EFFECTS OF SEISMIC ENERGY RELEASES ON THE SURVIVAL AND DEVELOPMENT OFZOEAL-LARVAE OF DUNGENESS-CRAB (CANCER-MAGISTER)

In blind, controlled field experiments, early Stage II zoeae of Dungen ess crab (Cancer magister DANA) were exposed to sounds from single dis charges of a 13.8-litre array of seven air guns. Their survival and de velopment were followed during subsequent laboratory culture. Immediat e mortality was low (0 to 2%) and showed no significant difference bet ween control and exposed larvae (alpha > 0.05). Across all treatments and blocks of the experiment, survival to the molt to Stage III averag ed 88.8%. The conditional Stage IV survival rate averaged 69.8%. The t imes to the molts to Stage III and Stage IV averaged 14.4 and 34.9 day s, respectively. For immediate and long-term survival and time to molt , the field experiment revealed no statistically significant (alpha > 0.05) effects on zoeae for exposures as close as 1 m from the array, n or for mean sound pressure as high as 231 dB re 1 muPa and cumulative energy density up to 251 J/m2. Post hoc power calculations showed that any reduction in zoeal survival as a result of sound exposure was les s than 7% for survival to Stage III and less than 12% for Stage IV con ditional survival (1-beta = 0.90. alpha = .0.05 one-tailed). The sound exposures in our study were at the maximum levels likely to be experi enced by a zoea during an actual survey.