Hatchery Atlantic Salmon Research Articles

Atlantic salmon of wild and hatchery origin have different migration patterns

Hatcheries are frequently used to support or restore threatened Atlantic salmon populations. However, little is known about how rearing affects behaviour and fitness of hatchery adults that return to the river to spawn. We used acoustic telemetry to compare migration patterns exhibited by hatchery ( N = 16) and wild ( N = 12) Atlantic salmon spawners within a river system in Norway. Hatchery Atlantic salmon in this study were released as smolts and were identified by their missing adipose fin upon return to rivers after 1+ winters spent at sea. Hatchery-origin Atlantic salmon displayed aberrant reverse movement behaviour, by moving with frequent reversals between the river and the fjord, a behaviour that was not observed in any wild Atlantic salmon. No difference in survival and outmigration timing after spawning was found for the two groups. The observed effect of hatchery origin on behavior may have implications for stock assessments made to assess the progress of restoration in the river, particularly if behavioural differences impact catchability or detections of returning adult salmon. The consequences of different movement patterns are uncertain; however, movements are energetically costly and may ultimately impact the fitness of hatchery Atlantic salmon.

Personality in hatchery Atlantic salmon (Salmo salar) is associated with growth but not metabolic rate or performance

The pace of life hypothesis (POLS) predicts that personality traits, like activity and boldness, are positively correlated with growth and metabolism. Here, we assess whether personality could predict body mass, metabolic rate, and performance under stress for hatchery-raised Atlantic salmon ( Salmo salar) 15 months post fertilization. Personality was evaluated for individual fish using a series of repeated trials alongside two stressful events (PIT tagging, simulated transport), to determine performance under stress. Standard metabolic rate (SMR) was then assessed via intermittent flow respirometry, and the relationships between personality, body mass, performance, and SMR were evaluated. Fish displayed repeatable behaviours, but not in accordance with POLS hypothesis. Smaller fish were more active and responsive to stimuli, while personality was not associated with SMR. Although smaller fish and fish with higher SMR both performed better under stress, body mass was unrelated to SMR. We discuss the utility of supporting the occurrence of a wider range of growth rates and body sizes in hatchery environments, as a means of promoting greater stress tolerance as well as faster growth.

Movement, Survival, and Delays of Atlantic Salmon Smolts in the Piscataquis River, Maine, USA

AbstractMovement, delays, and survival of hatchery Atlantic Salmon Salmo salar smolts were evaluated through the Piscataquis River, a tributary of the Penobscot River in Maine, USA. We explored the effects of the river’s four dams (Guilford, Dover, Browns Mill, and Howland dams) from 2005 to 2019. During this period, the downstream‐most dam (Howland Dam) transitioned from full hydropower generation to seasonal turbine shutdowns and later was decommissioned with the construction of a nature‐like fish bypass in 2016. We estimated survival through open‐river reaches and at each dam using acoustic telemetry (n = 1,611). Dams decreased survival, with per‐river‐kilometer (rkm) apparent survival averages of 0.972, 0.951, and 0.990 for Guilford, Dover, and Browns Mill dams compared to a per‐rkm survival of 0.999 for open‐river reaches. Turbine shutdowns increased survival at Howland Dam (to around 0.95), which was further increased by the nature‐like fish bypass (0.99). We used radiotelemetry in 2019 (n = 75) and demonstrated that approximately one‐third of the fish used the bypass, while the remaining fish used alternative routes. Smolts successfully passing the three upstream dams had lower apparent survival through Howland Dam than smolts that were released upstream of Howland Dam. Although smolts passing Browns Mill Dam had high survival, the dam caused extended delays, with median delay times surpassing 48 h in most years. Most of the delays caused by Browns Mill Dam occurred after fish had passed the dam and may indicate a sublethal effect of passage. Overall, while survival through Howland Dam has improved, passage and delays at the three upstream dams in aggregate represent a critical impediment to the effective use of the high‐quality spawning habitat found upstream.

