Invertebrate drift and a survey of island wide water chemistry in Dominica

The Commonwealth of Dominica is located in the Lesser Antilles. Dominica remains one of the least developed islands in the Caribbean with 60% forest cover, is geothermally active, and has abundant rivers and streams. The objectives of this study were to obtain initial data on basic water chemistry (pH, conductivity, temperature, dissolved oxygen, turbidity) near the mouths of major rivers and quantify the timing of migratory drift of macroconsumers. In spite of varying levels of geothermal activity across the island, stream water chemistry did not vary much in the 37 rivers sampled. With regard to migratory drift, we measured the magnitude and timing of downstream drifting larval fishes and shrimps from 12:00h to 24:00h in the Layou River, approximately one mile upstream from the river mouth. Larval shrimps were most abundant in the drift. Shrimp, fish, and crab larvae all exhibited diel periodicity with peak abundance occurring between 18:00-20:00h. These findings contradict a previous study from Dominica but support findings from other Caribbean islands. Knowledge of the magnitude and timing of migratory drift can guide how and when managers of water resources extract water for human use, which can substantially mitigate some of the negative effects of water withdrawals.