Sampling larval fishes with a nightlight lift-net in tropical inshore waters

Abstract

The applicability of a nightlight lift-net for sampling ichthyoplankton assemblages was evaluated in inshore habitats off southwestern Puerto Rico. The effects of lunar periodicity, habitat, light duration, and gear type (nightlight vs. plankton tow) were investigated. Overall, 36 piscine taxa were collected with the nightlight lift-net from inshore habitats (i.e. coral reef, mangroves, seagrass bed, sand flat). Larval fishes (80.6%), particularly clupeids ( Jenkinsia spp. and Harengula spp.), were the predominant developmental stage collected. Juvenile and adult fishes accounted for 14.7% and 4.7% of the catch, respectively. Nightlight collections showed marked patterns in larval fish abundance during different lunar phases with peak catchability occurring during the new moon phase. New moon samples accounted for 65.7% of all larvae collected during the complete lunar cycle. Significant lunar effects were observed in coral reef, seagrass bed, and sand flat habitats. No lunar related trends were observed in mangrove cay or nearshore mangrove habitats. Spatial patterns in nightlight catches were present with many taxa showing significant differences in abundance among habitats sampled. During lunar periodicity trials, catches were highest in the seagrass bed and coral reef habitats. Taxonomic diversity was greatest in seagrass bed and coral reef habitats with 16 and 11 taxa, respectively. Low abundance and taxonomic diversity characterized mangrove cay and nearshore mangrove habitats; however, increases in taxonomic diversity were observed during a fall survey of nearshore mangrove habitats. Light duration experiments indicated that larval abundance increased with increasing sampling duration and maximum catch per unit time was obtained at 10 min. Longer and shorter durations resulted in lower catch per unit effort and greater coefficients of variation. Trends in species composition and development stage were detected among nightlight lift-net and plankton net-tow methods.