Improving bypass performance and passage success of Atlantic salmon smolts at an old fish-hostile hydroelectric power station: a challenging task

Old hydroelectric power stations often provide unsafe migration routes to fish, apart from passing through mobile gates during high flow. The installation of retrofitted bypass is considered to be a potential solution to improve fish passage at such old structures, but their performances are often insufficient. In the Amblève River (Belgium), a mobile 3.3 m high dam feeds two principal Francis turbines (12 + 14 m3 s−1) and is equipped with three mobile gates, a modern vertical slot upstream fish pass and a retrofitted downstream bypass functioning at a very low flow (1% of maximum turbined flow). A bypassed river section (length 8.4 km) downstream of the dam was set at 3 m3 s−1 and supplies a Francis microturbine. From 2015 to 2016, we used 1150 hatchery Atlantic salmon smolts (Salmo salar), and we placed antennae with automatic radio-frequency identification (RFID) stations to analyse the migration routes used (n = 5). We tested the attraction efficiency and the performance of the bypass with and without the placement of a guidance system at the entrance and examined the proportion of smolt passage at the different migration routes under three functioning configurations. The placement of the guidance system markedly improved the attraction efficiency and the overall passage efficiency. The median time spent at the entrance of the bypass was from 7 to 12 min, and the time spent near the entrance of the bypass was less than 1 h for 67.1% (release 1), 88.2% (release 2) and 63.7% (release 3) of the smolts. During the three release events, the smolts arrived near the entrance of the bypass mostly during the dusk and dark periods (87.5%, 96.0% and 95.5%, for releases 1, 2 and 3, respectively). In a configuration without opening a mobile gate, the bypass was the most used migration route, followed by the microturbine and the main turbine. Stopping the microturbine and opening a mobile gate has consequences of making it the first choice of passage followed by the main turbine and the bypass. The re-establishment of safe and quick downstream migration has to be considered with a holistic view of the functioning of the hydroelectric powerstation.

Assessment of Early Migration Dynamics of River‐Specific Hatchery Atlantic Salmon Smolts

AbstractMany Atlantic Salmon Salmo salar populations within the southern extent of the species’ range are at critically low abundances, while others have been extirpated. The focus of many ongoing recovery efforts is on maximizing the number of smolts that reach the ocean, where marine survival is low, primarily through hatchery supplementation and improvement of in‐river hydropower system management. However, estuaries also are known to be sites of high mortality, although in many cases the correlates of this mortality are poorly characterized. We acoustically tagged hatchery smolts (n = 666) during 2001–2005 to evaluate migration performance through freshwater, estuarine, and bay reaches of the small but tidally dynamic Dennys River, Maine, USA, to investigate potential drivers contributing to low returns within the system. Migration behaviors (e.g., migration timing and tidal use) were typical for Atlantic Salmon smolts, but reversals during migration were observed upon entry into the estuary environment more frequently in this system than in regional rivers. We used Cormack–Jolly–Seber mark–recapture models to estimate apparent survival within the study environment during this period. We found two distinct periods of survival, with much lower survival in 2003–2005 than in 2001 and 2002 (more than a 40% decrease). Among the variables considered, temperature and migratory behavior had the largest effects on survival. We found that survival increased by about 28% across the range of temperatures observed during these years; additionally, survival increased by about 15% for fish that reversed direction during migration compared to fish that did not. These results indicate that extreme environmental changes during the transition through this coastal system constitute a significant obstacle to Atlantic Salmon restoration stocking efforts.

Silver spoons in the rough: can environmental enrichment improve survival of hatchery Atlantic salmon Salmo salar in the wild?

