Julian and Beeson: Estimates of marine mammal, turtle, and seabird mortality 
279 
Figure 2 
Approximate location of observed incidental marine mammal kills in the driftnet 
fishery during the period July 1990-December 1995, all species. 
three sperm whales, Physeter macrocephalus). Ob- 
served mammal bycatch in this fishery consisted pre- 
dominantly of common dolphins ( 196). Northern el- 
ephant seals, Mirounga angustirostris, were the sec- 
ond most commonly entangled mammal (83). The 
wide variety of mammal species incidentally en- 
tangled, over 25, is notable. 
There was no statistically discernible trend in the 
estimates of total effort during the study period. Co- 
efficients of variation for estimates of marine mam- 
mal incidental kill ranged from 0. 18 to 0.95. The high- 
est observed incidental kill in a single CDFG fishing 
block was in block 918, the southernmost block, which 
had 10% of the total observed mammal bycatch. Wa- 
ters off central California west of 122°W longitude 
also had 10% of the observed 
mammal bycatch. Locations of 
marine mammal mortality from 
observer records indicate that 
mortality was concentrated in 
areas of heavy effort but geo- 
graphically unrestricted (Figs. 1- 
2). On a quarterly basis, observed 
mammal bycatch and swordfish 
catch were correlated (r=0.8), but 
on a per set basis this correlation 
was not evident (r=0.0). This 
change in correlation is perhaps 
due to the inclusion of substan- 
tial effort (quarterly) versus per 
set consideration, i.e. both catch 
and bycatch are related to effort. 
Observed seabird mortality 
was very low in the driftnet fish- 
ery (three kills observed during 
the period). Marine turtle en- 
tanglement was more common, 
with 25 observed (13 released 
alive). All but one of the 15 leath- 
erback entanglements occurred 
north of 35°N latitude. Estimated 
turtle entanglement increased 
from 23 for 1990 to 81 for 1993 and 
then fell to 32 for 1995. 
Setnet fishery 
Mortality estimates in the setnet 
fishery pertain to fishing effort 
targeting halibut or angel shark. 
By law, effort targeting these spe- 
cies required gillnets with 
stretched mesh sizes of 21.6 cm 
(8.5 inches) or greater. This re- 
sulted in the elimination of 665 
out of 8,614 observer records (net pulls) with mesh 
size less than 21.6 cm from the original data because 
they pertained to effort in another fishery. There were 
an additional 179 observed net pulls with no posi- 
tion data. This effort was assigned to geographic 
strata based on the specific vessel’s known fishing 
grounds or was apportioned out to strata according 
to fishing effort from NMFS observer records with 
known positions. 
From 1990 through 1993, estimated effort in the 
halibut and angel shark fishery was fairly stable with 
heavy setnet fishing effort along the southern Cali- 
fornia coast up to Pt. Conception (excluding the re- 
gion from Rocky Pt. to Pt. Bume, where there was 
no commercial fishing, and an area around Newport 
