Salmon Carcasses Research Articles

Episodic Fish Kills in an Acidified Salmon River in Southwestern Norway

Abstract The objective of this study was to conduct fish kill assessments of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) and associate the cause of the kill with environmental acidification during the snowmelts. The study was carried out in the river Vikedalselva in southwestern Norway each spring from 1982 to 1985. River acidity was measured daily in 1982 and continually from 1983 to 1985. Fish kill was assessed daily by inspecting stretches of the river bottom. A total of 680 carcasses of Atlantic salmon and brown trout were either recovered or counted. Most of the dead specimens were juvenile fish, of which a predominant fraction were ≥ 2 years old (presmolts). Mortality varied considerably between years, from a high of 376 specimens in 1984 to a low of 34 in 1985. Another 39 specimens were observed drifting in the river. The fish kills were generally episodic, and usually followed sudden increases in discharge and depressions of river pH. With the exception of 1983, a correlation anal...

Agonistic Asymmetries and the Foraging Ecology of Bald Eagles

We investigated the effects of both asymmetries and differing food levels on contest outcomes of wintering Bald Eagles (Haliaeetus leucocephalus) feeding on chum salmon (Oncorhynchus keta) carcasses. Large eagles, regardless of age, were more successful in pirating than smaller eagles. Small pirating eagles were usually unsuccessful unless they were adults attempting to supplant other small eagles. Feeding eagles were more successful in defeating pirating eagles according to (1) whether their heads were up to prior to a pirating attempt, (2) how long their heads had been up, and (3) whether they displayed. During periods of food scarcity pirating eagles were less successful, a fact attributed in a proximate sense to the increase incidence of retaliation by feeding birds. When food was scarce and eagles had a choice between scavenging the pirating, they chose to scavenge more often. Body size appears to be an important factor in determining social dominance and influencing differences in foraging modes of wintering Bald Eagles.

The Retention of Coho Salmon (Oncorhynchus kisutch) Carcasses by Organic Debris in Small Streams

Twenty marked coho salmon (Oncorhynchus kisutch) carcasses were placed in each of nine small streams on the Olympic Peninsula of Washington during the fall–winter spawning period. Distribution of the carcasses in 500 m of stream below each release site was followed for 4 wk. One week after placement, 78 of the 180 carcasses were found in the nine study reaches; 80% were found in the first 200 m downstream of the release sites. A general positive trend was observed between the number of carcasses retained and the amount of debris in the stream channel (r = 0.61). Terrestrial animals rapidly consumed carcasses during the experiment, and removed many of them to the riparian zone.

Effects of Kokanee Salmon (Oncorhynchus nerka) Decomposition on the Ecology of a Subalpine Stream

The role of kokanee salmon (Oncorhynchus nerka) carcass decomposition in the nutrient cycles and energy flow of a subalpine stream was investigated during a season (1970–71) of high spawner abundance and a season (1972–73) of low spawner abundance with a December storm flushing the stream of carcasses. Primary production, periphyton biomass, heterotrophic activity, and nutrient concentrations were greater downstream than upstream during the peak carcass decomposition of 1971, whereas they were the same at other times of that year and in 1972–73. Calculations showed that upstream–downstream differences in phosphate could be accounted for by the salmon carcasses.

The IsopodMesidotea entomonin the Chignik Lakes, Alaska

Studies on the isopod Mesidotea entomon (Linnaeus) from 1961 to 1964 in the two Chignik lakes, Alaska, showed that at least part of the population was benthic during daylight and pelagial at night. In Chignik Lake the isopod was most abundant in association with organic and mud bottoms and areas where salmon carcasses accumulate. Abundance decreased from early to late summer, perhaps because of a postreproductive mortality. It is suggested that males grow faster than females, though both sexes mature at age I+ and that growth terminates with maturation. Most reproduction apparently occurs in early summer but some ovigerous females were found as late as September. Length at maturity in both sexes was less than reported by other workers in Arctic marine populations. Mature isopods were smaller in the upper lake (males 40–46 mm, [Formula: see text]; and females 29–38 mm, [Formula: see text]) than in the lower lake (males 41–65, [Formula: see text]; and females 29–47 mm, [Formula: see text]) of the Chignik River system. Females in the upper lake had a higher average fecundity and a greater increase in fecundity per unit increase of length than those in the lower lake.

Primary Productivity in the Babine Lake System, British Columbia

Primary productivity in Babine Lake, British Columbia, as measured by the C14 in situ method in 1966 was slightly lower in the North Arm (outlet) and Morrison Arm (an inlet) than in the main lake region. An unusually high rate of photosynthesis at one part of the main lake in September may have been related to the decomposition of salmon carcasses in a nearby stream. Morrison Lake, a major tributary, was much lower in rate of photosynthesis, pH, alkalinity, compensation depth, and total dissolved solids than any part of Babine Lake. The rate of carbon fixation of Babine Lake was much less on a per unit area basis than those reported by other workers for the majority of 24 sockeye salmon lakes in southwestern Alaska but was similar to most per unit volume of the euphotic layer. Much of this difference is attributable to a shallower euphotic zone in Babine Lake. Ranked with the 24 Alaskan lakes, Babine was first in alkalinity, third in TDS, and fifth in pH.The productivity measurements suggest that the carrying capacity for sockeye salmon per unit of nursery area of the main lake region is at least as great as that of the North Arm.