FISHERY BULLETIN: VOL. 84, NO. 1 



In addition, a variety of observations made from the 

 submersible substantially improved our understand- 

 ing of factors controlling the distribution and abun- 

 dance of the entire deep slope fauna at Johnston 

 Atoll. 



DESCRIPTION OF THE STUDY AREA 



A National Wildlife Refuge since 1926, Johnston 

 Atoll is located 1,250 km southwest of Oahu, HI. The 

 atoll's physical environment has been reviewed by 

 Amerson and Shelton (1976) and is summarized 

 here. 



Located between lat. 16°40'-16°47'N and long. 

 169°24'-169°34'W (Fig. 1), Johnston Atoll lies in the 

 North Pacific central water mass, where salinities 

 range from 34.8 to 35.3°/ 00 . Surface water temper- 

 atures show little seasonality, ranging from 25° to 

 27 °C. The atoll is directly in the path of the wester- 

 ly flowing North Equatorial Current, with surface 

 currents typically 0.5 kn (0.25 m/s). Deeper layers 

 flow smoothly past the atoll, but an island wake 



forms in lee surface waters, with effects evident up 

 to 600 km downstream (Barkley 1972). 



The atoll is composed of a coral platform, encom- 

 passing over 130 km 2 of reef under water <30 m 

 deep. A narrow lagoon lies between the northwest 

 barrier reef and Johnston and Sand Islands to the 

 southeast (Fig. 1). The atoll is unusual in that the 

 main outer reef extends only about one quarter of 

 the way around its perimeter (Fig. 1). A large por- 

 tion of the atoll lies exposed to prevailing easterly 

 weather conditions without benefit of barrier reef 

 protection. Evidence suggests that subsidence and 

 tilting of the reef platform to the southeast created 

 this unusual condition. 



The climate is tropical marine, i.a, there is little 

 seasonal variation in temperature and windspeed, 

 but substantial variation in rainfall. A 4-mo "winter" 

 season extends from December to March, when 

 temperatures drop slightly, winds become more vari- 

 able, and precipitation increases. The mean annual 

 air temperature is 26.3 °C, with a daily range of 

 4.0° -4.5° C. Daily maximum and minimum temper- 



169°30' W 



I ^ 1 



16°45'N 



A-J Makalii dive sites 



1-6 Cromwell fishing stations 



Figure 1— Map of Johnston Atoll. The lines encircling the atoll are isobaths of constant depth (fathoms). The four shaded areas 

 at the upper left are emergent lands (Johnston, Akau, Hikina, and Sand Islands). Letters (A-J) indicate the 10 dive sites of the Makalii 

 during the study. Numbers (1-6) indicate fishing stations of the Townsend Cromwell. 



142 



