Abundance In Autumn Research Articles

Ecology of Amblyomma neumanni (Acari: Ixodidae)

The life cycle of Amblyomma neumanni was described studying the seasonal distribution of free-living stages and parasitic phases during two consecutive years. Development periods of engorged ticks under different photoperiod conditions were recorded. Larvae of A. neumanni have the peak of abundance in autumn. Nymphs reach the peak in winter. Females were collected on cattle from autumn to late spring. The seasonal distribution pattern of females showed a bimodal curve, with a peak in autumn and other during early and middle spring. The engorged females exposed at shortest photoperiod regimen (10 h light–14 h dark) under both laboratory and field conditions undergo morphogenetic diapause, expressed as a delay in the oviposition. It is concluded that females of A. neumanni that feed and copulate in autumn undergo morphogenetic diapause, and they will lay eggs in spring, simultaneously with the females that feed and copulate in this season. Climate niche analysis shows that adequate suitability for A. neumanni depends mainly from temperature (mean, absolute maximum and minimum, and mean temperature in wettest and driest quarters) as well as from rainfall in warmest and coldest quarters. Sequences of 16S rDNA gene belonging to different populations of A. neumanni, showed no intraspecific genetic differentiation.

Zooplankton fluctuations in Jurumirim Reservoir (São Paulo, Brazil): a three-year study

During three consecutive years, monthly samples of zooplankton were taken in the lacustrine (dam) zone of Jurumirim (São Paulo, Brazil). The seasonal effect on basic limnological features (thermal regime, oxygen distribution, phytoplankton biomass, etc.) was also examined. The influence of the seasonality on the fluctuation of the zooplankton composition and abundance was not clearly detected (low degree of recurrent patterns). Rotifers (32 taxa) were the most abundant organisms during almost the entire study period with some seasonal alternations in the maximum abundance peaks of the main taxa (Conochilus unicornis, Keratella americana, K. cochlearis and Hexarthra spp.), except for Polyarthra (mainly P. vulgaris). Only occasionally copepods were numerically dominant. Higher copepod abundance was positively associated to periods of increase in the water retention time. Among the Copepoda (10 taxa) the calanoids (mainly Notodiaptomus iheringi) were more abundant, especially in warmer periods. Conversely, cyclopoids had higher abundance in autumn and winter. The species Thermocyclops minutus and T. decipiens co-occurred, but the first attained higher abundance. Some evidence of co-existence strategies between both species are considered. Cladocera (17 taxa) was never numerically dominant and the main taxa (Bosmina spp., Ceriodaphnia spp. and Diaphanosoma spp.) occurred almost the whole study period and did not present a seasonal pattern of fluctuation. Diaphanosoma (mainly D. birgei) attained the highest abundance among cladocerans. Most organisms were always found at the surface, but they also occupy the whole water column, even in periods of stratified conditions and low oxygen concentration in the bottom layers. Among the main zooplanktonic taxa, only Hexarthra avoids deep layers. An exceptionally high concentration of Copepoda nauplii on the surface was influenced by low transparency, high concentration of phytoplankton at this layer and low oxygen concentration at the bottom. In periods of higher retention timevariability there was a more heterogeneous distribution of the zooplankton in the water column. The increase in the retention time seems also to favor the copepod development. Finally, some inter-decade changes are considered on the basis of zooplankton assemblage structure observations.

Spatial and temporal dynamics of phytoplankton and bacterioplankton biomass in Sanya Bay, northern South China Sea

The composition of phytoplankton and the dynamics of phytoplankton and bacterioplankton biomass (PB and BB, respectively) of Sanya Bay, South China Sea, were determined. A total of 168 species (67 genera) phytoplankton were identified, including Bacillariophyta (diatom, 128 species), Pyrrophyta (35 species), Cyanophyta (3 species), and Chrysophyta (2 species). Annual average abundance of phytoplankton was 1.2 × 10 7 cells/m 3, with the highest abundance in autumn, and the lowest in summer. Annual average diversity index ( H') and evenness (J) values were 3.96 and 0.70, respectively. Average chlorophyll- a was 2.5 mg/m 3 and the average PB was 124 mg C/m 3 with the highest value in autumn. Surface PB was higher than the bottom, except for summer. Annual mean bacterioplankton abundance and BB were 6.9 × 10 11 cells/m 3 and 13.8 mg C/m 3 respectively. The highest BB was found in summer, followed by winter, spring, and autumn. Surface BB was higher than bottom all year round. The spatial distribution patterns of PB and BB were very similar with the highest biomass in the estuary, and decreased seaward, primarily due to the terrestrial input from the Sanya River and influx of oceanic water. The main factor influencing PB and BB was dissolved inorganic nitrogen (DIN). Other factors such as temperature, which is above 22°C throughout the year, had a negligible impact. The correlation between BB and PB was significant (P < 0.01). The annual average ratio of BB/PB was 0.12 (0.06-0.15). Phytoplankton primary production was one of the most important factors in controlling the distribution of bacterioplankton.

