Temporal and spatial variation in potential and realized growth rates of age‐0 year northern rock sole

The possibility of prey limitations on the growth performance of age‐0 year northern rock sole Lepidopsetta polyxystra was evaluated at three sites along the north‐east coast of Kodiak Island, Alaska, U.S.A., by comparison of observed to potential growth rates. Growth potential was measured in the laboratory across the range of temperatures encountered by this species during the first summer of life. Growth potential ( g _L, mm day⁻¹) increased with water temperature (T) between 2 and 13° C, according to: g _L = 0·0151 + 0·3673·log₁₀(T). There were significant differences in growth rate between the three field sites such that Holiday Beach fish were 7·1 mm longer than Shakmanof Beach fish by mid‐September, with Pillar Creek Cove fish of intermediate size. Temperature differences between sites accounted for less than half of this variation. The remainder may have been related to differences in prey availability among the sites in association with observed differences in sediment characteristics. In addition to the spatial variability, there was significant monthly variation in growth performance. Realized growth rates between July and August were in excess of 85% of potential. Between August and September, however, realized growth fell to 43–71% of potential indicating a decline in conditions for growth. The spatial variation in growth rates was not density‐dependent as the site with the highest fish densities (Holiday Beach) also supported the highest growth rates. The available data indicates that for this subtidal species, interannual variation in growth may be more important than site variation.     

Assessing mortality changes from size‐frequency curves

The relationship between the instantaneous mortality rate ( Z ) and the instantaneous change in length‐frequency distribution of organisms per unit of animal size (μ _L ) takes the following form: Z  = μ _L k ( L _∞ −  L ) +  k , where k and L _∞ are coefficients of the von Bertalanffy equation, and L is organism size (length). Z and μ_L change coherently when they are measured for a specific size or age class. Therefore, observations of μ _L can provide information on the relative changes in mortality. This is useful when no precise information about animal growth is available and growth curve is assumed to be invariable. This method was tested on a heavily exploited population of St Peter's fish (mango tilapia) Sarotherodon galilaeus in Lake Kinneret, Israel, where large fluctuations in the size structure of the catch have occurred over the past few years. Analysis of the changes in the length‐frequency distributions showed that the changes in μ _L over multiple years estimated for fully exploited fish reflected the respective changes in Z .     

Inter‐individual differences in rates of routine energy loss and growth in young‐of‐the‐year juvenile Atlantic cod

Inter‐individual differences in rates of routine (non‐feeding) metabolism and growth were evaluated in young‐of‐the‐year (YOY) juvenile Atlantic cod Gadus morhua . Rates of O₂ consumption, CO₂ production and ammonia (TAN) excretion were measured in 64, 25–43 mm standard length ( L _S) YOY growing at different rates (0·27–0·47 mm day⁻¹) in a common rearing tank. Parameter rates ( y ) increased allometrically ( y = a·M^b ) with increasing body mass ( M ) with b ‐values for O₂ production, CO₂ consumption and TAN excretion equal to 0·81, 0·89 and 0·56, respectively. In some cases, residuals from these regressions were significantly negatively correlated to fish growth rate. In no cases did residuals of parameter rates increase with increasing growth rate. These data suggest that, during unfed periods, relatively fast‐growing fish were more metabolically efficient than slower‐growing fish from the same cohort. The fish condition factor, derived from     , also significantly decreased with increasing growth rate. Results indicated differences in both the rates of routine energy loss and the patterns of growth allocation among YOY Atlantic cod. Since these physiological attributes were positively correlated with growth rate, they may be indicative of 'survivors' in field populations.     

Effects of temperature, body size and feeding on rates of metabolism in young‐of‐the‐year haddock

The mean rate of oxygen consumption (routine respiration rate, R _R, mg O₂ fish⁻¹ h⁻¹), measured for individual or small groups of haddock Melanogrammus aeglefinus (3–12 cm standard length, L _S) maintained for 5 days within flow‐through respiratory chambers at four different temperatures, increased with increasing dry mass ( M _D). The relationship between R _R and M _D was allometric ( R _R = α  M ^b ) with b values of 0·631, 0·606, 0·655 and 0·650 at 5·0, 8·0, 12·0 and 15·0° C, respectively. The effect of temperature ( T ) and M _D on mean R _R was described by     indicating a Q ₁₀ of 2·27 between 5 and 15° C. Juvenile haddock routine metabolic scope, calculated as the ratio of the mean of highest and lowest deciles of R _R measured in each chamber, significantly decreased with temperature such that the routine scope at 15° C was half that at 5° C. The cost of feeding ( R _SDA) was c . 3% of consumed food energy, a value half that found for larger gadoid juveniles and adults.     

