Spatial Variation In Size Research Articles

Reproduction ecology of an emerging fishery resource, the amphibious mudskipper Periophthalmus chrysospilos, in the Mekong Delta.

Populations of Periophthalmus chrysospilos, the Gold‐spotted mudskipper, within the Mekong Delta are facing extirpation risks due to indiscriminate harvesting for the growing aquarium and food‐fish trade. This study provides some of the first information on reproductive ecology—such as spawning type and season, length at first maturity, and batch fecundity—of this species, to be used in their management. The sex ratio of wild populations, based on 1031 individuals (523 males and 508 females) is 1:1. The gonadosomatic index (GSI) values are exhibit a non‐normal distribution and changed with gender, season, and site. A combination of GSIs and the monthly appearance of mature gonads suggest that this species reproduces throughout the year, with peak from July to October. This species exhibits sexual and spatial variation in size at first maturity (Lm ) as Lm is 6.2–8.6 cm in males and 6.4–7.3 cm in females. The batch fecundity (F = 2614 to 23,465 eggs/female) exhibits non‐normal distribution and varies with site, with the highest values at Dam Doi, Ca Mau (13,336 ± 1,279 SE) and the lowest at Tran De, Soc Trang (6654 ± 851 SE). In addition, batch fecundity is directly proportional to body size due to high determination relationships between batch fecundity and fish size (r 2 > 0.64 for all cases). Information derived on the reproductive biology of this species can inform its conservation, sustainable exploitation, and ex situ propagation.

Spatial variation in size and age at maturation and growth of the channeled whelk (Busycotypus canaliculatus) in Southern Massachusetts

The channeled whelk (Busycotypus canaliculatus) fishery in Massachusetts reached record levels in landings in the early 2010’s. At the same time, fishery independent surveys indicated a depleted resource. This study was conducted to determine size and age at maturity and compare these traits between specific locations within Massachusetts waters. A total of 1,787 channeled whelk (n = 940 males, n = 847 females) were collected from four different areas in Massachusetts waters. Results indicated that females matured at a significantly larger size and older age than the males in all areas sampled. There were also differences in size and age at maturity between areas for both sexes. Spatial variation in female size at maturity was inversely correlated with water temperatures, such that female channeled whelk matured at larger sizes in cooler waters. Male size at maturity exhibited a nonsignificant inverse relationship with temperature. These relationships were true for this study and across a broader spatial scale. No females were mature at the minimum legal size in Massachusetts study areas. This suggests that action is needed to manage the fishery in a sustainable manner. Record high levels of landings without any protection of the spawning stock could lead to stock collapse.

Spatial Variation in Size and Shape of Land Plots in Mazowieckie Voivodship

The aim of the study is to evaluate the spatial variation in the size and shape of land plots in Mazowieckie voivodship. For the purposes of the study both the shape and the compactness of the plots were measured, and the typology of communes was drawn based on this information. Subsequently, based on the two indicators related to the shape of plots, four types of communes were distinguished, depending on whether their values were higher or lower than the average (Dzieciucho­wicz and Dmochowska-Dudek, 2014). In addition, the paper includes calculations for the average share of unused land in the plot surface area, the average horizontal intensity of parcel development, and an indication of the type of land coverage dominant in the plots, by commune type. Pearson’s correlation coefficient was used in the analyses. It has been found that the studied area is dominated by plots characterised by small diversity in shape and high degree of compactness – mainly in the north-western part of the voivodship, as well as those where plots are highly diverse in shape and low in compactness – in the south-eastern part of the voivodship.

Temporal and spatial variation in size at maturity of the common whelk (Buccinum undatum)

Abstract There is little common rationale for the 45 to 75 mm total shell length (TSL) minimum landing sizes (MLS) for Buccinum undatum among countries in the Northeast Atlantic. Size at maturity and length frequency of B. undatum populations vary over small spatial scales; however, the driving mechanism for this is unknown. Size at maturity research for B. undatum dates back to the late 1980s; since then, there has been little consensus on laboratory methods or in which season to undertake the research. Here, we assess small-scale spatial variation in size at maturity over a year to identify the seasons that increase error in visual maturity estimates. We compare and contrast results from methods used in the literature to estimate maturity for B. undatum. Monthly, B. undatum samples were obtained from Welsh fishers between May 2013 and May 2014 from eight sites at four locations (n = 5080). All whelks were sexed, weighed, and measured, and up to 60 whelks from each location were assessed for maturity (n = 1659). Mature whelks were found in all months, with a peak in reproductive activity through summer and early autumn, followed by the onset of spawning in November. Size at maturity varied between sexes and sites, and ranged from 51 to 76 mm TSL. Whelks caught in shallow waters (0–10 m) matured at a smaller size than those from deeper waters (up to 60 m). Length frequency varied at each site suggesting that a single increase in MLS would impact fishers disproportionately. No methodology trialled was found without inherent errors when used in isolation, though a combination of methods proved ideal. The seasonal variation in maturity estimates suggested that assigning maturity is increasingly difficult outside annual reproductive periods and that prespawning is the ideal time to undertake visual gonad assessments for whelks.

