Stock and parental effects on embryonic and early larval development of winter flounder Pseudopleuronectes americanus (Walbaum)

A hierarchical breeding design was used to determine if winter flounder Pseudopleuronectes americanus embryos and yolk-sac larvae sired by Georges Bank males developed and grew larger than fish sired by Passamaquoddy Bay males, and to examine parental contributions to variations in fertilization success, time to 50% hatch, hatch success and larval morphological development. Significant stock effects were detected for time to hatch and larval development. Eggs fertilized by Passamaquoddy Bay males reached 50% hatch significantly earlier than eggs fertilized by Georges Bank males. Larvae sired by Georges Bank males were significantly larger during larval development for four of the six traits measured at 12 days post-hatch: head depth, jaw length, myotome height and body area. Embryo and larval development were strongly influenced by maternal contributions; there were significant maternal variance components for the majority of the variables measured. Paternal variance components were significant for fertilization success, time to hatch, larval jaw length and larval head depth, however, they acted principally through parental interactions. This information has important implications for the long-term sustainable development of winter flounder for aquaculture purposes as well as for understanding winter flounder genetic variation in the wild.     

Factors affecting the post‐release survival of cultured juvenile Pseudopleuronectes americanus

Laboratory experiments were performed with cultured and wild juvenile winter flounder Pseudopleuronectes americanus to evaluate differences in behaviour and adaptation affecting post‐release vulnerability to predation. Studies revealed that the cryptic abilities of cultured winter flounder increased over time. Sediment‐naïve, cultured fish required a minimum of 2 days to improve their burying skills and at least 90 days for colour adaptation to match the sediment. Cultured winter flounder selected sediments consisting of small grains and colours matching their own pigment. Cultured winter flounder, regardless of their colour, were significantly more vulnerable to predation by birds. Additionally, cultured fish reacted differently than wild winter flounder when exposed to cues from a potential predator.     

Distribution and reproduction of the Patagonian toothfish Dissostichus eleginoides Smitt around the Falkland Islands

Population characteristics of the Patagonian toothfish Dissostichus eleginoides were investigated based on material collected from both trawl and longline fisheries in Falkland Islands' waters. The fish occurred between 56 and 2122 m and attained 225 cm total length ( L _T). Males matured earlier, L _T at 50% maturity was 86 cm for males v . 90 cm for females. Subadult fish foraged at depths of <600 m, whereas adult Patagonian toothfish lived at >600 m. Spawning occurred on slopes of the Burdwood Bank at c . 1000 m depth with a minor peak in May, and a major peak in July to August. Males arrived at the spawning grounds first. Between spawning peaks both sexes remained around the Burdwood Bank with males occurring at greater depths than females. The Patagonian toothfish in south‐east Patagonia and the Falkland Islands had a long juvenile and sub‐adult period in the relatively shallow and warm waters of the outer shelf and upper slope unlike that of juveniles in other Patagonian toothfish populations. The migratory life style of the south‐west Atlantic population is probably very different from that of other populations, which tend to be resident as they are inclined to inhabit the waters around oceanic islands and sea mounts with narrow shelf areas.     

Microsatellite analysis indicates an absence of population structure among Hippoglossus hippoglossus in the north‐west Atlantic

To explore the population structure of Atlantic halibut Hippoglossus hippoglossus , 160 fish from four locations in the north‐west Atlantic (Bay of Fundy, Scotian Shelf, Gulf of St Lawrence and Iceland) were examined for evidence of population structure using 18 microsatellite markers. Pair‐wise F _ST and a model‐based cluster analysis revealed no significant differentiation between samples, although uncertainties surrounding Atlantic halibut reproductive behaviour made it difficult to ascertain that only a single breeding population had been sampled at each location     

First record of Polyprion oxygeneios(Perciformes: Polyprionidae) for the south‐west Atlantic and a northernmost range extension

The occurrence of Polyprion oxygeneios (Perciformes: Polyprionidae) is recorded for the first in the south‐west Atlantic. Twenty specimens were caught off Rio Grande do Sul (33°41·8'–34° 15·3' S, 370–854 m depth) during winter cruises of the commercial fishing fleet.     

Southernmost occurrence of Epinephelus marginatus in the south‐west Atlantic

The southernmost occurrence of the dusky grouper Epinephelus marginatus in the south‐west Atlantic (Argentina) was recorded at 36°S, expanding its range 1200 km southward from that previously reported.     

