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REFERENCE COPY DO Not Remove from the Library U. S, Fish and Wildlife Service
N- Wetlands Research Center Biological Report 82 (I 1.70) 780 C a i ~ ~ n Dome Boulevard TR EL-82-4 August 1987 Lafqyetta, Louisiana 70506
Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (Pacific Southwest)
COHO SALMON
Coastal Ecology Group Fish and Wildlife Service ~ a t e r w a v s ~ x ~ e r i m e n t station
U.S. Department of the Interior U.S. Army Corps of Engineers
B i o l o g i c a l R e p o r t 82(11.70) TR EL-82-4 August 1987
Spec ies P r o f i l e s : L i f e H i s t o r i e s and E n v i r o n m e n t a l Requi rements o f Coas ta l F i s h e s and I n v e r t e b r a t e s ( P a c i f i c Sou thwes t )
COHO SALMON
Thomas J. H a s s l e r C a l i f o r n i a C o o p e r a t i v e F i s h e r y Research U n i t
Humboldt S t a t e U n i v e r s i t y A r c a t a , CA 95521
P r o j e c t Manager Edward P e n d l e t o n P r o j e c t O f f i c e r
D a v i d Moran
U.S. F i s h and W i l d l i f e S e r v i c e N a t i o n a l Wet l ands Research Cen te r
1010 Gause Bou leva rd S l i d e l 1, LA 70458
Per fo rmed f o r
C o a s t a l Eco logy Group Waterways Exper imen t S t a t i o n U.S. Army Corps o f Eng inee rs
V i c k s b u r g , MS 39180
and
U.S. Depar tment o f t h e I n t e r i o r F i s h and W i l d l i f e S e r v i c e Research and Development
N a t i o n a l Wet l ands Research Cen te r Washington, DC 20240
T h i s s e r i e s may be re fe renced as f o l l o w s :
U.S. F i s h and W i l d l i f e Serv ice. 1983-19-. Species p r o f i l e s : l i f e h i s t o r i e s and envi ronmenta l requ i rements o f coas ta l f i shes and i n v e r t e b r a t e s . U .S. F i s h W i l d l . Serv. B i o l . Rep. 82(11) . U.S. Army Corps o f Engineers, TR EL-82-4.
Th i s p r o f i l e may be c i t e d as f o l l ows :
Hassler, T.J. 1987. Species p r o f i l e s : l i f e h i s t o r i e s and envi ronmenta l requi rements o f coas ta l f i s h e s and i n v e r t e b r a t e s ( P a c i f i c Southwest)--coho salmon. U.S. F i s h W i l d l . Serv. B i o l . Rep. 82(11.70). U.S. Army Corps o f Engineers, TR EL-82-4. 19 pp.
PREFACE
T h i s spec ies p r o f i l e i s one o f a s e r i e s on c o a s t a l a q u a t i c organisms, p r i n c i p a l l y f i s h , o f s p o r t , commercial , o r e c o l o g i c a l impor tance. The p r o f i l e s a r e des igned t o p r o v i d e c o a s t a l managers, eng inee rs , and b i o l o g i s t s w i t h a b r i e f comprehensive ske t ch o f t h e b i o l o g i c a l c h a r a c t e r i s t i c s and env i ronmenta l requ i rements o f t h e spec ies and t o d e s c r i b e how p o p u l a t i o n s o f t h e spec ies may be expected t o r e a c t t o env i ronmenta l changes caused by c o a s t a l development. Each p r o f i l e has s e c t i o n s on taxonomy, 1 i f e h i s t o r y , e c o l o g i c a l r o l e , env i ronmenta l requ i rements , and economic impor tance , i f appl i c a b l e . A t h r e e - r i ng b i n d e r i s used f o r t h i s s e r i e s so t h a t new p r o f i l e s can be added as t h e y a r e p repared . T h i s p r o j e c t i s j o i n t l y p lanned and f i nanced by t h e U. S. Army Corps o f Engineers and t h e U.S. F i s h and W i l d l i f e Se rv i ce .
Suggest ions o r ques t i ons r e g a r d i n g t h i s r e p o r t shou ld be d i r e c t e d t o one of t h e f o l l o w i n g addresses.
I n f o r m a t i o n T r a n s f e r Spec ia l i s t N a t i o n a l Coasta l Ecosystems Team U.S. F i s h and W i l d l i f e S e r v i c e NASA-S l ide l l Computer Complex 1010 Gause Bou levard S l i d e l l , LA 70458
U.S. Army Engineer Waterways Exper iment S t a t i o n A t t e n t i o n : WESER-C Pos t O f f i c e Box 631 V icksburg , MS 39180
CONVERSION T A B L E
M e t r i c t o U . S . Customary
Mu1 t i p l y
m i l l i m e t e r s (mm) c e n t i m e t e r s (cm) me te rs (m) me te rs (m) k i l o m e t e r s ( km) k i l o m e t e r s (km)
square m e t e r s (m2) squa re k i l o m e t e r s (kmz) h e c t a r e s (ha )
l i t e r s ( 1 ) c u b i c me te rs (m3) c u b i c me te rs (m3)
mi l l i grams (mg) grams ( g ) k i lograms ( k g ) m e t r i c t o n s ( t ) m e t r i c t o n s ( t )
k i l o c a l o r i e s ( k c a l ) C e l s i u s degrees ( O C )
i n c h e s i n c h e s f e e t ( f t ) fa thoms s t a t u t e m i l e s ( m i ) n a u t i c a l m i l e s (nm i )
square f e e t ( f t 2 ) square m i l e s ( m i 2 ) a c r e s
g a l l o n s ( g a l ) c u b i c f e e t ( f t 3 ) a c r e - f e e t
ounces (02 ) ounces (02 ) pounds ( l b ) pounds ( l b ) s h o r t t o n s ( t o n )
B r i t i s h t h e r m a l u n i t s ( B t u ) F a h r e n h e i t degrees (OF)
U . S . Customary t o M e t r i c
25 .40 2 . 5 4 0 .3048 1 .829 1 . 6 0 9 1 .852
To O b t a i n
i nches i nches f e e t f a thoms s t a t u t e m i l e s n a u t i c a l m i l e s
squa re f e e t squa re m i l e s a c r e s
g a l l o n s c u b i c f e e t a c r e - f e e t
ounces ounces pounds pounds s h o r t t o n s
B r i t i s h t h e r m a l u n i t s F a h r e n h e i t deg rees
m i l l i m e t e r s c e n t i m e t e r s m e t e r s m e t e r s k i l o m e t e r s k i l o m e t e r s
squa re m e t e r s squa re k i l o m e t e r s h e c t a r e s
1 i t e r s c u b i c me te rs c u b i c m e t e r s
m i l l i g r a m s grams k i l og rams m e t r i c t o n s m e t r i c t o n s
k i l o c a l o r i e s C e l s i u s degrees
CONTENTS
Page
.............................................................. PREFACE CONVERSION FACTORS ................................................... ACKNOWLEDGMENTS ......................................................
.......................................... NOMENCLATURE/TAXONOMY/RANGE ................................... MORPHOLOGY AND IDENTIFICATION AIDS
REASON FOR INCLUSION I N SERIES ....................................... L I F E HISTORY .........................................................
M i g r a t i o n dnd S p d w n i n g ............................................... ...................................................... Eggs dnd L d r v a e
F r y and S m o l t s ....................................................... ...................................................... Ocean R e s i d e n c e
S u r v i v d l ............................................................. ............................................... GROWTH CHARACTERISTICS
THE FISHERY .......................................................... ECOLOGICAL ROLE ......................................................
........................................... ENVIRONMENTAL REQUIREMENTS T e m p e r a t u r e .......................................................... D e p t h ................................................................
............................................................. V e l o c i t y D i s s o l v e d Oxygen ..................................................... S u b s t r a t e ............................................................ T u r b i d i t y ............................................................ O t h e r F a c t o r s ........................................................