Variations in reproductive potential between nearshore and offshore spawning contingents of hogfish in the eastern Gulf of Mexico

Hogfish, Lachnolaimus maximus (Walbaum), have multiple traits that confound measuring reproductive potential: they are protogynous, relatively long-lived harem-forming fish that spawn daily for months. Additionally, recent evidence demonstrates that size, age and timing of sex change vary on a spatial scale within the study area (West Florida shelf, USA). This study investigates the effect of this spatial variation on hogfish reproductive potential by evaluating spawning seasonality, spawning frequency and batch fecundity using an indeterminate egg production model. Offshore females were larger than nearshore females, and batch fecundity was related in a log-linear manner to female size. Gonad histology demonstrated a more protracted reproductive period for females offshore (8 months) than nearshore (4 months). Spatial variations in size coincide with ontogeny because hogfish move offshore with growth; however, even after accounting for fish size, offshore females spawned more. In areas where male removal rates are elevated, spawning harems are disrupted; thus, greater fishing effort nearshore may further reduce the reproductive potential of these females. These nearshore and offshore spawning components of the population are not genetically distinct, but instead represent two contingent spawning strategies that likely enhance total population stability and resilience of this stock in the eastern Gulf of Mexico.

Latitudinal and Size Segregated Compositional Variability of Aerosols over the Indian and Southern Ocean during 2010 Austral Summer

To characterize the spatial variations in size segregated aerosols, samples were collected over the Indian and Southern oceans (7°N to 68°S) during the Indian expedition to Southern Ocean (January–February 2010). The chemical and mass concentrations of ions were measured in nine size classes (0.4–> 10 µm) of aerosols through ion-exchange chromatographic system and gravimetric estimates, respectively. Mass concentrations of coarse aerosols increase towards the Antarctic coast which is well correlated with the increasing humidity suggesting growth of particles. The study area was found to be predominately impacted by sea salt aerosols with a sea salt load of 91%. F–, Cl– and NO3– reflected anthropogenic impact within the fine mode aerosols but the marine influence dominated the coarse mode. Methanesulphonic (MSA) was predominantly of biogenic origin but a substantially low MSA/nssSO42– ratio suggested that DMS contribution to the total nssSO42– concentration was low. NH4+ concentrations showed a shift from fine to coarse particles, with a trimodal distribution over the Southern Ocean. Our study reports a significant Cl– depletion in the aerosols and the degree of Cl– deficit was size-dependent, increasing with decreasing particle sizes. The neutralization ratios suggested differential behavior of ions with respect to the prevailing meteorological conditions. The coarse mode aerosols were neutralized by ammonia leading to the formation of NH4NO3 particles. The fine modes were predominately composed of NH4HSO4 and its formation is favored by the high humidity and foggy conditions over the study area. Factor analysis support that the Southern Indian Ocean (10°S to 59°S) had the highest loading of anthropogenic and sea salt aerosols, which lead to the formation of secondary aerosols through gas to particle transformations. The rocky Antarctic coastline, act as a source of coarse crustal aerosols over the Southern Ocean (60°S to 65°S).

Latitudinal and stock-specific variation in size- and age-at-maturity of female winter flounder, Pseudopleuronectes americanus, as determined with gonad histology

Female winter flounder were examined using gonad histology to determine the adequacy of routine macroscopic maturity classification methods and to determine the spatial variation in size and age of maturity in U.S. waters. Sampling occurred in spring and autumn, which was adequate to collect immature, mature, spawning-active, and non-active females. Females were collected in coastal waters from Delaware Bay, USA, to the Scotian Shelf, Canada, including in Long Island Sound and on Georges Bank, which covered all U.S. stock areas. Mature fish spawned in spring, when gonads comprised up to 30% of the total body weight. Direct comparisons of maturity assignment by macroscopic versus microscopic methods demonstrated that both schemes are compatible, but the more cost-effective macroscopic method had trouble distinguishing larger immature from smaller resting females. Spatial comparisons, using gonad histology only, supported the existence of three stocks in U.S. waters, but also revealed significant variation in age at maturity within the two coastal stocks. Age-at-maturity was more variable than size-at-maturity, which is consistent with known stock-specific patterns of growth rates and a postulated life history tradeoff to delay maturity until a size threshold is reached. The within-stock variation in median age at maturity, about one year for coastal stocks, recommends further investigation of using static, stock-specific maturity ogives to calculate reference points for management.

