FISHERY BULLETIN: VOL. 74, NO. 4 



spite of its proximity to land, the area appears to 

 be representative of the open waters of the central 

 North Pacific. Meroplankton is sometimes abun- 

 dant, particularly larval stomatopods, but never 

 dominates the zooplankton. The light regime at 

 night may be affected by light from the urbanized 

 areas of Oahu, although direct light from Honolulu 

 is shielded by mountains. Doty and Oguri (1956) 

 found enhanced values of primary productivity 

 near the Hawaiian Islands (the "island mass 

 effect"), but Gilmartin and Revelante (1974) found 

 this effect only within about 1 km of land. The 

 advantages of nearness to port and convenience of 

 study greatly outweigh the potential disadvan- 

 tages of being affected by nearshore processes. 



Vertical Distribution: 

 Teuthis Sampling Program 



Most of the material studied was collected 

 during the "Teuthis" program, a series of 23 

 cruises during 1971-73 by the University of 

 Hawaii's RV Teritii. The primary objective of the 

 program was to determine the vertical distribu- 

 tions of the various species of micronekton during 

 the daytime and at night. For this purpose an 

 extensive series of horizontal tows was made 

 using a modified Tucker trawl (MT) with a mouth 3 

 m wide. The trawl can be opened and closed at the 

 desired sampling depth, avoiding contamination 

 of the sample by organisms from shallower depths 

 during setting and retrieval. It is lined with 

 knotless nylon mesh, with apertures about 7 mm in 

 diameter. The cod end is a 1-m plankton net of 

 303-ium Nitex.- Mounted on the trawl is a time- 

 depth recorder (Benthos 1170) which provides a 

 record of the depths sampled by the trawl. 



This basic configuration was extensively 

 modified during the course of the sampling pro- 

 gram to obtain more reliable operation and better 

 data. The original acoustic-controlled opening- 

 closing system (Inter-Ocean) was replaced by a 

 more reliable messenger-operated double-trip 

 mechanism (modified General Oceanics No. 4020). 

 A digital flowmeter (General Oceanics No. 2030) 

 was added at the beginning of 1972, giving a more 

 accurate estimate of the volume of water sampled 

 by the trawl. An acoustic telemeter (AMF No. 

 1024) allowed real-time monitoring of trawl depth 

 beginning in November 1972; earlier tows wan- 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



dered vertically over 10-20% of their maximum 

 depth. 



The limitations of time and unreliability of 

 sampling gear forced abandonment of plans for a 

 uniform series of standard tows. Each cruise 

 attempted instead to sample depths not yet sam- 

 pled or to answer questions raised by previous 

 sampling. Informal as this protocol was, the actual 

 depths sampled often differed greatly from the 

 plan. Before a telemeter was available, the sam- 

 pling depth was set by the amount of wire paid 

 out; two tows with the same amount of wire out 

 often showed a twofold variation in modal depth. 

 Over the course of the program the upper 1,200 m 

 was sampled rather thoroughly, with a few deeper 

 tows down to 2,300 m. 



A typical cruise lasted 4 days. On each day two 

 tows were made during the daytime and two at 

 night, avoiding the twilight periods when many 

 mid-water animals are migrating. Tows sampled 

 for 3 h at a towing speed of about 4 knots. The 

 catch was immediately placed in chilled seawater, 

 and live specimens were removed to an aquarium 

 for observation. The rest of the catch was sorted 

 and preserved in buffered 5% Formalin seawater. 

 The inside of the net was picked clean of animals 

 after each tow to prevent contamination of sub- 

 sequent tows. Physical conditions recorded in- 

 cluded ship's position at the beginning and end of 

 sampling, weather conditions and sea state, time 

 of sunrise and sunset, and lunar phase. Bathy- 

 thermograph casts were made during the early 

 cruises, later replaced with expendable bathy- 

 thermograph casts; at least one was taken per 

 cruise (Maynard et al. 1975). The 1973 cruises also 

 recorded biological sound scattering at 25 kHz and 

 surface light irradiance (Walters in prep.). In the 

 laboratory, the sergestids were sorted to species, 

 sexed, and counted, and the carapace length (CL) 

 from the base of the rostrum to the posterior 

 margin of the carapace at the dorsal midline was 

 measured to the nearest 0.1 mm with an eyepiece 

 micrometer in a dissecting microscope. 



Between February 1971 and June 1973, 16 

 cruises produced 160 horizontal tows (Table 1). 

 Daytime (DAY) tows were lumped together, but 

 nighttime tows were divided into tows during the 

 dark of the moon or with the moon obscured by 

 clouds (NIGHT) and tows made under substantial 

 amounts of moonlight (MOON). Total trawling 

 time for each 25-m interval of the water column to 

 1,500 m for the entire series was calculated from 

 time-depth records (Table 2). 



800 



