rôle de la dispersion dans la réponse des populations de truites … · riffle-run habitat were...
TRANSCRIPT
Bull. Fr. Pêche Piscic. (1995) 337/338/339 :179-190 — 179 —
Present address : National Biological Service, Aylesworth Hall NW, Colorado State University, Ft. Collins, CO 80523, USA.
Présent address : Fisheries Centre, 2204 Main Mail, University of British Columbia, Vancouver, B.C. V6T 1Z4, Canada.
RÔLE DE LA DISPERSION DANS LA RÉPONSE DES POPULATIONS DE TRUITES AUX HABITATS FORMÉS PAR LES GRANDS DÉBRIS LIGNEUX DANS LES RUISSEAUX DE MONTAGNE DU COLORADO.
K.D. F A U S C H , C. G O W A N , A N N D. R I C H M O N D * , S .C . R I L E Y "
Depa r tmen t of F ishery a n d Wi ld i i fe Bio logy, Co lo rado State Univers i ty , Ft. Co l l i ns , Co lo rado 8 0 5 2 3 , U S A .
R É S U M É ( t radui t par les éd i teurs)
U n peu par tou t dans le m o n d e , les a m é n a g i s t e s des pêches ut i l isent s o u v e n t des rond ins pour réaliser des moui l les pour les sa lmon idés , souvent pour c o m p e n s e r l 'absence de g rands débr is l igneux (LWD) due à la déforestat ion o u à d 'autres per turbat ions d e s forêts a l luv ia les . Des m e s u r e s d e s L W D réa l i sées su r 11 ru isseaux d e m o n t a g n e d u Co lo rado dra inant de viei l les forêts d e rés ineux (P/cea - Abies) montrent qu' i ls sont à l 'or igine de la p lupar t d e s mou i l l es . Les m o r c e a u x qu i con t r i buen t à la f o rma t ion des mou i l l es sont , e n m o y e n n e , p l u s g r a n d s q u e c e u x qu i n ' en f o r m e n t p a s . L a p l u p a r t e n j a m b e le c h e n a l perpend icu la i rement à l 'écoulement et f o rme d e s moui l les de chute («p lunge pool») et des moui l les de re tenue ( « d a m m e d pool»). Les aménag is tes des pêches qui ut i l isent d e s troncs perpend icu la i res à l 'écou lement pour réal iser des mou i l les cons idè ren t g é n é r a l e m e n t q u e ce t te add i t ion d 'habi tat amé l io re la surv ie d e s sa lmon idés rés idents pendan t les pér iodes c r i t i q u e s c o m m e l 'h iver. U n e e x p é r i e n c e d e l o n g u e d u r é e , r é a l i s é e p o u r t e s t e r ce t te hypo thèse dans six ru isseaux de m o n t a g n e d u Co lo rado , a mon t ré q u e les populat ions d e t r u i t e s r é s i d e n t e s a u g m e n t a i e n t r a p i d e m e n t et s i g n i f i c a t i v e m e n t d a n s d e s p o r t i o n s expér imenta les de 2 5 0 m , par rapport à des témo ins ad jacents . Cependan t , des mesures d e la d ispers ion réal isées par des p iégeages et des recaptures de t ru i tes ma rquées ont montré que les moui l les fo rmées par des t roncs augmen ten t les popu la t ions d e t ru i tes adul tes e n p e r m e t t a n t aux t ru i tes qu i é ta ien t en p h a s e d e d é p l a c e m e n t d e rester d a n s les por t ions expé r imen ta les plutôt qu ' en amé l io ran t la surv ie h ive rna le sur p lace , c o m m e le décr ivent d 'au t res au teu rs . La recherche sur les s a l m o n i d é s d 'eau cou ran te non m ig ra teu rs et leur gest ion a jusqu 'à présent été marquée par un modè le impl iquant des dép lacemen ts limités, ce qu i i m p l i q u e q u e les a d u l t e s so ien t r e l a t i v e m e n t s é d e n t a i r e s . C e p e n d a n t , l ' ana lyse d 'é tudes antér ieures sur les dép lacemen ts démon t re que la plupart des expér imenta teurs ne s ' in téressent qu 'aux po issons recapturés dans les port ions où ils ont été re lâchés, ce qui est cr i t iquable si l 'on souha i te met t re des m o u v e m e n t s en év idence . Le fait q u e les po issons présentent des dép lacemen ts conséquen ts a des impl icat ions impor tantes pour l 'améliorat ion et la restaurat ion de l 'habitat, et p la ide pour une gest ion prenant en c o m p t e le bass in versant .
T H E R O L E O F D I S P E R S A L IN T R O U T P O P U L A T I O N R E S P O N S E T O HABITAT F O R M E D BY L A R G E W O O D Y D E B R I S IN C O L O R A D O M O U N T A I N S T R E A M S .
