Gilles L. Lacroix

Effects of Implanted Dummy Acoustic Transmitters on Juvenile Atlantic Salmon

Abstract The effects of intraperitoneally implanted dummy acoustic transmitters on juvenile Atlantic salmon Salmo salar of comparable size to wild presmolts and smolts were examined in two laboratory experiments. In the first experiment, different-sized tags (24, 28, and 32 mm × 8-mm diameter) that mimicked acoustic transmitters suitable for long-term studies were assessed. There was 60% mortality (3 of 5 fish) with the 32-mm implant early in the 316-d study and 20% mortality (1 of 5 fish) with the 28-mm implant. All fish surviving with 28- and 32-mm implants eventually expelled their tags, compared with only 20% of fish (1 of 5) with the 24-mm implant. Tag expulsion was not a cause of death. After implantation, tags were first encapsulated in a thick membrane and then expelled between 142 and 217 d after surgery, exiting at a site where pressure of the tag on the abdominal wall was greatest. Growth of tagged fish was initially delayed and lagged that of control and sham-tagged fish, but survivors from th...

Influence of origin on migration and survival of Atlantic salmon (Salmo salar) in the Bay of Fundy, Canada

Atlantic salmon (Salmo salar) smolts of wild and hatchery origins (n = 522) were tagged with ultrasonic transmitters and monitored at successive arrays of submerged receivers during migration from five watersheds in three regions of the Bay of Fundy (BoF), Canada. Two of the regions had endangered inner BoF salmon populations. Migration success of postsmolts leaving the BoF varied widely among 13 groups monitored (3%−70%) and was influenced by behaviour and passage time. Region of origin was the key variable in habitat-specific survival models selected using the Akaike information criterion. Rearing origin, migration and release timing, and smolt size were important variables in some habitats. Estimated survival rates (overall and habitat specific) differed markedly among salmon populations of different regions. Mediocre estuarine survival of smolts (0.54) from the outer BoF region affected overall survival (0.66). Poor survival (0.21) in coastal areas of the distant inner BoF region and mediocre survival...

Migration of Atlantic Salmon Postsmolts in Relation to Habitat Use in a Coastal System

Abstract Acoustic telemetry was used to monitor the early marine migration of Atlantic salmon Salmo salar from two rivers of Passamaquoddy Bay, a coastal system with numerous Atlantic salmon farms and weirs for Atlantic herring Clupea harengus on the border of Canada and the United States. Monitoring at fixed sites, active tracking, and systematic searches for tagged fish were combined. The migration success of hatchery-reared (N = 96) and wild (N = 38) smolts out of the estuaries was high (range, 90–97%), and the overall success of postsmolts moving out of Passamaquoddy Bay and into the several passages leading to the Bay of Fundy was reasonable (range, 71–88%). Estuary transit times were usually rapid (<36 h), and almost all smolts entered the bay during an ebb tide. Migration routes through Passamaquoddy Bay were then closely related to the counterclockwise residual surface current in this bay. Routes differed among groups monitored, and they influenced the location of exit from the bay. The majority o...

Aluminum dynamics on gills of Atlantic salmon fry in the presence of citrate and effects on integrity of gill structures

Abstract The effect of citrate as organic acid anions (A−) on the accumulation of aluminum (Al) on gills of Atlantic salmon (Salmo salar) fry was examined in acidic media. Treatments with (Al−A−) = +10, 0, and −10 μeq/1([Al] = 0, 10, 20, 30, 40, 50, 60 μeq/1 and [citric acid] = 0, 10, 20, 50 μeq/1) were used. Depuration of gills loaded with Al (10 μeq/l) was also examined in the presence of citric acid (0, 10, 20, 40 μeq/l). Elimination of Al from gills was a much more rapid process (