This study tested the 'silver spoon' hypothesis which posits that individuals that develop under favourable conditions should enjoy a fitness advantage later in life because they are more likely to recognize and settle in high-quality habitats. Atlantic salmon Salmo salar of two age classes (0+ and 1+ years) were reared in environmentally enriched or standard hatchery tanks for a short period (c. 10 weeks), were then released into a natural river and sampled on repeated occasions to test for silver-spoon effects. Compared with controls, enriched fish had a 6.4% higher recapture rate and settled in higher velocity habitats when they were stocked as 0+ year fry, but not when they were stocked as 1+ year parr. The opportunity for selection was generally higher for environmentally enriched fish than for controls, and also higher for 0+ than for 1+ year fish. Selection favoured individuals with high condition factor, extensive fat reserves and longer than average pectoral fins in both age classes but favoured a small body size in 1+ year and a large body size in 0+ year releases. Stomach analysis showed that enriched fish ate more, and adapted quicker to natural prey than controls. These results provide support for silver-spoon effects in fish and indicate that enrichment can improve post-release performance in conservation programmes, but seemingly only if fish are not kept in captivity for too long.

Use of Stable Isotopes to Identify Redds of Putative Hatchery and Wild Atlantic Salmon and Evaluate Their Spawning Habitat and Egg Thiamine Status in a Lake Ontario Tributary

AbstractBoth wild and hatchery Atlantic Salmon Salmo salar can contribute to restoration but can exhibit differences in spawning habitat selection (e.g., water depth, current speed) and egg nutritional quality (e.g., thiamine), which affect reproductive success. Hence, there is a need to be able to differentiate the spawning contribution of the two groups in the wild. As diets of wild and hatchery‐reared spawners are markedly dissimilar and diet is known to influence stable isotope signature, egg stable isotope signatures offer the potential to discriminate redds of each. Using stable isotope analysis of carbon and nitrogen (δ13C and δ 15N) of naturally spawned Atlantic Salmon eggs, we were able to discriminate the redds of putative wild (i.e., previously stocked life stage feeding in Lake Ontario; EWSR) from putative hatchery‐reared Atlantic Salmon (EHSR). Eggs of EWSR were significantly more enriched in nitrogen (δ15N: 15.0 ± 0.5‰ [mean ± SE]) but more depleted in carbon (δ13C: −26.6 ± 0.3‰) than eggs of EHSR (δ15N = 9.8 ± 0.6‰; δ13C = −17.5 ± 0.0‰). Eggs of EHSR were indistinguishable from eggs of known hatchery Atlantic Salmon for both δ13C and δ 15N. Using stable isotopes to discriminate redd type, few differences were found between the spawning habitat of putative wild and hatchery spawners. Similarly using the same criteria, thiamine levels in eggs of EWSR (8,474 ± 840 pmol/g) were not significantly different from eggs of known wild Atlantic Salmon (3,691 ± 782 pmol/g) or of eggs of EHSR (14,865 ± 1,050 pmol/g), whose thiamine levels were indistinguishable from eggs of known hatchery Atlantic Salmon (14,200 ± 1,167 pmol/g). Egg thiamine levels for all groups were above established mortality thresholds. Our results indicate that both hatchery and wild Atlantic Salmon can make reproductive contributions, which can be differentiated and quantified using stable isotope signatures.Received August 24, 2012; accepted May 15, 2013

Migratory strategies of Atlantic salmon (Salmo salar) postsmolts and implications for marine survival of endangered populations

The migration of wild and hatchery Atlantic salmon (Salmo salar) postsmolts of different origins was monitored using ultrasonic tags and arrays of acoustic receivers across the Bay of Fundy (BoF), Canada. Postsmolts from outer BoF populations migrated rapidly into the Gulf of Maine (GoM) and did not return, and most were classified as distant migrants (77%–100%). In contrast, postsmolts from inner BoF populations were usually classified as coastal migrants that returned to the BoF for the summer (30%–90%). They used well-defined migration corridors, close to shore, associated with prevailing surface currents. An Akaike information criterion (AIC) evaluation of migration models identified region and watershed, date of river exit, and migration speed as important predictive variables for coastal residency. A late or slow migration increased residency, as did delaying hatchery releases. The BoF provided returning postsmolts with a summer thermal refuge (8–14 °C) encircled by warm water (>20 °C), but extended residency in this coastal habitat increased exposure to sources of mortality absent further at sea. This reduced marine survival of inner BoF salmon to almost nothing. It is likely that the different migratory strategies of inner and outer BoF salmon populations influenced their relative marine survival and endangered status.

