Evaluation of two release operations at Bonneville Dam on the smolt-to-adult survival of Spring Creek National Fish Hatchery fall Chinook salmon

Transcription

1 Evaluaton of two release operatons at Bonnevlle Dam on the smolt-to-adult survval of Sprng Creek Natonal Fsh Hatchery fall Chnook salmon By Steven L. Haeseker and Davd Wlls Columba Rver Fshery Program Offce U.S. Fsh and Wldlfe Servce 1211 SE Cardnal Court, Sute 100 Vancouver, WA Abstract In March 2004, two groups of coded wre tagged subyearlng fall Chnook were released from Sprng Creek Natonal Fsh Hatchery to drectly evaluate the effects of alternatve operatons at Bonnevlle Dam on smolt-to-adult survval (SAR). The frst group, released on March 1 st, passed Bonnevlle Dam durng a four-day, 25 kcfs spll operaton wth the corner collector closed. The second group, released on March 10 th, passed Bonnevlle Dam durng a four-day, 5 kcfs corner collector operaton wth the spllways closed. Tagged adults were subsequently recaptured n ocean fsheres, Columba Rver fsheres, and at the hatchery durng The overall SAR was 0.118% for the fsh released durng the spll operaton and 0.100% for fsh released durng the corner collector operaton. The overall SAR for fsh released durng the spll operaton was 18% hgher than the SAR for fsh released durng the corner collector operaton, however ths dfference was not statstcally sgnfcant. Usng Bayesan statstcal methods, we estmated an 80% probablty that the SAR for the spll operaton release was hgher than the SAR for the corner collector operaton release. Applyng the results from the 2004 March release operatons to the March releases over , we estmate that a foregone loss of 15,200 adults (range 2,400-38,900) may have occurred due to corner collector-only operatons durng Addtonal years of comparatve study would be useful to quantfy the degree of evdence that these results are consstent across years or not. Introducton Sprng Creek Natonal Fsh Hatchery (SCNFH), located upstream of Bonnevlle Dam on the Columba Rver, annually produces tule fall Chnook (Oncorhynchus tshawytscha) that are released n the sprng of each year as subyearlngs. Half of the total producton of 15 mllon fsh s released n March, pror to the onset of the Bologcal Opnon spll program for ESA-lsted salmonds. Although SCNFH Chnook salmon are lsted under the Endangered Speces Act (ESA) as part of the Lower Columba Rver Chnook ESU, they are deemed not necessary for recovery and therefore are avalable for harvest. The 7.5 mllon fsh that are released n March are very mportant to Unted States/Canada treaty and domestc West Coast fsheres because these fsh make up a sgnfcant porton of the Chnook caught n West Coast Vancouver Island (WCVI) fsheres, near shore fsheres off the Washngton and northern Oregon coast, and local 1

