Biological Report 82(11.123) 

December 1989 

Species Profiles: Life Histories and 

Environmental Requirements of Coastal Fishes 

and Invertebrates (Pacific Northwest) 

DOVER AND ROCK SOLES 

Fish and Wildlife Service 

Coastal Ecology Group 

Waterways Experiment Station 

U.S. Department of the Interior U.S. Army Corps of Engineers 
Biological Report 82(11.123) 

TR EL-82-4 

December 1989 

Species Profiles: Life Histories and Environmental Requirements 

of Coastal Fishes and Invertebrates (Pacific Northwest) 

DOVER AND ROCK SOLES 

Howard F. Horton 

Department of Fisheries and Wildlife 

Oregon State University 

Corvallis, OR 97331 

Project Officer 

David Moran 

U.S. Fish and Wildlife Service 

National Wetlands Research Center 

1010 Gause Boulevard 

Slidell, LA 70458 

Performed for 

Coastal Ecology Group 

Waterways Experiment Station 

U.S. Army Corps of Engineers 

Vicksburg, MS 39180 

and 

U.S. Department of the Interior 

Fish and Wildlife Service 

Research and Development 

National Wetlands Research Center 

Washington, DC 20240 
Suggested citation for this series: 

U.S. Fish and Wildlife Service. 1983-19-. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates. U.S. Fish Wildl. Serv. Biol. Rep. 82(11). U.S. Army 

Corps of Engineers, TR EL-82-4. 

Suggested citation for this profile: 

Horton, H.F. 1989. Species profiles: life histories and environmental requirements of coastal fishes 

and invertebrates (Pacific Northwest)--Dover and rock soles. U.S. Fish Wildl. Serv. Biol. Rep. 

82(11.123). U.S. Army Corps of Engineers, TR EL82-4. 17 pp. 
PREFACE 

This species profile is one of a series on coastal aquatic organisms, principally fish, of sport, commercial. 

or ecological importance. The profiles are designed to provide coastal managers, engineers, and biologists 

with a brief comprehensive sketch of the biological characteristics and environmental requirements of the 

species and to describe how populations of the species may be expected to react to environmental changes 

caused by coastal development. Each profile has sections on taxonomy, life history, ecological role, 

environmental requirements, and economic importance, if applicable. A three-ring binder is used for this 

series so that new profiles can be added as they are prepared. This project is jointly planned and financed by 

the U.S. Army Corps of Engineers and the U.S. Fish and Wildlife Service. 

Suggestions or questions regarding this report should be directed to one of the following addresses. 

Information Transfer Specialist 

U.S. Fish and Wildlife Service 

National Wetlands Research Center 

NASA-Slidell Computer Complex 

1010 Gause Boulevard 

Slidell, LA 70458 

U.S. Army Engineer Waterways Experiment Station 

Attention: WESER-C 

Post Office Box 631 

Vicksburg, MS 39180 
CONVERSION TABLE 

Metric to U.S. Customary 

Multiply BY 

millimeters (mm) 0.03937 

centimeters (cm) 0.3937 

meters (m) 3.281 

meters 0.5468 

kilometers (km) 0.6214 

kilometers 0.5396 

square meters (m2) 10.76 

square kilometers (km2) 0.3861 

hectares (ha) 2.47 1 

liters (1) 0.2642 

cubic meters (m3) 35.31 

cubic meters 0.0008110 

milligrams (mg) 0.00003527 

grams (g) 0.03527 

kilograms (kg) 2.205 

metric tons (t) 2205.0 

metric tons 1.102 

kilocalories (kcal) 3.968 

Celsius degrees (" C) 1.8 ("C)+32 

U.S. Customary to Metric 

inches 25.40 

inches 2.54 

feet (ft) 0.3048 

fathoms 1.829 

statute miles (mi) 1.609 

nautical miles (nmi) 1.852 

square feet (ft2) 2 

0.0929 

square miles (mi ) 2.590 

acres 0.4047 

gallons (gal)3 3.785 

cubic feet (ft ) 0.0283 1 

acre- feet 1233.0 

ounces (oz) 28350.0 

ounces 28.35 

pounds (lb) 0.4536 

pounds 0.00045 

short tons (ton) 0.9072 

British thermal units (Btu) 0.2520 

Fahrenheit degrees (" F) 0.5556 (" F - 32) 

To Obtain 

inches 

inches 

feet 

fathoms 

statute miles 

nautical miles 

square feet 

square miles 

acres 

gallons 

cubic feet 

acre- feet 

ounces 

ounces 

pounds 

pounds 

short tons 

British thermal units 

Fahrenheit degrees 

millimeters 

centimeters 

meters 

meters 

kilometers 

kilometers 

square meters 

square kilometers 

hectares 

liters 

cubic meters 

cubic meters 

milligrams 

grams 

kilograms 

memc tons 

metric tons 

kilocalories 

Celsius degrees 
CONTENTS 

PREFACE ...................................................... CONVERSION FACTORS .......................................... FIGURES ...................................................... ACKNOWLEDGMENTS ............................................ 

NOMENCLATURED'AXONOMY/RANGE .............................. MORPHOLOGY/IDENTIFICATION AIDS .............................. DoverSole .................................................... RockSole .................................................... REASON FOR INCLUSION IN THE SERIES ............................ LIFEHISTORY .................................................. Reproduction .................................................. Migration and Movement of Adults ................................... GROWTH CHARACTERISTICS ...................................... ECOLOGICAL ROLE ............................................. Food and Feeding ............................................... ENVIRONMENTAL REQUIREMENTS ................................ Substrate ..................................................... Temperature ................................................... Currents and Upwelling Events ...................................... Depth ....................................................... Parasites ...................................................... Disease ...................................................... THEFISHERY .................................................. 

