Origin and Straying of Hatchery Winter Steelhead in Oregon Coastal Rivers

Transactions of the American Fisheries Society

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R. Kirk Schroeder , Robert B. Lindsay & Ken R. Kenaston

To cite this article: R. Kirk Schroeder , Robert B. Lindsay & Ken R. Kenaston (2001) Origin and Straying of Hatchery Winter Steelhead in Oregon Coastal Rivers, Transactions of the American Fisheries Society, 130:3, 431-441, DOI: 10.1577/1548-8659(2001)130<0431:OASOHW>2.0.CO;2

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Download by: [Oregon State University] Date: 02 December 2016, At: 13:22 Transactions of the American Fisheries Society 130:431±441, 2001 ᭧ Copyright by the American Fisheries Society 2001

Origin and Straying of Hatchery Winter Steelhead in Oregon Coastal Rivers

R. KIRK SCHROEDER,* ROBERT B. LINDSAY, AND KEN R. KENASTON Oregon Department of Fish and Wildlife, 28655 Highway 34, Corvallis, Oregon 97333, USA

Abstract.ÐWe evaluated the origin and straying of hatchery steelhead Oncorhynchus mykiss among 16 rivers on the Oregon coast to examine rearing or release practices that might contribute to straying. Data were collected on the returning adults of three brood years that had been differentially marked and released as smolts in 1990±1992. The percentage of strays averaged 11% (range, 4±26%) of the samples of hatchery and wild ®sh in 11 streams where hatchery steelhead were released. Stray hatchery ®sh composed a mean of 22% (range, 9±43%) in 5 streams without hatchery releases. The two predominant factors that contributed to straying were releases of stocks transplanted from their natal basins and releases into adjacent basins. Releases of transplanted stocks into adjacent basins accounted for 41% of the strays, while releases of transplanted stocks into nonadjacent basins accounted for 29% of the strays. Local stocks of steelhead released into adjacent basins accounted for 16% of the strays. The incidence of straying by hatchery ®sh and its widespread occurrence in Oregon coastal rivers present genetic and ecological risks to wild populations of winter steelhead. Strategies to reduce straying may include using local brood stocks, rearing and releasing ®sh within their natal basins, reducing the numbers of hatchery ®sh released, and eliminating some hatchery releases altogether.

Homing of adult anadromous salmonids to their the genetic diversity between populations and de- natal stream has been recognized as an important crease the ®tness of wild populations through the adaptation in establishing and maintaining distinct displacement or breakdown of locally adapted gene spawning populations through reproductive iso- complexes (Emlen 1991; Waples 1991a). Gene ¯ow lation (Ricker 1972; Horrall 1981). Mature ®sh increases between nonnative hatchery and wild pop- that migrate to and spawn in a stream other than ulations when hatchery strays successfully spawn the one where they originated are considered strays with wild ®sh, and it can result in the reduced fre- (Quinn 1993). Straying is a natural behavior that quency and subsequent loss of locally adapted alleles enables salmonids to colonize new habitat (Milner (Felsenstein 1997). Hatchery strays spawning in sev- and Bailey 1989), to avoid locally unfavorable eral rivers can also result in a genetically homoge- conditions (Leider 1989), to maintain genetic di- nous population (Adkison 1995; Felsenstein 1997). versity within stocks (Horrall 1981), and to per- A potential ecological effect of stray hatchery ®sh petuate metapopulations (Hanski and Gilpin on wild ®sh is competition in spawning and rearing 1997). The genetically distinct structure of anad- areas (Fresh 1997). In addition, large numbers of romous salmonid populations (e.g., Reisenbichler strays can mask trends in the population abundance et al. 1992) suggests that the successful reproduc- of wild ®sh and bias estimates of the survival and tion of strays naturally occurs at low levels. How- exploitation of wild and hatchery stocks (e.g., La- ever, straying of hatchery ®sh concerns ®sh man- belle 1992). agers because of the potential negative impacts on Concerns about the genetic and ecological im- wild populations of interbreeding between wild pacts of hatchery ®sh on wild ®sh have led to and hatchery ®sh (e.g., Waples 1991a). De®ning proposals for assessing and altering hatchery pro- the ``home'' of hatchery ®sh can be dif®cult be- grams (e.g., NRC 1996) as well as to policy chang- cause local stocks are often reared and released in es in ®sh management agencies. For example, a different locations. In addition, stocks of hatchery wild ®sh management policy adopted in Oregon ®sh are often transplanted to nonnatal streams. sets guidelines for the percentage of hatchery ®sh Stray hatchery ®sh can have genetic and ecolog- allowed in a wild spawning population (ODFW ical effects on wild ®sh populations. Hatchery ®sh 1992). The National Marine Fisheries Service that stray and hybridize with wild ®sh can reduce (NMFS) is also developing guidelines for man- aging stray hatchery ®sh in its efforts to protect * Corresponding author: [email protected] natural populations under the Endangered Species Received April 11, 2000; accepted January 4, 2001 Act (McElhany et al. 2000). Strategies to reduce