2 fsheres n the Columba Rver. Hstorcally, Sprng Creek NFH fsh contrbuted up to 9% of the Chnook catch n the WCVI fsheres and 27% of the Chnook catch off of the Washngton and northern Oregon coasts. Sprng Creek NFH has contrbuted as many as 65,600 fsh to treaty Indan fsheres (1976) and 41,500 fsh to non-treaty commercal fsheres (1977) n the Columba Rver (PFMC, 1996). More recently, the average catch of Sprng Creek NFH orgn fall Chnook n the fall season treaty Indan fsheres above Bonnevlle Dam was 54,900 Chnook, whle non-treaty n-rver commercal and sports fsheres averaged another 12,600 Chnook (PFMC, 2006). In addton to supplyng large numbers of fsh for harvest, the hgh abundance of tule fall Chnook stocks has lkely provded some level of stock protecton for other depressed stocks of concern n mxed-stock fsheres. Under the Chnook harvest celng management regme mplemented by the Pacfc Salmon Treaty n 1985, abundant Columba Rver tule and uprver brght fall Chnook stocks had the effect of bufferng mpacts on other Chnook stocks of concern n certan Canadan and south east Alaskan ocean fsheres. Wth the adopton of an aggregate abundance-based management (AABM) regme for these ocean fsheres under the renegotaton of the Pacfc Salmon Treaty n 1999, the bufferng effect of these Columba Rver stocks only occurs when harvest for a partcular fshery s constraned to a level substantally less than allowed under the AABM regme for that partcular fshery. Ths management scenaro has, n fact, been the case for the WCVI Canadan troll fshery n several recent years where Columba Rver tule fall Chnook stocks are a sgnfcant contrbutor to the overall stock mx of ths fshery. Up untl 2003, the WCVI troll fshery has been managed by Canada to harvest a much lower number of Chnook than allowed under the AABM regme, prmarly to address domestc concerns for depressed WCVI naturally spawnng stocks and the need to rebuld ths stock group. Begnnng n 2003, the WCVI troll fshery agan expanded up to AABM quota lmts as the fshery ostensbly found ways to maxmze total catch, ncludng sgnfcant numbers of Columba Rver stocks, whle mnmzng mpacts on ther depressed local wld stocks through ntensve tme and area management actons. However, even when AABM fsheres are harvested at ther full allowable levels, harvest rate celngs for partcular stocks of concern (e.g., threatened Snake Rver fall Chnook and lower Columba Rver Chnook) are now n place under ESA management constrants to provde an approprate level of protecton for these stocks whle provdng the opportunty to shape coastal and n-rver fsheres to optmze the harvest of comngled healthy stocks when abundance levels for these stocks are hgh. For example, n addton to the AABM framework of the Pacfc Salmon Treaty n Canadan and southeast Alaskan ocean fsheres, Washngton, Oregon, and Calforna ocean fsheres are managed under an ESA constrant that lmts the annual allowable ocean fsheres mpact on Snake Rver fall Chnook (ncludng Canadan and Alaskan mpacts) to 70% of the base perod average mpacts. A smlar 30% base perod reducton n mpacts for ths stock n Columba Rver fsheres s also requred to provde an approprate level of protecton whle allowng for management flexblty for other stocks. These mpact rates are currently beng revewed by NOAA Fsheres relatve to Snake Rver fall Chnook stock status and fsheres mpacts. As fsheres are ncreasngly constraned to protect ESA-lsted and other stocks of concern, the fshery management agences are contnually seekng ways to mantan a reasonable level of harvest opportunty for stocks wth harvestable surpluses. Markselectve fsheres are now n place for nearly all non-indan steelhead sport fsheres, many non-indan marne and freshwater sport and commercal coho fsheres, and most 2