Maternal effects on offspring Igs and egg size in relation to natural and experimentally improved food supply

1. Maternal effects have been suggested to function as a mechanism for transgenerational plasticity, in which the environment experienced by the mother is translated into the phenotype of the offspring. In birds and other oviparous vertebrates where early development is within the egg, mothers may be able to improve the viability prospects of their offspring at hatching by priming eggs with immunological and nutritional components. 2. We studied how resource availability affects maternal investment in offspring by feeding Ural owl (Strix uralensis, Pall.) females prior to egg-laying in 3 years of dramatically different natural food conditions. 3. Supplementary feeding prior to laying increased body mass and the level of Igs of females measured at clutch completion. Supplementary fed Ural owl females laid larger eggs than control females, and had offspring with higher levels of Igs at hatching compared to offspring of control females. 4. We found variation in maternal allocation of resources to the eggs in response to environmental conditions: during a year of rapidly declining food abundance, maternal Igs in hatchlings were higher, whereas egg size was smaller compared to years with a more stable food supply. 5. Egg size had a positive effect on offspring body mass at fledging, whereas Igs at hatching did not affect Igs at fledging. 6. We conclude that maternal body condition and maternal Igs, as well as hatchling Igs and egg size are limited by food resources during egg production. Hatchlings rely on maternally derived Igs and, hence, our results suggest that mothers with high levels of Igs passively transfer higher Igs levels to their eggs instead of active manipulation of Igs levels in eggs. Ural owl egg size appears to be highly sensitive to short-term changes in food abundance, with important consequences for nestling growth.

Algal communities at Gouqi Island in the Zhoushan archipelago, China

The kelp bed of Gouqi Island lies in the east of the East China Sea, in the Shengsi Archipelago. It is a key component of the island-reef ecosystem. This study evaluated kelp beds on intertidal and subtidal zones from 2004 to 2006. We evaluated seasonal variations in the community structure of macroalgae, and their relationship with water temperature, nitrogen and phytoplankton. The Gouqi Island kelp bed consists mainly of species of Sargassum. Sargassum horneri was the dominant species in subtidal zones, representing 90% of the total biomass. The dominant species in intertidal zones were S. fusiforme, S. horneri, S. thunbergii and Undaria pinnatifida. Fifty-four phytoplankton species were found in the Gouqi Island kelp bed, of which 51 species were found inside the kelp beds, 43 species outside the kelp beds, and 40 species were present both inside and outside the kelp beds. Diatoms were dominant both inside and outside the kelp beds. Except in winter, Skeletonema costatum was dominant, and its abundance in autumn was over 98% of the total abundance. Water temperature was found to be the primary factor influencing the growth of S. horneri in the Gouqi Island kelp bed. S. horneri grew slowly from November to March, and rapidly from March to June. The upper temperature limit for growth of S. horneri was about 18°C. Higher water temperatures can result in a decline in the kelp bed. Nitrogen seemed to be a limiting factor for macroalgal growth. This was particularly true for S. horneri and phytoplankton. Since nitrate is the primary nutrient for S. horneri, its absorption by S. horneri resulted in seasonal changes of nitrate in the ecosystem.

