Fishing with sound: Insights into the plainfin midshipman's reproductive ecology from field acoustic playbacks.

The long-duration advertisement "hums" produced by type I male plainfin midshipman fish (Porichthys notatus) are tonal signals consisting of a fundamental frequency and multiple harmonics. Using acoustic playback of synthetic, hum-like stimuli under natural conditions, we found that the fundamental frequency is likely required for females' final entry into a type I male's nest, whereas higher harmonics may play a limited role. We found no evidence of phonotaxis in type I and type II males. Additionally, the observed decrease in body size of captured individuals over the breeding season suggests that larger individuals migrate earlier to spawning sites.