LITERATURE CITED .....................................................
iii i v v i
ACKNOWLEDGMENTS
I g r a t e f u l l y acknowledge the rev iew by Thomas McMahon o f the Canada Depart- ment o f F i she r ies and Oceans, Nanaimo, B.C. The o r i g i n a l drawing, used w i t h per- miss ion as F igure 1 i n t h i s p r o f i l e , was produced f o r the f o l l o w i n g p u b l i c a t i o n : McPhail , J. D. , and C. C. Lindsey. 1970. Freshwater Fishes o f Northwestern Canada and Alaska. - - B u l l . F ish. k. Board Can. 173:381 p. --
F i g u r e 1. Coho salmon a d u l t s , w i t h spawning phase o f ma le a t t h e b o t t o m ( S c o t t and Crossman 1973) .
COHO SALMON
S c i e n t i f i c name . . . . . Oncorhynchus k i s u t c h (Walbaum)
P r e f e r r e d common name . . Coho salmon ( F i g u r e 1 )
Other common names . . S i l v e r salmon1, coho, sea t r o u t , b lueback , j a c k salmon, hooknose, s i l v e r s i d e s (Sha- pova lov dnd T a f t 1954; S c o t t and Crossman 1973; F r y 1979)
C l a s s . . . . . . . . . . O s t e i c h t h y e s Order . . . . . . . . . Salmoni formes F a m i l y . . . . . . . . . . Salmonidde
Geogrdph ic rdnge: Anadromous a l o n g t h e P a c i f i c c o a s t f r o m Chamalu Bay,
'1n Cal i f o r n i a , t h e " o f f i c i a l " common name i s s i l v e r salmon. I n t h e r e s t o f t h e U n i t e d S t a t e s and i n Canada coho salmon i s used. The C a l i f o r n i a S t a t e L e g i s l a t u r e had d e c l a r e d " s i l v e r " t o be o f f i c i a l b e f o r e t h e r e was g e n e r d l agreement e lsewhere.
Mex ico (Mi l l e r and Lea 19721, t o P o i n t Hope, A l a s k a , t h r o u g h t h e A l e u t i a n s , and f r o m t h e Anadyr R i v e r , U.S.S.R., s o u t h t o Hokkaido, Japan. Most abundant between Oregon and s o u t h e a s t A l a s k d ( H a r t 1973) . Coho salmon have been i n t r o d u c e d ( w i t h v a r i o u s degrees o f success ) i n t o l a k e s dnd r e s e r v o i r s i n A laskd, Washington, Oregon, C a l i f o r n i d , Montana, and A l b e r t a , Canadd; i n t h e G r e a t Lakes, f i r s t s u c c e s s f u l s t o c k i n g i n 1966; d l o n g t h e A t l d n t i c c o a s t f r o m Maine t o Mdry land; i n C h i l e and A r g e n t i n a ( S c o t t and Crossman 1973) . M a j o r spawning r i v e r s i n t h e P a c i f i c Southwest Reg ion a r e shown i n F i g u r e 2. Coho salmon were r a r e i n t h e Sacramento R i v e r sys tem u n t i l t h e C a l i f o r n i a Depar tment o f F i s h and Game s tocked l a r g e numbers o f f r y i n t o t h e system i n 1956-58 ( H a l l o c k and F r y 1967 1. Coho salmon r e t u r n e d t o spawn b u t d i d n o t m a i n t a i n a n a t u r a l run ; t h e f i s h have a g a i n become s c a r c e dnd
Figure 2. Major spawning rivers of coho salmon in the Pacific Southwest; the species is found in all marine waters of the region (Berger 1982). Short lines perpendicular to rivers represent impassable bdrriers.
dny t h a t e n t e r t h e Sacramento R i v e r s h o u l d be r e g a r d e d as s t r a y s . Coho salmon do n o t e n t e r t h e San Joaqu in R i v e r .
chum salmon (0. w) and sockeye salmon (2. n e r k a ) ; t h e low p y l o r i c caeca c o u n t ( < 8 3 ) s e p a r a t e s t h e coho f r o m any salmon excep t t h e sockeye ( F r y 1979) .
MORPHOLOGY AND IDENTIFICATION AIDS REASON FOR INCLUSION I N SERIES
M e r i s t i c c h a r i c t e r s : d o r s a l 9 - 13, ana l 13-16, p e c t o r a l 13-16, p e l v i c 9-11 w i t h a x i 11 a r y p rocess ; ad ipose smdl 1 , s l e n d e r , and f l e s h y , cauda l o n l y s l i g h t l y i n d e n t e d ; c y c l o i d s c a l e s , 121-144 i n l a t e r a l l i n e row; p y l o r i c caeca 45-83; g i I 1 r a k e r s 19-25 on l o w e r l i m b o f f i r s t g i l l a r c h ; b r a n c h i o s t e y a l r a y s 11-15; v e r t e b r a e 58-66 (Shapova lov 1947; M i l l e r and Lea 1972) .
Body f u s i f o r m , 1 a t e r a l l y compressed; f o r k l e n g t h ( F L ) u s u a l l y 4 1 t o 64 cm, maximum 80 cm (Shapova lov and T a f t 19541, and w e i q h t t o 13.6 kg b u t n o t u s u a l l y ove r 6 .8 k g ( ~ o d e i 1953 1.
The j u v e n i l e s a r e b l u e - g r e e n on t h e back, and have s i l v e r y s i d e s and 8-12 p a r r marks na r rower t h a n t h e i n t e r s p a c e s ; l a t e r a l l i n e passes t h r o u g h p a r r marks; da rk p igmented ad ipose f i n ; ana l f i n p igmented between r a y s r e s u l t i n g i n b l a c k band ing; orange t i n t s on ana l , p e c t o r a l , and p e l v i c f i n s (McConnel l and Snyder 1972; S c o t t and Crossman 1973) . A d u l t s i n ocean a r e s t e e l - b l u e t o g r e e n i s h d o r s a l l y ; s i d e s s i l v e r y , and v e n t r a l s u r f a c e w h i t e ; smal 1 b l d c k s p o t s on back, upper s i d e s , base of d o r s a l f i n , and upper l o b e of cauda l f i n . M a t u r i n g ma les become d a r k e r , deve lop a b r i g h t r e d s t r i p e on o t h e r w i s e d u l l s i d e s , and a r e g r a y t o b l a c k v e n t r a l l y ( S c o t t and Crossman 1973 1.
A d u l t coho sdlmon have a w h i t e gum l i n e ( t h r o u g h wh ich t e e t h p r o j e c t ) t h a t d i s t i n g u i s h e s them f r o m ch inook salmon (Oncorhynchus t s h a w y t s c h d ) , wh ich have b l a c k gums. Dark s p o t s on t h e back, d o r s a l f i n , and upper l o b e o f t a i l d i s t i n g u i s h coho salmon frorn
The coho salmon s u p p o r t s v a l u a b l e commerc ia l and s p o r t f i s h e r i e s i n t h e P a c i f i c Southwest Region. A c c o r d i n g t o t h e P a c i f i c F i s h e r y Management C o u n c i l (PFMC), t h e s p o r t f i s h e r y accoun ted f o r 58% of t h e t o t a l c a t c h of coho salmon a l o n g t h e C a l i f o r n i a c o a s t i n 1985 (PFMC 1986) . Coho salmon a r e anadromous and t h u s occupy f r e s h w a t e r , e s t u a r i n e , and ocean ic h a b i t a t s . They a r e e x t e n s i v e l y r e a r e d i n h a t c h e r i e s f o r r e l e a s e .