Spatial patterns of the biological traits of freshwater fish communities in south‐west France

Spatial patterns in the combinations of biological traits of fish communities were studied in the Garonne River system (57 000 km², south‐west France). Fish species assemblages were recorded at 554 sampling sites, and the biological traits of species were described using a fuzzy‐coding method. A co‐inertia analysis of species distributions and biological traits identified some spatial patterns of species trait combinations. Fish species richness progressively increased from up‐ to downstream sections, and the longitudinal patterns of fish assemblages partitioned the river into clear biogeographic areas, such as the brown trout Salmo trutta (headwater streams), the grayling Thymallus thymallus , the barbel Barbus barbus and the bream Abramis brama zones (most downstream sections), which fitted with Huet's well‐known zonation for western European rivers. Only a few biological traits, chiefly related to life‐history attributes, significantly influenced the observed fish distributions. Fecundity, potential size, maximum age and reproductive factor increased from headwater to plain reaches. As a theoretical framework for assessing and predicting the functional organization of stream fish communities, spatial variations in species traits can be related to habitat conditions, thus providing explicit spatial schemes that may be useful to the design of both scientific studies and river management.     

Survival and behaviour of post‐smolt Atlantic salmon in coastal habitat with extreme tides

The early marine migration of 55 Atlantic salmon post‐smolts tagged with acoustic transmitters was automatically monitored using 13 to 25 km long arrays of receivers deployed inside the Bay of Fundy, a coastal system on the east coast of Canada. The survival of post‐smolts from groups with short‐ and long‐term transmitters in coastal habitat up to 10 km from the river was 92 to 100%, indicating a successful transition to salt water and departure. Migration for 68 to 77% of post‐smolts followed a direct route and it was rapid (transit time usually <12 h). Post‐smolts initially migrated in a south to south‐west direction ( i.e . orientation towards the mouth of the bay) and they were aggregated near the coast. Post‐smolts with long‐term transmitters were monitored 20 km from the river where they continued to be aggregated, moving near the coast through a 'common corridor', and their survival to that point was at least 84%. Post‐smolts from both groups travelled heading out of the coastal system during ebb tides. Flood tides interrupted migration, and they caused changes in travel direction and delays in departure for post‐smolts not leaving by a direct route. Monitoring of coastal habitat inside the Bay of Fundy intercepted 62% of migrating post‐smolts with long‐term transmitters returning after an initial absence of 2 to 22 days. Returning post‐smolts displayed a resident behaviour, using the habitat monitored inside the Bay of Fundy during July and August.     

Climatic and biogeographical associations of southern African dung beetles (Coleoptera: Scarabaeidae s. str.)

Climatic and biogeographical associations of southern African dung beetles (Scarabaeinae, Coprinae) were analysed from a collection amassed between 1971 and 1986. Endemism to Africa south of 15°S was much greater in southwesterly climates (winter rainfall, bimodal spring/autumn rainfall, arid late summer rainfall) than to the north‐east in the moist, mid‐summer rainfall region. Major biogeographical groups centred to the south‐west comprised predominantly southern African endemics, Western/Eastern Cape coast, Karoo, Karoo/Namib, northern Namibia and the south‐western Kalahari. Biogeographical groups centred on the south‐eastern highlands and the subtropical east coast (mid‐summer rainfall) also comprised predominantly southern African endemics. All other major groups centred to the north‐east in the mid‐summer rainfall region comprised predominantly species with widespread tropical biogeographical affiliations, pan‐southern Africa but centred in the east, pan‐mid‐summer rainfall region, eastern mid‐summer rainfall region, tropical east Zimbabwe/central Moçambique, subtropical/tropical game reserves (non‐ruminant dung specialists). There were cross‐climatic differences in taxonomic composition of the fauna. Within the winter rainfall region, percentage species composition of Scarabaeinae was greater whereas that of the coprine tribe, Onthophagini, was lower than within the other three climatic regions. Percentage species richness of most other tribes of Coprinae differed little between most climates but that of Scarabaeinae declined from west to east (Canthonini, Scarabaeini), east to west (Sisyphini) or to either side of the late summer rainfall region (Gymnopleurini).     

In vitro pattern‐related effects of forskolin on melanophore adrenoceptor‐mediated responses of winter flounder

In vitro experiments were performed on melanophores on scales carrying small slips of skin (scale slips) sampled from the white spot, dark band and general background components of patterning in winter flounder Pseudopleuronectes americanus . In vitro , forskolin (10⁻⁴ to 10⁻⁷ M) was employed to increase melanophore intracellular cytosolic adenosine‐3'‐5'‐monophosphate (cAMP) levels by stimulating adenylate cyclase. Such increase shifted noradrenaline concentration‐response curves to the right, general background melanophores being least sensitive to the forskolin, indicating a relatively higher proportion of α₂‐adrenoceptors, and those from white spots the most sensitive. Melanosome dispersion, in balanced salt solution, was also enhanced by such raised levels of cAMP. Without forskolin, melanophores from white spots displayed the shortest pigment dispersion time in balanced salt solution, the slower melanophores from the other pattern components being those most affected by the addition of forskolin. The results demonstrate that differences in melanophore physiological responsiveness associated with flatfish patterns involve differential intracellular levels of cAMP, as well as differences in melanophore size and rates of melanosome movement.     

