Spawning, egg development, 

and early life history dynamics 

of arrowtooth flounder 

(Atheresthes stomias) 

in the Gulf of Alaska

Deborah M. Blood

Ann C. Matarese

Morgan S. Busby

NOAA Professional Paper NMFS 7

U.S. Department 

of Commerce

May 2007
U.S. Department

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National Oceanic

and Atmospheric

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National Marine 

Fisheries Service

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for Fisheries

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NOAA Professional Paper NMFS 7

Spawning, egg development, and early life 

history dynamics of arrowtooth flounder 

(Atheresthes stomias) in the Gulf of Alaska

Deborah M. Blood

Ann C. Matarese

Morgan S. Busby

May 2007

U.S. Department of Commerce

Seattle, Washington
Suggested reference

Blood, Deborah M., Ann C. Matarese, and Morgan S. Busby. 2007. Spawning, egg 

development, and early life history dynamics of arrowtooth flounder (Atheresthes 

stomias) in the Gulf of Alaska. NOAA Professional Paper NMFS 7, 28 p.

Online dissemination

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to cause directly or indirectly the advertised product to be used or purchased 

because of this NMFS publication. 
Abstract—Arrowtooth flounder (Atheresthes stomias) has the highest biomass 

of any groundfish species in the Gulf of 

Alaska, is a voracious predator of age 

1 walleye pollock (Theragra chalcogramma), and is a major component in the 

diet of Steller sea lions (Eumetopias jubatus). Owing to its ecological importance 

in the Gulf of Alaska and the limited 

information available on its reproduction, interest has intensified in describing its spawning and early life history. 

 A study was undertaken in late January–

February 2001–2003 in the Gulf of Alaska 

to obtain information on adult spawning 

location, depth distribution, and sexual 

maturity, and to obtain fertilized eggs 

for laboratory studies. Adults were found 

200–600 m deep east of Kodiak Island 

over the outer continental shelf and upper slope, and southwest along the shelf 

break to the Shumagin Islands. Most ripe 

females (oocytes extruded with light pressure) were found at 400 m and most ripe 

males (milt extruded with light pressure) 

were found at depths ≥450 m. Eggs were 

fertilized and incubated in the laboratory 

at 3.0°, 4.5°, and 6.0°C. Eggs were reared 

to hatching, but larvae did not survive 

long enough to complete yolk absorption 

and develop pigment. Eggs were staged 

according to morphological hallmarks 

and incubation data were used to produce 

a stage duration table and a regression 

model to estimate egg age based on water 

temperature and developmental stage.

 Arrowtooth flounder eggs (1.58–1.98 

mm in diameter) were collected in ichthyoplankton surveys along the continental shelf edge, primarily at depths ≥400 m. 

Early-stage eggs were found in tows that 

sampled to depths of ≥450 m. Larvae, 

which hatch between 3.9 and 4.8 mm 

standard length, increased in abundance 

with depth. Observations on arrowtooth 

flounder eggs and early-stage larvae were 

used to complete the description of the 

published partial developmental series.

1

Spawning, egg development, and early 

life history dynamics of arrowtooth flounder 

(Atheresthes stomias) in the Gulf of Alaska

Deborah M. Blood

Ann C. Matarese

Morgan S. Busby

Resource Assessment and Conservation Engineering Division

Alaska Fisheries Science Center

National Marine Fisheries Service

National Oceanic and Atmospheric Administration

7600 Sand Point Way NE 

Seattle, WA 98115-6349

E-mail address: Debbie.Blood@noaa.gov

Introduction

The worldwide commercial, recreational, and ecological importance 

of flatfishes warrants our efforts to 

understand factors that determine 

recruitment success or failure. The 

early life history of these fishes is primary to that understanding. Knowing 

whether eggs are demersal or pelagic 

helps us to know if human activities 

such as trawling or dredging will affect a species’ reproduction. Knowledge of the timing of spawning and 

duration of incubation are necessary 

in the assessment of prey availability 

(Wilderbuer et al., 2002). Locations 

and depths where eggs are spawned 

determines when and where they will 

hatch, and to where the larvae will 

disperse prior to assuming a benthic 

lifestyle (Bailey and Picquelle, 2002). 

Learning about the early life history 

of a fish species could be considered 

the first step to discerning its role in 

its environment.

Arrowtooth flounder, Atheresthes stomias (Jordan and Gilbert, 1880), a 

large, piscivorous member of the righteyed flounder family Pleuronectidae, 

has dramatically increased in biomass 

since the mid-1970s and, at present, 

is the most abundant groundfish in 

the Gulf of Alaska (GOA) (Mundy 

and Hollowed, 2005; Turnock et al., 

2005). Estimated biomass of arrowtooth flounder has increased six-fold 

since 1970 and the projected biomass 

of age 3+ fish for 2006 is 2,140,170 

metric tons (Turnock et al., 2005). 

Larval abundance also increased notably in the 1990s relative to the previous decade (Matarese et al., 2003; 

Doyle, 2004). Despite the abundance 

of arrowtooth flounder, it has limited 

commercial value due to poor quality 

of the flesh and the Pacific halibut 

(Hippoglossus stenolepis) bycatch that 

occurs with bottom trawling (Cullenberg, 1995). However, recent processing discoveries have allowed incidentally-caught arrowtooth flounder 

to be used for marketable products, 

including surimi and frozen fillets 

(Greene and Babbitt, 1990; Porter et 

al., 1993). 

Although of limited commercial 

importance, arrowtooth flounder is 

ecologically important at higher trophic levels in the GOA food web. For 

example, it has been identified as a 

significant food source for Steller sea 

lions (Eumetopias jubatus), occurring 

in their diet 21–35% of the time in the 

area around Kodiak Island (Sinclair 

and Zeppelin, 2002). Whereas walleye pollock (Theragra chalcogramma) 

has consistently been the greatest 

component of the Steller sea lion diet 

in the area around Kodiak Island, arrowtooth flounder may be replacing 

other secondary food sources. Also, 
2 Professional Paper NMFS 7

an increasing trend in the natural mortality of walleye 

pollock at young ages has been attributed to the growing impact of arrowtooth flounder predation (Bailey, 

2000; Hollowed et al., 2000).

Arrowtooth flounder ranges from Cape Navarin, Russia, to the Aleutian Islands in the eastern Bering Sea, 

throughout the Gulf of Alaska and Northeast Pacific 

Ocean southward to central California off San Simeon, 

and along the east coast of Kamchatka and the Commander Islands. It is found on soft, muddy bottom 

12–900 m deep, usually offshore at depths of 50–300 m, 

and has been reported to attain lengths of 86 cm and 

weights of 7.7 kg (Mecklenburg et al., 2002). At present, most life history information is restricted to adults. 

Hirschberger and Smith (1983) collected arrowtooth 

flounder in spawning condition along the outer continental shelf east of Kodiak Island from March to August, 

but others have concluded that spawning occurs during 

fall and winter (Pertseva-Ostroumova, 1961; Novikov, 

1974; Rickey, 1995). Rickey (1995) determined that arrowtooth flounder are synchronous batch spawners off 

the Washington coast. Zimmermann (1997) examined 

maturity and fecundity of arrowtooth flounder in the 

GOA and described maturity states from macro- and 

microscopic (histological) observations. Details of 

spawning behavior, timing, and depth distribution in 

the GOA are unknown. 

Information on the early life history of arrowtooth 

flounder in the GOA is incomplete. Eggs and earlystage larvae are unknown. Larvae >6 mm standard 

length (SL) are easily distinguished from other flatfish 

larvae in the GOA by morphological characters and pigment patterns; in addition, arrowtooth flounder larvae 

possess preopercular and supraocular spines that are 

unique among pleuronectids in the GOA (Matarese et 

al., 1989). Arrowtooth flounder larvae cannot currently 

be distinguished from its congener Kamchatka flounder 

(Atheresthes evermanni; Jordan and Starks, 1904) in areas 

where adults co-occur (Bering Sea and Aleutian Islands). Kamchatka flounder is rare in the GOA; only 25 

adults have been identified in Alaska Fisheries Science 

Center (AFSC) GOA surveys since 19901, and there is no 

data to support that it spawns in the area. Arrowtooth 

flounder larvae have been collected in the GOA February through June (Matarese et al., 2003); the smallest 

larvae identified thus far (6–7 mm SL, preflexion) have 

been collected in greatest numbers over the outer continental shelf and upper slope during February–April, 

suggesting mid- to late winter deep water spawning. 

These small larvae have been collected in lesser numbers through May. From analysis of juvenile otoliths and 

1

 Orr, James. Personal commun. 2006. National Marine Fisheries 

Service, Alaska Fisheries Science Center, 7600 Sand Point Way NE, 

Seattle, WA 98115-6439.

AFSC ichthyoplankton data, Bouwens et al. (1999) estimated mean length at hatch to be 8–9 mm SL, 15 April 

as the mean date of hatch, and 8 September as the mean 

date of settlement for arrowtooth flounder in the GOA; 

however, their mean length at hatch was based on the 

most common length class collected during standard 

ichthyoplankton tows (≤200 m depth) and larval stage 

of development was not determined. Sea valleys and 

troughs in the GOA appear to be transport pathways 

for onshore movement of arrowtooth flounder and Pacific halibut larvae (Bailey and Picquelle, 2002). They 

found higher abundances of larger larvae in troughs 

and sea valleys and in nearshore shelf areas, particularly 

when El Niño/Southern Oscillation (ENSO) events 

occurred in the equatorial Pacific. Survival of larvae 

is often a recruitment bottleneck for commercial species; perhaps the nature of the transport pathways for 

arrowtooth flounder larvae enables them to more successfully negotiate this critical stage than other species. 