Resource tracking by avian frugivores in mountain habitats of northern Spain

Systems comprising avian frugivores and fleshy‐fruited plants are commonly used as models to study how animals respond to temporal and spatial variations in food abundance and distribution. Results have been far from conclusive, partly because of methodological constraints. In this study we investigated the fulfilment of a necessary condition for food tracking: correlation over time and space between the abundance of food and the abundance of food trackers. We used a paired‐sample design in which fruit sites were compared with fruitless sites on two different spatial scales (landscape and habitat patch) in eight different river basins in the Cantabrian Mountains (NW Spain). Fruit and bird abundances were recorded monthly (October to February) at all sites during three consecutive fruiting seasons. Fruiting seasons (“years”) could be ranked by fruit abundance as low (2003), intermediate (2002) and high (2004). Since fruit sites were located at considerably higher elevations than fruitless sites, the possible effects of altitude, together with those of other uninvestigated factors, were taken into account by using non‐frugivorous birds. Our results apparently suggest a temporal and spatial association between frugivores (avian seed dispersers) and fruit availability at the landscape scale but not at the smaller (habitat patch) scale. This, together with the absence of a similar pattern in non‐frugivores, suggests that fruit availability is an important ecological factor affecting the autumn and winter abundance patterns of frugivorous birds and that this factor operates at the landscape scale but not at the habitat patch scale. Moreover, the negative elevational gradient in bird abundance that is typical of temperate mountain ecosystems was clearly reversed for frugivores in the intermediate and high fruiting years (suggesting that the negative effect of higher altitude may have been counterbalanced by the greater availability of food). As in other European upland areas, traditional farming practices in the Cantabrian Mountains are declining and, as a result, the proportion of fruitless habitats is increasing. Our study suggests that in these upland ecosystems frugivorous bird abundances in autumn and winter are associated to fruit supply, thus this habitat change tendency will probably have, in the long‐term, a negative effect on bird populations.

Temporal and Spatial Variations in the Species Composition, Distribution, and Abundance of Protozoa in East Dongting Lake, China

ABSTRACT Investigations of protozoa were carried out during four surveys of East Dongting Lake, China. A total of 160 protozoan species belonging to 71 genera was identified, of which 53 were flagellates, 37 sarcodines, and 70 ciliates. Among them, Peritrichida (32.6% of frequency), Arcellinida (16.2%), Volvocales (13.6%), Peridiniales (13.1%), and Chrysomonadales (9.1%) were the main groups and contributed to 84.5% of the overall species. Ciliates were mainly composed of sessile species and small species. The total protozoan abundance varied from 2,400 cells L−1 to 20,250 cells L−1. The highest protozoan abundance occurred in spring; the lowest number was in autumn. The highest abundance of ciliates occurred in spring and winter, whereas flagellates developed the highest abundance in summer and autumn. Pearson correlation analysis and linear regressions indicated that chlorophyll a and water velocity were the main factors affecting temporal and spatial variations of the protozoan abundance.

Over‐wintering growth and losses in a small population of the threespine stickleback,Gasterosteus aculeatus(L.), in mid‐Wales

Abstract – Mark‐recapture was used to estimate the population abundance of threespine stickleback,Gasterosteus aculeatus, in a backwater of Afon Rheidol in mid‐Wales in autumn and early spring, from 1984 to 1998. For the 0+ cohort, there was no evidence of density‐dependent losses (mortality and emigration) or growth in the over‐wintering period. No systematic size‐dependent loss was detected. There was an inverse relationship between autumn abundance and the annual rate of change in abundance of the 0+ cohort.

REPRODUCTION OF KLUNZINGER MULLET, LIZA KLUNZINGERI, IN COASTAL WATERS OF KHUZESTAN PROVINCE (PERSIAN GULF)

Some reproduction characteristics of keeled mullet, Liza klunzingeri, were studied during Apr. 2003 to Feb. 2004 in Khuzestan waters of the Persian Gulf. A total of 836 samples were monthly collected from two fish landings of Bahrekanand Hendijan; 727 specimens were studied from point of sex determination, and 60specimens were studied from the fecundity point of view. This species was found tohave more abundance in autumn (esp. Oct-Nov). The samples composed of89 (12٫2٪) male, 467 (64٫2٪) female and 171 (23٫6٪) immature; the sex ratio wasM: F = 1: 5. The advanced stages of maturity (4th & 5th) were found in Octoberonward. The highest Gonadosomatic Index was in December and the lowest was inJune. The maximum absolute and relative fecundities were 183040 and 2232, respectively; the minimum absolute and relative fecundities were 44700 and 582, respectively. The minimum and maximum egg diameter was 0٫04mm (stage 2nd) and0٫75mm (stage 6th).

Sewage Sludge Effects on Mesofauna and Cork Oak (Quercus suberL.) Leaves Decomposition in a Mediterranean Forest Firebreak

Effects of sewage sludge on litter mesofauna communities (Collembola and Acari) and cork oak (Quercus suber L.) leaf litter decomposition have been studied during 18 mo using litterbags in an in situ experimental forest firebreak in southeastern France. The sludge (2.74 t DM ha(-1) yr(-1)) was applied to fertilize and maintain a pasture created on the firebreak. Litterbag colonization had similar dynamics on both the control and fertilized plots and followed a typical Mediterranean pattern showing a greater abundance in spring and autumn and a lower abundance in summer. After 9 mo of litter colonization, Collembola and Acari, but mainly Oribatida, were more abundant on the sludge-fertilized plot. Leaf litter decomposition showed a similar pattern on both plots, but it was faster on the control plot. Furthermore, leaves from the fertilized plot were characterized by greater nitrogen content. Both chemical composition of leaves and sludges and the decomposition state of leaves have significantly affected the mesofauna community composition from each plot.

