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Fishery Bulletin 101(4) 



cells, swelling the cells, and leading to increases in hemato- 

 crit, and in plasma ion concentration and osmotic pressure. 

 Red cell volume is regulated in animals through transport 

 of intracellular and extracellular solutes. Although there is 

 minimal information available in the literature concerning 

 regulatory volume transport in reptiles, the mechanisms of 

 regulatory volume increase (RVI) and regulatory volume 

 decrease (RVD) are known in other lower vertebrates. For 

 example, Cala (1983) reported that in Amphiuma (am- 

 phiuma [common name]) red cells, the mechanism of RVD 

 is K+„^j/H+jj^ counter-transport coupled with Chg^j/HCOg'jj, 

 exchange (where the subscripts in and out represent 

 transport into and out of the cell, respectively), whereas 

 RVI is accomplished by Na^j^/H+^j^^j transport coupled with 

 Cl-,^/HC03-„,jt exchange (Cala, 1983). Other studies have 

 suggested that red cell RVD occurs because of electroneu- 

 tral KCl cotransport out of the cell and RVI occurs because 

 of electroneutral NaK2Cl or NaCl cotransport into the cell 

 (Haussinger and Lang, 1991). It is impossible to determine 

 which of these mechanisms, if any, were involved in regu- 

 lating red cell volume in sea turtles during and following 

 forced submergence. These transporters, however, have 

 been shown to be sensitive to cellular hypoxia (i.e. low Pog) 

 and low blood pH (Cossins and Gibson, 1997) — conditions 

 present in the experimental turtles following submergence. 

 In addition, hypoxic and acidotic conditions were absent 

 in nonsubmerged control turtles which did not experience 

 substantial shifts in plasma ion concentrations, osmotic 

 pressure, or hematocrit. 



Effects of handling 



Significant changes in blood pH, Pco.2, and lactate were 

 occasionally detected in nonsubmerged control turtles. 

 However, it is impossible to determine if these changes 

 resulted from repetitive handling during blood sampling or 

 from increased activity while free-swimming in a large cir- 

 cular tank following blood collection. Nevertheless, control 

 turtle blood lactate concentration was substantially less 

 than the lactate measured following forced submergence in 

 experimental turtles (Figs. 1 and 2). In addition, the blood 

 pH remained fairly constant in the control turtles during 

 collection of the seven serial samples. 



Laboratory versus field experimentation 



It should be noted that conducting the study under labo- 

 ratory and field conditions provided unique benefits for 

 analyzing the physiological effects of submersion. For 

 example, the laboratory conditions permitted collection of 

 blood samples immediately upon termination of the sub- 

 mersion period, whereas in the field, sea turtles had to be 

 transported back to the trawl vessel for postsubmersion 

 blood sampling. Turtles forcibly submerged under labora- 

 tory or field conditions hyperventilated upon surfacing. 

 Stabenau et al. (1991) reported a 9- to 10-fold increase 

 in the breathing frequency of trawled Kemp's ridley sea 

 turtles. Comparable breathing rates were observed in the 

 present study after submersion and, thus, it is plausible 

 that the blood PcOg measured in turtles under field condi- 



tions underestimated the actual buildup in blood COg (see 

 Table 3 for a comparison of the blood Pco, under labora- 

 tory and field conditions). In contrast, the field experiment 

 permitted examining the physiological stress of semiwild 

 turtles in TED-equipped commercial fishing nets following 

 a minimum of 21 days of in-water conditioning. The greater 

 acidosis measured in forcibly submerged turtles resulted 

 from increased swimming activity during the forced sub- 

 mergence. This is confirmed by a postsubmergence increase 

 in blood lactate of 10.1 niM under trawling conditions 

 versus 8.8 mM following laboratory submergence. Under 

 laboratory and field conditions, the behavior of the turtles 

 following submergence was monitored up to their release. 

 It is unclear, however, if the acid-base and ionic imbal- 

 ance caused by forced submersions would alter long-term 

 normal physiology and behavior. It is plausible that repeti- 

 tive alteration of blood pH by the magnitude measured in 

 the present study may have pathological consequences. For 

 example, no information is available on whether turtles 

 resume normal diving and feeding behavior following pro- 

 longed or multiple forced submersions, or whether turtles 

 become more susceptible to repeated submersions in TED- 

 equipped nets. 



Use of turtles reared in captivity 



Two-year-old loggerhead sea turtles reared in captivity 

 were used for all of the submergence experiments. It was 

 assumed that these animals were adequate surrogates 

 for wild sea turtles. In fact, similar-size animals from the 

 NMFS Galveston Laboratory are used in annual TED 

 certification trials. Nevertheless, there may be differences 

 in the physiology of captive and wild turtles subjected to 

 forced submergences. For example, it is possible that wild 

 sea turtles would be exposed to forced submergences fol- 

 lowing lengthy, voluntary dives. No information is available 

 in the literature on the acid-base and ionic status of wild 

 sea turtles following prolonged voluntary dives or forced 

 multiple submergences. If dives are anaerobic, then sub- 

 jecting wild sea turtles to multiple forced submergences 

 may adversely affect survival potential. 



Conclusions 



The data suggest that forced submergences of 2-year-old 

 loggerhead sea turtles reared in captivity produce signifi- 

 cant blood metabolic and respiratory acidosis. Repetitive 

 submergences did not augment the acidosis, rather subse- 

 quent submergences resulted in less severe acid-base dis- 

 turbances. Under trawl conditions, the turtle must recover 

 from any physiological acid-base disturbance when it is 

 freed from a TED-equipped net. Recovery is accomplished, 

 in part, by the turtle immediately surfacing and hyper- 

 ventilating (Jackson, 1985; Stabenau et al., 1991). This 

 behavior was observed following each submergence epi- 

 sode. Turtles would then resume normal voluntary diving 

 behavior, presumably after partial-to-eomplete recovery 

 from the acid-base disturbance. These data suggest that 

 repetitive submergences of sea turtles in TED-equipped 



