Frable et al: A new species of Sebastes 
373 
nus. However, this measurement differed only slightly 
significantly in a pairwise comparison (Student’s f-test: 
P=0.03). The posteriormost corner of the opercle ap- 
pears to be pointed in S. diaconus rather than rounded 
in S. mystinus ; however, this shape difference is not 
apparent in juvenile specimens and may best be used 
as a field character rather than as a diagnostic. Se- 
bastes diaconus specimens also possess, on average, 
longer first and second anal-fin spines: anal-fin spine I: 
2. 6-5. 3% (3.9%) SL in S. mystinus versus 3. 3-6. 2% SL 
(4.6% SL) in S. diaconus, anal-fin spine II: 6. 4-9. 9% SL 
(8.3% SL) versus 7.3-12.2% SL (9.5% SL) in S. diaco- 
nus. The slopes of regressions for these spine lengths 
versus SL differ significantly (Figure 6, B and C). 
Collection and dissection of specimens from off the 
Oregon coast between 2009 and 2014 indicate that 
ovary color of breeding females may also differ diag- 
nostically (Hannah et al. 5 ). Ovaries of breeding female 
S. diaconus examined immediately after capture were 
always pink-cream, whereas the ovaries of S. mysti- 
nus were always bright yellow. We did not observe this 
difference in the specimens used for genetic analysis; 
however, those specimens were not freshly deceased at 
the time of dissection. 
Both S. mystinus and S. diaconus can be distin- 
guished from the other potentially co-occurring dark- 
colored Sebastes species, such as S. melanops and S. 
ciliatus, on the basis of morphology and pigmentation. 
The color pattern of S. diaconus is very similar to that 
of some S. melanops', however, S. melanops tends to be 
darker black to brown with irregular gray blotches, 
mottling or speckling. The trunk coloration of S. mys- 
tinus, with large gray blotches, is generally lighter 
than that of S. melanops, and S. melanops is gener- 
ally darker and more irregular in coloration. Addition- 
ally, both S. diaconus and S. mystinus have a smaller 
gape than that of <S. melanops, with maxilla extend- 
ing only to or just beyond the posterior margin of the 
pupil rather than beyond the posterior margin of the 
orbit. Some sources cite anal-fin shape to differentiate 
S. mystinus (and likely S. diaconus): a rounded anal 
fin versus a straight anal fin in S. melanops (Kramer 
and O’Connell, 1995). However, this character does not 
seem to be discrete because variation in fin shape be- 
tween rounded and straight occurs in all 3 species. 
Sebastes diaconus and S. mystinus are distinguished 
from S. ciliatus by having 4 bars of dark pigmentation 
across the head and nape, whereas S. ciliatus usually 
has uniform cephalic coloration (2 faint bars appear be- 
low the orbit occasionally) (Orr and Blackburn, 2004). 
As in S. melanops, the gape of S. ciliatus is larger than 
that of the other 2 species, with the maxilla extending 
to the posterior margin of the orbit. Sebastes ciliatus 
5 Hannah, R. W., D. W. Wagman, and L. A. Kautzi. 2015. 
Cryptic speciation in the blue rockfish (Sebastes mystinus ): 
age. growth and female maturity of the blue-sided rockfish, 
a newly identified species, from Oregon waters. Fish Div., 
Oregon Dep. Fish Wiidl. Inf. Rep. 2015-01, 24 p. [Available 
at website.]. 
is further distinguished from S. mystinus by having a 
more pronounced symphyseal knob, similar to that of 
S. diaconus. Sebastes ciliatus is known to occur mainly 
in Alaska and may range into northern British Colum- 
bia (Orr and Blackburn, 2004), whereas S. mystinus 
and S. diaconus occur farther south (all specimens of 
“S. mystinus ” from Alaska examined were S. ciliatus 
or S. variabilis). Finally, S. mystinus and S. diaconus 
possess 26-27 vertebrae, and S. ciliatus has 28-29 ver- 
tebrae (Orr and Blackburn, 2004). 
Discussion 
Potential mechanisms for segregation 
Although both pre- and postzygotic barriers may sepa- 
rate the 2 species, Burford et al. (2011a) suggested that 
a prezygotic explanation is more likely owing to the 
lack of hybrid individuals and strong Wahlund effect 
in areas of sympatry. Sympatric species of Hexagram - 
mos in the northeastern Pacific show similar patterns 
of segregation (Crow et al., 2010). Prezygotic barriers 
may result generally from variable courtship behavior, 
incompatible reproductive morphological features, dif- 
ferent reproductive timing, segregation of habitat type, 
or a combination of these factors. A least 3 of these 
factors are plausible in the specific case of S. mystinus 
and S. diaconus. 
If differential courtship helps isolate these species, 
the development of species-specific characteristics at a 
size near, or preceding, early estimates of the length of 
first maturity (-150 mm SL in California populations 
of S. mystinus, Wyllie Echeverria, 1987; Love et al., 
2002; Key et al. 6 ; however, see Hannah et al. 5 ) may fa- 
cilitate prezygotic isolation by allowing breeding pairs 
to cue visually and tactilely on differences in body color 
(Fig. 1), in the size of the symphyseal knob (Fig. 6), 
or in the length of the lower jaw. In the only study to 
describe courtship behavior in S. mystinus, individuals 
were observed in Southern California (and, therefore, 
were clearly not S. diaconus) and during courtship the 
male was found to graze the snout of the female with 
its body (Helvey, 1982:fig. 3). The presence or absence 
of a moderately large symphyseal knob and longer low- 
er jaw may act as an indication of species identity at 
this point. Comparison of the mating behavior of both 
species would be an important first step in exploring 
this hypothesis. Additionally, more recent work on both 
species in Oregon waters indicates larger lengths at 
first maturity for both species: around 260 mm fork 
length (FL) for S. mystinus and 270 mm FL for the 
other species (Hannah et al. 5 ). The inclusion of more 
morphometric data from large individuals could eluci- 
date further species-specific sexual characteristics. 
6 Key, M., A. D. MacCall, J. Field, D. Aseltine-Neilson, and K. 
Lynn. 2007. The 2007 assessment of blue rockfish (Se- 
bastes mystinus) in California, 112 p. Pacific Fishery Man- 
agement Council, Portland, OR. [Available at website.] 