L IFE HISTORY
M i g r d t i o n and Spawning
I n t h e P a c i f i c Southwest, coho salmon e n t e r s m a l l c o a s t a l s t reams and r i v e r s f rom t h e Mon te rey Bay a rea n o r t h w a r d t o t h e Smi th R i v e r ( F r y 1960; Be rge r 1982) . They b e g i n t o e n t e r f r e s h w a t e r i n September (Snyder 1931) b u t u s u a l l y e n t e r f r o m October t o March, p e a k i n g i n December and January (Shapova lov and T a f t 1954) . Many s m a l l c o a s t a l s t reams i n C a l i f o r n i a a r e c l o s e d by sand b a r s a t t h e i r mouths d u r i n g a p o r t i o n of t h e yea r , and f i s h canno t e n t e r t h e s t ream u n t i l t h e b a r i s b roken by t h e f i r s t heavy r a i n s o f t h e r a i n y season. I n l a t e summer and fa1 1, coho salmon may t h u s c o n c e n t r a t e i n t h e ocean near t h e s e s t reams.
The homing o f salmon t o t h e i r n a t a l s t r e a m a f t e r t h e y e n t e r f r e s h w a t e r i s w e l l documented and i s a t t r i b u t a b l e t o o l f a c t o r y cues t h a t a r e s p e c i f i c f o r each l o c a t i o n and a r e " l e a r n e d " by j u v e n i l e salmon s h o r t l y b e f o r e t h e y m i g r a t e t o t h e sed ( H a s l e r and Wisby 1951; H a s s l e r and Kucas 1982; H a s l e r and Schol z 1983) . Homing
may a l s o be i n f l u e n c e d by i n h e r i t a n c e (Bams 1976).
I n C a l i f o r n i a , ups t ream m i g r a t i o n o f coho salmon c o i n c i d e s w i t h l a r g e i n c r e a s e s i n s t r e a m f low, e s p e c i a l l y i n s t reams i n w h i c h t h e f l o w i s low i n summer. The f i s h move r a p i d l y upst ream b u t s t o p i f s t r e a m f l o w sudden ly drops. A s m a l l r i s e i n f l o w t h e n causes t h e f i s h t o move aga in . They m i g r a t e upst ream m a i n l y i n dayt ime, and do n o t t r d v e l more t h a n 240 km above t h e mouth o f t h e s t ream (Shapova lov and T a f t 1954) . Spawning u s u a l l y peaks f r o m November t o January . Coho salmon spawn i n r i f f l e s d t t e m p e r d t u r e s o f 6 t o 12 OC ( B r i g g s 1953; Shapovdlov and T a f t 1954) . On t h e spawning grounds, males d r e more abundant t h a n females , due t o t h e presence of j a c k s ( s e x u a l l y p r e c o c i o u s ma les ) ; however, t h e numbers of females and o l d e r males d r e s i m i l a r . Males a r e t h e more numerous i n t h e e a r l y p o r t i o n o f t h e r u n and fema les i n t h e l a t e r p o r t i o n . U s u a l l y more t h a n one ma le spawns w i t h a f e m a l e (Shapova lov dnd T a f t 1954) .
The f e c u n d i t y o f coho salmon v d r i e s w i t h s i z e o f female , ared, and y e d r . H a r t (1973) r e p o r t e d f e c u n d i t y of 2,500-5,000 eggs f o r f ema les 55-70 cm l o n g i n B r i t i s h Columbid, and S c o t t and Crossman (1973) 1 i s t e d f e c u n d i t y o f 2,100-2,789 eggs p e r f e m a l e ( n o l e n g t h s g i v e n ) i n B r i t i s h Columbid and 1,440-5,700 eggs f o r f ema les 40-70 cm l o n g i n Washington. S h a p 0 ~ d l 0 ~ and T a f t (1954 deve loped t h e f o l l o w i n g f e c u n d i t y f o r ~ n u l d :
number o f eggs = 0.01153 x FL 2.9403
Female coho salmon choose a n e s t i n g s i t e i n g r a v e l d e p o s i t s a t t h e l o w e r end of d p o o l j u s t above a r i f f l e ( B r i g g s 1953; Shdpovalov and T a f t 1954) . The fema le p r e p a r e s a r e d d (an a r e a c o n t a i n i n g s e v e r a l egg p o c k e t s o r n e s t s ) b y t u r n i n g on h e r s i d e and r e p e a t e d l y f l e x i n g h e r body dnd t a i l t o f o r c e g r d v e l and f i n e sed imen ts i n t o t h e wa te r column; t h e s e
sed imen ts a r e d e p o s i t e d a s h o r t d i s t a n c e downstream. The comp le ted egg p o c k e t forms an o v a l d e p r e s s i o n ( p i t ) w i t h a mound o f g r a v e l l o c a t e d i m m e d i a t e l y downstream.
D u r i n g spawning, a domindnt ma le salmon accompanies t h e f e m a l e and chases away o t h e r males f rom t h e r e d d area. The ma le p o s i t i o n s h i ~ n s e l f b e s i d e t h e female, b o t h face upstream, and t h e eggs and sperm a r e r e l e a s e d i n t o t h e p i t . One o r more ma les p o s i t i o n themse lves b e s i d e t h e f e m a l e o p p o s i t e t h e dominant male dnd a l s o r e l e a s e sperm ( B r i g g s 1953; S c o t t and Crossman 1973) . A f t e r t h e eggs a r e r e l e a s e d , t h e f e m a l e moves s l i g h t l y ups t ream and r e p e a t s t h e n e s t b u i l d i n g and spawning d c t . T h i s p r o c e s s i s r e p e d t e d s e v e r d l t i m e s b e f o r e spdwning i s comp le ted i n 2-7 o r more days ( B r i g g s 1953; Shapovdlov and T a f t 1954) . A comple ted r e d d ( c o n t a i n i n g s e v e r a l n e s t s ) c o v e r s dn a r e a o f 1.7 t o 5.2 m2 (Buck dnd B d r n h a r t 1986) . The eggs a r e i m m e d i d t e l y cove red w i t h 18 t o 38 cm o f g r a v e l d i s p l a c e d f r o m t h e upst ream s i d e o f t h e n e s t ( B r i g g s 1953) . The fema le may gudrd t h e n e s t f o r up t o two weeks o r u n t i l she becomes t o o wedk t o m a i n t a i n a p o s i t i o n a g a i n s t t h e c u r r e n t ( B r i g g s 1953) . B o t h t h e male dnd fernale d i e d f t e r spawning.
Eggs dnd L a r v a e
Coho salmon eggs a r e l a r g e , o range- red , and demersd l . S c o t t and Crossman (1973) r e p o r t e d egg d i dmeters o f 4.5-6.0 mm f o r west c o d s t p o p u l a t i o n s ; R o u n s e f e l l ( 1957) d e r i v e d a d i d m e t e r o f 7.2 mm f r o m d a t a p u b l i s h e d b y Shapovdlov and T a f t (1954) .
The t i m e r e q u i r e d f o r coho salmon eggs t o h a t c h i s i n v e r s e l y r e l d t e d t o wa te r t e m p e r a t u r e . Shapovalov and T a f t (1954) r e p o r t e d t h a t eggs u s u a l l y ha tched i n 35-50 days a t t h e t e m p e r a t u r e s p r e v a i 1 i n g i n Waddel l Creek, C a l i f o r n i d ; i n h a t c h e r i e s t h e y
r e p o r t e d h a t c h i n g i n about 38 and 48 ddys d t averdge t e m p e r d t u r e s o f 11' and 9 OC. L a u f l e e t a l . ( 1986) r e p o r t e d t h a t 86-101 ddys were r e q u i r e d a t 4.5 O C .
Coho sdlmon l a r v d e s t a r t emerg ing frorn t h e g r d v e l 2-3 weeks a f t e r h d t c h i n g , and c o n t i n u e t o emerge f o r dn a d d i t i o n a l 2-7 weeks (Shdpovd lov dnd B e r r i a n 1940) . The l d r v d e have a l a r g e y o l k sac, wh ich t h e y absorb w h i l e t h e y a r e s t i l 1 i n t h e g r d v e l . The l d r v a e a r e i n i t i a l l y p h o t o - n e g a t i v e , b u t become p h o t o p o s i t i ve ds t h e y approdch emergence ( D i 1 l 1969 1.
