Ryer et al. : Depth distribution, habitat associations, and differential growth of Chionoecetes bairdi 
265 
Mean daily seawater temperatures at 15 m (MLLW) 
for the period from 20 May through 22 August 2011, 
were 8.2°C, 8.1°C, 8.0°C and 7.7°C for Womens, Pil- 
lar, Holiday, and Kalsin, respectively. Mean daily sea- 
water temperature increased though the season (F[i 
3Y5]=7475.2 1, P<0.001) and differed among sites (F^ 
375]=31.95, P<0.001), with mean temperature at Wom- 
ens and Pillar higher than that at Holiday and with 
mean temperature at Holiday higher than at Kalsin 
(Tukey’s HSD: P<0.05). 
Discussion 
Our results illuminate several aspects of the early life 
history and habitat use of recently settled Tanner crab. 
First, data indicate that settlement and metamorpho- 
sis by Tanner megalopae in the northwestern Gulf of 
Alaska begins in April and continue into July. We did 
not sample before May; therefore, our inference that 
settlement begins in April is based on the observation 
that in May nearly all age-0 Tanner crabs at our study 
sites were in the Cl molt stage, indicating that they 
had been on bottom for a relatively short period. By 
July, Cl instars were infrequent in scrape tows and 
were completely absent in August. This recruitment 
schedule resulted in increasing crabs densities from 
May to a peak in July, and it is consistent with the 
pattern of egg hatching (April-May) that has been re- 
ported for both primiparous and multiparous females 
(Stevens, 2003b; Swiney, 2008). Because the timing of 
settlement at our various sites was comparable and the 
4 sites are separated by only tens of kilometers, we 
posit that larval sources for these sites were the same. 
Stevens (2003b) speculated that hatching of Tanner 
eggs in Chiniak Bay is synchronized with spring tides, 
which act to break down dominant costal circulation 
patterns and potentially result in greater larval reten- 
tion within the Chiniak Bay system. 
Depth had a strong influence on crab density, al- 
though this effect varied between embayments. At 
Pillar and Holiday, recently settled crabs were absent 
or scarce from scrape tows at depths <8 m, but they 
became more abundant with increasing depth out to 
23 m. Trawl tows conducted during July 2010 at Pillar 
revealed that crab density was highest at depths of 30- 
35 m, decreasing farther offshore, at depths of 50-80 
m. By August, densities had declined and there was no 
longer a maxima at intermediate depths. In contrast 
with densities at Pillar and Holiday, at Womens and 
Kalsin, crab density was generally highest at depths 
between 10 and 15 m, although there was variability 
among months. We did not conduct trawl sampling at 
either Womens or Kalsin and have no knowledge of 
what crab densities were at depths greater than those 
sampled by the scrape (25 m). 
We suspect that the difference in crab depth distri- 
bution between Pillar and Holiday, on one hand, and 
Womens and Kalsin, on the other, is primarily relat- 
ed to wave energy. Womens is the most protected of 
the study sites, with a narrow entrance and offshore 
islands that dissipate wave energy. Although not as 
protected as Womens, the Kalsin study site is located 
near the head of the Kalsin Bay and, as such, typi- 
cally experiences lower wave action than the sites at 
Pillar and Holiday. Pillar and particularly Holiday are 
more exposed and frequently experience strong wave 
action from the Gulf of Alaska. Although bottom surge 
associated with wave action may directly affect crabs, 
by interfering with settlement, impeding foraging, or 
dislodging crabs from the bottom, we suspect that the 
influence of wave energy on sediment characteristics is 
also a primary factor. 
Because of the inverse relationship between depth 
and wave-induced bottom scour, sites such as Pillar 
and Holiday are characterized by coarse sand in shal- 
low water (depths <10 m), by fine sands or silty sands 
at depths of 10-25 m, and finally by an increasing con- 
tribution of mud at depths >25 m (Stoner et ah, 2007). 
At Womens and Kalsin, as a result of lower wave en- 
ergy, compared with that at other sites, finer silts and 
muddy sediments occur at shallower depths (senior au- 
thor, personal observ. ). For juvenile Tanner crabs, the 
ability to bury themselves in silty or muddy sediments 
is their first line of defense against predators. Similar- 
ly, juvenile flatfish use burial as a predation deterrent 
and preferentially choose sediment in which they can 
easily bury themselves (Stoner and Ottmar, 2003). Fur- 
thermore, fine sediments around Kodiak typically have 
higher organic content than coarse sediment (Stoner 
et ah, 2007). Tanner crabs consume not only a variety 
of infaunal prey, including bivalves, polychaetes, and 
other crustaceans, but also detrital material (Jewett 
and Feder, 1983), which presumably occurs in higher 
concentrations in silty and muddy sediments than in 
coarser sediments. After the spring bloom, diatoms set- 
tle to the bottom and accumulate in low wave-energy 
areas. This flocculent material is readily observed on 
the surface of fine sediment in Womens Bay during late 
spring and summer months (Munk 4 ). 
Juvenile crabs and fishes often seek physically struc- 
tured habitats. Juvenile red king crab and blue king 
crab ( Paralithodes platypus) prefer highly structured 
habitats, which consist of pebbles, cobble, hydroids, 
macroalgae, shell material, etc., where they are less 
vulnerable to predators (Stoner, 2009; Pirtle and Ston- 
er, 2010). Tanner crabs, like snow crabs, generally are 
thought to prefer sandy, silty, and muddy sediments — 
a preference that might be explained by their lack of 
spines that would, if present as in king crabs, inhibit 
them from rapidly burying themselves (senior author, 
personal observ.). However, in beam trawl hauls con- 
ducted during 2009, we observed that recently settled 
Tanner crabs were most common at depths of 15-30 
m, the same depth range where S. sibirica is most 
abundant (Ryer et ah, 2013). On the basis of this re- 
4 Munk, E. 2008. Personal commun. Kodiak Laboratory, 
Alaska Fisheries Science Center, 301 Research Ct., Kodiak, 
AK 99615. 