S U M M A R Y
F i s h e r y m a n a g e r s c o m m o n l y u s e l o g s to c r e a t e poo l h a b i t a t f o r s a l m o n i d s in m o u n t a i n s t r e a m s t h roughou t the w o r l d , o f ten to c o m p e n s a t e for a lack of na tu ra l large w o o d y d é b r i s ( L W D ) d u e to d é f o r e s t a t i o n o r o t h e r d i s t u r b a n c e s in r i p a r i a n f o r e s t s . M e a s u r e m e n t s of LWD in 11 Co lo rado m o u n t a i n s t r eams that d ra in pa t ches of o ld -g rowth spruce- f i r (Picea-Abies) fo res t ind ica ted tha t mos t poo ls w e r e f o r m e d by L W D . T h è s e poo l -
Article available at http://www.kmae-journal.org or http://dx.doi.org/10.1051/kmae:1995020
Bull. Fr. Pêche Piscic. (1995) 337/338/339 :179-190 — 180 —
f o r m i n g p i è c e s we re , on a v e r a g e , la rger than p ièces that d id not fo rm poo ls . The major i ty s p a n n e d t h e c h a n n e l p e r p e n d i c u l a r to f l o w a n d f o r m e d p l u n g e a n d d a m m e d p o o l s . F i s h e r y m a n a g e r s tha t use pe rpend icu la r l egs to f o rm poo ls genera l ly a s s u m e that the a d d e d hab i ta t wil l i nc rease surv iva l of rés ident sa lmon ids dur ing cr i t ical per iods s u c h as win ter . R e s u l t s of a l ong - te rm expe r imen t to test th is hypo thes is in six Co lo rado m o u n t a i n s t r e a m s s h o w e d t h a t r é s i d e n t t r ou t p o p u l a t i o n s i n c r e a s e d rap id iy a n d s i gn i f i can t l y in 2 5 0 - m t r e a t m e n t sec t i ons ve rsus ad jacent con t ro l s . However , recap tu res of m a r k e d t rout a n d d i rec t t r app ing to m e a s u r e d ispersa i i nd i ca ted that the poo l - fo rm ing logs i nc reased a d u l t t r o u t p o p u l a t i o n s p r i m a r i l y by i n d u c i n g f i sh t ha t w e r e m o v i n g to r e m a i n in t h e t r e a t m e n t s e c t i o n s , ra the r t h a n by i nc reas ing in situ ove rw in te r su rv iva l as repo r ted by o t h e r s . R e s e a r c h and m a n a g e m e n t of rés ident s t r e a m sa lmon ids has been gu ided by the res t r i c ted m o v e m e n t p a r a d i g m , w h i c h states that mos t adul t f ish are relat ively sedentary . H o w e v e r , ana lys i s of p rev ious m o v e m e n t s tud ies revea led that most invest igators f o c u s e d on l y on f ish recap tu red in the r e a c h e s where they w e r e re leased . a cr i t ical des ign f law that c a u s e s a b i a s a g a i n s t d e t e c t i n g m o v e m e n t . S u b s t a n t i a l f ish m o v e m e n t has i m p o r t a n t i m p l i c a t i o n s f o r h a b i t a t e n h a n c e m e n t a n d r e s t o r a t i o n , a n d c a l l s f o r a w a t e r s h e d m a n a g e m e n t a p p r o a c h .
I N T R O D U C T I O N
S t r e a m channe l s t h roughou t the wor ld have been s impl i f ied by a var iety of h u m a n ac t iv i t ies . In m a n y fo res ted w a t e r s h e d s of the centra l Rocky Mounta ins , and e l sewhe re in w e s t e r n Nor th A m e r i c a , r ipar ian fo res ts were c learcu t dur ing 1860-1940 to prov ide t ies for a t r a n s c o n t i n e n t a l ra i i road a n d w o o d for mining t imbers a n d bui ld ings ( Y O U N G et al., 1994) . M o r e o v e r , to faci l i tate dr iv ing the logs d o w n s t r e a m dur ing spr ing snowmei t runoff, bou lde rs a n d logs tha t obs t ruc ted the channe l were genera l l y r e m o v e d . Any w o o d remain ing in the c h a n n e l a f te r t hèse «f ie d r i ves» gradua l ly ro t ted a n d w a s h e d away, and little n e w large w o o d y déb r i s (LWD) en te red f rom the r iparian forest for the next 100-150 years ( M U R P H Y a n d K O S K I , 1989) . T h e comb ina t i on of thèse p rocesses e n s u r e d that habi tat for sa lmon ids in m a n y m o u n t a i n s t r e a m s b e c a m e progress ive ly s impl i f ied .
A l t h o u g h f i shery m a n a g e r s on ly recent ly r e c o g n i z e d the effect that th is l ong - te rm réduc t i on in L W D recru i tment af ter forest harvest had on s t ream channe ls , they did respond to t h e s imp l i f i ed habi tat by add ing structures m a d e f rom logs or bou lders (e .g , , W H I T E and B R Y N I L D S O N , 1967 ; S E E H O R N , 1992) . The rat ionale w a s usual ly that deep , s table poo ls w i th c o m p l e x s t ruc ture p rov ide she l ter f rom h igh f l ows , v isuel isolat ion f rom other f ish, or h id ing c o v e r f rom p reda to rs ( F A U S C H , 1993), and thereby increase surv ival of sa lmon ids du r i ng w in te r or s u m m e r However , a l though s u c h habi tat e n h a n c e m e n t has been p rac t i ced for a t least 6 5 years (e .g . , H U B B S et al., 1932 ; T A R Z W E L L , 1936), there have been few l o n g - t e r m s tud ies of t he e f fec t i veness of any of the me thods for increas ing popu la t ions of s t r e a m f i shes (e.g. , H U N T 1 9 7 1 , 1988 ; W H I T E , 1975) .
T h e p u r p o s e of this paper is to in tegrate and syn thes ize the resul ts of two research p ro jec ts a i m e d at unde rs tand ing the rôle of L W D in fo rming habi tat for s t ream sa lmon ids in m o u n t a i n s t r e a m s of nor thern Co lo rado . The first project invest igated the rôle of L W D in f o r m i n g p o o l s in s t r e a m s d r a i n i n g pa tches of o l d - g r o w t h fo res t s , a n d c o m p a r e d t h è s e resu l ts to d i s tu rbed s t r e a m s w h e r e L W D was lack ing . T h e s e c o n d is an ongo ing long- te rm, l a r g e - s c a l e e x p e r i m e n t to d é t e r m i n e h o w t rou t p o p u l a t i o n s r e s p o n d to i n c r e a s e d poo l hab i ta t c r e a t e d by a d d i n g L W D to s impl i f ied s t r eam reaches , T h u s , resul ts f rom the t w o s tud ies c a n b e l inked to s h o w h o w t rout popu la t ions a re l ikely to respond to rehabi l i ta t ion of o the r s imp l i f i ed s t ream reaches by a d d i n g LWD, in fo rmat ion needed by those w h o m a n a g e fo res ts a n d s t r e a m sa lmon ids .
T H E R O L E O F L W D I N F O R M I N G P O O L S
La rge w o o d y débr is has a var ie ty of func t ions in t empera te s t ream e c o s y s t e m s . It f o r m s p o o l s , s t o r e s s é d i m e n t , is a l o n g - t e r m s o u r c e of o r g a n i c mat te r , a n d p r o v i d e s h e t e r o g e n e o u s habi ta t for f ish and thei r inver tebrate food supp ly ( B I S S O N et al., 1987 ; N A K A M U R A a n d S W A N S O N , 1993) . However , most research on LWD to da te has been
Bull. Fr. Pêche Piscic. (1995) 337/338/339 :179-190 — 181 —
c o n d u c t e d a l o n g the Pac i f i c c o a s t of n o r t h w e s t e r n Nor th A m e r i c a (e .g . , F A U S C H and N O R T H C O T E . 1992 : R A L P H et al.. 1994) , and a f ew o ther loca t ions (e .g . , B I L B Y and L I K E N S , 1980 ; E V A N S et al.. 1993) , w h e r e a s a lmos t noth ing is k n o w n abou t its rôle in R o c k y M o u n t a i n w a t e r s h e d s w h e r e c l i m a t e , g e o l o g y , a n d t ree s p e c i e s d i f fer f r o m t h e Paci f ic Nor thwes t .
