservation particularly of seaward edges

Highlights

Estuarine habitats are often important nursery areas for juvenile fishes and crustaceans (Laegdsgaard and Johnson, 1995; Rozas and Minello, 1997; Sheridan and Hays, 2003; Barbier, 2011; Lefcheck et al, 2019)
Nursery habitats are defined as areas that contribute disproportionately to adult populations of fish, with juveniles occurring in high densities, or achieving better growth or survival, or all of these combined (Beck et al, 2001)
The scarcity of permanent residents in intertidal mangrove habitats means that fish within commonly found families such as Lethrinidae, Lutjanidae and Monodactylidae (Kimani et al, 1996; Wainaina et al, 2013), which may be heavily reliant on mangroves at a given site, must utilise other habitats as well

Summary

Introduction

Estuarine habitats are often important nursery areas for juvenile fishes and crustaceans (Laegdsgaard and Johnson, 1995; Rozas and Minello, 1997; Sheridan and Hays, 2003; Barbier, 2011; Lefcheck et al, 2019). Nursery habitats are defined as areas that contribute disproportionately to adult populations of fish, with juveniles occurring in high densities, or achieving better growth or survival, or all of these combined (Beck et al, 2001). Gajdzik et al, 2014) These studies and others give evidence that mangroves can provide shelter and food for juvenile fish, but it is still challenging to prove that these juveniles successfully move from mangrove nurseries to adult habitats (Beck et al, 2001; Gillanders et al, 2003). The scarcity of permanent residents in intertidal mangrove habitats means that fish within commonly found families such as Lethrinidae, Lutjanidae and Monodactylidae (Kimani et al, 1996; Wainaina et al, 2013), which may be heavily reliant on mangroves at a given site, must utilise other habitats as well.

Results

Discussion

Conclusion