Hatchery Smolts Research Articles

Migration of Atlantic Salmon, Salmo salar, Smolt through the Estuary Area of River Ellidaar in Iceland

We tagged both wild and hatchery Atlantic salmon, Salmo salar, smolts from River Ellidaar (64 ° 08′ N, 21 ° 50′ W) with ultrasonic tags. We caught the wild smolts in a smolt trap and selected the largest individuals from the run. We implanted the transmitters in the abdominal cavity of the fish and then released them in River Ellidaar close to the estuary. We used four ultrasonic receivers; one in the river’s estuary, one outside the estuary and two further away on both sides of an island in the estuary zone. The receivers recorded all transmitters within a 600 m radius. The hatchery smolts were larger than the wild smolts. Some of the smolts were lost on the way through the estuary. Only 4 out of 9 wild smolts and 14 of 17 hatchery smolts were recorded all the way through. The tags and the tagging likely affected the survival of the smolts especially the smaller fish. There were no differences in the smolt migration between the 2 years of study and no differences in the migration behavior between the wild and the hatchery smolts. After being released the smolts stayed on average for 10 h in the river then migrated into the estuary were they stayed for 54 h on average. Then they migrated straight through the area to the sea at approximately 0.2 fish lengths per second. We recorded large differences in the migration.

Gene expression patterns in Atlantic salmon Salmo salar: gene expression during osmoregulation in intestine tissue

Ireland has the world's largest stocks of wild Atlantic salmon. A better understanding of gene expression will benefit conservation of wild stock as well as salmon aquaculture. We describe the PRTLI project designed to advance the fundamental understanding of the genome of Atlantic Salmon Salmo salar. The major objective is to create the first comprehensive database of gene expression and functional information using cDNA libraries and Microarray technology. One key area of interest to salmon biology is osmoregulation, which is critical to the ability of salmon to adapt in seawater. Tissues implicated in this process are the gills, intestine and skin. To initiate studies, SSH (suppression subtractive hybridization) libraries were constructed from intestine RNA extracted from smolts sampled in January and May. A number of potentially interesting clones have been identified, among those a heat shock protein, hsp90 in the reverse library. Others SSH libraries from various tissues (pituitary, hypothalamus, brain, gill, intestine, head kidney and spleen) have also been constructed and will be used to construct a 5000 clone microarray slide. This slide will then be used to elucidate gene expression profiles in various tissues. Further sample collection has been carried out to answer questions regarding biologicaldifferences between one‐ year and two‐year old parr and wild and hatchery smolt.

Interactions between endangered wild and hatchery salmonids: can the pitfalls of artificial propagation be avoided in small coastal streams?

Hatchery and wild juvenile populations of steelhead Oncorhynchus mykiss and coho salmon Oncorhynchus kisutch, in a small coastal watershed in central California, were sampled throughout the year in a stream and at a hatchery. Both species grew faster in captivity than in the wild. Hatchery fish of both species had elevated gill Na+, K+‐ATPase activity, and thus were ready to enter sea water when planted during the wild fish migration. Downstream migrant trapping and stream surveys indicated that hatchery smolts went to sea soon after planting, consequently avoiding the effects of competition and predation that commonly occur when hatchery‐bred juveniles are released. Adult steelhead were also sampled throughout the watershed. The return of hatchery steelhead was highly synchronized with that of wild steelhead, indicating that hatchery propagation had no adverse effects on the timing of the run. A disproportionate number of hatchery steelhead returned to the tributary where the hatchery was located, despite being planted throughout the watershed. Hatchery steelhead did not differ in mean age or size from wild steelhead. Observations of spawning indicated that hatchery and wild steelhead interbreed. Competition for mates or spawning substratum was rarely observed between hatchery and wild steelhead. Many of the problems commonly associated with artificial propagation can be avoided in small coastal watersheds when wild broodstock are used and fish are released as smolts.

Early ocean survival and marine movements of hatchery and wild steelhead trout (Oncorhynchus mykiss) determined by an acoustic array: Queen Charlotte Strait, British Columbia

Early ocean movements, residency, and survival of steelhead (Oncorhynchus mykiss) were examinedin Queen Charlotte Strait, a large (20 � 100 km 2 ) marine area separating Vancouver Islandfrom the mainland . The results provide the first detailed data on the ocean biology of hatchery and wild steelhead smolts. Initial ocean movements were not strongly directed, with most smolts swimming in the range of 0.2–0.5 body length (BL) s � 1 . The majority (78%) vacatedQueen Charlotte Strait within 1 week of release in freshwater. Relative marine survival of hatchery smolts surgically implanted1 month prior to release was id entical to that of wildsmolts implantedon the d ay of release; survival of hatchery smolts transported to the study site, implanted, and released all on the same day was significantly lower. The results suggest that the early marine survival of hatchery andwildsmolts may be fundamentally similar, but that the cumulative stress of transportation andsurgery may red uce post-surgery survival. Hatchery smolts movedat higher average swimming speeds than wild smolts, but the difference was not statistically significant. Early marine survival within the study region appears to be relatively high (X55%), contradicting assumptions that the early marine phase is the critical periodfor d etermining salmon recruitment. r 2004 Elsevier Ltd. All rights reserved.

