—oe = ere en ee Ee eee 
ON J FMAM J JAS OND JSF MAM 
1973 1974 
DATES OF CRUISES 
MEAN NUMBER 
Figure 10.—Mean fish larvae abundance for 12 eastern Gulf of Mexico 
cruises, 1972-74. 
plankton volume was observed in June-July 1973, along with 
similar decreases in ichthyoplankton abundance. There was 
a recovery in abundance by August 1973. Mean abundance 
of fish eggs was less than 300 under 10 m? of sea surface 
during fall-winter but exceeded 550 during the spring-sum- 
mer months. Fish larvae mean abundance was less than 350 
under 10 m? in fall-winter, increasing to more than 500 in 
spring-summer. 
North-South Distribution 
Zooplankton and ichthyoplankton were examined for 
each cruise in relation to latitude. The study area was arbi- 
trarily divided into halves at lat. 27°15'N (Fig. 1). Catches 
north and south of this line were compared to determine if 
abundance differed greatly between the two areas. 
Mean abundance of eggs and larvae and zooplankton 
volumes usually were greatest north of lat. 27°15'N (Table 
3; Figs. 11, 12). Only fish larvae had a higher pooled mean 
abundance (number under 10 m?) in the southern half of the 
area for all cruises combined. The contour charts of 
organism distribution (Figs. 2-4) do not readily show that 
mean abundance tended to be higher north of lat. 27°15'N 
because of the patchy nature of the distributions. 
Mean zooplankton volumes were highest in the north- 
ern sector for 7 of the 12 cruises (Table 3; Fig. 11). Four of 
the five exceptions occurred during spring and summer 
cruises. Mean fish egg abundance was highest in the north 
during 6 of the 12 cruises (Table 3; Fig. 12). The pooled 
mean abundance of eggs for all cruises was highest for the 
Table 3.—Summary of plankton, fish eggs, and fish larvae data for each cruise, after dividing the cruise area 
into northern (above lat. 27°15'N) and southern (below lat. 27°15 N) portions. Tabulated values are means. 
Values in parentheses are the numbers of stations that were sampled. 
Plankton volume Fish eggs Fish larvae 
(ec/1,000 m*) (No./10 m’) (No./10 m?) 
Cruise Month North South North South North South 
1972 
GE 7202 & 76.9 65.9 722.3 221.8 162.9 297.1 
8B 7201 Feb. (10) (15) (13) (15) (13) (15) 
GE 7208 May 103.6 111.0 497.2 617.8 406.7 418.1 
(10) (18) (10) (20) (10) (20) 
GE 7210 June 142.2 352.5 656.4 469.8 340.3 342.1 
(4) (9) (4) (9) (4) (9) 
IS 7205 Sept. 218.1 158.1 764.2 464.0 7164.4 863.2 
(13) (21) (13) (21) (13) (21) 
IS 7209 Nov. 132.1 108.0 166.2 205.2 206.6 377.9 
(23) (26) (24) (26) (24) (26) 
1973 
IS 7303 Jan. 164.4 143.1 451.3 307.0 219.3 374.3 
(23) (27) (24) (27) (24) (27) 
IS 7308 May 220.9 188.4 845.2 898.1 477.2 744.4 
(24) (25) (24) (25) (24) (25) 
IS 7311 June-July 108.2 131.9 415.5 481.4 466.6 633.0 
(25) (26) (25) (25) (25) (26) 
IS 7313 Aug. 255.9 141.5 909.2 492.4 621.9 541.2 
(25) (25) (25) (25) (25) (25) 
IS 7320 Nov. 145.1 118.1 150.7 175.1 288.9 401.0 
(25) (26) (25) (26) (25) (26) 
1974 
IS 7405 Mar. 80.0 101.5 191.1 391.1 60.4 50.2 
(19) (17) (16) (16) (16) (16) 
IS 7412 May 157.3 278.8 926.1 884.5 497.2 545.8 
(22) (21) (23) (19) (23) (19) 
Pooled means 157.1 150.3 545.4 463.4 380.5 486.9 
(223) (256) (226) (225) (226) (255) 
14 