The distribution and abundance of eggs, larvae, and 

juveniles, and transport mechanisms to nursery areas, 

are largely unknown. Identifying areas where eggs and 

newly hatched larvae are found is important to verify the 

hypothesis of Bailey and Picquelle (2002) and may aid 

in understanding why this species dominates the GOA 

groundfish assemblage.

More complete life history data are needed to assess 

the impact of arrowtooth flounder on the GOA ecosystem. The outlook for commercial and forage fish that 

make up its diet, and for Steller sea lions that prey on 

them, could be significantly altered if arrowtooth flounder continues to increase in abundance or experiences 

a drastic decline. More early life history information is 

also needed to assess the potential impacts of climate 

and ecosystem shifts. For example, Anderson and Piatt 

(1999) suggest the 1977 shift to a warm regime has favored earlier-spawning fishes due to earlier zooplankton 

availability. Information on the timing, location, and 

dynamics of arrowtooth flounder spawning and early 

life history is needed to assess this hypothesis and to 

understand how factors affecting arrowtooth flounder 

might impact the GOA trophic web. 

The primary objective of this study included identifying timing, duration, and location of arrowtooth 

flounder spawning in the GOA, and collecting spawning adults to obtain fertilized eggs for incubation studies. The morphological development of arrowtooth 

flounder eggs was described and temperature-specific 

equations were generated to estimate duration of development time to specific egg stages. Data were also collected on adult maturity states, sex ratios, mean length 

and percent maturity for each sex at different depths, 

and physical characteristics of the water column where 

spawning adults were collected. Other objectives included locating yolk-sac larvae to help describe their 
3

onshore transport pathways. The ichthyoplankton 

surveys also provided preliminary data on abundance 

and distribution (geographic and vertical) of eggs and 

larvae. Yolk-sac and transforming stages, not previously 

described, were illustrated to complete the developmental series.

Methods

Historical ichthyoplankton data, used to determine 

times and locations where the smallest arrowtooth 

flounder larvae (6–7 mm SL) have been collected, were 

obtained from surveys conducted by the AFSC Recruitment Processes Program. Data for cruises prior to 1988 

were found in Dunn and Rugen (19892), and those 

from 1989 to 2003 in the AFSC ichthyoplankton cruise 

database (Rugen 20003

). Ichthyoplankton data are accessible in the AFSC larval fish database (ICHBASE). 

Surveys

The first cruise was conducted 28 January–5 February 2001 aboard the NOAA ship Miller Freeman in the 

GOA from just southeast of Kodiak Island to Sanak 

Island (Fig. 1A). Both bottom trawl and oblique bongo 

sampling were conducted day and night over the outer 

continental shelf and upper slope to depths of approximately 200, 400, and 600 m; an additional trawl at 500 m 

was added to locate more ripe fish. The upper slope was 

steep and the locations where gear could be towed at the 

three target depths were very close to one another, so 

most stations were clustered in groups of three. Opportunistic sampling occurred in shallow water (64–137 m) 

closer to Kodiak and Sanak Islands when conditions 

were too rough to sample further offshore. 

A second survey was conducted 3–9 February 2002, 

aboard the Miller Freeman, in the same general area 

as in 2001 (Fig. 1B). This cruise was restricted to bottom trawls (day and night) to collect adult arrowtooth 

flounder at locations where high abundances of eggs 

and larvae were found in 2001. Based on preliminary 

results of the 2001 cruise, stations were added at 500 

m to maximize opportunities to collect equal mixes of 

mature and ripe males and females.

The third cruise was conducted 13–22 February 2003. 

Designed primarily to survey a grid of stations to assess ichthyoplankton east and south of Kodiak Island 

2

 Dunn, J. R., and W. C. Rugen. 1989. A catalog of Northwest and 

Alaska Fisheries Center ichthyoplankton cruises 1965–1988. Alaska 

Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, 7600 Sand Point Way 

NE, Seattle WA 98115-6439. AFSC Proc. Rep. 89-04, 87 p.

3

 Rugen, W. C. 2000. Alaska Fisheries Science Center Ichthyoplankton Cruise Database, [Online]. Available: http://161.55.120.152/

icc/openframe.cfm (access date – August 2006).

(Fig. 2), the station plan allowed for opportunistic deep 

water sampling (day and night oblique bongo tows to 

depths of 200, 400, and 600 m) to collect arrowtooth 

flounder eggs and early-stage larvae. Once the survey 

grid was completed, bottom trawls were conducted, 

beginning southwest of Kodiak Island along the upper 

slope where we had collected spawning adult arrowtooth flounder during the previous two winter cruises. 

Trawl depths were 200, 300, 400, and 500 m.

Adult arrowtooth flounder were collected with a 

nylon Nor’eastern bottom trawl (Stark and Clausen, 

1995). A sample of up to 40 fish from each trawl (519 

total fish) in 2001 was sexed and measured to the nearest 1.0 cm fork length (FL); gonads were examined 

for macroscopic maturity states. Maturity categories of 

immature, mature, ripe, or spent were assigned to each 

individual examined. Maturity categories and criteria 

follow Zimmermann (1997) with some additions: 1) 

mature category for males further defined by being 

able to extrude only a drop of milt, 2) addition of ripe 

category for males defined as being able to extrude milt 

with light pressure, and 3) addition of mature category 

for females defined as ovaries large and filled with small 

eggs, but none able to be extruded. Up to four males 

and four females in each maturity category (18 total 

fish) were weighed individually, and their gonads were 

removed, weighed to the nearest 0.01 g, and preserved 

for histological examination. Microscopic examinations 

were used to verify visually-assigned maturity states, following Zimmermann (1997). In 2002, up to 181 fish 

from each trawl (599 total fish) were sexed, measured 

to the nearest 1.0 cm FL, weighed to the nearest 0.1 g, 

and examined macroscopically for maturity state. Adult 

data recorded in 2003 were numbers and lengths of fish 

used for spawning. At trawl stations where spawning 

arrowtooth flounder were found in 2001–2003, a SeaBird SBE-19 Seacat system was attached to the tow cable 

above the bongo net frame or a Sea-Bird 911 plus CTD 

system was deployed separately to collect conductivity, 

temperature, and depth (CTD) profiles.

Egg fertilization, incubation, and sampling 

Eggs stripped from ripe females were fertilized with milt 

from multiple males using the procedures described 

by Blood et al. (1994), except males had so little milt 

(<0.5 ml per male) that it was first collected in plastic 

pipettes rather than being expressed directly into a bowl 

with the eggs. In some cases, females collected at one 

depth were held in live tanks until ripe males could be 

collected at other depths. Fertilized eggs were placed 

into one-gallon glass jars in a large 3.0°C refrigerator. 

In 2001, eggs remained in the 3.0°C refrigerator for 

the duration of the cruise. In 2002 and 2003, eggs were 

held in the 3.0°C refrigerator for 3–5 h, then examined 
4 Professional Paper NMFS 7

Figure 1

Station map for 2001 and 2002 cruises. A) 28 January–5 February 2001. Deep bongo tows and bottom trawls conducted at 

each station. B) 3–9 February 2002. Only bottom trawls conducted at each station.
5

Figure 2

Station map for 13–22 February 2003, showing bongo tows (

●) and bottom trawls (

▲).
6 Professional Paper NMFS 7

using a microscope (25×); floating eggs having a perivitelline space were assumed to be fertilized (Alderdice, 

1988). Viable eggs were separated into three groups in 

multiple one-liter jars placed in small refrigerators set at 

3.0°, 4.5°, and 6.0°C. Up to 10 eggs were sampled from 

each group at 2–24 h intervals for the duration of each 

cruise (Table 1). In 2001–2002, eggs were sampled every 

12–24 h; in 2003, eggs were sampled every 2 h during 

the period of most rapid development until formation of 

the blastodisc. Eggs were sampled every 12 h thereafter. 

At the end of each survey, eggs were transferred into 

thermoses, placed in coolers, and transported to the 

rearing laboratory at the AFSC, Seattle, in 2001–2002, 

or to the AFSC Kodiak lab in 2003. In Seattle, eggs were 

placed in one-gallon glass jars in walk-in coolers (4.5°C 

and 6.0°C) or a refrigerator (3.0°C). Eggs reared in 

2001 were incubated with no aeration until fungus developed after day 17; all jars were aerated and received 

daily 50% water changes thereafter. One jar was treated 

with Maracyn® and acriflavine to kill the fungus; eggs 

in this jar were not used for subsequent incubation and 

hatch data, but live diameters of eggs were recorded and 

newly hatched larvae were transferred to a larger tank 

to document first appearance of pigment. All jars were 

aerated in 2002 and received 50% water changes daily. 

In Kodiak, eggs were incubated in 10-inch diameter 

screened (1 mm) PVC tubes suspended in troughs supplied by a flow-through seawater system at approximately 

5°C. Chillers were used in two troughs to reduce the 

water temperature to 3.0°C and 4.5°C and an aquarium 

Table 1

Station and biological data for arrowtooth flounder (Atheresthes stomias) spawning and egg incubation 2001–2003.