431 432 SCHROEDER ET AL. the number of hatchery ®sh in a river basin depend, categories, namely, local stocks and transplanted in part, on knowing the number and origin of the stocks. Local stocks were steelhead released into strays that occur with natural spawners. In addi- their natal basins and included those reared within tion, knowledge of hatchery release practices that the natal basin and those reared outside but re- contribute to straying is important for modifying leased within the natal basin. Transplanted stocks hatchery programs. were steelhead taken from their natal basin and Studies of straying have examined hatchery prac- released into another basin. Some transplanted tices such as release time (Unwin and Quinn 1993; stocks were reared within the basin where they Pascual et al. 1995) and release location (Pascual were released, but most were reared outside the and Quinn 1994; Pascual et al. 1995). A few studies release basin. have examined straying of hatchery salmon Oncor- Release groups returned as adults in the 1991± hynchus spp. over large geographic areas (Labelle 1992 through the 1993±1994 run years. We collected 1992; Unwin and Quinn 1993; Pascual and Quinn data on stray hatchery ®sh in 12 streams by using 1994). Studies of straying in steelhead O. mykiss have trap catches and creel surveys. Seven of these focused on small geographic scales (Shapovalov and streams were stocked with hatchery steelhead (the Taft 1954; Leider 1989) or the effects of smolt trans- Nestucca, Siletz, Yaquina, Alsea, Siuslaw, Coquille, portation in the Columbia River basin (Slatick et al. and Chetco rivers), and ®ve streams received no 1988). We are aware of just one study that examined hatchery ®sh (the Trask, Elk, Sixes, and Winchuck straying of steelhead over a large geographic area rivers, and Drift Creek) (Figure 1). In addition, we (Lirette and Hooton 1988). Our study was initiated used data reported by anglers to examine the per- to examine the origin and straying of hatchery winter centage of stray hatchery ®sh in four streams that steelhead among rivers on the Oregon coast, as well were stocked with hatchery steelhead (the Necani- as to examine the factors in¯uencing patterns of cum, Nehalem, Umpqua, and Rogue rivers). Anglers straying. voluntarily collected scales and reported clip information under an ODFW program to obtain infor- Methods mation about the catch of steelhead. In this study we considered hatchery steelhead We estimated straying within a surveyed basin as strays if they returned to a river basin other than as the percentage of the total sample of winter the one where they were released. Studies have steelhead (hatchery and wild) that was of stray demonstrated that hatchery steelhead tend to return hatchery origin. We could not calculate a stray rate to speci®c release sites within a river basin (Wag- (i.e., the percentage of a release group that strayed) ner 1969; Slaney et al. 1993). We examined the because we could not account for all adult returns origin of stray steelhead and their spatial distri- of a given release. The hatchery portion of the bution in rivers along the Oregon coast over a return to a basin was divided into a homing com- distance of about 500 km (Figure 1). ponent (those from releases into that basin) and a Hatchery winter steelhead were differentially straying component (those from releases into other marked by excising ®ns or maxillary bones for basins). In catch-and-release ®sheries, we deter- three brood years at seven steelhead hatcheries on mined the catch of wild ®sh from angler interviews the Oregon coast (Figure 1) and were released as during creel surveys. We assigned returning adults smolts in 1990±1992 (Table 1). We generally var- to a release year by using circuli patterns on scales ied the marks within and among release groups to determine age (Chapman 1958). Where no over the 3-year study to reduce bias in estimates scales were available, we used ®sh length to es- of straying attributed to particular groups. Because timate the age of adults. the number of distinct clip combinations is limited Some steelhead had marks that could not be as- and because a few hatcheries that released steel- signed to a particular release and were classed as head into several basins were unable to rear sep- ``unknown'' strays. We also included unmarked arate groups of steelhead, some groups were re- hatchery steelhead, as determined by scale analysis leased with duplicate marks (Table 1). However, of freshwater growth patterns (Chapman 1958), in in most cases we released steelhead with duplicate the ``unknown'' category for most rivers. However, marks in geographically distant areas of the coast. we sampled a large number of unmarked hatchery The release locations of hatchery ®sh were those steelhead in two southern Oregon rivers (Chetco and customarily used by the Oregon Department of Winchuck) in years when all Oregon releases were Fish and Wildlife (ODFW) and were not altered marked. We assumed these ®sh were from unmarked for this study. We grouped the releases into two releases of steelhead from northern California hatch- STRAYING OF HATCHERY STEELHEAD 433

