50 



Fishery Bulletin 93(1), 1995 



The percentage of eggs that hatched may have been 

 slightly affected by exposure, but our results were 

 inconclusive (P„„ M „„„_ „„ =0.036, but P, . , 



regression:arcsin lack of 



^•cO.OlO, and ^=0.10). The percentage of eggs hatch- 

 ing in the -5.3°h treatment differed significantly from 

 the control (Dunnett's test), but the difference was 

 minor (99.1% versus 99.8% hatching). 



Egg extrusion may have been influenced by expo- 

 sure, but the data were inconsistent. Elapsed time 

 between larval hatching and subsequent egg extru- 

 sion tended to be prolonged by exposure, but the re- 

 sponse was variable (P Hnea =0.005, P lack O ^,=0.719, 

 r 2 =0.19, rc=41). Egg extrusion generally occurred two 

 days (median) after zoeal release but ranged from 

 to 18 days; only crabs in the two most severe treat- 

 ments (<—4.3°h) exceeded nine days. The date of ex- 



Juveniles 



Adults 



60 



50- 

 40- 

 30- 



20 

 10 





 60 



control 



Ji BDQ Q - 



T 



^ 



I ' I ' I ' I 



50 

 40 



j§ 30- 



20 

 10-1 





 60 



-1.5 °h 



I ' I 



I ' I ' I 



I ' I ' I ' I ' I 



I ' I 



-2.0 °h 



24 32 



Days after exposure 



Figure 4 



Righting times of juvenile and adult Chionoecetes bairdi as a function of 

 time in days after emersion. Error bars are ±1 standard error. 



trusion (4 May ±7 days) may also have been changed 

 by exposure, but again the statistical results were incon- 

 elusive (P^ ar =0.011, P*^ ^=0.700, r^O.16, n=41). 

 Exposure did not affect the percentage of Tanner crabs 

 extruding eggs (93%, P linea =0.730, r^O.03, ra=6). 



Discussion 



Extreme exposure to cold air was lethal to Tanner 

 crabs. It is also possible that thermal shock caused 

 when the crabs were returned to water following expo- 

 sure was also damaging. Following sublethal exposure, 

 crabs exhibited a slowed righting response, autotomy 

 of pereiopods, depressed feeding rates (adults), and 

 weight loss or reduced weight gain (juveniles). 



Temperature and duration of treat- 

 ment were both critical factors in de- 

 termining how aerial exposure affected 

 Tanner crabs. In a similar experiment 

 with king crabs, the response of crabs 

 to exposure was clearly observed when 

 exposure was defined as the product of 

 temperature and the length of exposure 

 time (Carls and O'Clair, 1990). The use 

 of this composite variable worked well 

 with the current data set. However, our 

 approach may not be generally appli- 

 cable (for discussion see Carls and 

 O'Clair, [1990]). 



Design of this experiment precluded 

 independent analysis of temperature 

 and time factors. However, either fac- 

 tor may be predicted as a function of 

 the other. For example, at -10°C, 10% 

 of juvenile crabs may be killed by an 8- 

 minute exposure, and 50% may be killed 

 by a 20-minute exposure. Similarly, a 

 10-minute exposure would impair right- 

 ing in 50% of juvenile crab at -7°C. Pre- 

 dicted times and temperatures were 

 calculated from degree-hours causing 

 death (LC) or from effective degree-hours 

 causing cessation of righting (EC) esti- 

 mates (Tables 2 and 3); temperature 

 multiplied by time (units are Celcius 

 and hours) matched the LC or EC esti- 

 mates. Predictions of adult and juvenile 

 Tanner crab response are summarized 

 in Figure 10 and Appendices. In our ex- 

 ample (Fig. 10), short-term effects are 

 predicted by ability to right immedi- 

 ately after exposure; impaired crabs 

 may be subject to increased predation 

 at this time. Long-term effects are pre- 



-1.6 "h 



-2.2 "h 



