Sturdevant et al.: Feeding habits, prey fields, and potential competition of Theragrc chalcogrcimma and Clupea pallasi 
487 
1 600 t 
1400-- 
0 ) 
CD 
Summer Autumn 
□ 
Barnacle larvae 
Large calanoids 
Small calanoids 
Larvaceans 
Euphausiids 
| Decapod larvae 
Bryozoan larvae 
□ 
M 
Cladocera 
Chaetognaths 
Gammarld amphipods 
^ Other 
Malacostraca 
□ Cnidarians and 
ctenophorans 
□ Hyperiid amphipods 
[S3 Gastropods 
Figure 2 
Seasonal zooplankton density and composition by principal taxa in 
Prince William Sound, Alaska 1995, Zooplankton were collected in ver- 
tical tows of conical nets having 303-pm mesh in summer and 243-mm 
mesh in autumn. 
resented in both seasons. Only allopatric fish qualified in 
the summer of 1995, but both allopatric and sympatric fish 
qualified in the autumns of 1994 and 1995 (Table 2). In 
summer, 18 of the 62 trawl hauls caught sufficient sam- 
ples of either species. 4 Allopatric YOY pollock were col- 
lected at 12 stations in the central region and allopatric 
YOY herring were collected at one central and one north- 
eastern station in summer (Fig. 1). In autumn, 11 of the 
25 trawl hauls (total 14 in November 1994, 3 11 in October 
1995 4 ) caught sufficient samples of either species, and 36% 
of these caught sympatric fish in the northeastern region. 
Allopatric species were collected in different years: the 
allopatric pollock in November 1994 were collected in the 
southwestern region and the allopatric herring in October 
1995 in the central region (Table 2). The remainder of pol- 
lock and herring caught did not meet our study criteria for 
age, number, or composition of fish per haul. 
The magnitude and relative species composition of the 
catch varied considerably, and sampling time and depth 
differed between seasons. In summer, the number of pol- 
lock caught in trawls varied by two orders of magnitude 
between stations, from 22 to 1689 per haul (Table 2). Her- 
ring catches in the alternative gear, dip net or beach seine, 
were of similar magnitude. In autumn, from 14 to 4156 
pollock or herring were caught per trawl haul; the catches 
were not evenly partitioned between the species in sym- 
patric hauls. Similar numbers of pollock and herring were 
caught at some sympatric stations, whereas, at others, 
the number per species caught was an order of magni- 
tude greater. In summer, approximately half the samples 
were collected in the morning, half in the afternoon, and 
only one was collected at dusk (-22:00). The pollock were 
caught most often at 50-80 m trawl depths (Y=60 m) off- 
shore and the herring were caught at the surface and near 
shore. In autumn, sympatric samples were collected in 
darkness (approximately 22:00-23:00) at a mean depth of 
30 m in bays, whereas allopatric samples were collected 
during daylight and in deeper water (Table 2). 