R I C H M O N D and F A U S C H (1995) m e a s u r e d L W D and s t ream habi tat in 221-575 m reaches of 11 second - and th i rd-order s t r e a m s (3 .7-10.2 m bankfu l l width) d ra in ing pa tches of E n g l e m a n n spruce {Picea engelmannii)-suba\p\ne fir (Abies lasiocarpa) fo res ts at about 2 7 0 0 - 3 2 0 0 m al t i tude in the moun ta ins of nor thern Co lo rado . T h e s a m e charac ter is t i cs were m e a s u r e d in 250 -m reaches of four s imi lar s t r eams that lacked L W D due to past logging or natural d is tu rbances such as t ire. AH s t reams had modera te grad ient (0.4-6 % ) , a n d were m e a s u r e d at or near basef low in late summer .
R I C H M O N D a n d F A U S C H ( 1 9 9 5 ) f o u n d t h a t L W D p i è c e s in t h e 11 o l d - g r o w t h s t r e a m s w e r e substant ia l ly sma l le r in d i ame te r and shor te r t han t hose in s t r e a m s of t he Paci f ic Nor thwes t région of North A m e r i c a . Never the less , 81 % of pools ( n = 144) in the o ld -g r o w t h s t r e a m s w e r e f o r m e d by L W D , in con t ras t to on ly 32 % of t he poo l s in t h e four d is tu rbed s t reams (n = 38). T h e major i ty (57 %) of the 148 LWD p ièces that f o r m e d pools in t h e o ld -g rowth s t r eams we re or ien ted near ly pe rpend icu la r to f low a n d s p a n n e d the channe l (53 % ) , wh i ch w a s signi f icant ly di f férent than the r a n d o m distr ibut ion of the 1221 L W D pièces that d id not fo rm pools ( P < 0.001 by G-test) . Th i s b ias t owa rd pe rpend icu la r or ien ta t ion resu l ted in 82 % of the pools be ing d a m m e d or p lunge pools (see B I S S O N et al., 1982 for poo l t ypes) . Poo l - fo rming p ièces w e r e s ign i f icant ly longer and larger d i ame te r t h a n those that d id not fo rm pools ( P < 0.0001 by W i l c o x o n Rank S u m s test) .
T h e rôle of LWD in fo rm ing poo ls w a s a Iso re la ted to s t r eam s ize. R I C H M O N D a n d F A U S C H (1995) s h o w e d that s t r eams larger t han abou t 5 m bankfu l l w id th w e r e capab le of red is t r ibut ing w o o d into c l umps , to the c h a n n e l marg ins , or on to the f l oodp la in , s o that a h igher pe rcen tage of the LWD fo rmed poo ls in sma l le r t han in larger s t r e a m s . A s a resuit, s ing le L W D p ièces ly ing re la t ive ly p e r p e n d i c u l a r to f low f o r m e d the ma jo r i t y of poo ls in smal l s t r eams (ca. < 5 m wide) d ra in ing o ld g row th fo res ts , but in larger s t r e a m s only the largest p ièces , or c lumps of m a n y p ièces , f o r m e d poo ls . Moreover , desp i t e d i f férences in c l ima te and v é g é t a t i o n , t h è s e re la t i onsh ips a re s im i la r to t h o s e f o u n d fo r LWD in o ther rég ions (e .g . , R O B I S O N and B E S C H T A , 1990 ; B I L B Y and W A R D , 1991) .
T R O U T P O P U L A T I O N R E S P O N S E T O P O O L S F O R M E D BY L W D
Fishery m a n a g e r s that have u s e d pe rpend icu la r logs to f o rm poo ls in s t r e a m s of t he R o c k y M o u n t a i n s a n d e l s e w h e r e ( e . g . , G A R D , 1961 ; H O U S E a n d B O E H N E , 1985 ; M E R W A L D , 1987 ; HUNT, 1988) h a v e genera l l y a s s u m e d that t he a d d e d hab i ta t wou ld inc rease t rout surv iva l dur ing w in ter a n d pe r iods of h igh s t r eam d ischarge . It is c lear f rom the p rev ious sect ion that such poo ls a re g o o d ana logs of those f o r m e d by natura l LWD in sma l l m o u n t a i n s t reams , the major i ty of w h i c h a re p l unge a n d d a m m e d poo l s f o r m e d by s ing le perpend icu la r logs. However , to date there has been no c o m p r e h e n s i v e éva luat ion of their ef fects on trout popu la t ions .
In 1987 w e began a long- te rm e x p e r i m e n t to s tudy the response of t rout popu la t ions in s impl i f ied s t ream reaches to insta l l ing pe rpend icu la r logs that f o rm poo ls (hereaf ter , LWD poo ls ) . Six h igh-a l t i tude ( 2 4 2 5 - 2 9 2 5 m) s t r e a m s w i th 5 0 0 m of re la t ive ly h o m o g e n e o u s ri f f le-run habi ta t were c h o s e n for s tudy (see R ILEY et al., 1992 and R ILEY and F A U S C H , 1995 for déta i ls ) . Ail are smal l (3-6 m w i d e at base f low) , modera te -g rad ien t (1-2 %) s t reams that ha rbor se l f -susta in ing popu la t ions of w i ld b rook t rout (Salvelinus fontinalis), b r o w n t rout {Salmo trutta), ra inbow trout (Oncorhynctius mykiss), or a comb ina t i on of t hèse spec ies . Wa te r t empéra tu res are be low 0 °C for 4-6 m o n t h s per year, so t rout g row th is s low a n d m a x i m u m to ta l l e n g t h s a r e g e n e r a l l y l ess t h a n 2 2 5 m m in f ou r h i g h - a l t i t u d e s t r e a m s (> 2700 m) , and less than 300 m m in the two low-a l t i tude ones (< 2 5 0 0 m) .