REFERENCES .................................................. 

... 

111 

iv 

vi 

vii 
Number 

FIGURES 

Dover sole (Microstomus pacificus) ................................ 1 

Rock sole (Lepidopsetta bilineata) ................................. 1 

Distribution of Dover sole ..................................... 2 

Distribution of rock sole ..................................... 3 

Fecundity-length relationship for Dover sole captured off Oregon 

during winter of 1947-48 ...................................... 4 

Larval stages of Dover sole .................................... 5 

Length-age relationship for Dover sole ............................ 7 

Five-year running average length increments for female Dover sole 

plotted against 5-year running average upwelling indices ................ 7 

Walford graph of length at age t + 1 against length at t for 

female rock sole ............................................ 8 

Walford graph of length at age t + 1 against length at t for male rock sole . . 8 

Relation between mean seawater temperature from February to April 

off Triple Island. British Columbia. and year-class strength of rock sole ...... 9 
ACKNOWLEDGMENTS 

Special thanks are extended to the Canadian Department of Fisheries and Oceans for permission 

to reproduce Figures 1 and 2 from their Bulletin 180 of the Fisheries Research Board of Canada. 

I appreciate the permission given by Mary Yoklavich and Ellen Pikitch to refer to data in their 

unpublished manuscript. Robert Wolotira of the National Marine Fisheries Service provided a review. 

William Barss also reviewed the manuscript and was especially helpful in locating unpublished reports 

from the Oregon Department of Fish and Wildlife. Richard Bakkala generously provided reports on 

rock sole from the Northwest and Alaska Fisheries Center of the National Marine Fisheries Service. 

I appreciate the help provided by Jeannine Horton who redrew several of the figures. Sandy 

Enschede typed early drafts of the manuscript and was generally helpful in completing this report. 
Figure 1. Dover sole (Microstomus pacificus) Figure 2. Rock sole (Lepidopsetta bilineata) 

(illustration from Hart 1973). (illustration from Hart 1973). 

DOVER AND ROCK SOLES 

Scientific name ............ Microstomus 

pacificus (Lockington). 

Preferred common name ...... Dover sole 

(Figure 1). 

Other common names ....... Slime sole, 

slippery sole, smear dab, tongue sole, rubber 

sole, short-finned sole. 

Bering Sea (Hart 1973). Most common on 

the southern California continental shelf 

(Mearns and Harris 1975), and off northern 

California, Coos Bay, Oregon, and the 

Columbia River (Demoxy 1975). Moderately 

abundant off northern Washington, British 

Columbia, and the western Shumagin Island 

area (Demoxy 1975; Ronholt et al. 1986). 

Caught incidentally while fishing for other 

species in the eastern Bering Sea and the 

Aeutian Islands region (~akkala et al. 1981; Scientific name ............ Lepidopsetta Walters and Halliday 1987b). bilineata (Awes). 

.a , 

Preferred common name ...... Rocksole 

(Figure 2). 

Other common names ... Roughback sole, 

broadfin sole, gravel sole. 

Class ................... Osteichthyes 

Order .............. Pleuronectiformes 

Family ............... Pleuronectidae 

Geographic ranges: 

Dover sole (Figure 3): Occurs along the Pacific 

Coast from northern Baja California to the 

Recorded from the surface (Hart 1973) to a 

depth of 1,189 m (Allen and Mearns 1976). 

Adults rarely found shallower than 36 m 

(Demoxy 1975) and most of the commercial 

catch off northern California comes from 

depths of 82-823 m (Allen and Mearns 1976). 

Strongly prefers silt, mud, and muddy-sand 

bottom (Demoxy 1975; Demory et al. 1976b; 

Barss et al. 1977). Concentrates near deepwater municipal wastewater outfalls off 

southern California (Mearns and Harris 1975; 

Allen and Mearns 1976). 
Figure 3. Distribution of the Dover sole. 

Rock sole (Figure 4): Distributed from 

southern California to the Gulf of Alaska, 

along the Aleutian Chain, and as far north 

as the Gulf of Anadyr in the Bering Sea; 

then south off Kamchatka, the Kurile Islands, 

the eastern Okhotsk Sea, the Sea of Japan, 

and the east coast of Korea (Roedel 1953; 

Alton and Sample 1976). Centers of 

abundance off Kamchatka, in the 

southeastern Bering Sea and the western Gulf 

of Alaska, and along the coast of British 

Columbia (Alton and Sample 1976). Occurs 

from the surface to 732 m, but is a shallowwater species scarcely below 300 m (Alverson 

et al. 1%4; Hart 1973; Ronholt et al. 1986). 

Commercial fishery concentrated at depths of 

18-73 m in British Columbia (Forrester 1969), 

and from shallow depths to slightly over 200 

m in Alaskan waters (Alton and Sample 1976; 

Ronholt et al. 1986). Found on mud and 

sand substrata in the Bering Sea, on sandy or 

gravel bottom along the Pacific coast, and on 

rocky or firm, rapidly-sloping bottom in Puget 

Sound, Washington, waters (Nishishimamoto 

1958; Alverson 1960; Ronholt et al. 1986). 

MORPHOLOGY/IDENTIFICATION AIDS 

Dover Sole 

Body elongate, slender, compressed; caudal 

peduncle very short (Figure 1). Head slender, 

short; mouth terminal, small, asymmetrical, gape 

narrow, nearly equal on each side; teeth chiefly 

on blind side of jaws, never more than three in 

either jaw on eyed side; snout bluntly rounded; 

eyes small, lower eye in advance of upper eye; 

gill opening not extending above base of 

uppermost pectoral fin ray (Clemens and Wilby 

1961). Eyes dextral, with few exceptions 

(Follett et al. 1960). Lateral line nearly 

straight, with a short unconnected 

supratemporal branch (Norman 1934). On eyed 

side, color is rich and uniform in shades of 
Figure 4. Distribution of rock sole (Alton and Sample 1976). 

brown or mottled; blind side light to fairly dark 

gray; dusky on fins, especially near tips. Length 

to 71 cm total length (TL) and weight to 3.36 

kg for females; males are smaller. Secretes 

large amounts of slime; body flaccid (Hagerman 

1952; Hart 1973). 

