276 
Fishery Bulletin 96(2), 1998 
Table 4 
Observed (obs) and estimated (est) cetacean, pinniped, turtle, and seabird mortality, stratified by year, in the California halibut 
and angel shark set gillnet fishery during the NMFS Observer Program, July 1990-December 1995. Estimates of total mortality 
are reported to the nearest individual. Estimated coefficients of variation (CV) are included in parentheses; ( — ) indicates CV was 
undefined. Effort and estimates for 1990 pertain to the third and fourth quarters only. 
Year 
1990 
1991 
1992 
1993 
1994 
1995' 
Estimated days effort 
Observed days effort 
Percent observer coverage 
Observed trips effort 
3,041 
158 
5.2% 
406 
7,171 
706 
9.8% 
2,233 
5,577 
698 
12.5% 
2,123 
5,680 
875 
15.4% 
2,642 
1,943 
150 
7.7% 
547 
2,257 
0 
0% 
0 
obs 
est 
CV 
obs 
est 
CV 
obs 
est 
CV 
obs est CV 
obs 
> est 
CV 
obs 
est 
CV 
Harbor porpoise 
4 
37 
(0.56) 
5 
38 
(0.47) 
6 
48 
(0.46) 
2 
13 (0.64) 
1 
14 
(0.96) 
— 
14 
(0.64) 
Common dolphin 
(unknown stock) 
0 
0 
(— ) 
0 
0 
(— ) 
2 
15 
(0.65) 
0 
0 (— ) 
0 
0 
(— ) 
(— ) 
Unidentified cetacean 
0 
0 
(— ) 
0 
0 
(— ) 
1 
8 
(0.92) 
0 
0 (— ) 
0 
0 
(— ) 
— 
— 
(— ) 
California sea lion 
67 
867 
(0.22) 
142 
1,842 
(0.16) 338 
3,418 
(0.28) 
237 
1,942 (0.13) 
109 
905 
(0.15) 
— 
724 
(0.08) 
Unidentified sea lion 
1 
23 
(0.96) 
6 
109 
(0.53) 
7 
54 
(0.34) 
0 
0 (— ) 
0 
0 
(— ) 
— 
— 
(— ) 
Harbor seal 
30 
411 
(0.23) 
42 
601 
(0.23) 
90 
1,204 
(0.47) 
71 
475 (0.13) 
23 
227 
(0.33) 
— 
228 
(0.13) 
Northern elephant seal 
13 
119 
(0.40) 
3 
30 
(0.55) 
7 
51 
(0.35) 
11 
70 (0.27) 
2 
16 
(0.66) 
— 
47 
(0.29) 
Unidentified pinniped 
2 
42 
(0.79) 
3 
30 
(0.55) 
7 
50 
(0.39) 
7 
32 (0.90) 
1 
8 
(0.94) 
— 
17 
(0.83) 
Sea otter 
3 
27 
(0.53) 
0 
0 
(— ) 
0 
0 
(— ) 
0 
0 (— ) 
0 
0 
(— ) 
— 
— 
(— ) 
Green/black turtle 
0 
0 
(— ) 
0 
0 
(— ) 
1 
8 
(0.92) 
1 
6 (0.90) 
0 
0 
(— ) 
— 
2 
(0.61) 
Loggerhead turtle 
0 
0 
(— ) 
0 
0 
(— ) 
1 
8 
(0.92) 
0 
0 (— ) 
0 
0 
(— ) 
— 
— 
(— ) 
Leatherback turtle 
0 
0 
(— ) 
0 
0 
(— ) 
0 
0 
(— ) 
0 
0 (— ) 
1 
8 
(0.94) 
— 
— 
(— ) 
Unidentified turtle 
0 
0 
(— ) 
0 
0 
(— ) 
0 
0 
(— ) 
1 
6 (0.90) 
0 
0 
(— ) 
— 
2 
(0.61) 
Pacific loon 
0 
0 
(— ) 
1 
13 
(0.94) 
0 
0 
(— ) 
0 
0 (— ) 
0 
0 
(— ) 
— 
— 
(— ) 
Common loon 
0 
0 
(— ) 
2 
22 
(0.68) 
1 
7 
(0.92) 
0 
0 (— ) 
0 
0 
(— ) 
— 
— 
(— ) 
Unidentified loon 
1 
23 
(0.96) 
4 
48 
(0.48) 
0 
0 
(— ) 
0 
0 (— ) 
0 
0 
(— ) 
— 
— 
(— ) 
Western grebe 
0 
0 
(— ) 
1 
8 
(0.92) 
3 
23 
(0.70) 
1 
6 (0.90) 
0 
0 
(— ) 
— 
2 
(0.61) 
Unidentified grebe 
0 
0 
(— ) 
0 
0 
(— ) 
4 
31 
(0.92) 
1 
6 (0.90) 
0 
0 
(— ) 
— 
3 
(0.83) 
Double-crested cormorant 
2 
18 
(0.93) 
0 
0 
(— ) 
1 
7 
(0.92) 
0 
0 (— ) 
1 
8 
(0.94) 
— 
— 
(— ) 
Brandt’s cormorant 
2 
41 
(0.78) 
36 
409 
(0.44) 
14 
279 
(0.67) 
3 
13 (0.64) 
2 
16 
(0.66) 
— 
3 
(0.43) 
Pelagic cormorant 
1 
33 
(0.98) 
1 
8 
(0.92) 
0 
0 
(— ) 
0 
0 (— ) 
0 
0 
(— ) 
— 
— 
(— ) 
Unidentified cormorant 
9 
132 
(0.45) 
15 
450 
(0.92) 
9 
68 
(0.30) 
5 
32 (0.40) 
0 
0 
(— ) 
— 
10 
(0.35) 
Common murre 
142 1,300 
(0.21) 
289 2,201 
(0.27) 
292 
2,333 
(0.28) 
137 
879 (0.32) 
20 
284 
(0.29) 
— 
967 
(0.32) 
Unidentified alcid 
1 
9 
(0.93) 
0 
0 
(— ) 
0 
0 
(— ) 
0 
0 (— ) 
0 
0 
(— ) 
— 
— 
(— ) 
Unid. seabird 
0 
0 
(— ) 
2 
22 
(0.68) 
3 
23 
(0.53) 
1 
6 (0.90) 
0 
0 
(— ) 
— 
3 
(0.83) 
1 Estimates for 1995 were based on stratified rates from 1993 results. 
when a trip was chosen to be observed, the NMFS 
technician observed all net pulls during the trip. A 
single net per day was set at dusk and retrieved be- 
fore dawn. Net pulls and effort-days were equiva- 
lent units for this fishery. For estimation of inciden- 
tal kill, the collection of observed trips during a year 
was treated as a random sample (an approximation) 
and a ratio estimator was used. Trips were treated 
as sampling units and the number of days per trip 
was treated as an auxiliary variable. Stratification by 
quarter of year or set location was not used for yearly 
estimates because previous exploratory analysis had 
not found this type of stratification to be significantly 
related to incidental kill. Yearly estimates, 1991-95, 
were calculated for each species observed entangled 
(“Results” section). Estimates for 1990 correspond 
only to the last two quarters of that year. Formulae 
from Cochran (1977) were used for estimating kill 
rate, r , total incidental kill, m , and variances: 