T h e 5 0 0 - m reach of each s t r e a m w a s d i v i ded in t w o s e c t i o n s , o n e of wh i ch w a s randomly se lec ted to rece ive 10 LWD poo ls af ter t w o years of p re - t rea tmen t m e a s u r e m e n t
Bull. Fr. Pêche Piscic. (1995) 337/338/339 :179-190 — 1 8 2 —
( o n e y e a r in two s t r e a m s ) , w h i l e t h e other s e r v e d as an u n m a n i p u l a t e d c o n t r o l . T r o u t p o p u l a t i o n s , habi tat , a n d ang le r use were m e a s u r e d each year in each s t ream, w i th few e x c e p t i o n s . Deep , s low poo l habi tat inc reased signi f icant ly, immedia te iy after the logs w e r e ins ta l l ed . F e w or no ang le rs f i shed in the sec t ions , due to their remote locat ion, a n d few k i l led a n y f i sh b e c a u s e s igns w e r e p laced ask ing t h e m to re lease ail f ish al ive (see R ILEY a n d F A U S C H , 1 9 9 5 ) . T r o u t a b u n d a n c e w a s m e a s u r e d in e a c h t r e a t m e n t a n d con t ro l s e c t i o n by t h r e e - p a s s r e m o v a l e l ec t ro f i sh ing a f ter b l ock ing the sec t i on e n d s w i th f i ne -m e s h e d (5 m m ) se ines (see R ILEY a n d F A U S C H , 1992) . Th is me thod is h ighiy ef f ic ient, near l y a i w a y s cap tu r ing > 85 % of age-1 juvén i les a n d > 90 % of age-2 and o lder adu l t t rout in t h r e e p a s s e s , as es t ima ted by the max imum- l i ke l i hood genera l i zed remova l es t imato r of O T I S et al. (1978) .
T h i s h i gh c a p t u r e e f f i c iency has been va l i da ted in one of the con t ro l sec t i ons by re l eas ing a k n o w n n u m b e r of m a r k e d résident f ish, of wh i ch 98 % we re recaptured (Fausch a n d G o w a n , unpub. ) . Ai l f ish cap tu red dur ing each annua l e lect rof ish ing we re m a r k e d w i th a p e r m a n e n t f incl ip deno t i ng thei r sec t ion , a n d af ter 1987 those > 125 m m were t agged w i th u n i q u e l y n u m b e r e d F loy F ine-Fabr i c anchor tags in the two low-al t i tude s t reams . Th is m a r k i n g p r o g r a m a l l owed us to a s s e s s the m e c h a n i s m s respons ib le for any inc rease or d e c r e a s e in t rou t popu la t i ons after t he LWD poo ls w e r e c rea ted .
R o p u l a t i o n s of adu l t t rou t i nc reased rap id iy a n d d ramat i ca l l y in ail s ix s t r e a m s af ter t h e L W D p o o l s w e r e c o n s t r u c t e d in la te s u m m e r 1988 (e .g . , F ig . 1). T rou t a b u n d a n c e a v e r a g e d 4 2 % h igher ( r ange : 12 -73 %) in t r ea tmen t v e r s u s cont ro l sec t i ons by 1990 a n d 51 % h ighe r ( r a n g e : 3 6 - 9 3 % in ai l bu t o n e s t r eam) by 1993 (F ig . 2) , desp i t e t w o s t r e a m s h a v i n g h a d p r e - t r e a t m e n t a b u n d a n c e s t h a t w e r e 2 4 % a n d 3 3 % l o w e r in t r e a t m e n t t h a n con t ro l sec t i ons in 1987 before the logs w e r e ins ta l led . T h è s e i nc reases w e r e s i g n i f i c a n t fo r f i ve of s ix i nd i v i dua l s t r e a m s by s ta t i s t i ca l c o n t r a s t s ( P < 0 .001 ; s t a n d a r d e r r o r s of p o p u l a t i o n e s t i m â t e s were not ava i l ab le for s o m e spec ies in the s ix th , s e e R I L E Y a n d F A U S C H , 1 9 9 5 ) . M o r e o v e r , sp l i t -p lo t a n a l y s i s of v a r i a n c e c o m p a r i n g a v e r a g e a b u n d a n c e s be fo re ins ta l l ing logs ( 1 9 8 7 - 8 8 ) to 1993 for t he set of six s t r e a m s a I so i n d i c a t e d tha t adu l t t rou t popu la t i ons h a d i nc reased s ign i f i cant ly ( P < 0 .05 ; G o w a n a n d F a u s c h , unpub . ) . In con t ras t , a b u n d a n c e of age -1 t rout va r i ed annua l ly , gene ra l l y d id no t i n c r e a s e s ign i f i can t ly in i nd iv idua l s t r e a m s af ter t r ea tmen t , a n d w a s not s ign i f i can t ly d i f fé ren t fo r t h e six s t r e a m s overa l l ( P > 0.2 b y A N O V A ; R I L E Y and F A U S C H , 1995) . It is l i ke ly t h a t j uvén i l e r ec ru i tmen t in t h è s e moun ta in s t r e a m s is s t rong ly i n f l uenced by a n n u a l v a r i a t i o n in t h e m a g n i t u d e of s p r i n g s n o w m e i t runof f du r i ng the f i rst f e w w e e k s of l i fe ( N E H R I N G a n d A N D E R S O N , 1993 ) .
O t h e r t h a n by i n c r e a s e d recru i tment of age -1 t rou t , t h e on ly p r o c e s s e s tha t c a n i n c r e a s e t rou t a b u n d a n c e are h ighe r surv iva l or imm ig ra t i on . Ana lys i s of d i f f é rences in s u r v i v a l fo r t r e a t m e n t v e r s u s con t ro l sec t ions b a s e d on recap tu res of t a g g e d t rou t in t he t w o l o w - a l t i t u d e s t r e a m s d u r i n g 1 9 8 8 - 1 9 9 0 r e v e a l e d f e w s i g n i f i c a n t d i f f é r e n c e s , a n d t h è s e w e r e o p p o s i t e t o tha t e x p e c t e d . O f 13 s u c h e s t i m â t e s ca l cu la ted for t he t h ree t rou t s p e c i e s d u r i n g w i n t e r a n d s u m m e r p e r i o d s fo r w h i c h s u f f i c i e n t s a m p l e s i z e s w e r e a v a i l a b l e , on l y 2 s h o w e d s ign i f i can t d i f fé rences (R ILEY a n d F A U S C H , 1995) . Howeve r , in o n e c a s e t rou t su rv i va l w a s s ign i f i can t l y h igher in t h e t r ea tmen t sec t ion du r i ng s u m m e r , a n d in t h e o t h e r it w a s s ign i f i can t l y h igher in the con t ro l sec t i on du r ing winter , ne i the r of w h i c h s u p p o r t s the h y p o t h e s i s tha t t h e LWD p o o l s i n c r e a s e d t rou t surv iva l du r ing winter .