Mackerel icefish size and age differences and long‐term change at South Georgia and Shag Rocks

This study analysed the total length ( L _T)‐frequency distribution of mackerel icefish Champsocephalus gunnari at South Georgia and Shag Rocks from nine bottom trawl surveys at South Georgia and eight at Shag Rocks between 1987 and 2002. The estimated mean L _T of age‐classes 1+, 2+, 3+ and 4+ years during January were, respectively, 14·7, 23·5, 29·8 and 35·1 cm at South Georgia. Age‐classes 1+, 2+ and 3+ years were 18·3, 26·2 and 33·8 cm at Shag Rocks. The derived Bertalanffy growth parameters for South Georgia were: L _∞ = 51·7 cm, k  = 0·27 and t ₀ = −0·26. The mean L _T of each age‐class of C. gunnari at Shag Rocks was significantly larger than at South Georgia, equivalent to c . 5 months growth, although the annual growth in L _T was similar. This is further evidence that C. gunnari hatched earlier at Shag Rocks. At South Georgia, the mean L _T of age‐classes 1+ and 3+ years were correlated, and significantly decreased between 1987 and 2002, and were smaller following warmer summers. This decrease in the size of C. gunnari may be the result of reduced food availability linked to climate warming.     

Evidence for independent origin of two spring‐spawning ciscoes (Salmoniformes: Coregonidae) in Germany

Combined analyses of mitochondrial DNA (mtDNA) and microsatellite loci were performed to assess the genetic differentiation of two spring‐spawning ciscoes from each other and from sympatric Coregonus albula in two German lakes. Polymorphism was screened at six microsatellite loci and mtDNA for a total of 247 and 94 ciscoes, respectively. Microsatellite data showed a weak differentiation between spring‐spawning Coregonus fontanae and sympatric C. albula in Lake Stechlin ( F _ST = 0–0·008), whereas a significant differentiation was observed between spring‐spawning Coregonus lucinensis and sympatric C. albula in Lake Breiter Luzin ( F _ST = 0·013–0·039). A more pronounced genetic difference was observed between both spring‐spawning species ( F _ST = 0·05–0·128). Shared mtDNA haplotypes among sympatric species within both Lake Stechlin and Lake Breiter Luzin were observed, whereas no haplotype was shared between C. fontanae and C. lucinensis . These results suggest an independent origin for spring‐spawning ciscoes in each lake. Evidence is also provided for mtDNA introgression of Coregonus sardinella into C. lucinensis and C. albula in Lake Breiter Luzin. Postglacially, this species or at least a population which showed mtDNA introgression has colonized the Baltic Sea basin up to the glacial margin that was located between Lakes Stechlin and Breiter Luzin.     

Diffusion in the littoral zone: scoping emergence times and movement to essential habitat for young‐of‐year brook trout in lakes

Factors governing the process of dispersal of lake‐spawned brook trout ( Salvelinus fontinalis ) young‐of‐year (YOY) appear drastically different from those governing dispersal in more commonly studied stream salmonids. Rather than dispersal being highly density‐dependent and the result of territoriality and aggression, in brook trout it may be density‐independent and driven by a common need for coldwater habitat for summer survival. Emerging fish travel great distances from single spawning sites on lakes to cold groundwater habitat. Movement is a gradual, one‐dimensional diffusion around lake margins and represents a very unique and simplified natal dispersal pathway allowing for dispersal rates, distances, and factors controlling these parameters to be measured. We predicted timing of the emergence period for brook trout alevins from lake spawning sites using the known relation between water temperature and emergence times for salmonids. Emergence and dispersal was then observed in the field by visually estimating YOY density in segments of the littoral zone throughout the dispersal period. Fluxes in density in these sections were used to estimate rate of YOY spread. YOY behaviour and body condition was also assessed across the wave of spatial spread. We are working towards a spatially explicit model to identify critical groundwater rearing habitat needing protection from forestry activities.     

Coho salmon haematological, metabolic and acid‐base changes during exercise and recovery in sea water

Cannulated, seawater‐acclimated coho salmon Oncorhynchus kisutch were swum to exhaustion in a seawater tunnel (10° C, mean U _crit 50 cm s⁻¹), resulting in metabolic acidosis and increased plasma electrolyte and cortisol concentrations, which were corrected during a 4 h recovery. Because the swimming and physiological performance data were similar to those of other salmonids, it was concluded that life‐history limitations, besides their exercise capabilities in upwelling zones, probably explain declining coho salmon populations.     