Year 2001 2002 2003

Date 2 February 7, 8, 9 February 18, 21 February

Time (local) 1400 1915, 2230, 0300 0800, 1500

Location 54°30.94ʹN, 158°46.83ʹW 54°30.88ʹN, 158°46.76ʹW; 55°02.69ʹN, 157° 02.72ʹW;

54°28.99ʹN, 158°50.66ʹW; 56°15.23ʹN, 153° 17.41ʹW

54°29.04ʹN, 158°50.75ʹW 

Depth (m) 400 400, 400, 500 400, 300

Temperature at depth 4.7 4.8, 4.8, 4.3 5.0, 5.4

 of spawning females (°C)

n females 1 1, 2, 1 1, 5

 Lengths (cm FL) 60 81; 55, 69; 72 58; 81, 71, 74, 52, 80

 Weights (g) N/A* 5566; 1734, 3044; 3950 N/A*

n males 3 8, 14, 31 16, 20

 Length range (cm FL) 43–47 41–47, 36–50, 43–50 41–53, 41–57

 Weight range (g) N/A* 630–948, 616–1046, 636–1038 N/A*

Incubation location Seattle, WA Seattle, WA Kodiak, AK

Egg incubation temperatures (°C) 3.0 3.0, 4.5, 6.0 3.0, 4.5, 6.0

Incubation sampling schedule variable intervals every 12–24 h every 12 h; eggs did not sampled every 2 h until blastodisc

onboard ship; every 24 h thereafter survive incubation formed, then every 12 h

*Not available.

heater was used to increase the temperature in the third 

trough to 6.0°C. Eggs were sampled at 12–24 h intervals 

and held through hatching and the early yolk-sac stage. 

All eggs were staged according to developmental criteria 

described by Blood et al. (1994) with one exception: 

since the arrowtooth flounder embryo is not pigmented, 

those authors’ stage 14 (first appearance of pigment) 

was not used, and subsequent stages, defined by morphological changes, were assigned a number equaling 

stage number –1 (e.g., stage 15 for walleye pollock eggs 

equals stage 14 for arrowtooth flounder eggs). Eggs were 

preserved in 5% buffered formalin. Some eggs were also 

preserved in Stockard’s solution to clear the chorion and 

darken embryonic tissue. 

Ichthyoplankton data were collected in 2001 and 2003 

using a MARMAP bongo sampler (Posgay and Marak, 

1980) with an inside diameter of 0.6 m and 0.505-mm 

mesh nets. Bongo nets were lowered at a rate of 40 m 

of wire/min and retrieved at a rate of 20 m/min, sampling obliquely from the surface to within 10 m of the 

bottom or to targeted depths where deeper, following 

standard MARMAP procedures (Smith and Richardson, 

1977). Ichthyoplankton samples were preserved in a 5% 

buffered formalin-seawater solution and later sorted for 

ichthyoplankton, which were removed and identified to 

the lowest possible taxon at the Plankton Sorting and 

Identification Center in Szczecin, Poland (ZSIOP). Egg 

and larval identifications were verified at AFSC. A detailed account of sampling and identification protocols 

is available in Matarese et al. (2003). Position of embry-
7

onic and larval structures are presented as percentages 

of preserved standard length. All larval measurements 

reported are standard length. 

Analytical methods

For adult arrowtooth flounder, depth of capture was 

separated into three strata: 200 m (150–250 m), 400 

m (350–450 m), and >450 m (460–650 m). The depth 

stratum for the deepest samples for adults, eggs, and 

larvae was changed from 600 m to >450 m after the 

first cruise to include data from all hauls; one of four 

trawls (502 m) and two of five bongo tows (525, 536 m) 

would have been excluded from analysis if the deepest 

stratum had remained as 600 m. Sex ratios were determined for each stratum using the mean proportion of 

the fish that were females in all hauls. An ANOVA tested 

for significant differences of the proportion of females 

among the depths. The proportions of females were 

transformed using the arcsine of the square root of the 

proportion to rescale the data to satisfy the assumptions of the ANOVA. Percent maturity was calculated 

for males and females examined for maturity states in 

2001 and 2002.

For arrowtooth flounder eggs and larvae, depth of 

capture was separated into four strata defined by the 

maximum depth of the bongo array: <150 m, 200 m 

(150–250 m), 400 m (350–450 m), and >450 m (460–650 

m). Abundances of arrowtooth flounder eggs and larvae 

collected in ichthyoplankton samples were calculated 

as number/10m2 sea surface area (Kendall and Dunn, 

1985). Up to 100 eggs from each station in 2001 were 

staged as described above to determine age and stagespecific vertical distribution; all eggs were staged in 

2003. The diameters of 118 live reared eggs, 194 preserved reared eggs, and 510 randomly selected eggs 

collected in ichthyoplankton samples and preserved 

in 2001 were measured to the nearest 0.01 mm; 226 

preserved reared eggs and 71 randomly selected eggs 

collected in ichthyoplankton samples in 2003 were also 

measured. Newly hatched larvae in the laboratory (129 

of a total of 435) and up to 50 individuals from each 

ichthyoplankton sample were measured to the nearest 

0.1 mm SL; newly hatched larvae were measured when 

alive, while field-collected larvae were measured after 

preservation in 5% formalin. Range, mean, mode, and 

standard deviation were calculated for egg diameter 

and larval length measurements. An ANOVA was used 

to test for significant differences in mean lengths of larvae collected from bongo tows that sampled to depths 

of 400 m and >450 m in 2001 (no larvae were collected 

in tows that sampled to 200 m) and 200 m, 400 m, and 

>450 m in 2003. 

Egg incubation data were used to generate temperature-specific equations to estimate duration of development and age of the eggs. Endpoints, midpoints, and 

duration of stage (in hours) were estimated for eggs 

incubated at each temperature, as described in Blood 

et al. (1994), except the midpoint of the last stage (19) 

was taken as the midpoint between the end of stage 

18 and the sampling time during which the last egg 

hatched, rather than the time of 50% hatch as defined 

by Blood et al. (1994). A piecewise, least-squares, linear 

regression model (SAS, vers. 6.0, SAS Inst., Inc., Cary, 

NC) was applied to estimate age (hours) of eggs at a 

specific stage incubated at any temperature within the 

limits of our data.

Results

Spawning and maturity of arrowtooth flounder

The sex ratio of arrowtooth flounder varied significantly 

by depth stratum (Fig. 3). Females dominated the catch 

at 200 m, the sex ratio was more evenly distributed 

at 400 m, and males dominated the catch at >450 m. 

The proportion of females in the catch at >450 m was 

significantly lower (P<0.05) than the proportion of females at 200 m and 400 m, but the proportion was not 

significantly different between the 200 m and 400 m 

strata. Few females collected at 200 m and >450 m were 

mature (54 of 369) and only one female was ripe. At 

400 m, 23–26% of the females were mature and 0–10% 

of the males were mature (Fig. 4); among these, 51% 

of females and less than 2% of males were ripe. Most 

ripe males were collected at depths >450 m: 50% of 

ripe males in 2001 and 100% of ripe males in 2002 were 

collected from this stratum. Females averaged 51.5 cm 

FL and males averaged 43.4 cm FL in 2001 and 47.8 cm 

FL and 39.6 cm FL, respectively, in 2002 (Fig. 5). Water 

temperature at the depths where spawning females were 

collected was 4.7°– 4.8°C (400 m) and 4.2°C (500 m) 

(Table 1). 

No maturity data were collected in 2003; however, 

many spent females were encountered in areas where 

in previous years we obtained ripe individuals. It was 

necessary to travel farther north than in 2001–2002 to 

find ripe females along the slope (Table 1, Fig. 2). The 

temperature at 400 m where the first spawning adults 

were collected in 2003 was warmer (5.0°C) compared 

to the prior two years. The second group of spawners (5 

females, 20 males) was collected from 300 m (5.4°C); no 

spawners had previously been collected at that depth.

Macroscopic maturity states of selected adults in 2001 

agreed with histological maturity states for all males and 

most females (Table 2). The distinction between mature 

and ripe males was difficult to assess at times; mature 

males had only a drop or two of milt that could be expressed and ripe males usually had about 0.5 ml of milt 
8 Professional Paper NMFS 7

Figure 3

Sex ratios of adult arrowtooth flounder (Atheresthes stomias) collected in bottom trawls in 

(A) 2001 and (B) 2002.

(ca. 14 drops). It was difficult to express enough milt 

from males to assess their maturity and still have enough 

milt left to fertilize eggs. Histological examination of 

males classified as ripe confirmed that even though the 

quantity of milt produced was very small, there were 

more spermatozoa (Fig. 6A) than in those males classified as immature (Fig. 6B). The gonadal somatic index 

(GSI) for males was inconsistent; immature male GSI 

(n = 4) ranged from 0.13 to 0.33 and mature male GSI 

(n = 3) was 0.16–0.38. Histology slides prepared from a 

ripe female’s ovaries show the hydrated, yolked eggs and 

the postovulatory follicles that characterize this stage 

of maturity (Fig. 7A,B). The preliminary assessment of 

the 53-cm FL female (Table 2) as mature was incorrect; 

although that individual did have many small eggs in the 

lumen of the ovary, most of the larger eggs were atretic 

(Fig. 8) (as described by Zimmermann, 1997). The 

GSI calculated for females was distinct for each of the 

four maturity states. Immature female GSI (n = 3) was 

0.54–0.79 and spent female GSI (n = 5) was 1.08–2.69; 

mature (n = 1) and ripe (n = 1) female GSI was 9.93 and 

23.83, respectively. 
9

Figure 4

Percent maturity by depth for arrowtooth flounder (Atheresthes stomias) collected in bottom 

trawls in (A) 2001 and (B) 2002; n equals number of individuals sampled at each depth, 

r equals number of ripe individuals in each depth sample.

