Inmature icthyofauna from soft bottoms during the dry-rainy season transition in the Pacific coast of Colombia

Based on ichthyoplancton research along the southern Pacific coast of Colom bia, which revealed high concentrations of fish larvae in this area, a juve nil fish survey was conducted in shallow waters (<10 meter water depth) dur ing the transition period from dry to wet season (July 21 to July 31, 1994) . The twelve sampling stations, were distributed in front of the four main of this coastline, where the highest concentrations of juvenile fish were e xpected. At each sample station, three 15 min oblique hauls were conducted every 8 hours using a bottom trawl for juvenile fish of 4 mm mesh size; 53 species in 20 families were identified (21 not known as adults in the area) . They were distributed as follows: Sciaenids (11), Ariids (7), Pristigaste rids (6), Engraulids (6), Carangids (5), Clupeids (2), Soleids (2), Batrach oidids (2), Tetraodontids (2), Urolophids (I), Polynemids (I), Synodontids (1) and Taeniopedids (1). This ichthyofauna is common in open tropical estu aries. Abundances and biomass were 0.35 ind./m(3) and 1.61 g/m(3) respectiv ely, higher than in other tropical shallow water systems. The niches of the 25 species whose abundance (A) and biomass (B) contributed 97.5 % and 93.3 % respectively to the total catches were: (1) pelagic-neritic (53 % A, 34 % B); (2) demersal-pelagic (18 % A, 28 % B); (3) demersal (22 % A, 23 % B) and (4) benthic (8 % A, 15 % B). The Shannon-Weaver diversity index in the four subareas ranged from 0.89 to 1.1, within the range reported for other tropical American estuarine systems. An ordination analysis (non-metric Mul ti-Dimensional Scaling, MDS) of the data revealed significant differences i n the species composition between day and night and an important associatio n among some species. Station position, tides and environmental parameters did not markedly influence species composition. It is concluded that: (1) T he area surveyed represents an important nursery and growth habitat for juv enile fish of many species that are more common as adults over soft bottoms in deep waters of the continental shelf; (2) this shallow soft bottom fish community is clearly separated from those species inhabiting intertidal sa lt marshes, interior bays and mangrove areas; and (3) some of the fish spec ies commonly living in rocky and reef habitats in adult stages, spend their juvenile stage over shallow water soft bottoms. These results confirm a ra ther strong niche separation between juvenile and adults fish species stage s in tropical waters.