Short‐term freshwater exposure benefits sea lice‐infected Atlantic salmon

Atlantic salmon Salmo salar were infected with sea lice Lepeophtheirus salmonis (0·08 ± 0·007 sea lice g⁻¹) over a period of 4 h. Both infected and non‐infected fish were swim tested in sea water (SW) and fresh water (FW). The ventral aorta of each fish was fitted with a Doppler cuff in order to measure cardiac output, stroke volume and heart rate during swim testing. Blood samples were taken at rest and after exercise. Critical swimming speed of infected fish in SW (2·14 ± 0·08 body lengths, bl s⁻¹) was significantly lower ( P  < 0·05) than infected fish switched to FW (2·81 ± 0·08 bl s⁻¹) and non‐infected fish in SW (2·42 ± 0·04 bl s⁻¹) and FW (2·61 ± 0·08 bl s⁻¹). Cardiac and blood results indicated infected fish exposed to FW did experience stress, but relief from osmotic and ionic distress probably reduces energy expenditure, allowing the increase in performance. As the performance of sea lice‐infected fish improved upon transfer to FW, it is likely that heavily infected salmonids do return to FW to restore compromised osmotic and ionic balance, and remove sea lice in the process.     

Variability in growth of longfinned eels among coastal catchments of south‐eastern Australia

Longfinned eels Anguilla reinhardtii were captured by both fishery‐dependent and independent sampling methods from three rivers in New South Wales, south‐eastern Australia. Growth rates were examined in two zones (fresh water and tidal) in the Hacking, Hawkesbury and Clarence Rivers. Mean annual growth increments of sampled longfinned eels ranged from 30 to 60 mm year⁻¹ using age‐length analyses and up to 167 mm year⁻¹ based on tag‐recapture model estimates (GROTAG), with both methods showing high intra‐ and inter‐population variability. Growth was significantly faster in younger (5–15 years) fish than older (>15 years) fish, with females growing an average 10 mm year⁻¹ faster than males of similar age and capture location. Longfinned eels found in tidal areas grew significantly faster than those in non‐tidal freshwater areas as a result of longer growing seasons in the highly productive estuarine habitats. Other possible factors influencing variability in growth rates for this species include habitat preference, density and fishing pressure.     

Population structure of lake‐type and river‐type sockeye salmon in transboundary rivers of northern British Columbia

The population structure of 'lake‐type' and 'river‐type' sockeye salmon Oncorhynchus nerka , primarily in transboundary rivers in northern British Columbia, was examined with a survey of microsatellite variation. Variation at 14 microsatellite loci was surveyed from c . 3000 lake‐type and 3200 river‐type sockeye salmon from 47 populations in six river drainages in British Columbia. The mean F _ST for the 14 microsatellite loci and 47 populations was 0·068, and 0·034 over all river‐type populations. River‐type sockeye salmon were more genetically diverse than lake‐type sockeye salmon, with expected heterozygosity of river‐type sockeye salmon 0·72 and with an average 12·7 alleles observed per locus, whereas expected heterozygosity of lake‐type sockeye salmon was 0·65 with and average 10·5 alleles observed per locus. River drainage of origin was a significant unit of population structure. There was clear evidence of genetic differentiation among river‐type populations of sockeye salmon from different drainages over a broad geographic range in British Columbia.     

Temperature and state‐dependence of feeding and gastric evacuation in juvenile Pacific halibut

Relationships between nutritional state, behavioural response to prey and gastric evacuation rates were examined in juvenile Pacific halibut Hippoglossus stenolepis feeding on squid. Pacific halibut reared at 2, 6 and 10° C were fasted for 1 or 7 days to generate variation in energetic state. The 7 day fast resulted in measurable declines in condition indices at 10 and 6° C but not at 2° C. At 10° C, all Pacific halibut consumed the first meal offered, but fish previously fasted for 7 days took significantly longer to locate and consume the meal than fish fasted for only 1 day. At 2° C, Pacific halibut fasted for 7 days did not generally consume the first meal offered, but resumed feeding 2·1 days sooner, on average, than fish fasted for only 1 day. The gastric evacuation rate of the squid meal was best described by a power model with near‐exponential curvature ( a  = 1·011). The evacuation rate was strongly temperature‐dependent ( Q ₁₀ = 3·65) but displayed the same degree of variability at each temperature. The evacuation rate in Pacific halibut was not affected by feeding history, body size or energetic state. Furthermore, individual variation in gastric evacuation rate was not correlated with feeding responsiveness at any temperature. These results indicate a general plasticity in the behavioural but not physiological aspects of energy acquisition.     

