125 



Abstract — Size-related differences 

 in power production and swim speed 

 duration may contribute to the 

 observed deficit of nursing calves in 

 relation to lactating females killed 

 in sets by tuna purse-seiners in the 

 eastern tropical Pacific Ocean (ETP). 

 Power production and swim-speed 

 duration were estimated for north- 

 eastern spotted dolphins iStenella 

 attenuata), the species (neonate 

 through adult) most often captured 

 by the fishery. Power required by 

 neonates to swim unassisted was 

 3.6 times that required of an adult 

 to swim the same speed. Estimated 

 unassisted burst speed for neonates 

 is only about 3 m/s compared to about 

 6 m/s for adults. Estimated long-term 

 sustainable speed is about 1 m/s for 

 neonates compared to about 2.5 m/s 

 for adults. Weight-specific power 

 requirements decrease as dolphin 

 calves increase in size, but power 

 estimates for 2-year-old spotted dol- 

 phin calves are still about 40% higher 

 than power estimates for adults, to 

 maintain the same speed. These esti- 

 mated differences between calves and 

 adults are conservative because the 

 calculations do not include accommo- 

 dation for reduced aerobic capacity in 

 dolphin calves compared to adults. 

 Discrepancies in power production are 

 probably ameliorated under normal 

 circumstances by calves drafting next 

 to their mothers, and by employing 

 burst-coast or leap-burst-coast swim- 

 ming, but the relatively high speeds 

 associated with evasion behaviors 

 during and after tuna sets likely 

 diminish use of these energy-saving 

 strategies by calves. 



Duration of unassisted swimming activity 

 for spotted dolphin iStenella attenuata) calves: 

 implications for mother-calf separation 

 during tuna purse-seine sets 



Elizabeth F. Edwards 



Southwest Fisheries Science Center 



National Marine Fisheries Service 



8604 La Jolla Shores Drive 



La Jolla, California 92037 



E mail address Elizabeth Edwardsigi noaa.gov 



Manuscript submitted 15 February 2005 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 25 July 2005 by the Scientific Editor. 



Fish. Bull. 104:125-135 (2006). 



Dolphin calves draft in echelon posi- 

 tion next to their mothers for the first 

 few weeks after birth and continue 

 to return to drafting in echelon posi- 

 tion frequently throughout at least 

 their first year (EdwardsM. "Echelon 

 position' is the physical positioning 

 of the calf within a few centimeters 

 of the mother, near her mid-section, 

 with fin motions reduced or absent 

 (e.g., Norris and Prescott, 1961). This 

 position takes advantage of the moth- 

 er's flow field, reducing or effectively 

 eliminating the energy cost to the 

 calf of moving forward through the 

 water (Weihs, 2004). Because draft- 

 ing appears to be ubiquitous among 

 dolphin calves, particularly during 

 the neonate stage, it appears likely 

 that drafting is an essential factor 

 in maintaining physical association 

 between calves and their mothers, 

 especially when the calves are small. 

 In the eastern tropical Pacific 

 Ocean (ETP) a situation occurs in 

 which it becomes important to con- 

 sider the consequences for calves of 

 losing their drafting association with 

 their mother. In this area, a tuna 

 purse-seine fishery targets schools of 

 large yellowfin tuna that associate 

 closely with schools of dolphins, pri- 

 marily the spotted dolphin (SteneUa 

 attenuata) (NRC, 1992). The associ- 

 ated schools of tunas and dolphins 

 are located by a helicopter sent out 

 from the purse-seine vessel and are 

 subsequently captured through the 

 actions of several high-powered speed- 

 boats, which are released from the 

 purse-seiner to overtake and herd the 



associated animals into the closing 

 arc of the purse-seine (NRC, 1992). 

 Examination of the dolphins found 

 dead in the net has revealed that 

 75% to 95% of the lactating females 

 killed in the sets are not killed with 

 an accompanying calf (Archer et al., 

 2004). This observed calf deficit is a 

 potentially important factor in the 

 lack of recovery of ETP dolphin popu- 

 lations despite over a decade of very 

 low fishery mortality (Wade et al.^), 

 but little is known about why or how 

 the separation of mothers and calves 

 occurs (Archer et al., 2004). 



The chase, encirclement, and re- 

 lease procedure of purse-seine fish- 

 ing operations tends to be relatively 

 prolonged — chases averaging about 

 30 minutes, capture and confine- 

 ment about 90 minutes, and postre- 

 lease swimming at least 90 minutes 

 (Myrick and Perkins, 1995; Chivers 



1 Edwards, E. 2002. Behavioral contri- 

 butions to separation and subsequent 

 mortality of dolphin calves chased by 

 tuna purse-seiners in the eastern tropi- 

 cal Pacific Ocean. National Oceano- 

 graphic and Atmospheric Administra- 

 tion Administrative Report LJ-02-28, 

 33 p. Southwest Fisheries Science 

 Center, 8604 La Jolla Shores Drive, La 

 Jolla, CA 92037. 



- Wade, P., S. Reilly, and T. Gerrodette. 

 2002. Assessment of the population 

 dynamics of the northeastern offshore 

 spotted and eastern spinner dolphin 

 populations through 2002. National 

 Oceanographic and Atmospheric Ad- 

 ministration Administrative Report 

 LJ-02-13, 58 p. Southwest Fisheries 

 Science Center, 8604 La Jolla Shores 

 Drive, La Jolla, CA 92037. 



