'THE ENGLISH SOLE
Compiled by
William H. Barss
INFORMATIONAL REPORT 76-1
Oregon Department of Fish and W i ldl i f e
February 1976
INFOWlATIOM REPORT
- ENGLISH SOLE
INTRODUCTION
The English sole i s a major contributor t o Pacific Ocean trawl ftshertes off the
United States and Canada.
Only Dover sole and sometimes petrale sole provide greater
annual landings i n Oregon.
English sole are considered f i n e eating sole and usually enjoy a good market.
I n B r i t i s h Columbia, local consumers o f t h i s popular f i s h have learned t o r e l i s h the
"iodine" flavor t h a t can be detected i n f i s h from some inshore waters.
I n Canada i t i s known as the lemon sole because o f i t s resemblance i n shape and
color t o the lemon sole found o f f Europe,
I n California i t has been called the point
sole because of i t s characteristic pointed head.
The development o f the Oregon trawl fishery i n the l a t e 1930's produced the f i r s t
large landings o f English sole.
Demand f o r English sole increased during lrlorld War I 1
and Oregon landings peaked a t about four m i l l i o n pounds i n 1946.
There was an abrupt
drop i n landings I n 1949 t o about one m i l l ton pounds reflecting a declining demand
for bottom fish.
Since then, annual landings have fluctuated around two m i l l i o n
pounds with the exception of low landings i n the mid 1950's and an exceptional 3.5
m i 11ion pounds i n 1966.
Total U.S.
pounds a year.
and Canadian landings have maintained a ten-year average o f 10 m i l l i o n
Oregon ranks t h i r d i n production with California leadtng I n annual
landings.
DESCRIPTION
English sole are easily recognized by t h e i r pointed head and jaws.
are on the r i g h t side.
Both eyes
The f i s h i s slender and pointed, with brown color r e s t r l c t e d
t o the r i g h t side; i t s l e f t (blind) side i s pale yellow t o white, tinged w l t h reddish
brown, especially on the head.
Mature females can be sexed by "candling".
When a mature female i s held up t o
the l i g h t the long ovary can be seen from below the stomach area tapering toward the
I
tail.
The absence of t h i s feature i n f i s h caught by commercial t r a w l almost always
indicates a male.
Immature f i s h a r e u s u a l l y sexed i n t e r n a l ly.
The immature male
gonad i s s i m i l a r t o the l a r g e r gonad found i n a mature male and i s a s o l id, beanshaped organ found a t t h e back p a r t o f t h e stomach c a v i t y .
The ovary o f an tnnnature
female i s small and pink and contains a hollow center.
REPRODUCTION
Some Oregon female English s o l e mature a f t e r 3 years (12$-inches) and most a r e
mature a t 4 years of age.
Most males mature a t about lo&-inches and 4 years of age.
C a l i f o r n i a English s o l e mature about one year e a r l i e r .
Egg production increases
w i t h s i z e of f i s h from about 150 thousand (12-inches) t o 2 m i l l i o n (17%-inches) per
female.
Spawning occurs from December through A p r i l b u t the m a j o r i t y o f f Oregon spawn
i n December through February.
Spawning f i s h a r e concentrated i n somewhat deeper water
than i s the case d u r i n g the summer.
A t Cape Lazo o f f B r i t i s h Columbia, a mean
spawning depth o f 42 fathonis has been observed.
EARLY LIFE HISTORY
The eggs a r e small and average about 1/30 i n c h (0.9 m i l l i m e t e r s ) i n diameter.
These transparent white t o p a l e bluish-purple eggs d r i f t w i t h currents.
Time o f
hatching depends upon water temperature b u t general l y s t a r t s a f t e r 90-98 hours, and
contfnues f o r about 10 hours f o r a batch o f eggs.
Upon hatching, larvae a r e almost
0.11 i n c h (2.8 m i l l i m e t e r s ) long.