Identification of surrogates of protection against yersiniosis in immersion vaccinated Atlantic salmon.

Simple cost-effective bacterins are the earliest and most successfully used commercial vaccines in fish. In particular, those prepared from Yersinia ruckeri have proven effective at controlling Enteric Red Mouth Disease (ERM) and yersiniosis in rainbow trout and Atlantic salmon, respectively. However, the emergence of outbreaks of ERM caused by atypical biotypes of Y. ruckeri and reports of vaccine failure resulting in mass mortality of hatchery Atlantic salmon has reinvigorated interest in vaccines against fish bacterial diseases. Therefore the objective of this study was to identify surrogates of protection against yersiniosis using cDNA microarray to characterise the response of host genes in the gills of unvaccinated and vaccinated Atlantic salmon challenged with Y. ruckeri. Differentially expressed genes were identified using two-way ANOVA and restricted to those with >2.5-fold change at P<0.05. Using cDNA microarray we identified the expression of 6 genes in response to infection and 4 genes associated with the protective host response to yersiniosis. Analysis by real-time PCR confirmed that three immunologically relevant genes, namely a cathelicidin (47-fold) and a C-type lectin (19-fold) increased in response to yersiniosis. Including collagenase (17-fold increase), an important tissue remodelling and repair enzyme, these genes represent 3 of 6 non-protective and/or pathological responses to yersiniosis. Genes associated with the protective host response included an immunoglobulin gene and a selenoprotein that showed significant fold changes (15-fold increases each), highlighting the importance of antibody-mediated protection against yersiniosis. These findings provide much needed knowledge of the host-pathogen interaction in response to bacterial infection and immunisation in fish. Significantly, we identified a transcriptional biosignature consisting of predominantly immune-relevant genes (14 up and 3 down-regulated) in the gills of Atlantic salmon after immersion vaccination and before bacterial challenge. This biosignature may be used as a surrogate of protection and therefore as a predictor of vaccine success against yersiniosis.

Descaling Injury Impairs the Osmoregulatory Ability of Atlantic Salmon Smolts Entering Seawater

AbstractThe effect of descaling injury on the osmoregulatory ability of hatchery Atlantic salmon Salmo salar smolts in seawater was investigated. Experimental series were initiated during early, middle, and late periods of the spring smolt migration (April 25, May 11, and May 31, respectively). For each time series, descaled smolts (subjected to descaling on 10% of the body surface area) and control smolts (held out of water for 15 s) were transferred to seawater at 0, 1, 3, or 7 d posttreatment. After fish were held in 35‰ seawater for 24 h, gill and blood samples were collected and analyzed for Na+,K+‐ATPase activity and plasma osmolyte levels. Based on gill Na+,K+‐ATPase activity, the three series spanned the period from early smolting (increasing activity) to de‐smolting (decreasing activity). In each series, descaled fish transferred to seawater at 0 and 1 d posttreatment had greater plasma osmolality than control fish; descaled fish transferred to seawater at 3 d posttreatment did not differ from controls. The greatest perturbation in osmolality (70 milliosmoles) was observed at the peak of smolting (middle series), whereas lesser increases were seen for early and late‐series smolts. The observed osmotic perturbations in descaled fish would probably reduce performance and decrease survival during smolt migration.

Different ocean and climate factors control the marine survival of wild and hatchery Atlantic salmon Salmo salar in the north‐east Atlantic Ocean

The influence of climate and ocean conditions on the marine survival of 1SW Irish Atlantic salmon Salmo salar was explored. Generalized additive models (GAM) explained c. 85% of the observed variations in survival and provided an insight into the mechanisms involved. A positive phase of the North Atlantic oscillation (NAO) and increasing sea surface temperatures (SST) were linked to a decrease in S. salar survival. The NAO in the winter before the smolts migration contributed to c. 70% of the deviance in marine survival of wild fish. The abundance of the copepod Calanus finmarchicus in the north‐east Atlantic Ocean explained a further 25% of these variations in wild S. salar survival. By contrast, hatchery populations seem to be controlled by additional processes involving coastal SST. The marine recruitment of hatchery S. salar was largely explained (70% of the deviance) by SST close to the Irish coast in the spring before the year of the smolts migration. This study constitutes the first description of the processes controlling marine recruitment for these populations.