FIGURE 1.ÐMap showing Oregon coastal rivers where winter steelhead were sampled or where juvenile hatchery steelhead were released. Numbers indicate hatcheries that rear winter steelhead; 1 ϭ Nehalem, 2 ϭ Cedar Creek, 3 ϭ Alsea, 4 ϭ Rock Creek, 5 ϭ Bandon, 6 ϭ Elk River, and 7 ϭ Cole Rivers. eries (Busby et al. 1996). Hatchery summer steelhead released marked winter steelhead, which we recov- from northern California hatcheries have been sam- ered in Oregon rivers. pled in the Rogue River in southern Oregon (Everest We used slightly different data to estimate the 1973; Satterthwaite 1988). California hatcheries also percentage of strays and to determine their origin. 434 SCHROEDER ET AL.

TABLE 1.ÐFin clips and numbers (thousands) of winter steelhead smolts released from hatcheries on the Oregon coast, 1990±1992. Clip abbreviations are as follows: Ad ϭ adipose, Rp ϭ right pectoral, Lp ϭ left pectoral, Rv ϭ right ventral, Lv ϭ left ventral, Rm ϭ right maxillary, and Lm ϭ left maxillary. Clip designations separated by commas indicate more than one release; clip designations that are run together indicate multiple clips per ®sh. Stock abbreviations are as follows: AG ϭ Applegate (Rogue basin), AL ϭ Alsea, CO ϭ Coos, CQ ϭ Coquille, CT ϭ Chetco, NC ϭ Necanicum, NH ϭ Nehalem, RO ϭ Rogue, SI ϭ Siuslaw, SU ϭ South Umpqua, and TR ϭ Three Rivers (Nestucca basin).

1990 release 1991 release 1992 release Release Number Number Number Hatchery (Stock) location Fin clip(s) (1,000s) Fin clip(s) (1,000s) Fin clip(s) (1,000s) Local stocks reared and released in natal basin Nehalem (NH) Nehalem Rv, Lv 157 Ad, AdRv, 154 Lp, AdRv, 160 AdLv AdLv Cedar Creek (TR) Nestucca Ad 130 Ad 130 Alsea (AL) Alsea AdRm, AdLm 116 AdRp, AdLp 120 AdRp, AdLp 120 Rock Creek (SU)a South Umpqua RvLm 19 AdRv, LvLm 70 Bandon (CQ)b Coquille AdRv 116 Lp, RvRm 184 RvLm, RvRm 120 Cole Rivers (RO)c Rogue Ad, AdRp, 150 Ad, AdRv, 150 Ad, AdLvRm, 150 AdLp AdLv AdLvLm Cole Rivers (AG)c Applegate Ad, AdRvRm, 150 Ad, AdRpRm, 150 Ad, AdRvRm, 150 AdRvLm AdRpLm AdRvLm Local stocks reared outside and released in natal basin Nehalem (NC) Necanicum Rv 2 Alsea (SI) Siuslaw LpLm 35 Alsea (CO) Coos AdLv 120 Alsea (CQ) Coquille LvLm 25 Bandon (CO)b Coos Ad 10 Rm 10 Elk River (CT) Chetco Lv 52 AdLm 42 AdLm, AdRm 50 Transplanted stocks reared in release basin Rock Creek (AL)a South Umpqua AdLv 46 LvRm 35