Fry and Smo l t s -- Coho sdlmon f r y u s u d l l y emerge
f rorn t h e g r d v e l a t n i g h t f r o m March t o May. The f r y move t o s h a l l o w g r d v e l - b o t t o m e d a reds near t h e banks o f t h e s t redm, where t h e y f o r m schoo ls . As t h e f r y grow, t h e y d i s p e r s e upst redm and downstream and s e l e c t and defend a t e r r i t o r y , o f t e n i n r e l d t i v e l y deep p o o l s w i t h ove rhang ing l o g s (Shdpovd l ov and T a f t 1954) . I n summer, coho salmon f r y p r e f e r a m i x t u r e of d i f f e r e n t t y p e s o f p o o l s dnd r i f f l e s w i t h l a r g e woody d e b r i s , u n d e r c u t banks, o v e r h d n g i n g v e g e t a t i o n , g l i d e s , average wa te r t emperd tu res o f 10 t o 15 O C , d i s s o l v e d oxygen near s d t u r d t i o n , and r i f f I e s w i t h 1 i t t l e sed imen t ( R e i s e r and B j o r n n 1979; T s c h a p l i n s k i 1982; Murphy e t a l . 1984) . I n w i n t e r , j u v e n i l e s p r e f e r 1 a r g e mains t ream, bdckwater , and seconddry channe l p o o l s c o n t a i n i n g l a r g e woody d e b r i s , and u n d e r c u t banks and d e b r i s a l o n g r i f f l e m d r g i n s (Murphy e t a l . 1984; H e i f e t z e t a l . 1986 1.
Coho salmon f r y b e g i n f e e d i n g as soon as t h e y emerge f rom t h e g r d v e l , and grow r d p i d l y . I n C a l i f o r n i d , b e g i n n i n g i n J u l y and August , f r y moved i n t o deep p o o l s , where f e e d i n g was reduced, dnd g r o w t h r d t e decredsed (Shapovalov dnd T a f t 1954) . The p e r i o d o f decreased g r o w t h o f f r y was
a s s o c i d t e d w i t h t h e p e r i o d o f maxirnum s t redm t e m p e r a t u r e and minimum s t ream f l o w . The f r y f e d l i g h t l y and grew 1 i t t l e d u r i n g t h e r d i n y season (December-February) b u t grew r a p i d l y i n March. R i s i n g w a t e r t e m p e r a t u r e and abundant f ood were a s s o c i a t e d w i t h t h e i n c r e a s e d f e e d i n g and g rowth .
Coho sdlmon s t a y i n f r e s h w a t e r f o r d few weeks t o 2 yed rs , depending on d rea ( S c o t t and Crossman 1973) . I n C a l i f o r n i a , most o f t h e f i s h m i g r d t e t o t h e ocedn i n A p r i 1 and May, about a y e d r d f t e r t h e y emerge f rom t h e g r d v e l . A few m i g r d t e ds dge 0 f i s h , b u t c o n t r i b u t e few o r no f i s h t o t h e ddu l t p o p u l a t i o n (Shapovd lov dnd T a f t 1954) . M i g r d t i n g f i s h (medn f o r k l e n g t h , 103-117 mm) move downstream i n s c h o o l s a t t w i l i g h t and a t n i g h t .
I n some dreas o f t h e P a c i f i c n o r t h w e s t , coho salmon f r y r e d r i n e s t u a r i e s . I n ~ 0 u t h e d S t A l a s k a ( P o r c u p i n e Creek -Stedmer Bay E s t u d r y ) coho salmon f r y e n t e r e d t h e s t r e a m l e s t u a r y eco tone ( s a l i n i t y 8-25 p p t ) i n s p r i n g and r e d r e d t h e r e d u r i n g summer, g r o w i n g f a s t e r t h a n i n f r e s h w d t e r dreas upst ream (Murphy e t a l . 1984) . Most f i s h moved o u t o f t h e e s t u a r y a r e a t o upst redm f r e s h w a t e r a reds t o o v e r w i n t e r . I n C a r n d t i o n Creek (Vancouver I s 1 and, B.C. coho f r y e n t e r e d t h e e s t u a r y ( s d l i n i t y t o 20 p p t ) i n s p r i n g and r e d r e d t o f d l I, h d v i n g h i g h r a t e s o f s u r v i v d l and g r o w t h ( T s c h d p l i n s k l e t a l . 1982) . I n f a l l , most f i s h e m i g r a t e d seaward w i t h t h e f i r s t sedsond l f r e s h e t s . Coho f r y t h d t r e a r e d i n t h e e s t u d r i e s c o n t r i b u t e d t o t h e p o p u l d t i o n s o f spdwning f i s h wh ich r e t u r n e d t o t h e systems.
Coho salmon f r y undergo a c h a r d c t e r i s t i c t r d n s f o r m a t i o n f r o m p a r r t o s m o l t s b e f o r e t h e y m i g r a t e t o t h e ocean. D i s t i n c t m o r p h o l o g i c a l , p h y s i o l o g i c a l , and b e h a v i o r a l changes accompany t h i s t r a n s f o r m a t i o n (Hoar 1976; Fo lmar and D i c k h o f f 1980) . The onse t o f smol t i f i c a t i o n and m i g r a t i o n i s a s s o c i a t e d w i t h f i s h age and s i z e ,
and e n v i r o n m e n t a l c o n d i t i o n s -- p r i m a r i l y i n c r e a s i n g ddy l e n g t h and wa te r t e m p e r a t u r e (Wedemeyer e t a1 . 1980). The c h a r a c t e r i s t i c changes a s s o c i d t e d w i t h s m o l t i f i c a t i o n and m i g r d t i o n a r e r e v e r s i b l e i f coho salmon a r e p r e v e n t e d f r o m e n t e r i n g seawater (Zaugg dnd McLain 1970; Woo e t a l . 1978) .
Ocean Res idence
The ocean ic m i g r a t i o n p a t t e r n s and ocean h a r v e s t d i s t r i b u t i o n s o f a d u l t coho salmon a l o n g t h e N o r t h American P a c i f i c coas t , as judged b y r e c o v e r i e s o f marked s m o l t s and coded- w i r e t a g s ( F i g u r e s 3 and 41, i n d i c a t e t h a t coho salmon rema in c l o s e r t o t h e i r r i v e r o f o r i g i n t h a n do ch inook salmon, b u t may n e v e r t h e l e s s t r a v e l s e v e r a l hundred m i l e s . Fo r example, marked coho salmon f r o m Waddel l Creek, C a l i f o r n i a , were caugh t 322 km t o t h e n o r t h ( T a f t 19371, and o t h e r s have been c a p t u r e d as f a r as 1,930 km f r o m t h e i r p o i n t o f o r i g i n ( L a u f l e e t a l . 1986). Coho salmon a r e p e l a g i c and r e a d i l y move and d i s p e r s e f r o m one mar ine a r e a t o a n o t h e r ( F r a i d e n b u r g e t a l . 1985): A long t h e C a l i f o r n i a coas t , coho salmon p r o b a b l y remain w i t h i n t h e l i m i t s o f t h e C o n t i n e n t a l S h e l f o r w i t h i n about 160 km f r o m shore (Shapova lov and T a f t 1954) .
A d u l t coho salmon u s u a l l y spend two g row ing seasons a t sea b e f o r e t h e y r e t u r n t o f r e s h w a t e r t o spdwn. A t Waddell Creek, Cal i f o r n i a, Shapovalov and T a f t (1954) f o u n d t h a t t h e f i s h r e t u r n e d e i t h e r ds p r e c o c i o u s males (16% o f r u n ) i n t h e season a f t e r downstream m i g r d t i o n ( i . e . , a f t e r one g row ing season i n f r e s h w a t e r and one i n t h e ocean) , o r as fema les and males (84% o f r u n ) i n t h e second season a f t e r downstream m i g r a t i o n ( a f t e r one g r o w i n g season i n f r e s h wa te r dnd two i n t h e ocean).
