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NOAA Technical Memorandum NMFS-NWFSC-XX

ECOLOGICAL AND BEHAVIORAL

IMPACTS OF ARTIFICIAL PRODUCTION

STRATEGIES ON THE ABUNDANCE OF

WILD SALMON POPULATIONS

A Review of Practices in the Pacific Northwest

By

Thomas A. Flagg, Barry A. Berejikian, John E. Colt, Walton W.

Dickhoff, Lee W. Harrell, Desmond J. Maynard, Colin E. Nash,

Mark S. Strom, Robert N. Iwamoto, and Conrad V.W. Mahnken

National Marine Fisheries Service

Northwest Fisheries Science Center

Resource Enhancement and Utilization Technologies

2725 Montlake Blvd. E., Seattle, WA-98112-2097
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SUMMARY

Production hatcheries play a major role in supplying Pacific salmon and trout to the

common property fishery, and benefiting commercial, sport, tribal, and non-tribal fishers. In the

Pacific Northwest hatchery fish currently contribute between 70-80% of coastal fisheries.

In the past production hatcheries have also played a role in slowing the decline of natural

populations. Now, however, they are becoming increasingly implicated as one of the factors

causing the decline. Among their citations include the transplantation and straying of fish, overharvest, and effects on carrying capacity of receiving environments.

Most production hatcheries were built when wild salmon stocks were healthy, and genetic

diversity of stocks was not a concern. Today, many stocks in the Pacific Northwest are listed as

threatened or endangered under the terms of the U.S. Endangered Species Act (ESA), and the

need to preserve biodiversity has brought about a new era of management strategies for the

conservation of wild stocks. As current hatchery practices and methods are now recognized as

contributors to the overall decline, there have been strong arguments for the reform of hatchery

management, particularly in the Columbia River Basin. The goal is to reduce the overall impact

of hatchery fish on the survival of wild stocks.

This document reviews the issues behind the major theoretical and observed ecological

and behavioral impacts of salmonid hatchery production strategies on the abundance and trends

of wild salmonid populations. The major focus is on potential effects of differing artificial

production strategies as they relate to stocks within:

• the ESU (evolutionarily significant unit) of spring/summer chinook (O. tshawytscha) in the

Snake River, and

• the ESU of steelhead (O. mykiss) in the Upper Columbia River.

The document is divided into three principal sections, as follows:

Comparison of Hatchery and Wild Salmon Biology

Some major differences between hatchery and wild salmonids are reviewed in sections

describing survival, foraging behavior, social behavior, habitat preference, response to predators,

differences in morphology and physiology, and reproductive behavior. The reviews conclude that

artificial culture environments condition salmonids to respond to food, habitat, conspecifics, and

predators differently than fish reared in natural environments. Present culture techniques also

alter selection regimes, which may result in genetic divergence between hatchery and wild

populations. Finally, the phenotypic differences observed between cultured and wild fish are

both genetically and environmentally controlled.
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Impacts of Artificial Production Releases on Wild Fish

The impacts of hatchery reared fish on the population abundance of wild fish are

reviewed and discussed in five sections concerning the effects of artificial production releases

(supplementation) on wild fish population abundance, competitive social interactions, predation,

health, and migratory behavior. Each section provides relevant conclusions drawn from the

review.

Conclusions and Recommendations

The final section draws some overall conclusions from the completed reviews and

analyses, and makes recommendations. It includes summary tables which detail an assessment

of the potential effects of artificial production strategies on population abundance of wild spring/

summer chinook and steelhead in their respective ESUs. In this section the authors conclude that

hatchery strategies offer the potential to stabilize and amplify salmonid populations, but the

artificial environment conditions salmonids to respond in ways different from fish reared in

natural environments. Fundamental changes in the dynamics of hatchery production policy and

implementation may be necessary both where hatchery supplementation is used to maintain some

populations until underlying causes of decline are corrected, and where production hatchery

operations overlap listed stocks. However, the overall effectiveness of supplementation to

maintain a population until underlying causes of decline are corrected is unknown. Little specific

numerical information exists regarding population abundance dynamics or interactive factors,

therefore assessments can only be prescribed in directional trends rather than absolute values.

Finally, the authors conclude that the direction of future use of artificial propagation in

the Columbia Basin will be a function of both the status of the natural populations and their

habitats. For supplementation and recovery purposes, the productivity of naturally spawning

populations will be a key parameter. Current information is not adequate to assess properly the

potential effects of hatchery operations on wild stocks. The authors recommend that the Region

should focus research to develop policies and procedures which properly integrate the roles of

hatcheries for conservation and sustainability of salmonid populations. Artificial propagation

risks may be ameliorated by development and implementation of conservation hatchery protocols

which may improve fitness and survival of hatchery fish.

The report includes a bibliography of some 270 citations.
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CONTENTS

I. Introduction ......................1

II. Comparison of Hatchery and Wild Salmon Biology ......................3

III. Impacts of Artificial Production Releases on Wild Fish ....................13

A. Production Strategies .......................................13

1. Supplementation Projects ......................................13

2. Conservation Hatchery Protocols ......................................29

B. Competition ......................................36

C. Predation ......................................46

D. Fish Health ......................................51

E. Migratory Behavior ......................................56

IV. Conclusions and Recommendations ....................59

V. Citations .....................63

VI. Appendices ....................85
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I. INTRODUCTION

Development of the hatchery system for Pacific salmon (Oncorhynchus sp.) began in the

late nineteenth century and ever since it has played an increasingly prominent role in

enhancement of the resources throughout the Pacific Northwest. Most public hatcheries were

built originally to mitigate for loss of natural spawning habitat, and their goal was simply focused

on enhancing the harvest of adults in the commercial fisheries. In the Columbia River Basin

alone, for example, there are now nearly 100 hatcheries. They produce about 200 million

juveniles each year, which provide up to 80% of the fish in several key salmon fisheries. Today,

these hatcheries play a major role in supplying salmon and trout to the common property fishery,

and benefiting commercial, sport, tribal, and non-tribal fishers. Unfortunately, they are so

instrumental in supplying fish that it is nearly impossible to separate the management of the

fisheries from the management of the hatcheries.

The majority of production hatcheries were built at a time when wild salmon stocks were

healthy, and genetic diversity of stocks was not a concern. However, times have begun to

change. With the near catastrophic decline of Pacific salmon species on the west coast of the

United States many stocks have been listed as threatened or endangered under the terms of the

U.S. Endangered Species Act (see Matthews and Waples 1991, Nehlson et al. 1991, Waples et al.

1991a and 1991b, Hard et al. 1992, Schmitten et al. 1995, and Weitkamp et al. 1995). The need

to preserve biodiversity has brought about a new era of salmon fisheries management strategies

for the conservation of wild stocks. This unquestionably will have an increasing impact on the

operation and management of production hatcheries, and the traditional users of hatchery fish.

The public hatchery system in the Pacific Northwest may have slowed the decline of

some natural salmon populations. However, current hatchery practices and methods have been

considered significant factors leading to the overall decline of several salmonid species.

Recently, the National Research Council (NRC) called for the reform of hatchery management in

the Columbia River Basin, including changes in the approach, operation, and expectations from

artificial propagation (NRC 1996).

The overall impact of hatchery fish can be divided into three broad categories. First,

over-harvest of wild stocks in mixed stock fisheries can have a profound impact on survival of

wild stocks. When abundant hatchery stocks are targeted for high harvest, less abundant wild

stocks cannot withstand the high exploitation rates, resulting in under-escapement of wild fish.

Second, there are a number of detrimental ecological interactions that can take place between

hatchery and wild fish. These can take the form of competition for food and territory, predation

by larger hatchery fish preying on smaller wild cohorts, and negative social interactions when

large numbers of hatchery fish are released on top of small numbers of wild fish. Third, there is

a series of genetic risks associated with hatchery rearing. Where hatchery operations conflict

with recovery of ESA-listed stocks the options appear to be either, 1) isolation of hatchery

production (e.g., near-tidewater rearing/release and terminal harvest), or 2) altering hatchery

operations to include a conservation mandate.
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This document reviews the issues behind the major theoretical and observed ecological

impacts of salmonid hatchery production strategies on the abundance and trends of wild

salmonid populations. The effects of genetic manipulations are intrinsically involved in these

impacts. Genetic risks (such as hybridization, inbreeding depression, outbreeding depression,

etc.) have been discussed extensively in recent publications (Hindar et al. 1991, Waples 1991,

Busack and Currens 1995, Campton 1995, Waples 1995, Allendorf and Waples 1996, NRC 1996,

Waples 1999).

Genetic risks are not considered in detail in the present document. Rather, the major

focus is on potential ecological and behavioral effects of differing artificial production strategies

as they relate to stocks within:

- the ESU (evolutionarily significant unit) of spring/summer chinook (O. tshawytscha) in the

Snake River, and

- the ESU of steelhead (O. mykiss) in the Upper Columbia River.

The document is divided into four major sections. Following this brief Introduction,

Section II outlines the general differences in morphology, behavior, life history, and survival

imposed by artificial production strategies on hatchery fish compared with wild fish. Section III

details the effects of artificial production releases (supplementation) on wild fish population

abundance, competitive social interactions, predation, health, and migratory behavior. Section

IV draws some overall conclusions and makes recommendations. It includes summary tables

detailing an assessment of the potential effects of artificial production strategies on population

abundance of wild spring/summer chinook and steelhead in their respective ESUs.
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II. COMPARISON OF HATCHERY AND WILD SALMON

BIOLOGY

Introduction

Salmon culture at Pacific Northwest hatcheries is conducted in a plethora of

configurations of rearing vessels running the continuum from earthen ponds through small vats,

circular tanks, and large production raceways. All conventional rearing techniques, except

perhaps earthen ponds, share the common feature of being geared toward mass-production under

conditions which are best described as ‘unnatural’.

Maynard et al. (1995) describe hatchery conditions as, “Groups of fish ... reared in the

open, over uniform concrete substrates; conditioned to minimal raceway flow regimes; provided

no structure in which to seek refuge from water current, predators, or dominant cohorts; held at

high, stress-producing densities; surface fed; and conditioned to approach large, moving objects

at the surface.” Similarly, Reisenbichler and Rubin (In press) state, “Seemingly the only

similarities in hatchery and wild environments for salmonids are water and photoperiod.” It is

therefore not surprising that fish reared under these ‘conventional’ regimes are markedly

different from their wild counterparts in behavior, morphology, survival, and reproductive ability.

Some of the major differences between hatchery and wild salmonids are summarized in Table1,

and described in detail in the following pages.

Table 1. Relative differences between wild and hatchery reared salmonids.
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Survival

Although the protective nature of hatchery rearing increases egg-to-smolt survival (see

overviews of Leitritz and Lewis 1976, Piper et al. 1982, Pennell and Barton 1996, etc.) the postrelease survival of cultured salmonids is often considerably lower than that of wild-reared fish.

Studies during the 1950s and early 1960s were the first to document that the survival of hatcheryreared fish released in the natural environment is often significantly lower than that of their wildreared counterparts. Over a period of several years Greene (1952) recovered wild brook trout

fingerlings at rates 8.4 to 18.6 times higher than those of hatchery fingerlings planted in the same

lake. Salo and Bayliff (1958) found the survival of seaward migrating smolts of wild coho

salmon was three times better than that of their hatchery-reared counterparts. Reimers (1963)

found that 30% of rainbow trout planted in streams died within 44 days of release, while only

one wild trout died during the same period.

In some of these early studies it is not clear if survival differences between hatchery- and

wild-reared fish were primarily the result of genetic or environmental differences. The work of

Miller (1953) suggests both genetic strain and rearing environment play a role in the post-release

survival of hatchery produced fish. He found that only 5% of hatchery-reared cutthroat trout

planted in streams survived a year after release, compared with 46% of the transplanted wild

trout during the same period. Stream-reared hatchery fish had an intermediate survival value of

17.2%.

Research conducted since the mid-1960s suggests that poor post-release survival of

hatchery fish represents both adaptive differences between hatchery and wild populations, and

environmental differences between hatchery and natural rearing environments. When Mason et

al. (1967) compared survival of wild, domestic, and hybrid strains of brook trout, reared from

fertilization to parr under identical environmental conditions, they found that each pure strain

was best adapted to its own rearing environment. In their study, wild brook trout showed the

poorest growth and survival in the hatchery, but 10.2% survived when released into test stream

sections compared with only 3.6% survival for hybrid trout and 0.7% for domestic trout.

Apparently the rearing environment also affected post-release survival, as almost twice the

number of naturally-reared wild fish (19.7%) survived compared with hatchery-reared wild fish

(10.2%) after both were transplanted into test stream sections.

Fraser (1981) stocked equivalent numbers of domestic, wild, and domestic/wild hybrid

strains of brook trout in nine lakes. In six of the lakes he recovered wild fish at a rate two to four

times above that of domestic fish. In the three other lakes the recovery rate was similar for all

three strains. In a subsequent study (Fraser 1989) he concluded that wild and hybrid strains

established self- perpetuating breeding populations more frequently than pure domestic strains

released into the same lakes.

LaChance and Magnan (1990a, 1990b) found that wild and hybrid strains of brook trout

survived in lacustrine habitats better than a domestic strain planted in the lake during the same

period. All three strains were reared from eggs in the hatchery before being released into lakes,

and were influenced by the presence of intra- and inter-specific competitors.
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Poor survival of both hatchery strains in natural environments and wild strains in hatchery

environments suggests that selection, in many cases, has resulted in the genetic divergence of

hatchery populations from their wild ancestors. Reisenbichler and McIntyre (1977) examined the

growth and survival of hatchery, wild, and hatchery-wild hybrid strains of steelhead trout reared

from eggs under identical conditions in streams and a hatchery pond. Again, each pure strain

was best adapted to its environment, with more wild fish surviving in the stream and more

hatchery fish surviving in the hatchery. Hybrid fish surviving in the stream grew faster than their

wild counterparts, whereas hatchery fish grew faster in the hatchery pond.

In studies by Chilcote et al. (1986) and Leider et al. (1990), naturally spawned and reared

offspring of hatchery steelhead experienced greater mortality than offspring of wild steelhead

during all three major life history stages, e.g., egg-to-fry, fry-to-smolt, and smolt-to-adult. These

studies strongly suggest that adaptive differences occurred between hatchery and wild

populations in a relatively short evolutionary time period.

Foraging Behavior

Starvation is a primary cause of poor post-release survival in hatchery fish. Miller (1952)

believed the high mortality of hatchery cutthroat trout in his studies was due to starvation.

Hochachka (1961) reached a similar conclusion after examining the stomach contents of wild

and hatchery trout 28 days after release into a stream: the latter had less food in their stomachs

and lower mean body weights. Reimers (1963) concluded that the continuous and eventually

lethal weight loss he observed in hatchery trout resulted from their inability to compete or forage

in the wild.

Sosiak et al. (1979) concluded that hatchery-reared parr of Atlantic salmon foraged less

effectively than naturally reared parr for at least 2 months after being released into streams. The

wild parr consumed more food and a greater diversity of organisms than their hatchery

counterparts. In addition, the wild parr fed primarily on benthic organisms while the hatcheryreared fish concentrated on terrestrial and winged insects, suggesting that hatchery parr continue

to feed at the surface even after release. O’Grady (1983) also found that hatchery-reared trout ate

less than their naturally reared counterparts immediately after release.

Myers (1980) found that hatchery chinook salmon, examined shortly after their release,

were inept foragers compared with wild fish. The average ratio of stomach content to body

weight was more than three times greater in wild fish (5.7%) than in hatchery fish (1.7%). In

addition, newly released hatchery fish appeared to be non-selective feeders; 67% of their stomach

contents was indigestible algae compared with 84% of anchovy in the stomachs of wild chinook

salmon. The dietary composition of their stomach contents only converged after extended

residence in the estuary. This suggests that hatchery fish eventually learn to forage more

efficiently, or that only the efficient foragers remain to be sampled after inept foragers starved.

At least two studies suggest that foraging differences between wild and hatchery strains

of salmonids are partially innate. Mason et al. (1967) found that wild, hatchery, and hybrid
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strains of brook trout, reared from eggs in identical environments, exhibited different foraging

behaviors. Wild-strain fish fed only from the bottom, hatchery fish readily fed at the surface, and

hybrids exhibited intermediate behavior. Uchida et al. (1989) found innate differences in the

foraging behavior of wild and domestic strains of the larvae of ayu reared under identical

conditions. Again, the hatchery strain readily fed from the surface while the wild strains would

not.

