INFORMATION
REPORTS
NUMBER 2006-__
FISH DIVISION
Oregon Department of Fish and Wildlife
Life History and Reproductive Characteristics of Hatchery and NaturalFemaleImnahaRiver Chinook Salmon Spawned in Captivity, Brood Years 1982-2000
This program receives federal financial assistance from the U.S. Fish and Wildlife Service and prohibits discrimination on the basis of race, color, national origin, age, sex or disability. If you believe that you have been discriminated against as described above in any program, activity or facility or if you desire further information, please contact ADA coordinator, Oregon Department of Fish and Wildlife, 3406 Cherry Drive NE, Salem, OR 97303, 503-947-6000, or write Office for Human Resources, U.S. Fish and Wildlife Service, Department of the Interior, Washington, DC 20240.
This report is available at: RESEARCH PROJECT
FISH RESEARCH PROJECT
OREGON
Life History and Reproductive Characteristics
of Female Hatchery and NaturalImnahaRiver Chinook Salmon
Spawned in Captivity
Prepared by:Debra L. Eddy
Timothy L. Hoffnagle
Richard W. Carmichael
Oregon Department of Fish and Wildlife
203 Badgley Hall
Eastern OregonUniversity
La Grande, OR 97850
This project was funded by the U.S. Fish and Wildlife Service under the Lower Snake River Compensation Plan.
Contents
PageTable of Contents …………………………………………………. / ii
List of Figures …………………………………………………….. / iii
Abstract …………………………………………………………… / iv
Introduction ………………………………………………………. / 1
Methods…………………………………………………………… / 4
Results ……………………………………………………………. / 6
Age …………………………………………………………… / 6
Body Size and Condition ……………………………………... / 7
Eyed Egg Weight ……………………………………………... / 11
Fecundity ……………………………………………………… / 12
Ovosomatic Index ……………………………………………... / 14
Spawn Timing ………………………………………………… / 15
Discussion ………………………………………………………... / 16
Age …………………………………………………………… / 16
Body Size and Condition ……………………………………... / 17
Egg Weight, Fecundity, and Ovosomatic Index ……………… / 17
Spawn Timing ………………………………………………… / 19
Broodstock Collection ………………………………………… / 22
Supplementation ………………………………………………. / 23
Conclusion……………………………………………………….... / 25
Acknowledgements ………………………………………………. / 26
References ………………………………………………………... / 27
List of Figures
PageFigure 1. Number of Chinook salmon redds in spawning
ground survey index sections (15.6 km) of the ImnahaRiver,
1949-2004. …………………………………………………………………. / 3
Figure 2. Percent age 5 hatchery and natural Imnaha River Chinook
salmon females spawned in captivity, brood years 1982-2000...... / 6
Figure 3. Mean (± 1 SD) age of hatchery and natural ImnahaRiver
Chinook salmon females spawned in captivity, brood years 1982-2000…… / 7
Figure 4. Mean (± 1 SD) length of hatchery and natural ImnahaRiver
Chinook salmon females spawned in captivity, brood years 1982-2000…… / 9
Figure 5. Mean (± 1 SD) weight of hatchery and natural ImnahaRiver
Chinook salmon females spawned in captivity, brood years 1982-2000…… / 10
Figure 6. Mean (± 1 SD) condition factor (K) of hatchery and natural
Imnaha River Chinook salmon females spawned in captivity, brood years
1982-2000…………………………………………………………………... / 11
Figure 7. Mean (± 1 SE) eyed egg weight of hatchery and natural Imnaha
River Chinook salmon females spawned in captivity, brood years
1982-2000…………………………………………………………………. / 12
Figure 8. Mean (± 1 SD) fecundity of hatchery and natural ImnahaRiver
Chinook salmon females spawned in captivity, brood years 1982-2000….. / 13
Figure 9. Mean (± 1 SD) ovosomatic index of hatchery and natural Imnaha
River Chinook salmon females spawned in captivity, brood years
1982-2000..…………………………………………………………………. / 14
Figure 10. Mean (± 1 SD) spawn week of hatchery and natural Imnaha
River Chinook salmon females spawned in captivity, brood years
1982-2000…………………………………………………………………... / 15
Abstract
The natural population of Imnaha River Chinook salmon Oncorhynchus tshawytscha has been supplemented with hatchery-produced salmon since 1984. This supplementation program has incorporated both hatchery and natural salmoninto each year's broodstock in an effort to maintain the genetic and life history characteristics of the population. We examined data collected during hatchery broodstock spawningof the 1982-2000 brood years for differences between natural and hatchery females and for changes over time in spawning characteristics within females of the same origin. Natural females were older, longer, and heavier at spawning. Eggs of natural females weighed more thaneggs of hatchery femalesand this difference seemed to be an effect of both age and origin. Mean ovosomatic index was higher in hatchery females than natural females. Three-quarters of the hatchery females matured at age 4, while only 46.5% of natural females matured at age 4. We found that natural femalesspawnedearlierin the year than hatchery femalesand that age 5 females also spawned earlier than age 4 females. Mean age at spawning, egg weight, female length, female weight, condition factor,ovosomatic index and mean spawn time remained stable over the brood years studied for both groups. Although supplementation has had no apparent effect on fecundity of natural females, the difference in age at maturity between hatchery and natural females is cause for concern. In addition, the difference in spawn timing, though not great, may impede interbreeding between natural and hatchery salmon in the hatchery and in nature. This may hinder supplementation efforts and be detrimental to the naturally-reproducing population of Imnaha River Chinook salmon.
