Ripples in the pond: acoustic communication of Centrarchids in field and laboratory settings

Background/Question/Methods In marine systems, researchers have examined how “drumming” or “knocking” patterns influence reproductive behaviors in fish species and how fish temporally and spatially partition habitats. However, most of this research has been with marine or estuarine species, with relatively little work on freshwater species. Here we report on acoustic signatures and calling patterns of two freshwater fish species, bluegill (Lepomis machrochirus) and redear sunfish (Lepomis microlophus). What little work has been done on these species has only reported on calling during the breeding season. Here we report on nonbreeding calls and calling patterns. The diurnal call patterns for the bluegill and redear were recorded within isolated-species-ponds of The Cheraw Fish Hatchery in Cheraw, SC. A Wildlife Acoustics Song Meter SM3 equipped with a hydrophone was used for all recordings. Field recordings were done for one week in September, 2016 and one week in October, 2016. Hydrophones recorded 30 minutes of every hour for 7 days. Song Scope software was used to analyze the recordings. We also did a small pilot study where we put single bluegill or pairs of bluegill (males, females or one of each) in tanks for 30 minute trials to observe behavior and record calls.

Results/Conclusions In the field recordings, we found that calls are typically short; low frequency “grunts” under 1 KHz, in bursts of single, double, triple or multiple amplitudes. Both bluegill and redear sunfish showed two peaks in calling activity: morning (around 10:00 a.m.) and evening (around 6:00 p.m.), with redear calling significantly more in October than September (p < 0.001). In addition to field recordings, bluegill were recorded in the lab to confirm call types. Eight bluegill fish from the Cheraw Fish Hatchery were isolated and recorded during select 24-hour periods in a 50 gallon oval Rubbermaid cattle tank. These calls matched ones recorded in the field, confirming that we were correctly identifying calls. We got relatively few results in our small pilot study, but interestingly, the only time we recorded sound was when two females were in the same tank. We hope to build on this work in the future by breaking down calls by type and understanding the role of calls for both nonbreeding and breeding communication using field recordings, laboratory recordings and playback experiments.