Description of eggs and 

morphological development

Arrowtooth flounder eggs are pelagic, with a smooth, 

clear chorion and homogeneous yolk. The perivitelline 

space is narrow and oil globules are absent. Live eggs 

fertilized at sea were 1.64–1.97 mm in diameter (n = 

118, mean 1.83 mm, mode 1.84 mm, SD 0.06 mm); 

formalin-preserved eggs fertilized at sea had a wider 

size range, 1.58–1.98 mm (n = 419, mode 1.80 mm, SD 

0.06 mm), but were slightly smaller on average (mean 

1.82 mm). Eggs collected in ichthyoplankton tows had 

a slightly greater mean diameter of 1.86 mm (n = 581, 

range 1.76–1.98 mm, mode 1.84 mm, SD 0.04 mm). 

The yolk and embryo are unpigmented throughout 

development (Fig. 9). Nineteen developmental stages 

were defined as follows: 

Stage 1 (precell – early stage) – Cytoplasm is concentrated at the animal pole, appearing as a raised cap of 

undivided cellular material. The edge of the cytoplasm 

is diffuse, with no clear margin.

Stage 2 (2 cells – early stage) – Cytoplasm is divided 

into two equal-sized cells. The outer margins of the 
10 Professional Paper NMFS 7

Figure 5

Histogram of fork lengths of male and female arrowtooth flounder 

(Atheresthes stomias) collected in bottom trawls in (A) 2001 and (B) 

2002.

cells are diffuse, whereas the margin between cells is 

well defined.

Stage 3 (4 cells – early stage) – Cell cap consists of four 

cells of equal size.

Stage 4 (8 cells – early stage) – The eight cells comprising the cell cap form a single-layer rectangle two cells 

wide by four cells long, with the four inner cells smaller 

than the four outer cells. The outer margins of the cells 

are now distinct.

Stage 5 (16 cells – early stage) – Fourth and last division of cells in a single layer. Cells form a rough square 

four cells wide and four cells long.

Stage 6 (32 cells – early stage) – Number of cells >16 

and ≤32. The blastodisc is greater than one cell thick 

and has a round edge, appearing similar to a raspberry. 

During this stage, the cells multiply and become smaller, 

but the size of the blastodisc remains constant.

Stage 7 (blastodermal cap – early stage) – Individual 

cells are not visible at 50× magnification. The blastodisc 

appears to sit on top of the yolk and the periblast begins 

to form.

Stage 8 (early germ ring – early stage) – The center of 

the blastodisc becomes thinner and the cytoplasm appears granular, while the edge of the blastodisc remains 

thick. The center of the blastodisc (blastocoel) remains 

thin and granular and toward the end of this stage a 

portion of the germ ring that will form the embryonic 

shield bulges toward the center. In profile, the germ 

ring extends less than 1⁄4 of the way down the yolk.

Stage 9 (germ ring extends 1⁄4 of the way down the 

yolk – early stage) – The embryonic shield is small and 

projects 1⁄4 of the way across the blastocoel.

Stage 10 (germ ring extends to half-way down the 

yolk – early stage) – The embryonic shield is large and 

extends to the top of the yolk. The neural 

keel is prominent, but the margin of the 

embryonic shield is diffuse.

Stage 11 (germ ring extends 3⁄4 of the 

way down the yolk – early stage) – The 

developing embryo is very slender and no 

differentiation of the body is apparent.

Stage 12 (late germ ring – early stage) – 

The germ ring has almost completed overgrowth of the yolk, but the blastopore 

remains open. Optic vesicles are apparent 

and the notochord is visible ventrally. Myomeres (12–17) are visible and Kupffer’s 

vesicle can be seen in the live egg.

Stage 13 (early middle stage) – The 

blastopore is closed. The tail margin is 

indistinct and flat, but the medial portion 

of the tail begins to expand dorsoventrally. 

Kupffer’s vesicle is visible in the Stockard’s 

preserved egg and 19 myomeres can be 

counted. 

Stage 14 (late middle stage) – Optic vesicles are very apparent and the heart and 

hindbrain can be distinguished. The tail 

is plump and the tip appears to be lifting 

from the yolk surface, but the tail margin 

is still attached. About 27 myomeres are 

formed.

Stage 15 (early late stage) – The tail tip is 

lifted away from the yolk surface. 

Stage 16 (tail extends to 5

/8 of the way 

around the yolk – early late stage) – A 

greater portion of the tail is lifted from 

the yolk surface as it elongates and tapers 

toward the end. At the beginning of this 

stage the tail is opposite the head (embryo 

extends half-way around the yolk); at the 

end of the stage the tail extends to 5

/8 of the 
11

Table 2

Collection data, gonadal somatic index (GSI1), macroscopic maturity states, and histological (microscopic) maturity states (based on Zimmermann, 1997, in part) for selected 

arrowtooth flounder (Atheresthes stomias) adults collected in 2001.

 Fork Somatic Gonad Macroscopic

Date Depth (m) Sex length (cm) weight (g) weight (g) GSI1 maturity Histological maturity2 Comments

30–Jan 395 F 53 1399.6 36.71 2.69 Mature Atretic – Spent A few hydrated eggs remaining in ovary30–Jan 395 F 54 1492.0 287.10 23.83 Ripe Spawning – postovulatory follicles present Many hydrated eggs present30–Jan 395 F 55 1587.8 143.43 9.93 Mature MN – Late developing No hydrated eggs present 1–Feb 127 F 42 595.5 4.69 0.79 Immature Immature Immature 1–Feb 127 F 43 653.8 3.53 0.54 Immature EP, LP – Immature Immature 2–Feb 400 M 39 493.8 0.63 0.33 Immature Immature No spermatozoa visible 2–Feb 400 M 40 531.4 0.77 0.13 Immature Immature No spermatozoa visible 2–Feb 400 M 41 571.0 0.91 0.15 Immature Immature A few spermatozoa in early development 2–Feb 397 M 37 424.1 1.40 0.18 Mature Mature Only a few spermatozoa visible 2–Feb 397 M 40 531.4 0.97 0.16 Ripe Mature Only a few spermatozoa visible 2–Feb 397 M 43 656.1 1.07 0.16 Immature Immature No spermatozoa visible 2–Feb 397 M 49 962.6 3.69 0.38 Ripe Mature Many spermatozoa visible 2–Feb 397 M 51 1083.2 2.72 0.25 Mature Mature Only a few spermatozoa visible 5–Feb 390 F 59 2007.1 21.51 1.08 Spent LP, CA – Spent Atresia noted 5–Feb 390 F 60 2121.3 24.03 1.15 Spent LP, CA – Spent Atresia, a few hydrated eggs present 5–Feb 390 F 61 2239.4 15.32 0.69 Immature LP, CA Immature, not spent 5–Feb 390 F 69 3331.0 52.24 1.59 Spent CA – Spent Atresia, a few hydrated eggs present 5–Feb 390 F 70 3486.8 52.32 1.52 Spent CA – Spent Atresia noted

1 Gonadal somatic index = 100 × gonad weight/(somatic weight - gonad weight).2 Histological stages according to Zimmermann (1997): MN = migratory nucleus, EP = early perinucleus, LP = late perinucleus, CA = cortical alveoli.

way around the yolk and the tip has 

begun to curve away from the lon-

gitudinal plane of the embryo. The 

finfold forms on the posterior half 

of the tail. Otic capsules are visible.

Stage 17 (tail extends to 3⁄4 of 

the way around the yolk – middle 

late stage) – The tail continues to 

lengthen and taper while it bends 

further out of the longitudinal plane 

of the embryo. The anus is formed, 

positioned at 60% SL, and is the 

point at which the body bends. The 

dorsal finfold extends anteriorly to 

50% SL. 

Stage 18 (tail extends to 

7/8 of the 

way around top half of the yolk – 

middle late stage) – The embryo is 

now positioned around the top half 

of the yolk; the entire body of the 

embryo can be seen on one side of 

the yolk. The anus is now positioned 

at 50% SL and the finfold extends 

anteriorly to 30% SL.

Stage 19 (tail completes full circle 

around top half of the yolk – late 

stage) – The tail of the embryo al-

most touches the head. The anus 

is at 40% SL and the dorsal finfold 

extends to just anterior to the anus.

Egg incubation 

Water temperature for eggs incu-

bated in 2001 varied no more than 

0.2°C above or below the target tem-

perature of 3.0°C except on day 81 

(Fig. 10A); average temperature was 

3.1°C. Eggs were first sampled 22.5 

h after fertilization, at which time 

they were classified as stage 4. Eggs 

began to hatch at stage 18 (512 h); 

midpoint of hatch was at 562 h. The 

hatching period lasted 143 h and the 

last sample was taken at 655 h. Larvae did not survive to yolk absorption 

and remained unpigmented.