The young f i s h a r e a t the mercy o f water movement for 6-10 weeks,
The f i s h
then metamorphose t o the a d u l t form; t h a t i s , the l e f t eye "migrates8' t o t h e r i g h t
side o f the head, t h e body takes on the f l a t t e n e d appearance and t h e f i s h assumes
a s i d e swimming behavior.
They then s e t t l e t o t h e bottom.
Reproductive success v a r i e s from year t o year.
The Canadians have found t h a t
population s u r v i v a l o f young i s r e l a t e d t o development time, and p o s s i b l y extremes i n
water temperature and t r a n s p o r t by water movements from spawning grounds t o nursery
grounds.
Their e a r l y l i f e i s spent i n protected inshore areas, bays and estuaries.
growth t h e f i s h move i n t o deeper water.
With
Several Oregon bays a r e apparently important
nursery areas f o r f i s h during t h e i r f i r s t year of l i f e .
ADULT LIFE HISTORY
D i s t r i b u t i o n and Abundance
English s o l e occur from Baja C a l i f o r n i a t o Unimak I s l a n d i n western Alaska.
They
a r e found t o a depth o f 300 fathoms although commercial q u a n t i t i e s a r e normally found
a t l e s s than 90 fathoms.
Largest catches t y p i c a l l y occur between 30 and 70 fathoms.
Major areas of abundance a r e found f r o n Santa Barbara, C a l i f o r n i a t o northern Hecate
S t r a i t , B r i t i s h Columbia.
English s o l e a r e a l s o t h e most abundant o f commercially
important f l a t f i s h i n t h e Puget Sound area.
There i s a s h i f t o f t h e a d u l t concentration t o shallow water i n spring and back
t o deeper water i n wintnr.
Research was done by t h e Oregon Department o f F i s h and
W i l d l i f e i n 1967 and 1968 o f f t h e Colurrlbia River.
Adults were found i n 10 t o 40
fathoms i n August b u t i n w i n t e r they were found i n 20 t o 50 fathoms.
Canadian studies
showed t h a t a d u l t English s o l e a r e g e n e r a l l y found around 20 fathoms i n t h e summer
and 40 fathoms
ih
winter.
English s o l e occur almost e n t i r e l y over sand bottoms o r mixed sand and mud
bottom.
Aquarium observations o f j u v e n i l e s suggested that, given a choice, they bury
themselves thus l i m i t i n g them t o a sand bottom i n t o which they can e a s i l y "burrow".
I n t h e area frcm t h e ColunSia R i v e r t o Cape Blanco i n 10 t o 100 fathoms we
estimated t h e r e w e x about 42 m i l l i o i i pounds o f English sole, b u t o n l y about 14
m i l l i o n pounds o f t h i s i s usable o r a v a i l a b l e t o t h e f i s h e r y .
Our data suggests a
-4sustainable y i e l d of approximately 3-4 mi 11i o n from the survey area without harm t o
the English stocks.
Three m i l l i o n pounds of English s o l e i s n o t a magic number.
catch w i l l vary w i t h the status of t h e f i s h and the f i s h e r y .
Allowable commercial
I f we have one o r more
very successful year classes, the c o m e r c i a 1 harvest could be increased.
the catch would r e q u i r e r e d u c t i o n f o l l o w i n g year class f a i l u r e s .
Likewise
Since English s o l e
males a r e now underharvested, development of a commercial use f o r small males could
a l s o increase the sustainable catch.
Feeding Habits
English s o l e have a small mouth w i t h i n c i s o r t e e t h best s u i t e d f o r c u t t i n g .
Their d i e t consists mainly o f small bottom organisms, such as clams and clam siphons,
other small molluscs, marine worms, small crabs and shrimp, b r i t t l e s t a r s and occas i o n a l l y other invertebrates and small f i s h .
Migrations & Tagging
Tagging has provided evidence o f segregated major stocks.
Most tag recoveries
occurred near t h e tag re1ease s i te, i n d i c a t i n g 1ittl e exchange between most stocks.
Some tagged English s o l e made extensive migrations, suggesting a small h i g h l y
migratory element.
Extensive migrations were more usual of females than o f males.
