Skates (family Rajidae) are oviparous and lay tough, thick-walled eggs. At least some skate species lay their eggs in spatially restricted nursery grounds where embryos develop and hatch (Hitz, 1964; Hoff, 2007). After hatching, neonates may quickly leave the nursery grounds (Hoff, 2007). Egg densities in these small areas may be quite high. As an example, in the eastern Bering Sea, a site <2 km2 harbored eggs of Alaska skate (Bathyraja parmifera) exceeding 500,000/km2. All skate nursery grounds have been

identified over soft sea floors (Lucifora and García, 2004; Hoff, 2007)

Cochrane, Guy

Love, Milton S.

Schroeder, Donna M.

Snook, Linda

York, Anne

English

Aquatic Commons

471
Skates (family Rajidae) are ovipa-
rous and lay tough, thick-walled eggs. 
At least some skate species lay their 
eggs in spatially restricted nursery 
grounds where embryos develop and 
hatch (Hitz, 1964; Hoff, 2007). After 
hatching, neonates may quickly leave 
the nursery grounds (Hoff, 2007). Egg 
densities in these small areas may 
be quite high. As an example, in the 
eastern Bering Sea, a site <2 km2 har-
bored eggs of Alaska skate (Bathyraja 
parmifera) exceeding 500,000/km2. 
All skate nursery grounds have been 
identified over soft sea floors (Lucifora 
and García, 2004; Hoff, 2007). 
In 2005, while conducting f ish 
surveys using a manned submers-
ible over natural reefs in the Santa 
Barbara Channel, southern Califor-
nia, we found an area of high skate 
egg density, located on the edge of 
Hueneme Submarine Canyon. Until 
that date, we had rarely observed 
skate eggs in our southern California 
surveys. For example, in 362 other 
submersible dives, in waters between 
18 and 365 m deep and encompass-
ing 395 km of transects over a wide 
range of habitats, we had observed 
All their eggs in one basket:  
a rocky reef nursery for the longnose skate  
(Raja rhina Jordan & Gilbert, 1880)  
in the southern California Bight
Milton S. Love (contact author)1
Donna M. Schroeder2
Linda Snook1
Anne York3
Guy Cochrane4
Email address for M. S. Love: love@lifesci.ucsb.edu
1 Marine Science Institute
 University of California
 Santa Barbara, California 93106 
2 Minerals Management Service
 770 Paseo Camarillo
 Camarillo, California 93010
3 6018 Sycamore Avenue
 Seattle, Washington 98107
4 United States Geological Survey
 400 Natural Bridges Dr.
 Santa Cruz, California 95060
Manuscript submitted 14 February 2008.
Manuscript accepted 13 May 2008.
Fish. Bull. 106:471–475 (2008).
The views and opinions expressed  
or implied in this article are those  
of the author and do not necessarily  
reflect the position of the National  
Marine Fisheries Service, NOAA.
only 44 skate eggs. In 2006, we re-
turned to the Hueneme Submarine 
Canyon site and examined this nurs-
ery ground more closely. 
Material and methods
We conducted the study on 24 October 
2006 on a feature located on the west 
side of Hueneme Submarine Canyon 
(Fig. 1). The study area is a rocky 
outcrop located at approximately 
34°02.3ʹN, 119°18.1ʹW. Rocks exposed 
at the site are likely a submerged 
extension of the Miocene volcanic 
rocks that make up Anacapa Island 
(Vedder et al., 1986). These rocks form 
gently north-dipping strata of volca-
nic flows, breccias, conglomerates, or 
tuffs. Faults and joints observed on 
the Island, and from the submersible 
at the site, increase rock resistance 
against gravitational failure. Bathy-
metric high spots, such as that of the 
skate nursery grounds, are north-
dipping volcanic-layer outcrops that 
have not collapsed because of the local 
strength of the rock substrate in com-
bination with the buttressing struc-
ture formed by faulting and jointing. 
Several diminutive taxa, including 
squarespot (Sebastes hopkinsi), sword-
spine (Sebastes ensifer), and pygmy 
(Sebastes wilsoni) rockfishes, domi-
nate the fish fauna. Among structure-
forming invertebrates, the volcanic 
outcrop also harbors high densities of 
barrel, flat, foliose, and vase sponges, 
gorgonian corals, the large anemone 
Metridium sp., basketstars, and the 
deep-water antipatharian coral Anti-
pathes dendrochristos. 
This survey was conducted aboard 
the small (4.8 m in length) research 