Transplanted stocks reared outside release basin Nehalem (NH) Necanicum Lv 40 Ad 40 Lp 40 Cedar Creek (TR) Tillamookd Ad 25 Ad 25 Wilsond Ad 120 Ad 120 Kilchisd Ad 40 Ad 40 Miamid Ad 10 Ad 10 Alsea (AL) Salmon Lp 37 Rp 35 Lv 35 Siletz Lp 108 Rp 100 Lv 100 Yaquina Lp 30 Rp 30 Lv 20 Siuslaw Lp 178 RpRm, RpLm, 127 RpRm RpLm, 166 LpRm LpLm, LpRm Smith Lp 65 Rp 65 Lv 65 Coos Lp 40 Rp 65 Tenmile Lp 30 Alsea (CO) Tenmile Rv 30 AdLv 25 Alsea (CQ) Coos LvLm 79 RvRm 54 a North Umpqua basin. b Coquille basin. c Rogue basin. d Rivers entering Tillamook Bay.

We estimated the percentage of strays by using all only where we could assign hatchery steelhead to data where steelhead could be classi®ed as either a particular release group. In this case, we included wild, homing hatchery, or straying hatchery ®sh information reported by anglers for all streams, (including unknown strays). We included infor- including those where fewer than 20 samples were mation voluntarily reported by anglers when we received and those where wild steelhead were re- received 20 or more samples for a speci®c stream leased under catch-and-release regulations. in a given year or where angling regulations al- We statistically analyzed differences in straying lowed the harvest of wild steelhead. In contrast, between six releases (®ve local stocks and one we evaluated the origin of strays by using data transplanted stock) for which we had suf®cient re- STRAYING OF HATCHERY STEELHEAD 435 coveries. Local stocks were further divided into TABLE 2.ÐNumber of wild, homing hatchery, and groups reared within and outside their natal basins straying hatchery winter steelhead recovered in Oregon (both were released within their natal basin). We coastal rivers, 1991±1994 run years. Data are from creel surveys, traps, and voluntary angler reports. Angler reports used an arcsine and square-root transformation of were used only where wild steelhead could be kept. data and a one-way analysis of variance (ANOVA) to test for differences in the percentage of strays. Streams Origin sampled Percent Equality of variances was tested with Bartlett's (number Homing Straying strays test. We chose P ϭ 0.10 as our level of signi®cance of years) Wild hatchery hatchery (SE) to increase the ability to detect differences. Streams with hatchery releases We examined the effects of run size and stream Necanicum (1) 13 32 5 10 (4.2) ¯ow on straying within the Siletz, Alsea, and Sius- Nehalem (1) 11 62 12 14 (3.8) law rivers, where data were consistently collected Nestucca (3) 182 255 39 8 (1.3) Siletz (3) 148 141 56 16 (2.0) during the 3 years of the study. We used the total Yaquina (3) 121 106 26 10 (1.9) counts of wild and homing hatchery steelhead as Alsea (3) 287 508 283 26 (1.3) an index of run size, along with the average No- Siuslaw (3) 927 1482 104 4 (0.4) Umpqua (3) 283 52 48 13 (1.7) vemberϪMay stream ¯ow from U.S. Geological Coquille (3) 760 1191 100 5 (0.5) Survey records. We did not compare straying and Rogue (1) 38 31 7 9 (3.3) run size among basins because sampling intensity Chetco (3) 832 273 71 6 (0.7) differed from basin to basin. To estimate the dis- Streams without hatchery releases tance that hatchery ®sh strayed from their release Trask (3) 130 39 23 (3.2) a basins, we used the shortest distance by ocean be- Drift (3) 107 82 43 (3.6) Sixes (1) 61 8 12 (3.8) tween the mouths of river basins. We considered Elk (1) 48 5 9 (4.0) ®sh to be long-distance strays if they were sampled Winchuck (3) 196 52 21 (2.6) more than 100 km from their release basin (Hard a Tributary of the Alsea River that enters Alsea Bay. and Heard 1999). On a larger spatial scale, we examined straying from releases of a local stock into the Chetco River between Oregon coastal basins to the north of Cape Blanco and those to the south (Figure 1). Cape and from releases into northern California basins. Blanco was used by NMFS as the geographic de- Based on all streams sampled, transplanted lineation between two evolutionarily signi®cant stocks of hatchery steelhead accounted for a higher units (ESUs; Waples 1991b) of coastal steelhead proportion of strays than local stocks. Strays from (Busby et al. 1996). The delineation of these ESUs releases of steelhead transplanted outside their na- was based, in part, on the genetic distinctiveness tal basins accounted for 70% of strays reported in of their populations, which assumes little straying Oregon coastal basins, with releases of transplant- between ESUs. We calculated the percentage ed stocks into adjacent basins accounting for 41% strays that originated from the neighboring ESU of the strays. Releases of transplanted stocks com- in steelhead populations to the north and south of posed 42% of the annual smolt releases in Oregon Cape Blanco. coastal basins. Strays from transplanted releases were predominant in 6 of 16 streams we sampled. Local stocks reared and released in their natal ba- Results sins accounted for 18% of all strays from 51% of In Oregon coastal rivers where hatchery steel- smolt releases and composed the majority of strays head were released, the incidence of straying was in 4 of 16 sampled streams. Local stocks reared 4±26% of the total sample (Table 2). Stray hatch- outside but released in their natal basins accounted ery steelhead composed 9±43% of winter steel- for another 12% of the strays from 7% of the smolt head in ®ve streams where no hatchery ®sh were releases and composed the majority of strays in released (Table 2). The Alsea River, Drift Creek two streams. The composition of strays in the re- (a tidewater tributary of the Alsea River), and the maining four streams was not predominated by a Trask River (a tidewater tributary of Tillamook release type. Bay) had the highest percentage of strays. Stray Paired releases into the Siuslaw and Umpqua hatchery ®sh in these streams predominantly orig- rivers further suggested that transplanted stocks inated from large releases of transplanted stocks contributed more to straying than local stocks (Ta- into nearby rivers. The Winchuck River also had ble 3). In the Siuslaw River, fewer local Siuslaw a high percentage of strays, most of which were than transplanted Alsea steelhead strayed, al- 436 SCHROEDER ET AL.

