Objectives of Cruise:
The object of this cruise was to conduct studies on how hydrographic and/or
atmospheric events affect the growth and survival of pollock larvae in
Shelikof Strait. Eddies are common circulatory features generated in Shelikof
Strait which may entrain pollock under optimal or sub-optimal conditions
for growth. Sampling operations were planned within and outside of an eddy
containing pollock larvae. Another process study was to examine the effects
of storms upon the conditions for growth and survival by pollock larvae
if one occurred during the cruise.
Summary of Operations:
ADCP Lines 0
ADCP backtrack "L" 0
CTD casts 49
Bongos, 60 cm 77
Bongos, 20 cm 4
Tucker trawls 14
MOCNESS tows 5
Live tows 2
Methot trawls 0
Mooring deployment 0
Mooring recoveries 0
Satellite tracked buoy deployment 5
Loran-C drifters deployed 0
Loran-C drifters recovered 0
Chlorophyll samples 164
Nutrient samples 190
Microzooplankton samples 95
Plankton samples 95
Predator samples 0
Stomach samples 0
Pollock samples 0
Pollock larvae samples 1861
Pollock egg samples 0
Summary of Cruise:
The cruise began with an occupation of 48 stations located between FOCI
grid lines 153 and 174 from 3-5 May, 1998. A total of 44 60 cm bongo net
tows were conducted to determine the distribution and abundance of pollock
larvae (Figure 1). Four satellite-tracked drifters were deployed, two of
them in an area of high larval abundance, in order to detect circulation
features in the sea valley. SeaCat CTD profiles from the bongo tows were
contoured at 40 m depth, revealing significant structure within the sea
valley and the intrusion of warmer, more saline water at the exit region
of the sea valley (Figures 2 and 3)
The next phase of operations was occupation of 17 stations for the El Nino
study, four of them at Line 8 and 13 in the sea valley and exit region
of Shelikof Strait (Figure 4). Plankton sampling was conducted with 20
cm and 60 cm bongo nets and Tucker trawls (Table 1). Microzooplankton,
chlorophyll, nutrients, and irradiance were sampled during 14 CTD casts
taken at these stations.
The final phase of operations was a process study of an eddy in Shelikof
Strait from 7-10 May. Satellite-tracked drifter trajectories indicated
the presence of an eddy feature in the sea valley (no figure yet. PMEL
can include one if they want to). A 28 x 48 km grid composed of 30 stations
was chosen to be coincident with this feature. Twenty one stations were
occupied for MOCNESS, Tucker, and 60 cm bongo tows (Figure 5). CTD casts
were conducted at selected stations to profile water column structure and
collect microzooplankton at stations in and out of the eddy. A storm event
occurred on 8 May, suspending sampling operations for approximately 4 hours.
Temperature profiles from CTD casts taken at the same station before and
after the storm indicated an increase in the mixed layer depth (Figure
6). Sampling for post-storm effects was conducted at selected stations
for the remainder of the cruise
Table 1. 4MF98 Cruise Summary of operations.
Table 2. 4MF98 Cruise Sampling summary statistics.
Figure 1. 4MF98 Bongo tow stations. Solid contours indicate larval abundance
(individuals per 10 m2).
Figure 2. 4MF98 Temperature profiles from Bongo tow stations contoured
on 40 m depth.
Figure 3. 4MF98 Salinity profiles from Bongo tow stations contoured on
40 m depth.
Figure 4. El Nino stations occupied during 4MF98.
Figure 5. Eddy stations occupied during 4MF98.
Figure 6. Temperature profiles from station F3 before and after storm event
during eddy study.