FISHERY BULLETIN; VOL. 85, NO. 1 



Table 2.— Depth horizon data for discrete-depth samples collected 

 during Columbus Iselin cruises I, II, and III. 



Groups of associated species were determined for 

 both day and night and were defined based on the 

 minimum depth of occurrence (the shallowest 

 discrete depth capture of a species) and zone of max- 

 imum abundance, using the Columbus Iselin data. 

 These associations included the abundant and 

 common species, as well as those uncommon species 

 whose sample size was sufficient to determine 

 depth range or which had a very narrow range of 

 capture. 



Although our data were limited, effects of lunar 

 phase on vertical distribution of abundant species 

 were examined by comparing the minimum depth 

 of captures between new and full moon phases. 

 Three cruises were defined as new moon (Joie de 

 Vivre, Dan Braman, Bellows cruise I, Table 1); the 

 remainder as full. 



RESULTS 



Hydrography 



The circulation of the eastern Gulf of Mexico is 

 dominated by the Loop Current (Leipper 1970; 

 NowHn 1971; Jones 1973; Molinari and Mayer 1980). 

 This current, of Caribbean origin, enters the Gulf 

 through the Yucatan Straits and moves anti- 

 cyclonically, exiting through the Florida Straits. The 



extent of penetration into the Gulf is latitudinally 

 variable and seasonally unpredictable. The Loop 

 Current can be identified by the depth of the 22 °C 

 or 20 °C isotherms which occur at 100 m and 150 

 m, respectively (Leipper 1970; Maul 1977; Sturges 

 and Evans 1983). Meanders of the Loop Current 

 often pinch off to form cold core eddies which spin 

 cyclonically and drift southward along the eastern 

 edge of the Loop Current off the West Florida Shelf 

 (Vukovich and Maul 1985). Some of these cyclonic 

 eddies have been tracked through our eastern sam- 

 pling areas (EC and SE). 



All of the southeastern (SE) collections were in 

 waters covered by the Loop Current at the time of 

 sampling, whereas the more northerly samples (EC 

 and NE) were from what is termed Loop Transition 

 Water. The characteristics of Loop Transition 

 Water during the collection period (summer) were 

 as follows: a mixed layer of variable depth, usually 

 extending 25 to 50 m with surface temperatures 

 of 27° to 30° C; a sharp thermocline from the base 

 of the mixed layer to approximately 150 m depth 

 where the temperature was 15° to 18°C; a gradual 

 temperature decline from 150 m to about 4°C at 

 1,000 m. Figure 2 illustrates a typical profile of 

 the Loop Transition Water during the summer 

 months. 



Productivity measurements within the Loop Cur- 

 rent and in Loop Transition Waters indicate an 



TYPICAL WARM MONTH THERMAL PROFILE 

 e GOM 



E 



X 

 H 

 Q. 

 liJ 

 O 



600 



1 r~r-i — I 1 I I — r-| — i i i i | i i i — i—j — i i i i — |— i — n — r 



5 10 15 20 25 30 



TEMPERATURE "C 



Figure 2.— Typical warm month thermal profile for the eastern 

 Gulf of Mexico (eGOM). 



84 



