A.M. Sutterlin’s research while affiliated with Memorial University of Newfoundland and other places

This study examined ecological and behavioral differences between migratory and resident forms of Atlantic salmon occurring in a watershed of southeastern Newfoundland, Canada. Lake-dwelling, resident forms of Atlantic salmon (Salmo salar), in which males and females mature at a small size (14 and 20 cm, respectively), were captured in two separate areas of a watershed, equipped with sonic tags, and released from a third site 1 week prior to the anticipated spawning time. The location of these 10 fish was determined for 15 consecutive days, and 8 of the 10 fish converged at their initial recapture site near the outlet of one of the lakes and were found in this area for the same 5 consecutive days. Eggs were later found scattered between crevices of rocks and boulders (5–30 cm diameter) at the confluence of the outlet stream and lake in water 1–1.5 m deep. No signs of excavated redds were found in this area. At a distance of 8 km downstream from this spawning area and 2–3 km above head of tide, much larger anadromous salmon (40–60 cm) were observed by divers to be inhabiting pools in the main river for a period of 2 weeks prior to spawning. Excavated redds were found in adjacent gravel areas that contained eggs that were much more brightly pigmented than those recovered from near the lake outlet. Because there are no barriers preventing access between these two spawning sites within this system, we suggest that large anadromous females and small resident females select different areas and substrates for spawning. The possibility of genetic difference between the two forms, arising from such reproductive segregation, is considered.

Several limitations in water volume, temperature and quality have caused problems in producing sufficient numbers of Atlantic salmon presmolts at a research institute in eastern Canada. The adoption of a water re-use system employing ozone treatment and a nitrifying biofilter, containing Astroturf(R) substrate, has resulted in improved water quality and higher rates of growth and survival.

Pelleted LHRH analogue formulated for long term hormone delivery was administered by two routes to maturing, spring spawning, female rainbow trout in an attempt to accelerate spawning. At water temperatures ranging from 0.5–2.0°C, spawning was advanced by approximately 27 days. Rapid increases in the level of plasma gonadotropic hormone at 2 weeks indicates that pituitary stimulation occurred well in advance of ovulation, despite low temperatures. Egg diameter and fertility were comparable in sham control and experimental fish. Heavy mortalities occurred in eggs taken from accelerated spawners, however, eggs from 35% of these females were still viable at the eyed stage. Although further studies directed at egg quality appear warranted, pelleted LHRH implants could prove useful in advancing spawning time in order to meet schedules of smolt production or assist in synchronizing the spawning time of salmonid brood stock reared or held in salt water.

Laboratory feeding trials were conducted in which excess rations of four different size classes of mussels were provided to three different size classes of starfish. Although differences in size-selective feeding behaviour occurred between different size classes of starfish feeding separately and those feeding aggregately, the total food intake remained the same. The consumption of mussel meat by starfish based on the relative ash-free dry weights of both prey and predator ranged from 6 to 8.6% day−1. Patterns of size-selective feeding behaviour and feeding rates of starfish observed in the laboratory appear consistent with the changes in relative abundance among year class cohorts of mussels and starfish residing on culture nets at a mussel farm. It is concluded that the impact of starfish predation at the mussel farm is not likely to affect adversely the marketable yield of older mussels, and may provide a beneficial influence through the culling of undersized mussels.