Water temperature in the ther-

moses transported to Seattle in 2002 

dropped to 

≤1°C during shipping. 

Few of these eggs survived to hatch. 

Eggs incubated at 4.5°C survived 

only to stage 13; the 3.0°C and 6.0°C 

eggs appeared to have hatched pre-

maturely (larvae were curled). Incu

-
12 Professional Paper NMFS 7

Figure 6

Section of the testes of male arrowtooth flounder (Atheresthes stomias). 

(A) Ripe – heads of the spermatozoa are visible as the black dots; light 

gray threads among the heads are the flagella (400×); (B) immature – 

vacuoles are small and contain no visible spermatozoa (250×).

bation data were not used because of the drop in water 

temperature during shipping. No larvae were measured 

and none survived long enough to develop pigment.

Water temperature for eggs incubated at 3.0°C in 

2003 varied more than in 2001 (Fig. 10B) and averaged 

3.2°C. Development to the end of stage 17 was docu-
13

Figure 7

Section of ovaries of ripe female arrowtooth flounder (Atheresthes stomias). 

(A) H – Hydrated eggs (uniform gray structures) (25×); (B) POF – Postovulatory 

follicle (160×).

mented; shortly thereafter, there were no eggs left to 

sample in the incubator. 

Few eggs incubated at 4.5°C survived past stage 16 and 

few hatched. Egg mortality was high and data were not 

considered reliable. 

Eggs incubated at 6.0°C reached stage 19 in less 

than one-half of the time (276 h) required at 3.0°C 

(610 h; Fig. 10C); average temperature throughout 

incubation was 6.2°C. Hatching was first observed at 

281 h; the last egg hatched at 353 h. No yolk-sac lar-
14 Professional Paper NMFS 7

Figure 8

Section of ovaries of spent female arrowtooth flounder (Atheresthes stomias); A – Degenerating 

(atretic) ova (100×).

Figure 9

Arrowtooth flounder (Atheresthes stomias) egg; stage 18 (tail 7

/8 around top half of yolk).
15

Figure 10

Development of incubated arrowtooth flounder (Atheresthes stomias) eggs. (A) 

3.1°C in 2001, (B) 3.2°C in 2003, and (C) 6.2°C in 2003. Open circles represent 

occurrence of stages at sampling times. Black triangles represent temperature 

of water in incubators at sampling times. Black squares indicate the midpoint 

between the end of stage 18 and the sampling interval during which the last egg 

hatched. 
16 Professional Paper NMFS 7

Table 3

Endpoint, midpoint, and duration in hours (h) of stage of development of arrowtooth flounder (Atheresthes stomias) eggs 

incubated at 3.1°C (2001), 3.2°C (2003), and 6.2°C (2003).

3.1°C (2001) 3.2°C (2003) 6.2°C (2003)

 Endpoint Midpoint Duration Endpoint Midpoint Duration Endpoint Midpoint Duration

Stage (h) (h) (h) (h) (h) (h) (h) (h) (h)

 1 10.00 5.00 10.00 8.00 4.00 8.00

 2 14.00 12.00 4.00 10.00 9.00 2.00

 3 18.00 16.00 4.00 10.75 10.38 0.75

 4 25.50 20.00 19.00 2.00 12.25 11.50 1.50

 5 31.50 28.50 6.00 24.00 22.00 4.00 18.00 15.13 5.75

 6 41.50 34.50 10.00 33.00 28.50 9.00 33.00 25.50 15.00

 7 104.00 74.25 65.50 101.00 67.00 68.00 64.00 48.50 31.00

 8 129.00 116.50 25.00 149.00 125.00 48.00 76.00 70.00 12.00

 9 176.50 152.75 47.50 185.00 167.00 36.00 101.00 88.50 25.00

10 224.00 200.25 47.50 203.00 194.00 18.00 113.00 107.00 12.00

11 237.50 230.75 13.50 215.00 209.00 12.00 119.00 116.00 6.00

12 272.50 255.00 35.00 260.00 237.50 45.00 155.00 137.00 36.00

13 309.50 291.00 37.00 305.00 282.50 45.00 179.00 167.00 24.00

14 357.00 333.25 47.50 347.00 326.00 42.00 197.00 188.00 18.00

15 391.00 374.00 34.00 383.00 365.00 36.00 203.00 200.00 6.00

16 428.75 409.88 37.75 461.00 422.00 78.00 239.00 221.00 36.00

17 512.50 470.63 83.75 509.00 485.00 48.00 257.00 248.00 18.00

18 609.50 561.00 97.00 275.00 266.00 18.00

19 655.50 632.50 46.00 353.00 314.00 78.00

vae survived to yolk absorption and none developed 

pigment. 

Endpoint, midpoint, and duration of each stage were 

estimated for the 2001 and 2003 3.0°C groups and the 

2003 6.0°C group (Table 3). Data were incomplete for 

the 3.0°C groups. When the midpoints of stages at 3.0°C 

for each year were compared using an analysis of covariance (ANCOVA) using stage as the covariant, they were 

not found to be significantly different (P>0.05). Therefore, midpoint data for 3.0°C development for 2001 

and 2003 were pooled together. Stage duration, which 

equals the endpoint of a stage minus the endpoint of 

the previous stage (Blood et al., 1994), was very different between 2001 and 2003 for some stages (particularly 

stages 8, 10, 16, and 17); using midpoints moderated 

the degree of variability in development present among 

individual eggs. The 3.0°C and 6.0°C midpoint data 

were used to construct a piecewise nonlinear regression 

describing the relation between time to stage at the extremes of mean temperature (3.1°– 6.2°C). The piecewise regression model has two separate components and 

is discontinuous between stages 6 and 7 (Fig. 11); the 

divergence of developmental rates after stage 6 required 

two equations to obtain the best fit over the entire incubation time. The two components are described by the 

following equations:

component 1: stages 1–6

Age (h) = 9.32 + 4.5(stage) – 2.08(temp), 

adjusted R2 = 0.923, 

mean squared error = 8.269 

component 2: stages 7–19

Age (h) = –547.13 + 122.25(stage) 

+ 49.47(temp) – 7.59(stage)(temp) 

– 5.89(stage2) + 0.18(stage3),

adjusted R2

 = 0.991, 

mean squared error = 219.752.

Incorporating both temperature and stage as variables 

into the equations allows estimation of egg age at any 

temperature between 3.1°C and 6.2°C. Whereas separate 

equations for 3.1°C and 6.2°C would have given results 

closer to the recorded stage midpoints, the regression 

above allows for estimation of egg age at temperatures 

where spawning adults were found (4.3°–5.4°C). Incubation time at this in situ temperature range is estimated 

to be 372 h (5.4°C) to 477 h (4.3°C).

Description of larvae

A total of 129 reared and 184 plankton-caught larvae 

was examined for morphological development and for 
17

first appearance and changes in pigmentation. Newly hatched larvae are slender, 

lack pigment, and possess a large yolk mass 

(length × depth = approx. 30% × 24% 

SL) (Fig. 12A). Size range at hatching is 

3.9–4.8 mm SL (mode 4.3 mm, mean 4.4 

mm, SD 0.2 mm) and preanal length is 

approximately 40% SL. At about 6.0 mm 

SL, the mouth begins to form and a horizontal streak of pigment is present on the 

eye, extending from each margin through 

the center (Fig. 12B). In addition, a small 

saddle of pigmentation, beginning as a 

single melanophore on the dorsal midline, is present at about 75% SL, between 

myomeres 36–39. In some specimens of 

this length, an additional small patch of 

pigment is present ventrally on the body 

over the posterior end of the yolk sac 

(Fig. 12C). Yolk absorbtion is complete 

between 6.5 and 7.0 mm SL and the mouth 

appears functional. Preanal length is reduced to approximately 25% SL.

Preflexion through postflexion arrowtooth flounder larvae 10.0–25.6 mm SL are illustrated 

and briefly described in Matarese et al. (1989), and are 

described in more detail here (Fig. 12D, 13A–B). In 

late preflexion larvae, the pigment patch over the end 

of the yolk sac has expanded dorsally over the hindgut, 

the posterior dorsal patch on the tail has expanded to 

between myomeres 36–45, and a second dorsal patch 

has formed at about 50% SL, between myomeres 21–27 

(Fig. 12D). In addition, pigment appears on the crown 

and between the eyes, and 3–4 preopercular spines 

are visible. The dorsal patches fuse by late flexion and 

some lateral and ventral pigment develops posteriorly 

under the dorsal patch (Fig. 13A). Additional pigment 

on the crown and laterally on the gut appears along 

with nape pigment and melanophores on the mandible 

and jaw articulation. A second row of spines forms on 

the preoperculum. Dorsal body pigment in postflexion 

larvae is scattered (Fig. 13B). Pigment is concentrated 

on the caudal peduncle, crown, and posteriorly on the 

gut, and small melanophores are visible on the snout 

and isthmus.

Transforming specimens (Fig. 13C) are slenderbodied, with body depth approximately 27% SL. Fine 

pigment is scattered over most of the head, with larger 

melanophores present on the snout, upper and lower 

jaws, gular region, preoperculum, and operculum. The 

pectoral-fin base and proximal region of the pectoralfin rays are moderately pigmented. The peritoneum 

is dark, and the lateral surface of the gut is covered 

with fine pigment and a few larger melanophores. 