Body size variation in insects: a macroecological perspective

Body size is a key feature of organisms and varies continuously because of the effects of natural selection on the size-dependency of resource acquisition and mortality rates. This review provides a critical and synthetic overview of body size variation in insects from a predominantly macroecological (large-scale temporal and spatial) perspective. Because of the importance of understanding the proximate determinants of adult size, it commences with a brief summary of the physiological mechanisms underlying adult body size and its variation, based mostly on findings for the model species Drosophila melanogaster and Manduca sexta. Variation in nutrition and temperature have variable effects on critical weight, the interval to cessation of growth (or terminal growth period) and growth rates, so influencing final adult size. Ontogenetic and phylogenetic variation in size, compensatory growth, scaling at the intra- and interspecific levels, sexual size dimorphism, and body size optimisation are then reviewed in light of their influences on individual and species body size frequency distributions. Explicit attention is given to evolutionary trends, including gigantism, Cope's rule and the rates at which size change has taken place, and to temporal ecological trends such as variation in size with succession and size-selectivity during the invasion process. Large-scale spatial variation in size at the intraspecific, interspecific and assemblage levels is considered, with special attention being given to the mechanisms proposed to underlie clinal variation in adult body size. Finally, areas particularly in need of additional research are identified.

Spatial variation in size and density of adult and post-settlement Semibalanus balanoides: effects of oceanographic and local conditions

Regional oceanographic processes are emerging as strong influences on growth and recruitment of intertidal species, with important consequences for populations. Yet local conditions such as wave exposure are also important. To disentangle these effects for the intertidal barnacle Semibalanus balanoides, we surveyed 259 sites around Scotland in July and August over 6 yr (from 2001 to 2006). Scaled digital photographs at 3 shore levels gave sizes and densities of juvenile and adult barnacles for comparison with wave fetch, remotely sensed chlorophyll a (chl a) concentration and seasonal sea surface temperature (SST). Patterns were also compared with site 'openness': the area of connected open sea <30 km away. Patterns at the 3 shore levels were similar. Hierarchical partitioning (HP) showed that survey year had the biggest effect and improved the predictive power of other variables: wave fetch for adult and juvenile densities, chl a for juvenile size and openness for adult size. SST had little effect. Regression models selected using information theoretic measures included positive effects of chl a, varying among surveys, on average size of barnacles (R 2 from 0.5 to 0.6), and larger high shore barnacles in greater wave exposure. Population densities of adults and juveniles increased with wave fetch, with chl a only influencing density at high shore levels (R 2 from 0.1 to 0.4). Despite temporal and spatial variation in responses to chl a and wave fetch among surveys, relationships were consistent with growth and size in S. balanoides being limited by food supply, and increased recruitment and adult densities in increased wave exposure. Large-scale ecological patterns in this rocky intertidal species thus result from large-scale oceanographic effects on food concentration with habitat-scale wave-mediated effects on supply of food and larvae.

Variation in hatch date distributions, settlement and growth of juvenile plaice ( Pleuronectes platessa L.) in Icelandic waters

Hatch date distribution, larval phase and subsequent growth of juvenile plaice ( Pleuronectes platessa L.) in different regions around Iceland were determined by otolith microstructure analysis. Length, age and hatch date frequency distributions were obtained from juveniles captured in a 1 m beam trawl on 31 stations at 0.5–1 m depth all around Iceland in July 2006. The main spawning has previously been assumed to take place on the south and south-west coasts with eggs and larvae then distributed by currents along the west and north coasts. Contrary to this expected dispersal pattern, both size and age of juvenile plaice decreased from south to north. The results indicate that the observed spatial variation in size of the juveniles is not explained by different growth rates but by age. The juveniles at the south coast hatched earlier than juveniles on the north and east coasts and had a shorter larval period. Growth differed between regions and was partially explained by temperature. The study provides evidence that the juvenile plaice population may in fact originate from multiple spawning sites located not only along the south and south-west coasts, but along the entire coast of Iceland. The findings are discussed in relation to currents and temperature in Icelandic waters.

