Late spring has arrived to the Pacific Northwest, and its signs are nothing short of blatant: myriad flowers blossoming in field and forest, insects buzzing about, lawnmowers droning away, and pollen and cottonwood seed filling the air, drifting amidst the vociferous broadcasting of birdsong. As landlubbers we’re likely to note these developments with little interest, if we note them at all; they are occurrences of a perennial sort, the natural and quotidian accompaniment to longer days and warmer temperatures. With a tilt of the earth, our landscape is transformed—nothing new there. But what of the changes being wrought in that more primal realm, beneath the churning sea? What wonders of the Puget Sound are unfolding beyond our shorebound, air-breathing purview?
Allow me to introduce the plainfin midshipman (Porichthys notatus), nighttime crooner of the intertidal coast. Big-mouthed, bug-eyed, up to nine inches in length, midshipmen are named for the rows of photophores, or light-producing organs—used by the fish to attract prey in the darkness—running laterally down their bodies, which apparently reminded someone way back when of the buttons on a naval uniform. Since I know nothing about nautical regalia, I’ll have to assume this comparison makes sense. But the fish’s rather homely appearance is a red herring of sorts, because what the midshipman lacks in beauty marks, it more than makes up for in vocal prowess.
On late spring and summer nights along the western edge of North America, if one is near the water and listening close, an eerie concerto can sometimes be heard burbling up from the depths. Sounding at times like frogs croaking, at others like an underwater dial tone, the mating vocalizations of male midshipmen fill the aqueous medium with benthic, buzzing music. When a group of males gather and sing in chorus, the resulting drone is sometimes loud enough to drown out above-water conversation. To be clear, it’s not quite right to call these sounds “vocal,” as the midshipman possesses nothing resembling a vocal cord. The noise is instead produced by rapidly contracting muscles around its swim bladder, a gas-filled organ typically used by fishes to control buoyancy. Because the bladder is hollow, it acts as a resonating chamber, amplifying the minute grunts and croaks and buzzes to deafening effect.
Which brings up an interesting point: If the midshipman uses its swim bladder to not only produce sound but receive it as well, how does it avoid blowing out its stereo system with each mic check (so to speak)? The answer lies in the wiring of the midshipman’s brain. Both sound and hearing are controlled by neural impulses coming from a single portion of the fish’s brain: when a signal is given to muscles controlling the swim bladder, vibrating them to generate sound, a simultaneous signal is sent to the hair-like cells of the fish’s ear nearby, stiffening them and inhibiting their sensitivity. Thus, at the precise moment a fish buzzes, its ear is temporarily deafened. These synchronized signals can occur almost 100 times a second, allowing the fish to pause, listen for predators or potential mates, and then resume calling, almost seamlessly.
From the coast of Alaska down to California, these sculpin-like fish engage in nightly singing contests, much like those of birds in the spring: males grunt, croak, and hum to attract females to their nests, which are scooped-out depressions in the sand. If a female likes what she hears, she lays her eggs in the chosen male’s nest, whereupon he fertilizes them and stands watch until they hatch. He continues to sing, however, and will attempt to woo as many females as possible into entrusting their brood in his care. Curiously, there are two types of male midshipman: type I and type II. Type I males are big, barrel-chested crooners, capable of long-winded hums that can last for an hour or more. Type II males are smaller—an eighth the body mass of the first type—and can’t sing for nearly as long, but they are well-endowed in other ways: reproductive organs of type II males are, on average, seven times larger than those of type I. The first type relies on its singing to attract females, while the second, being roughly the size of a female midshipman, sneaks into other males’ nests to fertilize the just-laid eggs. Such is the soap opera existence of the midshipman.
On a low tide, you can find these fish holed up in the sand or curled under a rock, refusing to let even the absence of water get in the way of their egg-sitting. Stubbornly, unremittingly paternalistic, the male midshipman—if he’s type I, that is—guards his brood with growls and grunts, and may even bite if provoked. A fishy father figure, indeed.