submersible Delta (Delta Oceano-
graphics, Ventura, CA). During the 
dive, we tried to maintain a constant 
distance within 1 meter of the sea-
floor and a constant speed between 
0.5 and 1.0 knot. The survey was 
made during daytime hours and we 
documented the egg density of long-
nose skates in that area with an ex-
ternally mounted hi-8 video camera 
positioned above the middle viewing-
porthole on the starboard side of the 
submersible. The scientific observer 
conducted a belt-transect survey 
through this same starboard viewing 
port, verbally recording onto the vid-
eotape all skate eggs observed within 
2 m of the submersible. 
Navigation fixes (latitude and lon-
gitude coordinates) were received 
from a Thales GeoPacific Winfrog 
ORE Trackpoint 2 USBL (Fugro-
Pelagos, San Diego, CA) system at 
two-second intervals, and a Winfrog 
DAT file was generated for the re-
search dive. Distance and duration 
between f ixes were calculated to 
obtain a point-to-point submersible 
speed; errant navigation fixes were 
removed when speed exceeded 2 m/
sec. The navigation fixes were then 
smoothed by using a nine-point mov-
ing average, and transect length was 
472 Fishery Bulletin 106(4)
Figure 1
(Lower map) The general location (black box) of the longnose skate (Raja 
rhina) nursery ground on the edge of Hueneme Submarine Canyon, south-
ern California Bight. (Upper map) The area within the black box in the 
lower map has been enlarged and the white box represents the nursery 
ground within that area; the other white lines in the upper map denote 
transects followed by the Delta submersible. Transects outside the box 
did not contain skate eggs.
estimated from the total distance between the smoothed 
points. Transect length was divided by transect dura-
tion to obtain an average transect speed. The length of 
individual habitat patches was estimated from average 
speed of the submersible during each transect.
During the survey, the observer verbally noted each 
egg or egg aggregation, estimated the number of eggs 
in the aggregation, and whether the eggs were living 
or dead. We assumed that yellow or green, shiny and 
full eggs still contained embryos and that those that 
were dark, deflated, and heavily biofouled were empty. 
It should be noted that in other studies dark egg cases 
have been found to still hold living embryos and thus 
our estimates of viability may be low. At that time, the 
observer also described whether the egg(s) had been 
laid on rock, cobble, sand, or on such structure-forming 
animals as sponges and gorgonians. Lastly, in order to 
identify the species using this nursery ground, five eggs 
were collected.
In the laboratory, the abiotic habitats of the nurs-
ery ground were also characterized from the survey 
videotape. We defined these habitats using the differ-
ent categories of substrata and standard geological 
definitions defined by Yoklavich et al. (2000). In order 
473NOTE Love et al.: A rocky reef nursery for Raja rhina in the southern California Bight 
Table 1
Expected and actual (observed) longnose skate (Raja 
rhina) egg numbers by habitat type. Observations were 
made from the Delta submersible, eastern Santa Barbara 
Channel, October 2006. Habitat types were rock ridge 
(R), boulder (B), cobble (C), and sand (S). A two-character 
code was assigned each time a distinct change in substra-
tum type was noted. The first character of the code rep-
resents the substratum that accounted for at least 50% 
of the survey patch, and the second character represents 
the substratum accounting for at least 20% of the patch. 
Expected numbers were calculated by assuming that 
the density of skate eggs was not different across habi-
tat types. Expected numbers were rounded to the near-
est integer. Habitats are ordered from most to least area 
surveyed (m2).
 Area surveyed Expected Actual
Habitat  (m2) egg numbers  egg numbers
RR 2219.0 1513 1721
RC 208.6 142 13
RB 76.1 52 2
RS 37.6 26 4
CR 10.4 7 0
Table 2
Number of observations (from the Delta submersible) of 
each size of longnose skate (Raja rhina) egg cluster (no. of 
eggs in cluster) in the nursery ground on the edge of Hue-
neme Submarine Canyon, October 2006, categorized by 