Acoustical estimates of fish and zooplankton distribution in the Piaseczno reservoir, Southern Poland

Hydroacoustical surveys in the Piaseczno reservoir were performed in May and September 2002 using a Biosonics 101 dual beam echo sounder. They have revealed very scarce fish populations in pelagic waters with twice-higher abundance in autumn (530 fish ha−1) as compared with spring (280 fish ha−1). Small and very small fish (below 10 cm length) dominated. Apart from fish, Chaoborus larvae were producing acoustical echoes of the TS similar or slightly weaker than that of small fish. Invertebrates formed a thin layer, less than 2 m thick at the border of an anoxic zone, and were changing their depth position between 6 and 16 m, both diurnally and seasonally.

Effect of field borders and nest-predator reduction on abundance of northern bobwhites

Fallow-field borders along edges of crop fields have been promoted for increasing northern bobwhites (Colinus virginianus) on farms and are a component of recovery plans for this species. However, research on bobwhite population response to field-border practices is sparse. Previous research on 2 farms documented increased use of farm fields and greater reproduction by bobwhites on farms with field borders, but nesting success was low during May and June. Bobwhite population response to field-border practices may increase when they are combined with nest-predator reduction on farms. Effect of nest-predator reduction on bobwhite populations on farmed landscapes has not been investigated in the Southeast. Therefore, we tested the effects of field borders and mesomam-mal nest-predator reduction on bobwhite abundance on 12 farms in eastern North Carolina, 1997–1999. We applied treatments to farms as factorial combinations. Reduction of mesomammal nest predators, including raccoons (Procyon lotor), Virginia opossums (Didelphis virginiana), and foxes (Urocyon cinereoargenteus and Vulpes vulpes), occurred from February-May of each year. To assess bobwhite response to treatments, we measured summer abundance of males using variable-radius point counts and covey abundance on farms in September and October using morning covey-call surveys. Bobwhites were more abundant on farms with field borders during summer (P=0.08). On field-border farms we heard 1.8x the number of coveys heard on farms without field borders (P=0.004). Summer abundance of bobwhites did not differ as a result of predator reductions (P=0.37), and we heard slightly fewer coveys on predator-reduction farms (P = 0.084) during autumn. However, we heard more coveys on farms with both field borders and predator reduction compared to all other farms (P=0.022). Field-border systems were a practical management technique to increase autumn abundance of bobwhites on individual farms in eastern North Carolina.

Multi-stage sampling for large scale natural resources surveys: A case study of rice and waterfowl

Large-scale sample surveys to estimate abundance and distribution of organisms and their habitats are increasingly important in ecological studies. Multi-stage sampling (MSS) is especially suited to large-scale surveys because of the natural clustering of resources. To illustrate an application, we: (1) designed a stratified MSS to estimate late autumn abundance (kg/ha) of rice seeds in harvested fields as food for waterfowl wintering in the Mississippi Alluvial Valley (MAV); (2) investigated options for improving the MSS design; and (3) compared statistical and cost efficiency of MSS to simulated simple random sampling (SRS). During 2000–2002, we sampled 25–35 landowners per year, 1 or 2 fields per landowner per year, and measured seed mass in 10 soil cores collected within each field. Analysis of variance components and costs for each stage of the survey design indicated that collecting 10 soil cores per field was near the optimum of 11–15, whereas sampling >1 field per landowner provided few benefits because data from fields within landowners were highly correlated. Coefficients of variation (CV) of annual estimates of rice abundance ranged from 0.23 to 0.31 and were limited by variation among landowners and the number of landowners sampled. Design effects representing the statistical efficiency of MSS relative to SRS ranged from 3.2 to 9.0, and simulations indicated SRS would cost, on average, 1.4 times more than MSS because clustering of sample units in MSS decreased travel costs. We recommend MSS as a potential sampling strategy for large-scale natural resource surveys and specifically for future surveys of the availability of rice as food for waterfowl in the MAV and similar areas.