3 non-indan Columba Rver sprng and summer Chnook fsheres. Although, markselectve ocean Chnook fsheres and n-rver fall Chnook fsheres have not yet been broadly mplemented, they are clearly a lkely management strategy on the horzon as the States of Washngton and Oregon begn to mass mark ther federally funded fall Chnook hatchery producton consstent wth Congressonal mandates. Sprng Creek NFH hatchery producton has been mass marked for several years (begnnng wth the 2003 brood year) and these fsh are now avalable for mark-selectve harvest as these types of management strateges are mplemented. Mantanng hgh survval rates for mass marked hatchery fsh producton s crtcal to the success of any mark-selectve fshery management program snce all unmarked (naturally produced fsh) must be released and the abundance of the targeted stocks must be large n relaton to the cost (ncdental mortalty mpact) on the stocks of concern. Preseason plannng for 2007 ocean and Columba Rver fsheres used 21,300 Sprng Creek tule fall Chnook as an expectaton for rver mouth run sze after accountng for modeled ocean fshery mpacts. Ths s a very sharp reducton from the average n-rver run sze abundance of 148,500 Sprng Creek stock adult fsh. As a result, the 2007 PFMC area ocean Chnook fsheres north of Cape Falcon and Columba Rver fall Chnook fsheres were severely constraned (low quotas and short seasons) because of low tule fall Chnook abundance and the need to protect the co-mngled stocks of concern. Prelmnary post-season estmates for the 2007 adult return of Sprng Creek fall Chnook to the Columba Rver ndcate a run sze of approxmately 17,000 fsh and Sprng Creek NFH barely made ts broodstock egg take goal n The 2008 return s, however, expected to be mproved from the very low run n 2007 based on an mproved jack return n Over the past 13 years, fsh hatchery programs for Columba Rver producton have been reduced sgnfcantly due to Congressonal reducton or flat fundng for Mtchell Act programs. These fundng cuts have resulted n a very substantal reducton n the producton of tule fall Chnook salmon (approxmately 25.0 mllon snce 1995) at both state and federal fsh hatcheres and have caused the closure of some facltes. The State of Oregon has drastcally reduced ts producton of tule fall Chnook salmon n the Columba Rver system. Sprng Creek NFH s now the only faclty producng tule fall Chnook above Bonnevlle Dam. Nearly all of the remanng Columba Rver tule producton s released from hatcheres n the State of Washngton below Bonnevlle Dam. These reductons and hatchery closures make maxmzng survval and producton at Sprng Creek NFH even more mportant for mantanng and mprovng fsheres opportunty n the Pacfc Ocean and Columba Rver, especally n years of low ocean productvty. Spll s generally accepted as the safest route for fsh passage at Federal Columba Rver Power System (FCRPS) facltes n terms of both mmedate and delayed survval effects. However, nether route-specfc nor comparatve lfe-cycle survval studes have been conducted on March releases from Sprng Creek NFH due to the sze lmtatons of telemetry and PIT-tag approaches. Varous survval studes have been cted for ndrectly examnng these questons based on dfferent speces groups and dfferent tmes of the year usng drect survval estmates (no estmates of delayed survval or lfe-cycle survval), wth unknown applcablty for makng nferences on the March release from SCNFH. Hstorcally, the March release of juvenle fsh at Sprng Creek NFH has produced 44% of the returnng adults (based on a recent 5-year average). The Servce has released juvenle fall Chnook n March, Aprl, and May to maxmze the rearng capacty of the 3

4 faclty by splttng the Aprl and May releases nto avalable empty pond space after the March release has occurred. Along wth maxmzng rearng capacty, ths release strategy also balances the rsks assocated wth the possblty of low survval from a partcular release month. As descrbed n the paragraphs above, maxmzng the survval of the March release fsh s mportant for nternatonal and domestc fsheres operatng both n the ocean and n-rver. Hstorcally, the Bonnevlle Power Admnstraton (BPA) allowed spll at Bonnevlle Dam, concdng wth the tmng of the SCNFH releases n March to provde a non-turbne/non-bypass passage route and to mprove ther survval past Bonnevlle Dam. The duraton and volume of spll that BPA has allowed at Bonnevlle Dam for the Sprng Creek March releases has vared over tme. Snce 1992, there have been three general categores of the duraton and volume of spll allowed at Bonnevlle Dam durng the March releases (Fgure A3). Durng , spll duraton and volume averaged 178 hours (7.4 days) and 1100 KAF. Durng , average spll duraton and volume were reduced to 59 hours (2.5 days) and 177 KAF. Durng 2005, 2006, and 2007, BPA dd not allow spll for the March releases. However, begnnng n 2004, the Bonnevlle Dam corner collector was operated durng the March releases, provdng a non-turbne/non-bypass passage route through the dam. Durng the March releases, the corner collector was operated for 85 hours usng 35 KAF on average durng the March releases. These recent volumes usng the corner collector are 3.2% of the volumes allowed usng spll durng The provson of spll at Bonnevlle Dam for the SCNFH March releases has been an mportant ssue among the FWS, other fshery management agences, commercal and sport fshng groups, and the Acton Agences. In 2004, the FWS developed and dstrbuted a research proposal to drectly evaluate the effects of Bonnevlle Dam operatons on the lfe-cycle survval of SCNFH March releases (USFWS 2004). Because ths study desgn utlzed coded wre tags (CWT) that could be appled to March-released fsh, the study could drectly measure the lfe-cycle survval rates for groups of Marchreleased fsh. Ths proposed study conssted of three years of CWT markng and releases under three operatons at Bonnevlle Dam: a spll-only operaton, a spll plus corner collector operaton, and a corner collector-only operaton. Parttonng the March release nto three groups was ntended to balance the rsks caused by uncertanty about the newly-constructed corner collector route, and ths balanced desgn would ad n understandng the addtve and/or multplcatve effects of the components of spll and corner collector operaton on effcency (through hydroacoustcs) and lfe-cycle survval (through coded wre tag recovery rates). To acheve ths balanced desgn, FWS requested that the treatment operatons be: 75 kcfs spll-only, 75 kcfs spll wth the corner collector, and the corner collector-only. Spll levels for the spll and spll wth the corner collector needed to be smlar n ths study desgn to assess whether the effect of the corner collector was addtve or not. FWS beleved that spll levels at 75 kcfs would provde adequate survval condtons and would provde a level of precauton aganst the unknown survval rates assocated wth the other passage routes. The proposal to conduct the study over three years was made to ensure confdence and relablty n the results. Followng the dstrbuton of ths proposal, dscussons between the FWS and the Acton Agences resulted n a sngle year of CWT-markng, only two operatons beng evaluated (spll versus corner collector), reduced levels of spll (50 kcfs nstead of the proposed 75 kcfs), and no spll requests for two years. For the most part, ths s what occurred. A major excepton was that calbraton errors n spll rates resulted n actual spll rates of 25 kcfs nstead of the agreed-to level of 50 kcfs n Adults wth CWTs 4