Rack Sole 

Body elongate, deeply ovate, compressed, 

dextral. Head deep; mouth terminal, small, 

asymmetrical, gape narrow; teeth chiefly on 

blind side of jaws; snout bluntly rounded 

(Figure 2). Maxillary extends to forward part 

of lower eye. Eyes small, lower eye slightly in 

advance. Caudal peduncle moderate. Lateral 

line with an abrupt high arch over pectoral fin 

and with a short supratemporal accessory branch 

(Roedel 1953; Clemens and Wilby 1961; 

Wilimovsky et al. 1%7; Hart 1973). Rough 

tuberculated scales on the eyed side of the 

body. Usually deep brown on eyed side, 

frequently mottled with dark blotches, 

occasionally with scattered small red spots or 

pale blotches, reddish yellow to white on blind 

side; caudal and anal fins with dark blotches or 

bars (Roedel 1953; Clemens and Wilby 1961). 

Females reach a length of 60 cm TL, males 53 

cm (Hart 1973). Weigh 2.3-2.7 kg (Norman 

1934; Roedel 1953). 

REASON FOR INCLUSION IN THE SERIES 

The Dover sole has been an important component of the California trawl fishery since its 

inception in 1876 (Hagerman 1952). In Oregon, Dover sole made the largest contribution 

to total biomass of flatfishes landed commercially (Demory et al. 1976a). The excellent 

quality of the flesh, fresh or frozen, and long 

shelf life have made it one of the most important of the small flatfishes on the Pacific Coast 

(Hart 1973). Dover sole are commercially 

important from Santa Barbara, California, to 

British Columbia (Allen and Mearns 1976). 
The rock sole is listed as one of the key 

species in Washington inside waters where it is 

the target of commercial trawl fisheries and is 

caught by recreational anglers (Pederson and 

DiDonato 1982). The rock sole is relatively 

abundant north of Coos Bay, Oregon (Cannon 

1953). It is listed by Browning (1974) as a 

principal flatfish species in the North Pacific 

commercial fisheries. The estimated maximum 

sustained yield for rock sole in the eastern 

Bering Sea and the Aleutian Islands region was 

100,000 t in 1987 (Walters and Halliday 1987a). 

LIFE HISTORY 

Reproduction 

Dover sole females off northern California 

and Oregon first reach maturity at 33 cm TL; 

at 38 cm, 50% are mature; and at 45 cm and 

11 years of age all are mature (Hagerman 1952; 

Harry 1959; Demory 1975). Some males mature 

at 30 cm TL, and all mature by 39 cm and 7 

years of age (Hagerman 1952). Frey (1971) 

indicated that maturity starts at age 5 off 

northern California. ~~e at mat~rity-~robabl~ 

varies by region and increases progressively from 

south to north. Recently, Yoklavich and Pikitch 

(1988) found that all Dover sole collected off 

northern Oregon were mature at 32 cm TL; the 

smallest mature fish was 24 cm. They suggested 

that difficulties in differentiating post-spawning, 

inactive, mature ovaries from immature ones 

may have contributed to the size at maturity 

discrepancies. 

Dover sole spawn at specific sites in offshore 

waters between 80 and 732 m (Demory 1975; 

Garrison and Miller 1982; Hirschberger and 

Smith 1983). The spawning period varies by 

region and occurs from January to August in 

the Gulf of Alaska and from November through 

March off Washington, Oregon, and California, 

with January and February being the peak 

months (Harry 1959; Demory 1975; Garrison 

and Miller 1982; Hirschberger and Smith 1983). 

Fecundity is a function of size and ranges from 

37,000 ova for a 36.0 cm TL fish, to 265,800 

ova for a 57.5 cm TL fish (Harry 1959; Frey 

1971). The length-fecundity relationship is 

illustrated in Figure 5 for Dover sole captured 

off Oregon (Harry 1959). Fecundity estimates 

for 42-64 cm TL Dover sole captured off 

northern California (Hagerman 1952) are 

slightly higher than for Oregon fish of the same 

size. 

Female rock sole from Puget Sound, 

Washington, mature in their fourth or fifth year, 

while males reach maturity in their third year 

(Smith 1936). In nearby British Columbia 

waters, Forrester (1969) observed mature 

females at 31 cm TL and mature males at 28 

cm TL. These lengths represent age4 fish. No 

sexual dimorphism is apparent (Alton and 

Sample 1976). 

Rock sole spawn during winter and spring 

throughout their range (Alton and Sample 

1976). In British Columbia, spawning is 

believed to take place during late winter and 

early spring (Forrester 1969). In winter in the 

Shumshu Islands of the Okhotsk Sea, large 

sexually mature rock sole stay at depths of 125- 

250 m (Shvetsov 1978). In Puget Sound, 

Washington, mature rock sole were captured 

at 150 m in February 1950, but they usually 

LENGTH OF FISH IN CENTIMETERS 

Figure 5. Fecundity-length relationship for 

Dover sole captured off Oregon during the 

winter of 1947-48 (Harry 1959). 
occurred in water less than 55 m deep 

(Nishishimamoto 1958). It thus appears that 

fish move into deeper water in winter and 

spring to spawn. Rock sole produce about 0.4 

million ova at 35 cm TL and 1.3 million at 46 

cm TL (Forrester 1%9). 