Fine pigmentation covers the entire lateral line. Small, 

faint melanophores cover about 75% of the body on 

the eyed side. Larger dark melanophores are present 

as blotches dorsolaterally on the body and dorsal-fin 

pterygiophores at approximately 20%, 35%, and 50% 

SL. Similar blotches are present ventrolaterally on the 

body and anal-fin pterygiophores at approximately 

30%, 50%, and 80% SL. Two aggregations of pigment 

resemble bands at 70% and 90% SL. Melanophores 

are scattered between the bands and blotches near the 

dorsal and ventral body margins. 

Light pigment outlines the hypural margin and is 

present on the entire fin in a subtle banding pattern. 

Light pigment is also present on the remnant finfold 

on the caudal peduncle.

Blind side pigment is greatly reduced. Anteriorly, 

pigment is present on the snout and gular region, with 

large internal spots on the peritoneum. The lateral line 

is pigmented starting at approximately 50% SL and 

there is a dorsolateral pigment blotch at about 50% 

SL. A row of melanophores is present along the base of 

the dorsal pterygiophores. Posteriorly, melanophores 

are present as remnants of bands at about 90% SL, and 

outlining the caudal peduncle and hypural margin.

Distribution and abundance 

of eggs and early-stage larvae

Arrowtooth flounder eggs were collected at 75% of deep 

bongo stations and also in eight shallower tows that were 

part of the 2003 survey grid (depth 160–205 m) (Fig. 14, 

Table 4). Except for one station, all eggs were collected 

Figure 11

Time (h) to midpoint of stage of arrowtooth flounder (Atheresthes 

stomias) eggs incubated at mean temperatures of 3.1°, 3.2°, and 6.2°C. 

Symbols are observed values; fitted lines are results of regression 

models (3.1° and 3.2°C values combined for one model stages 1–6 

and one model stages 7–19). Time (h) to midpoint of stage
18 Professional Paper NMFS 7

Figure 12

Newly hatched and early larvae of arrowtooth flounder (Atheresthes stomias). (A) Newly hatched yolk-sac larva (reared); 

(B) yolk-sac larva (UW cat. no. 104797); (C) yolk-sac larva (UW cat. no. 104818); (D) preflexion larva (Matarese et al., 

1989).
19

Figure 13

Arrowtooth flounder (Atheresthes stomias). (A) Flexion larva (Matarese et al., 1989); (B) postflexion larva (Matarese et al., 

1989); (C) transforming (UW cat. no. 104591).
20 Professional Paper NMFS 

7

Figure 14

Collection localities and abundances of arrowtooth flounder (Atheresthes stomias) eggs for 2001 and 2003. Map was created using 

the method described in Matarese et al. (2003).
21

Table 4

Station, haul, date, bottom depth, location, gear depth, and standardized catch of arrowtooth flounder (Atheresthes stomias) 

eggs and catch information plus mean length of larvae at each station for bongo tows in 2001 and 2003. Only stations with 

a positive catch for eggs and/or larvae are shown. Shaded rows denote stations that were part of the 2003 survey grid which 

limited gear depth to the lesser limit of either 10 m off bottom or 200 m.

Larvae

 Bottom Latitude Longitude Maximum Eggs Mean

Station Haul Date depth (m) (°N) (°W) gear depth (m) catch/10m2 Catch/10m2 length (mm)

 2 29-Jan-01 224 57.96 150.12 212 6.95 0

3 29-Jan-01 419 57.92 149.42 415 1376.72 177.12 3.83

4 29-Jan-01 630 57.86 149.39 630 586.07 0

5 30-Jan-01 179 57.24 150.85 172 310.23 0 

6 30-Jan-01 432 57.14 151.08 423 883.18 218.91 5.24

7 30-Jan-01 566 57.19 150.97 536 956.71 306.87 5.09

 8 30-Jan-01 208 56.59 151.93 198 118.51 0

11 31-Jan-01 137 56.74 153.55 127 13.60 0

12 1-Feb-01 216 55.68 155.32 200 53.34 0

13 1-Feb-01 415 55.65 155.30 401 1078.82 7.01 6.50

14 1-Feb-01 606 55.62 155.31 571 798.71 511.53 5.05

15 1-Feb-01 404 55.05 157.02 393 1875.26 28.63 6.08

16 1-Feb-01 578 55.03 157.05 525 1863.20 237.86 4.82

18 2-Feb-01 406 54.51 158.80 406 258.09 58.28 6.43

 6 2 14-Feb-03 673 57.11 151.04 200 22.05 22.05 7.97

7 1 14-Feb-03 186 57.24 150.85 175 0 6.91 8.00

8 1 14-Feb-03 400 57.14 151.09 400 226.52 290.23 4.99

9 1 14-Feb-03 574 57.19 150.97 551 252.06 1138.32 6.09

10 1 14-Feb-03 968 56.94 150.79 200 95.02 14.62 7.50

11 1 14-Feb-03 911 56.80 151.11 202 0 26.59 8.10

12 1 14-Feb-03 884 56.97 151.35 203 7.12 28.48 8.43

13 1 14-Feb-03 100 57.14 151.59 90 0 6.48 7.50

19 2 14-Feb-03 298 56.83 151.68 201 0 6.89 8.00

20 2 15-Feb-03 1054 56.74 151.53 199 0 16.86 9.17

20 3 15-Feb-03 1046 56.74 151.53 606 0 25.71 8.90

21 3 15-Feb-03 1000 56.54 151.77 602 0 74.14 6.60

30 1 15-Feb-03 1952 56.39 152.07 200 26.14 13.07 8.60

30 2 15-Feb-03 1952 56.39 152.07 601 36.34 814.05 6.57

31 2 15-Feb-03 949 56.26 152.39 205 114.13 7.13 6.00

31 3 15-Feb-03 949 56.26 152.38 602 1139.34 762.55 5.87

32 2 16-Feb-03 132 56.43 152.63 122 0 11.71 7.40

39 1 16-Feb-03 168 56.29 152.93 160 6.36 6.36 7.80

40 1 16-Feb-03 1206 56.16 153.24 200 55.23 6.14 8.10

40 2 16-Feb-03 1134 56.16 153.25 600 179.25 590.02 5.92

40 3 16-Feb-03 462 56.21 153.32 446 221.17 475.10 6.35

45 2 17-Feb-03 244 56.17 153.82 200 0 6.68 13.50

47 2 17-Feb-03 789 55.88 153.86 200 7.14 7.14 8.00

47 3 17-Feb-03 767 55.87 153.87 601 394.01 1173.65 6.70

51 1 17-Feb-03 203 55.68 155.33 192 0 20.10 7.57

52 1 17-Feb-03 412 55.65 155.30 391 21.48 200.43 6.77

53 1 17-Feb-03 594 55.62 155.29 575 12.04 312.94 6.19

54 1 18-Feb-03 198 55.11 157.05 189 0 13.58 6.75

55 1 18-Feb-03 393 55.06 157.03 374 208.37 266.71 6.49

56 1 18-Feb-03 599 55.03 157.07 569 364.63 689.84 6.01

57 2 19-Feb-03 952 54.44 158.98 600 17.48 555.79 5.70

58 5 19-Feb-03 395 54.51 158.82 377 304.73 124.15 6.46

59 1 20-Feb-03 250 54.57 158.71 240 52.11 26.05 7.52
22 Professional Paper NMFS 7

Figure 15

Depth and stage distribution of arrowtooth flounder (Atheresthes stomias) eggs. Numerals on pie charts are combined 

numbers of staged eggs grouped into early, middle, and late stages of development.

close to or along the continental shelf edge; eggs were 

collected from all except six stations over the continental slope (>160 m). Over 92% of all eggs were from 

tows sampling to depths ≥400 m and 58% of all staged 

eggs were in the early stage of development (Fig. 15). 

Less than 10% of the eggs were from tows sampling to 

depths ≤200 m, and about 50% of those eggs were in 

the late stage of development. Eggs were most abundant 

(1863–1875/10m2) at two locations approximately 125 

km west of Chirikof Island (Stations 15–16, 2001); these 

stations had the greatest percentage of early-stage eggs. 

The greatest percentage of late-stage eggs was found 

east of Kodiak Island (Stations 5–7, 2001).

Depth of the tows having the greatest percentage of 

eggs was 400 m in 2001 and >450 m in 2003. Although 

more deep plankton tows were taken in 2003, more eggs 

were collected in 2001. In addition, there were more 

very early-stage eggs (stage 1–6) in 2001, indicating that 

spawning and fertilization had occurred just hours before the eggs were collected. For both years, early-stage 

eggs (stages 1–12) comprised the largest percentage of 

the catch in each of the three depth strata, except for 

the 200 m stratum in 2001, in which 60% of the eggs 

were late stage. 

Arrowtooth flounder larvae were collected in 2001 

and 2003 from 41 of 84 stations, all located close to or 

along the continental shelf edge (Fig.16). At station 

clusters (2–3 closely-spaced stations sampling 2 or 3 

depth strata) where larvae were collected, abundance 

increased with depth (Table 4). Highest abundances 

were at depths >450 m east and south of Kodiak Island (1138/10m2

 and 1173/10m2, Stations 9 and 47, 

2003). 

Most larvae collected in 2001 were yolk-sac stage. 