habitat type. Habitat types were rock ridge (R), boulder 
(B), cobble (C), and sand (S). A two-character code was 
assigned each time a distinct change in substratum type 
was noted. The first character of the code represents the 
substratum that accounted for at least 50% of the patch, 
and the second character represents the substratum 
accounting for at least 20% of the patch.
 Number of observations
Number of 
eggs in cluster RB RC RR RS
  1 0 13 145 4
  2 1 1 38 0
  3 0 0 23 0
  4 0 0 9 0
  5 0 0 6 0
  6 0 0 4 0
  8 0 0 1 0
 10 0 0 6 0
 12 0 0 1 0
 20 0 0 3 0
 24 0 0 1 0
 25 0 0 1 0
 30 0 0 4 0
 40 0 0 2 0
≥50 0 0 8 0
Total 1 14 1722 4
of decreasing particle size, these substrata were the 
following: rock ridge (R), boulder (B), cobble (C), and 
sand (S). A two-character code was assigned each time 
a distinct change in substratum type was noted. The 
first character of the code represented the substratum 
that accounted for at least 50% of the survey patch, 
and the second character represented the substratum 
accounting for at least 20% of the patch. Thus, RB rep-
resented a patch composed of at least 50% rock ridge 
and at least 20% boulders. 
Results
In the nursery area, we surveyed 2551.8 m2 of sea floor 
in waters between 125 and 151 m depth (average depth 
139 m) and with bottom temperatures ranging from 
9.1° to 10.1°C (Fig. 1). The study site was primarily 
composed of high-relief rocky ridge (RR), along with 
lesser amounts of rock-cobble (RC), rock-boulder (RB), 
rock-sand (RS), and cobble-rock (CR) (Table 1). 
We observed 1740 eggs, of which 238 were character-
ized as intact. As far as we could ascertain, all of the 
eggs observed were those of the longnose skate (Raja 
rhina Jordan & Gilbert, 1880) (Fig. 2). We observed a 
range of egg states, from those that appeared to be new-
ly deposited to ones that had almost disintegrated. The 
eggs did not appear to have been randomly laid over the 
substrata because significantly more eggs were observed 
over the highest relief areas (habitat RR) than over the 
other habitats (chi-square=13.1, df=4, P=0.01) (Table 1). 
Eggs also appeared to be clumped in their distributions. 
Although many of the eggs were deposited singly, we 
observed several aggregations with 300 or more eggs 
(Table 2). Most of the eggs were laid on rocks and rela-
tively few on such invertebrates as sponges, deep-water 
corals, and sea anemones (Table 3). However, the eggs 
that were laid on invertebrates were significantly more 
likely to be intact than were those on rocks (intact on 
invertebrates=95%, 95% confidence interval, 83–99%; 
intact on rock=12%, 95% confidence intervals 10–13%; 
chi-square=225, df=1, P<0.0001). 
We estimated the total number both of all eggs and 
only those that were intact. We assumed that our sur-
vey transect path demarcated the outer perimeter of the 
nursery grounds because we noted eggs all along the 
transect path. Using densities of both all eggs (0.68183/
m2) and only intact ones (0.093 eggs/m2) and the area 
bounded by our transects (27,878 m2), we estimated 
that there were 19,008 eggs in the nursery grounds, of 
which 2593 were intact. 
Discussion
According to our many years of visual observations, 
skate nursery grounds are uncommon in southern 
474 Fishery Bulletin 106(4)
Table 3
Numbers of intact and empty longnose skate (Raja rhina) 
eggs on abiotic (rocks and fishing line) and biotic sub-
strata, observed from the Delta submersible, eastern 
Santa Barbara Channel, October 2006.
 Number of Number of
Substrata eggs intact eggs empty
Abiotic
 Rocks 197 1500
 Fishing line 1 0
 Total abiotic 198 1500
Biotic
 Sponges 35 1
 Gorgonians 3 1
 Corals 1 0
 Sea anemones 1 0
 Total biotic 40 2
Figure 2
(A) An intact longnose skate (Raja rhina) egg, (B) an aggregation of eggs (see arrows), many of which are 
covered in fine sediment.
California waters (at least at depths <360 m), and 
like that observed by Hoff (2007) the nursery site 
that we observed was relatively small in area because 
visual transects conducted within 1 km over similar 
habitats yielded no eggs (Fig. 1). However, whereas 
previously described skate nursery grounds lay on soft 