Other studies suggest foraging differences between wild and hatchery-reared fish are

affected by conditioning. Johnson and Ugedal (1986) released hatchery-reared brown trout into a

lake. Initially the fish fed on surface-dwelling prey but after several weeks of residency they

were feeding on natural prey. In later analyses the diets of both wild and hatchery-reared trout

were similar. The percentage of inedible and energetically unprofitable items eaten by the

hatchery-reared trout decreased over time, suggesting that foraging efficiency can be improved

with experience.

Regardless of rearing environment or strain, the experimental salmonids used by Bryan

(1973) and Paszkowski and Olla (1985) always preferred live prey to commercial pellet diets.

This suggests that prey movement is a primary cue stimulating prey attack behavior. Bryan

(1973) found rainbow trout had an innate preference for live prey over pellets, but he also

determined that fish developed weak and readily reversible training biases for familiar foods over

novel foods. He concluded that cues other than familiarity were probably important in the

natural foraging behavior of trout. Paszkowski and Olla (1985) demonstrated that experience

with live prey improved the foraging performance of hatchery-reared coho salmon smolts

challenged to feed on Cragon spp. However, even after repeated strikes, some smolts were never

able to ingest large individuals even though they were within suitable size limits. Subsequently,

Maynard et al. (1996b) documented improvements in foraging efficiency after live food training

for chinook salmon.

In summary, all these studies on foraging behavior indicate that live food supplementation

may be useful in training young salmon to handle live prey more efficiently. It may also prevent

the fish developing dietary preference against natural feeds.

Social Behavior

Many studies have indicated that the hatchery rearing environment can profoundly

influence social behavior of Pacific salmon, and social divergence of cultured fish may begin as

early as the incubation stage. For example, the lack of substrate and high light levels which may

occur in the hatchery incubation environment can induce excess alevin movement, lowered

energetic efficiency, reduced size, and aberrant behaviors (Poon 1977, Leon and Bonney 1979,

Mighell 1981, Murray and Beacham 1986, Fuss and Johnson 1988). Food availability and

rearing densities in hatcheries far exceed those found in natural streams, and may contribute to

differences in agonistic behavior between hatchery- and wild-reared fish (Symons 1968,

Bachman 1984, Uchida et al. 1989, Grant and Kramer 1990, Olla et al. 1990, Berejikian 1995a,
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Olla et al. 1998). Hatchery rearing environments may also deprive salmon of the psycho-sensory

stimuli necessary to develop anti-predatory behavior fully (Olla et al. 1998).

Juvenile salmonids establish and defend foraging territories through agonistic contests,

and levels of aggression have been positively associated with dominance in these contests

(Egglishaw 1967, Fenderson and Carpenter 1971, Holtby et al. 1993, Berejikian 1995a). Both

Fausch (1984) and Metcalfe (1986) found that dominant individuals tended to obtain more

energetically profitable stream positions; hence, fish with relatively high levels of aggression

may be expected to have a competitive advantage over less aggressive fish.

Evidence suggests that, although agonistic behavior has a genetic basis, it can be

profoundly influenced by environmental (rearing) conditions. In comparative study of hatchery

and naturally reared Atlantic salmon of common ancestry, Fenderson et al. (1968) and Fenderson

and Carpenter (1971) found that agonistic activity of hatchery-reared fry was greater than that of

naturally reared fry over a range of rearing densities, while wild fry were more aggressive at only

the lowest densities. Bachman (1984) noted that hatchery-reared brown trout were equally

successful in agonistic contests against wild brown trout in a natural stream, but hatchery trout

abandoned their territories and moved more frequently among territories than did wild trout.

Both Symons (1968) and Olla et al. (1990) deduced that an internal motivation, such as hunger,

appeared to be positively associated with aggression, while Grant and Kramer (1990) concluded

that territorial hierarchies can break down at high social densities.

Levels of aggression appear to differ between domesticated and wild populations,

suggesting that genetically based changes can occur in a hatchery population after only a few

generations of culture. Offspring from a domesticated brook trout population demonstrated

higher levels of aggressive activity than offspring from a wild population when both populations

were reared under similar hatchery conditions (Moyle 1969). Swain and Riddell (1990) observed

that newly emerged, ‘socially-naïve’ coho salmon fry from two domesticated populations

demonstrated significantly greater levels of aggression than fry from geographically proximate

wild populations. In a companion study (Riddell and Swain 1991) aggression in coho salmon

was found to be a heritable trait. The results of these studies demonstrate a genetic basis for the

differences found between hatchery and wild populations.

Berejikian (1995b) suggested that newly emerged fry from a wild steelhead population

initially had higher levels of aggression than fry from a locally derived, domesticated population.

However, after several months of rearing, offspring of domestic steelhead were significantly

more aggressive than offspring of wild steelhead when both were reared in food-limited and/or

low-density environments (including a natural stream channel).

In summary, juvenile salmonids from domesticated and wild populations appear to

demonstrate adaptive differences in agonistic behavior, and the behavioral development of

domesticated and wild fish appears dependent upon their rearing environment.
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Habitat Preference

Cultured and naturally reared salmonids are known to respond differently to habitat; in

most cases wild fish utilize both riffles and pools in streams, while newly released hatchery fish

primarily use pool environments similar to their raceway rearing experience. Using an artificial

stream channel, Dickson and MacCrimmon (1982) observed that hatchery-reared Atlantic salmon

parr persistently held positions higher in the water column than naturally reared parr from the

same parent population. This indicated that the hatchery rearing environment caused a shift in

habitat preference. In a study by Bachman (1984) hatchery brown trout released into a stream

occupied foraging sites which were less energetically efficient than those used by wild trout, even

though they frequently displaced wild trout from their sites. The hatchery trout also had higher

energy costs as they constantly moved from site to site.

Hatchery strains are typically more surface-oriented than wild strains. The cultured

Atlantic salmon parr observed by Sosiak (1978) swam closer to the surface and spent more time

in contact with the surface than wild parr. Similarly, Mason et al. (1967) found hatchery strains

of trout were more surface-oriented than wild strains reared from eggs in the same environment.

Uchida et al. (1989) observed that larvae of wild ayu were found at greater depths than hatchery

larvae reared and observed in the same environment.

In summary, with regard to habitat preference, most of the innate surface orientation of

hatchery fish is probably an adaptive response to the common culture practice of introducing

food at the surface of the water.

Response to Predators

Predation is a major factor affecting the post-release survival of hatchery-reared fish.

Experimental evidence indicates that hatchery strains of salmonids have increased risk-taking

behavior and lowered fright responses compared with wild fish. Surface feeding may condition

hatchery fish to approach the surface of the water column (Uchida et al. 1989, Maynard et al.

1995, Olla et al. 1998), and this behavior increases their vulnerability to predators. Studies by

Donnelly and Whoriskey (1991), and Maynard et al. (1996a) have also attributed increased

vulnerability to predators to their decreased camouflage (crypsis) in stream environments caused

by the monochrome concrete surroundings in the hatchery. The losses are significant. Ellis and

Noble (1960) estimated 12-30% of the juvenile chinook salmon released from a hatchery on the

Klickitat River were preyed on in the 40 miles between the hatchery and the Columbia River.

Furthermore, the predators are selective. In the Chehalis River hatchery coho salmon are more

vulnerable to predation by squawfish than wild coho salmon, as squawfish rarely feed on salmon

smolts until the hatchery smolts are released (William Waknitz, NMFS, pers. commun., July

1991).

Other evidence indicates that hatchery strains are more vulnerable to predation than wild

strains. Johnsson and Abrahams (1991) observed that offspring of crosses between wild
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steelhead and hatchery-strain rainbow trout were more willing to forage in the presence of a

predator, an adult rainbow trout, than offspring of pure wild steelhead crosses. However, the

hybrids were no better at avoiding predation in 15-second trials.

Increased risk-taking behavior without an increased ability to avoid predators may have

put domesticated rainbow trout at greater risk than wild steelhead. In several experiments by

Berejikian (1995b), the fry of wild steelhead from the Quinault River were better able to avoid

the prickly sculpin than fry from a locally derived hatchery population. The fry were reared

under laboratory conditions so that behavioral differences between the two populations were

probably genetically based.

Fish which approach the surface of the water column have been shown to increase their

risk to avian predators (Kramer et al. 1983). Therefore, the surface orientation of cultured fish,

and their tendency to approach large moving objects at the surface, exposes them to the predators

such as herons, mergansers, and kingfishers, etc. Mason et al. (1967) reared both hatchery and

wild strains of brook trout in raceways and observed that the wild strain fled humans while the

hatchery strain trout approached them. The tendency of hatchery fish to approach large moving

objects is partly innate.

Patten (1977) and Olla and Davis (1989) have shown that fright responses are at least

partially a conditioned behavior. In similar studies with cultured cod, Nordeide and Svassand

(1990) observed they approached larger cod more slowly and less closely than wild cod cohorts

did. The investigators speculated that, as cultured fish experienced more cannibalism in their

artificial rearing environment, they were more conditioned to be cautious with larger cod.

In laboratory trials Bams (1967) observed that naturally reared sockeye salmon fry were

less susceptible to predators than hatchery-reared fry. This susceptibility was inversely related to

the proportion of time alevins were reared with gravel in their incubation baskets. In these

studies, the vulnerability to predation was size-related and, as the fry reared in baskets without

gravel were smaller, he concluded that the rearing environment was responsible for increased

predation on hatchery fry.

Morphological and Physiological Differences

Taylor and Larkin (1986) developed a discriminate function model using morphometric

measurements to distinguish between hatchery and naturally reared coho salmon parr. In

addition to having a different shape, juvenile hatchery reared fish were less variable than

naturally reared parr. They concluded that these differences were under environmental rather

than genetic control. Bams (1967) and Taylor and McPhail (1985) indicated that hatcheryinduced morphological differences affected swimming speed and therefore the ability to escape

predators.

Jarvis (1990) determined that predator-naive Atlantic salmon smolts facing a new

osmotic environment suffered more severe physiological stress when predators were present than
10

did smolts previously exposed to predators. These, and other morphological and physiological

divergences between natural and hatchery-produced fish may significantly influence post-release

survival.

Reproductive Behavior

Hatchery practices have altered reproductive behavior by relaxing selection pressure on

secondary sexual characteristics used in breeding competition in the wild, while increasing

selection pressure on primary sexual characteristics. Fleming and Gross (1989) concluded that

relaxation of breeding competition in the hatchery has led to the evolution of female coho salmon

with less well developed kypes and breeding colors than their wild counterparts. The hatchery

strains studied expended energy in developing larger and more numerous eggs than equivalent

size members of the wild stocks from which they were derived.

Fleming and Gross (1992) found that the reproductive behavior of male coho salmon

differed between hatchery and wild strains. Hatchery-strain males allowed to spawn naturally

were less aggressive and generally less active than wild-strain males. It appeared that the

relaxation of competition among males for access to females in the hatchery, coupled with the

possibility of sperm competition which may have occurred as a result of hatchery spawning

techniques, resulted in hatchery-strain males investing disproportionate amounts of energy

towards testes production. The authors concluded that investing energy for sperm production,

rather than in secondary sexual characteristics that aid in obtaining access to females, was only a

disadvantage to hatchery-strain males spawning naturally in the presence of wild-strain males.

Similarly, Berejikian et al. (1997) observed that adult captive reared coho salmon were less

reproductively fit than their wild counterparts. In the absence of competition, hatchery-strain

males would probably breed as successfully as wild-strain males.

Either inadvertently or intentionally, hatcheries usually develop strains which spawn at

different times than their ancestral stocks. Studies by Salo and Bayliff (1958), Ricker (1972),

and Hager and Hopley (1981) have all demonstrated a genetic basis for spawning time.

Hatcheries often inadvertently select for early run timing by spawning a disproportionately higher

percentage of earlier returning fish. From a management perspective, the advantage of this

temporal separation is that it minimizes interbreeding between domestic and wild stocks, which

is generally believed to be harmful to wild populations (Reisenbichler and Rubin, In press). The

disadvantage is that the progeny of feral-spawning domestic strains emerge prior to peak

abundance of natural aquatic invertebrate blooms, and thus suffer high mortality rates (Nickelson

et al. 1986).

Conclusions

Artificial culture environments condition salmonids to respond to food, habitat,

conspecifics, and predators in a different manner than do fish reared in natural environments.
11

Present culture techniques also alter selection regimes, which may result in genetic divergence

between hatchery and wild populations. The phenotypic differences observed between cultured

and wild fish are both genetically and environmentally controlled. The affects of hatchery reared

fish on the population abundance of wild fish are discussed in Section III which follows.
12
13

III. IMPACTS OF ARTIFICIAL PRODUCTION

RELEASES ON WILD FISH

A. Production Strategies

1. Supplementation Projects

The use of hatcheries to supplement wild stocks is a controversial topic in the Pacific

Northwest. Unfortunately the information on supplementation projects is confusing. Over 60

separate supplementation projects have been proposed yet they appear to use different definitions

of supplementation, different interpretations of objectives, and different evaluations of success.

Smith et al. (1985) defined supplementation as the release of fish from hatcheries

at locations away from the hatchery to increase natural production in streams determined

to be seeded or used at less than optimal levels. Miller et al. (1990) defined it as the

planting all life stages of hatchery fish to enhance wild/natural stocks of anadromous

salmonids. Steward and Bjornn (1990) were the most specific, describing it as the

provision of surplus harvests of fish from stocks which may not otherwise naturally

produce sufficient fish to meet the demand from fishermen. Management opportunities

range from rebuilding threatened or endangered wild stocks to bolstering already selfsufficient natural runs. Hatchery fish used to supplement wild stocks of salmonids are

stocked at egg, fry, fingerling, smolt, and adult life-stages.

The definition used in the Regional Assessment of Supplementation Projects (RASP 1992) was

more pertinent to the relevance of ecological and genetic factors in the milieu of the species

involved. Consequently the RASP definition is adopted by the contributors to this document,

viz:

Supplementation is an attempt to maintain or increase natural production while

maintaining the long-term fitness of the target population, and keeping the

ecological and genetic impacts on non-target populations within specified

biological limits.

Using this definition, a successful supplementation project would have to meet the following

three criteria:

• Did the project maintain or increase natural production?

• Did the project maintain the long-term fitness of the target population?

• Did the project keep the ecological and genetic impacts on non-target population within

specified biological limits?

A project which does not meet all three tests must be judged to have failed.
14

A more practical definition of supplementation has been given by Cuenco (1993),

viz:

Supplementation is the stocking of fish into natural habitat to increase the

abundance of naturally reproducing fish populations.

Even though the RASP (1992) definition of supplementation is probably the most widely

accepted, in reality, this simple definition by Cuenco (1993) is what is actually implied.

Because of variability in year-to-year salmon returns and field sampling

limitations, defining the contribution of supplementation to wild populations is not a

simple task. The relationship of genetic changes in target and non-target populations to

population fitness is a subject of controversy. There is still significant ambiguity

regarding both definitions as it is not specified whether the increase in population must

continue after supplementation ceases.

The objectives of supplementation

The objectives of supplementation are threefold. These are conservation, transplantation,

or reintroduction. Their general parameters are summarized in Table 2.

In the Pacific Northwest most supplementation projects have the objective of

conservation or reintroduction of a specific anadromous salmon stock. The transplantation of

anadromous salmon either within or outside their natural range is not now a common objective.

The use of supplementation

Cuenco (1993, 1994) provided guidelines for deciding when to initiate supplementation

of a population. He believed four conditions were required:
15

• The wild populations were declining

• Sufficient spawning habitat was available and underused

• Other actions which could address the cause(s) of population declines could not be

implemented in a timely manner

• Hatchery technology and facilities were available to increase stock productivity above

replacement

The decision to use supplementation is complex. This is evident from a brief review of

some special cases. For example, the potential for supplementation to increase the population of

fish spawning in the wild depends strongly on the stock productivity. Stock productivity is the

number of adult fish which one generation contributes to the next. According to Cuenco (1994),

a stock productivity <1.0 means the population is decreasing; >1.0 means it is increasing, and

=1.0 means it is stable. For large populations, the stock productivity can decline <1.0 for

relatively long times without the population going extinct. Small populations have less time.

Salmon populations are characterized by extreme variation in year-to-year adult returns, and it is

not uncommon for healthy populations occasionally to experience stock productivity < 1.0.

