Differences of tributyltin accumulation in the masu salmon Oncorhynchus masou between sea‐run and freshwater‐resident types

In order to examine the accumulation pattern of tributyltin (TBT) in relation to the migratory pattern, TBT concentrations in muscles and strontium (Sr) concentrations in otoliths were determined in both sea‐run and freshwater‐resident masu salmon Oncorhynchus masou . Both TBT and Sr concentrations in sea‐run masu salmon were significantly higher than those of freshwater‐residents.     

Temporal variation in abundance, return rate and life histories of previously spawned Atlantic salmon in a large subarctic river

The 30 year time series analyses revealed large temporal variation in the return rates and a recent increase in abundance of previous spawning Atlantic salmon Salmo salar in the River Teno, northern Scandinavia. The mean proportion of repeat spawners was 7 and 4% in the total Atlantic salmon catch and 9 and 22% in multi‐sea‐winter (MSW) catch component for females and males, respectively. Previous spawners constituted on the average 7% of the catch in mass but up to 20%(31 t) and 30%(19 t) in 2003 and in 2004, respectively. In 1975–2000, the proportion of previous spawners varied between 1 and 6%(3–12% of MSW Atlantic salmon), whereas in 2001–2004, they accounted for 8–21%(16–35% of MSW Atlantic salmon) of the total Atlantic salmon catch. The number of previous spawners in the catch correlated significantly with the preceding numbers of respective 1–3 sea‐winter (SW) maiden Atlantic salmon 2 years earlier. The recent increase in the numbers of 1S1 and 2S1 (1 or 2 years at sea followed by first spawning and 1 year reconditioning period at sea) alternate spawning Atlantic salmon was a consequence of higher numbers of maiden 1SW and 2SW Atlantic salmon in the catches and increased sea temperatures. Similarly, the return rate of 1SW Atlantic salmon to second spawning has improved in recent years. Most previous spawners ascended and were captured early in the fishing season. The smolt and sea‐age combinations of repeat spawners comprised 68 age groups contributing with the annual mean of 15 age groups to the great diversity of the River Teno Atlantic salmon population complex.     

Diel activity patterns of juvenile Atlantic salmon in rivers with summer water temperature near the temperature‐dependent suppression of diurnal activity

Direct day and night underwater observations of juvenile Atlantic salmon Salmo salar during summer and autumn showed a duality in response to temperature between 7 and 11° C for young‐of‐the‐year (YOY) Atlantic salmon. They were predominantly diurnal in early summer and nocturnal in late summer although water temperatures were similar. Post‐YOY Atlantic salmon did not show a strong response to temperature as they were mostly nocturnal during the study period. It is suggested that the difference in activity patterns between YOY and post‐YOY Atlantic salmon can be explained by size‐dependent trade‐off between growth and predation risk.     

Return migration of one‐sea‐winter Atlantic salmon in the River Tana

Fifty‐three one‐sea‐winter Atlantic salmon Salmo salar (45–63 cm L _T) were radio‐tagged in the Tana fjord, Barents Sea, in 1995. Thirty‐seven fish (70%) entered the freshwater zone of the River Tana in an average of 3 days after release in the fjord. The migration speeds in the lowest river section below the first riffle area were significantly higher than in the subsequent river section below the second riffle area. Similarly, the observed time spent in the first riffle area was significantly lower than in the next riffle area. The majority of Atlantic salmon entered the river during the hours of high tide and the subsequent ebb tide. In addition, most river entries were recorded around midnight. No effects of river flow on the river entry or migration speed were detected, but the migration speed of Atlantic salmon in both river sections examined was greater at lower temperatures. Twenty‐eight fish (72%) were recaptured in the river, 71% of them with weirs and gillnets, and 29% by rod and line. Over half of the Atlantic salmon (54%) were recaptured within 3 weeks following river entry, and within the first 100 km of the river (56%). The results are discussed in relation to earlier studies on multi‐sea‐winter Atlantic salmon in the River Tana.     

Temporal and spatial variation in growth of juvenile Atlantic salmon

Spatial and temporal variation in length‐at‐age and environmental factors affecting variation in growth rate of juvenile Atlantic salmon Salmo salar were studied using data from a long‐term study in the River Stjørdalselva, central Norway. Mean annual instantaneous growth rate among 1+ and 2+year juvenile Atlantic salmon varied between 0·59 and 1·50 g g⁻¹ year⁻¹ and mean instantaneous daily growth rate of young‐of‐the‐year (YOY) varied between 0·013 and 0·033 g g⁻¹ day⁻¹. Between year variation in growth was larger than the within year intra‐watercourse spatial variation. For YOY and 1+year Atlantic salmon, a major part of the observed between year variation in growth rates was explained by variation in mean daily water discharge and spring temperature. For 2+year juvenile Atlantic salmon, mean daily water discharge and cohort density were the only variables to significantly explain variation in growth rates. A large part of the within water‐course spatial variation could not be explained by temperature variations and juvenile Atlantic salmon in the uppermost areas of the river, experiencing the lowest ambient temperatures during the growth period, displayed the highest growth rates. Within the baselines set by temperature, biotic and abiotic factors connected to water flow regime and variation in food availability are suggested to be a major determinants of the temporal and spatial variation in juvenile Atlantic salmon growth rates.     