sea f loors, the study site was a rocky outcrop sitting 
on the edge of a submarine canyon. This reef appears 
to be a relatively high-energy area (little sediment 
was found on the substrata) with high densities of 
structure-forming invertebrates. Because so few visual 
surveys have been conducted on the Pacific Coast, we 
do not know if the nursery ground that we observed 
was atypical or if there are other such grounds in 
Pacific Coast waters.
Longnose skates do not randomly lay their eggs over 
the sea floor. Among the various habitat types in the 
nursery area, rock ridges contained statistically more 
eggs and these eggs were often found in clumps. It 
would be expected that eggs laid on the highest relief 
would be most exposed to currents and arguably less 
475NOTE Love et al.: A rocky reef nursery for Raja rhina in the southern California Bight 
available to at least some predators than eggs lying on 
low substrata.
Skate reproduction, with its emphasis on highly spa-
tially restricted nursery grounds, appears to be an 
example of “predator swamping” (Van Montfrans et al., 
1995). In addition, the observation that intact skate 
eggs are more likely to be found on sponges than on 
bare rocks may reflect an antipredator strategy by 
adult skates. Boring snails, including those in the fam-
ilies Muricidae, Naticidae, and likely Ranellidae, are 
major predators on skate eggs and predation rates in 
nursery grounds can reach 40% or more (Lucifora and 
García, 2004; Hoff, 2007). Snails of all of these families 
are found in southern California waters (McLean and 
Gosliner, 1993). Although they could not identify them 
in their trawl-based study, Lucifora and Garcia (2004) 
speculate that microhabitat differences in egg place-
ment could lead to variable protection from predators. 
It is possible that sponges, with their spicule-rich skel-
etons and potent chemical defenses, may deter snails 
or other egg predators.
The Bering Sea skate nursery ground that Hoff 
(2007) investigated was notable for having 1) high 
currents and productivity and 2) the presence of only 
mature fish. The nursery site of our study was com-
posed of high-relief rocks situated on the edge of a 
submarine canyon. Because of the relative absence of 
fine particulates on the substrata and the presence of 
unusually high densities of sponges, gorgonians, and 
other structure-forming invertebrates, we surmised 
that this nursery ground is bathed by high currents 
and is likely quite productive. In addition, we observed 
no juvenile or adult skates, providing additional evi-
dence for Hoff ’s (2007) hypothesis that newly hatched 
skates quickly leave their nursery grounds.
In the context of this nursery ground much about 
longnose skate reproduction remains unknown. For 
instance, we do not know when the eggs are laid, their 
incubation period, nor the fate of the juveniles. We do 
not know how many skates use this habitat and how 
they migrate. Lastly we note that the extent to which 
female skates seek out sponges is unknown. However, 
if skate eggs deposited on sponges are at a competitive 
advantage, damage to these invertebrate communities 
(i.e., through destructive fishing practices) and the 
subsequent increase in egg predation, would have a 
detrimental effect on skate reproductive success. 
Acknowledgments
D. Ebert identified the skate eggs and J. Hoff provided 
a great deal of useful background information on skate 
nursery grounds and provided us with a copy of his 
Ph.D. thesis. Also very useful were the discussions with 
D. Cadien on sponge and snail ecology. We thank the 
pilots of the research submersible Delta, J. Lilly and 
C. Ijames, and the crew of the research vessel Velero for 
support in the field.
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All their eggs in one basket: a rocky reef nursery for the longnose skate (Raja rhina Jordan & Gilbert, 1880) in the southern California Bight

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All their eggs in one basket: a rocky reef nursery for the longnose skate (Raja rhina Jordan & Gilbert, 1880) in the southern California Bight

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