TABLE 3.ÐPercentage of the stray hatchery steelhead recovered in Oregon coastal rivers from releases of local and transplanted stocks into the Siuslaw and Umpqua rivers. Numbers of recoveries were adjusted to account for unequal release numbers.

Location of release Siuslaw Rivera Umpqua Riverb Location of Siuslaw Umpqua strays stock Alsea stock stock Alsea stock Alsea River 1 6 Ͻ1 4 Other riversc 0 1 (1) 1 (1) 10d (7) a Reared in the Alsea basin. b Reared in the Umpqua basin; Alsea stock eggs were incubated at FIGURE 2.ÐMean percentage of stray hatchery steel- Alsea Hatchery and transferred as eyed eggs. head recovered in Oregon coastal rivers from six release c Number of basins is given in parentheses. groups. The groups consisted of (1) ®ve local brood- d Mean value. stocks that were reared either within or outside of their natal basins and then released into those basins and (2) one stock that was transplanted into several basins. The though both were reared in the Alsea basin before vertical lines represent the ranges for percent strays. their release into the Siuslaw. In the Umpqua Riv- er, more Alsea than Umpqua steelhead strayed, of the strays reported in coastal basins (Figure 3) although both stocks were reared and released in and composed the majority of strays in 10 of 16 the Umpqua basin (Table 3). Because Alsea steel- streams. Alsea stock steelhead transplanted into head were incubated to the eyed egg stage at Alsea the Siuslaw River but returning to the Alsea River Hatchery prior to their transfer to the Umpqua Riv- accounted for over 50% of the ®sh that strayed to er, straying of adults back to the Alsea suggested an adjacent basin. If these ®sh are excluded, re- some ®sh imprinted during egg incubation. A ge- leases into adjacent basins accounted for 38% of netic component to homing could also have been all strays (Figure 3). The median distance between a factor. Few Umpqua steelhead strayed to the Al- adjacent basins where hatchery steelhead were re- sea River. leased was 37 km, whereas the median distance However, we found no signi®cant difference (P that steelhead strayed from their release basin was ϭ 0.41) among the mean percentages of strays 54 km (range, 5±456 km). Long-distance strays from releases of a transplanted stock and two types (Ͼ100 km from their release basins) composed of local stocks (Figure 2) for six releases that could 24% of the strays. Strays from hatchery releases be statistically compared. The composition of into northern California rivers were most frequent, strays from these transplanted and local releases reported in 11 of the 16 Oregon streams we sur- was highly variable in the recovery basins and veyed (Table 4). Of the hatchery releases into generally ranged from 1 to 50%, with the exception of one basin where the transplanted stock composed almost 80% of strays (Figure 2). Transplanted and local releases of steelhead that returned to their rearing basins instead of their release basins accounted for 39% of all the strays reported in the surveyed rivers. However, most of these strays were from releases of Alsea steelhead into the Siuslaw River that returned to the Alsea basin. Excluding these ®sh, 9% of all strays were ®sh returning to their rearing basin. Steelhead returning to their natal or incubation basins rather than to their release basin composed less than 1% of all reported strays, although these types of re- FIGURE 3.ÐFrequency distribution of stray hatchery leases were limited. steelhead in Oregon coastal basins by proximity to their Hatchery releases into adjacent basins (de®ned release basin, 1991±1994 run years. Data are shown with as the nearest basin with hatchery releases north and without transplanted Alsea Hatchery releases into and south of the subject basin) accounted for 57% the Siuslaw River that strayed to the Alsea basin. STRAYING OF HATCHERY STEELHEAD 437