In con t ras t , by 1990 the h igh inc idence of u n m a r k e d adul t t rout in success i ve annua l s a m p l e s s u g g e s t e d tha t i m m i g r a t i o n w a s h i g h ( e . g . , F i g . 3 ; see R I L E Y et al., 1 9 9 2 ) . B e c a u s e m o s t age-1 a n d o lder t rout w e r e cap tu red a n d m a r k e d dur ing e lec t ro f ish ing e a c h y e a r , m o s t a g e - 2 a n d o l d e r t r o u t c a p t u r e d t h e n e x t y e a r s h o u l d h a v e b e e n m a r k e d . H o w e v e r , a m é d i a n of 52 % of adu l t t rout captured in 22 annua l surveys dur ing 1988 -1990 ( R I L E Y et al., 1992) lacked any f inc l ips, desp i te a very low inc idence (es t imated < 0.1 %) of c o m p l e t e l y r e g e n e r a t e d f inc l ips for t a g g e d t r ou t tha t w e r e recap tu red . Moreove r , f ew of t h è s e f i sh b o r e f i nc l i ps f r o m t h e a d j a c e n t t r e a t m e n t or con t r o l s e c t i o n e i t he r ( F i g . 3 ) , s u g g e s t i n g tha t m a n y had immig ra ted f r om longer d is tances . T h u s , by 1990 it had b e c o m e a p p a r e n t t h a t i m m i g r a t i o n w a s m o s t l ikely a n impo r tan t m e c h a n i s m a c c o u n t i n g for t he i n c r e a s e in t rou t popu la t ions af ter habi ta t e n h a n c e m e n t .
Bull. Fr. Pêche Piscic. (1995) 337/338/339 :179-190 — 183 —
300 T NORTH FORK CACHE LA POUDRE RIVER AGE-2 AND OLDER BROOK TROUT
1987 1988 1989 1990 1991 1992 1993
F igure 1 : A b o n d a n c e d e s s a u m o n s d e f o n t a i n e adu l tes d a n s c h a c u n e d e s sec t ions e x p é r i m e n t a l e (trait c o n t i n u ) et t é m o i n (trait point i l lé) d e 2 5 0 m d e la rivière Nor th Fork C a c h e la P o u d r e , C o l o r a d o , U S A , d e 1 9 8 7 à 1 9 9 3 . D ix t roncs p e r p e n d i c u l a i r e s o n t é t é i n s t a l l é s d é b u t A o û t 1 9 8 8 p o u r r é a l i s e r d e s moui l les d a n s la s e c t i o n e x p é r i m e n t a l e ent re les é c h a n t i l l o n s d e Juil let et A o û t 1 9 8 8 . L e s l i g n e s v e r t i c a l e s i n d i q u e n t l ' i n te rva l l e d e c o n f i a n c e a u r i s q u e 9 5 % s u r l e s e s t i m a t i o n s d e p o p u l a t i o n p a r le m a x i m u m d e v r a i s e m b l a n c e .
F i g u r e 1 : A b u n d a n c e of adul t b r o o k t rou t in 2 5 0 - m t rea tment (so l id l ine) a n d control ( d a s h e d l ine) s e c t i o n s of t h e Nor th Fork C a c h e la P o u d r e River , C o l o r a d o , U S A , f r o m 1 9 8 7 t o 1 9 9 3 . T e n p e r p e n d i c u l a r l o g s w e r e i n s t a l l e d to f o r m poo ls in t h e t r e a t m e n t s e c t i o n in ear ly A u g u s t 1988 , b e t w e e n the s a m p l e s s h o w n in Ju ly a n d A u g u s t 1 9 8 8 . Vert ical l ines s h o w 9 5 % prof i le - l ike l ihood c o n f i d e n c e in terva is o n m a x i m u m - l i k e l i h o o d p o p u l a t i o n e s t i m â t e s .
T H E R O L E O F M O V E M E N T IN T H E T R O U T P O P U L A T I O N R E S P O N S E
T h e apparen t innportance of immig ra t i on led us to beg in s tudy ing m o v e m e n t directiy i n 1 9 9 1 . G o w a n i n s t a l l e d t w o - w a y f i sh w e i r s a t t h e e n d s o f t h e 5 0 0 - m r e a c h and t h e b o u n d a r y b e t w e e n t rea tmen t a n d con t ro l sec t ions on t w o of t h e six s t r e a m s , a n d m e a s u r e d f ish m o v e m e n t for abou t 5 0 d a y s fo l l ow ing s n o w m e i t runoff du r i ng late s u m m e r in 1991 (see R ILEY et al.. 1992 for déta i ls) a n d 100 d a y s (ca. Ju l y -Sep tembe r ) in 1992 a n d 1993 . AH f ish w e r e g iven f inc l ips to ident i fy t he we i r t hey had p a s s e d , a n d f ish > 120 mm tota l l eng th w e r e t a g g e d w i th F loy a n c h o r o r V isua l Imp lan t tags ( s e e M O U R N I N G et al., 1994 for t agg ing p rocédures ) .
Resu l ts f r om t rapp ing ind ica ted tha t t rout m o v e m e n t rates w e r e h igh . In ail bu t one of s ix cases , s ign i f icant ly m o r e f ish m o v e d t h rough the t raps du r ing c a . 5 0 - 1 0 0 d a y s in late s u m m e r and ear ly fall t han w e r e p résen t in the sec t ions du r i ng annua l e lec t ro f i sh ing in late s u m m e r of e a c h year , b a s e d o n t h e p o p u l a t i o n e s t i m â t e s a n d t he i r 9 5 % c o n f i d e n c e in terva is ( G O W A N a n d F A U S C H , unpub . ) . Net immigra t ion ( immig ran ts m i n u s emigrants ) into t rea tmen t (and contro l ) sec t ions du r i ng late s u m m e r w a s h igh in s o m e y e a r s for bo th
Bull. Fr. Pêche Piscic. ( 1995) 337/338/339 :179-190 — 184 —
PE
RC
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,
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EA
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EN
T V
. C
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OL
1 0 0 %
- 5 0 %
AGE-2 A N D OLDER TROUT
WAL CC NFP JACK LBC SSV
1 9 8 7
Figure 2 : Dif férences en pourcentage sur les estimations des populations des sections expérimentales et témoins de six ruisseaux du Nord Colorado, USA, où des mouil les ont été réalisées à partir de LWD en 1988. Des d i f f é r e n c e s sont p résentées pour 1 9 8 7 , avan t que les t r o n c s perpendiculaires aient été installés pour réaliser des mouilles, et pour 1990 et 1993, après leur mise en place (voir figure 1). Les noms des cours d'eau sont, de la gauche vers la droite, ruisseaux de Walton et de Colorado, rivière de North Fork Cache la Poudre et ruisseaux de Jack, de Little Beaver et de South St. Vrain (pour les détails, voir RILEY et FAUSCH, 1995).
