Whole body-element composition of Atlantic salmon Salmo salar influenced by migration direction and life stage in three distinct populations.

Body-element content was measured for three life stages of wild Atlantic salmon Salmo salar from three distinct Newfoundland populations as individuals crossed between freshwater and marine ecosystems. Life stage explained most of the variation in observed body-element concentration whereas river of capture explained very little variation. Element composition of downstream migrating post-spawn adults (i.e. kelts) and juvenile smolts were similar and the composition of these two life stages strongly differed from adults migrating upstream to spawn. Low variation within life stages and across populations suggests that S. salar may exert rheostatic control of their body-element composition. Additionally, observed differences in trace element concentration between adults and other life stages were probably driven by the high carbon concentration in adults because abundant elements, such as carbon, can strongly influence the observed concentrations of less abundant elements. Thus, understanding variation among individuals in trace elements composition requires the measurement of more abundant elements. Changes in element concentration with ontogeny have important consequences the role of fishes in ecosystem nutrient cycling and should receive further attention.

Comparing mercury concentrations across a thirty year time span in anadromous and non-anadromous Arctic charr from Labrador, Canada.

Anadromous and non-anadromous Arctic charr (Salvelinus alpinus) from multiple sample sites in Labrador, Canada were used to investigate possible differences in total mercury concentration ([THg]) between 1977-78 and 2007-09. The mean [THg] of anadromous Arctic charr was 0.03 µg/g wet weight (ww) in 1977-78 and 0.04 µg/g ww in 2007-09, while mean concentrations in non-anadromous conspecifics were 0.18 µg/g ww in 1977-78 and 0.14 µg/g ww in 2007-09. After correcting for the effects of fish age and fork-length, there was no widespread difference in the mean [THg] of anadromous or non-anadromous fish between the two time periods. However, at individual sites sampled during both time periods, [THg] increased, decreased, or did not change. The mean age of sampled fish declined from 9.0 years in 1977-78 to 8.2 years in 2007-09 for anadromous fish, and from 11.7 years to 10.5 years in non-anadromous Arctic charr. Similarly, mean fork-lengths decreased from 450 mm to 417 mm in anadromous and from 402 mm to 335 mm in non-anadromous fish between 1977-78 and 2007-09. The mean annual temperature at four Labrador weather stations increased by 1.6°C to 2.9°C between the two sampling periods. The lack of an overall trend in anadromous or non-anadromous Arctic charr [THg] despite warming temperatures that favour increased mercury methylation suggests that regional changes in climate-driven factors have had limited impacts on mercury exposure in Labrador freshwater or marine fish.

Comparative analysis of total mercury concentrations in anadromous and non-anadromous Arctic charr (Salvelinus alpinus) from eastern Canada.

Previous research has documented that total mercury concentrations ([THg]) are lower in anadromous Arctic charr than in non-anadromous conspecifics, but the two life-history forms have rarely been studied together. Here, data from nine pairs of closely-located anadromous and non-anadromous Arctic charr populations were used to explore the impact of biological and life-history factors on individual [THg] across a range of latitudes (49-81° N) in eastern Canada. Unadjusted mean [THg] ranged from 20 to 114 ng/g wet weight (ww) in anadromous populations, and was significantly higher in non-anadromous populations, ranging from 111 to 227 ng/g ww. Within-population variations in [THg] were best explained by fish age, and were often positively related to fork-length and δN-inferred trophic level. Differences in [THg] were not related to differences in length-at-age (i.e., average somatic growth rate) among populations of either life-history type. Mercury concentrations were not related to site latitude in either the anadromous or non-anadromous fish. We conclude that the difference in Arctic charr [THg] with life-history type could not be explained by differences in fish age, fork-length, trophic position, or length-at-age, and discuss possible factors contributing to low mercury concentrations in anadromous, relative to freshwater, fish.

Basal mercury concentrations and biomagnification rates in freshwater and marine food webs: effects on Arctic charr (Salvelinus alpinus) from eastern Canada.