The eggs and larvae of Dover sole are 

buoyant and pelagic (Norman 1934; Hagerman 

1952). Diameters of ovarian eggs average 2.33 

mm, ranging from 2.05 to 2.57 mm (Hagerman 

1952). The yolk is homogeneous and oil 

globules are lacking. Larvae are about 6.5 mm 

standard length (SL) at hatching. They become 

deep bodied (Figure 6) and remain in the larval 

stage until about 50 mm SL. Two spines 

develop on the back of the head of advanced 

larvae. Certain meristic features simplify 

identification of Dover sole larvae: caudal rays, 

21-22; vertebrae, 50-53; dorsal rays, 94-106; 

and anal rays, 80-88. Larvae were captured in 

Figure 6. Larval stages of Dover sole 

(Ahlstrom and Moser 1975). 

standard ichthyoplankton hauls (this method is 

described in Kramer et al. 1972) off California 

chiefly from April through July (Ahlstrom and 

Moser 1975), but were taken off Oregon with 

mid-water trawls and plankton nets throughout 

the year (Pearcy et al. 1977). The occurrence 

of advanced larvae during the spawning season 

indicates that Dover sole larvae are pelagic for 

at least a year (Pearcy et al. 1977). 

Dover sole larvae are widely distributed off 

Oregon; peak Isaacs-Kidd midwater trawl 

(IKMWT) catches are at 46 km and f~h occur 

at distances as great as 550 km offshore (Pearcy 

et al. 1977). Off Baja California, Dover sole 

larvae have been caught with IKMWT as far as 

840 km offshore (Berry and Perkins 1966). 

North-south movement off Oregon is more or 

less random, but more large larvae are found 

near the continental shelf and slope (where they 

eventually settle) than in inshore waters (Pearcy 

et al. 1977). Dover sole off Oregon appear to 

take up benthic life on the continental shelf in 

January and February; they are then about 1 

year old and are less than 50 mm SL (Demory 

1975; Pearcy et al. 1977). 

Small Dover sole (<I8 cm TL) occur on the 

continental shelf off the Oregon-southernWashington coast mostly between 55 and 146 

m (Demory 1971). In February, most occur at 

depths greater than 128 m and none occur at 

depths less than 73 m. During May, July, and 

August, most small fish are found between 55 

and 90 m. In November, they mostly occur 

between 91 and 108 m (Demory 1971). 

Although there is overlap in the depth 

distribution of smaller and larger Dover sole, it 

appears that "adultsn are often distributed in 

deeper water, with the possible exception of 

July and February. Demory's (1971) study, 

however, was completed before Oregon's deep 

water Dover sole f~hery was established. The 

deep water f~hery has produced mostly males 

except for catches of concentrated mature males 

and females in winter. 

The yellowish-orange eggs of rock sole are 

demersal and adhesive and have a diameter that 

averages 0.92 mm and ranges from 0.87 to 1.00 

mm (Forrester lWa, 1Wb; Ahlstrom et al. 

1984). The yolk is homogeneous, and oil 
globules are lacking. Larvae range from 3.4 to 

5.0 mm SL when hatched and are 17.7-20.0 mm 

SL at transformation. As in the Dover sole, 

identification is facilitated by meristic features: 

caudal rays, 18-19 (12 are branched); vertebrae, 

39-42; dorsal rays, 65-84; and anal rays, 50-65 

(Pertseva-Ostroumova 1%1; Ahlstrom et al. 

1984). 

Young rock sole in Kamchatka swim on their 

sides and assume their bottom-dwelling existence 

at about 20 mm SL (Pertseva-Ostroumova 

1%1). They occur in shallow water on beaches 

in some localities (Hart 1973). Little is known 

of the whereabouts of rock sole in their first 

year of life on the seafloor, but by age 1 they 

are found with the adults (Forrester 1969; Alton 

and Sample 1976). 

Migmtion and Movement of Adults 

Dover sole adults undergo annual bathymetric 

migrations in Pacific Northwest waters. From 

May through October the fish are generally 

found in shallow waters less than 150 m deep. 

After October, fish move back to deeper waters; 

this return coincides with the principal spawning 

season of November through March with a peak 

in January and February (Alverson 1960; 

Westrheim and Morgan 1963; Barss 1982; 

Quirollo and Kalvass 1987; Barss and Demory 

1988). 

Dover sole exhibit very little north-south 

seasonal migration in the Pacific Northwest. 

Fargo et al. (1985) recovered 745 of 5,145 

Dover sole tagged off northern Hecate Strait, 

British Columbia, and reported negligible 

dispersal of about 0.4% per year. Of 260 

tagged fish recovered off Willapa, Washington, 

only 7 were recaptured more than 48 km from 

the original tagging area. Maximum migrations 

were 161 km north and 579 km south 

(Westrheim and Morgan 1963). Barss and 

Demory (1988) reported on the recovery of 

2,194 Dover sole out of 22,336 tagged off 

Oregon and Washington in eight experiments 

during 1948-75. Maximum time at liberty was 

22 years. They found only modest north-south 

movement with 98% of the recaptures occurring 

within 93 km of the tagging site. Of 1,235 

tagged Dover sole recovered off southern 

Oregon and northern California by Quirollo and 

Kalvass (1987), only 13 were recaptured outside 

the original tagging area. The mean movement 

from the point of release was 19 km. A Dover 

sole tagged off Mad River in northern 

California was at liberty 2,234 days when 

recaptured and had a net movement of only 

40.2 km (Best 1957). These small movements 

suggest a limited exchange of stocks among 

adjacent offshore areas from northern California 

to British Columbia. 