Under most conditions, if stock productivity for the wild stock is consistently less than

the replacement, then a supplementation program will not result in a self-sustaining wild

population. The population may increase during the supplementation phase due to higher

contribution from the hatchery program, but when supplementation is terminated the population

will continue to decline because the reasons for the low survival have not been corrected.

There is one potential exception to this result. Due to predatory and competitive impacts

a population can be ‘trapped’ in a lower stability region (Peterman 1977) or extinction vortex

(Soulé 1986). Supplementation can increase stock productivity by itself if it is large enough to

move the population into a high stability region. In this situation the size of the supplementation

project and release protocols are critical; for example, if heavy predation is a cause of low

density then release of larger groups of fish would increase survival (Fresh and Schroder 1987;

Supplementation Work Group 1999).

When stock productivity is consistently <1, a supplementation program must be viewed

as an interim measure to maintain a population temporarily until environmental conditions

change or anthropogenic impacts are corrected. While supplementation may have some negative

impacts on wild fish these are preferable to extinction.

Supplementation is not needed for a depressed stock with productivity >1, as it should be

able to recover on its own. A supplementation program may increase the population size above

some critical level more rapidly and therefore accelerate recovery.
16

The risk in using supplementation

A generalize decision tree for supplementation is presented in Figure 1. The first

decision is whether or not to use supplementation. When the probability of extinction is high,

the choices may be limited to:

(a) starting a supplementation program,

(b) starting a limited captive brood program to maintain genetic integrity (Flagg and

Mahnken 1995), or

(c) letting the population go extinct.

But, as noted previously, there is significant uncertainty in the predication of extinction

risk. Therefore, the basic trade-off in the start of a supplementation program is balancing the risk

of extinction (outcome 2 in Figure 1) against a decrease in the long-term fitness of the population

(outcome 14).

There is a significant difference of opinion of the risk and benefits of supplementation

(Sterne 1995). One view favors widespread use of supplementation while another favors reduced

hatchery intervention. The former is influenced by the desire to recover the runs as quickly as

possible (Sterne 1995), while the latter is concerned that attention is diverted from the real issues

behind population decline and the potential impacts of hatchery programs on the long-term

fitness of the populations. Waples (1991) noted that the potential impact of hatchery releases on

wild stocks included direct genetic impacts, indirect genetic impacts, and ecological impacts.

The controversy is fueled by the fact that many proclaimed impacts of supplementation

are not based on experimental work with Pacific salmon, but with other species, and even plain

theory. This is because the experimental work needed to confirm the genetics impacts of

salmonid supplementation are extremely costly and may require 5-10 years or more to complete.

The dynamic of a hypothetical supplementation project is illustrated in Figure 2 as a

function of time. The overall project is divided into three time periods:

(1) pre-supplementation with a declining population,

(2) supplementation, and

(3) post-supplementation.

The figure does not include all the different outcomes presented in the supplementation decision

tree (Figure 1). This figure is the basis for discussion of the general characteristics of a

supplementation project.

The statistics of supplementation are quite complex and obviously specific to any project.

Nonetheless some fundamental questions about supplementation projects in general need to be

addressed. For example:
17

Figure 1. Generalized decision tree for supplementation.
18

• How long does supplementation have to be conducted before the population increases?

• How long does supplementation have to be conducted before the population increase can

be detected (Decision 5, Figure 1)?

• How long does supplementation have to be conducted before impacts on fitness of the

target population or ecological and genetics impacts on non-target stocks can be detected

(Decision 7)?

• How long does the supplementation project have to last (Decision 9)?

• After supplementation stops, how long is needed to determine if a population is selfsustaining (Decision 11)?

Figure 2. Dynamics of a hypothetical supplementation project.

In general, the success of a supplementation project can only be determined after the

planting of hatchery fish has stopped (Decision 11). A successful supplementation program

should result in a self-sustaining population. In the special case where the stock productivity is

consistently <1 it could also be argued that an increase in population can be considered a success

(Decision 5). In this case the alternative to not supplementing the stock is extinction.
19

The length of time to detect a statistical change in escapement depends on the variability

of the escapement, the accuracy of the escapement estimates, and the degree of certainty needed

(Peterman 1990, Korman and Higgins 1997). Based on a Monte Carlo simulation Korman and

Higgins (1997) found that there was generally less than a 50% chance of detecting a population

response unless the population change was large (more than a twofold increase) or the posttreatment monitoring period was long (>10 years). Statistical power was improved by increasing

the precision of the escapement estimate. Lichatowich and Cramer (1979) found that 20 to 30

years of escapement data may be needed to produce an 80% chance of detecting a 50% change.

For discussion purposes it is assumed that 10-15 years of supplementation and 10-15

years of post-supplementation monitoring will be needed. Therefore, the total time required to

evaluate a project is 20-30 years. Due to the length of time needed for statistical testing it may be

difficult to differentiate the impacts of supplementation from those arising from changes in the

freshwater or ocean conditions. This issue as it relates to genetic monitoring has been reviewed

by Hard (1995).

An evaluation of some previous supplementation projects

A number of past supplementation projects were judged to be successful within their

definition of the term and their specific goals. The individual objectives of these projects were

primarily introduction, and they were frequently associated with the removal of upstream

barriers. Those successfully resulting in self-sustaining populations are summarized in Table 3.

Table 3. Supplementation projects resulting in self-sustaining populations.

It is relevant to note here that the historic long-distance transplants of salmonids, for

example, to South Africa and New Zealand, etc., are not considered supplementation projects

within this section. Information on these inter-basin programs can be found in Withler (1982)

and Fedorenko and Shepherd (1986).

There are two important listings of successful supplementation projects. Miller et al.

(1990) reviewed 316 supplementation projects, of which only 26 fitted their definition of

supplementation. Twenty-five of these projects were considered a success by the project
20

managers, but only 18 were subjected to quantitative evaluation. The authors concluded that

none of the evaluated projects had rebuilt natural runs to self-sustaining levels. Using their more

restrictive definition of supplementation, RASP (1992) concluded that none of these projects

qualified as supplementation projects at all. At issue was the evaluation of the genetic impacts of

supplementation on the population itself. Therefore, RASP concluded, supplementation had

neither been attempted nor evaluated.

Chilcote et al. (1986) found the reproductive success of hatchery fish spawning in the

wild was only 28% of the value for wild fish. The basis for this reduction in reproductive

success was thought to be selective pressures from conventional spawning or rearing protocols.

Reisenbichler and McIntyre (1977) planted eggs or un-fed fry in natural streams from

hatchery x hatchery, hatchery x wild, and wild x wild crosses. In the wild, wild x wild crosses

had the highest survival.

Nickelson et al. (1986) found that stocking of large pre-smolts contributed little to

rebuilding the population. The hatchery population used in this work spawned much earlier than

the wild fish (probably due to hatchery practices). When these fish returned to spawn their eggs

and emergent fry were subjected to high flows and scour. They concluded that fish used for

supplementation should be the same size as wild fish and spawn at the same time.

Reisenbichler (1988) found that the further coho salmon were transferred, the lower their

smolt-to-adult ratio (relative to the smolt-to-adult ratio at the release hatchery). Therefore, local

broodstock is much more desirable than out-of-basin broodstock.

There are many supplementation projects currently being conducted all over the Pacific

Northwest. Some major ongoing projects are listed in Table 4. However, those with adequate

monitoring and evaluation programs, or have operated long enough to produce results, are

surprisingly small in number. Information on three current supplementation projects is presented

in Appendices A-C.

Fundamental assumptions of supplementation

Supplementation from an ecological point of view is based on two assumptions:

• The production of smolts is limited by one or more of the following reasons: (a)

escapement of adults to the basin, (b) spawning area, (c) egg to alevin survival, or (d)

alevin to smolt survival

• There is the carrying capacity (space and food) for additional fish in the basin

If either assumption is incorrect then there is no reason to believe that supplementation will

increase the number of salmon spawning in the wild.
21

Table 4. Major ongoing supplementation projects.

Assessing carrying capacity of a stream is more difficult than is generally assumed.

RASP (1992) noted, “One cannot assume that a stream that previously supported a now-depleted

abundant and productive salmon population has vacant habitat equivalent to the difference

between the past and present populations.” Even in the most isolated headwaters the carrying

capacity may be significantly less than historical levels due to interventions, such as mining,

logging, construction of splash dams, elimination of beaver dams, removal of other channel

obstructions, and grazing. These have all contributed to changes in channel morphology (water

depth, complexity, etc.), water temperature, water flow, and energy flow. Many of these changes

may have occurred more than a century ago.

Returning adults are important contributors of nutrients and energy to the spawning and

rearing conditions in the freshwater environment. First, during redd-building they disturb the

gravel. Although this may result in egg loss from older redds, removal of fine sediments

improves overall egg survival (McNeil and Ahnell 1964) and displaced salmon eggs are an

important energy input to the stream (Kline et al. 1995). Second, if the adults are not directly

consumed by predators, the disintegrating carcasses are absorbed in one of four ways (NRC

1996). They may be fixed autotrophically by aquatic plants and subsequent transfer through

periphyton-based food webs; fixed heterotrophically by bacteria and fungi and transfer through

decomposer-based food webs; taken up abiotically by sorption within the stream substrate, and

consumed directly by fish and other aquatic organisms. Cederholm et al. (1989) concluded that

the ability of streams to retain carcasses has been greatly reduced by removal of low water dams,

rocks, and reducing the complexity of the river channel and riparian zone. The benefit of large

numbers of adult spawners in excess of those needed for alevin production has not been

recognized by salmon harvest managers.
22

The importance of carcasses in the nutrition of salmon has been illustrated recently by

Kline et al. (1995) in Alaska, and Larkin and Slaney (1997) in British Columbia. For some

stocks, up to 91% (mean = 61%, range 27-91%) of the nitrogen in the smolts was of marine

origin, i.e. carcasses and eggs. The availability of carcasses and eggs to pre-smolts may be

especially important in winter and early spring when other food is scarce.

Another consequence of fewer returning adults is the decrease in quality of the gravel

with the accumulation of sediments. Interventions, such as logging, farming, and construction,

continuously add to input of sediments. In addition, the body size of many stocks has been

declining due to selective pressures, hatchery practices, declining ocean productivity, densitydependent affects of large hatchery releases, or a combination of any of these factors (Weitkamp

et al. 1995). Smaller-sized fish produce fewer eggs and are less able to make long spawning

migrations. Van den Berghe and Gross (1984) found that nest depth was strongly correlated with

female size, therefore eggs from smaller females are at more risk from scour and redd superposition by later spawners.

The solution, however, is not planting larger numbers of fry or fingerling. This in itself

will not result in a significant increase in adult returns if the cumulative lack of spawners and

carcasses over time has destroyed the productivity and base of the food chain in the inter-gravel

spawning and rearing environment. Consequently one recent supplementation project in the

Willapa River area included carcass addition to support stream-side egg boxes. However, it is

likely this practice will have to be repeated over many years to develop the productivity to

historic levels. Unfortunately, the necessary background information to identify the levels of

intervention is typically lacking.

Finally, supplementation projects have been largely viewed as hatchery projects and have

been staffed with hatchery or evaluation biologists. In practice they are multi-disciplinary

projects, requiring specialists in fields such as benthic ecology and food chain productivity.

Practical problems of supplementation programs

Supplementation programs have evolved from traditional production hatchery programs.

The full impact of the change in objectives from production to supplementation has not been

reflected in any real changes in hatchery operations or facilities. Some of the most serious

practical problems are discussed below.

(i) Location of the weir - Selective collection of broodstock is a serious problem in many

supplementation projects. Bugert (1998) listed six criteria for effective broodstock collection.

These were:

• An ability to collect only the targeted populations for supplementation

• A capability to capture all age-classes of the target populations without injury or stress

• An equal collection efficiency during both peak and nadir of the hydrograph

• An ability to sort marked (hatchery) and unmarked (natural) salmonids
23

• Unimpeded passage of non-targeted species and populations and, at times, most of those

fish in the targeted populations

• Compatibility with federal designated ‘wild and /or scenic’ rivers (PL 90-542,82)

Some of these criteria are in conflict, especially for high-elevation and high-gradient

streams. For example, a weir which meets the first four criteria is likely to impede the passage of

non-target fish, and may not be compatible with ‘wild and scenic’ legal restrictions.

Consequently, Bugert (1998) recommended less reliance on a single-objective, single-location

collection strategy.

(ii) Location of release sites - Acclimation ponds are widely used with supplementation projects

even though there is little data to show any cost-effectiveness. Bugert (1998) listed four criteria

for the use of acclimation ponds:

• The site must be accessible in early spring (and winter if possible) to transfer fish from

the hatchery. Continuous access is required to feed and maintain the health of fish,

prevent vandalism, and remove debris or slush accumulations at pond intakes

• The site must be far upstream to ensure proper homing and spawning distribution within

the supplemented watershed

• The site must often use river water which is non-consumptive, and preferably gravity-fed

as power may not be available. Supplemental groundwater may be required to temper

river water in winter and spring if ice accumulation is a problem

• The site must meet development standards of ‘wild and/or scenic’ rivers (PL 90-542,82)

and any local jurisdictions

Again some criteria are in conflict. The first, for example, favors acclimation sites low in

the basin while the second favors those high in the basin. Electrical power lines for pumped

surface water or groundwater are usually more available low in the basin, and it is always easier

to site a facility with a pumped water supply.

(iii) The life history patterns of released fish - In cases where all the salmon have been

extirpated from a basin then a donor stock has to be used for supplementation. Reisenbichler

(1988) showed that, for coho salmon, the transfer distance is inversely related to smolt-adult

survival. Therefore, nearby local stocks are preferred to those introduced from the edge of the

basin, or even greater distances.

At many hatcheries spawning is ended once the required number of eggs for that stock is

obtained. This practice results in the selection for early spawning fish which, in some cases, can

advance the mean spawning time by 2-3 months (Flagg et al. 1995b). Nickelson et al. (1986)

found that for production operations this advance had little impact on post-release survival, but if

the fish were used for supplementation then their progeny might be exposed to adverse

environmental conditions. Therefore this resulted in little contribution to the wild population.

As hatchery fish are typically larger than wild fish, because of (a) selection for the early portion

of the run, (b) use of warmer groundwater for incubation and early rearing, and (c) artificial

feeds, the authors concluded that larger hatchery fish can dominate smaller wild fish causing
24

their emigration or death. They recommended that hatchery fish used for coho supplementation

should be released at a size similar to the local wild fish. In addition, the life history patterns of

the hatchery fish should be similar to the wild stock.

In summary, with reference to all these case studies, the following conclusions might be

drawn about ‘successful’ supplementation projects:

• There are examples of successful supplementation projects which have resulted in selfsustaining populations. On the other hand more examples have not.

• The impacts on fitness of the targeted stock, and the genetic and ecological impacts on

non-targeted stocks, have been largely ignored.

• The level of monitoring and evaluation has not been adequate in many of the past and

current supplementation projects.

• It is impossible to determine if a self-sustaining population has resulted because hatchery

fish are still being released.

• Until 10-15 years of post-release data are collected, the use of supplementation as a

management tool to maintain or increase natural production cannot be fairly judged.

Supplementation Models

There have been a number of attempts to model the impact of supplementation on

population dynamics (Byrne et al. 1992; Cuenco, 1994; RASP, 1991) and genetics (Hard, 1995;

Waples & Do, 1994).

A generalized model of combined stock abundance and productivity of a supplementation

project is presented in Figure 3a for year 1 of an internal supplementation program (using local

broodstock). The figure is based on nomenclature used by Cuenco (1994). Figures 3b-3d are

based on one possible classification scheme. Different authors have made fundamental

assumptions about which lineage of fish to be followed, and their fitness in relationship to the

original wild stock. In many cases there is little experimental evidence to support one set of

assumptions over another.

In Figure 3a the total number of adult fish is equal to Nwh. Of this number of fish, some

are taken into the hatchery and reared (Nh). The total number of recruits is equal to Nwhr and

comprise of Nwr (from the wild) and Nhr (from the hatchery). The biological cycle is repeated

with the Nwhr becoming the Nwh for the next generation. Once hatchery fish start to return the

model becomes more complex (Figure 3b). In both the wild and the hatchery there are three

different combination of spawning fish (wild x wild, hatchery x wild, and hatchery x hatchery).

