emporal and tidal rhythms shape courtship and agonistic calls in plainfin midshipman toadfish

In many species, acoustic communication is essential for successful reproduction, parental care, and predator defense. The plainfin midshipman, Porichthys notatus, is a soniferous toadfish that relies on acoustic communication, with nest-guarding males emitting long, tonal ‘hums’ to attract mates, and short ‘grunts’ and ‘growls’ to defend nests and offspring from competitors and predators in their intertidal breeding grounds. Although these three vocalizations are a critical part of this species’ repertoire, we still know relatively little about how these fish modulate their vocal communication in the complex acoustic environment of the marine intertidal zone. In this study, we recorded plainfin midshipman vocalizations at two sites on Vancouver Island, British Columbia, Canada, in 2018 and 2020 to better understand how season and abiotic conditions influence the occurrence of hums, growls and grunts. Hum presence at both locations peaked in June, increased at night compared to daytime, and positively correlated
with water depth (tidal height). Hums also fluctuated in accordance with the lunar cycle, with elevated call presence observed during the quarter moon and associated neap tide phases. Growls similarly varied with the lunar cycle, but less notably than hums while grunts did not clearly
covary with the lunar cycle. Growls and grunts both increased with water depth and were produced at similar rates both during the day and night. Our study demonstrates that plainfin midshipman adjust their acoustic behaviour to match natural environmental cycles, and that the lunar and tidal cycles are important factors affecting reproductive behaviour in this vocal intertidal fish.