5 were captured n ocean fsheres, n-rver fsheres, and at the hatchery durng The followng analyses summarze the return data from the 2004 releases. The objectves of ths research paper are therefore to: 1) summarze the lfe-cycle survval rates (SARs) for the two release groups derved from the CWT recaptures, 2) calculate the percent dfference n the SARs for the two release groups to quantfy relatve survval of the two release operatons, and 3) quantfy the uncertanty n these estmates. An addtonal objectve was to provde context for the results by examnng the potental mplcatons of ths study on the releases that occurred n wthout spll or a comparatve evaluaton. In addton to tradtonal frequentst statstcal approaches, we used Bayesan statstcal methods to quantfy uncertantes through posteror probablty dstrbutons, reflectng easly-nterpreted probabltes for the unknown quanttes of nterest condtoned on the observed data. Methods Sample sze calculatons Pror to the releases, we conducted sample sze calculatons to quantfy the dfferences that could be detected for varous release szes, at specfed levels for type-i and type-ii error rates (Snedecor and Cochran 1967). We determned that a release of 220,000 fsh could detect a 27% reducton n the SAR of fsh released durng corner collector operaton wth 80% power (β = 0.2) and α = 0.1, assumng the SAR for fsh released durng spll was 0.16% (the average SAR for March-released fsh over brood years durng spll operatons). These levels of precson and detectable dfferences were determned to be acceptable, and the study proceeded usng a total release of roughly 220,000 CWT fsh. Taggng and releases Sprng Creek NFH staff randomly selected nne rearng ponds and tagged approxmately 25,000 fngerlngs wth CWT from each pond. Four ponds were randomly assgned for release durng the spll operaton and the remanng fve were assgned to release durng corner collector operaton. Mean fsh weght at taggng was 2.2 grams for the spll release group fsh and 2.3 grams for the corner collector release group fsh. The spll release group fsh were released from the hatchery n the early afternoon of March 1 and had a mean weght of 2.7 grams. The corner collector release group fsh were released from the hatchery n the mornng of March 10 and had a mean weght of 3.2 grams. After accountng for tags that were shed, there were 98,932 CWT fsh n the spll release group and 122,853 CWT fsh n the corner collector release group. In total, 221,785 CWT fsh were released. Bonnevlle Dam operatons Followng the March 1 release, spll began at Bonnevlle Dam at 20:00 hours on March 2 wth a spll target of 50 kcfs (actual spll rate was 25 kcfs, after accountng for spllgate ms-calbraton). After 96 hours, spll was termnated at 20:00 hours on March 6. Followng the March 10 release, corner collector operaton began n the afternoon of March 11 and contnued for 96 hours, untl the afternoon of March 15. Flow n the corner collector was approxmately 5-6 kcfs. 5