1
Introduction
Supplementation has been defined as “the use of artificial propagation in 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 nontarget populations within specified biological limits” (RASP 1992). Supplementation has been selected as a primary management strategy to enhance natural production for many salmon Oncorhynchus sp. populations in the ColumbiaRiver Basinand many concerns have arisen regarding potential risks of these programs on the natural populations they are intended to help (Waples 1999). Goodman (2005) noted that artificial propagation tends to produce domestication selection - adaptation to artificial propagation conditions rather than the natural environment. The result is that the genetic composition of the supplemented population differs from what it would have been in the absence of a hatchery program. Unfortunately, adaptations for good performance in captivity can have the opposite result in nature, reducing the overall performance of the natural population due to interbreeding of hatchery and natural fish (Miller and Kapuscinski 2003).
The Imnaha River Chinook Salmon Supplementation Program is operated as an integrated hatchery program, in which both hatchery- and natural-origin Chinook salmon O. tshawytchaare managed as a single gene pool (Campton and Mobrand 2004). Each year, both hatchery and natural salmon are spawned together in the broodstock. As the resulting progeny return,the expectation is thatnatural selection in the wild willdetermine the overallfitness of the population, regardless of individual origin.
Hatchery programs within supplemented populations, by necessity or convenience, are often generated from a limited number of broodstock. Allendorf and Phelps (1980) noted that “genetic variability is the primary biological resource in the successful artificial propagation of any species." The smaller the number of parents which contribute gametes, the less likely they are to represent the full spectrum of genetic resources of the population. This results in aloss of genetic variability, which can seriously impact a population’s ability to adapt to changes in the environment and thus reduce its chances of long-term survival (Fleming and Petersson 2001). In addition, hatchery-reared salmonmay survive better, especially in early life stages, and thus make a greater relative contribution to the progeny than natural salmon,further decreasingthe genetic variabilityof an already limited broodstock. Because more offspring are produced by fewer (hatchery) parents, a potentially serious result is that supplementation may actually reduce the effective population size of the parent generation below what it would have been without any supplementation at all (Ryman and Laikre 1991), rapidly reducing the genetic diversity of the population.
Detrimental effects caused by loss of genetic variability in salmon stocks include changes in life history traits and physical characteristics, such as survival of eggs and fry, growth rate, feed conversion, and body shape. Heath et al. (2003) reported that mean egg size in hatchery-reared salmon becomes smaller over time, concluding that hatchery rearing has relaxed the natural selection for larger eggs. However, Quinn et al. (2004)found no change in egg size in the Chinook and coho salmonO. kisutchthey examined. Larger eggs survive better in nature and produce larger offspring, which in turn survive better in the wild, perhaps because they are able to avoid predation and cope with competition better than smaller members of their cohort (Ojanguren et al. 1996; Quinn et al. 2004). Likewise, run timing and spawn timing are heritable traits that may affect population survival (Hendry et al. 1999; Quinn et al. 2002). Fecundity is also heritable, as are age and size at maturity, with which fecundity is correlated (Kinnison et al. 2001; Smoker et al. 2000). A major goal of any supplementationprogram must be the preservation of natural genetic variation of the supplemented population. This genetic material and the heritable life-history characteristics of the natural population can best be preserved by including local natural-origin salmon in the broodstock (Allendorf and Phelps 1980).