Figure 2 : Percentage difference in population estimates of adult trout in treatment versus control sections of six streams in northern Colorado, USA, where LWD pools were installed in treatment sections in 1988. Differences are shown for 1987, before perpendicular logs were added to form the pools, and for 1990 and 1993, after the treatment (see Fig. 1). Names of streams are, from left to right, Walton and Colorado creeks, the North Fork Cache la Poudre River, and Jack, Little Beaver, and South St. Vrain creeks (see RILEY and FAUSCH 1995 for details).
s t r e a m s , but o the r yea rs it w a s low, o r m o v e m e n t resu l ted in net emigra t ion . Never the less , t he h igh ra tes of m o v e m e n t du r ing a 2-3 month per iod indicate that this m e c h a n i s m can eas i l y e x p l a i n t h e rap id i nc rease in t rout popu la t ions in t rea tmen t sec t ions .
C o m b i n i n g results f rom all samp l ing also ind icated that many fish move long d is tances. R e c a p t u r e s of indiv idual ly- tagged trout dur ing 1991 to 1993 in the weirs , and by electrof ishing w i t h i n t h e sec t i ons a n d in ad jacen t reaches up to 2 k m away f rom the reach boundar ies s h o w e d that wh i le about 40 % of the f ish were recaptured wi th in 50 m of their original locat ion, the o ther 6 0 % had m o v e d up to 1 km away or more (e.g., Fig. 4 ; G O W A N and F A U S C H , unpub . ) . Moreover , t he highly kurtot ic distr ibution wi th very long tai ls indicates that m o v e m e n t to a n y g i ven d is tance > 5 0 m f rom the location of re lease is a relatively rare event that will be diff icult to detec t by samp l ing , a point w h o s e importance wil l b e c o m e evident below.
7 5 %
5 0 %
2 5 %
0 %
- 2 5 %
1 9 9 0 1 9 9 3
Bull. Fr Pêche Piscic. 11995) 337/338/339 :179-190 — 185 —
NORTH FORK CACHE LA POUDRE TREATMENT SECTION
200
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NORTH FORK CACHE LA POUDRE CONTROL SECTION
RESIDENTS UNMARKED FROM TREATMENT BOTH MARKS
Jul-88 Aug-88 1989 1990 1991 1992 1993
Figure 3 : Nombre d'ombles de fontaine adultes (âge 2 et plus) capturés dans les sections expérimentale (en haut) et témoin (en bas) de la rivière de North Fork Cache la Poudre, dont les marques de nageoire indiquent qu'ils ont été auparavant capturés et marqués dans le témoin, la section expérimentale ou dans les deux, ou qu'ils n'ont jamais été capturés (non marqués). Les résidents sont les poissons dont les marques de nageoire proviennent uniquement de la section où ils ont été recapturés. Les flèches indiquent que les troncs perpendiculaires ont été installés pour réaliser des mouilles début Août 1988.
Figure 3 : Number of adult (age-2 and older) brook trout captured in 250-m treatment (top) and control (bottom) sections of the North Fork Cache la Poudre River that bore finclips indicating that they had been previously captured and marked in the control, treatment, or both sections, or had never been captured (unmarked). Residents are fish that bore finclips only from the section where they were recaptured. Arrows indicate that perpendicular logs were installed to form pools in early August 1988.
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RESIDENTS UNMARKED FROM CONTROL BOTH MARKS
Jul-88 Aug-88 1989 1990 1991 1992 1993
Bull. Fr. Pêche Piscic. (1995) 337/338/339 :179-190 — 186 —
Total distance moved (m)
Figure 4 : D i s t a n c e s e n t r e les s i tes où les s a u m o n s de f o n t a i n e m a r q u é s individuellement dans le ruisseau de Jack, Colorado, ont été capturés et recapturés entre les étés de 1991 et 1993. Les poissons ont été capturés par des barrages ou à la pêche électrique, à l'intérieur ou à l'extérieur des tronçons expérimentaux de 500m (voir texte).
Figure 4 : Distances between locations where individually-marked brook trout in Jack Creek, Colorado were captured and recaptured between the summers of 1991 and 1993. Fish were captured in weirs, or by electrofishing within or outside of the 500-m experimental reach (see text).
THE RESTRICTED MOVEMENT PARADIGM
T h e preva i l ing t heo ry conce rn i ng movemen t of resident s t ream sa lmon ids , a n d o ther r e s i d e n t s t r e a m f i s h e s a s w e l l , is t h a t the m a j o r i t y of adu l t f i sh a re s e d e n t a r y , o f t e n s p e n d i n g the i r ent i re l ives in shor t reaches of s t ream (e.g. , < 20 -50 m ; M I L L E R , 1957 ; B A C H M A N , 1984) . Th is theory, wh i ch we h a v e ca l led the restr ic ted m o v e m e n t p a r a d i g m ( G O W A N et al., 1994 ) , w a s f o rma l i zed in a c lass ic paper by G E R K I N G (1959) and has b e e n s u p p o r t e d by m a n y s tud ies s ince . Based on th is pa rad igm, it w a s genera l ly a s s u m e d tha t res iden t t rout popu la t ions w o u l d respond to a d d e d habi ta t by inc reased recru i tment or su rv i va l in situ, ra ther t han by immigra t ion , s ince t h e s e f ish w e r e though t to m o v e litt le. I n d e e d , th is w a s t h e a priori h ypo thes i s for t he l ong - t e rm e x p e r i m e n t d e s c r i b e d a b o v e . T h e r e f o r e , t he h igh rates of t rout movemen t w e f ound w e r e initially surpr is ing , and led us to rev iew t h e f ind ings of t he f ew o ther invest igators tha t had m a d e deta i led s tud ies of t rout p o p u l a t i o n s af ter hab i ta t e n h a n c e m e n t , as we l l as to cr i t ica l ly eva lua te o ther s tud ies of s t r e a m f ish m o v e m e n t .