There is no indication that bathymetric 

migrations of rock sole are as extensive as those 

of some other flounders in Pacific Northwest 

waters. However, there is some evidence that 

rock sole move to shallow water (18-27 m) for 

the summer and return to deep water for the 

winter (Alverson 1960: Forrester 1969; Shvetsov 

1978). Rock sole off Shumshu Islands in the 

Okhotsk Sea overwinter on the edge of the 

continental slope at a depth of 125-320 m from 

December to April. From April to June, the 

fish return to the continental shelf to depths of 

50-120 m (Shvetsov 1978). Shvetsov (1978) 

believes that the movement from winter to 

spring grounds is in response to warming 

temperatures in the shallow waters, whereas the 

summer movements are related to distribution 

of prey on the seafloor rather than to water 

temperature. The principal stimulus for moving 

to deep water in winter is the peaking of 

physiological condition prior to spawning 

which results in diminished feeding (Shvetsov 

1978). 

All rock sole tagged in Hecate Strait of 

British Columbia were recovered in the general 

vicinity of the tagging and previous capture sites 

(Forrester and Thomson 1969). This apparent 

lack of significant movement suggests the 

existence of several discrete subpopulations in 

the northwest (Forrester 1969). 

GROWTH CHARACTERISTICS 

Dover sole generally were aged by counting 

annuli on the surface of scales or otoliths prior 

to about 1980. Scales were collected from the 

central portion of the eyed side of the body, 

mounted between glass slides, and read under 

magnification with transmitted light. Otoliths 
(sagittae) were collected by excision, stored in 

5050 glycerin and water with a small amount of 

thymol, and read under magnification with 

reflected light on a black background (Demory 

1972; Mearns and Harris 1975; Hayman and 

Tyler 1980; Kreuz et al. 1982). Both scales and 

otoliths provided satisfactory estimates of age 

for young and fast-growing fish up to age 5 for 

males and age 6 for females (Demory and 

Pikitch 1986). After age 5, Pikitch and Demory 

(1988) calculated that the underestimation 

worsens with advancing age. For older 

specimens, Chilton and Beamish (1982) 

recommended counting annuli on a cross section 

of the otolith, since surface counts on scales 

and otoliths tended to underrepresent advanced 

ages. Demory and Pikitch (1986) recommended 

that the broken-and-burned otolith method 

(Christensen 1964) be used to replace the scale 

method for the routine aging of Dover sole. 

Their otoliths were stored dry or in 30%-50% 

ethyl alcohol. 

The weight of a Dover sole increases by the 

cube of its length. Both males and females 

closely approximate this "cubic law," though 

males gain weight at a slightly slower rate 

(Hagerman 1952). Dover sole are about 11.4 

cm long at age 2, and begin to enter the 

commercial trawl catch by age 4 at about 24.1 

cm TL and a weight of about 136 g. By age 8 

they are about 35.5 cm long, weigh about 450 g 

and are fully recruited to the trawl fishery 

(Demory 1975). Differential growth between 

male and female Dover sole becomes apparent 

near age 5 (Figure 7). The difference continues 

throughout the life of the fish: at age 20, 

females average 53.3 cm TL in length and 

weigh 1,452 g, while males at the same age 

average 45.7 cm and 862 g (Demory 1975). 

Annual growth rates of Dover sole vary by 

as much as 16%. These annual changes can be 

explained partly by changes in water 

temperatures at 100 m depth which, in turn, 

correlate with upwelling events (Figure 8) 

(Kreuz at al. 1982). The average age of Dover 

sole differs from port to port due to differences 

in the intensity of the local fishery and the 

relative year-class strengths in adjacent 

populations (Demory 1975). Demory (1972), 

who read the scales of 782 Dover sole captured 

AGE GROUP 

Figure 7. Length-age relation for Dover sole 

(Hagerman 1952). Note that Hagerman 

considers fish to be age 0 after 1 year of life. 

1958 59 6U 61 62 63 64 65 6r3 ' (i <C G? ill il 72 73 74 75 

YEAR 

Figure 8. Five-year running average length 

increments for female Dover sole plotted 

against 5-year running average upwelling 

indices (Bakun 1973, 1975; Kreuz et al. 1982). 

off the Columbia River, found the maximum 

age to be 24 years. Subsequently, Demory and 

Pikitch (1986) reported a maximum age of 37 

years for male and female Dover sole using the 

broken-and-burned otolith method. Fish up to 

45 years old were reported by Chilton and 

Beamish (1982), who examined cross sections of 

Dover sole otoliths. Barss and Demory (1988) 

reported a 46-year-old female and the recapture 
of a Dover sole that had been at liberty off 

Oregon for 22 years. These observations 

confirm the long life potential of the species. 

Rock sole are generally aged by counting 

annuli on the interopercle or the otoliths. 

Interopercles are removed by excision, immersed 

in hot water for about 10 min, cleaned, and 

stored dry in suitable containers. Surface 

features of both interopercles and otoliths are 

examined under magnification and reflected light 

over a dull or dark background. For young fish, 

examination of the external otolith surface gives 

satisfactory results. For older fish, examination 

of the interopercle surface or burned cross 

sections of the otolith is necessary 

(Nishishimamoto 1985; Chilton and Beamish 

1982). Fargo and Chilton (1987) validated the 

use of burned cross sections of rock sole 

otoliths for age determination. 

The weight of rock sole, like that of the 

Dover sole and many other fishes, increases at 

a rate about equal to the cube of its length. 

Kaimmer et al. (1976) found that the overall 

length-weight relation for rock sole in the 

Bering Sea could be described by the equation: 

where W equals the predicted weight in grams 

of a fish L cm in TL. 

Forrester and Thomson (1969) found that 

growth of rock sole in British Columbia occurs 

in two phases: in both males and females, the 

growth increment increases annually to age 4, 

and decreases annually from age 5 onward 

(Figures 9 and 10). Female rock sole reach 7- 

10 cm TL in 1.5 year, 22 cm in 3 years, and 35- 

39 cm in 5.5 to 7 years (Forrester 1969). 

