Julian and Beeson: Estimates of marine mammal, turtle, and seabird mortality 
283 
In the driftnet fishery, the wide variety of ceta- 
cean species killed is attributable to the large geo- 
graphic range of the mammals, nonselectivity of gear, 
and the amount and location of fishing effort. Ceta- 
cean bycatch in the driftnet fishery is greater and 
more diverse than for the setnet fishery because area 
of driftnet effort contains more diverse habitat than 
the area of setnet fishery. Data from recent years 
show that effort is increasing off the coasts of north- 
ern California and Oregon, and beginning in 1995, 
the state of Oregon allowed 10 driftnet fishing ves- 
sels to land fish in a limited number of Oregon ports 
(landings were not permitted prior to 1995). Yearly 
effort is expected to continue at 3,500-4,500 sets per 
year. The mortality rate averaged 0.11 (SD=0.25) 
mammals/set (or day) during the observer program, 
from January 1991 through December 1995; initial 
effort in 1990 was omitted because of low coverage 
rate. Incidental seabird catch has been almost non- 
existent and there is currently no reason to expect 
an increase. The amount of seabird by catch contrasts 
with the Japanese driftnet fishery in which many 
seabirds are incidentally caught (Ito et al., 1993), in 
part, because swordfish drift nets are extended be- 
low the surface, typically 11 m. The Japanese salmon 
drift nets, set at the surface, would naturally en- 
tangle more seabirds. Migration of seabirds in rela- 
tion with the fishing season and effort location may 
play a role in seabird bycatch. No trend is evident in 
the estimated yearly turtle entanglements. Regard- 
ing cetaceans, at this time there are 10 species that 
are being entangled at a rate greater than potential 
biological removal (PER) according to the U.S. Pa- 
cific Marine Mammal Stock Assessment Report 
(Barlow et al., 1995). The impact of driftnet mortal- 
ity on individual cetacean stocks is examined in this 
report. In order to reduce entanglement of cetaceans, 
NMFS, in conjunction with driftnet fishermen and 
the California Department of Fish and Game, have 
implemented a Pacific Cetacean Take Reduction 
Team whose goal is to decrease cetacean bycatch. 
Over the past five years, estimated effort in the 
halibut and angel shark setnet fishery was fairly 
stable until 1994, when a restrictive California voter 
proposition banned gillnet fishing within three miles 
of the coast from Pt. Arguello south to the US-Mexico 
border. Before 1994, effort in this fishery varied sub- 
stantially during the year. Since early 1994, gillnet 
fishing has occurred mainly off Ventura, Morro Bay, 
and Bodega Bay (Fig. 3). There has also been some 
effort off Imperial Beach, near the US-Mexico bor- 
der. Effort north of Pt. Arguello has not been affected 
by the 1994 resolution and is not expected to change. 
Pinniped mortality in the setnet fishery was sub- 
stantial during 1990-95. More pinnipeds were ob- 
served entangled in the setnet fishery than the 
driftnet fishery because effort coincided substantially 
with pinniped habitat. In particular, setnet effort 
around the Channel Islands and near the ports San 
Pedro, Ventura, and Santa Barbara frequently en- 
tangled pinnipeds. Effort in the driftnet fishery re- 
sults in less overall pinniped entanglement by vir- 
tue of this effort being placed farther from shore. It 
is interesting to note, however, that entanglement of 
northern elephant seals in the driftnet fishery is sub- 
stantially greater than for the setnet fishery because 
these mammals typically range greater distances 
from shore than do sea lions and harbor seals. Esti- 
mates of California sea lion and harbor seal mortal- 
ity are expected to decline and then stabilize because 
of reduced effort south of Pt. Arguello. 
Similarly, we expect the number of seabirds killed 
south of Pt. Conception to decline, because setnet 
effort was been pushed offshore 5.6 km (3 n mi) by 
regulation. There has been more bycatch of birds in 
the set fishery because the entangled species are typi- 
cally resident and their habitat overlaps substan- 
tially with setnet effort. Driftnet effort results in few 
seabird entanglements because drift nets are re- 
trieved after an overnight soak (set nets typically 
soak 24 hours) and drift nets are typically extended 
over 11 m below the surface. In addition, mesh size 
for drift nets is almost three times greater than mesh 
size for set nets, resulting in fewer entanglements. 
The mortality of common murres entangled in set 
nets is expected to continue at the same level. Murre 
were primarily observed entangled in the Monterey 
Bay area. The nets in this area are set on the bottom 
in typically 55.8 m (30.5 frn, SE=0.2 fm) of water. 
Using a chi-square (j£ 2 ) test, we determined that there 
is some dependency between entanglement and soak 
time of the net (P<0.05). Odds of entanglement more 
than doubled for an increase from 1 to 2 days of soak 
time (reasonable checking for confounding factors 
was done). Turtles will continue to be entangled in 
the setnet fishery, but the number and rate of en- 
tanglement will be unknown because observer cov- 
erage in this fishery has been eliminated. 
Acknowledgments 
Special thanks are given to Al Jackson and Rand 
Rasmussen of NMFS for assistance with observer 
data and to NOAA observer- technicians and port co- 
ordinators who carry out the California gillnet moni- 
toring programs. Tim Price kindly provided the sam- 
pling design description. Jay Barlow, Karin Forney, 
Doyle Hanan, Mark Lowry, and Peter Perkins re- 
viewed this report and provided valuable input. Help- 