6 Estmatng SARs Tagged adults from the 2004 releases (2003 brood year) were subsequently recaptured n ocean fsheres, Columba Rver fsheres, and at the hatchery durng (Table 1). In all years, adults returnng to the hatchery were randomly selected across the duraton of the run for examnaton of CWT presence. Smlarly, the coastwde CWT montorng program randomly sampled commercal and recreatonal fsheres for CWT presence. When these samplng programs examne a subset of the total catch or return, the observed CWTs are expanded for the proporton sampled to estmate the total number of CWT fsh that were present. For example, f 50% of the catch n a fshery s sampled for CWT and fve CWT fsh were observed, the expanson factor would be 2.0 and the resultng estmate for the total number of CWT fsh n that fshery would be 10. To calculate overall SARs, we dvded the sum of the expanded CWT recaptures n fsheres and at the hatchery by the number of CWT fsh released for each release group: R SAR =, N where refers to releases durng the spll operaton or the corner collector operaton, R s the number of expanded recoveres for group, and N s the number of CWT fsh released n group. We calculated an estmate of the rato of the SARs (SAR Spll :SAR CC ) as: SAR rato = SAR Spll SARCC. As descrbed above, the overall number of recoveres s the sum of the expanded fshery recoveres and hatchery recoveres across years The observed recoveres can be modeled usng a bnomal dstrbuton for calculatng the varance of the observed recovery rates. However, the expanson factors need to be accounted-for when calculatng the varances of the overall SARs. To calculate the varances of the SARs, we appled three statstcal propertes. Frst, for a random varable (X) multpled by a constant (c), the varance of cx s c 2 var(x). Second, for a bnomal proporton p (n ths applcaton p = (number of observed recoveres) / (number of CWT fsh released)), the varance of p s p ( 1 p) / n. Thrd, for ndependent random varables X, the var( X ) = var(x ). Combnng these statstcal propertes, we calculated the varances of the SARs as 2 var( SAR ) = c j, k p j, k (1 p j, k ) / N j k where c j,k s the expanson factor and p j,k s the observed recovery proporton ( p j, k = nobs., j, k N ) for observed fshery or hatchery (k = fsheres or hatchery) recoveres n year j. To quantfy the relatve magntude of the SARs for the two releases, we calculated the percent dfference n the SARs as SARSpll SARCC Percent dfference = 100%. SAR 6 CC

7 We conducted a two-taled test of the null hypothess H 0 : SAR Spll = SAR CC, versus the alternatve hypothess H A : SAR Spll SAR CC, usng a test statstc based on the standard normal devate z: z = SAR var( SAR Spll Spll SAR CC ) + var( SAR CC, ) estmatng the SARs and ther assocated varances as defned above. Quantfyng uncertanty We appled Bayesan statstcal methods for quantfyng uncertanty n the SARs and a rato of the SARs. Bayesan statstcal methods quantfy the probablty of observable and unobservable quanttes n a problem through posteror probablty dstrbutons that are condtoned on the observed data (Gelman et al. 1995). A key advantage of a Bayesan approach s that t allows for common-sense nterpretaton of statstcal conclusons that are reflected by the posteror probablty dstrbutons. These dstrbutons quantfy the probablty that a parameter of nterest, or a functon of those parameters, takes on a partcular value (Gelman et al. 1995, p. 23). In contrast, tradtonal frequentst confdence ntervals strctly reflect the sequence of smlar nferences that mght be made under repeated samplng of the same process and samplng n the same manner. Because our prmary focus was on quantfyng the degree of evdence for quanttes of nterest based on the observed data, rather than boundng a quantty of nterest as defned under repeated samplng, we appled Bayesan statstcal methods n ths evaluaton. The three quanttes of nterest were the SARs for the spll and corner collector release groups and the rato of these two SARs. We were nterested n the rato of the SARs (SAR Spll :SAR CC ) because values less than one reflect the probablty that the corner collector release group had a hgher SAR and values greater than one reflect the probablty that the spll release group had a hgher SAR. Addtonally, the magntude of the ratos and ther assocated probabltes reflect the probabltes of dfferences n lfecycle survval between the release groups. A Bayesan analyss nvolves combnng pror nformaton wth a lkelhood functon for the observed data to arrve at a posteror dstrbuton. Ths posteror dstrbuton summarzes the probablty that a parameter of nterest, or a functon of that parameter, takes on a partcular value, after condtonng on the observed data. In ths applcaton, we used three unnformatve pror dstrbutons n conjuncton wth the observed return data to calculate posteror dstrbutons for the SARs as well as the rato of those SARs. We assumed a bnomal lkelhood for the observed return data and used a beta dstrbuton for specfyng the pror. The beta pror dstrbuton s a conjugate famly for the bnomal lkelhood (Gelman et al. 1995, p. 36), and through applcaton of Bayes rule, the posteror has a beta dstrbuton: p( θ n, y) Beta(y + α, n y + β), where p( θ n, y) s the posteror dstrbuton for the return rate θ, n s the number of CWT fsh released, y s the number of observed returns. The parameters α and β defne the pror dstrbuton. Three unnformatve pror dstrbutons have been suggested for 7