Female rock sole grow faster than males and 

become longer (Nishishimamoto 1958; Alton 

and Sample 1976; Kaimmer et al. 1976). The 

largest rock sole recorded by Forrester (1%9) 

was a 60-cm-TL female estimated to be 15 years 

old. A maximum age of 25 years was reported 

for rock sole by Chilton and Beamish (1982), 

who used the broken-and-burned otolith 

method. 

LENGTH (Qt) CM 

Figure 9. Walford graph of length of age t + 

1 (age in years) against length at age t for 

female rock sole (Forrester and Thomson 

1969). 

10 20 30 40 

LENGTH (J,) CM 

Figure 10. Walford graph of length of age t + 

1 (age in years) against length at age t for 

male rock sole (Forrester and Thomson 1969). 
Growth rate of rock sole varies from area to 

area and from year to year. Kaimmer et al. 

(1976) found absolute differences in the lengthweight relations and between sexes of about 

5%-10% among all areas sampled in the eastern 

Bering Sea. Levings (1967) found that rock 

sole from the British Columbia coast had a 

higher rate of growth than certain northern 

populations in the western Gulf of Alaska and 

northwest Bristol Bay. Nishishimamoto (1958) 

noticed great variation in the growth rate of 

rock sole from different locations in Puget 

Sound, Washington. Both Nishishimamoto 

(1958) and Forrester and Thomson (1969) cite 

density-dependent relations (in which growth 

rate decreases as density increases) as affecting 

growth of rock sole in some locations, and 

hydrographic conditions in others. In particular, 

Forrester and Thomson (1%9) associated mean 

surface temperatures near 6.1 "C with betterthan-average year-classes of rock sole (Figure 

11). Whether temperature per se had a direct 

or indirect effect was not known. Forrester and 

Thomson (1969) also present data suggesting a 

density-dependent relationship among rock sole 

off central British Columbia. 

ECOLOGICAL ROLE 

Food and Feeding 

Dover sole feed almost exclusively on benthic 

infaunal and epifaunal invertebrates, mainly 

5 6 7 8 9 

SURFACETEMPERATURE 'C 

Figure 11. Relation between mean surface 

seawater temperature during February to April 

off Triple Island, British Columbia, and yearclass strength of rock sole (redrawn from 

Forrester and Thomson 1969). 

polychaetes, ophiuroids, and mollusks (Pearcy 

and Hancock 1978; Gabriel and Pearcy 1981; 

Cross et al. 1985). Hagerman (1952) reported 

that no vertebrate had ever been found in the 

stomach of a Dover sole. Feeding on benthos 

is typical of flatfishes that have asymmetrical 

jaws, small stomachs, and long intestines 

(DeGroot 1971). Off Oregon, Dover sole feed 

most often on polychaetes of the families 

Pectinariidae, Glyceridae, Sternaspidae, and 

Opheliidae, in addition to Ophiuroidea. 

Amphipods--especially the genera Hapiniopsis, 

Melphidippa, Ampelisca, and Nicipe--are important crustacean prey. Pelecypods, particularly 

the genera Macoma, Adontorhina, and 

Axinopsida, make up most of the molluskan 

biomass consumed (Gabriel and Pearcy 1981). 

Annelids usually dominate in the diets of 

juvenile Dover sole in both summer and winter. 

Both juveniles and adults consume more prey in 

summer than in winter regardless of fish size 

(Pearcy and Hancock 1978). In general, Dover 

sole are not opportunistic feeders but tend to 

select food items. Larger Dover sole select 

larger prey and tend to feed in deeper water 

(Gabriel and Pearcy 1981). Pearcy and 

Hancock (1978) reported that Dover sole 

select habitats where their principal prey are 

most abundant, regardless of depth and bottom 

type. 

Rock sole are predominantly benthophagous 

and feed mostly on benthic infaunal and 

epifaunal invertebrates. The principal prey off 

Oregon are ophiuroids of the genus Ophiura, 

polychaetes, pelecypods, sipunculids, and 

amphipods (Kravitz et al. 1976; Becker and 

Chew 1987). In Hecate Strait off central 

British Columbia, Forrester and Thomson (1969) 

listed polychaetes, crabs, shrimp, and clams as 

the most abundant items in the diet of 184 rock 

sole less than 29 cm TI,. For fish longer than 

29 cm, sandlance (Ammodytes hexaptems), crabs, 

shrimp, scallops, and herring were the principal 

prey consumed. Because the diet of fishes 

normally is related to feeding behavior, digestive 

tract morphology, and mouth structure 

(DeGroot 1971), the consumption of sandlance 

and herring may be unusual. The mouth of 

rock sole is small; the jaws and dentition are 

better developed on the blind side; the teeth 
are bluntly conical; and the gill rakers are 

without teeth (Kravitz et al. 1976). 

ENVIRONMENTAL REQUIREMENTS 

The Dover sole is a deep-water species and 

shows a strong preference for mud or silt 

bottom (Demory et al. 1976b; Barss et al. 1977; 

Pearcy 1978). In their study area off Oregon, 

Pearcy and Hancock (1978) concluded that 

depth-related factors had a greater influence 

than sediment type on the composition of 

benthic fishes, fish food, and invertebrate fauna. 

There was a shallow-water and deep-water 

association in the composition of the diet of 

Dover sole in their study. 

Temperature 

Dover sole appear to grow most rapidly 

during spring and summer months off Oregon 

(Demory 1972; Kreuz et al. 1982). Seawater 

temperatures at 50 m and 150 m are coldest 

during these months and were not significantly 

correlated with growth of Dover sole (Kreuz et 

al. 1982). However, the annual changes in 

growth rate for Dover sole are explained partly 

by lower water temperatures that are correlated 

with upwelling (Kruse 1981; Kreuz et al. 1982). 