F a c t o r s t h a t i n f l u e n c e t h e r e t u r n o f a d u l t sa lmon ids t o t h e i r n a t a l s t reams a r e among t h e l e a s t unders tood f a c e t s o f salmon b i o l o g y . B i o l o g i s t s
b e l i e v e t h a t h i g h seas n d v i y a t i o n i s i n n a t e l y c o n t r o l l e d , and t h a t t h e r o l e o f e x t r i n s i c e n v i r o n m e n t a l f d c t o r s i n c r e d s e s i n impor tance ds t h e sdlmon approach t h e i r home e s t u d r y (Brdnnon 1981) . O r i e n t a t i o n i n t h e ocedn i s b e l i e v e d t o i n v o l v e rndgnet ic dnd c e l e s t i a l i n f o r m a t i o n , i n t e r p r e t e d by t h e i n n a t e l d t i t u d i n a l and c d l e n d d r senses of t h e f i s h (Brdnnon 1981; Quinn 1981) . The l e n g t h o f ddy, r d t e o f change i n ddy l e n g t h , sun p o s i t i o n , and l i g h t p o l a r i z d t i o n d r e suggested cues. Nearsho re m i g r a t i o n may be enhanced by onshore winds t h d t c o n c e n t r d t e r i v e r wd te r c l o s e t o shore , where 01 f d c t o r y cues f u r t h e r g u i d e t h e salmon (Banks 1969) .
S u r v i v a l
S u r v i v d l o f coho salmon v d r i e s by a r e a and yed r . A t Wdddel l Creek, C a l i f o r n i a , t h e e s t i m a t e d s u r v i v d l was 1.16% t o 1.56% from eggs t o smol t s , 0.98% t o 7.72% f r o m s m o l t s t o d d u l t s , and 0.02% t o 0.30% f r o m eggs t o a d u l t s (Shdpovd lov dnd Ta f t 1954) . Murphy (1952) deve loped a method f o r e s t i m a t i n g s u r v i v a l of coho sdlmon i n C a l i f o r n i d d u r i n g t h e i r l d s t y e d r o f ocean l i f e . The a p p l i c d t i o n s o f h i s method t o coho salmon c o u n t s (1939-50) a t Benbow Dam C o u n t i n g S t a t i o n (Sou th Fork , E e l R i v e r ) y i e l d e d e s t i m a t e s o f t h i r d - y e d r s u r v i v d l o f 16% t o 57%. Jensen and Hyde (1971) m o d i f i e d t h e method f o r s i t u a t i o n s where t h e sex r a t i o was o t h e r t h a n 1:l. The Washington Depar tment o f F i s h e r i e s p r e d i c t e d an averdge p r o d u c t i o n o f 75 s m o l t s p e r female coho sdlmon ( L a u f l e e t a l . 1986) . The p r e d i c t i o n a p p l i e d o n l y t o 3 - y e d r - o l d f i s h t h a t spen t 2 y e d r s a t sea s o u t h o f c e n t r d l B r i t i s h Columbia.
GROWTH CHARACTERISTICS
I n C a l i f o r n i a , coho salmon m i g r a t e t o t h e ocean a t age 1 and r e t u r n t o f r e s h wa te r e i t h e r as p r e c o c i o u s males i n t h e season a f t e r downstream m i g r a t i o n (age 1/1 -- one
P A C I F I C O C E A N
P O R T ORCORD
Columbia R l v s r i1.h ..-.._ . . _ . C I C C M T C I T Y
Scale in Miles
F i g u r e 3. Ocednic m i g r a t i o n p d t t e r n s o f a d u l t coho sdlmon a l o n q t h e west c o a s t o f B r i t i s h Columbia, Washington, Oregon, and n o r t h - e r n Cal i f o r n i a , as d e t e r m i n e d f r o i n tagged and marked h d t c h e r y srnol t s ( W r i g h t 1968).
g r o w i n g season i n f r e s h w a t e r and one i n t h e ocean) o r -as fema les and males i n t h e second season a f t e r downstream m i g r a t i o n (age 112 -- two g r o w i n g seasons i n t h e ocean) . (An a l t e r n a t e method of e x p r e s s i n g t h e s e ages y i e l d s 2, and 3,, where t h e i n t e g e r i s t o t a l age and t h e s u b s c r i p t i s y e a r o f l i f e a t o u t m i g r d t i o n . )
I n C a l i f o r n i a , coho salmon average 10.3 t o 11.7 cm FL a t o u t m i g r a t i o n . The f i s h average 40.6 cm a t age 111 ( a l l ma les ) , 64.7 cm a t age 112 (ma les ) , and 63.9 cm a t age 112 ( f e m a l e s ) when t h e y r e t u r n t o spawn (Shapova lov and T a f t 1954).
THE FISHERY
Coho salmon a r e c o n s i s t e n t 1 y caught a l o n g t h e C a l i f o r n i a c o a s t frorn t h e Mon te rey Bay a r e a t o Oregon. T r o l l i n g i n ocean w a t e r s i s t h e o n l y forrn o f commerci a1 f i s h i n g perrni t t e d i n C a l i f o r n i a . G i l 1 n e t t i n g was p e r m i t t e d i n t h e K lamath and Smi th r i v e r s u n t i l t h e e a r l y 1 9 3 0 ' s and i n t h e Sacramento R i v e r u n t i l 1957 ( F r y 1977) . S p o r t f i s h i n g f o r salmon i s p e r m i t t e d i n t h e ocean and i n r i v e r systems t h a t have d sdlmon r u n . However, p a r t s o f some r i v e r systems and some t r i b u t a r i e s d r e c l o s e d t o salmon f i s h i n g .
Coho salmon p r o v i d e an e x t e n s i v e commercial and s p o r t f i s h e r y d l o n g t h e C a l i f o r n i a c o d s t ( T a b l e 1 ) . A long t h e P a c i f i c c o a s t ( C a l i f o r n i a , Oregon, Washington) i n 1976-85, n e d r l y 13% of t h e e s t i m a t e d t o t a l coho salmon c d t c h b y t r o l l i n g and 4% of t h e s p o r t c d t c h were cdugh t o f f C a l i f o r n i a (PFMC 1986) . The dverdge ex -vesse l v a l u e o f coho (exp ressed i n 1985 d o l l d r s ) ranged f r o m $3.12 p e r pound i n 1979 t o $1.57 p e r pound i n 1985, and t h e annual d ressed w e i g h t v a l u e of t h e c d t c h rdnged f rom $3,276,000 t o $125,000 (PFMC 1986) . The ocedn s p o r t f i s h e r y e f f o r t (number o f d n g l e r t r i p s ) was 185,600 i n 1985 and 123,600 i n 1984, and averaged 242,200 i n 1971- 75.
T a b l e 1. Annual ocean commercial ( t r o l l ) and s p o r t c a t c h o f coho salmon ( thousands of f i s h and thousands o f pounds o f f C a l i f o r n i a (PFMC 1986) .
Ca tch by commerci a1
t r o l l i n g S p o r t c a t c h
Year Numbers poundsa Numbers
a ~ r e s s e d w e i g h t . b ~ r e l i r n i n a r y .
The P a c i f i c F i s h e r y Management C o u n c i l fnandges coho sdlmon as d u n i t i n a r e g i o n e x t e n d i n g f r o m L e d d b e t t e r P o i n t , Wdshington ( a b o u t 40 km above t h e mouth o f Co lumbia R i v e r ) , t o t h e U.S.-Mexico b o r d e r . The d rea i s r e f e r r e d t o as t h e Oregon P r o d u c t i o n Index (OPI) a rea . Coho salmon l i n t h e OPI ared, wh ich o r i g i n a t e i n t h e Columbia R i v e r dnd i n Oregon and Cal i f o r n i a c o d s t a l s t reams dnd h a t c h e r i e s , a r e i n t e r m i x e d i n t h e ocedn dnd c o n t r i b u t e t o f i s h e r i e s o f f t h e s o u t h e r n c o d s t o f Wdshington and t h e c o d s t s o f Oregon dnd C a l i f o r n i a . Most o f t h e p r o d u c t i o n o f coho sdlmon i n C a l i f o r n i a i~ f r o m h d t c h e r i e s , wh ich p roduce about 1 m i l l i o n o f t h e 63 mi 11 i o n j u v e n i l e coho sdlmon produced a n n u a l l y i n h d t c h e r i e s i n t h e OPI a rea ( G r e e n l e y 1985) .