Probable f a c t o r s a f f e c t i n g m i g r a t i o n a r e t h e necessity t o concentrate for
spawning, and dispersal f o r summer feeding.
I n Canada, English s o l e have generally
been found t o t r a v e l against currents t o reach spawning areas and t o disperse w i t h
t h e c u r r e n t f o r feeding.
Most Washington and C a l i f o r n i a tagging showed fa1 1 southerly
movenient w i t h a r e t u r n m i g r a t i o n i n t h e spring.
A p o r t i o n o f the stocks displayed
1i t t l e north-south movement.
About 4,600 English s o l e were tagged and released a t 58-71 fathoms o f f Cape
Lookout, Oregon i n A p r i l 1975.
Tag r e t u r n s have shown a concentration o f f i s h off
c e n t r a l Oregon and a second o f f northern bdashington.
There i s evidence of a r e s i d e n t
- 5( f i s h t h a t d o n ' t migrate) population and a spawning concentration i n both areas.
Also, a p o r t i o n o f t h e f i s h migrate between t h e two areas.
These conclusions a r e
supported by tagging o f f northern Washington.
Some i n t e r e s t i n g high1i g h t s from our tagging program were t h a t 755 f i s h were
recovered (16.4%) and t h a t the greatest speed of t r a v e l was 125 mi l e s i n 56 days o r
2.2 m i l e s per day.
Most d i s t a n t movement was confined t o t h e north, b u t recoveries
came from Cape F l a t t e r y , Washington t o Eureka, Cal if o r n i a .
was i n 200 fathoms o f f Eureka C a l i f o r n i a .
The deepest recovery
The f u r t h e s t movement was southwest o f
Eureka about 265 m i l e s from t h e tagging s i t e .
Cal i f o r n i a , Oregon, Washington and Canada have tagged Engl i s h sole.
provide valuable i n f o r m a t i o n on movement and stock size.
considering c o s t o f tags, vessel time and man hours.
Tag r e t u r n s
Tagging i s c o s t l y when
Therefore, t a g recoveries a r e
valuable and we must o b t a i n as muck good, complete information as possible.
Full
recovery data includes date and l o c a t i o n o f capture ( l o r a n and depth), tag number,
sex and l e n g t h o f f i s h .
We a l s o l i k e t o o b t a i n t h e f i s h t o determine sex and age.
As an i n c e n t i v e f o r good tag recoveries, a l l English tagging programs offer
rewards and i n f o r m a t i o n regarding tag release-recovery information.
Age and Growth
The i n t e r o p e r c l e bone i s used t o determine age o f English sole.
f l a t bone found on t h e g i l l cover.
This i s a t h i n
The bone i s "aged" much l i k e a tree.
The pre-
pared bone displays broad opaque bands representing r a p i d summer growth separated
by narrow t r a n s l u c e n t bands o f slow w i n t e r growth.
The bone i s aged by counting t h e
number o f w i n t e r growth bands.
lilhile English s o l e a r e one o f t h e smaller commercially used f l a t f i s h , t h e record
female was measured a t 22.5 inches and t h e l a r g e s t male measured 19.3 inches.
The
o l d e s t female and male English s o l e we have aged were 17 years old.
The growth r a t e i s about t h e same f o r both males and females d u r i n g t h e f i r s t
-6two years.
By the end o f t h e f i r s t summer young English s o l e a r e 4 t o 5 inches long.
They a r e 8 inches long by t h e end of t h e i r second year of 1i f e .
Thereafter, females
grow much f a s t e r than males, and females become l a r g e r than ma1es i n head length,
t b t a l length, and body depth.
Few males ever a t t a i n commercial s i r e .
English s o l e f i r s t enter t h e commercial f i s h e r y a t t h e age o f three.
time they a r e about 12 inches long and weigh 1/2 pound.
o l d f i s h support t h e b u l k o f Oregon landings f o r f i l l e t s .
13 t o 15 inches and weigh 3/4 t o 1 pound.