Strontium:cakium concentration ratios in otoliths of herring larvae as indicators of environmental histories

Synopsis Elemental analyses, using wave-length dispersive electron microprobe techniques on otoliths from reared Atlantic herring larvae, Clupea harengus, showed trace quantities of strontium relative to that of calcium, and an inverse relationship between Sr/Ca concentration ratios and rearing temperature. These data are consistent with those for coral aragonite, in that there appears to be an inverse temperature effect on physiological incorporation of strontium in the otolith aragonite. Our determinations of Sr/Ca concentration ratios of lab-reared herring larvae showed that the deposition of strontium relative to calcium and the rearing temperature were related, where: T (° C) = −2.955 [Sr/Ca] × 1000 ± 19.172. This principle thus makes it possible to use Sr/Ca concentration ratios in fish otoliths to delineate past temperatures experienced by an individual. Further, combining electron microprobe analyses with scanning electron microscope (SEM) examinations of daily increments in the same otolith makes it possible to reconstruct the temperature history for an individual fish on a time scale of days. An example of the application of the technique to an approximately six-month-old field-caught herring larva is given, and the limitations of the technique are discussed.     

Migration flexibility between freshwater and marine habitats of the pond smelt Hypomesus nipponensis

The life histories of the pond smelt Hypomesus nipponensis collected from Japanese fresh waters and brackish (sea) waters were studied by examining the strontium (Sr) and calcium (Ca) concentrations in their otoliths. The Sr:Ca ratios in the otoliths changed with the salinity of the habitat. The pond smelt living in a freshwater environment showed consistently low Sr:Ca ratios throughout the otolith, averaging 1·2–1·3 × 10⁻³. These samples were identified as a standard freshwater type. In contrast, fish collected from the intertidal zone showed higher otolith Sr:Ca ratios than those in the standard freshwater type, and the ratios fluctuated along the growth phase. In addition to the two representative life‐history types of H. nipponensis , i. e . freshwater and anadromous life‐history types, other pond smelts were found to have an estuarine resident life history‐type with no freshwater phase, indicating that the pond smelt has a flexible migration strategy with a high degree of behavioural plasticity and an ability to utilize the full range of salinity in its life history.     

Size and age of maturity of Atlantic salmon correlate with the North Atlantic Oscillation Index (NAOI)

Sea‐age at maturity of Atlantic salmon Salmo salar decreased with increasing values of the seasonal NAOI from February to April. Body mass increment from smolts to adults of one‐sea‐winter Atlantic salmon increased with increasing NAOI in May at the time when the juveniles moved to sea.     

Seasonal growth of Atlantic cod: effects of temperature, feeding and reproduction

Growth of 2659 Atlantic cod Gadus morhua aged 4 to 9 years examined in Placentia Bay, Newfoundland, peaked in most cases in June and was at a minimum in October or November. Water temperature, partial fullness index ( I _P) and gonado‐somatic index ( I _G) explained between 31 and 52% of the monthly variability in growth. Temperature and I _P of capelin Mallotus villosus had significant effects on growth of all age groups and explained most of the variance for ages 6–8 and 4–5 years, respectively. The I _P of large invertebrates (ages 4 to 7 years), sandlance ( Ammodytes sp. age 6 years) and demersal fishes (age 9 years) had age‐specific effects in the model. Overall, amphipods, decapods and echinoderms dominated the Atlantic cod diet in most seasons, but fish consumption by Atlantic cod was high in June and July, particularly on capelin. The rapid increase in somatic mass during June and July occurred despite cold water temperatures ( < 3° C at 50 m) and moderate to high gonado‐somatic index. The findings of this study suggest that when food was not a limiting factor, growth tended to increase even when Atlantic cod occupied colder waters, but when food was limiting, the opposite may have occured.     

Effect of diet on otolith composition in Pomatomus saltatrix, an estuarine piscivore

To test the hypothesis that elemental composition of otoliths (sagittae) could be influenced by differences in natural prey type, young‐of‐the‐year bluefish Pomatomus saltatrix were captured immediately after their migration from oceanic waters into mid‐Atlantic Bight estuaries and fed either shrimp, Crangon septemspinosa and Palaemonetes spp. or fish Menidia menidia under similar temperature and salinity regimes in two separate 60 day experiments. Unlimited rations of fish and shrimp prey were provided in the first experiment which led to differences in bluefish growth rate between the two prey treatments; fish prey was limited in the second experiment to ensure that growth rates of bluefish in the two prey treatments were similar. Concentrations of seven elements in bluefish otoliths were determined using solution‐based inductively coupled plasma mass spectrometry (ICPMS). There was no significant effect of diet on five of the seven elements examined (Na, Mg, K, Ca and Mn). The levels of Sr and Ba in the otoliths of shrimp‐fed bluefish, however, were significantly higher than fish‐fed bluefish in both experiments. Concentrations of Ba in shrimp‐fed bluefish otoliths were double that found in fish‐fed bluefish. The results suggest that diet can explain some of the variation in otolith chemistry previously attributed to physical and chemical properties of the water.