Coho salmon F i s h e r i e s i n C a l i f o r n i a and Oregon ( s o u t h o f t h e
Columbia R i v e r ) d r e managed f o r maxirnum use o f h a t c h e r y p r o d u c t i o n , c o n s i s t e n t w i t h t h e dchievernent o f t h e annudl escdpement god1 f o r Oregon c o a s t a l n a t u r a l s t o c k s (PFMC 1986) . A t t a i n m e n t o f t h i s mdnagement o b j e c - t i v e r e q u i r e s t h d t a q u d t i c dnd r i p d r i a n h a b i t a t s t h a t s u p p o r t coho spawning dnd r e a r i n g be p r o t e c t e d , r e h a b i 1 i t a t e d , dnd enhanced ; t h d t s t o c k s i ze be assessed, h d t c h e r y p r o d u c t i o n be mdxirni zed ( i n qud l i t y dnd q u a n t i t y ) , and ocean h a r v e s t r d t e s be c o n t r o l l e d (Oregon Depar tment o f F i s h dnd W i l d l i f e 1985) . W r i g h t (1981) sugge5ted t h d t t h e sdlmon f i s h e r y needs t o he r e g u l d t e d f o r optimum y i e l d . He b e l i e v e 5 t h a t optirnum y i e l d mdy be redched by u s i n g a rea and season c l o s u r e s , minimum s i z e l i m i t s , and gear r e s t r i c t i o n s . A more d i r e c t method would be t h r o u g h t h e e s t d b l i shment o f l i m i t e d e n t r y or- c a t c h quo tas . Oregon dnd Wdshington i n i t i a t e d a l i m i t e d e n t r y o f new f i s h i n g b o d t s i n t o t h e e x i s t i n g f l e e t and C a l i f o r n i a hds a m o r a t o r i u m on t h e i r e n t r y (PFMC 1984) . Catch quo tas have been i n s t i t u t e d I n Oregon, Wdshington, and C a l i f o r n i a (PFMC 1987 1.
ECOLOGICAL ROLE
I n f r e s h w d t e r , coho salmon and s t e e l head (Salmo q d i r d n e r i d r e s i m i l a r i n geogrdph ic d i s t r i b u t i o n , spawning l o c a t i o n s , f o o d h d b i t s , and t h e l e n g t h o f t i rne t h e young spend i n f r e s h w a t e r (Mi l n e 19481, a1 though s t e e l head u s u a l l y remd in i n f r e s h w a t e r l o n g e r t h d n 1 y e d r . Hartman (1965) r e p o r t e d t h a t i n s p r i n g and summer, most coho salmon l i v e i n p o o l s and most s t e e l h e d d l i v e i n r i f f l e s . Seve ra l i n v e s t i g a t o r s have r e p o r t e d t h a t t h e s p e c i e s a l s o s e g r e g a t e by depth ; coho salmon l i v e near t h e s t ream s u r f a c e and s t e e l h e a d near t h e b o t t o m (Hartman 1965; P e t e r s o n 1966; Edmundson e t a l . 1968; B u s t a r d and Narve r 1975 1. A1 though coho salmon h d t c h e a r l i e r and a r e l a r g e r a t f i r s t , s t e e l h e a d f r y grow f d s t e r and by l a t e
summer t h e s i z e d i f f e r e n c e i s s m a l l . I n t e r s p e c i f i c c o m p e t i t i o n i s p r o b a b l y n o t s e r i o u s because of t h e i n i t i a l d i f f e r e n c e i n s i z e , d i f f e r e n c e s i n h a b i t a t p r e f e r e n c e , and t h e d i f f e r e n c e i n age a t e m i g r d t i o n t o t h e sea ( F r d s e r 1969 1.
Coho salmon occupy f resh , b r d c k i s h , and sea w a t e r h d b i t d t s d u r i n g d i f f e r e n t l i f e s tdges . Y o l k - sdc l a r v d e rema in i n t h e g r d v e l f o r s e v e r d l weeks w h i l e t h e y a r e n o u r i s h e d by t h e y o l k . The f r y b e g i n f e e d i n g ds soon ds t h e y emerge f rom t h e g r d v e l , and grow r d p i d l y . Coho f r y f e e d m a i n l y on d r i f t i n g d q u d t i c and t e r r e s t r i a l i n s e c t s (Shapova lov and T a f t 1954; Dernory 1961; Mundie 1969; S c o t t and Crossman 1973) . I n A laskd, coho f i n q e r l i n q f e d on sockeye sdlmon f r y ( ~ n c o r h ~ n c h ~ u s - n e r k a ) , even though s t i c k l e b d c k s were more dbundant (Roos
Coho salmon grow r d p i d l y i n t h e ocedn, where t h e y f e e d on b o t h i n v e r t e b r d t e s and f i s h e s . The f o o d of j u v e n i l e coho sdlmon d l o n g t h e Oregon dnd Washington c o d s t s i n 1980 compr ised seven ~ n a j o r p r e y groups (Emmett e t a l . 1986) . I n l d t e May t o e a r l y June, t h e salmon f e d p r i r n d r i l y on f i s h ; c r d b l d r v d e , c a l a n o i d copepods, and t h e gdmmdrid dmphipod A r t y l u s t r i d e n s were o f secondary -- -- - - - - - - - - impor tance . I n e d r l y J u l y , f i s h and t h e euphdus i i d ~ h y s ~ n o e s s h y i n i f e r a were t h e p r i r n d r y f o r d g e ; crdb- l d r v d e and h y p e r i i d amphi pods were secondary . I n l d t e August t o e d r l y September, h y p e r i i d amphipods and t h e p e l a q i c g a s t r o p o d -- L i m d c i n a sp. were t h e p r i m a r y f o r d g e ; c r d b l a r v d e and f i s h were secondary . D i e t o v e r l a p w i t h j u v e n i l e ch inook salmon was h i g h e s t f r o m l a t e May t o e a r l y June and l o w e s t f rorn l a t e August t o e a r l y September. D u r i n g l a t e May t o m i d - J u l y , ch inook and coho salmon a t e s i m i l a r f i s h s p e c i e s as t h e p r i m a r y p r e y b u t d u r i n g l a t e August t o e a r l y September, p r o p o r t i o n a l l y more f i s h were e a t e n by ch inook salmon t h a n by coho salmon, wh ich a t e more L i m a c i n a sp. The
i n t e n s i t y o f f e e d i n g (as measured b y p e r c e n t stomach f u l l n e s s ) i n c r e a s e d f o r coho salmon f r o m May t o September. P e t e r s o n e t a l . (1982) found t h a t t h e m a j o r f o o d of j u v e n i l e coho salmon a l o n g t h e Oregon Coast was t h e euphausi i d s i n i f e r a , h y p e r i i d amphipods, ;d The d i e t ove r1 ap between j u v e n i l e ch inook and coho salmon was a l s o h i g h .
