Abstract
AbstractAssessment of early life history characteristics requires effective sampling methods for larval fishes. Different gears are suitable for different habitats and frequently select different sizes or life history stages. In this study, two passive sampling methods were compared for use in collecting larval freshwater and estuarine fishes in two tropical streams. Drift nets and light traps were identified a priori as the most appropriate gears for sampling in these systems based on stream characteristics (including accessibility, size, and morphology). Catches were compared between sampling methods. Additionally, catches under different environmental conditions (flow, tide stage, and moon phase), during different sampling periods (time of day and week of summer), and at different depths were compared using mixed‐effects analysis of variance. A total of 2,156 fish were captured in 954 h of sampling. The significant (α < 0.05) explanatory variables for total larval catch were stream, sampling method, week of summer, time of day, and moon phase. Eleven families were represented in the samples, with the families Gobiidae (n = 948), Eleotridae (n = 391), and Syngnathidae (n = 276) comprising 94.9% of the identifiable larvae collected. The variables that explained both the Gobiidae and Syngnathidae catches were gear, week of summer, and time of day. The Syngnathidae catch was highest in drift nets, but the Gobiidae catch was highest in light traps. Nighttime light trap sampling appeared to be the best overall technique for larval collection in these systems. However, a combination of light traps and drift nets would reduce the biases associated with size and species selectivity found for individual gears, and this approach would be preferable for sampling small tropical streams.Received January 26, 2011; accepted October 5, 2011
Highlights
Different gears are suitable for different habitats and frequently select different sizes or life history stages (Leis 2000)
Total larval catch in drift nets was highest at night (t = 5.26, df = 206, P < 0.001), peak in catch occurring just before dawn (Figure 1)
Attracting larval fish with light is a well-known sampling method (Lucas and Baras 2001), and the findings from this study are consistent with similar studies
Summary
Passive sampling methods include drift sampling, activity traps, and light traps These passive gears are stationary, require less labor, and have lower associated operation costs (Kelso and Rutherford 1996). Spatial distributions of larvae can vary from the surface to the bottom of the water column, and larval abundance can vary with light, temperature, and flow (Kelso and Rutherford 1996) All of these factors, and more, can influence the choice of sampling season, time, and method.
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