280 
Fishery Bulletin 96(2), 1998 
Beach; Fig. 3). There was also effort in the Morro 
Bay and Monterey Bay areas, as well as in some ar- 
eas around the Channel Islands. Estimated effort for 
1994 decreased sharply because gillnet fishing was 
banned inside the area within 5.6 km (3 n mi) of shore 
from Pt. Arguello south to the U.S. -Mexico border. 
During each year, observed mammal bycatch peaked 
during the second quarter, as did estimated total ef- 
fort (Tables 4 and 5). California sea lions were the 
most frequently killed mammal (899), followed by 
harbor seals (257), northern elephant seals (36), and 
then harbor porpoises (18). Fourteen of the eighteen 
observed harbor porpoise mortalities occurred in the 
northern portion of Monterey Bay; three others were 
observed in the Monterey Bay area, and the remain- 
ing mortality was in the Morro Bay area (none was 
released alive). There were 1,025 seabird mortali- 
ties: 1 Pacific loon, Gavia pacifica, 5 common loon, 
Gavia immer, 5 unidentified loon, Gavia spp., 6 west- 
ern grebe, Aechmophorus occidentalis, 5 unidentified 
grebe, Podiceps spp., 4 double-crested cormorant, 
Phalacrocorax auritus, 70 Brandt’s cormorant, 
Phalacrocorax penicillatu, 2 pelagic cormorant, 
Phalacrocorax pelagicus, 38 unidentified cormorant, 
Phalacrocorax spp., 880 were common murre, Uria 
aalge, 1 unidentified alcid, Alcidae, and 8 unidenti- 
fied seabirds, Aves. Of the common murre mortali- 
ties, 99% occurred north of Pt. Conception — predomi- 
nantly in the Morro Bay area (Fig. 4). All other bird 
species were entangled south of Pt. Conception with 
few ( 12) exceptions (Tables 4 and 5). The six observed 
marine turtle kills were separated either in time or 
location, but four occurred offshore of Ventura. Lo- 
cations of observer-recorded effort and bycatch indi- 
cated that no fished area was 
entirely free of mammal mortal- 
ity due to gillnets (Figs. 3 and 
5). Estimated total marine 
mammal mortalities for the 
setnet fishery rose from approxi- 
mately 1,500 in 1990, to 4,800 in 
1992, and fell to 1,300 in 1994. 
Discussion 
Data co!!ection and effort 
estimation 
Although many resources were 
used to obtain accurate esti- 
mates of mortality and fishing 
effort, several significant diffi- 
culties were encountered in 
data collection and estimation 
of total effort. Difficulties in 
implementing the sampling 
plan included availability of ob- 
servers and type of notification 
given to fishermen. Generally, 
observers were hired by the Pro- 
gram according to how much 
fishing effort was expected. Be- 
cause this aspect of the program 
was well monitored, little sea- 
sonal bias was expected. Previ- 
ous exploratory analysis has in- 
dicated that pre- and post- 
notification is a significant fac- 
tor for the setnet fishery (Per- 
kins et al. 5 ). In this fishery, out 
of 2,588 days of observations, 
Figure 3 
Approximate location of observed sets in the setnet fishery during the period July 
1990-December 1995. 