A critical question is the rapidity with which the hatchery influence on fitness diminishes

with each successive generation of natural spawning and whether or not progeny of hatcheryreared parents ever approach the fitness of their native counterparts (RASP 1991). If the progeny

of wild x wild, wild x hatchery, hatchery x hatchery mated with wild fish in F2 and F3

generations, the following combinations result (Table 5):
25

Figure 3a. Year 1 of an internal supplementation program.

Table 5. Possible permutation of crosses with successive generations (F1 - F3)

If the supplementation project continues long enough, there may come a time when it is

impossible to differentiate the parentage of the fish (Figure 3c). The hatchery would still produce

more recruits/spawner because of higher early survival.

The test of supplementation occurs when the hatchery program is terminated (Figure 3d).

Is the stock productivity of the wild fish >1, and greater than that which would have occurred if

the stock had not been supplemented? It is probably not valid simply to compare the pre-project

stock productivity (Rw in Figure 3a) with the post-supplementation value (Rmix,w in Figure 3d) due

to potential environmental changes.
26

For any one of the different crosses in the wild, it is possible to write a simple equation

for stock productivity, viz:

Where % Female = Percent females in populations

% Spawning = Percent of female that successfully spawn in the wild

Egg/female = Number of eggs per female

Egg/smolt = Percent egg-to-smolt survival

SAR = Percent smolt-to-adult survival

Additional research on the comparison of hatchery and wild fish with respect to mate

selection and spawning and egg-to-fry survival is needed. The source of broodstock used for

supplement projects should be subject to much more analysis and discussion.

Figure 3b. Internal supplementation program after hatchery fish return.

Nwhr

Nwh

= (% Female)(% Spawning)(Egg / Female)(Egg / Smolt)(SAR)
27

Figure 3c. Year n of an internal supplementation program.

Figure 3d. Post-supplementation phase of an internal supplementation program.
28

The future operation of supplementation hatcheries

Supplementation has been largely viewed as a fisheries management practice with

important genetic components. Ecological impacts and husbandry requirements have been

viewed with much less importance.

In production hatcheries there is an overwhelming emphasis on producing fish of uniform

size and adhering rigidly to size and time-of-release goals. The practice of volitional release is

simply not possible because of the demands on the facilities. Therefore hatchery operations

themselves impose major selective pressures on the stock. These domestication pressures can be

adaptive for hatchery rearing but may be very non-adaptive for fish that must spawn in the wild.

A stock used in a supplementation project should have a life history as varied as wild

stocks (Bugert, 1998). The maintenance of genetic diversity through broodstock selection and

fertilization protocols is well developed, but little attention has been given to genetic diversity

through their subsequent life history protocols.

Potential aspects of hatchery operations for supplementation projects might include the

following:

· Broodstock collection throughout the seasonal run, and maintenance of differences in

resulting size until release

· Reduction in rearing density to allow survival of slower growing fish. This might also

require variation in feeding levels between different raceways

· True volitional release and multi-year rearing cycles for some species of fish

· Use of surface water supplies to maintain normal growth patterns

· Use of natural environment rearing components (NATURES), predation training, and

exercise

· Natural mate selection and natural incubation systems

· Use of substrate and reduced light levels in artificial incubation (if used)

· Modification of production diets and/or natural food items

Implementation of some of these rearing strategies may require significant additions in

capital costs and operational costs. There might also be some reduced production.

Conclusions

1. Supplementation can maintain a population until underlying causes of decline are corrected.

2. The genetic impacts of supplementation can be minimized with appropriate broodstock

collection, fertilization, and rearing protocols.

3. Monitoring and evaluation of most older supplementation projects is inadequate. At least five

major projects with appropriate monitoring and evaluation plans are underway in the Pacific

Northwest. All are still in the supplementation period. The response of these populations in

the post-supplementation period is unknown at this time.
29

4. The fitness of supplementation fish can be improved with more appropriate rearing and

release protocols. The use of conventional rearing protocols significantly reduces success.

5. The use of out-of-basin stocks or highly domesticated hatchery stocks is highly undesirable.

6. Because of the high variability of adult escapement estimates, 10-15 years of data (or more) is

needed to determine if the population has increased or decreased. Alternative monitoring

parameters are needed for estimating the impacts of supplementation.

2. Conservation Hatchery Protocols

Introduction

It is clear from the preceding section that attempts to use supplementation to rebuild

naturally-spawning populations of Pacific salmon have yielded poor results so far. One of the

reasons is that production hatchery fish do not have the same capacity to survive as their wild

cohorts, as they are generally different in behavior, morphology, and physiology. The solution,

and the challenge, is to develop protocols which produce fish from hatcheries with ‘wild-like’

attributes, thereby reducing impacts on wild fish and increasing survival. In this section, the

potential impacts of artificial propagation on the biology and behavior of fish are first

summarized, and then conservation hatchery strategies to help mitigate the unnatural

conditioning provided by hatchery rearing are discussed.

Potential impacts of hatchery rearing

Hatcheries figure prominently in the management of Pacific Northwest salmon fisheries.

For the most part, hatcheries have been successful in producing fish for the fishery (Mahnken et

al. 1998). However, hatcheries and hatchery management practices have often worked to the

detriment of wild fish (Waples 1991, Flagg et al. 1995b, NRC 1996, Waples 1999). Present

hatchery practices are geared toward mass-production under unnatural conditions. These have

been described in Section III.A.1, above.

Although the protective nature of hatchery rearing increases egg-to-smolt survival, it has

been reported for many years (Greene 1952, Miller 1952, Reimers 1963) that post-release

survival and reproductive success of cultured salmonids are both considerably lower than that of

wild-reared fish. Hatchery practices which induce genetic changes (domestication, etc.) are often

considered prime factors in reducing fitness of hatchery fish in natural ecosystems (Reisenbichler

and McIntyre 1977, Nickelson et al. 1986, Goodman 1990, Waples 1991 and 1999, and Hilborn

1992). Rearing practices which disrupt innate behavioral responses may also play a major role in

reduced performance of hatchery fish after release.

Behavioral deficiencies in released animals have been cited as causes of failure to re

establish wild populations by, among others, Gipps (1991), Johnson and Jensen (1991), DeBlieu

(1993), and Olney et al. (1994). Current fish culture techniques may be imparting similar

behavioral deficiencies in hatchery reared salmon. Studies by Maynard et al. (1995) indicated
30

that the hatchery rearing environment can profoundly influence social behavior of Pacific

salmon, and social divergence of cultured fish may begin as early as the incubation stage. Poon

(1977), Leon and Bonney (1979), Murray and Beacham (1986), and Fuss and Johnson (1988)

demonstrated that lack of substrate and light levels of the hatchery incubation environment

induced excess alevin movement, lowered energetic efficiency, reduced size, and, in some wild

stocks, death. Similarly, as food availability and rearing densities in hatcheries far exceeded

those of natural streams, Symons (1968), Bachman (1984), and others have all concluded that

such factors contributed to differences in agonistic behavior between hatchery- and wild-reared

fish.

Work by Olla et al. (1998) suggested that hatchery rearing environments deprived salmon

of the psycho-sensory stimuli necessary to develop anti-predator behaviors fully. Maynard et al.

(1995) reviewed information indicating that hatchery strains of salmonids have increased risktaking behavior and lowered fright responses compared with wild fish. These authors, together

with Uchida et al. (1989) suggested that surface feeding conditioned hatchery fish to approach

the surface of the water column, thus increasing their susceptibility to avian predation.

Maynard et al. (1996a) and Donnelly and Whoriskey (1991, 1993) also attributed

increased vulnerability of hatchery fish to predators to decreased crypsis (camouflage coloration)

for stream environments. This lack of camouflage coloration is caused by the monochrome

background of the (concrete) rearing environments of the hatchery raceways.

Finally, Allee (1974), Dickson and MacCrimmon (1982), Berejikian (1995a), and others,

have demonstrated that cultured and naturally-reared salmonids respond differently to habitat. In

most cases, for example, wild fish utilized both riffles and pools in streams while newly released

hatchery fish primarily used pools. The pool is more similar to a raceway environment.

Reisenbichler and Rubin (In press) summarized the current situation by concluding that,

“.. the only similarities in hatchery and wild environments for salmonids are water and

photoperiod.” Almost every other component of the hatchery rearing environment, such as food,

substrate, density, temperature, flow regime, competitors, and predators, etc., differed from those

naturally experienced by wild fish. Consequently, the National Research Council (NRC 1996)

and, more recently, others (Anders 1999, Flagg and Nash 1999, Waples 1999,) have suggested

that operational strategies of production hatcheries can be changed to conservation strategies for

the protection of wild stocks. A number of hatchery strategies for the conservation of Pacific

salmonids are discussed below. A complete array of conservation hatchery strategies are fully

described in Flagg and Nash (1999).

The concept of the conservation hatchery

The strategic role of a conservation hatchery is to promote restoration of wild stocks of

fish. This requires fish rearing be conducted in a manner that mimics the natural life history

patterns, improves the quality and survival of hatchery-reared juveniles, and lessens the genetic

and ecological impacts of hatchery releases on wild stocks.
31

It has been recommended (SRT 1998, Flagg and Nash 1999) that conservation hatcheries:

· determine spawning, hatching and emergence times of the local population, and duplicate

these in the hatchery by controlling water temperature to natural profiles

· use low rearing densities and base their goals for growth and size at emigration on natural

population parameters

· simulate growth rate, body size, and body (proximate) composition by controlling water

temperature, diet composition, and feeding rates

· have incubation and rearing vessels with options for habitat complexity to produce fish more

wild-like in appearance, and with natural behaviors and higher survival

· provide prerelease training experiences, such as forage conditioning and antipredator

conditioning which, while many yet are still theoretical, are beginning to show improved

survival and fitness.

Important factors effecting quality of hatchery reared fish include:

Rearing density – Rearing density is one of the most important and well-studied factors

affecting fish quality. Westers and Copeland (1973) and Maheshkumar (1985) found that the fin

condition of Atlantic salmon deteriorated with increasing rearing densities. Soderberg and

Meade 1987), however, indicated there was no relationship with fin condition, growth, or inculture survival at rearing densities of 8.5 to 68.7 kg/m3 (0.53 to 4.29 lbs/ft3). Reftsie (1977)

demonstrated that both growth and condition factor of rainbow trout are inversely related to

rearing density.

Inverse relationships between rearing density and growth, condition factor, and food

conversion efficiency have been observed in coho salmon by Fagerlund et al. (1981). In addition,

coho salmon reared at high densities suffered greater physiological stress as measured by body

water content, fat and protein contents, inter-renal cell nuclear diameter, and mortality rates. For

coho salmon smolts, Wedemeyer (1976) discovered that rearing densities as low as 16 kg/m3 (1

lb/ft3) induced physiological stress. Pitano et al. (1986) found increased rearing densities reduced

levels of plasma thyroid hormones, and Banks (1992) found they reduced levels of gill ATPase

levels.

In a survey of 85 variables related to strain and culture conditions by Homer et al. (1979),

only the five associated with either water flow, amount of living space, or relative water level in

rivers explained the post-release survival of Atlantic salmon. Unpublished data by Sandercock

and Stone (cited in Fagerlund et al. 1981) indicated that the adult return of coho salmon appeared

to be inversely related to rearing-pond density, although this was not totally confirmed in work by

Hopley et al. (1993).

Martin and Wertheimer (1989) examined the effect of low, intermediate, and high rearing

densities on the post-release survival of chinook salmon. In the hatchery, all four rearing

densities showed similar high survival (99.5% or greater), but fish reared at higher densities were

smaller at release. The low density group showed the highest adult return (1.0%), followed by

the two intermediate-density groups (0.9 and 0.7%) and the high density group (0.6%).
32

However, the increased number of smolts produced at the two higher densities compensated for

their reduced return rate and yielded a higher number of adult returns per unit volume of rearing

space.

These and other studies with chinook salmon (Hopley 1980, Fagerlund et al. 1987,

Denton 1988, Downey et al. 1988, Banks 1990) have shown a consistent inverse relationship

between rearing density and percentage of fish surviving to recruit to the fishery and spawning

area. However, in most cases the greatest number of adults per unit volume can still be produced

by rearing fish at intermediate densities. Some interesting relationships were found when data

were combined by species. For example, the SAR for chinook tended to decrease with

increasing rearing density, but for coho little relationship could be found. The adult yield for

coho salmon increased with increasing density, while the adult yield for chinook remained

constant. Until further data are available, lowered density indices as proposed by Banks (1994),

and Ewing and Ewing (1995) of 0.08-0.15 lb/ft3/in for spring and fall chinook salmon, and

between 0.30-0.40 lb/ft3/in for coho, should used in attempts to maximize adult return.

Enriched rearing habitats – Research on higher vertebrates has shown that simple and practical

(habitat enrichment) changes to the way animals are kept and grown can have beneficial effects

on their physiology as well as their behavior (Gipps 1991). Providing animals with more

complex rearing habitats which approximate natural conditions is an increasingly popular

method for improving the well being of animals in zoos. In many cases, behavioral repertoires

may be recovered even after many generations of absence simply by recreating the correct

environmental stimuli. These habitat enrichment techniques, according to Johnson and Jensen

(1991), DeBlieu (1993), Olney (1994), and others, may also have application to salmonid

hatchery populations.

Fish culturists have long recognized that fish reared in earthen-bottom ponds have better

coloration than those reared in concrete vessels (Piper et al. 1982). However, only recently has it

been understood that rearing salmonids over natural substrates, similar to those over which they

will be released, increases survival by enhancing cryptic coloration. Research by Fuji (1993)

indicates these morphological color changes can take weeks to complete, as pigments and

chromatophore units are developed to match the general background. The cryptic coloration

ability generated by these long-term stable color adaptations appears to reduce detection by

predators. Donnelly and Whoriskey (1991) found that brook trout reared for 11 weeks over

distinct background colors were significantly less vulnerable to predators when challenged over

background colors similar to those over which they were reared.

Prolonged work by Maynard et al. (1995, 1996a, 1998b) with salmonids reared in natural

rearing enhancement systems, which promote full development of the morphological camouflage

pattern needed after release, showed that survival was increased. In these systems (called

NATURES) the complexities of the experimental artificial rearing habitats simulate the release

habitats. Substrates were configured in several ways, using sand, gravel, artificial corrugated

inserts, or painted patterns. Every effort was made to match the color of the substrate (which

produces the cryptic coloration patterns in fish) to that of the receiving-stream environment to

produce body camouflage patterns (fish crypcisity) most likely to reduce vulnerability to
33

predators. In these studies, the in-stream post-release survival of fish reared in NATURES were

compared with the survival of fish reared in conventional hatchery tanks. The results of the

studies are briefly summarized below:

• 1991-1992. Fall chinook salmon were reared from swim-up to smolt in 400-L raceways

fitted with cover, structure, and substrate. Relative post-release survival to a collection weir

about 2 km downstream was about 50% higher (40 versus 60%; P=0.007) for NATURES

fish.

• 1994. Spring chinook salmon were reared for 3 months in 400-L raceways fitted with cover,

structure, and substrate. Relative post-release survival to a collection weir about 225 km

downstream was about 23% higher (22 versus 27%; P<0.05) for NATURES fish under clear

water conditions, but not in turbid water conditions (34 versus 31%; P=0.285).

• 1994. Fall chinook salmon were reared hatchery from swim-up to smoltification in pilot

scale 5,947-L raceways fitted with cover, structure, substrate, and an underwater feed

delivery system. Relative post-release survival to a collection weir about 20 km downstream

was 26% higher (38 versus 48%; P=0.001) for NATURES fish.

• 1997. Fall chinook were reared to smolt for about 3 months in 18,000-L production scale

raceways fitted with cover, structure, and substrate at a WDFW hatchery. Relative postrelease survival to a collection weir about 20 km downstream was similar (69% each) for

both groups.

• 1998. Fall chinook were reared to smolt in the 18,000-L raceways. Relative post-release

survival to a collection weir about 20 km downstream was 11% higher (60 versus 67%;

P<0.001) for NATURES fish.

These results suggest that in-stream post-release survival of fish reared in these special

habitats is significantly greater than that of their counterparts reared conventionally.

Consequently, although not yet documented, it is assumed that survival to adulthood will be

improved. The studies in 1997 and 1998 included components to evaluate ocean returns, but the

data will not be available for a number of years.

