Energetics Consequences of Chase by Tuna Purse-Seiners for Spotted Dolphins ('Stenella Attenuata') in the Eastern Tropical Pacific Ocean

摘要

Daily energy costs and mass-specific power outputs were estimated for un-associated Stenella attenuata ranging in size from neonate through adult under normal (non-chase) conditions and for conditions including 1 chase of 15, 30, or 60 minutes with swimming velocity ranging from 0.25 to 7.5 meters/second. Daily costs and mass-specific power outputs were also estimated for drafting mother-calf pairs under conditions of gliding drafting or full drag gliding. At the most likely chase reaction speed of about 3 m/second and chase duration of 30 minutes, estimated increase in daily caloric cost ranged from about 12% in neonates to about 6 % in adults. Estimated cost increases were halved for 15 minute chases and doubled for 60 minute chases. The relative infrequency of chase (about on the order of 8 times per year) implies that chases probably do not cause an significant long-term adverse impact on daily energy costs for Stenella attenuata in the ETP. In contrast, estimated mass-specific power outputs indicate that size-specific power production capacity likely significantly limits the ability of non-drafting Stenella calves to maintain speed with adult dolphins in a school fleeing tuna vessel speedboats during chase. Due to observed decreases in fraction of total body mass composed of propulsive muscle with decreasing body size, as well as simple decreases in total body size with decreasing age, neonate dolphins for example apparently must expend about 4.6 times the power as an adult, to maintain the same speed. Even two-year old calves likely require about 1.5 times the power needed by an adult, to maintain any given speed. As a result, the duration of time over which Stenella attenuata of various sizes can maintain any given speed decreases rapidly with body size.