Spatial variation in size at onset of maturity of female southern rock lobster &lt;i&gt;Jasus edwardsii&lt;/i&gt; around Tasmania, Australia

The size at onset of maturity (SOM) of female Jasus edwardsii (Hutton, 1875) was estimated at 50 sites around Tasmania, Australia, based on the presence of ovigerous setae. There was a distinct spatial cline with the largest SOM being found at northwestern sites and the smallest at southwestern sites. Variation in SOM between sites was substantial and ranged from 59 mm to 112 mm carapace length. The observed decline in SOM from north to south was the reverse of that described for the same species at similar latitudes in New Zealand, which suggests that SOM in J. edwardsii is regulated by factors in addition to temperature. The effect of density on female SOM was investigated by comparing SOM estimates from two marine reserves with adjacent fished sites; however, there was no evidence of a decline in SOM with increasing density as predicted. A model of SOM predicted by latitude and longitude is described to facilitate spatial modelling of lobster stocks. The substantial and predictable spatial variation in SOM implies that management of this fishery would be improved by incorporating spatial elements, such as regional legal minimum size limits.

Spatial variations in size, weight and condition factor of the females of Acartia clausi (Copepoda: Calanoida) along a salinity gradient in two contrasting estuaries of the Basque coast (Bay of Biscay)

Variations in prosome length and width, dry weight and condition factor of female Acartia clausi copepods were studied at three salinities (35, 34 and 33 psu) in the euhaline region of two estuaries (Bilbao and Urdaibai) of the Basque coast, with different level of anthropogenic impact. Effect of the environmental variables upon the morphology of A. clausi females on a small geographic scale is discussed. In general, biometric variables showed no significant differences between the two estuaries, but dry weight and condition factor were significantly higher in the estuary of Urdaibai at 35 and 34 psu, whilst at 33 psu they were higher in Bilbao. Body dimensions decreased significantly with decreasing salinity in both estuaries, however, no similar trends were observed for dry weight and condition factor. Temperature appeared the main variable to account size variations, but once eliminated seasonal effect of the temperature body size was related with oxygen concentration in the estuary of Bilbao and with salinity in Urdaibai. This study reveals that morphological characteristics of A. clausi not are only dependent on the temperature, but also, within a limited geographical zone, on local differences in environmental variables, mainly salinity and oxygen concentration.

Body size patterns in Drosophila inhabiting a mesocosm: interactive effects of spatial variation in temperature and abundance

Body size is a major component of fitness. However, the relative contributions of different factors to optimal size, and the determinants of spatial and temporal variation in size, have not been fully established empirically. Here, we use a mesocosm of a Drosophilidae assemblage inhabiting decaying nectarines to investigate the influence of spatial variation in temperature on adult body size in Drosophila simulans Sturtevant. Two treatments were established; one in the sun where developing larvae were exposed to high temperatures and the other in the shade where temperature conditions were milder. The simple developmental effects of temperature differences (i.e. larger flies are likely to emerge from cooler environments), or the simple effects of stressful temperatures (i.e. high temperatures yield wing abnormalities and smaller flies), were overridden by interactive effects between temperature and larval density. Emergences were lower in the sun than shade, probably as a result of temperature-induced mortality. However, flies attained the same final sizes in the shade and sun. In addition, abnormally winged flies were clustered in the shaded treatments. In the shade treatments, where emergences were higher than in the sun, stressful conditions as a result of high larval density likely resulted in wing abnormalities and small size. Consequently, there was little spatial variation in size across the mesocosm, but substantial spatial variation in abundance. Under natural conditions both mortality and non-lethal effects of temperature and/or crowding are likely to play a role in the evolution of body size.

Frequency dependence of scattering from the cold‐temperate transition surface in a polythermal glacier

Radar surveys of the cold‐temperate transition in polythermal glaciers have been used to investigate the polythermal structure, as well as the stability of the temperature regime, in glaciers. The mapping is based on the detection of small water‐filled pockets present in the temperate ice beneath the cold surface layer. I compare radar profiles recorded at different frequencies on a polythermal glacier to show that the apparent depth to the cold‐temperate transition reflection at a center frequency of 155 MHz is significantly greater than that detected at frequencies above 345 MHz. This increase appears to be the result of a reduction of scattering efficiency from the uppermost part of the temperate ice, as the theory of electromagnetic scattering from small objects indicates a strong decrease in scattering efficiency from objects much smaller than the wavelength of the incident wave. Thus I interpret this apparent depth increase to indicate that the average radii of the water pockets of the cold‐temperate transition is on a subdecimeter scale. Spatial variation in the difference between cold‐temperate transition depths at 155 MHz and higher frequencies may arise from spatial variations in size or the number density of scatterers.