In conclusion, it appears habitat enrichment strategies can aid in the production of ‘wildlike’ hatchery fish more suited for enhancement programs than fish reared in conventional

systems.

Forage training – Foraging theory suggests that supplementing standard pellet diets with live

foods will profoundly increase post-release foraging ability of cultured fish. Field trials generally

confirm that live-food supplemented diets improve the post-release foraging ability and survival

of cultured fish. Gillen et al. (1981) found that previous experience in capturing live prey

enhanced the foraging behavior of tiger muskellunge by decreasing the time and number of

strikes required to capture natural live prey. Johnson (1978) found that tiger muskellunge reared

in the hatchery on a live fish diet had higher post-release survival than their cohorts reared only

on pellets. Similarly, Hesthagen and Johnsen (1989) demonstrated that brown trout reared in

earth-bottom ponds with natural food supplementation had a higher post-release survival than

control trout reared in tanks and fed only pellets.
34

Maynard et al. (1996b) investigated the use of live-food supplementation to increase the

post-release foraging ability of hatchery-reared fall chinook salmon. Trained salmon were found

to feed on twice the number of familiar and novel prey as untrained fish. In addition, even

though food was abundantly supplied to both treatment groups, the growth and natural coloration

of fish reared on the live-food supplemented diet was better than that of fish fed only pellets.

These and other studies suggest that live-food supplementation can increase the post-release

foraging ability of hatchery-reared fish. However, rearing fish in semi-natural habitats with

natural foods may not always enhance survival, as observed by Mundie et al. (1990) in a study

with coho salmon.

Anti-predator conditioning – Studies on salmonids carried out over many years have

demonstrated an increase in post-release survival of juveniles following anti-predator

conditioning in hatchery vessels. Thompson (1966), working in a natural stream,

demonstrated that post-release survival of chinook salmon smolts exposed to electrified

predator models was greater than unconditioned smolts, and Kanayama (1968) reported

improved post-release survival of chum salmon after similar conditioning.

More recently, juvenile salmonids from wild and hatchery populations were shown to

exhibit differences in predator avoidance behavior (Johnsson and Abrahams 1991) and ability

(Berejikian 1995a, 1995b). This suggested genetic basis for these traits. However, the ability of

juvenile salmonids to avoid predation improved with experience.

Laboratory studies by Patten (1977), Healey and Reinhardt (1995), and others,

demonstrated that anti-predator behavior and predator avoidance ability of juveniles of several

salmon species improved following exposure to actual predation events. Suboski (1988) and

Olla and Davis (1989) suggested that anti-predator conditioning involved various combinations

of visual, olfactory, and auditory stimuli, all of which could trigger innate anti-predator

responses. Brown and Smith (1997 and 1998) and Berejikian et al. (1999) demonstrated that

conditioning by a combination of injured con-specific predator odors in the absence of visual and

auditory stimuli improved subsequent predator recognition and avoidance behavior in rainbow

trout and chinook salmon, respectively.

The use of predator avoidance training as tool to increase the post-release survival of

chinook salmon has been investigated by Maynard et al. (1998a). Fall chinook salmon reared in

pilot scale raceways were exposed to limited predation by birds (great blue heron and hooded

merganser) and fish (largemouth bass and brown bullhead). The in-stream post-release survival

of the conditioned fish was 26% higher than naive controls.

In conclusion, these studies suggest anti-predator training can be used to increase the

post-release survival of hatchery-reared fish. There is no evidence that anti-predator

conditioning has a detrimental effect on post-release survival.
35

Reintroduction strategies

A number of potential reintroduction strategies have been suggested for progeny reared in

conservation hatcheries. There appears to be no clear information on the outcome to fitness from

varying release strategies but it seems reasonable that conservation hatcheries should release

smolts at a size which equals the size distribution of smolts in the wild population. The greatest

risk of releasing oversized hatchery fish is that they will out-compete smaller wild fish. For a

long time it has been known that, in intra specific contests over food and space, all else being

equal, the largest fish usually wins (Hoar 1951, Chapman 1962, Mason and Chapman 1965,

Abbot et al. 1985).

Fish from conservation hatcheries should be released on their own volition, and outmigrate during windows for natural downstream migration. The key to volitional release,

assumed by NRC (1996), Brannon et al. (1982), Kapuscinski (1997), is that fish will not leave

the hatchery until certain physiological processes, such as smoltification, trigger their

downstream migratory behavior. The need is to provide windows of opportunity for outmigration which mimic time and age patterns found in the wild populations. Within these

windows, fish may leave if they wish or remain behind to fend for themselves and smolt,

residualize, or perish as natural selection takes it course.

Conservation hatcheries should therefore adopt practices to reduce straying to no more

than 5% (Grant 1995). According to Sholes and Hallock (1979), Labelle (1992), Unwin and

Quinn (1993), Pascual et al. (1995), Dittman et al. 1995), and others, juvenile salmon must

experience the odors of their natal system at various times and physiological states when they can

be learned to maximize imprinting opportunity. Conservation hatcheries should, therefore, rear

fish for their entire juvenile freshwater lives in water from the intended return location. When

this is not possible, a period of acclimation on intended return water should improve imprinting

and homing and reduce straying. Conservation hatcheries should program their releases to

accommodate the natural spatial and temporal patterns of abundance in wild fish populations and

release numbers should not exceed carrying capacities of (freshwater and oceanic) receiving

waters.

Even though there appears to be no clear information on the outcome to fitness from

varying release strategies, adhering to these guidelines should markedly decrease negative effects

of hatchery releases on the wild fish population.

Conclusions

A number of conservation hatchery type rearing protocols can be used to improve fitness

and survival of hatchery fish. For some strategies, such as NATURES rearing, there is good

evidence of a potential range of survival increase. For many other strategies, no clear

‘improvement’ range has yet been described. Nonetheless, most proposed conservation hatchery

strategies combine sound conservation principles and basic salmon biology. They are common
36

sense approaches to increasing the quality of hatchery fish. It would not appear optimistic to

conclude that, using a combination of conservation hatchery protocols, the survival of hatchery

fish could be improved by 50-100% or greater, while reducing the ecological impacts of the

release.

B. Competition

Introduction

The following section reviews what is known about the potential for competition between

hatchery and wild reared chinook salmon and steelhead trout.

When salmonids harm one another in contests over limiting resources they are

considered, in general, to be in competition (Birch 1957, Horner and Bjornn 1976). This

competition may occur when fish fight for feeding territories, displace one another from critical

hibernation habitat, graze down estuarine food resources before other fish can utilize them,

monopolize available mates, or dig up the redd of another fish.

If contests between fish populations are over limiting resources, as required for true

competition to occur, then a density dependent relationship will exist in which increases in one

population will produce decreases in the growth, survival, etc., of the other. Conversely, if

resources are not limiting, competition does not occur, and the relationship between the growth

and survival of the two groups will be density independent. It is this density dependent

relationship that most biologist use to conclude that inter-specific competition is occurring

between salmonids. Thus Hearn (1987) suggested inter-specific competition may be occurring

between salmonids in a watershed when the decline of one species is accompanied by a

concomitant increase in another. However, it should be remembered that this may be a casual

rather than causal relationship, with factors other than competition responsible for the

relationship between the two populations.

Intra-specific competition occurs more often and has greater severity than inter-specific

competition because there is greater niche overlap between members of a species than individual

of different species (Fraser 1969, Lonzarich 1994, Fresh 1997). When species evolve

sympatrically their niche requirements tend to diverge, which further reduces the potential for

inter-specific competition between them. Therefore when groups (morphs, life history strategies,

races, or species) which have evolved sympatrically are introduced or reintroduced into a

common habitat, then competition is generally less intense between them than groups which have

evolved allopatrically (Hearn 1987).

By definition, hatchery and wild reared salmonids will not compete unless they require

the same limiting resources. Thus, the modern enhancement strategy of releasing chinook

salmon and steelhead trout as smolts markedly reduces the potential for hatchery and wild fish to
37

compete for resources in the freshwater rearing environment. Miller (1953), Hochachka (1961),

and Reimers (1963), among others, have noted that this potential for competition is further

reduced by the fact that many hatchery salmonids have developed different habitat and dietary

behavior than wild salmonids. If similar ecological divergence has occurred in Snake River

salmonids, for example, it may further alleviate the potential for competition between wild and

hatchery fish in the migratory corridor, estuary, and marine environments.

It has been suggested by Fresh (1997) that competition is most likely to occur between

hatchery and wild salmonids in the estuarine and near-shore environments where food resources

are limited, and the fish become concentrated on their way to the open ocean. However, as little

is known about salmonid behavior and ecology in these habitats, it is difficult to determine if

hatchery and wild salmonids are actually competing for limited resources. Even for coho salmon

in the Oregon Production Index (one of the better studied populations) McNeil (1991) believed

there was no clear cut density dependent relationship between hatchery and wild fish which

indicated that competition is occurring in the marine environment. Although studies by Fresh

(1997) and others have shown that hatchery fish can disrupt the growth, survival, and abundance

of native salmonid communities in streams, the role of competition in causing these changes is

unclear. Further, these results of presmolt competition in the territorial freshwater-life stage

cannot be readily extended to the schooling migratory marine-life stage of most post-smolt

hatchery and wild salmonids.

The following review mostly concerns competition between wild and hatchery reared

steelhead trout and spring-summer chinook salmon. The review is broken down into three

sections, namely the intra-specific competition between wild and hatchery-reared chinook

salmon; the intra-specific competition between wild and hatchery-reared steelhead trout, and the

inter-specific competition between chinook salmon and steelhead trout.

Wild and hatchery-reared chinook salmon

Snake River spring-summer chinook salmon typically rear at least one summer in streams

and then undergo a fall downstream migration to hibernation areas, where they hibernate in

suitable bottom rubble that protects them from predators and displacement. In the spring they

emerge from hibernation, resume feeding, and then migrate downstream as yearling smolts about

mid-spring. Edmundson et al. (1968) demonstrated that summer chinook salmon fry in their

natal streams during their first spring maintained a permanent station which they aggressively

defended during the day and abandoned at dusk when they moved into quieter inshore waters to

shelter.

Everest (1969) observed that the microhabitat used by chinook salmon in streams

changed as the fish grew, with larger fish seeking deeper and faster water. Just after emergence

from the gravel the fry resided in quiet shallow water over a variety of substrates ranging from

silt to 20 cm rubble. Spring chinook fry exhibiting a territorial life style tended to be closely

associated with substrate, while those fry living in hierarchical social groups preferred to live in

quieter water where they swim up to 0.8 m above the substrate. Some yearling fish (precocious
38

males) remained in freshwater and spawned about the time they turned two years old. Larger

yearling precocious males which remained in freshwater for a second year utilized deeper water

microhabitat than under-yearling chinook salmon (Everest and Chapman 1972). They believed

suitable over-wintering habitat was the primary limiting factor for presmolt chinook salmon in

freshwater.

When yearling (spring) chinook salmon begin their down-river migration they utilize

different habitat than both hatchery and wild under-yearling (presumably fall) chinook salmon.

Dauble et al. (1989) observed that, in general, under-yearling fall chinook salmon remain close to

the shore, while yearling spring chinook salmon tend to migrate down the mid-river channel.

These and other investigators (Richards and Cernera 1989, Roper and Scarnecchia 1996, ) noted

the downstream migration of chinook salmon was temporally separated, as hatchery chinook

salmon migrated downstream at different times of day than wild chinook salmon.

It is unclear whether or not hatchery and wild chinook salmon utilize similar or different

resources in the estuarine environment. The best available information comparing the use of

estuarine resources by the two rearing types is primarily based on ocean-type (fall) chinook

salmon data. In a study by Fisher and Pearcy (1989) in Coos Bay, Oregon wild and hatchery fall

chinook salmon were generally found to utilize the same habitat at the same time. Spring

chinook salmon released from a hatchery were found to be both spatially and temporally

separated from these fish. In addition the hatchery spring chinook salmon collected in Coos Bay

were found in large aggregations suggesting migratory behavior, while both the hatchery and

wild fall chinook salmon were more evenly distributed indicating they were residing in the

estuary.

In contrast to the Coos Bay study, hatchery and wild chinook salmon in the Campbell

River estuary were found by Levings et al. (1986) to display little habitat overlap. When released

into the estuary hatchery fish were much larger than wild chinook, which resulted in their

utilization of deeper water habitat than the wild chinook fry in seawater. In addition to being

spatially separated, the two rearing types utilized the estuary for different lengths of time, with

wild chinook residing in the estuarine environment for two months and hatchery fish only one

month. Therefore there was little dietary overlap. In a later study by Brown et al. (1987), wild

and hatchery fish were both found to eat calanoid and harpacticoid copepods, amphipods, and

cladocerans in the estuary. However, hatchery fish alone were found to feed on cumaceae, while

wild fish only fed on insects and decapod crustaceans. Although there was some dietary overlap

it was not complete, and therefore the two types may not be in competition if they are foraging in

different microhabitats. Levings et al. (1986) concluded that competition between wild and

hatchery fish was not occurring as the release of hatchery fish did not appear to reduce the

residence time of wild fish, and there was no evidence of a density dependent relationship

between the two rearing types.

Korman et al. (1997) found some later evidence of competition between wild and

hatchery chinook salmon in the Campbell River estuary. There was again spatial separation with

wild chinook salmon having the greatest density in the estuarine zone sites, while the density of

hatchery chinook salmon was highest in the transition zone sites. In addition, both groups
39

showed different seaward emigration patterns. However, the peak abundance of wild and

hatchery chinook in the estuary did coincide, and there was some indication of a density

dependent relationship between the two rearing types indicating that competition was occurring.

Myers (1980), working in Yaquina Bay, found the dietary overlap of hatchery and wild

chinook salmon changed over time. Initially after release from the hatchery there was little

overlap, but as time passed the diet of hatchery chinook began to approximate more closely to

that of wild chinook salmon. Although there was some habitat overlap between the two rearing

types, wild chinook tended to be more abundant in the upper estuary, while hatchery chinook

were more abundant in the lower estuary. Again this data, which is primarily on fall chinook

salmon, suggests some competition may be occurring between wild and hatchery fish in that

estuary.

Further information on competition between hatchery and wild chinook salmon is not

available until the life-stages of reproduction. Chebanov and Riddell (1998) observed no

noticeable difference in the morphology of ocean ranched and wild chinook salmon. When

hatchery and wild chinook salmon were placed in test enclosures the wild males generally

dominated hatchery males. However, quite unexpectedly, hatchery females dominated the wild

females and obtained the preferred spawning sites. As wild male preferentially spawned with

wild females and ranched males choose to spawn with ranched females, ranched fish of both

sexes were the more successful spawners. It should be noted that there was some mating

crossover with wild males also spawning with ranched females. The authors explain the

unexpected reproductive advantage experienced by hatchery females as an artifact of the

conditions the fish were held in prior to testing. However, if the experimental findings are valid

and hatchery fish stray onto wild salmon spawning areas they may well compete with them for

spawning sites.

Bjornn (1978) studied the effect of supplementation releases of chinook salmon fry on

chinook salmon production in the Lemhi River. Unfortunately his study lacked controls and

provided no observations on the in-stream behavior of hatchery and naturally produced salmon,

and therefore provides little information on intra-specific competition. He did observe that the

growth rate of chinook salmon fry was density dependent, which suggests that intra-specific

competition is occurring at this life stage. In another supplementation study by Hillman and

Mullan (1989), the release of 0-age hatchery-reared spring chinook salmon fry into the

Wenatchee River system resulted in the displacement of naturally-reared spring chinook salmon

fry. Both these studies and general theory on intra-specific competition suggest that planting

spring chinook salmon fry will produce some level of competition with any naturally rearing

chinook salmon they may encounter.

Intraspecific competition between wild and hatchery reared chinook salmon most likely

occurs when they share the same microhabitat and dietary needs. This is a function of both

when, where, and how hatchery fish are released, as well as the microhabitat and dietary

preferences shown by the two rearing types. The less hatchery fish share the habitat and dietary

requirements of wild fish, the less likely the two forms are to compete. Thus the release of

spring chinook salmon fry into habitat with resident wild chinook salmon has great potential for
40

producing competition between the two rearing types. In contrast, the release of well imprinted

and rapidly migrating spring chinook salmon smolts from hatcheries which are geographically

separated from wild fish rearing and spawning areas may generate very little competition

between wild and hatchery reared chinook salmon.

