Pearcy and Fisher: Ocean distribution of Alosa sapidissima along the Pacific coast of North America. 
451 
Table 3 
Data on counts of shad ( Alosa sapidissima) in limited-entry groundfish catches, summarized for “summer” (April-October) and 
“winter” (November-March), by state (California, Oregon, and Washington) for as many as eight years, 2002-09. Counts were 
collected by onboard observers. 
State 
Season 
Shad count 
Years 
Tows with 
shad 
All observed 
tows 
% of tows 
with shad 
No. of shad 
per positive tow 
CA 
Summer 
3224 
8 
324 
4940 
6.6 
10 
CA 
Winter 
1035 
8 
37 
2002 
1.8 
28 
OR 
Summer 
22,068 
8 
1056 
11,147 
9.5 
21 
OR 
Winter 
1853 
8 
133 
4150 
3.2 
14 
WA 
Annual" 
9381 
3 
96 
620 
15.5 
98 
WA 
Summer 
14,402 
5 
466 
1969 
23.7 
31 
WA 
Winter 
346 
5 
59 
527 
11.2 
6 
“ For three of eight years only the annual catch off Washington was available. 
Table 4 
Correlation coefficients ( R ) between counts of American shad ( Alosa sapidissima) at Bonneville Dam on the Columbia River and 
frequency of occurrence (FO) and abundance of shad determined from data from the Alaska Fisheries Science Center (AFSC) 
and Northwest Fisheries Science Center (NWFSC) demersal sampling survey over the continental shelf (<200 m depth) from 
44°N-50°N in different years. Tows that were negative for shad were included when calculating abundance. Shown also is the 
correlation ( R ) between average corrected weight of shad for the combined AFSC and NWFSC sampling survey in different years 
(Fig. 7B) and for the count of shad at Bonneville Dam. 
n 
% FO 
Log 10 (catc/i+l) 
Catch 
Weight 
AFSC 
10 years 
0.61, P=0.06 
0.77, P=0.01 
0.73, P=0.02 
-0.77, P<0.001 
NWFSC 
6 years 
0.84, P=0.03 
0.88, P=0.02 
0.89, P=0.02 
Prolonged infection by this parasite may cause mor- 
tality of larger adult fish that spend more years in 
the ocean and may relate to the decrease in size we 
observed in later years (Fig. 7, Table 4). Other possible 
explanations for declining numbers include changes in 
the temperature and river flows that may affect sur- 
vival (Leggett and Whitney, 1972; Crecco and Savoy, 
1986; Petersen et al., 2003), competition for zooplankton 
with forage fishes in the ocean that increase during cool 
ocean conditions (Emmett and Brodeur, 2000), dietary 
overlap with salmonids in the estuary (McCabe et ah, 
1983), and increased predation by seabirds in the Co- 
lumbia River estuary (Petersen et al., 2003). 
Conclusions 
In conclusion, American shad along the Pacific coast of 
North America were mainly confined to the continental 
shelf and highest catches occurred from Oregon north- 
ward into British Columbia and near San Francisco Bay. 
Shad were bigger in deeper water. No evidence was found 
for large-scale seasonal migrations as reported along 
the Atlantic coast. The abundance of shad was highly 
correlated with the counts of shad passing Bonneville 
Dam on the Columbia River, and negatively correlated 
with the survival of coho salmon. 
Acknowledgments 
We are grateful to NOAA’s Alaska Fisheries Science 
Center and Northwest Fisheries Science Center’s West 
Coast Groundfish Survey for providing their databases 
for shad. We especially thank B. Horness and M. Wilkins 
for their cooperation. We also thank many others who 
generously provided data: M. Bellman and J. Majewski 
(NWFSC) and J. Olson (Pacific State Marine Fisheries 
Commission) for data obtained from bottom trawl sur- 
veys and observers in the limited entry trawl fisheries, 
J. Davidson and J. Fargo (Department of Fisheries and 
Oceans, British Columbia) for data from British Colum- 
bia, M. Karnowski and N. Hurtado (Oregon Department 
of Fish and Wildlife) for Oregon data, and T. Larinto 
(California Department of Fish and Game) for California 
data. We also thank D. Sweetman (California Depart- 