The ImnahaRiverspring/summer Chinook salmon population of northeast Oregon is a portion of the ESA-listed Snake River ESU (Federal Register 1992, volume 57, number 78). It experienced a major decline during the decades of lower Snake River dam construction and subsequent operation (Figure 1). In 1976, the Lower Snake River Compensation Plan was authorized to mitigate for losses of fishery resources that resulted from dam construction and operation (Herrig 1998) and, in 1982, the Oregon Department of Fish and Wildlife(ODFW) initiated the Imnaha River Chinook Salmon Supplementation Program, using only native Imnaha River Chinook salmon adults captured as they returned to their natal spawning groundsfor broodstock (Carmichael and Messmer 1995). Broodstock are spawned in captivity, most years at Lookingglass Fish Hatchery, and the resulting offspring are raised to smolt before their release into the ImnahaRiver(Carmichael and Wagner 1983; Carmichael and Messmer 1985; Carmichael et al. 1986; 1987; 1988; 1999; 2004; Carmichael 1989; Messmer et al. 1989; 1990;
Figure 1. Number of Chinook salmon redds in spawning ground survey index sections (15.6 km) of the Imnaha River, 1949-2004.
1991; 1992; 1993; Hoffnagle et al. 2005a; Monzyk et al. 2005). Fishery managers hoped that carefully supplementing naturally-produced salmon with hatchery salmon would give the ImnahaRiver system sufficient time to restore to a self-sustaining population, while ensuring that both the genetic and life history characteristics of hatchery salmon mimic those of naturally-produced salmon (Carmichael and Messmer 1995). That is, the physical and genetic traits of both naturally- and hatchery-produced salmon should be the same. However, Hoffnagle et al. (2005b) found that hatchery-produced Chinook salmon arrived at the weir later, spawned later in nature, and were distributed more downstream than naturally-produced salmon.
The ImnahaRiver weir is installed each year after flows have decreased, to approximately 26 m3/s, to prevent it from being blown-out by debris in high discharge. Consequently, it is not usually operational until early July, well after a portion of the run has already passed the weir site. Due to these constraints, Hoffnagle et al. (2005b) estimated that a mean of only 60% of the Chinook salmon passing the ImnahaRiver weir are captured each year. This means that all salmon collected for broodstock have been taken from the late-returning portion of the run. Indeed, during the beginning years of the program (1982-1984) all broodstock were taken from the extreme late portion of the run (late August – early September).
In light of the findings of Hoffnagle et al. (2005b), we examined data from the 1982-2000 brood years Imnaha River Chinook salmon, collected for hatchery broodstock and spawned in captivity to determine if divergence between hatchery and natural salmon is evident here, as well. We compared age at spawning, eyed egg weight, female length, weight and condition factor, ovosomatic index, fecundity, and spawn timing between hatchery and natural females spawned in captivity. We also looked for changes in these characteristics over time, within females of the same origin.
Methods
We examined data collected as part of monitoring Imnaha River Chinook Salmon Supplementation Program spawning at Lookingglass Fish Hatchery (1986-1988, 1990-2005) and the Imnaha River Spawning and Acclimation Facility (1984-1985, 1987, 1989). Female length, origin (hatchery vs. natural, based on fin clips), fecundity, and spawn date were recorded from ImnahaRiver females spawned in captivityfrom 1984-2005. Egg weight, female weight, and female age were also recorded, beginning in 1988. We have data for 847 hatchery and 521 natural female Imnaha River Chinook salmon spawned in captivity. However, not all data were collected during all years.
During each spawning season, females were checked for ripeness weekly, beginning approximately the first week of August and continuing through the end of spawning. Spawning took place at or near the time females became fully ripe. We weighed females to the nearest 0.1 kg prior to being spawned and collected eggs in a clean, dry colander. After each female was spawned, we measured length to the nearest 1 mm and collected snouts containing coded-wire tags (hatchery salmon) or scale samples (natural salmon) from most salmon to determine age and confirm origin. When coded-wire tags or scales were not available, we estimated age by fork length of the female using a relationship developed previously for Imnaha River Chinook salmon:< 650 mm = age 3; 650-849 mm = age 4; ≥ 850 mm = age 5.
Methods of measuring mean egg weight and fecundity changed over the course of the Imnaha River Chinook Salmon Supplementation Program. The protocols used in some years were not specifically designed to compare hatchery versus natural characteristics or to examine changes in these parameters over time, but the data are comparable. From 1984 – 1987, 1989, 1990, and 1997 - 2000, eggs from multiple females were combined in a single tray, so we do not have individual egg weight or fecundity data available for these years.