A summary of the studies on intra-specific competition between wild and hatchery-reared

chinook salmon is given in Table 6.

Table 6. Studies observing competition between wild and hatchery reared chinook salmon.

Wild and hatchery-reared steelhead trout

Most summer steelhead trout in the Snake River spend three growing seasons in

freshwater. Each fall the fish seek hibernation cover in their rearing area or migrate downstream

to areas with suitable bottom rubble. In the spring the fish emerge from the rubble and resume

feeding in their rearing areas. Steelhead fry, like chinook, maintained a permanent station which

they defended aggressively during the spring and summer, according to Edmundson et al. (1968).

At night they abandoned these territories and moved into quieter inshore waters where they

shelter overnight.

Age-0 steelhead prefer shallow quiet water a few feet from shore. They are strictly

territorial bottom dwellers intimately associated with large rubble substrate. As they grow they

continuously shift their distribution into deeper and faster water. Thus age-1+ steelhead are

found in deeper faster water towards the center of the stream. They are also territorial and
41

intimately associated with the substrate. Everest (1969) noted they are typically found over

larger rubble than age-0 steelhead. He concluded that suitable over-wintering habitat was the

primary limiting factor for presmolt steelhead trout production in freshwater. Chrisp and Bjornn

(1978) stated that summer steelhead trout must be at least 140-160 mm in length before they

begin to smolt and migrate to the sea.

Both steelhead trout and rainbow trout are two life history strategies of a single species.

According to Barnhart (1991) and Smith (1991) this makes it impossible for investigators to

distinguish morphologically or behaviorally between the fry while they are rearing in streams.

Because of their physical similarity and the high likelihood that they share similar freshwater

habitat and feeding strategies, intra-specific competition between the two life history types has

been included in this review.

The planting of hatchery steelhead fry into wild rainbow-steelhead habitat generally

produces some form of competition between the two rearing types. When hatchery-reared

steelhead trout fry were planted by Allee (1974) into artificial stream channels containing a

resident population of wild steelhead trout the wild fry emigrated from the channel. He

concluded that the hatchery fry remained in the channel not because they socially dominated the

wild steelhead, but rather because they tolerated greater intra-specific rearing densities than the

wild fry. When hatchery fry were released into a stream of the Quinault River system by

Berejikian (1995a) they also displaced the wild fry from the most heavily utilized stream habitat.

Bjornn (1978) released large numbers of hatchery reared steelhead fry into Big Spring Creek for

over a decade. Although the significance of the results is weakened by the lack of controls, he

observed that the release of hatchery steelhead trout fry markedly reduced the resident rainbow

trout population over time. Over-wintering habitat, rather than food, appeared to be the limiting

resource for this Snake River steelhead-rainbow trout population. It appears from all these

studies that the release of steelhead fry into streams negatively affects wild steelhead fry rearing

in the area whether competition occurs or not.

The planting of catch-size rainbow-steelhead trout in a habitat with an established wild

trout population can produce an impact ranging from negligible to severe. When catch-size

hatchery rainbow trout were stocked in the Madison River, Montana by Vincent (1987) he noted

a dramatic decrease in the wild trout population. After the planting ended the natural population

took four years to recover its original level. Although the author collected no supporting data, he

attributed the wild population decline to hatchery fish disrupting the social structure of wild

trout.

In Idaho streams, stocking catch-size rainbow trout had only a minor impact on the wild

steelhead trout population. Although Pollard (1969) and Pollard and Bjornn (1973) found that

the stocking of hatchery trout depressed the wild fish population temporarily, it rapidly returned

to pre-stocking levels within two weeks. Even though hatchery trout were observed to displace

wild steelhead from their feeding positions, they were usually found to prefer deeper and faster

water than the age-0 and age-1 steelhead. This produced good microhabitat separation between

the hatchery and wild reared trout. Competition between the two was further reduced by hatchery

rainbows feeding less readily on floating or drifting insects than their wild counterparts. These
42

dietary differences have also been observed in the Salmon River (New York) by Johnson (1981),

where the diet of wild and hatchery reared yearling rainbow trout did not significantly overlap.

Petrosky (1985) demonstrated that stocking rainbow trout at low densities (50-100 fish/stream

section) did not affect the abundance, dispersal, mortality rate, growth rate, or condition factor of

wild rainbow trout. However, at high densities (400 fish/section) the mortality rate of wild fish

was significantly increased.

Leider et al. (1984) investigated the reproductive activity of wild and hatchery reared

winter and summer run steelhead trout placed in enclosures. There was some temporal

segregation of spawning with hatchery summer steelhead (average date, January 10) spawning

before wild summer steelhead (average date, February 15), which spawn before hatchery winter

steelhead (average date, March 6), that in turn spawn before wild winter steelhead (average date,

April 14). For both hatchery and wild summer steelhead the selection of spawning sites was

randomly distributed throughout the enclosures. In contrast, wild winter steelhead primarily

spawned in the lower sections of the enclosures. Although there was some overlap, most

interactions occurred among members of the same spawning group. Wild winter and hatchery

summer steelhead were the most reproductively discrete spawning groups, having 95.1 and 93 %

intra-group spawning activity, respectively. Reproductive exchange was greatest for hatchery

winter steelhead, with only 36.7% intra-group crosses; and intermediate for wild summer

steelhead, with only 63.9% intra-group crosses. Complete reproductive isolation was not

observed between wild and hatchery steelhead in Gober Creek. This suggested that, although

temporal segregation may reduce spawning between wild and hatchery reared steelhead trout,

spatial separation was also required to eliminate interbreeding and reproductive competition.

As with chinook salmon, intra-specific competition between wild and hatchery reared

steelhead-rainbow trout will probably occur whenever they share the same microhabitat and

dietary needs. This is a function of both when, where, and how the hatchery fish are released, as

well as the microhabitat and dietary preferences shown by the two rearing types. The less

hatchery fish share the habitat and dietary requirements of wild fish the less likely the two forms

are to compete. Thus the release of steelhead trout fry or pre-smolts into habitat with resident

wild steelhead-rainbow has great potential for producing competition between the two rearing

types. In contrast, the release of well imprinted and rapidly migrating steelhead trout smolts

from hatcheries which are geographically separated from wild fish rearing and spawning areas

may generate very little competition between wild and hatchery reared steelhead-rainbow trout.

A summary of the studies on intra-specific competition between wild and hatchery-reared

steelhead trout is given in Table 7.
43

Table 7. Studies observing possible competition between wild and hatchery reared steelhead

trout.

Competition between steelhead trout and chinook salmon

In theory, inter-specific competition between age-0 steelhead trout, age-1 steelhead trout,

and age-0 spring chinook salmon is minimized by each age-species class occupying different

spring-summer microhabitats. The diet and microhabitat requirements of the two species are

very similar, with fish of both species moving into faster more food rich waters as they grow.

This progressive movement of juveniles into higher velocity water, coupled with different

species-specific emergence times, minimizes inter-specific competition between the two species.

Everest (1969) observed that earlier emerging and larger spring chinook fry generally moved into

faster water habitat before the smaller age-0 steelhead trout fry emerged. Similarly, the larger

age-1 steelhead trout parr primarily occupied faster water than age-0 spring chinook salmon.

In field studies both within and outside the Snake River Basin over a long period (Everest

1969, Chapman and Bjornn 1969, Everest and Chapman 1972, Hillman et al. 1989, Roper et al.

1994), spring chinook salmon fry were shown to occupy primarily different spring-summer

microhabitat than either 0-age or I-age steelhead-rainbow trout. However, there was usually

some minor overlap (about 10-20%) in microhabitat use between the two species. This overlap

suggested that the in-stream distribution of the two species was probably the product of either the

size-microhabitat theory discussed above or displacement from inter-specific aggression.

The microhabitat differences between steelhead trout and spring chinook salmon fry have

also been observed outside the Columbia River Basin. Roper et al. (1994) observed that

steelhead trout used every type of habitat in the study stream, while juvenile spring chinook were

heavily concentrated in pool habitats. This led the authors to conclude that the two species were

primarily utilizing different summer habitats. This habitat separation should act to minimize

inter-specific competition.
44

Some inter-specific aggression was observed between steelhead trout and spring chinook

salmon fry in Snake River tributaries by Everest (1969). However, similar inter-specific

aggression between the two species was not observed in Wenatchee River system, even though

intra-specific aggression among spring chinook salmon fry was observed by Hillman et al.

(1989a, 1989b). Everest (1969) found that removal of steelhead trout from sections of Idaho

streams resulted in shifting the distribution of spring chinook salmon. Although he concluded

that inter-specific competition between steelhead trout and spring chinook salmon did not exist,

his observation of inter-specific aggression between the two species, and finding that spring

chinook salmon fry shifted their habitat distribution when steelhead were removed, raises the

possibility that some level of inter-specific competition between the two species exists.

Bjornn (1978) observed that, between 1963 to 1967, the production of spring chinook

salmon from Big Springs Creek, a tributary of Lemhi River, declined coincidentally with the

planting of 0-age steelhead trout. When hatchery spring chinook salmon were later planted in the

system steelhead trout production was similarly reduced. Although he explained the reduction of

spring chinook salmon fry as a function of adult seeding, inter-specific competition between the

wild-produced spring chinook salmon fry and the planted hatchery trout fry might have occurred.

When 0-age hatchery produced steelhead trout fry were released into the Wenatchee River

system, no similar negative impact was observed by Hillman and Mullan (1989) on wildproduced spring chinook salmon fry. Although suggestive of inter-specific competition between

the two species, these results do not conclusively prove that it does or does not occur.

The interaction between chinook salmon and steelhead trout in the Yakima River system

has been studied by McMichael et al. (1997) in relation to a proposed supplementation program.

They found little evidence of competition between steelhead trout and chinook salmon. The

residual steelhead trout from releases of hatchery reared fish did not adversely effect the growth

of wild spring chinook salmon, even when the trout were nearly twice as large as the salmon.

Similarly, McMichael and Pearson (1998) found that the growth of steelhead-rainbow trout in

small cages and enclosures was not negatively impacted by the presence of spring chinook

salmon parr. Observations by scuba divers during the course of this study indicated that spring

chinook salmon held higher in the water column and over deeper water than steelhead-rainbow

trout.

Bjornn (1978) observed that most spring chinook salmon migrated in the fall from their

spring-summer rearing tributaries into the main stem of the Lemhi river where they overwintered and out-migrated as smolts the following fall. Everest (1969) and Hillman et al.

(1989a, 1989b) found that both steelhead-rainbow trout and spring chinook salmon ceased to

feed in winter and hibernated in low velocity interstices in the substrate. This might suppose that

there is no inter-specific competition in this critical over-winter microhabitat, but carefully

designed and well controlled experiments with allopatric and sympatric populations will be

required to determine if this is the case. Any such study should also include research on interspecific aggression and habitat displacement.

When migrating to sea as smolts in the mid-Columbia River it appears that both yearling

spring chinook salmon and steelhead trout migrate downstream in the main channel away from
45

the shore. Dauble et al. (1989) recovered steelhead out-migrants primarily between mid-water

and the bottom. Although this migration pattern separates the two from juvenile fall chinook

salmon habitat, it places them in similar migration corridor habitat allowing for the possibility of

inter-specific competition.

Finally, Everest (1969) pointed out that, although steelhead and chinook may spawn in

the same areas in streams, the timing of spawning was such that incubation and emergence of

each species was completed before spawning areas were again utilized. Thus inter-specific

competition for spawning sites should be negligible.

A summary of the studies on intra-specific competition between steelhead trout and

spring chinook salmon is given in Table 8.

Table 8. Studies observing possible competition between steelhead trout and spring chinook

salmon.

Hatchery practices for minimizing competition

For a number of years new and improved strategies for minimizing the occurrence of

competition between wild and hatchery reared salmonids have been developed. Generally these

strategies involve reducing the habitat and diet overlap between the two rearing types. Releasing

hatchery salmonids as true smolts which rapidly migrate downstream to the estuary and marine

environment minimizes or eliminates competition with wild fish rearing in streams, rivers, and

lakes. By ensuring these fish are properly imprinted and can return to their natal hatchery, fish

managers can minimize the opportunity for them to compete with wild reared salmonids for

rearing sites. The possibility of competition can be further reduced by locating hatcheries away

from natural spawning areas.
46

Managers can also consider increasing the spatial and temporal separation between

hatchery and wild fish by releasing hatchery fish so that they remain spatially and temporally

separated from wild salmon in estuarine and oceanic habitat. Suggested approaches include

producing large fish which do not utilize the same microhabitat as smaller wild salmonids,

releasing hatchery fish after wild salmonids have moved out of estuarine habitats, and releasing

hatchery fish in habitat downstream of that used by wild-reared salmonids. Manager might also

consider the intentional development of salmonid strains with different temporal (migration and

reproductive timing), spatial (microhabitat use), and dietary requirements than wild reared

salmon to reduce the potential for competition between the two stocks.

C. Predation

Introduction

The effects of artificial propagation on predator prey-interactions involving ESA-listed

salmonid populations can be divided into three major categories. First, salmon released from

hatcheries might prey on wild fish. Second, releases of hatchery fish may influence the behavior

and dynamics of predator populations, which can indirectly affect wild fish. Third, hatchery

rearing and release protocols can influence the vulnerability of hatchery-reared salmonids

(cultured for conservation purposes) to predators after release. This review focuses on predatorprey interactions of anadromous Pacific salmon and, where information is available, focuses on

chinook salmon and steelhead in the Columbia/Snake River system.

Predation by hatchery-reared steelhead and chinook salmon on wild steelhead and/

or chinook salmon

Five separate studies investigated predation by hatchery released steelhead on wild

chinook salmon in Columbia and Snake River tributaries. Predation by hatchery steelhead and

hatchery chinook on wild chinook was reported in two additional studies in Northern California

by Menchen (1981) and Sholes and Hallock (1979), and one in British Columbia by Levings and

Lauzier (1989). Details are discussed in the following paragraphs.

Whitesell et al. (1993) and Jonasson et al. (1994, 1995) found a very low incidence of

residual steelhead predation on wild chinook salmon juveniles. In fact in two of the three years

they found no evidence of predation in stomach samples of 368 and 641 residual steelhead.

These studies did not attempt to estimate predator or prey abundance, and made simple estimates

of consumption rates without error estimates.

Martin et al. (1993) estimated that a total of 456 chinook juveniles were eaten by residual

steelhead over a 6 month period in the Tucannon River and Asotin Creek, both tributaries of the

Snake River. They did not estimate prey abundance and therefore it was impossible to estimate

the proportion of the chinook population consumed.
47

Cannamella (1993) provided perhaps the most complete investigation of hatchery

steelhead predation on wild chinook salmon. The study reported predator abundance, estimated

consumption per predator (based on empirically derived gastric evacuation rates), and estimated

prey abundance. Based on data provided in the report, an estimated 4.8% to 21.7% (95% C.I.) of

naturally spawned chinook fry were consumed by steelhead during the 50 days following the

release of 744,000 steelhead smolts. However, this probably underestimated the total predation

impact, because estimates were not expanded to include possible predation by residual steelhead

predation beyond June 3, and the study was conducted in a year in which prey abundance was

low.

Two reports from Northern California indicated much higher levels of predation by age-1

hatchery chinook salmon (Sholes and Hallock 1979) and steelhead (Menchen 1981) on wild

chinook salmon than have been reported in the Columbia/Snake River system. However, neither

of these studies estimated prey abundance, nor did they estimate error associated with the

reported predation rates.

There was no documentation of predation by hatchery-released salmon or steelhead on

wild steelhead fry, although some of the ‘unidentified salmonids’ reported in these studies may

have been steelhead.

The US Fish and Wildlife Service (USFWS 1992) summarized existing information for

the Columbia/Snake River system. The study concluded that the number of fry/fingerlings eaten

by hatchery-produced steelhead was, “...low or negligible, either because of low rates of

predation, the lack of coexistence, or both; and too many assumptions would have to be made to

confidently estimate the actual number of chinook salmon fry and fingerlings consumed (or to

calculate their resulting adult equivalents).” Information summarized since the completion of

that report, by Whitesell et al. 1993, and Jonasson et al. 1994, 1995) supported their conclusions.

In conclusion, existing evidence suggests that hatchery-released steelhead and chinook

salmon will consume wild chinook salmon juveniles, and possibly steelhead juveniles in the

Columbia/Snake River system. The range of impact on the prey populations may range from 0%

to greater than 22% in tributaries of the Columbia and Snake Rivers.