TABLE 4.ÐNumber and origin of hatchery winter steelhead in Oregon coastal rivers with and without hatchery releases, 1991±1994 run years (except Elk and Sixes rivers, which are 1991±1992 run year only). Homing hatchery returns are indicated by numbers in bold italics. Sampled streams and release groups are listed from north to south from top left.

Release group Cedar Creek Alsea Un- Streams Necan- Neha- Hatch- trans- Alsea Ump- Ten- Co- Cali- known sampled icum lem erya plantb local Siuslawc qua mile Coosd quille Rogue Chetco fornia strays Streams with hatchery releases Necanicum 56 3 6 2 Nehalem 63 4 1 9 Nestucca 5 255 29 1 4 Siletz 1 141 3 2 21 3 5 39 Yaquina 106 1 10 15 Alseae 4 49 567 221 4 9643 4 24 Siuslaw 42945 2,205 13 11 9 5 18 Umpqua 1 52 2 2 22 21 Coquille 20f 3 8 10 11 1,191 8 25 12 3 Rogue 1 1 1 44 11 0 Chetco 3 10 273 29 29 Streams without hatchery releases Trask 9492 1 Drift 10 1374 72 4 17 Sixes 4 4 Elk 1 2 2 Winchuck 12222 7 a Released into the Nestucca and Tillamook Bay rivers. b Includes hatchery steelhead released into Salmon, Siletz, Yaquina, Smith, and Coos rivers; does not include releases into the Siuslaw River. c Released from Alsea Hatchery into the Siuslaw River. d Includes some ®sh that may have been released into nearby Tenmile Creek. e Two steelhead released from hatcheries in the lower Columbia River were also recovered in the Alsea River. f Probably from releases into the nearby Coos River.

