FISHERY BULLETIN: VOL. 85, NO. 1 



no pattern is discernable, peaks being found in 

 November and May (Table 1). The lowest plasma 

 calcium for an individual was 0.19 mM and the high- 

 est 4.90 mM. For the whole population the mean is 

 1.53 ± 0.76 mM{n = 115). 



Magnesium 



The population mean is 2.10 ± 0.542 mM(n = 88). 

 The lowest and highest values for individuals were 

 0.96 and 3.80 mM respectively, a smaller excursion 

 than that found for calcium. It appears that plasma 

 magnesium levels are under comparatively tight 

 control. 



Osmotic Pressure 



The osmotic pressure values showed the greatest 

 absolute excursion, individuals ranging from 258 to 

 360 mOsm. The lowest monthly means were found 

 from January to March of each year (Table 1). The 

 average osmotic pressure for the whole population 

 was 321.3 ± 24.10 mOsm (n = 117). 



Urea 



Plama urea values showed the greatest relative 

 range in individuals, 0.4-23.8 mM. Interestingly, the 

 pattern of changes is remarkably similar to that of 

 the osmotic pressure (Fig. 1), suggesting strongly 

 that both are linked in some way. The mean value 

 for the population (6.57 + 5.82 mM, n = 101) is very 

 similar to that reported for the same species (6.0 

 mM, Dessauer 1970). 



Glucose 



In the field blood glucose was remarkably steady 

 at about 1 mM (Table 1), suggesting that blood glu- 



cose levels are highly regulated. This value is con- 

 siderably lower than that reported earlier for the 

 loggerhead sea turtle (3.3 mM, Dessauer 1970). 



Lactate 



For most loggerhead sea turtles the blood lactate 

 concentrations ranged from 3 to 4 mM shortly after 

 capture (Table 1). However, noticeably higher lac- 

 tate values (8.8-16.2 mM) were obtained from sea 

 turtles caught in a single trawl (August 1982). This 

 was possibly the result of more severe trawl stress. 

 Rates of recovery while on deck varied. For 6 in- 

 dividuals, lactate had declined an average of 16.8% 

 from the initial value after 3 h; for 4 sea turtles after 

 4 h, average lactate had declined 52.6%; and for 4 

 sea turtles lactate had declined 16.4% after 5 h. 



DISCUSSION 



This study examines, for the first time, the month- 

 ly changes in the blood chemistry of a marine turtle. 

 However it must be borne in mind that this is a field 

 study without "controls" and alterations in body 

 chemistry and metabolism could be due to intrinsic 

 biological rhythms cued to extrinsic factors such as 

 photoperiod or could be directly determined by en- 

 vironmental changes in, for example, temperature. 

 As turtles are ectotherms (with the possible excep- 

 tion of leatherbacks) seasonal changes in tempera- 

 ture will be accompanied by matching changes in 

 body temperature. It was not possible, therefore, 

 to distinguish between temperature effects per se 

 and changes due to annual rhythms acting as Zeit- 

 gebers. Temperature effects are the subject of a 

 separate study (Lutz and Dunbar-Cooper 1984). 



The total sample number assembled over the 

 course of this study for each blood constituent is 

 very large, as far as we are aware the set is much 



Figure 1.— Seasonal changes in plasma urea (■) and osmotic pressure (♦) in the 

 loggerhead sea turtle, December 1979 to September 1981 and November 1981 to 

 August 1982. 



40 