Mitigation of low stream pH and its effects on salmonids

Crushed limestone (200 tonnes) was spread in bars on the bed of an acidic brook (mean pH 5.0) in Nova Scotia, Canada. A seasonally variable but significant increase in pH of running water resulted, and a longitudinal pH gradient over the limed section extended to the mouth of the brook. The effectiveness persisted after 3 years, during which pH downstream of the limestone increased an average of 0.4 pH units (range < 0.1-1.3 pH units) along with significantly increased Ca, Mg and acid neutralizing capacity. Total and exchangeable Al were not altered by the limestone and non-exchangeable forms dominated. The interstitial water was nearly neutral (mean pH 7.1) in limestone beds but it was acidic (mean pH 5.4) in gravel beds of the control section upstream. Spawning Atlantic salmon (Salmo salar) dug three times more redds in gravel of the limed section than in the control. Salmon fry survived and they were significantly more abundant in the limed section than in the control. The density of juvenile salmon increased over time, indicating a recovery of the population. The density of brook trout (Salvelinus fontinalis) also increased and trout fry were usually more abundant in the limed section than in the control. The observed benefits for salmonids suggest that small-scale application of limestone to stream beds and spawning sites can be used to mitigate the effects of low stream pH.

Identification by Scale Analysis of Farmed Atlantic Salmon Juveniles in Southwestern New Brunswick Rivers

Abstract A procedure was developed to identify whether the natal origin of juvenile Atlantic salmon Salmo salar in the Magaguadavic River, New Brunswick, was farmed or wild. Farmed juveniles enter this river as escapees from commercial hatcheries. The discriminant function was developed using measured scale characteristics for the first year of growth, as determined from samples of farmed and wild juvenile Atlantic salmon of known origin. Eight scale characteristics proved to be significant predictors of origin. In a jackknife cross-validation, the discriminant function was 90% accurate in predicting the origin of juvenile Atlantic salmon in the Magaguadavic River. The procedure was then applied to juvenile Atlantic salmon of unknown natal origin sampled from the Magaguadavic and neighboring Waweig and Digdequash rivers, which also support salmon hatcheries. Of the juvenile Atlantic salmon sampled in the Magaguadavic River in 1996, 1997, and 1998, 36, 59, and 43%, respectively, were estimated to be of far...

Adult Return of Farmed Atlantic Salmon Escaped as Juveniles into Freshwater

Abstract The origin of Atlantic salmon Salmo salar adult returns from the ocean to the Magaguadavic River, New Brunswick, was determined for the 1996 smolt cohort by using scale examination of the freshwater–seawater transition zone and a discriminant function analysis based on scale measurements depicting the first year of growth in freshwater. Adult returns consisted of 57% farmed fish that escaped from sea cages, 34% wild fish that were the progeny of naturally spawned fish, and 9% farmed fish that were demonstrated to have escaped from hatcheries into the river as juveniles—the first report of farmed hatchery escapees into freshwater returning as adults. The analysis determined that 20% of returns previously thought to be wild were in fact farmed salmon that had escaped into freshwater from hatcheries. By comparison, using the same analysis, we determined that 51% of smolts from the same cohort migrating out to sea 1 and 2 years earlier were farmed escapees from hatcheries. The difference in proportio...

Stability of Microhabitat Use by Brook Trout and Juvenile Atlantic Salmon after Stream Acidification

Abstract Microhabitat use by brook trout Salvelinus fontinalis and juvenile Atlantic salmon Salmo salar in a small acidic brook was examined in response to the acidification episodes typical of rivers of southwest Nova Scotia in the fall, and to a longitudinal pH gradient related to liming. Several microhabitat variables were measured for age-0 and age-1 and older fish of both species. Some of the measurements were made relative to the fishs focal point (height of the fish above the bottom) and included water depth and focal elevation, focal water velocity, focal water pH and temperature, and bed material grain size. The presence of a small, longitudinal pH gradient ( 1 pH unit; final pH, <4.8) did not cause any major shift in microhabitat use by either species between summer...