M o r t a l i t y o f coho salmon may be h i g h d u r i n g emergence and downstream m i g r a t i o n . Shapovalov dnd Ta f t (1954) suggested t h a t t h e f a c t o r s r e s p o n s i b l e f o r l o s s e s a f t e r t h e f i s h emerged i n Waddel l Creek i n c l u d e d p r e d a t o r s , d r y i n g s t r e a m channe ls , and d i sease . They s t a t e d t h a t h i g h wa te r t empera tu res , p o l l u t i o n , and l a c k o f s u i t a b l e f o o d a l s o caused l o s s e s i n o t h e r Cal i f o r n i a s t reams. P r e d a t o r s i n C a l i f o r n i a s t reams, o t h e r t h d n f i s h , i n c l u d e d g a r t e r snakes and t h e American d i p p e r , C i v i l u s mex icanus. I n west c o a s t areas, coho salmon a r e a t t a c k e d b y ldmpreys dnd p reyed on b y l a r g e r coho, c u t t h r o a t t r o u t ( ~ a l m o c l a r k i 1, s t e e l head, Do1 l y Varden ( S a l v e l i n u s .- malma), squawf i sh , and s c u l p i n s . K i n g f i s h e r s , l o o n s , mergansers, and o t h e r b i r d s and s m a l l mammals sometimes e a t j u v e n i l e s ( S c o t t and Crossman 1973) . H igh seas p r e d a t o r s o f salmon a r e s e a l s , sha rks , sea l i o n s , and o t h e r salmon.
P r o d u c t i o n o f j u v e n i l e coho salmon i n c o a s t a l s t reams v a r i e s w i t h s t ream and y e a r . Annual p r o d u c t i o n r a t e i n t h r e e Oregon s t reams f o r 4 c o n s e c u t i v e y e a r s averaged abou t 9 g/mZ p e r y e a r (Chapman 1965) . M o n t h l y p r o d u c t i o n was 1.9-2.8 g/m2 a f t e r emergence, d e c l i n e d t o 0.2-0.3 g/m2 i n w i n t e r , and t h e n i n c r e a s e d t o 0.5-0.6 g/m2 b e f o r e e m i g r a t i o n . Biomass averaged 5-12 g/m2 j u s t a f t e r emergence, and t h e n d e c l i n e d and remained a t about 2 - 4 g / m 2 u n t i l e m i g r a t i o n o f s m o l t s t h e f o l l o w i n g s p r i n g . M o n t h l y coho salmon p r o d u c t i o n i n a C a l i f o r n i a s t ream f r o m June t o Oc tober ove r d span of 3 y e a r s averaged 0.05 g/m2 (Burns 1971) .
ENVIRONMENTAL REQUIREMENTS
I n C a l i f o r n i a , coho salmon u s u a l l y m i g r d t e ups t ream when s t ream f l o w s i n c r e d s e and wa te r t empera tu res a r e 4-14 OC, and spawn when t e m p e r a t u r e s a r e 6-12 OC ( B r i g g s 1953; Shapovalov and Taf t 1954) . Coho salmon p r e f e r c o l d wa te r ; 25.8 OC i s t h e i r upper l e t h a l l i m i t ( T a b l e 2 ) . G o d f r e y (1965) r e p o r t e d t h a t coho salmon were caugh t i n t h e ocean a t w a t e r t e m p e r a t u r e s o f 4-15.2 OC.
Emmett e t a l . (19861, who de te rm ined f o o d of j u v e n i l e coho salmon i n t h e ocean f rom f i s h cdugh t i n a p u r s e se ine , i n d i c a t e d t h a t f e e d i n g and w a t e r t e m p e r a t u r e may be r e l a t e d . The number o f j u v e n i l e s c a p t u r e d was s m a l l e s t and t h e pe rcen tage o f f i s h w i t h empty stomachs h i g h e s t when s u r f a c e wa te r t empera tu res had i n c r e d s e d and dveraged 15.2 OC.
Depth
Coho salmon spawn i n 0.1-0.54 m o f w a t e r i n C a l i f o r n i d ( B r i g g s 1953; Buck dnd B d r n h a r t 1986) . As t h e f r y grow t h e y move i n t o p r o g r e s s i v e l y deeper r i f f l e s and p o o l s ( T a b l e 2 ) .
V e l o c i t y
Water v e l o c i t y i n c o a s t a l s t reams may exceed t h e swimming a b i l i t y o f m i g r d t i n g coho salmon d u r i n g s t o r m r u n o f f . A d u l t s can m i g r a t e a t w a t e r v e l o c i t i e s o f 2.44 m/s ( T a b l e 2 ) b u t a r e r e t a r d e d a t v e l o c i t i e s o f 3-4 m/s ( R e i s e r and B j o r n n 1979) . I n C a l i - f o r n i a , coho salmon spawn i n w a t e r mov ing a t v e l o c i t i e s o f 0.18-0.76 m/s ( B r i g g s 1953; Buck and B a r n h a r t 1986) .
D i s s o l v e d Oxygen
D i s s o l v e d oxygen (DO) c o n c e n t r a - t i o n s a r e i m p o r t a n t t o a l l l i f e s tages o f coho salmon. When DO wds o f < 5 mg/L, t h e i n c u b a t i o n p e r i o d was - leng thened and new ly hd tched f r y were s m a l l e r t h a n averdge (Shumwdy e t a l .
T d b l e 2. P r e f e r r e d h d b i t a t r e q u i r e m e n t s f o r coho salmon i n s t redms ( R e i s e r dnd B j o r n n 1979) .
V d r i d b l e Vdl ue and u n i t -- ----
Temperdture A d u l t m i y r d t i o n upst redm Spawning I n c u b a t i o n Upper l e t h d l P r e f e r r e d rdnge
Water d e p t h A d u l t m i g r d t i o n upst redm (minimum) 0.18 m Spdwning (minimum) 0.18 m Age 0 f i s h ( p r e f e r r e d ) 0.30 - 1.22 m (60% o f r i f f l e s h o u l d be submerged)
Wdter v e l o c i t y A d u l t m i g r d t i o n upst redm (maxirnum) Spawning Age 0 f i s h ( p r e f e r r e d ) R i f f l e v e l o c i t y f o r r e d r i n g Poo l v e l o c i t y f o r r e d r i n g A d u l t swimming speeds
C r u i s i n g S u s t d i n e d D a r t i n g
I n v e r t e b r d t e f o o d organ isms
D i s s o l v e d oxygen Weight g d i n i n f r y s t a g e (4-9 mg/L) 70% - 100% g a i n i n 19 - 28 days Food c o n v e r s i o n ( 9 mg/L maximum t e s t e d 4 - 9 mg/L J u v e n i l e swimming speed (maximum) 100% s a t u r d t i o n I n c u b d t i o n Near s a t u r a t i o n ( 2 5 mg/L)
Spdce ( a r e a ) Average s i z e o f r e d d 2.8 m2 Recornmended a r e d p e r spawning p a i r 11.7 m2 Yedr 1+ f i s h 2.4 - 5.5 m 2 / f i s h
S u b s t r d t e s i z e Spawning 20% f i n e sed iment
<6.4 mm i n r i f f l e s u b s t r d t e
S i l t l oads <25 mg/L p r e f e r a b l e
O t h e r Cover R i f f 1e:pool r a t i o
Good overhedd dnd submerged 1: 1
1964) . S u s t a i n e d swimming speeds of j u v e n i l e coho salmon were reduced when DO was 7 mg/L o r be low a t 10-20 OC
( D a v i s e t a l . 1963) . I n Waddel l Creek, Cal i f o r n i a, oxygen s a t u r a t i o n was u s u a l l y above 85% d u r i n g a d u l t n i i y r d t i o n (Shdpovd lov and T a f t 1954) . H i g h d i s s o l v e d oxygen c o n c e n t r d t i o n s d r e a l s o i ~ n p o r t d n t f o r f i s h g r o w t h ( T a b l e 2 ) .
S u b s t r a t e p a r t i c l e s i z e i s impor - t a n t f o r coho salmon spawning and egg i n c u b a t i o n . R e i s e r and B j o r n n (1979) r e p o r t e d t h a t g r d v e l 1.3-10.2 cm i n d i a m e t e r was a c c e p t a b l e ds coho salmon spawning s u b s t r a t e . P r o d u c t i v e redds i n P r d i r i e Creek d ra inage , Cal i f o r n i a , were i n g r a v e l o f 3.8-12.7 cm ( B r i g g s 1953 1. Spawning coho salmon i n T r i n i t y R i v e r , C a l i f o r n i a , p r e f e r r e d g r a v e l o f 7.5-15.0 cm t h a t was u s u a l l y <20% embedded (Buck and B a r n h a r t 1986) . Most redds were w i t h i n 10 m of cove r and h a l f were w i t h i n 5 m.