Flow-conditioned HUVECs support clustered leukocyte adhesion by coexpressing ICAM-1 and E-selectin

Endothelial sequestration of circulating monocytes is a key event in early atherosclerosis. Hemodynamics is proposed to regulate monocyte-endothelial cell interactions by direct cell activation and establishment of flow environments that are conducive or prohibitive to cell-cell interaction. We investigated fluid shear regulation of monocyte-endothelial cell adhesion in vitro using a disturbed laminar shear system that models in vivo hemodynamics characteristic of lesion-prone vascular regions. Human endothelial cell monolayers were flow conditioned for 6 h before evaluation of monocyte adhesion under static and dynamic flow conditions. Results revealed a distinctive clustered cell pattern of monocyte adhesion that strongly resembles in vivo leukocyte adhesion in early- and late-stage atherosclerosis. Clustered monocyte cell adhesion correlated with endothelial cells coexpressing intercellular adhesion molecule-1 (ICAM-1) and E-selectin as result of a flow-induced, selective upregulation of E-selectin expression in a subset of ICAM-1-expressing cells. Clustered monocyte cell adhesion assayed under static conditions exhibited a spatial variation in size and frequency of occurrence, which demonstrates differential regulation of endothelial cell adhesiveness by the local flow environment. Dynamic adhesion studies conducted with circulating monocytes resulted in clustered cell adhesion only within the disturbed flow region, where the monocyte rate of motion is sufficiently low for cell-cell interaction. These studies provide evidence and reveal mechanisms of local hemodynamic regulation of endothelial adhesiveness and endothelial monocyte interaction that lead to localized monocyte adhesion and potentially contribute to the focal origin of arterial diseases such as atherosclerosis.

Fine‐scale spatial patterns in populations of the clonal moss Hylocomium splendens partly reflect structuring processes in the boreal forest floor

Spatial patterns of important population or individual characteristics are expected to reflect structuring ecosystem processes to the extent that populations with strikingly different spatial patterns most likely have been structured by different processes. Few studies of spatial pattern in plant assemblages, bryophyte assemblages in particular, still exist and pattern has only vaguely been linked with process. In this study we describe fine‐scale spatial variation in size and the occurrence of terminated (non‐branching) segments in 21 Norwegian populations of the dominant boreal forest moss Hylocomium splendens, in search for general patterns of spatial structure.All Hylocomium splendens segments in the investigated plots were followed for a 10‐year period; their size (dry mass, estimated from in situ measurements) and fate (terminated or ramifying) were recorded annually. The spatial structure of size and terminating segments at scales from 0.5 to 16 cm was described for each population as fractal dimension profiles, derived from semi‐variograms. For about one half of the populations size and terminating segments could be assigned to a specific spatial pattern, the predicted outcome of one of three main structuring processes: (i) negative spatial dependence (fractal dimension F&gt;3.0) on the scale of individuals (below 2 cm), indicative of negative interactions; (ii) positive spatial dependence (F&lt;3.0) on the scale of individuals, indicative of positive interactions; and (iii) positive spatial dependence on broader (4–8 cm) scales, indicative of structuring by environmental factors or patchy disturbance. Patterns (i) and (iii) were observed both for size and terminated segments more often than expected. Fractal dimension profiles for size obtained separately for each year revealed temporal patterns of spatial structure that tended to be invariant over years. Negative spatial dependence of size, possibly due to large size difference between buried segments and other segments during self thinning, was typical of populations rapidly growing in number. Positive spatial dependence with a range of influence by the spatial process of 4–8 cm was observed in plots with sparse bryophyte cover and high cover of deciduous litter, probably due to accumulation of litter in depressions between shoots or groups of shoots. The main finding of this study is that different populations of the same species in the same type of ecosystem can be spatially structured in different ways. This accords with a model for the studied system as consisting of a mosaic of cells, of spatial extent of a few cm or larger, intergrading in space and temporally dynamic, the population characteristics of each cell being shaped by several structuring processes that vary, temporally and spatially, in their relative importance.