Environmental temperature may be an 

important contributor to variations in year-class 

strength. Forrester and Thomson (1969) presented data indicating that year-classes were 

better than average at temperatures near 6 "C, 

and poorer than average at higher or lower 

temperatures (Figure 11). Ames et al. (1978) 

determined that 24.9 "C was the upper lethal 

water temperature at which 50% of the rock 

sole survived. 

Currents and Upwelling Events 

Hayman and Tyler (1980), after investigating 

the influence of various environmental factors 

on Dover sole cohort strength, concluded that 

the strength of one cohort is positively correlated with the strength of the next cohort. For 

example, strong cohorts tend to be followed by 

strong cohorts. Spawning capacity (which is the 

egg production of a population) did not 

significantly affect cohort strength of Dover sole 

(Hayman and Tyler 1980, Hayman et al. 1980). 

The critical environmental period occurs from 

September of the year before hatching until 

May of the year after hatching. Cohort 

strength was not correlated with north-south 

water transport but rather with east-west water 

transport, which is associated with upwelling 

and, in turn, with food availability for larvae in 

June and July. Cohort strength just before and 

during settling of larvae was highly correlated 

with the offshore divergence index, which 

measures the acceleration of surface water 

transport at a point (Bakun 1973, 1975; Hayman 

and Tyler 1980). The offshore divergence index 

is correlated, in turn, with the convergence of 

inshore and offshore currents, which may be 

beneficial if they confine larvae to the area of 

the Continental Shelf where favorable habitat is 

available for them to settle (Hayman and Tyler 

1980). 

Depth 

Rock sole occupy relatively shallow water 

throughout their range. In waters of British 

Columbia and the Gulf of Alaska, the species 

is most common on the inner continental shelf 

at depths less than 91 m (Alton and Sample 

1976). In the Alaska Peninsula region, they 

occurred in 40% to 87% of the trawls on the 

inner shelf and were the dominant flounder 

(Alverson et al. 1%4). Throughout the 

Aleutian Islands region, rock sole are common 

from 100 to 300 m and occasionally are found 

at 500 m (Ronholt et al. 1986). In the eastern 

Bering Sea, rock sole occur from shallow waters 

to depths of 200 to 300 m (Alton and Sample 

1976). 

Encysted nematodes in the mesenteries and 

on the liver were reported for Dover sole examined in northern California (Hagerman 1952). 

Rohde (1984) reported that the nematode 

Philometra occurs between the rays of the 

dorsal and ventral fins and subcutaneously in 

the opercular region, gill cavity, and occasionally 

the caudal fin of rock sole. The parasites are 

always coiled and immobile. To extrude 

embryos, the female worm must bore through 

the host integument. 
Disease 

Skin tumors were observed in Dover sole 

throughout a broad geographic area. Allen and 

Mearns (1976) list fin erosion and tumors as 

affecting Dover sole captured off southern 

California near sewage outfalls. Cross (1985) 

collected Dover sole in the same area from 

1971 through 1982 and found that 34% of the 

specimens had fin erosion. The incidence of 

the disease was negligible in new recruits 40-50 

mm SL, but increased rapidly with increasing 

fish size. Cross (1985) found no significant 

difference in the length-weight relation or sizeat-age data between Dover sole with and 

without the disease; however, survival rate of 

fish older than 3 years was significantly lower. 

Sinderman (1979) reported that fin rot is the 

best known but least understood disease of fish 

from polluted waters. 

The number of tumors per affected Dover 

sole captured off Ventura, Los Angeles, and 

Orange Counties, California, ranged from 1 to 

10, with a mean of 1.8 (Mearns and Sherwood 

1974). Histopathological examination of the 

tumors indicated that the growth included 

angioepithelial nodules and epidermal 

papillomas (Wellings et al. 1x5). The presence 

of tumors appeared to be a function of fih 

size--usually occurring in specimens less than 

150 mm SL (Mearns and Sherwood 1974). 

While tumors have been associated with 

decreased growth and increased mortality in 

flathead sole (Hippoglossoides elassodon) (Miller 

and Wellings 1971), the actual fate of tumorbearing Dover sole has not been determined 

(Mearns and Sherwood 1974). 

As with Dover sole, skin tumors were 

observed in rock sole throughout an extensive 

geographic area. Alton and Sample (1976) 

reported that the incidence of skin tumors is 

higher in eastern Bering Sea rock sole than in 

other groundfish examined. In 1975, 1% of the 

fish sampled had tumors; the tumors were found 

only on the blind side of the fish. Peters 

(1984) found that up to 10% of the rock sole in 

the Bering Sea were infected with X-cell 

papillomatosis. Levings (1967) reported that 

about 10% of the rock sole captured in the 

western Gulf of Alaska and in northwest Bristol 

Bay were infected with a tumorous growth. 

Malins et al. (1984) reported the presence of 

lesions in the liver, kidney, and gills of rock sole 

captured in Puget Sound, Washington. The 

lesions were either associated with parasites and 

microorganisms or were of unknown etiology. 

The idiopathic lesions were correlated with the 

presence of a wide assortment of accumulated 

chemicals and compounds in the sediments; 

specific cause and effect relations were not 

identified (Malins et al. 1984). 

THE FISHERY 

Dover sole are caught with an otter trawl 

dragged on the bottom by a single vessel 

(Demory 1975; Hayman et al. 1980). Areas of 

major abundance are found off northern 

California, central Oregon, and the Columbia 

River; areas of lesser abundance are found off 

northern Washington and British Columbia. 