Assessment and control of non‐indigenous brown bullhead Ameiurus nebulosus populations using fyke nets in shallow ponds

In order to evaluate fyke nets as a tool for population assessment and mass removal of brown bullhead Ameiurus nebulosus populations, small, shallow ponds were sampled during late summer in 1999 and 2000. Catch efficiency, species and size selectivity of fyke nets were investigated with the mark‐recapture method. Two different strategies were applied: (1) on six occasions, the mark‐recapture method was applied to entire populations, and (2) in six other cases, sampling was done in two replicated enclosed areas (625 m²). When applied to entire populations, fyke nets were found to be size selective, and capture efficiency significantly increased with standard length. Conversely, no size selectivity of fyke nets was found in enclosed areas. Sampling in replicated enclosures yielded reproducible estimates of population density and biomass. The results suggest that double fyke nets, when combined with the mark‐recapture technique, are a very useful tool for the efficient and reliable assessment of brown bullhead populations. The results of the study also suggest that double fyke nets may potentially be a cost‐effective tool for the mass removal of non‐indigenous brown bullhead populations.     

Density‐dependent growth in hatchery‐reared brown trout released into a natural stream

Hatchery‐reared brown trout Salmo trutta stocked in a natural stream in addition to resident wild brown trout grew more slowly than those stocked with an experimentally reduced density of brown wild trout. In both cases, hatchery‐reared brown trout grew more slowly than resident wild fish in control sections. Mortality and movements did not differ among the three categories of fish. The results showed that growth of stocked hatchery‐reared brown trout parr was density‐dependent, most likely as a consequence of increased competition. Thus, supplementary release of hatchery‐reared fish did not necessarily increase biomass.     

Conservation genetics of Amorpha georgiana (Fabaceae), an endangered legume of the Southeastern United States

Amorpha georgiana (Fabaceae) is an endangered legume species found in longleaf pine savannas in the Southeastern United States. Approximately 900 individuals and 14 populations remain, most of which are concentrated in North Carolina. Eleven microsatellite loci were used to explore genetic diversity, population structure and recent population bottlenecks using genotypic data from 132 individuals collected at ten different localities. Although A. georgiana is quite rare, it exhibited high levels of genetic diversity (17.7 alleles/locus; H _o = 0.65, H _E = 0.75). Most of the genetic variation was found within rather than between populations of this species. The single remaining Georgia population was well differentiated from populations of the Carolinas ( F _ST > 0.1), which had weaker structure among them ( F _ST < 0.1). Only a geographically disjunct population showed strong evidence of a recent population bottleneck, perhaps due to a recent founder event. Hybridization with A. herbacea was also detected. For conservation management plans, A. georgiana populations in each geographic region (North Carolina, South Carolina and Georgia) plus a disjunct population in North Carolina (Holly Shelter) should be treated as separate management units for which in situ conservation, including habitat restoration and use of prescribed burns, should ensure persistence of this species and preservation of its evolutionary potential.     

Age and growth analysis of the central mudminnow, Umbra limi (Kirtland, 1840)

A rudimentary understanding of age, growth, and life-span is lacking for many non-game fishes. Growth characteristics of the central mudminnow ( Umbra limi ) have not yet been accurately described using reliable hard part analysis. The utility of scales and otoliths as ageing structures and quantified growth was examined in one lake and one stream population of central mudminnow. Scales were found to be of no utility in determining age due to inconsistent formation of yearly annuli and a high incidence of regenerated scales, while otoliths were easily extracted and considered to be an accurate ageing structure. Ages determined from scales were low compared to those from otoliths, and the difference in age interpreted from the two structures increased with fish age. A power function was fitted to describe the length-weight relationship for this species ( a  = 0.0069, b  = 3.175). Von Bertalanffy growth parameters were estimated and compared for each population (Lake: L _∞ = 114.20 mm, K  = 0.30, t ₀ = −0.93; Stream: L _∞ = 77.59 mm, K  = 0.63, t ₀ = −0.76). The lake population showed greater size at age compared to the stream population, especially at older ages, and achieved a larger maximum size. Growth rate was also greater in the lake population (Lake: 1.74; Stream: 1.09 g year⁻¹). Females were larger at age than males in both populations, however all individuals greater than age 3 were males. This work represents the first successful account of central mudminnow growth using hard part analysis.     

