Telemetered cephalopod energetics: swimming, soaring, and blimping

Cephalopods are uniquely suited to field energetic studies.Their hollow mantles that pump water for respiration and jettingalso can accommodate differential transducer-transmitters. Thesetransmitters indicate pressure-flow power output, which canbe calibrated against oxygen consumption by swim-tunnel respirometry.Radio-acoustic positioning telemetry (RAPT) records pressure-flowpower and animal movements with meter accuracy in nature. Despiteinherent inefficiencies, jetting is the primary mode of locomotionfor both primitive nautilus and powerful, migratory oceanicsquids. In between, large-finned squid and cuttlefish mix jettingwith fin undulation in complex gaits that increase locomotorefficiency. Our studies show that the complex nervous systemscephalopods evolved to control mixed gaits are also sensitiveto flow and density fields in nature and that they use theseto further reduce locomotion costs. Buoyed up by evacuated shells,nautilus and cuttlefish live in boundary layers and navigatecheaply through them like balloonists. Large-finned, negativelybuoyant squid soar like eagles in rising currents, but losecontrol in currents above one body length per second. Many muscularsquids have life histories linked to current systems. Neutrallybuoyant ammoniacal cephalopods in the mesopelagic are a limitingcase in need of study. The small density differential betweenseawater and isotonic ammonium chloride trebles their volume,making them blimp-like with very low power densities. Some specieslive entirely in this restricted habitat, but most become ammoniacallate in ontogeny, as they approach semelparous reproduction.Ammonium retained for buoyancy as carbon is terminally mobilizedfrom muscle protein for gametes and energy, compensates forlost muscle power.