eastern Gulf of Mexico, because the area has important 
commercial fisheries and is presently a focus of oil explora- 
tion. 
METHODS 
Data based on 12 cruises during 1972-74 are included in 
this report (Table 1). Plankton volumes were determined 
from a total of 482 stations and fish eggs and larvae were 
collected at 483 stations. Stations were located on a grid 
extending from lat. 24°30'N to lat. 29°30'N and from the 
10-m contour near the west Florida coast to approximately 
the 200-m contour at the edge of the continental shelf (Fig. 
1). The two cruises in 1974 included some stations in water 
as shallow as 4 m to compare plankton biomass and fish 
spawning there with offshore areas. The number of stations 
occupied on cruises ranged from 13 to 51 (Table 1). 
Plankton collections were made with the paired 61 cm 
Bongo net plankton sampler (Posgay et al. 1968). One net 
was fitted with 505-um Nitex mesh from which fish eggs and 
larvae were sorted. The second net was 333-um Nitex mesh 
and it was used to provide zooplankton for volume determin- 
ations; this net meets the specifications of a reference net 
prescribed by the National Academy of Sciences (1969) for 
determining zooplankton biomass. A TSK (Tsurumi-Seiki 
Kosakusho) flowmeter was secured in the mouth of the 
505-u~m mesh net to determine volume filtered during each 
tow. Tows were double oblique from within 5 m of bottom to 
surface, or from 200-m depth to surface at deep stations. 
Towing speed was 2 to 3 knots and winch speeds were 
controlled to ensure that all depths were sampled propor- 
tionately. A Benthos time-depth recorder was attached to 
the plankton sampler to record tow characteristics. Tow 
times varied from 1 min at stations shallower than 50 m to 
20 min at the deepest stations. Volumes filtered during a 
tow varied from approximately 100 m? at shallow stations 
to 400 m? at the deepest stations. 
All plankton collected by the nets was retained and 
preserved in 10% buffered seawater Formalin. In the 
laboratory all fish eggs and larvae were sorted from the 
505-um mesh net samples. After samples had been stored for 
at least 2mo to allow for changes in plankton volume due to 
preservation, volumes were determined using methods 
similar to those described by Thrailkill (1969) and Kramer et 
al. (1972). Zooplankton volumes are displacement volumes, 
Table 1.—Cruises and number of stations analyzed for zooplankton 
volumes and ichthyoplankton, 1972-74. 8B = RV Bellows, GE = RV 
Gerda, IS = RV Columbus Iselin, and CL = RV Calanus. 
Plankton Fish egg 
volume and larvae 
Cruise Dates stations stations 
8B 7201 & GE 7202 1-11 Feb. 1972 26 30 
GE 7208 1-10 May 1972 28 30 
GE 7210 12-18 June 1972 13 13 
IS 7205 9-17 Sept. 1972 34 34 
IS 7209 8-16 Nov. 1972 49 50 
IS 7303 19-27 Jan. 1973 50 51 
IS 7308 9-17 May 1973 49 49 
IS 7311 27 June-6 July 1973 51 51 
IS 7313 3-13 Aug. 1973 50 50 
IS 7320 6-14 Nov. 1973 51 51 
CL7405 28 Feb.-9 Mar. 1974 36 32 
CL7412 1-9 May 1974 45 42 
Totals 482 483 
reported as cubic centimeters per 1,000 m* of seawater 
filtered by the collecting net. Contour charts (Fig. 2) 
illustrate zooplankton concentrations for each cruise. These 
are mean values for the whole water column at a location 
since discrete depth strata were not sampled. 
Zooplankton displacement volumes were determined 
after removing nonplanktonic organisms (e.g., seaweeds, 
large fish) and large planktonic organisms (>5 cc; mostly 
coelenterates). The remaining zooplankton organisms were 
of 5 ce or less in volume. This fraction of the plankton 
sampled was aspirated onto a 35-um plankton mesh filter in 
a Buchner funnel under a 22 psi vacuum until less than one 
drop of water per 15 s was drawn from the sample. Samples 
with large numbers of jellylike organisms were aspirated for 
shorter times to avoid reduction in plankton volume due to 
body fluid loss. Volume was then determined by water 
displacement in a graduated cylinder. The zooplankton 
volumes given in this report, therefore, are for organisms 
less than 5 ec. The most numerous organisms were crusta- 
ceans, molluscs, and chaetognaths, all of which are impor- 
tant in food webs that sustain pelagic fish resources. 
Numbers of fish eggs and larvae were reported as 
numbers under 10 m? of sea surface, giving an estimate of 
abundance for each station. Contour charts of the abundance 
of fish eggs and larvae (Figs. 3, 4) show the distribution 
based on this method. Mean concentrations of fish eggs and 
larvae at a station also can provide useful information. These 
values are not illustrated or reported here but can be 
obtained from our abundance charts and a bathymetric chart 
of the eastern Gulf by multiplying our contoured abundance © 
values by 10/d (where d equals depth of tow in meters), to 
give numbers per 100 m?. Tow depths and volumes filtered 
for stations on each cruise are available in a comprehensive 
data report (Houde et al. 1976). If calculated, concentrations 
of fish eggs or larvae at a given station represent the mean 
concentration over the tow depth of that station because 
discrete depths were not sampled. 
Contour charts for zooplankton, fish eggs, and fish 
larvae were produced using the method proposed by 
Simpson (1959). Isopleths of zooplankton concentrations 
were drawn for the 25, 50, 100, 400, and 800 cc/1,000 m? con- 
tours (Fig. 2). Those for fish eggs and larvae were drawn at 
50, 100, 400, 800, and 1,600 under 10 m2 of sea surface (Figs. 
3, 4). 
Temperatures and salinities were obtained at each sta- 
tion by casts of 1.7 liter Niskin bottles equipped with 
reversing thermometers. A mechanical bathythermograph 
also was dropped at each station. An STD (salinity-temper- 
ature-depth) recorder was used on some cruises. Salinities 
from Niskin bottle samples were determined on a salinity 
bridge. 
Analyses of hydrographic data and contour plots of 
these data were provided us by physical oceanographers at 
the State University System of Florida Institute of Ocean- 
ography and the Rosenstiel School of Marine and Atmo- 
spheric Science.” 4 
3State University System of Florida, Institute of Oceanography, St. 
Petersburg, Fla. 1975. Final Report to Bureau of Land Management. 
Contract No. 08550-CT4-16. Compilation and summation of historical and 
existing physical oceanographic data from the eastern Gulf of Mexico, 97 
p. plus 7 appendices. 
‘Hydrographic data from cruises discussed in our report are 
available through the National Oceanographic Data Center, Washington, 
D. C. Data can be retrieved from the MAFLA (Mississippi-Alabama- 
Florida) file. 
