48 
Fishery Bulletin 110(1) 
tests for each phenomenon are independent from one 
another; detection of significant aggregation does not 
imply segregation, nor does detection of segregation 
indicate aggregation. 
Spatial aggregation analysis Nearest neighbor analy- 
sis (NNA), was performed as described by Selkirk and 
Neave (1984) to test for significant spatial aggregation 
of the following segments of the sampled population: 1) 
all halibut; 2) halibut too small to be legally retained 
by the commercial fishery (i.e., “sublegal-size”; <82 cm 
FL); 3) halibut large enough to be legally retained by 
the commercial fishery (i.e., “sublegal-size”; >82 cm FL); 
4) known female halibut; and 5) known male halibut, 
where “known” sex refers only to those individuals that 
were dissected. NNA was performed for all stations 
at which full 600-hook inventories were performed. It 
was the preferred test because the distance between 
events is taken into consideration. In short, NNA tests 
not only whether the tested population segments are 
“interrupted” by one another, but also whether they are 
interrupted by empty space; therefore, it is a true spa- 
tial statistic. NNA generates a scaled nearest neighbor 
distance (NND) that describes the degree of aggregation 
relative to the scale of measurement and compares that 
to transect-specific lower and upper critical limits at the 
Table t 
Number of Pacific halibut (Hippoglossus stenolepis) captured at 25 locations in Alaska and the significance associated with tests 
for spatial aggregation (nearest neighbor snalysis; NNA) and sequential segregation (runs test; RT), on a station-by-station 
basis, for five halibut event-types: all halibut; halibut large enough to be legally retained in the commercial fishery (legal size); 
halibut too small to be legally retained in the commercial fishery (sublegal size); male; and female. Refer to Figure 1 for station 
locations. NNA was performed only where complete information regarding the presence and position of all empty hooks was 
available; “A” indicates significant (P<0.05) spatial aggregation and “R” a random distribution. Individual P-values are listed for 
RT; values in bold indicate P< 0.05. RT results are reported for sublegal-size but not legal-size fish, because the only alternative 
to sublegal is legal. For sex-specific tests, only a proportion of individuals were known-sex because only legal-size fish were dis- 
sected. The final line indicates the percentage of stations at which either significant aggregation (NNA) or segregation (RT) was 
detected for each test category; some form of spatial structure was observed at 60% of all stations. 
Spatial aggregation Sequential segregation 
Station 
halibut 
all 
legal 
sublegal 
male 
female 
sublegal 
male 
female 
1 
25 
A 
A 
A 
A 
R 
0.944 
0.968 
0.992 
2 
62 
R 
R 
R 
R 
A 
0.085 
0.430 
0.542 
3 
96 
R 
R 
R 
R 
R 
0.308 
0.064 
0.667 
4 
39 
R 
R 
R 
A 
R 
0.912 
0.242 
0.992 
5 
49 
A 
R 
R 
R 
R 
0.603 
0.920 
0.187 
6 
44 
R 
A 
R 
R 
R 
0.757 
0.734 
0.401 
7 
97 
R 
A 
R 
R 
R 
0.689 
0.976 
0.682 
8 
74 
R 
A 
R 
R 
R 
0.001 
0.174 
0.764 
9 
102 
R 
R 
R 
R 
R 
0.041 
0.363 
0.087 
A 
34 
— 
— 
— 
— 
— 
0.234 
0.936 
0.110 
B 
107 
— 
— 
— 
— 
— 
0.358 
0.107 
0.017 
C 
43 
— 
— 
— 
— 
— 
0.001 
0.250 
0.051 
D 
106 
— 
— 
— 
— 
— 
0.509 
0.184 
0.849 
E 
49 
- 
— 
— 
— 
— 
0.332 
0.624 
0.050 
F 
99 
— 
— 
— 
— 
— 
0.032 
0.562 
0.040 
G 
137 
— 
— 
— 
— 
— 
0.441 
0.036 
0.726 
H 
62 
— 
— 
— 
— 
— 
0.818 
0.509 
0.342 
I 
73 
- 
— 
— 
— 
— 
0.373 
0.841 
0.107 
J 
31 
— 
— 
— 
— 
— 
0.834 
0.028 
0.031 
K 
208 
— 
— 
— 
— 
— 
0.401 
0.549 
0.332 
L 
66 
— 
— 
— 
— 
— 
0.435 
0.697 
0.535 
M 
33 
— 
— 
— 
— 
— 
0.589 
0.928 
0.818 
N 
80 
— 
— 
— 
— 
— 
0.103 
0.317 
0.026 
O 
76 
— 
— 
— 
— 
— 
0.516 
0.912 
0.347 
P 
85 
— 
— 
— 
— 
— 
0.156 
0.944 
0.689 
% significant 
22.2 
44.4 
11.1 
22.2 
11.1 
16.0 
8.0 
20.0 