Lengths of larvae varied from 3.2 to 9.6 mm SL, but 90% 

were less than 7 mm SL (Fig. 17A). Although there was 

variation within depth groups, mean length of larvae 

collected in tows that sampled to depths of 400 m (5.0 

mm SL) was not significantly different (P>0.05) from 

the mean length of larvae collected in tows that sampled 

to depths >450 m (4.9 mm SL).

Larvae collected in 2003 were 4.0–13.5 mm SL; 59% of 

these larvae were less than 7 mm SL (Fig. 17B). Larvae 

collected in the 200 m stratum were the largest among 

the four depth strata groups: lengths were 5.4–13.5 

mm SL, with a mean of 8.1 mm SL. These larvae were 

significantly larger than those collected in tows that 

sampled to 400 m and >450 m (P<0.05). Mean length 

of larvae in the 400 m stratum (6.0 mm SL) was significantly less (P<0.05) than the mean length in the >450 

m stratum (6.3 mm SL) (Table 4). Many more larvae 

were collected in 2003 than in 2001; there were more 

sampling locations than in 2001, but mean abundance 

in tows that sampled to depths >400 m in 2003 was 250% 
23

Figure 16

Collection localities and abundances of arrowtooth flounder (Atheresthes stomias) larvae for 2001 and 2003. Map was created using 

the method described in Matarese et al. (2003).
24 Professional Paper NMFS 7

Figure 17

Length frequency histograms for arrowtooth flounder (Atheresthes 

stomias) larvae collected in (A) 2001 and (B) 2003.

greater than mean abundance at those depths in 2001 

(Table 4).

Discussion

The spatial and temporal variability in spawning by GOA 

arrowtooth flounder and its early life history are poorly 

known. Hirschberger and Smith (1983) collected arrowtooth flounder in spawning condition at depths of 

108–360 m along the continental shelf in March and 

May–August. Zimmermann (1997) collected arrowtooth flounder from depths of 66–165 m east of Kodiak 

Island in September, and concluded from histological 

examinations that spawning occurs after September. 

Farther south, Rickey (1995) found ripe female arrowtooth flounder off the Washington coast in December 

at a depth of 475 m. 

Unlike previous studies, we used ichthyoplankton 

data to help pinpoint possible time, location, and depth 

of spawning. Prior to this study, the smallest arrowtooth 

flounder larvae we had collected were small preflexion 

larvae 6–7 mm SL. These larvae were first collected in 

late February, primarily over the outer continental shelf 

and upper slope, suggesting that early February (or 

perhaps late January) marked the beginning of spawning offshore and at depths >200 m. Only eggs of other 

species had been collected over the upper continental 

slope along with the small arrowtooth flounder larvae 

in February. Standard surveys conducted from 1971 to 

1985 deployed ichthyoplankton gear to only 200 m and 

missed both eggs and early-stage larvae of arrowtooth 

flounder, and no surveys were scheduled during February over the outer continental shelf 

and upper slope after 1985. 

During our study, spawning arrowtooth 

flounder were found along the continental 

slope southeast, south, and southwest of 

Kodiak Island at depths of 300–500 m in late 

January–February 2001–2003. The earliest 

spawning occurred at the more southerly 

sampling locations near the Shumagin Islands and later spawning was farther north, 

closer to Kodiak Island. Fewer ripe fish were 

found during the earliest cruise (28 January–5 February 2001) than in 2002 (trawling 

6–9 February), and more spent females were 

found during the latest cruise (trawling 18–22 

February 2003). For 2001–2003, spawning appears to begin before the end of January and 

accelerate through February. 

In general, females were predominant in 

trawl catches at 200 m, males were predominant at >450 m, and the sex ratio was more 

nearly equal at 400 m. Sexually mature fish 

were usually found at ≥400 m. Although 

some ripe females were found at 300 m (n

= 5) and 500 m (n = 1), most were found at 

400 m (n = 38). Some ripe males were found 

at 200 m (n = 1), 400 m (n = 19), and 600 m 

(n = 4), but most were found at 500 m (n = 

53). Rickey (1995) suggested that the majority of spawning off Washington is at depths 

exceeding 366 m. Our data agree, suggesting 

that most spawning in the central GOA takes 

place at 400–500 m. The depth segregation 

of ripe females and males suggests movement by the males toward the females when 

ready to spawn, since most spent females 

and the majority of ripe females were found 

at 400 m. 
25

Arrowtooth flounder eggs were smaller than we expected. In previous ichthyoplankton surveys, the smallest larvae collected were 6.0–7.0 mm SL. Larval length at 

hatching is usually 2.5–3.0 times the diameter of the egg 

(Ahlstrom and Moser, 1980), so it was expected that arrowtooth flounder eggs would be close to 3.0 mm diameter. Egg diameters are critical to identification, and we 

measured a large number of eggs to encompass the full 

size range. Reared, preserved arrowtooth flounder eggs 

range from 1.58 mm to 1.98 mm; field collected eggs are 

1.76–1.97 mm. Prior to this study, arrowtooth flounder 

eggs may have been misidentified as sablefish (Anoplopoma fimbria), whose embryos are unpigmented, reported 

to range from 1.80 to 2.20 mm in diameter, and also are 

spawned over the outer continental slope at depths of 

400 m in January and February (Mason et al., 1983; Kendall and Matarese, 1987). We measured reared sablefish 

eggs archived in the ichthyoplankton collection at AFSC 

to compare to the arrowtooth flounder egg diameters 

recorded from this study. From a sample of 316 sablefish eggs, 34% were ≤1.97 mm (range 1.85–2.09 mm, 

mean = 1.99, mode = 2.01). Since diameters overlap, 

arrowtooth flounder eggs may be difficult to distinguish 

from sablefish eggs until close to hatch when the anus 

is at 40% SL and myomeres (47–50) are formed (anus 

in sablefish is at 50–60% SL and myomeres = 61–66). 

However, most of the sablefish eggs in our collection 

are ≥2.00 mm and all of our reared arrowtooth flounder 

eggs are <2.00 mm. Along with the arrowtooth flounder 

eggs collected in the plankton in 2001 and 2003, many 

newly-hatched arrowtooth flounder larvae were present, 

but no sablefish larvae were found. Prior to this study, 

eggs 1.80–2.00 mm in size with unpigmented embryos 

that were collected at depths >200 m were all assumed 

to be sablefish because there was little information on 

the timing and depth of arrowtooth flounder spawning; 

arrowtooth flounder and sablefish eggs can now be differentiated, except for eggs that are 1.85–1.97 mm in 

diameter and younger than stage 19. 

The length of time for egg development ranged from 

632.5 h (26.4 days) at 3.1°C to 314 h (13.1 days) at 6.2°C 

(50% hatch). Over the range of temperatures where 

spawning adults were found (4.3°–5.4°C), incubation 

would take 372–477 h (15–20 days). The conditions 

under which the first group of eggs were reared (minimal water changes, no aeration to reduce movement) 

seemed the most optimal; eggs survived for over 630 h 

and larvae lived for an additional 144 h. No other group 

of eggs or larvae survived as long; the 6.2°C group in 

2003 survived to hatch, but that was only for 314 h.

The regression model created from incubation data 

allows estimation of the age of arrowtooth flounder eggs 

at in situ temperatures. Assignment of discrete stages to 

continuous development is arbitrary; stages are ordinal 

data based on morphological criteria without consideration for development time. However, ages predicted 

by the regression are estimates and are used as such. 

Bouwens et al. (1999) were not able to calculate spawning seasons from their hatch date estimates because they 

lacked data on egg incubation at various temperatures. 

Our regression model provides that data. During our 

first survey (2001), larvae were found within 24 h of the 

beginning of the cruise (station 3, 29 January). Time to 

the midpoint of stage 19 would take 429 h (approx. 18 

days) at 4.8°C, the average temperature at depth where 

spawning adults were found. Therefore, spawning was 

occurring on 11 January; the beginning of spawning 

may have been mid-December because we collected 

near-flexion stage larvae on that day. 

Arrowtooth flounder eggs are infrequently collected 

at depths <400 m; fewer than 8% of all eggs were 

collected at depths ≤200 m. Collections at shallower 

depths are likely the result of transport onto the shelf 

by a combination of strong onshore flow and tidal 

mixing (Bailey and Picquelle, 2002; Ladd et al., 2005). 

At standard ichthyoplankton stations (bongo gear 

lowered to 10 m off bottom or no deeper than 200 m), 

all eggs collected were stage 7 or later. The estimated 

64 hours required to reach stage 7 at 4.8°C (average 

bottom temperature at depths where ripe adults were 

collected), as calculated by the regression equation, requires that eggs be advected only 0.2 cm/sec to ascend 

the vertical distance of 200–300 m to the depth our 

standard bongo tows sample. The weakest recorded 

current in Chiniak Trough (near stations 5–7 of the 

2001 cruise) was 5 cm/sec in a northwest direction. 

This measurement was recorded in August–September, 

but the flow is not expected to be much different in 

winter4. Locations where late-stage eggs were collected 

in 2001 are all near troughs and canyons identified as 

areas where downwelling relaxation and cross-shelf 

flow typically occur in winter; tidal mixing is also important in these areas where canyon bathymetry diverts 

flow onto the shelf and aids in cross-isobath transport. 

