FISHERY BULLETIN: VOL. 76, NO. 2 



Figure l. — The island of Oahu, Hawaii, showing the major 

 study areas and the locations at which environmental data were 

 collected. 



of Oahu. Observations were made primarily dur- 

 ing daylight hours, but a few night observations 

 were made as well at Kahana River and Wailupe 

 Beach. Field observations were recorded as I fol- 

 lowed at a distance schools of mullet as they swam 

 about estuarine intertidal regions and estuarine 

 streams. Information about the distribution of 

 mullet was also collected by using seines. Be- 

 havioral and distributional records were kept and 

 the temperature and salinity of the water through 

 which the fish passed were measured with a tele- 



thermometer and compensated salinity refrac- 

 tometer, respectively. 



Young Mugil cephalus were distinguished and 

 differentiated from the young of a second sympat- 

 ric species of mullet, Chelon engeli, an introduced 

 species (Randall and Kanayama 1972), by differ- 

 ences in body pigmentation pattern and opercle 

 coloration. In addition, young C. engeli ^bO mm 

 standard length (SL) occurred in the intertidal 

 estuarine regions predominantly during the 

 summer and fall, whereas, striped mullet pre- 

 dominated in the winter and spring months. Only 

 observations of mullet that were unquestionably 

 identified as striped mullet were used in this re- 

 port. I 



Experimental Methods 



Experiments were carried out at the Oceanic 

 Institute during 1972 and 1973 (Table 1). An ex- 

 perimental thermal vertical gradient was estab- 

 lished in a 566-1 cylindrical Plexiglas^ tank, 91 cm 

 high and 89 cm in diameter, inside a lighttight 

 enclosure (Figure 2). Epoxy-coated copper coils 

 spiraled around the inside of the tank, having 

 entered through the surface above and through 

 the side at the bottom. These separate sets of coils 

 exited at midtank through the side. Pumps con- 



^ Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Figure 2. — Experimental apparatus 

 (diagramatic). Light excluding sides 

 Etnd covering have been removed from 

 frame. 



300 



