Do Penaeid Shrimps have a Preference for Mangrove Habitats? Distribution Pattern Analysis on Inhaca Island, Mozambique

Scientific information on how penaeid shrimps are distributed within mangrove ecosystems is scarce, which presents an obstacle for fisheries as well as mangrove management. This study investigated the prime nursery microhabitats for the two major commercial species in Mozambique—Penaeus indicus and Metapenaeus monoceros. Stake net enclosures were used to sample shrimps living among unvegetated shallows and mangroves at Inhaca Island, Mozambique, during three consecutive spring tide periods. Four microhabitats were sampled: (1) sand flat; (2) fringe Avicennia marina on sandy substrate; (3) fringe A. marina on muddy substrate; and (4) interior A. marina adjacent to the supratidal terrestrial margin. P. indicus had a significant preference for fringe mangroves over the adjacent sand flat (P<0·001 and P=0·05). Postlarval shrimps only occupied the sand flat, whereas the mangrove was utilized by postlarval, juvenile and sub-adult life stages. Within the fringe mangrove, there was no correlation between shrimp abundance and organic content of sediment (5·7–11·6 shrimps m 2). Shrimps utilized the most interior margin of the mangroves (0·35 shrimps m 2), although catch rates were significantly lower than in the mangrove fringe (P<0·001). M. monoceros was significantly (P<0·01), more abundant in the sand flat (0·44–2·1 shrimps m 2) than in the mangrove fringe (0·04–0·61 shrimps m 2), although this habitat preference was not evident for juvenile and sub-adult life stages. The results demonstrate the extensive use of mangrove habitats by penaeid shrimps. The confinement to mangroves for P. indicus, but not for M. monoceros, is discussed in the context of habitat characteristics and predation avoidance behaviour. Methodological considerations of the stake net technique are also outlined.