LONG-TERM STUDY OF ABUNDANCE OF THE HISPID COTTON RAT IN NATIVE TALLGRASS PRAIRIE

We studied patterns of and factors influencing abundance of hispid cotton rats (Sigmodon hispidus) in tallgrass prairie habitats from autumn 1981 to spring 2001 at the Konza Prairie Biological Station, Kansas. Abundance of cotton rats was low during autumn (X ¼ 0.57 individuals/trapline) and extremely low in spring (X ¼ 0.04 individuals/trapline). Autumn abundance varied widely in 20 years (range: 0.00‐2.50 individuals/trapline) and among 14 sites (0.05‐1.35 individuals/trapline). Spring prairie fires had a positive influence on cotton rats during the 1st (X ¼ 0.8 individuals/trapline) and 2nd autumns (X ¼ 1.0 individuals/trapline), but not during the 3rd or later autumns (X ¼ 0.2 individuals/trapline). Cotton rats were associated strongly with lowland prairie relative to breaks and upland prairie. Autumn abundance was correlated positively with previous winter (December‐ February) average maximum temperature, but was not correlated with previous winter precipitation, summer (June‐August) average maximum temperature, summer precipitation, or aboveground net primary productivity. Although previous winter maximum temperature accounted for only 32% of interautumn variation in abundance, winter harshness appears to be the major factor driving temporal variation in autumn abundance of hispid cotton rats.

Will Environmental Stewardship enhance small mammal abundance on intensively managed farmland?

1 The creation of grassy field margins, as part of the UK Government's Environmental Stewardship (ES) scheme, is one of a number of measures proposed to mitigate the adverse effects of arable intensification on wildlife. Widespread development of these margins will potentially increase the amount of habitat available to small mammals in arable landscapes, as many species do not inhabit the cropped area. 2 The aim of this study was to determine what impact ES-type margins might have on small mammals. We compared small mammal abundance and biomass in spring and autumn on 3-m-wide and 6-m-wide grassy margins with that on conventionally managed field edges that have no margin (0 m wide) and are intensively cultivated to the field edge. 3 Bank voles Clethrionomys glareolus, wood mice Apodemus sylvaticus and common shrews Sorex araneus were the most abundant species; few field voles Microtus agrestis were captured on any margin. In autumn, bank vole and common shrew numbers were higher on the grassy margins than on conventional field edges, and margin width per se was positively associated with bank vole abundance. The number of wood mice captured did not differ among the different margin types. 4 Total small mammal biomass increased between spring and autumn on the 3-m- and 6-m-wide grassy margins, but decreased on the 0-m-wide margins. Total biomass in autumn was three times higher on 6-m-wide margins compared with the conventional arable field edges.

Horizontal distribution and dominant species of heteropods in the East China Sea

This article discusses the horizontal distribution and dominant species of heteropods in the East China Sea. The ecological characteristics of heteropods and their adaptability to the environments were also considered. Oceanographic census was carried out in the East China Sea (23 � 30 0 � 33 � Na nd 118 � 30 0 � 128 � E) in four seasons from 1997 to 2000. It was found that the total abundance showed obvious seasonal variations. It peaked in autumn with a mean value of 21.03 ind. (100 m 3 ) –1 , followed by summer (4.89 ind. (100 m 3 ) –1 ). The lowest abundance occurred in winter and spring. As to the horizontal distribution, abundance in summer and autumn was higher in the nearshore than in the offshore of the East China Sea. In winter and spring, heteropods were barely found in the northern nearshore. Three dominant species were observed in four investigated seasons, in which only Atlanta rosea dominated in winter, spring and summer while Atlanta peroni and Atlanta lesueuri mainly dominated in autumn. These two dominant species observed in autumn exhibited a rather higher occurrence frequency than A. rosea. Temperature was found to be a major influencing factor whereas salinity was a minor one. Comparing their adaptability, A. rosea can survive in a wider temperature range (16� 28 � C), which enables it to dominate in four seasons, while A. peroni survives in a relatively narrow temperature range (19� 28 � CC) and the range for A. lesueuri was even more narrow (21� 28 � CC). Moreover, A. rosea was also adapted to a wider range of salinity. However, the abundance of A. rosea in autumn was lower than those of A. peroni and A. lesueuri. It can be thereby inferred that the multiplication speed of A. rosea was lower than the other two species within the same favorable temperature range. Due to their adaptability to high salinity, the distribution of heteropods was closely related to the domain of the Taiwan Warm Current and Kuroshio. Especially for A. peroni and A. lesueuri, their high abundance areas are always indicative of the lasting existence of strong warm currents. The negative values of aggregation indices indicated relatively even distribution of heteropods in the East China Sea. The high abundance area (31 � 00 0 N, 126 � 00 0 E) of heteropods in autumn is on the migration pathway of the mackerel (Scomber japonicus Houttuyn). Thus, there is also a fishing ground of the mackerel. This suggested that the high abundance area of heteropods in autumn is important to the fisheries in the East China Sea. Comparing with the historical records, the abundance of heteropods appeared to increase in the past 40 years. This may be a result of strengthened warm currents due to global warming.

