Pm. Stegmann et Ja. Yoder, VARIABILITY OF SEA-SURFACE TEMPERATURE IN THE SOUTH-ATLANTIC BIGHT ASOBSERVED FROM SATELLITE - IMPLICATIONS FOR OFFSHORE-SPAWNING FISH, Continental shelf research, 16(7), 1996, pp. 843
We examined full-resolution (1 x 1 km) satellite images of sea-surface
temperature (SST) over five consecutive years (1981-1986) covering th
e Atlantic menhaden (Brevoortia tyrannus) recruitment period (November
-April) in the SABRE (South Atlantic Eight recruitment experiment) stu
dy site. The results of our image rime series indicated two processes
which could be possible mechanisms for the onshore transport of fish l
arvae into coastal regions. One is the influx of warm Gulf Stream wate
r that oscillates in and out of the Carolina Bays. These oscillations
occurred throughout the study period over distances of 20-40 km and on
time-scales as short as two days. The other is a tongue of relatively
cold water located adjacent to the Virginia coast that moved southwar
d and penetrated into Onslow Bay between January and March. Previous s
tudies showed that Atlantic menhaden preferentially spawn in 18-22 deg
rees C waters on the outer shelf. On the assumption that the 18 degree
s C isotherm (18DI) indicates where high larval abundance may occur, w
e used AVHRR-SST imagery to track the onshore-offshore movement of the
18DI along a transect extending onshore-offshore in Onslow Bay. Owing
to seasonal warming and cooling, this isotherm was always found close
st to the coast in early November, reached maximum offshore displaceme
nt by January/March, and then moved onshore again in April/May. Our re
sults also showed that the position of this isotherm can move offshore
or onshore in a matter of a few days. An important influence and poss
ibly the major cause of the higher frequency displacements of the 18DI
are Gulf Stream meanders or filaments moving through Onslow Bay. Our
estimates of onshore isotherm speeds as determined from satellite SST
ranged from 2 to 25 cm s(-1) and are within the same order as those ca
lculated by physical models or larval age determinations. If the onsho
re pulses of warm Gulf Stream water are indeed a mode by which menhade
n larvae are transported cross-shelf, then the use of satellite-based
observations to determine their frequency and onshore extent, as done
in the present study, is a useful tool to study variations in fish rec
ruitment.