Effects of hatchery releases on the behavior and dynamics of predator populations,

and indirect impacts on wild salmonids

Predator attraction – Northern pikeminnows are the primary predator on juvenile salmon in the

Columbia River Basin, according to Reimen et al. (1991). Predation by northern pikeminnows

on juvenile salmonids has generally been reported to be higher near hatchery release sites

(Ledgerwood et al. 1993, Collis et al. 1995) than away from release sites (Buchanan et al. 1981,

Poe et al. 1991, Ward et al. 1995). However, Shively et al. (1996) demonstrated that northern

pikeminnows quickly exploited hatchery-released spring chinook salmon approximately 60 km

away from their release site. In that study, northern pikeminnow diets consisted of 0% salmonids

one day prior to the release of 1.1 million spring chinook salmon. Eight days after their release,

spring chinook salmon were found in 86% of northern pikeminnows sampled.
48

Following three large-scale hatchery releases of spring chinook salmon into tributaries of

the Bonneville Pool, Collis et al. (1995) found that the abundance of northern pikeminnows near

hatchery release sites increased rapidly (within a day or so), and their diet shifted from

exclusively non-salmonids to a predominantly salmonid diet. Thus, hatchery releases can attract

predators to areas near hatchery release sites in the Columbia River Basin, and northern

pikeminnows can quickly exploit hatchery-released chinook salmon.

The rapid numerical response (predator abundance) and functional response (number of

prey eaten per predator per unit time) to large-scale hatchery releases could have either a positive

or negative impact on wild fish. For example, concentrating predators near hatcheries could

expose wild fish in those areas to greater predation pressure posed by significantly increased

numbers of predators. On the other hand, predators migrating towards large numbers of hatchery

fish concentrated near release sites would reduce their numbers in other areas of the migratory

corridor, which may reduce predation on wild fish in those areas. There was no evidence that

increased predator abundance or increased predation rates on recently released hatchery salmon

either increased or decreased predation on wild salmonids near or away from hatchery release

locations.

Predation buffer – Theoretically, predation on wild fish may be reduced if the numbers of

hatchery-produced fish released exceeds the capacity of the predator population to consume the

additional prey. Studies by Peterman and Gatto (1978), Ruggerone and Rogers (1984), Fresh and

Schroder (1987), and Peterson and De Angelis (1992) investigated the ‘functional response’ (i.e.,

number of prey eaten per unit time per predator) of predators to salmonid prey. In the Columbia

River, Petersen and De Angelis (1992) found that northern pikeminnow predation on juvenile

salmon below McNary Dam fitted a type II or type III functional response. Both of these curves

have an upper limit (asymptote) to the predation rate by a predator population. Numerous factors

can affect the functional response relationships, according to Ruggerone and Rogers (1984).

Generally, however, as prey abundance increased above a given level (the asymptote), predation

was depensatory.

The presence of large numbers of hatchery fish could reduce predation on wild fish under

such conditions only if the abundance of local predator population remained stable or decreased.

Collis et al. (1995) believed this would probably be a false assumption in the Columbia River.

Thus, without complimentary information on both the functional and numerical response of

predators to prey, predictions as to how increases or decreases in hatchery fish abundance will

affect predation on intermixed wild fish would be unfounded. In short, there is no information

which suggests that increased or decreased abundance of hatchery-produced salmon affects

predation on intermixed wild salmonids.

Long-term increase in predator populations – Increases in predator populations caused by

long-term hatchery production are likely to increase predation on wild fish. Kirn et al. (1986)

and Beamesderfer and Rieman (1991) demonstrated that Northern pikeminnow abundance in the

Lower Columbia River appeared to increase during the 1980s at the same time that hatchery

releases increased quite markedly. However, no causal relationship between increases in the

number of hatchery-released fish and long-term increases in population abundance of northern

pikeminnows, or any other predator, has been established.
49

In conclusion, releases of hatchery-reared fish do affect the behavior of predator

populations in the Columbia River system, however, no studies have demonstrated the effects of

such changes on intermixed wild populations. The effects could be either positive or negative for

wild populations.

Effects of hatchery rearing and release strategies on vulnerability of cultured

salmonids to predation.

(a) Rearing strategies

Color acclimation – Semi-natural rearing techniques have been implemented to improve

the cryptic coloration of salmonids and improve their post-release survival. Improved survival of

fish from rearing tanks containing gravel substrates has been attributed by Maynard et al. (1995

and 1996a) to greater cryptic coloration and consequent improvement in predator avoidance.

However, numerous potential behavioral or physiological attributes may have contributed to the

increases in post-release survival, and the reported differences in coloration were not directly

attributed to predation.

Color acclimation has been shown to reduce vulnerability to hooded mergansers in

laboratory raceways in some situations, but not all (Donnelly and Whoriskey 1991, 1993).

Atlantic salmon acclimated to tan colored substrates exhibited a 5:1 survival advantage over

brown-acclimated salmon when both were exposed to mergansers in tan colored raceways.

However, in brown raceways, the color-acclimated brown fish exhibited a 0.5:1 survival

disadvantage. Color-acclimated brook trout survived at a higher rate in tan (1.9:1 survival) and

brown raceways (1.5:1).

Anti-predator conditioning – Anti-predator conditioning efforts have involved various

combinations of visual, olfactory, and auditory stimuli, all of which can trigger innate antipredator responses. Conditioning, using a combination of injured conspecific predator odors in

the absence of visual and auditory stimuli, has been found to improve subsequent predator

recognition and avoidance behavior in rainbow trout and chinook salmon.

A few studies have demonstrated an increase in post-release survival of juvenile

salmonids following anti-predator conditioning in hatchery vessels. Both Thompson (1966) and

Kanayama (1968) demonstrated that post-release survival of chinook and chum salmon smolts

exposed to electrified predator models was greater than for non-conditioned smolts. Berejikian

et al. (1999) found that chemical anti-predator conditioning of chinook salmon smolts in hatchery

tanks containing complex structures improved their post-release survival in a natural stream, but

conditioning did not improve the survival of smolts reared in barren vessels. There is as yet no

evidence that anti-predator conditioning reduces post-release survival.

Fish health – Bacterial kidney disease (BKD) is a major pathogen of fish in hatcheries of

the Pacific Northwest, including the Snake and Columbia River Basins. Mesa et al. (1998) found

a significant effect of Rs infection on the ability of juvenile chinook salmon to avoid predation by
50

northern pikeminnows and smallmouth bass in experimental raceways. Infected fish were eaten

by about twice as frequently as non-infected fish by northern pikeminnows (1.98 infected: 1

control) and smallmouth bass (1.94 infected: 1 control). Measures to control the incidence of

BKD in hatcheries culturing ESA-listed stocks, and in natural streams, should decrease predation

mortality.

In summary, rearing strategies might be modified to reduce the vulnerability of cultured

salmonids to predators. The effects of the different strategies outlined above are probably not

additive. The benefits may range from the high of 50% decrease in predation related mortality

(described by Mesa 1998) to the low of 0% (reported by Berejikian et al. 1999).

Acclimating the color of fish in rearing vessels to that of post-release environment may

offer some reduction in their vulnerability to predators. However, techniques may probably have

to be developed for each rearing and release location, and perhaps for each species.

(b) Release strategies

Time of day - Ruggerone (1986) found that the number of salmonids consumed by gulls

in the Columbia River declined from approximately 400 fish per hour to nearly 0 fish per hour

between 1800 and 2030 hrs. Decreased light intensity also reduced predation by rainbow trout

on sockeye salmon fry (Ginetz and Larkin 1976). Patten (1977) found that torrent sculpin

consumed greater numbers of coho salmon fry (70% mortality) on moonlight nights compared

with darker nights (24% mortality) in laboratory aquaria. Predation by sculpin was not a

significant factor for salmon larger than ~60 mm, and therefore would only apply to programs

releasing age-0 juveniles.

Ginetz and Larkin (1976) found that predation by rainbow trout on sockeye salmon fry

increased as light intensity decreased from .30 ft-c to 0.05 ft-c, but predation decreased as light

intensity further decreased to 0.01 ft-c (simulated cloudy skies and moonlight nights). Predation

on salmonids appears to decrease at very low light levels, so releasing salmon at night may

reduce predation on them during the first several hours after release. Fish are presumed to be at

greatest risk of predation during the first hours to days following release, due to handling stress

and lack of experience in recognizing and avoiding predators.

Release method and abundance – The rate of predation on juvenile salmon will partly

depend on, among numerous other factors, the abundance of the prey and predator populations.

The issue for hatcheries is whether to release smaller numbers of fish over a protracted time

period (e.g., volitional release) or large number in a single ‘pulse’.

Fresh et al. (1980) found that freshwater survival of chum salmon released from a hatchery

increased from 40.3% to 91.5% as the numbers of salmon released increased from 517 fry to

50,155 fry. In a later study, Fresh and Schroder (1987) demonstrated concomitant mortality for

release numbers of chum salmon ranging between 50 and 1,200 fry. Wood (1987) determined

that predation by common mergansers on migrating salmonids (including chum, coho, chinook,

and steelhead) was depensatory during the period of seaward migration in Vancouver Island, BC
51

streams. He suggested that predation rates on hatchery released salmon would be reduced by

releasing large numbers of smolts over a short time period. Other studies by Neave (1953) on

chum and pink salmon, Hunter (1959) with pink, and McIntyre and Wilmot (1988) with sockeye,

have all demonstrated depensatory mortality in natural predator-prey systems. However, no

studies have directly investigated the effects of release number and duration on predation of

chinook salmon and steelhead.

In summary, release strategies for large numbers of hatchery reared chinook salmon and

steelhead at night should decrease overall predation. The level of predation will depend on

numerous environmental factors as well as characteristics and abundance the predator

populations.

Table 9, which follows, summarizes known data for predator-prey interactions between

wild and hatchery-reared salmonids in the Pacific Northwest.

D. Fish Health

Introduction

Infectious diseases are an integral part of the existence of all animals, including both

cultured and wild fish populations. Hedrick (1998) summarized the many perceptions and

misperceptions held by the public and scientific community regarding the spread of infectious

disease from cultured or hatchery raised fish to wild fish. While it is true that human activities

have affected fish health through direct changes in habitat and ecosystems, these changes do not

necessarily mean that fish pathogens were, or are, actively introduced through these actions.

With the exception of the unintentional introduction of ‘exotic’ pathogens in an ecosytem,

fisheries pathologists indicate that most if not all pathogenic microorganisms existed in wild fish

populations before the introduction of hatcheries (Sinderman 1990, Kent et al. 1998, Whittington

et al. 1997). While hatchery populations can be considered reservoirs of infectious agents

because of exposure to higher rearing densities and stress, according to Saunders (1991), Hastein

and Lindstad (1991) said there was little evidence to suggest that disease transmission to wild

stocks is routine. Therefore, it is extremely difficult to determine the incidence of disease

transmission from hatchery to wild fish, as well as the impacts such transmission would have on

wild stocks.

Specific determination of the origin of any particular pathogen found in a wild fish

requires the ability to distinguish different strains of a pathogen at the genetic level. While such

epidemiological tracking can be done on all classes of infectious pathogens (i.e., bacterial, viral,

parasitic, and fungal) using a variety of molecular methods, these techniques have not been

applied to many salmonid pathogens. In many cases reliable genetic strain markers have not

been available, such as with Renibacterium salmoninarum the causal agent of bacterial kidney

disease. However, recent advances reported by Grayson et al. (1999) in genetics and molecular

biology may make this feasible in the near future.
52
53

In 1984, the Pacific Northwest Fish Health Protection Committee1 (PNFHPC) established

policies designed to prevent the spread of pathogens that might result in the release of seriously

infected salmon from hatcheries. This policy calls for destruction of fish infected with the most

serious pathogens. These policies were updated in 1989 by the PNFHPC2 followed by the

establishment of the Salmonid Disease Control Policy of the Fisheries Co-Managers in 1992. It

is suggested that any supplementation project be conducted in a manner that is consistent with

these guidelines, which define rearing, sanitation, and fish health practices that minimize the

incidence of disease outbreaks in propagated populations. For example, cultured salmon should

never be released that are infected with any of the virulent salmonid viruses, such as IHNV.

However, because of limitations in diagnostic procedures for many pathogens, it is difficult to

assure that any hatchery fish are 100% free of pathogens. In many cases this would also be

impractical, since as discussed previously, these same pathogens may be present in wild stocks as

well.

Important salmonid pathogens

The available scientific literature on the spread of infectious disease between hatchery

and wild populations of fish is somewhat limited. According to the PNFHPC guidelines, the

eight most important diseases of salmonids which should be part of fish health screens prior to

release from Pacific Northwest hatcheries are:

bacterial

• Bacterial kidney disease (BKD), caused by Renibacterium salmoninarum

• Bacterial coldwater disease (BCD), caused by Flexibacter psychrophilus

viral

• Infectious hematopoietic necrosis virus (IHNV)

• Erythrocytic inclusion body syndrome (EIBS), probably viral etiology

fungal

• miscellaneous species

parasitic

• Ceratomyxosis, caused by Ceratomyxa shasta

• Whirling disease, caused by Myxobolus cerebralis

• Gill and skin parasites Ichtyoptherius spp. and Ichtyobodo spp.

In addition to this list, infectious pancreatic necrosis virus (IPNV) and viral hemorrhagic

necrosis virus (VHSV) are included in routine health screens. IPNV is readily shed by infected

fish and thus they should not be released. However, the significance of VHSV infection in

1 The PNFHPC includes administrative and fish pathologist representatives from the Washington

Department of Fish and Wildlife, Oregon Department of Fish and Wildlife, California Department of Fish and

Wildlife, Idaho Department of Fish and Game, Alaska Department of Fish and Wildlife, U.S. Fish and Wildlife

Service, National Marine Fisheries Service (Northwest Region), Northwest Indian Fish Commission, and other

private parties representing aquaculture interests. 2

 Model comprehensive fish health protection program, Pacific Northwest Fish Health Protection

Committee, 1989, 19 p.
54

Pacific Northwest salmon is less clear. According to Kocan et al. (1997), the strain endemic to

the area appears to be highly pathogenic for Pacific herring but significantly less pathogenic to

salmonids than the European strain. Therefore, routine screening and isolation of VHSV should

be followed up by strain determination after Basurco et al. (1995).

There is no specific information pertaining to contraction of any of these infectious

diseases from interactions with hatchery stocks in the Upper Columbia River steelhead and

Snake River spring/summer chinook Evolutionarily Significant Units (ESUs). Therefore, this

review will serve to present an overview of selected data on spread of infectious disease in and

between fish populations, with an eye towards interpreting the studies as to how they may relate

to cultured and wild salmonids. It will focus on three areas, namely, the spread of infectious

agents (i) from cultured to wild stocks, (ii) from wild to cultured stocks, and (iii) through other

vectors.

The spread of infectious agents from hatchery fish to wild stocks

BKD - R. salmoninarum can be found world wide in both Salmo and Oncorhynchus genera.

Improvements in detection sensitivity has shown that the bacterium is present in most, if not all,

salmonid populations in the Pacific Northwest. Depending on the technique used to detect R.

salmoninarum, the percentage of fish infected in hatcheries can range from 10-100%, although

no disease symptoms are present (Rhodes et al. 1998). Using the enzyme-linked immunoadsorbent assay (ELISA), surveys of hatchery and wild spring-summer chinook collected at

various dams during out migration on the Snake and Columbia rivers by Elliott et al. (1997)

showed that 68-87% of the fish were infected, although only 1-11% of fish at any one site

showed symptoms of BKD.

There is little data available to help determine the chance of survival of infected fish to

maturity, although hatchery fish from broodstock with low R. salmoninarum levels have a

significantly increased chance of survival in seawater over the progeny of those with high R.

salmoninarum levels (Elliot et al. 1995). Stress is prime activator of quiescent R. salmoninarum

infections, and this includes the transition to saltwater and possibly during the crowding of fish in

transportation barges. Therefore it is possible that heavily infected hatchery fish could transmit

disease to wild stocks because of bacterial shedding that occurs in active R. salmoninarum

infections. However, this has not been shown directly.

Transmission of disease to wild trout from infected hatchery trout has been demonstrated

by Mitchum et al. (1979). Mitchum and Sherman (1981) also showed that wild trout could

transmit the disease to hatchery fish in small lake and stream systems. This may have some

bearing for the horizontal transmission of the bacterium between either juvenile fish after release

in stream systems or during spawning.