8 modelng bnomal data, and each s defned by dfferent values for α and β (Lee 1997, p ). A unform pror dstrbuton s obtaned by settng α = β = 1, a Haldane pror dstrbuton s obtaned by settng α = β = 0, and a Jeffreys pror dstrbuton s obtaned by settng α = β = 0.5. Consstent wth the conclusons of Lee (1997), the selecton of the dfferent prors had lttle effect on the posteror dstrbutons (see Appendx Fgures A1, A2). However, both the unform pror and the Jeffreys pror tended to shft the mean of the posteror n a postve drecton compared to the Haldane pror. Due to the consstency between the maxmum lkelhood estmate and the mean of the posteror dstrbuton when usng a Haldane pror (Lee 1997, p. 84), we selected Haldane prors for all subsequent analyses. The posteror dstrbutons for the SARs are functons of the posteror dstrbutons for the observed locaton- and year-specfc returns, accountng for the expanson factors. We generated 500,000 smulated values for defnng the posteror dstrbutons for the SARs as: p(sar Spll n, y) 3.51*Beta(6, 98926) *Beta(4, 98928) *Beta(31, 98901) *Beta(16, 98916) *Beta(4, 98928), and p(sar CC n, y) 1.17*Beta(6, ) *Beta(34, ) *Beta(27, ) *Beta(7, ). The 2.5% and 97.5% percentles of the smulated values were used to defne 95% credblty ntervals for the SARs. To quantfy the uncertanty n the SAR rato, we calculated the rato of the SARs (SAR Spll :SAR CC ) by dvdng the posteror dstrbuton values for the SAR Spll by the posteror dstrbuton values for SAR CC and calculated the proporton of values greater than 1. Implcatons for March releases durng The SAR rato calculated from the 2004 releases s the only estmate of comparatve lfe-cycle survval for March releases under two operatons at Bonnevlle Dam. March releases durng were provded no spll operatons and the SARs for these releases are uncertan, as adult returns wll not be complete untl To quantfy the potental effects of these operatons, relatve to effects that may have occurred f spll operatons had been provded, we estmated the number of adults that may have returned, gven a range of observed values for SARs and the estmated SAR rato from the 2004 releases. We determned the mnmum, average, and maxmum SAR over brood years (all brood years where spll operatons were provded) and multpled these by the number of fsh released each year n March, These were used to estmate the range of the expected number of adults that could have returned f spll operatons had been provded, as the mnmum, average, and maxmum SARs observed durng brood years were all provded spll operatons. Then we appled the estmated SAR rato to these calculated adults to estmate the number of adult returns that may have occurred under corner collector operatons. The dfferences between the two estmates across years and the range of SARs were used to quantfy the potental gans or losses of adults that may have occurred due to corner collector-only operatons durng