The influence of hatchery coho salmon (Oncorhynchus kisutch) on the productivity of wild coho salmon populations in Oregon coastal basins

To aid in the recovery of depressed wild salmon populations, the operation of hatcheries must be changed to reduce interactions of juvenile hatchery fish with wild fish. Evidence suggests that productivity of wild populations can be reduced by the presence of large numbers of hatchery smolts in lower rivers and estuaries that attract predators. An index of productivity based on the density-independent rate of reproduction of wild coho salmon (Oncorhynchus kisutch) in 12 Oregon coastal river basins and two lake basins was negatively correlated with the average number of hatchery coho salmon smolts released in each basin. The index of productivity was not significantly correlated with the average proportion of hatchery coho salmon in each naturally spawning population or with habitat quality. Alterations to hatchery programs that could encourage recovery of wild populations include (i) avoiding release of large numbers of smolts in areas with high concentrations of wild fish, (ii) decreasing the number of smolts released, and (iii) using a volitional release strategy or a strategy that employs smaller release groups spread temporally.

Effect of Acclimation on the Homing and Survival of Hatchery Winter Steelhead

Abstract We evaluated prerelease acclimation of hatchery winter steelhead Oncorhynchus mykiss in Whittaker Creek, a tributary of the Siuslaw River, Oregon, as a management strategy to attract returning adults to a release site where they could be removed. The objective was to reduce the number of hatchery fish in wild steelhead spawning areas while providing hatchery steelhead for recreational fisheries. We found no significant difference in homing rate or survival between hatchery steelhead acclimated for 30 d and those trucked from the hatchery and directly released. For the 1991–1993 broods, a mean of 92% of directly released fish and 97% of acclimated fish were accounted for in Whittaker Creek. In contrast, 15% of adults from hatchery smolts released at four traditional sites in the main-stem Siuslaw River were accounted for in Whittaker Creek. The spatial distribution of the catch in recreational fisheries was similar for the direct and acclimated groups; that catch, however, was nearer Whittaker Cre...

Influence of Short-Term Estuarine Rearing on the Ocean Survival and Size at Return of Coho Salmon in Southeastern Alaska

Abstract Hatchery smolts of coho salmon Oncorhynchus kisutch, cultured for 2–5 weeks in estuarine net-pens, were compared with those released directly from freshwater to determine whether short-term seawater rearing would influence their ocean survival or size at return. Samples of each experimental group were marked with coded wire tags before release, and ocean survival and size at return were estimated from tag recoveries. Releases of all experimental groups were timed to coincide with the peak emigration of wild smolts from local streams. After accounting for year-class variation, the duration of estuarine net-pen rearing had a significant positive effect on the rate (P = 0.012) and size (P < 0.001) of returning adults. Smolt size at release did not significantly affect either survival or size at return (P ≥ 0.34). The results suggest that short-term estuarine rearing before release may ameliorate the effects of osmotic stress on growth and survival during the critical period of seawater adaptation. T...

Metabolic enzyme activity during smolting in stream- and hatchery-reared Atlantic salmon (Salmo salar)

To evaluate the metabolic differences between Atlantic salmon (Salmo salar) parr and smolts and the effect of rearing environment, we examined metabolic enzyme activity in white muscle, liver, and heart in stream- and hatchery-reared juveniles. Spring increases in gill Na+,K+-ATPase (3.5-fold) and cardiosomatic index (37–69%) and decreases in condition factor (~17%) occurred in smolts, but not in parr. White muscle phosphofructokinase (PFK) increased during spring and was 3.6-fold higher in smolts than in parr by late spring. There were seasonal increases in liver citrate synthase (CS) (~42%), liver β-hydroxyacyl-coenzyme A dehydrogenase (HOAD) (~60%), and heart CS (~23%) and decreases in liver lactate dehydrogenase (LDH) (~28%) in parr and smolts. Activity of liver HOAD was greater in stream-reared smolts (~18%) than in parr or hatchery smolts. Heart PFK activity increased during spring in wild-reared parr and smolts, while it decreased in hatchery-reared smolts. White muscle LDH and PFK increased earlier in spring in hatchery- than in stream-reared smolts. Our results suggest that increased heart size and high white muscle PFK occur during smolting and may be adaptive for downstream and ocean migration. Hatchery- and stream-reared Atlantic salmon differ in the timing of metabolic changes during smolting, which may impact their long-term survival.