Annual changes in the proportions of wild and hatchery Atlantic salmon (Salmo salar) caught in the Baltic Sea

Abstract DNA-level information from an eight-loci microsatellite baseline database of 32 Atlantic salmon (Salmo salar) stocks was used with a Bayesian estimation method to assess the stock and stock group proportions of Finnish salmon catches in the Baltic Sea area. The proportions of seven stock groups, important to fisheries management, were assessed in catch samples taken between 2000 and 2005. In the Gulf of Bothnia area, the proportion of wild fish in catches showed an increasing trend in all areas until 2003, mainly because of the decrease in total catches caused by the relatively greater mortality of hatchery-reared fish compared with wild fish. In 2004, the total number of wild fish caught had also increased, indicating an increase in the abundance of wild stocks. In catches from the Åland Sea, the proportion of wild fish increased from 44% in 2000 to 70% in 2004, while the catch during the same period increased from 4628 to 7329 fish. In the Gulf of Finland, the local Neva salmon stock, which is released by Estonia, Finland, and Russia, made the largest contribution. In the western part of the Gulf of Finland, fish originating in the Baltic Main Basin also made a substantial contribution to catches. The threatened eastern Estonian and Russian wild stocks were recorded only in the western part of the Gulf of Finland, where the proportion of wild fish increased from 9% in 2003 to 19% in 2004.

Nest Site Selection and Spawning by Captive Bred Atlantic Salmon, Salmo salar, in a Natural Stream

We examined the physical habitat of nest sites chosen by hatchery Atlantic salmon, Salmo salar, in a recovery program for this extirpated species in Lake Ontario, Canada. We compared the sites used by these captive bred fish to a set of random locations in a wide range of available habitats. Compared to random locations in the stream, the nest sites chosen were lower in the relative abundance of sediment size classes that are detrimental to embryo and juvenile survival. In addition, the process of nest construction by these captive bred fish further reduced the proportions of these detrimental sediments. Although captive breeding may have changed some aspects of the nest site selection and construction behaviour, it has not caused a complete loss or major alteration of the trait and thus does not preclude hatchery fish from restoration or reintroduction programs.

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.

Determination of body shape variation in Irish hatchery‐reared and wild Atlantic salmon

Discriminant function analysis was used to distinguish morphologically between samples of parr, smolts and adult Atlantic salmon Salmo salar from several hatchery and river systems in Ireland. The effect of habitat shift was investigated in Atlantic salmon parr. Parr grown from the eyed‐egg stage with a non‐sibling group in a hatchery environment, came to resemble the mean body shape of their host hatchery Atlantic salmon stock more closely than that of a full sibling group grown at their natal hatchery. Wild Atlantic salmon smolts differed in shape from hatchery‐reared smolts. This difference was less pronounced, but still statistically significant when wild adults were compared with hatchery‐reared adults captured in the coastal drift‐net fishery after a year spent at sea. Rearing conditions had a significant impact on the production and growth of fish body shape. This in turn may have affected adaptability and survivorship of ranched Atlantic salmon in the marine environment.