9 Results Fsheres/Hatchery Returns and SARs The number of observed CWT recoveres, expanded CWT recoveres and expanson factors n the fsheres and at the hatchery are provded n Table 1. The 2007 ocean and n-rver fsheres nformaton for age-4 fsh s not yet avalable. Table 1. Number of observed CWT recoveres, expanded recoveres, and expanson factors for fsheres and hatchery returns, by age, for the spll operaton and the corner collector operaton release groups. Data from fsheres was downloaded from RMIS on January 31, 2008 and may be subject to change. Age-2 Age-3 Age-4 Hatchery Fsheres Hatchery Fsheres Hatchery Total Spll Group Observed N sp = 98,932 Expanded Expanson CC Group Observed N cc = 122,853 Expanded Expanson The estmated SARs for the two release groups were therefore: 117 SAR Spll = = 0.118%, and 98, SAR CC = = 0.100%. 122,853 The estmated SAR rato and the SAR percent dfference were: 117 / SAR Rato = = / Percent dfference = 100% = 18% In addton to the overall SAR rato calculated above, we also calculated that SAR rato for varous subsets of the data to nvestgate whether the lfe-cycle survval dfferences were consstent across other groups of nterest. Consderng hatchery-only returns, the SAR rato was Consderng fsheres-only returns, the SAR rato was Consderng full term adults-only returns (excludng the age-2 jack returns), the SAR rato was These results ndcate that the overall dfferences n lfe-cycle survval that were observed (overall SAR rato = 1.18) were partally due to a large jack return to the hatchery n 2005 for the spll release group and an absence of jacks for the corner collector release group. The test statstc z was 0.825, wth a resultng p-value = As the p-value was greater than the type-i error rate used n the study desgn (α = 0.10), we conclude that the dfference between the SARs were not statstcally sgnfcant based on ths test. 9

10 The posteror credblty ntervals were (0.087%, 0.155%) for the SAR Spll and (0.077%, 0.127%) for the SAR CC (Fgure 1). Usng the posteror dstrbuton for the SAR rato, we calculated a 80% probablty that the SAR Spll was hgher than the SAR CC, as ndcated by SAR ratos 1.0 (Table 2, Fgure 2). We also summarzed the posteror probabltes for other values of the SAR rato, and calculated a 63% probablty that the SAR Spll was at least 10% hgher than the SAR CC, a 46% probablty of the rato beng at least 20% hgher, a 30% probablty of the rato beng at least 30% hgher, and an 18% probablty of the rato beng at least 40% hgher (Table 2). Table 2. Posteror probabltes for the rato of the SAR Spll :SAR CC exceedng varous threshold values. Rato Probablty % % % % % % Fgure 1. Posteror probablty dstrbutons for the SAR Spll (sold lne) and the SAR CC (dashed lne). 10

11 Fgure 2. Posteror probablty dstrbuton for the SAR Spll : SAR CC rato. The arrow denotes the locaton of ratos equal to 1.0. The probablty mass to the left of the arrow descrbes the evdence that the SAR CC was greater than the SAR Spll, whle the probablty mass to the rght of the arrow descrbes the evdence that the SAR Spll was greater than the SAR CC. Across brood years of March releases wth spll, the mnmum, average, and maxmum SARs were 0.07%, 0.44%, and 1.12%, respectvely (Table 3). Durng March releases wth corner collector operatons, approxmately 7.5 mllon fsh were released each year. By applyng the range of SARs observed durng spll condtons n the past to these releases, we estmate that spll operatons may have resulted n 5,100-87,100 adults each year from the March releases. By dvdng these estmated adults by the observed SAR rato (1.18), we estmate that corner collector operatons may have resulted n 4,300-73,800 adults each year from the March releases. Takng the annual dfferences between the two operatonal estmates and summng across years, we estmate that a foregone loss of 15,200 adults (range 2,400-38,900 adults) may have resulted from corner collector-only operatons durng (Table 3). 11