Effects of Acidity and Aluminum on the Physiology and Migratory Behavior of Atlantic Salmon Smolts in Maine, USA

Atlantic salmon, Salmo salar, smolts of hatchery origin were held for 5 to 16 days in ambient (pH 6.35, labile Al = 60 µg L−1), limed (pH 6.72, labile Al = 58.4 µg L−1), or acidified (pH 5.47, labile Al=96 µg L−1) water from the Narraguagus River in Maine, USA. Wild smolts were captured in the same river in rotary traps and held for up to two days in ambient river water. Osmoregulatory ability was assessed by measuring Na+/K+ ATPase activity, hematocrit, and blood Cl concentration in freshwater, and after 24-hr exposure to seawater. Hatchery smolts exposed to acidic water and wild smolts displayed sub-lethal ionoregulatory stress both in fresh and seawater, with mortalities of wild smolts in seawater. Using ultrasonic telemetry, hatchery-reared ambient and acid-exposed, and wild smolts were tracked as they migrated through freshwater and estuarine sections of the river. The proportion of wild smolts migrating during daylight hours was higher than for hatchery-reared smolts. Wild smolts remained in the freshwater portions of the river longer than either group of hatchery smolts, although survival during migration to seawater was similar for all three treatments. Acid-exposed hatchery-origin and wild Narraguagus River smolts were both under ionoregulatory stress that may have affected their migratory behavior, but not their survival for the time and area in which we tracked them.

Spatial and temporal covariation in the recruitment and abundance of Atlantic salmon populations in the Baltic Sea

Synchronous trends in the abundance of hatchery and wild Baltic salmon populations are examined using correlation analysis. The river catch of wild adult salmon, the recruitment of age 0+ wild salmon parr, and the recapture rate of tagged hatchery smolts are positively correlated among rivers in the Baltic Sea. The spatial correlation among populations is greater than reported for other anadromous salmonids. Baltic salmon populations have undergone low frequency, high amplitude changes in abundance during the past 200 years. Recent production levels have been supported largely by hatcheries. EVorts to conserve the remaining wild populations through fisheries regulation appear to be having a positive eVect on spawner abundance. ? 1999 International Council for the Exploration of the Sea

Influence of Transmitter Attachment Procedures on Swimming Performance of Wild and Hatchery-Reared Atlantic Salmon Smolts

Effects of transmitter attachment procedures on smolts of Atlantic salmon Salmo salar have primarily been examined in the laboratory with hatchery-reared fish. Biotelemetry researchers must extrapolate findings of tagging studies to wild, migrating smolts. Because hatchery rearing can affect salmonid development and because field tagging procedures and environmental conditions can differ from those in the laboratory, we measured critical swimming speed of hatchery-reared Atlantic salmon smolts equipped with internal, external, or gastric dummy radio transmitters in the laboratory. We then repeated the experiment with wild, migrating fish in ambient environmental conditions. Swimming ability of hatchery smolts was not significantly affected by any attachment procedure, and no significant differences were found between fish tested 1 or 16 h after tagging. Similarly, wild smolts were not impaired by gastric transmitters; however, performance of wild fish tested 1 or 16 h after internal or external attachment was significantly lower than that of wild controls. Thus, reaction of hatchery-reared Atlantic salmon smolts to attachment procedures can differ from that of wild migrants. Biotelemetry researchers should exercise caution in interpreting data obtained from wild Atlantic salmon smolts equipped with internal or external radio transmitters during the first 16 h after tagging.

Comparative Diets of Hatchery and Wild Atlantic Salmon Smolts in the Merrimack River

We examined diets of smolts of 224 “wild” and 150 hatchery Atlantic salmon Salmo salar; wild smolts had been released as fry from the hatchery 2 years before collection, whereas hatchery fish were released as smolts from the hatchery 3–15 d before. Smolts were collected from 1991 to 1993 at trapping facilities at dams in the Merrimack River during spring outmigration. About 50% of the hatchery smolts and 50% of the wild smolts examined had empty stomachs. For smolts containing food, terrestrial invertebrates were the major prey of both hatchery and wild salmon. Adult aquatic dipterans (i.e., chironomids, culicids, and simuliids) also composed a large portion of the diet of both groups of salmon. Hydropsychid and chironomid larvae were the main benthic taxa consumed. Surface-oriented prey dominated the diet of hatchery (73.7%) and wild (62.4%) smolts. The coefficient of dietary overlap (Cλ) between hatchery and wild smolts was high during all years and ranged from 0.83 to 0.93. Stomach fullness of hatchery smolts was significantly less than that of wild smolts. Further research is needed to determine if the low food consumption of hatchery smolts affects survival.

