The influence of diel cycle, tidal direction and trawl alignment on beam trawl catches in an equatorial estuary

Abstract

SynopsisUsing a 3 m beam trawl, catch variation in the fish and prawn assemblage of the Labu estuary, Papua New Guinea was investigated during July and December 1981 and September 1984. About six times more organisms, three and a half times the biomass and twice as many species were caught per trawl at night than during the day. The greatest number of species, individuals and biomass were caught just after dusk. With the exception of Secutor ruconius, there was no significant difference in the catches trawled at ebbing and flooding tides. Over twice as many individuals of S. ruconius were caught during ebbing tides. Alignment of trawl direction in relation to the tidal current did not have a significant effect on the fish catch, but affected the prawn (Metapenaeus demani) catch. It is postulated that most species are not carried to and fro by tidal currents, but maintain their position in the estuary with respect to the substratum. Only prawns appeared to be carried by the currents. This study indicates that the most representative trawl results in terms of species diversity and abundance in shallow estuaries may be obtained at night and, that in estuaries with a small tidal range, tidal direction and velocity have 'little influence on catch. It also indicates that analyses of demersal nekton assemblages from daytime only estuarine trawl surveys must be approached with caution.

Diel variation of fish community in sandy beaches of southeastern Brazil

“…Behavioral studies show that many fishes are primarily active at night, searching for shelter during the day in inaccessible places to the net or in other protection areas. These fishes are rarely caught in diurnal samplings (QUINN;KOJIS, 1987). In the present study the major fish families presented different behavior in relation to the photoperiod.…”

Indo-Pacific seagrass beds and mangroves contribute to fish density and diversity on adjacent coral reefs

“…Since juvenile fish densities of all species groups whose juveniles were found in these areas were highest in the seagrass habitats, it is likely that seagrass habitats function as the most important juvenile habitats in areas outside the reef. In contrast to the high densities in seagrass habitats, the low fish densities and species richness in mangroves quantitatively support the suggestion that mangroves in the Indo-Pacific region are hardly used as a habitat by reef fish (Quinn & Kojis 1987, Robertson & Duke 1987, Thollot & Kulbicki 1988, Kimani et al 1996, Laroche et al 1997, Huxham et al 2004. A study in the Caribbean that used an approach comparable to that of the present study indicated that 30 of the 85 selected coral reef species used seagrass beds and mangroves as an important juvenile habitat (Nagelkerken et al 2000a).…”

“…Mar Ecol Prog Ser 302: [63][64][65][66][67][68][69][70][71][72][73][74][75][76] 2005 relatively minor, and have concluded that there is less interaction between mangroves and other coastal habitats than in the Caribbean (Quinn & Kojis 1987, Robertson & Duke 1987, Thollot & Kulbicki 1988, Kimani et al 1996, Laroche et al 1997, Huxham et al 2004). Other studies, however, did report the presence of juvenile coral reef fish in mangrove areas (Lal et al 1984, Little et al 1988, Robertson & Duke 1990, Wakwabi & Mees 1999, de Boer et al 2001.…”

Temporal variations of fish assemblage in the surf zone of the Nakdong River Estuary, southeastern Korea

“…Gibson et al (1996) recorded the highest abundance of such fish at night, indicating an onshore migration at dusk followed by an offshore migration at dawn, which may have been determined by their feeding activity and predator avoidance. Quinn and Kojis (1987) found more species, individuals, and biomass immediately after dusk, probably due to changes in illumination, gear efficiency, and/or the behavior of the animals. Despite the diel changes in the occurrence of some species in the Nakdong River Estuary, no strong evidence for the existence of distinct day and/or night communities was identified.…”