Life-stage-dependent supergene haplotype frequencies and metapopulation neutral genetic patterns of Atlantic cod,Gadus morhua,from Canada's Northern cod stock region and adjacent areas

Among highly migratory fish species, nursery areas occupied by juveniles often differ from adult habitats. To better understand the spatial dynamics of Canada's Northern cod stock, juveniles caught off the east coast of Newfoundland and Labrador were compared to adults from the same region as well as individuals from other areas in Atlantic Canada using double-digest restriction site-associated DNA sequencing–derived single nucleotide polymorphisms. A reduced proportion of homozygotes with a chromosomal inversion located in linkage group 1 (LG1) was detected between juvenile and adult samples in the Northern cod stock region, potentially indicating age-dependent habitat use or ontogenetic selection for attributes associated with the many genes located in LG1. No selectively neutral genetic differences were found between samples from the Northern cod stock; nevertheless, significant differences were found between some of these samples and cod collected from St. Pierre Bank, Bay of Fundy, Browns Bank and the southern Scotian Shelf. Clustering analysis of variants at neutral loci provided evidence for three major genetic units: (a) the Newfoundland Atlantic Coast, (b) eastern and southern Gulf of St. Lawrence and Burgeo Bank and (c) the Bay of Fundy, Browns Bank and southern Scotian Shelf. Both adaptive and neutral population structure within the Northern cod stock should be considered by managers to promote demographic rebuilding of the stock.     

Stepping stone gene flow in an estuarine‐dwelling sparid from south‐east Australia

Allozyme and mitochondrial DNA variation was surveyed in Acanthopagrus butcheri to examine the pattern of gene flow among estuaries in south‐east Australia. Allozymes distinguished two peripheral estuaries from the remaining six, although the pattern of genetic variation could owe more to selection than reproductive isolation, and overall structure was small (θ = 0·012). In contrast, mitochondrial DNA revealed a high degree of genetic structure (θ = 0·263), and a significant relationship with geographic isolation. Consequently, contemporary gene flow mostly between adjacent estuaries, consistent with a one‐dimensional stepping stone model, is evident in south‐east Australia. The data indicate that management of A. butcheri within the study range should be conducted at the scale of individual or geographically proximate estuaries.     

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.     

The genetic stock structure of larval and juvenile winter flounder larvae in Connecticut waters of eastern Long Island Sound and estimations of larval entrainment

Variability at six microsatellite loci was examined among 536 winter flounder Pseudopleuronectes americanus larvae collected from three locations in eastern Long Island Sound shown to be nursery areas for the species. Substantial genetic differences were seen among the putative source populations and thus appeared to be geographically based. These differences were used to characterize the most likely sources of winter flounder larvae entrained at the Millstone Power Station as well as recruitment to juvenile winter flounder collected in the Niantic River. Samples were classified to the most likely geographical source population both by a conditional maximum likelihood method and by a multi‐layer feed‐forward neural net trained on the differences in microsatellite allele frequencies. The classification of samples by both methods is compared and discussed in the context of winter flounder management.     

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.     

The occurrence of Acanthurus monroviae(Perciformes: Acanthuridae) in the south‐western Atlantic, with comments on other eastern Atlantic reef fishes occurring in Brazil

The presence of 'vagrants' of the eastern Atlantic surgeonfish Acanthurus monrovia e is confirmed for the south‐eastern coast of Brazil. Three other species, Aulostomus strigosus (Aulostomidae), Parablennius pilicornis (Blenniidae) and Epinephelus marginatus (Serranidae) have apparently also crossed the Atlantic from east to west, whereas the great majority of 'amphi‐Atlantic' species appears to have their origin in the western Atlantic.     

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.     

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.     

Variation in the sex ratio, size and age of longfinned eels within and 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. Sex ratios, catch per unit effort and population age and total length structure were examined in three zones (fresh water and upper and lower tidal) in the Hacking, Hawkesbury and Clarence Rivers. Females were found in relatively high proportions in all zones, ranging from 97% in a freshwater (non‐tidal) site down to 59% in a tidal site. Males were found primarily in tidal zones (only two of the 677 longfinned eels caught in non‐tidal fresh water were males), with the greatest proportions being found in the brackish upper tidal areas. The mean number of fish captured per trap was higher in the fresh water and upper tidal zones than in the lower tidal zones. The mean ±  s . e . age, 17·9 ± 0·3 years, and age range, 5–52 years for females were significantly higher than those of males 12·2 ± 0·4 years; range 5–22 years, which is typical of other anguillid species. Longfinned eels captured in fresh water were found be significantly larger and older than those in tidal zones due to the almost exclusive predominance of females.