Physiological and hormonal differences among Atlantic salmon parr and smolts reared in the wild, and hatchery smolts

Atlantic salmon which had been released as fry in tributaries of the Connecticut River (Northeastern USA) were captured during the migratory period (9 May to 6 June) 1 to 2 years later. Migrants (smolts) were captured above a dam on the main-stem; non-migrants (parr) were captured in two tributaries. Migrants were significantly larger than non-migrants (16.9 and 13.0 cm, respectively), but had a 20% lower condition factor. Relative to non-migrants, migrants had significantly higher gill Na +, K +-ATPase activity (5-fold), plasma glucose (1.8-fold), plasma thyroxine (8-fold), plasma cortisol (5-fold) and plasma growth hormone (100-fold). There were no significant differences in plasma [Na +], [K +] and [Ca 2+] between migrants and non-migrants. Most of the differences seen between non-migrants and migrants were similar to those that occurred seasonally in a captive (hatchery) population of the same stock of Atlantic salmon. However, hatchery smolts had lower levels of plasma thyroxine and exhibited no significant change in plasma growth hormone from February to June. The large differences between migrants and non-migrants may be related to both the parr-smolt transformation and migration.

Changes in Cortisol Dynamics in Wild and Hatchery-Reared Juvenile Coho Salmon (Oncorhynchus kisutch) During Smoltification

Cortisol dynamics were examined in hatchery and wild juvenile coho salmon (Oncorhynchus kisutch) over the spring of 1991 and 1992 when the fish were smolting. Wild fish were caught in the upper Quinsam River, British Columbia and at the downstream enumeration fence when they started to migrate. Two groups of hatchery fish were from the top and bottom ends of an earthen rearing channel. Plasma cortisol levels increased during the spring in all groups, but were significantly greater in wild than in hatchery smolts. The half-life of plasma cortisol decreased as fish smolted; however, there was no difference among the groups. Corticosteroid receptor (CR) concentration and affinity decreased during the spring. Wild fish consistently possessed the greatest gill concentration of CR. The change in dissociation constant (kD) was similar for hatchery and wild fish during spring 1991. In 1992, hatchery fish showed a similar gradual increase. In contrast, wild fish did not show an increase in kD until May. The changes in cortisol concentration in the plasma and the CR kD occurred synchronously with the increase in Na+K+ATPase activity in wild fish, which showed the greatest increase in kD, plasma cortisol, and Na+K+ATPase activity.

Modeling the Response of Native Steelhead to Hatchery Supplementation Programs in an Idaho River

Abstract A life history model was used to predict the response of native steelhead Oncorhynchus mykiss in the Lochsa River, Idaho, to long-term supplementation with hatchery fry and smolts. The four key factors affecting the response of the native fish to a stocking program were (1) the number of native spawners, (2) the number of stocked fish, (3) the number and fitness of progeny from stocked fish, and (4) the amount of mating between hatchery and native fish. Long-term stocking of fry or smolts led to the extinction of native fish in some scenarios. The model can be used to help assess the risks and benefits of proposed stocking programs.

Expansion of cultured Pacific salmon into marine ecosystems

Global harvest of salmon has increased steadily since the mid-1970's. Record harvest levels are currently being established largely from production of farmed and ranched salmon. Farmed salmon are hold captive throughout their lives, whereas reached salmon are released as juveniles into natural ecosystems where they mix with wild salmon. Observation of a nonlinear adult-to-smolt relationship in ranched salmon can be interpreted as evidence that marine waters have been overstocked, provided the ratio of adults to smolts declines as the number of smolts increases. Three ranching programs — Oregon coho, Japan chum, and Alaska pink salmon — are examined here for evidence that ocean mortality from natural causes is directly dependent on abudance of smolts. Interpretation of the data does not support the hypothesis that marine waters have been overstocked with hatchery smolts to a level where survival of salmon has been reduced. However, the possibility that industrial production of ranched salmon smolts is reducing, or may soon reduce, survival of fishery resources should not be ignored.