In general, horizontal transmission of R. salmoninarum results from fecal shedding of

bacteria by infected fish. Once shed, the bacteria can survive up to 21 days in feces or sediment

under freshwater conditions (Austin and Rayment 1985) and at least 2 weeks in filter-sterilized

seawater (Balfry et al. 1996). A fecal-oral route of transmission is implicated in horizontal
55

transfer in farmed salmon (Balfry et al. 1996) but infection through other epithelia such as skin or

gill may also occur (Flano et al. 1996). This is an important point to consider when trying to

assess the transmissibility of any infectious agent from hatchery to wild fish, and emphasizes the

prudence of thorough health screens on hatchery fish prior to release.

Furunculosis - Aeromonas salmonicida, the causal agent, is endemic in salmonids world wide.

The most significant outbreaks of disease occur in farmed Atlantic salmon or rainbow trout. The

disease usually occurs only under conditions of overcrowding or stress. Furunculosis has been

epidemic in some Norwegian fish farms since 1985, possibly after an initial introduction from

the importation of latent infected Atlantic salmon smolts from Scotland. It has been

hypothesized by Hastein and Lindstad (1991) that the disease spread to fish in 20 Norwegian

rivers from escaped fish, but the significance on overall wild fish survival is unknown..

Parasitic lesions - Gyrodactylus salaris is a parasite of Atlantic salmon which causes extensive

lesions over the body of infected fish. High infestations have been a significant cause of

mortality in Norwegian hatcheries and fish farms. Johnsen and Jensen (1986) found some

evidence that Gyrodactylus was introduced into the wild populations in several Norwegian rivers

from the release of infected hatchery fish, which in turn had become infected from fish imported

into the hatcheries from elsewhere in Scandinavia.. Recently, Soleng et al. (1998) demonstrated

that Atlantic salmon smolts could transmit the parasite to parr, and that adult salmon can serve as

reservoirs of the parasite.

Whirling disease - There are numerous publications on the spread of Myxobolus cerebralis in

the trout population, but little on the effects of the parasite in salmon. Chinook salmon and

steelhead are sensitive to infection with M. cerebralis and show typical disease if exposed at a

young age, while coho are resistant to disease even though they can be infected (Ronald P.

Hedrick, pers. commun.). To date there is no evidence available about the effect of whirling

disease on anadromous salmon populations.

Spread of infectious agents from wild fish to hatchery stocks

IHNV - Meyers (1998) recently reported that juvenile sockeye salmon in Alaska reared in virusfree hatchery water returned as IHNV-infected adults. The virus was isolated in high titers from

fish that matured in either fresh or salt water. However, as the author pointed out, it is difficult to

determine whether the source of virus was a reservoir in either fresh or seawater (possibly from

non-salmonid fish species), or whether there was vertical transmission from parents with

subclinical, undetectable infections. The report illustrates the difficulty in eliminating a pathogen

from anadromous fish populations.

Similar IHNV infections in returning chum and chinook salmon at an Alaskan hatchery

were noted by Follett et al. (1987). They raised the possibility that horizontal transmission of the

virus could have come from resident kokanee in the hatchery water supply.

BKD - Natural horizontal transmission of R. salmoninarum and subsequent development of

BKD was demonstrated by Mitchum and Sherman (1981) by exposing hatchery-raised brook,
56

brown, and rainbow trout to naturally infected brook trout kept in a small lake and stream

system. This study showed that R. salmoninarum is transmissible from fish to fish outside of a

hatchery setting. Previously, Mitchum et al. (1979) had demonstrated that infections of wild

trout could originate with hatchery fish as well.

Bacterial pathogens - Streptococcus iniae is a bacterial pathogen capable of causing infections

in salmonids, tilapines, and many other fish species. Zlotkin et al. (1998) isolated the pathogen

from diseased wild fish near marine fish culture facilities where gilthead sea bream and European

sea bass exhibited similar infections. Bacterial species-specific PCR and ribotyping confirmed

that the wild and cultured fish were infected by a single S. iniae clone, suggesting that the wild

fish are potential amplifiers of pathogenic bacteria.

Spread of infectious agents through other vectors

There have been numerous reports of transmission of infectious agents from fish to other

fish via passage through an intermediate host. The most famous example is the organism

responsible for whirling disease, M. cerebralis, that is passed from fish to fish through

oligochaete worms, Tubifex tubifex (Rognlie and Knapp 1998). However, birds appear to be able

to spread pathogens as well through their feces, after ingestion of infected fish. This has been

clearly shown for a number of salmonid and other fish pathogens, including IHNV and VHSV by

Peters and Neukirch (1986), epizootic haematopoietic necrosis virus (EHNV) in redfin perch by

Whittington et al. (1996), and M. cerebralis by Taylor and Lott (1978). Recent media reports

(Seattle Times, Jan. 17, 1998; Seattle Post-Intelligence, May 24, 1999) of Caspian terns eating

out-migrating juvenile salmon in the Columbia river suggest that these birds could serve as a

reservoir for infectious disease agents and subsequently transfer them to other wild fish

populations through their feces.

E. Migratory Behavior

Potential migratory behavioral interaction between hatchery and wild fish includes a

downstream schooling influence. This refers to the downstream sweeping of wild fish by large

numbers of downstream migrant hatchery fish, known commonly as the ‘pied piper effect.’ The

phenomenon has been observed and reported by scuba divers. Despite these reports, there is

little or no documentation of the frequency of the phenomenon, or the conditions under which it

occurs. There are no quantitative studies of the impacts of such behavior on subsequent survival

of Pacific salmon species, or data documenting the effects on differential survival between

hatchery and wild fish.

There are some reports of sweeping phenomena occurring during the out-migration of

young Atlantic salmon. Hansen and Jonsson (1985) observed that stocking receiving waters with

hatchery-reared smolts seemed to initiate formation of schools during the period of smolt outmigration. This school formation phenomenon is not absolute, as the simultaneous release of
57

two different stocks of juvenile Atlantic salmon showed that only some of one stock followed the

more rapidly migrating stock downstream, but the majority of the slower stock remained behind

(Aarestrup et al. 1999). Clearer documentation of the schooling phenomenon has been provided

by Hvidsten et al. (1995), who showed that the time to travel to a downstream trap was

independent of the distance from the point of release when the fish were traveling in schools.

There is no clear published evidence of the impact of downstream sweeping of smolts on

subsequent survival. Hvidsten and Johnsen (1993) suggested that such a phenomenon may result

in increased smolt-to-adult survival (SAR). They recorded 6.8% SAR for hatchery-reared

Atlantic salmon released into a stream during peaks of smolt out-migration compared with only

2.6% SAR during the troughs.
58
59

IV. CONCLUSIONS AND RECOMMENDATIONS

The recent listings of Northwest salmon stocks as threatened or endangered under the

ESA has initiated renewed focus on the operation of the public fish hatchery system in the

Pacific Northwest. Hatchery strategies offer the potential to stabilize and amplify salmonid

populations. Nonetheless, it is clear that the artificial culture environment conditions salmonids

to respond to food, habitat, con-specifics, and predators in ways different from those of fish

reared in natural environments. Consequently, fundamental changes in the dynamics of hatchery

production policy and implementation may be necessary both where hatchery supplementation is

used to maintain some populations until underlying causes of decline are corrected, and where

production hatchery operations overlap listed stocks.

Potential effects of artificial production strategies on population dynamics of wild salmon

is a primary concern for ESA-listed stocks. Tables 10 and 11 summarize an assessment of the

potential effects of artificial production strategies on population abundance of wild Snake River

spring/summer chinook and Upper Columbia River steelhead in their respective ESUs.

Unfortunately, the overall effectiveness of supplementation to maintain a population until

underlying causes of decline are corrected is unknown. Very little specific numerical information

exists regarding population abundance dynamics or interactive factors, such as competition,

predation, migration, and fish health. Therefore, for the most part, the assessments are couched

in terms of directional trends rather than absolute values.

Future use of artificial propagation in the Columbia Basin will be a direct function of

both the status of the natural populations and their habitats. For supplementation and recovery

purposes, the productivity of the naturally spawning populations will be a key population

parameter. Basically, if productivity is significantly >1, then populations can probably be

recovered without the risks of artificial propagation. If the ratio is <1, and modeling shows that

over time extinction will be imminent, then the benefits with artificial propagation should

outweigh the risks. Artificial propagation risks may be ameliorated by development and

implementation of conservation hatchery protocols which have the potential to improve fitness

and survival of hatchery fish.

It is clear from this review that the Region needs to focus research to develop policies and

procedures which properly integrate the roles of hatcheries for conservation and sustainability of

salmonid populations. Information currently available is not adequate to assess properly the

potential effects of hatchery operations on wild stocks. Among key questions to be answered by

scientific research include:

• Is it possible to produce more adaptable wild-like juveniles from conservation hatcheries with

the fitness necessary to aid rebuilding of ESA listed stocks?

• Is it possible to minimize the impacts on wild fish by releases from production hatcheries for

sustainable fisheries?

• What are the relative probabilities of meeting the survival and recovery goals for salmon in

the Columbia River Basin under different artificial propagation scenarios?
60

Finally, research data sets should be compiled in a manner to allow generalized

correlation between indicators of natural population productivity and artificial propagation

factors. Development of an overall complete understanding of the current and potential role(s) of

hatcheries on the sustainability of natural stocks is a vitally important undertaking for rebuilding

efforts for depleted stocks.
61
62
63

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85

APPENDIX
86
87

A. THE IMNAHA SPRING/SUMMER CHINOOK

SUPPLEMENTATION PROJECT

Species: Spring/summer chinook

Location: Imnaha Basin, North Eastern Oregon

Starting Date: 1982 broodyear

Planned Duration: Not known

Status: On-going

Production Level: 25,000 to 445,000/year

Size: 25 g mean size for 1990-1994 (mean wt. range 21 - 41 g)

1. The Status of the Stock before Supplementation

The program was initiated under the Lower Snake River Compensation Plan as a mitigation

program to provide surplus hatchery fish for harvest. The redd count in the Imnaha River Basin

has shown a general decrease over the past 40 years (see Figure 1).

1950 1960 1970 1980 1990 2000

0

200

400

600

800

Pre-Project

Supplementation

Year

Number of Redds

Figure 1. Redd counts, showing pre-project and supplement periods.

2. Monitoring and Evaluation

A monitoring and evaluation program was started in 1994. The objectives are to assess

the effectiveness of the hatchery program in increasing adult production, adult

progeny:parent ratios, and escapement to the Imnaha River; to estimate total annual adult

production (catch and escapement), smolt-to-adult survival, and smolt migration success
88

of hatchery fish; to monitor and compare life history characteristics of natural and

hatchery fish; and to make recommendations for improving the success of achieving

mitigation goals and management objectives (Carmichael and Messmer, 1995).

3. Results

The adult progeny:parent ratios (AD:P) of hatchery and wild fish (ODFW 1998) are detailed

below:

Year Wild Fish Hatchery Fish

AD:P Ratio Contribution1 AD:P Ratio Contribution1

1982 1.05 105 8.82 882

1983 1.15 115 1.25 125

1984 0.26 26 3.08 308

1985 0.17 17 1.96 196

1986 0.41 41 1.52 152

1987 0.44 44 3.73 373

1988 0.72 72 12.6 1260

1989 0.55 55 3.81 381

1990 0.2 20 0.51 51

1991 0.2 20 1.09 109

1992 0.5 50 0.62 62

Average 0.51 3.54

Total 565 3,899

1 Adult contribution based on a hypothetical spawning of 50 pairs of salmon

4. Conclusions

Based on published AD:P ratios, it appears that this supplementation project may be increasing

the number of returning adults. The AD:P ratio for the hatchery fish on the average, has been

about 7 times larger than for the wild fish. (Note: there are significant differences in AD:P ratios

listed in Carmichael and Messmer, 1995 and ODFW 1998. This is probably due to inclusion of

jacks in the adult counts.)
89

Based on a hypothetical 50 pair program (see above table), the supplementation program would

have contributed 3,899 adults over the 1982-1992 time period. If these hypothetical fish had

been allowed to spawn in the wild, only 540 adults would have been produced. The overall

population trend appears to still be downward (ODFW 1998).

B. THE BIG QUILCENE RIVER SUMMER CHUM

SUPPLEMENTATION PROJECT

Species: Chum salmon

Location: Hood Canal, Washington

Starting Date: 1992

Planned Duration: 12 years

Status: On-going

Production Level: 325,000 (mean) over last 7 years (range 24,784 to 612,598)

Size: 1.1 to 1.6 g

1. The Status of the Stock before Supplementation

In 1992 the stock was in critical condition (WDF et al. 1993). Escape had fallen to extremely

low levels and habitat conditions had become very poor in the lower river where summer chum

spawned. A supplementation project was begun in the Big Quilcene River and has for the most

part been successful (SWG 1999).

2. Monitoring and Evaluation

Since the inception of the project there has been only limited marking of hatchery

releases. Therefore differentiation between hatchery-origin and natural-origin fish on the

spawning grounds has not been feasible. However, all brood year 1997 and 1998

hatchery releases were marked with adipose fin clips and it is expected such marking will

continue the duration of the project (SWG 1999).
90

3. Results

Period Status Total Adult Escape over the Period

Big Quilcene Dosewallip (Control) Duckabush

(Control)

1984 - 1994 Pre-supplementation 1,069 2,434 2,204

1995 - 1998 Supplementation 22,091 10,146 4,176

Increase over the Supplementation/ x21 x4.2 x1.9

Pre-supplementation period (factor)

Excess due to supplementation based 18,884 — —

average increase in controls

Assuming that the 18,884 “excess” fish are of hatchery origin and a mean release of 325,000, the

smolt-to-adult return (SAR) of the hatchery fish would be 5.8%.

4. Conclusions

The Summer Chum Work Group considers this a successful supplementation project, even

though it is currently impossible to distinguish returning wild and hatchery-origin fish. The

escape to the Big Quilcene River has increased by a factor of x21 compared with the presupplementation levels. During this same period, the returns to the Dosewallip and Duckabush

only increased by factors of x4.2 and x1.9, respectively. These increases in escapement could

also be due to reduction in harvest rate, increases in marine survival, and improvements in

freshwater habitat (Johnson et al. 1997).
91

C. THE MID-COLUMBIA FALL CHINOOK

SUPPLEMENTATION PROJECT

Species: Fall Chinook

Location: Hanford Reach, Mid-Columbia

Starting Date: 1980

Planned Duration: ????

Status: On-going

Production Level: 8.09 million fish for 1983-1992 (ranged from 5.4 to 11.8 million)

Size: Release goal of 50/lb (9.1 g)

1. Status of the Stock before Supplementation

This program is operated as mitigation for fishery impacts caused by the Priest Rapids Projects

(Priest Rapids and Wanapum dams). The current escapement appears to be relatively stable

compared with the average historical run size. The increase in run size during the 1980s could be

due to the hatchery program (Dauble and Watson 1997).

1960 1970 1980 1990 2000

0

50000

100000

150000

200000

Year

Total Fall Chinook Run Size Over McNary Dam

Figure 1. Estimated total run size of fall chinook to the Hanford Reach (Dauble and Watson

1997).
92

2. Monitoring and Evaluation

The portion of marked hatchery fish has ranged from 3-19% over the last 10 years.

3. Results

The adult progeny:parent ratios of hatchery and wild fish are detailed below:

Year Wild Fish Hatchery Fish

AD:P Ratio Contribution1 AD:P Ratio Contribution1

1980 1.76 880 8.37 4,185

1981 4.34 2,170 4.41 2,205

1982 4.54 2,270 3.83 1,915

1983 2.58 1,290 1.86 930

1984 2.82 1,410 1.59 795

1985 2.18 1,090 1.52 760

1986 0.50 250 1.54 770

1987 0.50 250 1.07 535

1988 0.41 205 1013 565

1989 0.61 305 1.65 825

1990 0.87 435 1.16 580

1991 0.92 460 1.42 710

Average 1.84 2.46

Total 11,015 14,775

1 Adult contribution based on a hypothetical spawning of 250 pairs of salmon

4. Conclusions

Over the period of 1980-1995, the percentage adult contribution from hatchery releases averaged

5% (PSMFS 1999). Therefore, this program is a minor contribution to the larger healthy wild

stock.