At t h i s
Usually 4 through 7 year
These f i s h average about
Nale English sole, being much smaller
than t h e females, a r e u s u a l l y discarded a t sea o r u t i l i z e d as mink food.
Horta 1ity
M o r t a l i t y (death) r a t e i s h i g h f o r f i s h and i s made up o f f i s h i n g and n a t u r a l
mortality.
A y e a r l y m o r t a l i t y o f about 32% f o r male and 36% f o r female English s o l e
occurs off Oregon.
Since our commercial f i s h e r y mostly catches o r r e t a i n s female
English s o l e we would expect g r e a t e r t o t a l mortal ity on females.
Diseases and Parasites
English s o l e a r e attacked by several diseases.
A protozoan (one c e l l e d animal )
causes "milky" f l e s h and destroys market a c c e p t a b i l i t y .
This disease i s n o t t o x i c
t o humans, however.
Red colored nematode "worms" may i n f e s t t h e f l e s h and inner margins o f t h e f i n
This produces an unappetizing appearance t h a t u s u a l l y causes the f i s h t o
rays.
be unmarketable. These "worms" a r e n o t harmful t o man.
THE FISHERY
Oregon t r a w l e r s u s u a l l y f i s h f o r English s o l e i n s i d e o f 50 fathoms.
Our
survey work during t h e l a s t f i v e s a r s has shown major areas o f English sole abundance
from Cape Foulweather south t o Coos Bay and from Tillamook Head t o Destruction
Island.
Good catches a r e a l s o made o f f Brookings.
areas both n o r t h and south of Oregon as we1 1.
There a r e several major f i s h i n g
-7Small English s o l e a r e p a r t i c u l a r l y vulnerable t o the trawl because o f t h e i r
p r o t r u d i n g anal spine.
Many o f these small f i s h a r e mistaken f o r j u v e n i l e s and
discarded a t sea, but the g r e a t m a j o r i t y a r e actual l y mature males.
ivlales a r e
therefore underutilized; i n f a c t , we have observed t h a t under 25% o f males as o l d
as 13 years a r e kept.
I n comparison, over 30% of females a r e u t i 1ized a t age 3 and
80% a r e u t i l i z e d a t 5 years old.
Strong year classes have g r e a t l y affected t h e commercial catch.
A strong year
class i s an exceptionally l a r g e number of f i s h t h a t r e s u l t from a s i n g l e years'
spawning.
The 1961 year class was t h e strongest English s o l e year c l a s s noted f o r Oregon.
These f i s h dominated t h e landings i n 1966 when Oregon t r a w l e r s landed an impressive
3.5 m i l 1i o n pounds and continued t o dominate t h e catch f o r t h e next three years.
In
1975 we observed an impressive number o f these f i s h i n the catch which were then
14 years old.
L a t e l y we have n o t found e x c e p t i o n a l l y strong year classes, b u t they
would n o t appear i n our surveys f o r a t l e a s t 3 years and i n t h e commercial landing
f o r about 5 years a f t e r b i r t h .
Most English s o l e a r e f i l l e t e d and sold fresh.
mink food; however, market problems i n the U.S.
They a l s o a r e o f t e n used as
mink f u r i n d u s t r y i n r e c e n t years
have made t h i s a r e l a t i v e l y minor market.
I"~IANAGEblEi4T
Juvenile English s o l e could p o s s i b l y b e n e f i t from protected "nursery" areas,
b u t u n f o r t u n a t e l y they a r e found i n t h e same areas as mature f i s h , such as sanddabs
and sand sole.
tJe f e e l management i s best served by mesh s i z e regulations.
Through
mesh r e g u l a t i o n s we attempt t o a l l o w t h e escapement o f most j u v e n i l e s w i t h o u t o v e r l y
hampering the catch o f mature marketable f i s h .
ACKNOWLEDGEMENTS
We want t o thank t h e f i s h i n g i n d u s t r y f o r i t s aid.
Much o f our knowledge of the
English s o l e and i t s f i s h e r y has been obtained through i n d u s t r y help, i n c l u d i n g
logbook records and r e t u r n s o f tags.