Predator‐induced hyperventilation in wild and hatchery Atlantic salmon fry

Following exposure to a predator stimulus (a brown trout Salmo trutta), the opercular rate of Atlantic salmon Salmo salar fry increased by 35·3 ± 11·0%(mean ± 95% CI). The time taken for opercular rate to decline to baseline levels depended upon the occurrence of any associated locomotory activity. Opercular rates of fish that dashed when exposed remained elevated for 38·2 ± 20·6 min, whereas those of individuals that did not move (‘freezers’) recovered within 7·2 ± 2·9 min. The duration that opercular rate remained elevated was positively correlated with the magnitude of the elevation, which was higher in ‘dashers’ than freezers. The maximum opercular rate in ‘freezers’ was similar between wild fry and hatchery‐reared fry (from wild parents). There was a significant delay, however, in hatchery compared with wild fry in the time until peak ventilatory response and onset in the decline phase. This difference in opercular response suggests that hatchery fish were slower to realize fully the potential danger from the predator. Any delay in response could be directly attributed to the effect of hatchery‐rearing environment, rather than domestication or hatchery selection effects.

Atlantic salmon straying from the River Imsa

Mean estimated straying rate for Atlantic salmon Salmo salar L. leaving the River Imsa as smolts during 1976–1999 was 15% for hatchery fish and 6% for wild conspecifics. Hatchery Atlantic salmon selected for production traits during four or more generations strayed &gt;50%. The straying rate was higher for Atlantic salmon staying 2 rather than 1 year at sea before attaining maturity. For spawning, 96% of the strays entered streams within 420 km from the River Imsa, and c. 80% entered streams within 60 km of the mouth of the River Imsa, whether the fish were wild or hatchery released. Within the 60 km zone, the number of strays caught in a river increased with the Atlantic salmon catch in that river, but there was no significant relationship between straying rate and water discharge or distance from the river to the River Imsa. The observed straying rate of hatchery Atlantic salmon decreased with increasing number of fish entering the River Imsa. Sexual maturation as parr did not influence the tendency to stray. The results suggest that the establishment of temporary zones, free of fish farms, outside important Atlantic salmon rivers by the fisheries authorities in Norway should be large, whole fjords, to be effective.

Modeling the Effects of Poststocking Survival Rates on the Success of Stocking Hatchery Atlantic Salmon in a New Brunswick River

The effect of poststocking survival rate on the success of a hatchery stocking program to enhance Atlantic salmon Salmo salar was modeled with empirical data from the Nepisiguit River, New Brunswick, Canada. Removal of adults from the wild population for use as hatchery broodstock was beneficial to population growth if the survival rate of their hatchery-reared progeny was 10% or more of that of wild-reared juveniles in the first year following stocking and equivalent to the survival of wild-reared juveniles and adults thereafter. Returns of marked adult fish to a counting fence were consistent with average poststocking survival rates (relative to wild-reared fish) of 5–20%, so it appears the hatchery program was probably successful in enhancing returns of adult Atlantic salmon to the river.

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.

Some factors which influence the survival of hatchery Atlantic salmon ( Salmo salar) smolts utilized for enhancement purposes

Sixty-nine groups of 2+ Atlantic salmon smolts and 27 groups of 1+ smolts produced at the Mactaquac Hatchery were marked with modified Carlin tags and released in the Saint John River, N.B., during the 1973–1988 period. During the same period, 35 groups of tagged 1+ smolts produced at the Mersey Hatchery were released in the LaHave River, N.S. The numbers of tagged adult salmon subsequently recovered in distant and local commercial fisheries, in Native food fisheries, by anglers and at collection facilities operated by the Department of Fisheries and Oceans provided a measure of the survival of the various smolt groups. Neither release date nor river discharge at time of release significantly influenced the survival of tagged smolts. Survival rates for groups of smolts released in the LaHave River fluctuated from year to year in a pattern similar to that observed for groups of smolts released in the Saint John River. The year-to-year fluctuation in the survival of the LaHave and Saint John smolts was correlated and considered to reflect changing conditions at sea. Stepwise multiple regression analysis indicated that 44–68% of the variation in the survival rate of the 1+ and 2+ smolts was attributable to smolt weight at time of release, smolt quality (as determined by an index) and to sea conditions during a particular year. The results of the analysis provide rationale for modifying hatchery rearing practices and facilities to increase mean smolt weight and to improve smolt quality.