262 
Fishery Bulletin 95(2), 1 997 
mensely from year to year and within time scales on 
the order of weeks. Figure 1 shows the range in vari- 
ability of the northern perimeter of the Loop Current 
over the period studied. Not only do the size and north- 
south position of the front vary, but stability, length, 
shape, and intensity of the frontal system vary as well. 
Major changes in position may occur within time 
scales of weeks. In 1986 and 1987, the Loop Current 
was positioned south of 26°N during the first leg of 
the survey. In both years the front pushed north be- 
fore the second leg. In 1987 it moved almost 100 km 
north in 2 weeks. In other years, 1983, 1984, and 
1988, the Loop Current was already at 27°N when 
the survey began. Over the years studied, the length 
of the northern perimeter of the Loop Current front 
ranged from 880 km in 1988 to 182 km in 1986 (as 
measured along the 22°C isotherm in the area 
sampled). Length of this front in each year is sum- 
marized in Table 2. However, length and position in 
itself says little about the frontal interface and bio- 
logical response to hydrodynamic processes. 
Larval C. pauciradiatus were most numerous in 
both the eastern and western Gulf of Mexico in 1983. 
In this year the Loop Current had pushed north in 
Table 2 
Length of the Loop Current as measured at the 22° iso- 
therm at 100 m and number of C. pauciradiatus larvae 
caught at grid stations (under 10 m 2 ). 
Date 
Leg 
Length in 
kilometers 
No. of larvae 
under 10 m 2 
1983 
647 
1,445 
1984 
332 
258 
1986 
1 
182 
179 
1986 
2 
299 
124 
1987 
1 
564 
170 
1987 
2 
681 
44 
1988 
1 
697 
219 
1988 
2 
880 
307 
the winter and despite shedding a ring, had been 
stable for almost 6 months prior to the survey. Plank- 
ton displacement volumes were also high, averaging 
100 mL/1,000 m 3 in the eastern Gulf and 130 mL/ 
1,000 m 3 in the western Gulf. 
By remaining in a relatively stable position, the 
biological components have time to respond to physi- 