T u r b i d i t y
T u r b i d i t y cdn i n t e r f e r e w i t h a1 1 l i f e s tdges o f sa lmon ids . T u r b i d i t i e s o f 4,000 mg/L cause sa lmon ids t o cease moving, and l e v e l s o f 80-400 mg/L a r e c o n s i d e r e d d e t r i m e n t a l ( B e l l 1973) . Streams w i t h t u r b i d i t i e s o f (25 mg/L s h o u l d p r o v i d e good f i s h h a b i t a t ( T a b l e 2 ) . P ro longed exposure t o h i g h l y t u r b i d wa te r may cause t h i c k - e n i n g o f g i l l l a m e l l a e , c l o g g i n g of g i 1 I s , c u r t a i lment o f f e e d i n g , and avo idance o f a reas b y f i s h (Cordone and K e l l e y 1961; B e l l 1973; R e i s e r and B j o r n n 1979) . Coho salmon f r y (30-65 mm l o n g ) s u b j e c t e d t o c h r o n i c t u r b i d i - t i e s o f 25-50 mg/L showed g i l l - t i s s u e damage a f t e r 3-5 days exposure, and g r o w t h was reduced a t t u r b i d i t i e s o f o n l y 25 mg/L ( S i g l e r e t a l . 1984) . S i l t d e p o s i t s a r e more damaging t h a n s i l t suspended i n t h e w a t e r column. The d e p o s i t s can r e s t r i c t oxygen f 1 ow t o eggs dnd f r y , t r a p f r y t r y i n g t o emerge, reduce t h e q u a l i t y o f spawning h a b i t a t i n o t h e r ways, and d e s t r o y
f o o d s u p p l i e s (Cordone and Ke l l e y 1961; Be1 1 1973) .
O the r F a c t o r s
F i s h h a b i t a t i s c o n t i n u o u s l y b e i n g d e s t r o y e d o r degraded by many t y p e s o f deve lopments and n a t u r a l causes. Human a c t i v i t i e s such as t i m b e r h a r v e s t , 1 i v e s t o c k g r a z i n g , m i n i n g , r o a d c o n s t r u c t i o n , u r b a n i z a - t i o n , and w a t e r and h a r b o r development have a d v e r s e l y a f f e c t e d salmon h a b i t a t ( B e r g e r 1982) . Salmon s t o c k s t h r o u g h o u t t h e P a c i f i c Reg ion have d e c l i n e d d r a m a t i c a l l y because of t h e s e a c t i v i t i e s and o v e r f i s h i n g .
S t a t e , F e d e r a l , and p r i v a t e agenc ies a r e d e v e l o p i n g and u s i n g a number o f r e s t o r a t i o n and enhancement programs t o i n c r e a s e salmon s t o c k s . C u r r e n t knowledge o f how management p r a c t i c e s on f o r e s t and range l a n d s i n f 1 uence t h e h a b i t a t r e q u i r e m e n t s o f salmon and t r o u t , t h e e f f e c t s of v a r i - ous l a n d uses on t h i s h a b i t a t , and methods f o r r e s t o r a t i o n and enhdnce- ment o f h a b i t a t was c o m p i l e d by Meehan (1979) . I n f o r m a t i o n on improvement o f a q u a t i c h a b i t a t i n v e n t o r y t e c h n i q u e s was summari zed b y A r m a n t r o u t (1982) . C u r r e n t methods and t e c h n i q u e s f o r t h e r e h a b i l i t a t i o n o f h a b i t a t used b y anadromous sa lmon ids was c o m p i l e d by H a s s l e r (1981, 1984) . Methods t o e v a l u a t e h a b i t a t r e h a b i 1 i t a t i o n p r o - j e c t s were deve loped by B u e l l (1986) .
Resource managers need t o con- s i d e r t h e seasonal h a b i t a t r e q u i r e - ments f o r j u v e n i l e coho salmon when a s s e s s i n g l a n d and w a t e r development p l a n s . P r o d u c t i v e summer h a b i t a t , such as s m a l l e s t u a r i e s , may enhance w i n t e r s u r v i v a l o f j u v e n i l e coho salmon b y p r o d u c i n g f i s h i n good con- d i t i o n . The r e l a t i o n between o v e r - w i n t e r s u r v i v a l and f i s h body l i p i d c o n t e n t i n d i c a t e s t h a t ene rgy s t o r e d i n body f a t i n f a l l c o n t r i b u t e s t o h i g h e r w i n t e r s u r v i v a l (Mason 1976) . C l e a r c u t l o g g i n g has been shown t o i n c r e a s e s t r e a m p r o d u c t i v i t y and s a l m o n i d s t a n d i n g c r o p d u r i n g summer
(Murphy and Hal 1 1981); however, t h e s e t h a n and independen t o f t h o s e o f i n c r e d s e s may be n u l l i f i e d i f w i n t e r s t r e a m f r y ( T s c h a p l i n s k i 1982) . The h a b i t a t i s a d v e r s e l y a f f e c t e d . e s t u a r i e s can t h u s p roduce l a r g e ,
f a s t - g r o w i n g f r y , r e g a r d l e s s o f Coho salmon f r y i n e s t u a r i e s a r e ups t ream e v e n t s , w h i c h c o n t r i b u t e t o
r e 1 a t i v e l y u n a f f e c t e d b y e v e n t s o c c u r - t h e a d u l t s t o c k . P r a c t i c e s wh ich may r i n g upst ream. The f r y hdve r a t e s o f d e s t r o y o r a l t e r e s t u a r i n e h a b i t a t g r o w t h and s u r v i v a l t h a t a r e b e t t e r s h o u l d be avo ided o r m i n i m i z e d .
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0172 -101
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*U.S. Army Corps o f Engineers Report 140. TR EL-82-4 L *brtmd (Lhk zm -.dl)
T h i s species p r o f i l e sumnarizes taxonomy, morphology, d i s t r i b u t i o n , abundance, l i f e h i s t o r y , and e n v i r o m e n t a l requ i rements o f coho salmon i n t i le P a c i f i c Southwest ( C a l i f o r n i a ) . Coho salmon a r e anadromous and e n t e r f r e s h w a t e r i n f a l l t o spawn, a f t e r 1 i v i n g i n the ocean f o r two growing seasons. Spawning peaks i n November t o January. The f ry ha tch i n s p r i n g and m i g r a t e t o the ocean i n about a year . J u v e n i l e coho r e q u i r e a m i x t u r g o f poo ls and r i f f l e s , abundant ins t ream and bank cover, water temperatures o f 10-15 C i n summer, d i s s o l v e d oxygen near sa tu ra t i on , and r i f f l e s w i t h r e l a t i v e l y 1 i t t l 'e sediment and w i t h abundant a q u a t i c and t e r r e s t r i a l i n s e c t s f o r food. Coho salmon suppor t an ex tens i ve comnerc ia l and s p o r t f i s h e r y . H a b i t a t s t h a t suppor t coho salmon a r e c o n t i n u a l l y be ing des t royed o r degraded; State, Federal , and p r i v a t e agencies a r e working t o r e s t o r e and enhance these h a b i t a t s .
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DEPARTMENT OF THE IWTERIOR U.S. FISH AND Wl lDL lA SERVICE
As the Nation's principal conservation agency. the Department of the Interior has respon- sibility for most of our .nationally owned public lands and natural resources. This includes fostering the wisest use of our land and water resourcm, protecting our fish and wildlife, preserving thsenvironmental and cultural values of our national parks and historical places, and providing for the enjoyment of life through outdoor recreation. The Department as- sesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also has a major responsibility for American Indian reservation communities and for paople who live in island territories under U.S. administration.