The combination of strong, fluctuating tidal currents 

and steep, convoluted bathymetry results in enhanced 

vertical mixing (Ladd et al., 2005) and is likely the 

mechanism by which arrowtooth flounder eggs and 

larvae are advected to shallower depths and onto the 

continental shelf. Whereas all sampling for this study 

was carried out using bongo gear, any information on 

the vertical distribution of arrowtooth flounder eggs 

and larvae is circumstantial, since no vertical resolution is possible with bongo tows. Although coupling 

of shallow and deep tows at the same stations provides 

a strong indication of basic vertical distribution, only 

4

 Ladd, Carol. Personal commun. 2005. Office of Oceanic and Atmospheric Research, Pacific Marine Environmental Laboratory 

(PMEL), 7600 Sand Point Way NE, Seattle, WA 98115-6439.
26 Professional Paper NMFS 7

depth-stratified sampling will provide conclusive evidence and finer details.

Arrowtooth flounder larvae are easily distinguished 

from newly-hatched planktonic larvae of sablefish and 

Pacific halibut by preanal length (arrowtooth flounder = about 40% SL, sablefish = 50–60% SL, Pacific 

halibut = about 30% SL), number of myomeres 

(arrowtooth flounder = 47–50, sablefish = 61–66, Pacific 

halibut = 49–51), and size (arrowtooth flounder size at 

hatch = 3.9–4.8 mm SL, sablefish = 5–6 mm SL, Pacific 

halibut = 7.8–8.5 mm SL). From the first appearance 

of pigment (about 6.2 mm SL), arrowtooth flounder 

larvae are easily identified from other pleuronectids, 

most of which have complete bands on the body and/or 

postanal ventral melanophores (Matarese et al., 1989). 

In addition, arrowtooth flounder are the only pleuronectid larvae in the GOA that possess preopercular 

spines, which are present by 10.0 mm SL.

Size at hatch is smaller than the 8–9 mm SL estimated 

by Bouwens et al. (1999), who used a length frequency 

profile of planktonic arrowtooth flounder larvae and 

a linear regression model using total length, otolith 

diameter, and otolith focal diameter to determine size 

at hatch. In our study, reared arrowtooth flounder 

hatched at lengths of 3.9–4.8 mm SL; larvae in this size 

range were also present in our plankton samples. 

Most eggs and small larvae (ca. 4 mm SL) were collected in tows to depths ≥400 m. Less than 5% of eggs 

in 2001, and 10% of eggs and 5% of larvae collected in 

2003, were found in tows to depths ≤200 m. The large 

number of eggs and yolk-sac larvae in tows to depths 

≥400 m, coupled with lower numbers or absence of 

eggs and early-stage larvae in tows to depths <400 m, 

suggests spawning and hatching occur at ≥400 m depth. 

The smallest larva collected from depths ≤200 m was 5.4 

mm SL (mid- to late yolk-sac stage). All of our bongo 

tows were oblique and did not sample discrete depths, 

so we do not know the size of the largest larvae at ≥400 

m. Annual mean length of larvae at ≥400 m was 5.0–6.1 

mm SL; it is likely that larvae begin to ascend the water 

column prior to complete yolk sac absorption, which occurs after they reach 6.2 mm SL (Fig. 12B–C). Although 

a grid of stations directly east and south of Kodiak Island 

was surveyed in February 2003, only two larvae were 

found at stations inshore of the outer continental shelf 

(Fig. 16). For 2003, our data suggest that any onshore 

transport of larvae (Bailey and Picquelle, 2002) must 

have occurred later in the year. 

Prior to this study, Doyle et al. (2002) grouped arrowtooth flounder and Pacific halibut larvae together 

as part of a distinct early-spring shelf edge and slope 

assemblage. Pacific halibut larvae were also found in 

our deep-water samples. This flatfish shares a similar 

early-life-history pattern with arrowtooth flounder of 

eggs being spawned, incubated, and hatched at great 

depths in winter along the shelf edge and slope in the 

GOA (Thompson and Van Cleve, 1936). 

While our study clearly describes the early life history 

of arrowtooth flounder in the GOA, taxonomic issues 

make similar studies in the Bering Sea more problematic. In the Bering Sea, the Kamchatka flounder has a 

distribution that partially overlaps that of arrowtooth 

flounder. Kamchatka flounder ranges farther west to 

the Sea of Okhotsk and northern Sea of Japan and 

south only into the western GOA. In regions where the 

species overlap, Kamchatka flounder tend to occupy 

greater depths than arrowtooth flounder (Mecklenburg 

et al., 2002). Eggs and larvae of Kamchatka flounder 

are unknown and therefore cannot be distinguished 

from those of arrowtooth flounder. As a result, in the 

Bering Sea where both species spawn (Dolganov, 2000), 

eggs and larvae can only be identified at the generic 

level (Atheresthes spp.). Since Kamchatka flounder are 

uncommon in the GOA and are not known to spawn 

there, all Atheresthes collected in the GOA are assumed 

to be arrowtooth flounder. Future studies comparing 

Atheresthes larvae from non-overlapping regions of their 

geographic ranges will be helpful for determining taxonomic characters useful for distinguishing the two species. Molecular studies comparing DNA samples from 

larvae with samples from adults of known identity may 

also help resolve this problem.

Although the most basic questions concerning GOA 

arrowtooth flounder spawning, egg incubation and 

development, and egg and larval distribution and abundance have been addressed, this study has given rise to 

more questions about their spawning and early life history. Does spawning begin in December, as suggested by 

the duration of egg development and the occurrence of 

preflexion larvae in the plankton at the end of January? 

How has arrowtooth flounder managed to become so numerous, given that depth distributions of ripe males and 

females infrequently overlap and males have very little 

milt? Now that the eggs and early larvae can be identified, 

directed studies can obtain more precise data on their 

vertical distribution and abundance. This additional 

information, in addition to recruitment studies on late 

larvae and juveniles, may help to explain why arrowtooth 

flounder dominates the GOA groundfish assemblage.

Acknowledgments

The authors thank the officers and crew of the NOAA 

Ship Miller Freeman for their efforts at sea. We also thank 

the following individuals for providing at-sea assistance 

collecting, spawning, and rearing arrowtooth flounder 

eggs and larvae: Rachael Cartwright, Jim Stark, and 

Duane Stevenson; William Floering (PMEL); Fumihito Muto (formerly Hokkaido University); and Erin 
27

MacDonald (formerly UW). Elizabeth Chilton helped 

us greatly at sea, spent many hours setting up the Kodiak Lab incubation tubes, sampled eggs and larvae in 

the lab, and took helpful photographs of incubating 

eggs. Lisa Appesland, Frank Morado, Dan Nichol, Jim 

Stark, and Mark Zimmermann assisted in the histological preparations and interpretation of maturity data. 

Beverly Vinter (retired) illustrated the egg and larvae. 

Kathy Mier provided statistical analyses. Jeff Napp and 

Gary Stauffer accommodated requests for ship time and 

supported all facets of this research. Kevin Bailey, Janet 

Duffy-Anderson, and Jeff Napp reviewed early drafts 

and made helpful suggestions. Gary Duker provided 

invaluable editing during the in-house review. Three 

anonymous reviewers provided numerous comments 

and suggestions which greatly improved the manuscript. 

This research is contribution FOCI-0618 to NOAA’s 

Fisheries-Oceanography Coordinated Investigations.

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NOAA Professional Papers NMFS

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abbreviations and should be doublespaced on a separate page at the end 

of the manuscript. 

Copyright law does not cover government publications; they fall within the 

public domain. If an author reproduces 

any part of a government publication in 

his work, reference to source is considered correct form. 

Submission 

Send printed copies (original and three 

copies) to the Scientific Editor: 

Dr. Adam Moles 

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Once the manuscript has been accepted 

for publication, you will be asked to 

submit an electronic file of it. The file 

should be submitted in WordPerfect or 

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NOAA SCIENTIFIC AND TECHNICAL PUBLICATIONS

The National Oceanic and Atmospheric Administration was established as part of the Department 

of Commerce on October 13, 1970. The mission responsibilities of NOAA are to assess the 

socioeconomic impact of natural and technological changes in the environment and to monitor 

and predict the state of the solid Earth, the oceans and their living resources, the atmosphere, and 

the space environment of the Earth.

The major components of NOAA regularly produce various types of scientific and technical 

information in the following kinds of publications:

PROFESSIONAL PAPERS: Important definitive research results, major 

techniques, and special investigations.

CONTRACT AND GRANT REPORTS: Reports prepared by contractors or 

grantees under NOAA sponsorship.

ATLAS: Presentation of analyzed data generally in the form of maps showing 

distribution of rainfall, chemical and physical conditions of oceans and 

atmosphere, distribution of fishes and marine mammals, ionospheric 

conditions, etc.

TECHNICAL SERVICE PUBLICATIONS: Reports containing data, observations, 

instructions, etc. A partial listing includes data serials; predictions and outlook 

periodicals; technical manuals, training papers, planning reports, and 

information serials; and miscellaneous technical publications.

TECHNICAL REPORTS: Journal quality with extensive details, mathematical 

development, or data listings.

TECHNICAL MEMORANDUMS: Reports of preliminary, partial, or negative 

research or technology results, interim instructions, and the like.

Iinformation on availablity of NOAA publications can be obtained from:

U.S. Department of Commerce

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

www.ntis.gov