Lamkin: The Loop Current and abundance of larval Cubiceps pauciradiatus 
261 
ing can be seen in 1984 when there were two warm 
anticyclonic rings separated by a cold cyclonic ring 
at 26.5°N, 93.5°W (Fig. 3). Cubiceps pauciradiatus 
were distributed primarily around the edge of this 
cyclone and the leading edge of the incoming warm- 
core ring to the east. 
In 1988 the situation was similar. Most C. 
pauciradiatus larvae were found west of 89°W. Al- 
though at 100 m, the Gulf waters west of the Missis- 
sippi River seem fairly homogeneous, at 200 m there 
was considerable structure evident in the water col- 
umn (Figs. 8 and 10): in leg 1, the edge of a warm- 
core ring was evident at 26.5°N, 93°W with cooler 
water to the east (Fig. 9); by leg 2 there was a cold- 
core ring centered at 26.5°N, 93°W, approximately 
A 
Station number 
Figure 1 6 
Transect in 1988 south along 86° west, where (A) depicts depth 
of 15°C, 20°C, and 22°C isotherm and SST, (B) indicates SST 
and C. pauciradiatus at biological stations, and (C) shows 
total larvae under 10 m 2 (bongo) and neuston for the same 
stations as B. 
83 km in diameter as defined by the 14°C isotherm 
at 200 m (Fig. 11). These cold-core cyclonic rings may 
have a life span of 6 months or more, and it is not 
unusual for there to be a weak temperature signa- 
ture in the upper 100 m (Hamilton, 1992). In both 
legs of the 1988 survey west of 89°W, C. pa uciradiatus 
were distributed around the edges of the two cold- 
core rings and in the cooler waters to the east of these 
features. 
The basic pattern was the same in other years, but 
oceanographic features could not be as well defined 
as they were in 1984. First, the large anticyclonic 
rings often pass south of the survey area and thus 
are incompletely sampled. Second, after 1984, the 
number of stations in the western Gulf was reduced, 
and therefore the physical features could not be 
as densely sampled as they were the first two 
years. For a species such as C. pauciradiatus , the 
western Gulf of Mexico may at times provide a va- 
riety of frontal habitats, such as those that oc- 
curred in 1984. In other years the oceanographic 
conditions may be less favorable. 
Abundance 
This year-to-year change in the number and posi- 
tion of mesoscale oceanographic features occurred 
in both the eastern and western Gulf of Mexico, 
both within years and between years; the abun- 
dance of C. pauciradiatus changed similarly. (Fig. 
18). Cubiceps pauciradiatus larvae were abundant 
in 1983 but declined thereafter. These changes in 
abundance are the result of natural mortality be- 
cause there is no fishery for this species; owing to 
their pelagic nature, they are taken only occasion- 
ally as bycatch by longliners. 
lies and Sinclair (1982) and Sinclair (1988) ar- 
gued that the existence of a population “depends 
on the ability of the larvae to remain aggregated 
during the first few months of life,” and that abso- 
lute abundance was a function of the physical 
oceanographic processes of the spawning areas. 
Population abundance depended on the horizon- 
tal size scale of the physical system underlying 
larval retention. Rothschild et al. (1989) suggested 
that the physical environment underlies the pro- 
cesses acting on recruitment variability. Cubiceps 
pauciradiatus do not spawn at a specific geographic 
location as do herring populations, but instead have 
spawning sites that appear to be tied to dynamic 
oceanographic features, namely to the Loop Current 
and its associated rings. Larvae are spawned at the 
frontal zones regardless of geographic position. 
The physical oceanographic processes acting on 
the spawning sites of C. pauciradiatus change im- 