T h i s cr i t ica l r ev iew of t h e l i terature w a s e n l i g h t e n i n g ( G O W A N et al., 1994) . For e x a m p l e , in t h e two s tud ies of t rout popu la t ion response to habi tat e n h a n c e m e n t w h e r e f ish w e r e e i the r ba tch m a r k e d to indicate their o r ig in in t rea tmen t a n d cont ro l sec t ions , or w e r e t r a p p e d d i rec t l y at t he sec t i on boundar ies , net immig ra t i on w a s e i ther f o u n d to be h igh ( B U R G E S S , 1985) or c i rcumstan t ia l ev idence s u g g e s t e d that it w a s (HUNT, 1 9 7 1 , 1974 ; s e e G O W A N et al., 1 9 9 4 for a d e t a i l e d a n a l y s i s ) . A b r o a d e r r e v i e w of 37 s t u d i e s of m o v e m e n t by res ident s t r eam sa lmon ids ind icated tha t e r roneous conc lus ions of restr ic ted m o v e m e n t a re poss ib le w h e n ana lys i s focuses on ly on f ish recap tu red in a l imi ted a r e a
Nu
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0 0 250 500 750 1000 1250
Bull. Fr. Pèche Piscic. (1995) 337/338/339 : 179-190 — 187 —
near whe re they were marked and re leased . In most cases , mo re than half of the recaptured f ish w e r e f ound in the «home» reach w h e r e they we re or ig inal ly m a r k e d , yet f ewer than half of the f ish or iginal ly ma rked w e r e recap tu red ( F A U S C H and Y O U N G , in p ress) . Moreover , because capture ef f ic iency of s t r eam f ishes is of ten low, h igh propor t ions of u n m a r k e d f ish usual ly cou ld not be used to ind icate immig ra t i on , as w a s poss ib le in our research .
O u r da ta aIso s u g g e s t w h y au tho rs m a y have d r a w n inaccu ra te c o n c l u s i o n s f r om m o v e m e n t s m a d e by f ish recap tu red f r o m a l imi ted set of relat ively shor t r eaches . T h e h igh «peak» a n d exceed ing l y long tai ls of t he d is t r ibu t ion of m o v e m e n t d i s t ances tha t w e found (F ig . 4 ) , if gene ra l l y t h e c a s e , i nd i ca te tha t it w o u l d be v e r y d i f f icu l t to d e s i g n a mark-recap tu re s tudy to accu ra te l y a s s e s s res idency . B e c a u s e mo re t h a n half the popu la t ion m o v e d f r om 5 0 - 2 0 0 0 m ( G O W A N a n d F A U S C H , unpub . ) a n d t rave l to a n y spéc i f ie d is tance w a s a re la t ive ly rare even t , it w o u l d be di f f icul t t o de tec t m o s t of t h è s e m o v e m e n t s by recaptur ing f ish f rom a de f ined set of re lat ive ly shor t reaches . For e x a m p l e , F ig . 4 ind icates t h a t r e c a p t u r e s m a d e in f i ve a d j a c e n t 5 0 - m r e a c h e s , b e g i n n i n g at t h e l o c a t i o n w h e r e m a r k e d f ish we re or ig inal ly re leased , w o u l d have s h o w n that mos t t rout m o v e d less than 50 m, e v e n t h o u g h mo re deta i led s a m p l i n g ove r a longer reach led us to es t ima te tha t more t h a n half the popu la t ion had m o v e d fa r ther away. Moreover , th is es t ima te is consen /a t i ve b e c a u s e w e d i d no t s a m p l e a i l p o s s i b l e r e a c h e s > 5 0 m f r o m r e l e a s e p o i n t s , w h i c h p r e s u m a b l y w o u l d h a v e l e d to r e c a p t u r i n g e v e n m o r e f i s h t h a t h a d m o v e d g r e a t e r d i s tances . T h e resul ts of rad io te lemet ry (e .g . , T O D D a n d R A B E N I , 1989 ; M E Y E R S et al., 1992) a n d d e f a u n a t i o n s t u d i e s (e .g . , M E F F E a n d S H E L D O N , 1 9 9 0 ; P E T E R S O N a n d BAYLEY, 1993) aIso a rgue for a m u c h m o r e dynam ic v iew of s t r e a m f ish m o v e m e n t over la rger spat ia l sca les t han is no rma l l y poss ib le by m a r k - r e c a p t u r e s tud ies ( F A U S C H a n d Y O U N G , 1995) .
I M P L I C A T I O N S F O R HABITAT R E S E A R C H A N D M A N A G E M E N T
T h e récogni t ion that m a n y s t r e a m f i shes l ikely m o v e over m u c h larger spat ia l scales t h a n w a s p r e v i o u s i y t h o u g h t h a s i m p o r t a n t i m p l i c a t i o n s f o r n e a r l y ai l r e s e a r c h a n d m a n a g e m e n t of s t r e a m f i shes ( G O W A N et al., 1994 ; F A U S C H a n d Y O U N G , 1995 ) . S u c h m o v e m e n t impl ies that s t r eam reaches c a n n o t be rega rded as i n d e p e n d e n t uni ts , and that the l imits of f ish popu la t ions wil l be dif f icult t o de f ine . The re fo re , es t imâ tes of a b u n d a n c e , s u r v i v a l , a n d p r o d u c t i o n tha t a r e b a s e d o n m a r k i n g a n d r e c a p t u r i n g f i sh f r o m wha t a r e a s s u m e d to be c l osed popu la t ions wi l l o f ten be inaccura te . For e x a m p l e , how wou ld one a c c u r a t e l y es t ima te su rv iva l or p r o d u c t i o n o v e r an a n n u a l pe r i od for o n e of t h e s t ream r e a c h e s w e s tud ied , w h e n half of t he f ish p résen t at the e n d of the y e a r h a d immigra ted ? W e h a v e q u e s t i o n e d w h e t h e r in situ p r o d u c t i o n is e v e n a m e a n i n g f u i c o n c e p t in s u c h s i tuat ions ( G O W A N et al., 1994) .