Population dynamics of Capriniana piscium (Ciliophora, Suctoria) on the gill surface of Arctic char (Salvelinus alpinus) from high mountain lakes

Gills of Arctic char (Salvelinus alpinus) from an oligotrophic high mountain lake (Oberer Plenderlesee, Austria) were heavily infected with Capriniana piscium (a commensalic ciliate) displaying a distinct seasonal pattern with a maximum abundance in autumn and early winter and a minimum between late winter and summer. There was no evidence of tissue damage caused by C. piscium, and the rate of infection did not directly correlate with physical and chemical water parameters. Thus, the increase of the pelagic ciliate community during the ice-free period may have a major impact on the specific population dynamics of C. piscium as it represents its major food source.

Long‐term variation in the abundance of the brown shrimp Crangon crangon (L.) population of the German Bight and possible causes for its interannual variability

AbstractTime series on Crangon crangon densities in the German Wadden Sea show a considerable degree of interannual variability, for the entire region in spring and in autumn as well as for three subareas, North Frisia, East Frisia and Elbe estuary. Across the entire survey area C. crangon density was inversely related to water depth. In autumn after the recruitment, settlement shrimp densities are correlated across a larger spatial scale (&gt;100 km longshore), whereas in spring the overwintering adult spawning stock is uncorrelated across subareas. Interannually, extreme density variations can develop even over a short time span of 1 yr. On a large spatial scale shrimp abundance in autumn was correlated with year‐to‐year changes in physical environmental and biological parameters, winter water temperature, autumn river runoff and the winter NAO index. On a regional scale (North Frisia), density of gadoid predators was an additional component affecting shrimp stock abundance. No correlations to such parameters could be detected for the C. crangon stock in spring. Possible causes for the spring situation and additional sources for variability are discussed.

The relation between age-0 rainbow trout (Oncorhynchus mykiss) abundance and winter discharge in a regulated river

We identified and experimentally tested a discharge–abundance relation that predicted, based on the mean river discharge in the second half of winter (15 January – 31 March), the spring abundance of age-0 rainbow trout (Oncorhynchus mykiss) in a section of the Henrys Fork of the Snake River, Idaho, with complex bank habitat. We also considered a competing hypothesis in which autumn abundance determined spring abundance. We established that large abundances of age-0 trout were present in autumn (34 000 – 81 000) and lower abundances remained in spring (8000 – 15 000). Winter loss of age-0 trout was initiated in January. Spring abundance in 1996–1998 was related to autumn abundance (r2 &gt; 0.99) and mean discharge in the second half of winter (17.1–22.8 m3·s–1; r2 &gt; 0.99) but not mean discharge in the first half of winter (15.1–21.1 m3·s–1; r2 = 0.11). We experimentally maintained a high discharge (20–21 m3·s–1) in the second half of winter in 1999 to test model predictions. Autumn abundance failed to predict spring abundance (observed = 11 109; predicted = 6822; 95% prediction interval = 4669–8975). However, the discharge–abundance model accurately predicted spring abundance (predicted = 11 980; 95% prediction interval = 10 728 – 13 231). Higher discharge in the second half of winter may have provided more bank habitat at a critical time for survival.

Importance of instream cover for young masu salmon, Oncorhynchus masou , in autumn and winter

Densities of wild masu salmon, Oncorhynchus masou Brevoort, were investigated before (late-September) and after (mid-November) autumnal habitat shifts in a small river in Hokkaido, northern Japan. Abundance of instream cover habitat formed by coarse woody debris, submerged vegetation and undercut banks was quantified. Density of 1+ and older masu salmon was significantly correlated with cover abundance in autumn, although cover was not significant for density of 0+ fish, indicating that clear-cut reaches were utilized by 0+ masu salmon in autumn. In early winter, densities of 0+ and 1+ and older masu salmon were both correlated with cover availability. These results suggest that the amount of cover habitat is an important regulator for densities of juvenile masu salmon during winter.