In 1988, each colander with eggs was weighed and total weight minus colander weight was recorded as "ovary weight." Two samples of green eggs, ranging from 199-365 eggs each, were taken from each female, enumerated, and weighed to the nearest 0.1 g to determine mean green egg weight. All eggs not collected in the colander, including eggs spilled on the ground or remaining in the female, were counted and recorded as "eggs not spawned.” We estimated fecundity by dividing total ovary weight by mean egg weight and adding any eggs not spawned. From 1991-1996, we trayed each female’s eggs individually and recorded eggs lost from each tray. At eye-up we weighed and counted the number of eggs in one or more samples to determine mean eyed egg weight. From 1991-1994, one sample of 300 eggs was taken per female. From 1995-1996, two samples of 200 eggs each were taken per female. We estimated fecundity by dividing the total weight of each female’s eggs by her mean egg weight and adding any eggs lost prior to eye-up or at shocking. In 2001 and 2002, we measured individual weights for 20 green eggsfrom each female and in 2003, we measured both green and eyed egg weights for 20 eggs per female to develop an equation that allowed us to estimate eyed egg weight from green egg weight. This equation [eyed egg weight = 0.02066 + (green egg weight x 1.04432)] was highly significant (P < 0.0001) and the relationship was highly correlated (r2 = 0.9379). In 2001 and 2002, we also measured “ovary weight” and estimated fecundity by dividing total ovary weight by mean egg weight and adding any eggs not spawned. In 2003, 2004 and 2005, we weighed 20 eyed eggs from each female, to estimate mean eyed egg weight, and counted all eyed eggs from each female by Jensorter machine. We estimated fecundity by adding any eggs lost prior to eye-up (including at shocking) to each female’s eyed egg count. We calculated ovosomatic index (OSI) as the number of eggs/kg of body weight per female.
We compared mean age, fork length, body weight,condition factor (K), eyed egg weight (actual or estimated from green egg weight), fecundity, OSI, andspawn week (week of the year) of hatchery and natural females using a t-test and by MANOVA(Sokal and Rohlf 1995). We calculated the percent age composition, by broodyear, for hatchery and natural salmon and used an arcsine transformation of these percentage data to compare mean percentages of females in each age class between hatchery and natural salmon by t-test (Sokal and Rohlf 1995; Krebs 1989). We also examined trends in these variables over time, overall and by origin and age, using regression (Sokal and Rohlf 1995). Where age of the female affected the results (e.g., fork length, weight, mean egg weight, ovosomatic index, and fecundity) due to the effect of strong cohorts in one group, we compared these variables within age classes.
Results
Age
Natural females taken for broodstock matured at a greater mean age (4.5 years) than hatchery females(4.3 years; P0.0001). Slightly over half the naturalImnaha River Chinook salmon femalestaken for broodstock (53.5%) wereage 5 at spawning, while 73.7% of hatchery Chinook salmon females were age 4 and only 26.3% were age 5 (Figure 2).
Figure 2. Percent age 5 hatchery and natural Imnaha River Chinook salmon females spawned in captivity, brood years 1982-2000.
Figure 3. Mean (±1 SD) age of hatchery and natural Imnaha River Chinook salmon females spawned in captivity, brood years 1982-2000.
Body Size and Condition
Older females tended to be longer and heavier than younger females. Mean length of age 5 females (904.3 mm) was greater than mean length of age 4 females (788.9; P<0.0001)and mean weight of age 5 females (7.9 kg) was greater than mean weight of age 4 females (5.5 kg; P<0.0001). Bothfemale length and weight differed by origin. Mean length of natural females (854.2 mm) was greater than the mean length of hatchery females (817.0 mm; P<0.0001; Figure 4). Mean weight followed the same pattern, with natural females having a greater mean weight (6.8 kg) than hatchery females (6.1 kg; P<0.0001; Figure 5). At leastpart of this difference may be attributable to the higher proportion of age 5 natural females (53.5%) compared to the relatively low proportion of age 5 hatchery females (26.3%). However, there appears to be some intrinsic difference in female lengthbased on origin, as age 5 natural fish had greater mean length (909.6 mm) than age 5 hatchery fish (897.7 mm; P=0.0023). There was no difference in length at age 4 (P=0.4789). We found no difference in female weight by origin at ages 4 or 5 (P≥0.3190). Condition factor did not differ by age, origin, or by origin at ages 4 or 5 (P≥0.0725; Figure 6).