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 ϫ 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 the tagged groups eventually caught up and grew at the same rate as the other two groups. In the second experiment, 28-mm implants, representing 8.5% of body weight, had a negative effect on the fish 1 and 3 d after surgery by slightly reducing critical swimming speed compared with that of control fish. However, the swimming performance of tagged fish began to recover after 7 d. Surgical implantation of acoustic transmitters can meet the requirements for tagging and tracking small Atlantic salmon over a period of months. However, we recommend a transmitter length of 16% or less of fish length and a transmitter weight under 8% of fish weight for juvenile Atlantic salmon of about 14-15 cm and 35-45 g in order to maximize the chances of success in telemetry studies.

No abstract

The early marine migration of 55 Atlantic salmon post-smolts tagged with acoustic transmitters was automatically monitored using 13 to 25 km long arrays of receivers deployed inside the Bay of Fundy, a coastal system on the east coast of Canada. The survival of post-smolts from groups with short-and long-term transmitters in coastal habitat up to 10 km from the river was 92 to 100%, indicating a successful transition to salt water and departure. Migration for 68 to 77% of postsmolts followed a direct route and it was rapid (transit time usually <12 h). Post-smolts initially migrated in a south to south-west direction (i.e. orientation towards the mouth of the bay) and they were aggregated near the coast. Post-smolts with long-term transmitters were monitored 20 km from the river where they continued to be aggregated, moving near the coast through a 'common corridor', and their survival to that point was at least 84%. Post-smolts from both groups travelled heading out of the coastal system during ebb tides. Flood tides interrupted migration, and they caused changes in travel direction and delays in departure for post-smolts not leaving by a direct route. Monitoring of coastal habitat inside the Bay of Fundy intercepted 62% of migrating post-smolts with long-term transmitters returning after an initial absence of 2 to 22 days. Returning post-smolts displayed a resident behaviour, using the habitat monitored inside the Bay of Fundy during July and August. # 2005 The Fisheries Society of the British Isles

Development of coronary arteriosclerosis has been studied in all life stages of both wild and cultured Atlantic salmon (Salmo salar). Lesions accumulate slowly during juvenile growth in freshwater in both wild and cultured populations and increase sharply during early marine life; much of the progression occurs well before the onset of sexual maturity. Fewer than 5% of sexually mature Atlantic salmon (wild or fast-growing cultivated) were free of coronary lesions. Lesions were distributed over 45–85% of the length of the coronary artery. Lesions were less abundant and less advanced in a cultured strain of salmon that grew more slowly than another cultured, fast-growing strain. We conclude that prevalence and severity of lesions in Atlantic salmon accelerate in parallel with, and possibly in response to, those factors responsible for rapid growth in the sea. We discuss diet, endocrine changes associated with sexual maturation, metabolic aspects of parr–smolt transformation, and physiological stress as factors possibly influencing progression of lesions associated with rapid growth during the marine stage.

Atlantic salmon (Salmo salar) postsmolts surveyed by surface trawling in the Bay of Fundy and Gulf of Maine during 2001–2003 were aggregated in several areas in the Bay of Fundy and dispersed over a broader area in the Gulf of Maine. Postsmolt distribution reflected the major surface-current vectors and was independent of origin (wild vs. hatchery, inner vs. outer Bay of Fundy). Migration proceeded without disruption, and marked wild postsmolts from both the inner and outer Bay of Fundy were recaptured in the outer Bay of Fundy and the Gulf of Maine, where their distribution overlapped the commercial fishery for Atlantic herring (Clupea harengus). Marked postsmolts of wild origin were recaptured more frequently than those of hatchery origin but the overall density was low, and no schools of postsmolts were encountered that could offer protection from predators. Temperature and salinity in postsmolt habitat were favourable for growth and survival. Postsmolts were in excellent condition and had no bacterial or viral pathogens or salmon lice (Lepeophtheirus salmonis). They were feeding on pelagic prey (amphipods, euphausiids, and fish larvae) and the period of accelerated marine growth had started, indicating that environmental conditions and food supply were not limiting growth and survival.