Oregon basins, strays from Umpqua River releases from releases of Alsea stock steelhead into the were most frequent, reported in 8 of 16 streams Umpqua basin. (Table 4). Eighty-nine percent of these strays were The percentage of strays in 11 basins where data were collected for 3 years was highly variable (the mean coef®cient of variation, 100 ϫ SD/mean, ϭ 37%). However, we saw no clear effect of run size or stream ¯ow on straying in the Siletz, Alsea, or Siuslaw rivers, where data were suf®cient to examine these relationships. We saw some evidence within basins that the percentage of stray hatchery steelhead was higher in years when run size was low (Figure 4), but sample sizes were small. The incidence of straying was lower when examined at the scale of an ESU than at the smaller scale of individual basins. Of hatchery steelhead from known release groups, those straying from the neighboring ESU composed 2% of all hatchery FIGURE 4.ÐRelationship between percentage of stray ®sh in the northern ESU and 4% of hatchery ®sh hatchery steelhead and an index of run size within three in the southern ESU. The average number of hatch- Oregon coastal rivers, 1991±1994 run years. The run size index was derived from counts of wild and homing ery steelhead smolts released into northern ESU hatchery ®sh. Because sampling intensity differed basins was twice the average number released into among rivers, indices of run size are not comparable. southern ESU basins (including California). If 438 SCHROEDER ET AL. wild steelhead are included (assuming all wild ®sh some transplanted releases may be because the se- accurately homed), steelhead straying from the quence and timing of imprinting is disrupted or neighboring ESU composed 1% of all ®sh sampled because an inherited olfactory response to the re- in each ESU. The percentage of steelhead from a lease site is absent (McIsaac and Quinn 1988; Pas- neighboring ESU was highest in basins closest to cual et al. 1995). the ESU boundary. About 15% of all strays sam- The straying patterns of hatchery steelhead pled within an ESU were from the neighboring among Oregon coastal basins suggest that the po- ESU. tential for gene ¯ow between hatchery and wild ®sh is greatest in basins that are geographically Discussion proximate to the basin where the hatchery ®sh are The percentage of stray hatchery steelhead in released. These observations are consistent with a rivers where hatchery ®sh were released was gen- study of winter steelhead in Vancouver Island erally higher in Oregon rivers (4±26% of the total streams (Lirette and Hooton 1988) and other stud- catch) than that reported for six rivers (0±9% of ies of salmon (Labelle 1992; Pascual and Quinn the total catch) in British Columbia (Lirette and 1994; Hard and Heard 1999). However, proximity Hooton 1988). Hatchery steelhead also strayed to to a release site alone did not explain the occur- basins where no hatchery ®sh were released in ®ve rence of strays in all rivers. For example, we found Oregon streams (9±43% of the total catch) and in that the percentage of strays in the Siuslaw and two British Columbia streams (3% and 41% of the Coquille basins was low despite their proximity to total catch). Hatchery ®sh transplanted to other basins with large releases of hatchery steelhead. basins, which accounted for the majority of strays Factors such as watershed geology, ¯ow, temper- in both studies, composed a larger percentage of ature, and stream order may in¯uence straying the marked release in Oregon (42%) than in British (Lirette and Hooton 1988; Labelle 1992; Pascual Columbia (21%). However, the percentage of and Quinn 1994). strays is probably underestimated in Oregon rivers In addition to the effects on nearby populations, because we removed various ®ns or maxillary the occurrence of long-distance straying in our bones to identify hatchery steelhead, which may study (24% of the strays) indicates that hatchery cause higher mortality than the removal of adipose releases can potentially in¯uence wild ®sh popu- ®ns (Vincent-Lang 1993) in the British Columbia lations over a large geographic area. Even a low study. Stray steelhead composed 1% and 6% of rate of gene ¯ow from distant hatchery populations the wild steelhead counted in two adjacent coastal can reduce the genetic diversity of wild popula- California streams (Shapovalov and Taft 1954). tions (Adkison 1995; Felsenstein 1997). Long- In Oregon coastal basins the mean percentage distance straying can greatly increase the migra- of strays from transplanted stocks was about twice that from local stocks, although a statistical dif- tion of hatchery alleles into distant wild popula- ference could not be demonstrated. The incidence tions because the hatchery alleles can reach the of straying in Vancouver Island streams increased distant population without having to migrate an average of eight times when steelhead were through a string of populations (Felsenstein 1997). transplanted to other streams rather than locally Homing of anadromous salmonids is more ac- released (Lirette and Hooton 1988). Other studies curate when it is measured at large spatial scales also report that locally adapted populations stray than at small ones (Unwin and Quinn 1993; Quinn less than transplanted populations in the case of 1997). The incidence of stray steelhead in our chinook salmon O. tshawytscha (McIsaac and study was lower at the geographic scale of ESUs Quinn 1988; Pascual et al. 1995), coho salmon O. than at the scale of individual basins. Designation kisutch (Labelle 1992), and pink salmon O. gor- of two ESUs for steelhead in Oregon coastal basins buscha (Bams 1976). Pascual and Quinn (1994) was partially based on the genetic differentiation reported accurate homing of Rogue River salmon among populations (Busby et al. 1996). The pro- transplanted to the