A new method to evaluate egg‐to‐fry survival in salmonids, trials with Atlantic salmon

A new method to estimate the survival of salmonids from egg fertilization to fry emergence is described. Fine mesh screen cylindrical capsules, 12 cm³ in volume, filled with batches of 10 eggs of Atlantic salmon Salmo salar were implanted in the substratum using small removable guiding tubes inserted with a metal spike. The method was compared with two other commonly used techniques, capping redds with fry‐traps and fine mesh screen incubation‐emergence boxes buried into the gravel. Egg‐to‐fry survival was recorded for the three methods run in parallel in artificial redds created on three sites of the Nivelle River watershed (south‐west of France), two in the stream and one in an experimental spawning channel. In the channel, survival to the eyed stage and to hatching in capsules and incubation‐emergence boxes was also compared. The implant of capsules proved easier and faster to use than other methods, the structure of the surrounding substratum was less disturbed and the capsules were less vulnerable to spates. This technique provided survival values largely free of the bias induced by other methods and intermediate between that of incubators and of traps.     

Sex differences in pectoral muscles but not in pectoral fins in the three‐spined stickleback Gasterosteus aculeatus

The pectoral muscle index ( I _PM)( I _PM = 100 M _PM M⁻¹, where M _PM and M are the pectoral muscle and body masses, respectively) fin‐area and fin ray length were studied over a year in male and female three‐spined stickleback Gasterosteus aculeatus from a marine population (Öresund, Sweden) kept under simulated natural light and temperature conditions. A castration‐replacement experiment was used to test androgen effects on the I _PM, fin‐area and fin ray length. Non‐breeding males were castrated or sham‐operated in winter ( i.e . the fish had low levels of androgens). Castrated control and sham‐operated fish were implanted with empty Silastic capsules and castrated groups with capsules containing the androgens testosterone or 11‐ketoandrostenedione into the abdominal cavity. The experiment was terminated after 41 days, when the controls had matured. No morphological differences were found in pectoral fins between sexes during the year, except during the peak breeding season (May), where females showed larger fin‐area and longer fin ray in length compared to males. No effects of androgens treatment or of castration on pectoral fin‐area or fin ray length was observed. Breeding and non‐breeding males showed higher I _PM compared to females. The lower I _PM in females than in males could not be explained by the larger gonads in the former alone, as a sex difference in I _PM was still present after deduction of the ovaries from the female body mass. The I _PM was higher in sham‐operated compared to castrated fish. No effects of androgens treatment on I _PM was observed.     

Genetic diversity and genetic structure of populations of Ranunculus japonicus Thunb. (Ranunculaceae)

Abstract In order to clarify the genetic diversity and population structure of Ranunculus japonicus , allozymic analysis was conducted on 60 populations in southwestern Japan. Considerable genetic variati ons were detected among the populations of R. japonicus . The genetic diversities within species ( H _es = 0.215) and within populations ( H _ep = 0.172) were slightly higher than those of other perennial herbs with widespread distribution and outcrossing plants. Significantly higher values of fixation index were detected in some populations, which might have arisen from restricted mating partners. The majority of genetic variation (approx. 80%) resided within a population and a moderate level of genetic differentiation ( G _ST = 0.203) was observed among populations. The F _ST value (0.203) suggests the existence of a substantial population structure in this species. The highly significant correlation between geographic distance and F _ST values indicates that isolation by distance has played an important role in the construction of the genetic structure of this species.     

Female‐biased migration of stream‐dwelling Dolly Varden in the Shiisorapuchi River, Hokkaido, Japan

The first evidence for female‐biased migration in a partially migratory stream‐dwelling salmonid the Dolly Varden Salvelinus malma , a phenomenon well known in sea‐run and lake‐run populations, is presented. Dolly Varden in the Shiisorapuchi River in central Hokkaido, Japan, used both tributaries, of which there are many, and the main stem, but spawned only in tributaries. The size structures of Dolly Varden (≥age 1 + years) in tributaries were unimodal (<100 mm fork length, L _F) during non‐spawning seasons but changed to bimodal during spawning seasons (lower mode <110 mm, upper mode >120 mm L _F). Mature individuals were observed in both modal groups. From the trapping and census data, the small group appeared to be tributary resident and the large group main stem migrant. Males were common in both resident and migrant components. Most females, however, migrated to the main stem to mature, indicating female‐biased migration.