12 Table 3. Mnmum, average, and maxmum SARs for the March releases durng brood years under spll operatons, the number of fsh released n March , and forecasts of the expected number of total adult returns (fsheres and hatchery) for spll operatons and corner collector operatons usng the observed SAR rato (1.18). The dfferences between the forecasts and the sum of these dfferences across years s also presented. Expected Adult Returns Release Number Mn. SAR Avg. SAR Max. SAR Year Released (Mar.) Group 0.07% 0.44% 1.12% ,348,976 Expected wth Spll 5,071 32,328 82,441 Expected wth CC 4,297 27,397 69,865 dfference 774 4,931 12, ,591,028 Expected wth Spll 5,238 33,393 85,156 Expected wth CC 4,439 28,299 72,166 dfference 799 5,094 12, ,767,253 Expected wth Spll 5,359 34,168 87,133 Expected wth CC 4,542 28,956 73,842 dfference 818 5,212 13,291 Total across years: 2,390 15,237 38,857 Dscusson These results provde some evdence that the fsh released durng the spll operatons had hgher lfe-cycle survval than fsh released durng the corner collector operatons n However, the lack of strong contrast n the operatons provded at Bonnevlle Dam (5 kcfs corner collector versus 25 kcfs spll) lkely hndered the ablty to detect bologcally sgnfcant dfferences between the SARs of the release groups. Stll, applyng these results to the March releases that occurred n , a large number of adults may have been lost that otherwse could have been avalable to ocean fsheres, n-rver fsheres, and back to the hatchery. As dscussed n the ntroducton, n addton to possble foregone losses of harvest opportuntes n fsheres, other detrmental effects to ESA-lsted and other stocks of concern may have resulted. Due to the lag between release and adult return, the effects of those operatons, whatever they n fact were, wll contnue to be manfest as the adults from these releases contnue to return. Whle the evdence for the 2004 releases suggests that there may be a dfference n lfe-cycle survval, and the resultng estmate of the SAR rato s the only estmate of comparatve lfe-cycle survval, addtonal years of data are necessary to evaluate whether these results are consstent across years or not. The Bayesan methods presented n ths analyss provde a convenent framework for augmentng the results from ths experment wth those that may be obtaned from future experments. We envson that the observed SAR rato could be used as a pror dstrbuton for SAR ratos from subsequent experments to quantfy the evdence that these dfferences are consstent or not across years. 12

13 References: Gelman, A.B., J.S. Carln, H.S. Stern, and D.B. Rubn Bayesan Data Analyss. Chapman & Hall/CRC, Boca Raton, Florda. Lee, P.M Bayesan Statstcs: An Introducton. Arnold, London. PFMC (Pacfc Fshery Management Councl) Revew of Ocean Salmon Fsheres. (Document prepared for the Councl and ts advsory enttes.) Pacfc Fshery Management Councl, 7700 NE Ambassador Place, Sute 200, Portland, Oregon PFMC (Pacfc Fshery Management Councl) Revew of Ocean Salmon Fsheres. (Document prepared for the Councl and ts advsory enttes.) Pacfc Fshery Management Councl, 7700 NE Ambassador Place, Sute 200, Portland, Oregon Snedecor, G.W. and W.G. Cochran Statstcal Methods, Sxth Edton. Iowa State Unversty Press. Ames, Iowa. USFWS Importance of Spll and Hgh Survval of the March Release from Sprng Creek Natonal Fsh Hatchery to West Coast and Columba Rver Fsheres and the proposed treatments for 2004 March release survval experments. 13

14 Appendx: February 1, Fgure A1. Posteror probablty dstrbutons for the SAR Spll usng a Haldane pror (sold lne), Jeffreys pror (dashed lne), and a unform pror (lne wth open crcles) Fgure A2. Posteror probablty dstrbutons for the SAR CC usng a Haldane pror (sold lne), Jeffreys pror (dashed lne), and a unform pror (lne wth open crcles). 14

15 Hours KAF Hours of spll KAF of spll Outmgraton Year 0 Fgure A3. Hours of spll and KAF of spll at Bonnevlle Dam durng the March release of Sprng Creek NFH tule fall Chnook,