Columbia River but consider- portion of an ESU that consists of successfully able straying within the Columbia. In addition, a spawning strays has been estimated at much less study of chinook salmon in Alaska indicated that than 1% based on genetic data on Paci®c salmonids transplanted hatchery ®sh did not stray at high (McElhany et al. 2000). We estimated that hatch- rates when the gametes of adults were transported ery steelhead straying between neighboring ESUs to the release stream and were cultured to smolts composed 2±4% of the catch of hatchery ®sh and (Hard and Heard 1999). High levels of straying in 1% of the catch if wild ®sh were included. How- STRAYING OF HATCHERY STEELHEAD 439 ever, we could not determine whether these strays Healey 1994; Quinn 1997). Some studies of salm- successfully spawned. on have estimated that gene ¯ow between popu- The ESUs for coastal steelhead were also based lations was less than would be suggested by stray on assumed patterns of ocean migration. Steelhead rates (Labelle 1992; Tallman and Healey 1994). from rivers north of Cape Blanco are believed to Marking reduces the survival of ®sh (Vincent- migrate north into the Gulf of Alaska, while those Lang 1993) and can affect estimates of straying. from rivers south of Cape Blanco are believed to In this study, almost all hatchery ®sh were marked stay offshore of southern Oregon and northern Cal- with a combination of ®n and maxillary clips, ifornia (Everest 1973; Pearcy et al. 1990). How- which would have reduced their survival. This ever, data on steelhead distribution in the ocean probably decreased our estimates of the percentage are based on a few recoveries of juveniles or adults of strays in the total run in most basins. Compar- in limited areas. In our study, about 15% of the isons of straying within the hatchery component strays in each ESU were from the neighboring of the run were not affected because marking var- ESU. Our data suggest two possibilities: (1) some ied among and within release groups. steelhead overshoot their release basin on their Although straying is a natural phenomenon in spawning migration and enter a basin in the neigh- anadromous salmonids, the level of straying by boring ESU; (2) ocean migration patterns are more hatchery steelhead and its widespread occurrence variable than previously thought, and some southern ESU steelhead migrate north in the ocean as in Oregon coastal rivers raises concern about the juveniles and enter the northern ESU basins as they long-term genetic impacts on local wild popula- return south on their spawning migrations, and tions of winter steelhead. In addition, large num- vice versa. Because some steelhead have been bers of strays to a hatchery pose a risk to the ge- transplanted beyond the ESU boundary in the past netic integrity of local stocks of hatchery ®sh. If (e.g., Alsea River steelhead into the Chetco River), straying hatchery ®sh cannot be identi®ed, they our observations could be partially in¯uenced by could be incorporated into the local hatchery interbreeding of local and transplanted stocks. stock. The genetic integrity of locally adapted pop- However, most of the reported strays were from ulations can decrease with rates of gene ¯ow from releases that have no history of stock transfers stray hatchery ®sh as low as 5±10% (Emlen 1991; between ESU basins. Felsenstein 1997). Stray hatchery steelhead com- Our estimates of straying may have included ®sh posed 10% or more of the steelhead sampled in that were transitory and would not have spawned 10 of 16 Oregon coastal streams. Of particular in basins where they were sampled. Some ®sh ex- concern is the high percentage of strays (9±43%) hibit exploratory behavior and may ascend non- in streams where no hatchery ®sh were released. natal rivers before returning to their natal stream Our study indicates that using local brood to spawn (Ricker 1972; Labelle 1992). The genetic stocks, rearing and releasing hatchery ®sh within effects of stray ®sh on a local population depend their natal basins, or a combination of these strat- on interbreeding between the two groups, not just egies could reduce the straying of hatchery ®sh. the physical migration of ®sh (Tallman and Healey Hatchery ®sh reared in a location distant from their 1994; Felsenstein 1997). Although some steelhead release basin may more accurately home to that captured in this study could have been transients, release basin than ®sh reared in a nearby basin traps used to capture steelhead were generally lo- (Lirette and Hooton 1988; Quinn 1993). However, cated in small spawning tributaries distant from Labelle (1992) reported that certain stocks of coho the ocean where transitory strays might be less salmon were more susceptible to straying when prevalent. For example, the traps operated in ®ve river basins were an average of 62 km from the exposed to foreign water sources during rearing. ocean and 35 km upstream of tidal reaches. Some Because hatchery steelhead tend to return to their stray steelhead caught in sport ®sheries may not release locations (Wagner 1969; Slaney et al. have remained in the basin, although steelhead 1993), releases into tributaries rather than into the ®sheries in Oregon coastal rivers generally occur main stem may increase homing within and among upstream of tidal waters. Even if stray hatchery basins, but the residualism of hatchery smolts ®sh spawn in nonnatal rivers, strays may differ should be evaluated (Viola and Schuck 1995). Re- from native ®sh in their spatial and temporal dis- ducing the numbers of hatchery ®sh released or tribution on the spawning grounds or they may eliminating some hatchery releases altogether encounter barriers in mate choice (Tallman and would also decrease the numbers of strays. 440 SCHROEDER ET AL.

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