SQUID (LOLIGO-FORBESI) PERFORMANCE AND METABOLIC RATES IN NATURE

Squid are the fastest swimming invertebrates, but the metabolic cost o f speed, as assessed in swim-tunnels, is several-fold higher than in f ish, making squid appear uncompetitive. Because oxygen consumption can be correlated with jet pressure, it is possible to monitor pressure a nd thus estimate performance and energy costs in nature. Tracking in c ourse and depth gave a 3-D view of squid (Loligo forbesi) activities a nd costs for nearly three animal-weeks; five days of this included tel emetry of jet pressures. These 2-5 kg loliginids hovered off-bottom mo st of the time, perhaps to avoid predation or damage to delicate skins . Hovering consumes about 50 ml O-2 kg(-1) h(-1), twice as much as res ting on bottom and half of overall average costs. Jet pressures were n ot well correlated with horizontal movements or tidal cycles, suggesti ng squid may ''soar'' to reduce the cost of remaining in active curren t areas, acting as sit-and-wait predators. Maximal aerobic jetting vas rare and usually associated with vertical climbing. Thus, these squid appear to have adopted a suite of natural behaviours which compensate for those aspects of their physiology which are least competitive wit h fishes and accentuate those which are most competitive.