The 10-year average trawl catch of Dover sole 

off Washington, Oregon, and California for the 

period 1972-86 is shown in Table 1. 

Table 1. Ten-year average trawl catch (in 

thousands of pounds) of Dover sole off 

Washington, Oregon, and California, 1963-86. 

Data from Annual Reports 22-38 of the Pacific 

Marine Fisheries Commission (PMFC 1969-85), 

and Korson and Silverthorne (1987). 

State 

Period WA OR CA 
Rock sole are captured in trawl fisheries in the 

Pacific Northwest (PMFC 1%9-85). The 10- 

year average trawl catch of rock sole off 

Washington, Oregon, and California for the 

period 1972-85 is given in Table 2. 

Thi largest catches of rock sole have been 

taken from the eastern Bering Sea and the 

Aleutian Islands region. Rock sole were 

captured in the eastern Bering Sea by Asian 

trawlers as early as 1933 and were intensively 

harvested by fleets from Japan and the U.S.S.R. 

in 1%0 and 1%1 (Alton and Sample 1976). 

The early fishery was conducted with longlines, 

gill nets, and dragnets, and most of the catch 

was processed into fish meal by the Japanese. 

Table 2. Ten-year average trawl catch (in 

thousands of pounds) of rock sole off 

Washington, Oregon, and California, 1963-85. 

Data from Annual Reports 22-38 of the Pacific 

Marine Fisheries Commission (PMFC 1969-85). 

10-year State 

mean WA OR CA 

By 1972, as many rock sole were frozen for 

later consumption as were reduced to fish meal 

(Alton and Sample 1976). Historically, Japan, 

the U.S.S.R., and the Republic of Korea were 

the predominant harvesters of rock sole in the 

eastern Bering Sea. Beginning in 1980, U.S. 

fleets began operations for groundfish in this 

area. In 1987, U.S. fisheries were projected to 

take 95% of the total catch (Bakkala 1987), 

most of which was frozen. The all-nation 

catches, the estimated biomass, and the 

estimated maximum sustained yield for rock sole 

in the eastern Bering Sea and the Aleutian 

Islands region are given in Table 3. 

Table 3. All-nations catches, estimated 

biomass, and maximum sustained yield (MSY) 

estimates in metric tons for rock sole in the 

eastern Bering Sea and Aleutian Islands region 

of Alaska (odd years only). (Data from 

Walters and Halliday 1987a.) 

Year Catch Biomass MSY 

'Eastern Bering Sea only 
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Rohde, K 1984. Diseases caused by 

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Volume 4, part 1, introduction, Pisces. 

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Ronholt, L.L., K Wakabayashi, T.K 

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Admin., Natl. Mar. Fish. Serv., Northwest 

Alaska Fish. Cent., Seattle, Wk 187 pp. 

Unpubl. MS. 

Walters, G.E., and KL. Halliday. 1987b. 

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Unpubl. MS. 
Rock Soles. 7. Author(%) 8. Performing Organization Rept. N 

Howard F. Hortoi 

9. Performtng Organization Name and Address 10. PmiectlTasklWork Unit No. 

Department of Fisheries and Wildlife 

Oregon State University 11. Contract(C) or Grant(G) NO. 

Corvallis, OR 97331 -,= 

50172 -101 

-- 12. Sponsoring Organization Name and Address 

U.S. Department of Interior U.S. Army Corps of Engineers 

Fish and Wildlife Service Waterways Experiment Station 

National Wetlands Research Center P.O. Box 631 

Washington, DC 20241 Vicksburg, MS 39180 

15. Supp1ernentat-j Notes I *US. Army Corps of Engineers Report No. TR EL-82-4 

I 

3. Recio~ent's Accesston NO. 

5. Repon Date 

December 1989 

6. 

REPORT DOCUMENTATION I 1. REPORT NO, 

PAGE I Biological Report 82(11.123)* 

I 16. Abstract (Limit: 200 words) 

2. 

Species profiles are literature summaries of the taxonomy, morphology, range, life history, and 

environmental requirements of coastal species. Dover sole are found in deep waters and prefer silt 

to muddy-sand bottoms; rock sole occur in shallow waters on soft to firm bottoms. Dover sole mature 

at about 5 to 7 years and spawn buoyant eggs from November to April; rock sole mature at 3 to 5 

years and spawn demersal and adhesive eggs during winter and spring. Dover sole begin benthic life 

at age 1 and rock sole at 20 mm SL. Dover and rdk soles migrate to shallower waters for the 

summer and to deeper waters for the winter; neither exhibits significant north-south movements. 

Dover sole live to 46 years and rock sole to 25 years; broken and burned otoliths are used to age both 

fish. Dover and rock soles feed on benthic infaunal and epifaunal invertebrates. Throughout a wide 

geographic area both species are affected by skin tumors. These soles are harvested commercially with 

trawls; northern California and Oregon are the main areas for Dover sole, while the eastern Bering 

Sea and Aleutian Islands are most important to rock sole. 

4. Title and Subtitle 

Species Profiles: Life Histories and Environmental Requirements 

of Coastal Fishes and Invertebrates (Pacific Northwest)--Dover and 

17. Document Analysis a. Descriptom 

Flatfshes Feeding habits Temperature Fisheries 

Life cycles Depth Growth Sediments 

Contaminants 

b. IdentlhenlQpen.Ended Terms 

Dover sole Environmental requirements 

Microstomus pacificus Rock sole 

Lepidopsetta bilineata 

18. Ava~labllity Statement I 19. ~ecurnty class (~hls R~WR) 21. No. of Pages 

Unlimited distribution +---++

Unclassified 

m. Security Ui~classified class CThis Page) 

See ANSI-239.18) OPTIONAL CORY 272 (4-7 

(Formerly NTIS-35) 

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