Tinus Prey preference of Ophiodon elongatus, a top marine predator 
195 
Prey availability 
Prey availability was compared with observed 
prey consumption to evaluate prey preference. 
Lingcod are highly generalized visual preda- 
tors and visual surveys provide an estimate 
of relative prey density within a visual field. I 
evaluated prey availability with dive surveys 44°30'0"N 
in the areas where lingcod were collected for 
gut analyses (Starr et al., 2010). Dive surveys 
were conducted from a relatively small boat 
equipped with standard electronics. Ocean 
conditions had to be sufficiently benign for 
both safe boat handling and diver deploy- 
ment and recovery. Weather conditions were 44°0'0"N 
a limiting factor for dive surveys. In general, 
combined seas (wave and swell height) of less 
than two to three meters and wind velocities of 
less than 20 knots are necessary. Additionally, 
fog and strong currents at times prohibited 
safe dive and boat operation near shallow 
reefs. A single dive survey consisted of a single 43 ° 30 ' 0 "n 
100x4 m visual-count transect (Bohnsack, 
1996) during daylight between 1000 and 1500 
hours. I conducted surveys at site 1 in Janu- 
ary and June 2004, and in June 2005 (three 
surveys total), and at site 2 in January and 
October 2004, and in June (three surveys) and 
September 2005 (six surveys total) (Table 1). 
The exact locations of transects were deter- 43 00 N 
mined haphazardly from the surface by drop- 
ping a weighted line in an area as close as 
possible to where fishing for lingcod occurred 
and where depths were sufficiently shallow so 
that single dive surveys could be completed 
within one scuba dive (<35 m). Visibility was 
variable but was always sufficient to identify fish 
within two meters of the transect line, and fishes 
and invertebrates were approachable. I surveyed 
three basic habitat types within each transect: high- 
relief rocky reef, boulder mixed with cobble, and 
broken shell mixed with sand. I quantified the relative 
abundance of potential prey within the foraging range 
of lingcod, estimating age groups of rockfishes (year 
1, 1-2, 3+) from estimated total lengths. During dives 
I estimated fish lengths by comparing them against 
objects of similar shape and color of known lengths 
at various distances. I observed only adult lingcod on 
rocky reef habitat. Relative prey availability between 
sites 1 and 2 were compared by one-way analysis of 
similarity (ANOSIM; Clark, 1993). The ordination, 
associated tests, and species accumulation curves were 
produced with PRIMER analytical software (vers. 6.1.6, 
PRIMER-E Ltd., Plymouth, U.K. 2 ) by using an included 
ANOSIM method (Clark and Gorley, 2006). Additionally, 
a rank concordance test of prey category abundance was 
2 Mention of trade names or commercial companies is for 
identification purposes only and does not imply endorsement 
by the National Marine Fisheries Service, NOAA. 
124°30'0"W 124WW 123°30'0"W 123 WW 
Figure 1 
Map of study region (inset) and study sites (1 and 2) within 
the Oregon nearshore zone where stomach samples of lingcod 
(Ophiodon elongatus) were collected and dive surveys of potential 
prey were conducted. 
conducted for sites 1 and 2 (Sokal and Rohlf, 1995). For 
comparisons of two groups, t-tests were used unless a 
Shapiro-Wilk test for normality, equal variance, or both, 
failed, in which case a Mann-Whitney rank sum test was 
used. The Michaelis-Menten equation (MME) was used 
to generate species accumulation curves to evaluate how 
quickly the number of new species became asymptotic 
(curve stability) with additional sampling effort (Willott, 
2001; Williams et al., 2007). The beta value for the MME 
represents the number of samples required to detect 50% 
of the total number of species, or groups. 
Dietary composition 
Multiple anglers using lines with a single hook and attrac- 
tor on a chartered recreational fishing vessel in July (19 
and 17 fish in two sampling trips), August (12 fish), and 
September (12 fish) of 2003 (one trip each) collected a 
total of 60 lingcod at site 1. The lingcod collected at Site 
