Seasonal Abundance and Distribution of 
Zooplankton, Fish Eggs, and Fish Larvae in the 
Eastern Gulf of Mexico, 1972-74’ 
EDWARD D. HOUDE and NICHOLAS CHITTY? 
ABSTRACT 
Zooplankton volumes and abundance of fish eggs and fish larvae were determined for stations on 12 
cruises to the western Florida continental shelf. Contour charts of zooplankton volumes and of 
ichthyoplankton abundance are presented. A marked seasonality was observed for zooplankton and 
ichthyoplankton, highest zooplankton volumes and ichthyoplankton abundance occurring during May 
through September. Zooplankton volumes were highest and spawning by fishes most intense in the northern 
half of the study area (north of lat. 27°15'N). Fish larvae abundance (number under 10 m? of sea surface) 
was highest at stations deeper than 50 m. Simple correlations among biological variables showed fish egg 
abundance-zooplankton volumes and fish egg abundance-fish larvae abundance to be positively correlated on 
most cruises. No clear relationships were observed between abundance or concentration of biological 
variables and temperature or salinity. 
INTRODUCTION 
A fisheries assessment survey of sardinelike fishes in 
the eastern Gulf of Mexico was carried out from 1971 to 1974 
to estimate spawning biomass from the seasonal abundance 
and distribution of planktonic eggs and larvae (Houde 1973, 
1974, in press). A total of 12 cruises was completed during 
1972-74 from which both plankton samples and hydrographic 
data were collected. Zooplankton abundance and the abun- 
dance of both fish eggs and fish larvae were examined to de- 
termine which areas of the western Florida continental shelf 
(Fig. 1) were highly productive with respect to plankton and 
which areas might be important spawning areas for fishes. 
Abundance of these organisms was examined seasonally and 
in relation to temperature and salinity in the eastern Gulf. 
Most previous reports on plankton abundance from the 
western Florida shelf area included few sampling stations or 
were not carried out long enough to determine seasonality of 
production. Hopkins (1973) recently has reviewed plankton 
investigations in the eastern Gulf. Plankton abundance from 
shelf waters on a transect west of Charlotte Harbor (lat. 
26°30'N) in 1946-47 was reported by King (1949). Arnold 
(1958) summarized results of plankton-ichthyoplankton col- 
lections made throughout the Gulf of Mexico in 1951-53. His 
collections included 63 stations from the western Florida 
shelf that were sampled quantitatively. Soviet-Cuban 
fishery investigations in 1963-64 included some determina- 
tions of total plankton biomass from most parts of the Gulf of 
Mexico. These data were summarized by Bogdanov et al. 
(1968) and Khromov (1969). Recently, Austin and Jones 
(1974) reported on the physical oceanography and plankton 
biomass relationship on the Florida Middle Ground, a 
‘productive shelf area located northwest of Tampa Bay. 
Their data represented monthly observations from June 
1969 through August 1970 and included a single fixed station 
at lat. 28°30'N, long. 84°14’W, as well as three to five 
1 Contribution from the Rosenstiel School of Marine and Atmospheric 
Science, University of Miami, Miami, FL 33149. 
? Division of Biology and Living Resources, Rosenstiel School of 
Marine and Atmospheric Science, University of Miami, 4600 Ricken- 
backer Causeway, Miami, FL 33149. 
stations on a transect along lat. 28°30'N. Although earlier 
reports are incomplete in many respects, and sometimes 
incomparable due to collecting gear differences, they do 
offer a basis for comparison with our plankton distribution 
data which give more complete seasonal and areal coverage 
of the eastern Gulf. 
Identification of organisms was limited to the broad 
categories of zooplankton, fish eggs, and fish larvae. Thus, 
our results were used only in a relative sense, to define 
areas of high or low productivity on the western Florida 
shelf. The eggs and larvae of clupeid fishes were identified 
and future papers will describe their distribution and 
abundance, as well as estimates of stock abundance based on 
them (Houde in press). Results published here will be useful 
when considering possible effects of man’s activities in the 
FLORIDA 
28° 
1] northern sector 
27°15 southern sector 
a, 86° 84° 82° go° 
Figure 1.—Chart of eastern Gulf of Mexico ichthyoplankton survey area. 
Dots indicate stations. 