D u r i n g t h e l a s t 3 0 y e a r s t h e r e h a s b e e n i n c r e a s i n g i n t e r e s t i n d e v e l o p i n g m a t h e m a t i c a l m o d e l s t h a t p r e d i c t c h a r a c t e r i s t i c s of s t r e a m f i s h p o p u l a t i o n s f r o m m e a s u r e m e n t s of habi ta t (see F A U S C H et al., 1988 for a rev iew) . S u c h m o d e l s a re most o f ten u s e d by resea rche rs a n d m a n a g e r s to he lp p red ic t h o w a n t h r o p o g e n i c c h a n g e s in s t r e a m f l ows or channe l m o r p h o l o g y wil l a f fect s t r eam f ish popu la t i ons . T h e y a re usual ly d e v e l o p e d by cor re la t ing m e a s u r e m e n t s of f i sh a b u n d a n c e w i th va r i ous hab i ta t var iab les for a sma l l s a m p l e of re lat ive ly shor t s t r e a m reaches . M o d e l s d e v e l o p e d f r o m th is type of da ta a Iso impl ic i t ly a s s u m e that the f i sh popu la t i on s a m p l e d is p r imar i l y a f fec ted by the hab i ta t var iab les m e a s u r e d . However , if ra tes of f ish m o v e m e n t a re h igh t hen popu la t ions m a y a I so b e r e g u l a t e d by hab i t a t in u n m e a s u r e d r e a c h e s , t h e r e b y i n v a l i d a t i n g mode l a s s u m p t i o n s and lead ing to i naccura te p réd ic t ions abou t an th ropogen i c e f fec ts ( G O W A N et al., 1994) . In fact , loca l ized habi ta t dég rada t i on m a y affect f ish popu la t i ons ove r a m u c h la rger sca le than norma l l y c o n s i d e r e d , b e c a u s e f ish m a y m o v e d o w n s t r e a m to intercept the d i s tu rbance rather than be ing a f fec ted on ly by per tu rba t ions that o r ig ina te u p s t r e a m .
It is a l s o o b v i o u s f r o m t h e l o n g - t e r m r e s e a r c h d e s c r i b e d a b o v e t h a t h a b i t a t e n h a n c e m e n t m a y h a v e e f fec ts o v e r m u c h la rger s c a l e s t h a n p r e v i o u s i y t h o u g h t , a s a resui t of f ish m o v e m e n t . If ou r es t imâ tes of m o v e m e n t d i s tances a re représen ta t i ve , t hen the immig ran ts that co lon i zed the t r ea tmen t reaches w h e r e L W D poo ls w e r e a d d e d mos t l ikely c a m e f r om m a n y d i f férent d i s t ances bo th u p s t r e a m a n d d o w n s t r e a m f r om t h e 500-m expé r imen ta l reach . Simi lar ly , f i sh em ig ra t i ng f r o m the t r ea tmen t sec t ion m o v e d away to
Bull Fr. Pèche Piscic. 11995) 337/338/339 : 179-190 — 188 —
m a n y d i f férent d is tances up to 2 km away ( G O W A N and F A U S C H . unpub.) . Thèse da ta h a v e impo r tan t imp l ica t ions . S o m e f ishery m a n a g e r s , recogn iz ing that f ish m o v e m e n t is c o m m o n , a r e c o n c e r n e d tha t hab i t a t e n h a n c e m e n t on ly red is t r i bu tes f i sh , ra ther t h a n ac tua l ly inc reas ing t rout popu la t ions , thereby dep le t ing ad jacen t reaches. If this we re the c a s e , the mos t l ikely p lace to f ind such decreases wou ld have been in the ad jacent contro l sec t i ons , s ince more f ish m o v e d shor ter d is tances than long (Fig. 4) . H o w e v e r adult t rout p o p u l a t i o n s in cont ro l sec t ions genera l l y increased for severa l years after the logs we re ins ta l led (e .g . . Fig. 1). and did not decrease s igni f icant ly dur ing 1987-1993 (P > 0,05 by A N O V A ) , Moreove r , d e n s i t y - d e p e n d e n t surv ival of la rge j uvén i l es and adu l ts (e .g , . see ELL IOTT , 1994) , coup led wi th h igh movement rates, m a k e it l ikely that any vacant habi tat in the a r e a s f r om wh ich the immig ran ts c a m e wou ld be quick ly occup ied .
Ove ra l l , our resul ts c lear ly ind icate that habi tat for s t ream sa lmon ids must be s tud ied a n d m a n a g e d at spat ia l a n d t empo ra l scales that are appropr ia te for the life h is tones of va r i ous f o r m s , rather t han those that are conven ient to s tudy (see A D D I C O T T et al., 1987 ; W I E N S , 1989) , Many s a l m o n i d s are l ikely to m o v e to use habi tat at wa te rshed sca les (e .g . . N À S L U N D et al.. 1 9 9 3 ; R I E M A N a n d M C I N T Y R E , 1993) , Th is m a y be espec ia l l y t rue w h e r e hab i ta t comp lex i t y has been reduced by past forest ry pract ices in r ipar ian zones , w h i c h e l im ina ted subséquen t inputs of LWD that fo rm pools and structural cover, T h e effect of th is hab i ta t s impl i f icat ion is to inc rease the pa tch iness of sa lmon id habi tat in s t reams at w a t e r s h e d s c a l e s . w h i c h m a y fo rce f ish to m o v e to f ind su i tab le hab i ta t for op t im i z i ng f i tness du r ing dif férent seasons and l i fe-history s tages ( S C H L O S S E R , 1995).
A C K N O W L E D G E M E N T S
W e t h a n k the m a n y f ie ld a n d laboratory techn ic ians and vo lunteers , too n u m e r o u s to n a m e , w h o m a d e the research repor ted here poss ib le . Fund ing for the research on LWD w a s p r o v i d e d by the R o c k y M o u n t a i n Forest a n d R a n g e E x p e r i m e n t S ta t i on a n d t h e A r a p a h o and Rooseve i t Nat iona l Fores ts of the U.S. Forest Serv ice. T h e research on trout p o p u l a t i o n response to LWD poo ls w a s funded by the Fédéra l A id in Sport Fish Restora t ion p r o g r a m t h r o u g h t he C o l o r a d o Div is ion of Wi ld i i fe . W e thank Mike Young , Nick S c h m a l , D o n O r t h , a n d Mark Ba in for cons t ruc t i ve cr i t ic ism on the manuscr ip t ,
R E F E R E N C E S
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