Patterns of total Hg (THg) and methyl Hg (MeHg) biomagnification were investigated in six pairs of co-located lacustrine and marine food webs supporting a common predator, Arctic charr. Mercury biomagnification rates (the slope of log Hg concentration versus δ(15)N-inferred trophic level) did not differ significantly between the two feeding habitats for either THg or MeHg, but THg and MeHg concentrations at the base of the food web were higher in the lacustrine environment than in the marine environment. The proportion of THg as MeHg was related to trophic level, and the relationship was statistically similar in the lacustrine and marine habitats. The biomagnification rate of MeHg exceeded that of THg in both habitats. We conclude that the known difference in Hg concentration between anadromous and non-anadromous Arctic charr is driven by differential Hg concentrations at the base of the lacustrine and marine foodwebs, and not by differential biomagnification rates.

Residency time, migration route and survival of Atlantic salmon Salmo salar smolts in a Canadian fjord.

Atlantic salmon Salmo salar smolts (n = 181) from two rivers were surgically implanted with acoustic transmitters and released to determine migration route, residency time and survival in a 50 km long estuarine fjord located on the south coast of Newfoundland, Canada. Data obtained from automated receivers placed throughout the Bay d'Espoir fjord indicated that migrating smolts used different routes to reach the outer areas of the fjord. The duration of time that smolts spent in the immediate estuary zone also differed between the two localities (7 and 17 days) although the total time smolts were resident in the fjord was similar and extensive (40 days). Many smolts were resident for periods of 4-8 weeks moving back and forth in the outer part of the fjord where maximum water depths range from 300 to 700 m. Survival in the estuary zone was greater for smolts with prolonged residency in estuarine habitat. Overall smolt survival to the fjord exit was moderately high (54-85%), indicating that the initial phase of migration did not coincide with a period of unusually high mortality.

Effects of formalin and ethanol preservation on otolith delta18O stable isotope signatures.

The use of preserved otoliths for stable isotope analysis assumes handling and preservation procedures do not alter the isotopic composition of the otolith. Otoliths from wild and hatchery-reared salmonids (brook charr, Salvelinus fontinalis, and Atlantic salmon, Salmo salar) were used to test for possible delta(18)O preservation effects in ethanol and formalin preservation experiments at varying temperatures. Analysis of variance (ANOVA) demonstrated a significant interaction effect between species and preservative during preservation. Possible causes for the observed effect are discussed in relation to species-specific differences in otolith chemistry related to growth and environment including: (1) chemical mechanisms of dissolution-recrystallisation involving the precipitation of secondary minerals within and at the otolith surface; (2) adsorption of ions at available binding sites on the otolith surface; and (3) isotopic exchange during otolith surface dissolution and/or reprecipitation processes. Differential occurrence of vaterite and aragonite in otoliths is believed to account for some of the observed effects as a result of otolith density differences. Isotopic exchange is also argued to cause much of the observed variation in species-specific preservation effects. Biologically, study findings imply that preserved otoliths should not be used for baseline paleoclimatic or individual fish thermal reconstructions, or the development of delta(18)O-fractionation equations, without the prior use of pilot studies to determine preservation effects.

Importance of ontogenetic habitat shifts to juvenile output and life history of Atlantic salmon in a large subarctic river: an approach based on analysis of scale characteristics.

Juvenile and adult scale characteristics were used to compare two juvenile groups of Atlantic salmon in a large subarctic river in northern Scandinavia: individuals that have migrated from the main stem into small tributaries and those which remain in the main stem. Body size and scale measurements indicated enhanced growth in migratory parr as compared to their resident main stem counterparts. Analysis of adult salmon scale characteristics using maximum likelihood estimators revealed that 20% of the adults had been in the tributaries before the end of their second year of life, and more than 30% more had moved into the tributaries in the third year. Tributary fish matured at a smaller size and younger age (one-sea-winter salmon) than those rearing in the main stem which included a higher proportion of multi-sea-winter salmon. In addition, when smolt ages and ages at maturity were compared, older female smolts often resulted in smaller spawners and younger smolts, larger spawners. Small female spawners were more likely to survive to become repeat spawners.

Mark-recapture estimation of a salmon smolt population.

A mark-recapture experiment was conducted applying a two-sample stratified technique to estimate the number of Atlantic salmon smolts, Salmo salar, migrating out of the Conne River, Newfoundland. We developed a model where parameters are introduced to describe the mean time for the salmon to migrate between the release site and recapture site and to describe the probability of capture on a particular date. The latter are then used to expand the number of untagged smolts captured to estimate the daily run sizes. We discuss the advantages of this new approach over other models. For example, this formulation allows great flexibility in the experimental design, is robust to violations of assumptions, and allows the influence of environmental factors upon the parameters to be investigated.