Differences in life history and migratory behaviour between wild and hatchery-reared Atlantic salmon in nature

Hatchery smolts reared from crosses of wild Atlantic salmon of the River Imsa stock were released annually at the mouth of the River Imsa, 1981–1987. In the river, the smolts were released in May at the same time of year as wild smolts were migrating to sea. In the sea, wild salmon survived more than twice as well as hatchery fish, but sea growth did not differ significantly between the two groups. After 1 year in the sea, most surviving fish in both categories returned to coastal Norway as sexually maturing adults. Smaller numbers returned as multiple-sea-winter spawners. Wild fish ascended the River Imsa earlier in the season than did hatchery fish. Furthermore, wild fish strayed less than hatchery fish to rivers other than the River Imsa. Within the river, hatchery fish moved about more, and a higher proportion was injured during the spawning period than in wild fish. Moreover, hatchery fish stayed for a shorter period of time in the river than wild fish, and a larger proportion of the hatchery fish returned to sea without having spawned. Average river survival was high (>60%) for both groups.

Density-Dependence at Sea for Coho Salmon (Oncorhynchus kisutch)

The success of expanded salmon hatchery programs will depend strongly on the degree of density-induced diminishing returns per smolt released. Several authors have addressed the question of density-dependent mortality at sea in coho salmon (Oncorhynchus kisutch), but have come to conflicting conclusions. We believe there are compelling reasons to reinvestigate the data, and have done so for public hatchery fish, using a variety of approaches. The results provide evidence that survival of these public hatchery fish is negatively affected, directly by the number of public hatchery smolts and indirectly by the number of private hatchery smolts. These results are weak, statistically, and should be considered primarily as a caution to those who, on the basis of other published work, believe that density-dependence does not exist. The results reported here also re-emphasize the often overlooked point that inferences drawn from data are strongly biased by investigators' views of how the systems of interest work and by the statistical assumptions they make preparatory to the analysis of those data.

Patterns of Timing and Size of Wild Coho Salmon (Oncorhynchus kisutch) Smolts Migrating from the Keogh River Watershed on Northern Vancouver Island

Coho salmon (Oncorhynchus kisutch) smolts leaving the Keogh River and its tributaries demonstrated consistent patterns in their timing and size. An initial early peak in the mean size of migrating smolts occurred several weeks before the peak in their timing, and in several years when smolt migration was monitored until July, a late peak in size occurred near the end of the smolt migration. Changes in the mean size of smolts were not related to their origin within the watershed, and varying age compositions were only partially responsible for the two peaks in mean size. Fish overwintering in tributary lakes grew faster than fish overwintering in tributary streams. A greater proportion of lake-origin smolts migrated to sea after only 1 yr in freshwater than stream-origin smolts. It appears that fish that wait until their second spring to smoltify are among the first to emigrate that spring. These relatively large 2 + smolts, combined with fast growing 1 + smolts that leave early during their first spring, cause the first peak in size. The small numbers of large smolts leaving the Keogh River at the ends of several of the smolt runs apparently left then because of minor flow increases in the river. As has been found with releases of coho smolts from nearby hatcheries, fish that left the Keogh River early in the smolt run generally had a more northerly marine catch distribution than later migrating smolts. A greater proportion of fish migrating to sea late in the smolt run were caught in the fishery than fish migrating early. Additional work examining the marine survival of early and late migrating wild smolts is recommended to enable detailed comparisons to be made between the optimal timing and size of wild and hatchery smolts.

Use of Inclined-Plane Traps to Study Movement and Survival of Atlantic Salmon Smolts in the Connecticut River

Abstract We determined the utility of inclined-plane traps for capturing smolts of Atlantic salmon Salmo salar and studied the timing of the downriver run and survival of smolts in the Connecticut River in 1985 and 1986. We captured 22 smolts with one trap in 1985, and 45 with three traps in 1986. Although these numbers were small, the results from both years were similar. Mean total lengths of smolts (ranges in parentheses) were 186 mm (152–206 mm) in 1985 and 178 mm (152–201 mm) in 1986. The migration period in both years extended from early April to mid-May. Mean river temperatures when smolts were captured were 10.5°C (4.5–16.0°C) in 1985 and 10.3°C (4.5–15.0°C) in 1986. Most smolts were captured several weeks after the period of peak spring flows that probably would have provided the safest passage past electricity generating stations. The recapture rates of tagged hatchery smolts stocked 8 km upstream from the trap were 1 of 4,400 (0.023%) in 1985 and 1 of 2,900 (0.034%) in 1986. These rates were si...