Size and shape of the geographical ranges of Andean passerine birds: spatial patterns in environmental resistance and anisotropy

AimThe geographical distribution of 839 Andean passerine species was analysed using two biogeographical indices: environmental resistance (R50) and anisotropy (A50). R50 quantifies the loss of biotic resemblance occurring from any point in the map to the rest of the continent. A50 quantifies the extent to which the perimeter : area ratio of the geographical ranges of all species whose distributions overlap at any particular location depart from the perimeter : area ratio of a circle. Three predictions derived from the climatic‐tolerance hypothesis were tested: (1) the latitudinal Rapoport effect predicts an increase in the range‐sizes of species, and hence a decrease in the values of R50, towards the south; (2) Janzen’s argument that ‘mountain passes are higher in the tropics’ predicts greater anisotropy in the tropics; (3) because environmental conditions are relatively constant across the tropics, and begin to change at the boundaries, this predicts high spatial turnover – and hence rapid change of R50 values – at the limits of the tropics.LocationThe Andes, in South America.MethodsThe geographical ranges of 839 passerine species were drawn on a standardized grid map of the Andean region. The presence–absence (1–0) of each species in each of the 150 cells in the grid map was recorded. These data were used to create equiprobabilistic maps, which then were used to estimate a value of R50 and A50 for each cell in the grid map (sensuRapoport, 1975, 1979, 1982).ResultsThe spatial patterns in R50 and A50 offer partial support to the original predictions. The tendency for R50 data to decrease with latitude (Rapoport effect) vanishes after controlling for differences in species richness among latitudes compared. In contrast, A50 data clearly offer indirect support to Janzen’s prediction of narrower climatic tolerances of species around the tropics, even after controlling for differences in species richness. The Andean passerine species confirm that spatial turnover of species exists at the southern edge of the tropics, and also at different latitudes within the tropics.Main conclusionsThe analysis suggests that it is the major structural change in the topography of mountains – and not merely latitude – that ultimately governs the spatial variation in size and shape of species ranges along the Andes.

Spatial variation in hatch date distributions and origin of pelagic juvenile cod in Icelandic waters

Hatch date distributions, local spawning time and incubation temperatures at different spawning sites around Iceland were used to trace the most likely origin of 0-group cod. Length, age and hatch date frequency distributions were obtained from young larvae collected on the main spawning grounds off the south coast in 1995 and from pelagic 0-group cod captured in six nursery regions off the west, north and east coast of Iceland in 1995, 1996 and 1997. Historically, the 0-group cod found in coastal areas north and east of the country are believed to have originated from the main spawning grounds at the south-southwest coast. Contrary to the expected dispersal pattern, both size and age of 0-group cod decreased from west to north, when moving clockwise around the country away from the main spawning grounds in the south. It is shown that this spatial variation in size is not explained by different growth rates but by age. Consequently, the reconstructed spawning periods of surviving 0-group cod captured along the north and the east coast and the recorded spawning time for cod on the main spawning grounds in the south were not congruent. Large proportion of these 0-group cod, especially in 1995 and 1996, appeared to have hatched in June and July or considerably later than the recorded time period of hatching on the main spawning grounds in April and May. Therefore, rather than originating on the main spawning grounds in the south, some of the surviving 0-group cod originated from spawning that occurred in the western, northern and eastern fjords, during either the spring when local water temperatures were 3–4C colder, or in early summer at a much later time. Spawning females have been observed at these locations over an extended time period (April–June) and protracted incubation periods due to cold waters will result in delayed hatching of larvae. In some years the smaller northern spawning sites, may contribute significantly towards the surviving population of 0-group juveniles, and probably contributing to the relative stability in recruitment experienced by this stock. 2000 International Council for the Exploration of the Sea

Spatial variation in size and age structures and reproductive characteristics of the King George whiting (Percoidei : Sillaginidae) in South Australian waters

Adult King George whiting were sampled at 12 localities representing a range of habitat types across South Australia. Sampling was undertaken between March and May for a minimum of 2 years between 1995 and 1998. Fish were aged by otolith interpretation, and reproductive maturity was determined by gonad analysis using macroscopic and histological techniques. In total, 6961 fish comprising 3678 females and 3283 males were considered from four localities in each of three geographic regions. In both Gulf St Vincent and Spencer Gulf, age structures became more complex from north to south, associated with a shift in size towards larger fish. In the simplest age structures, &gt;90% of fish were from the 3-year age class, whereas the age range of the most complex was 3–17 years, with the 3–5 age classes most numerous. Males were more abundant in smaller size classes and females in the larger. Although some fish from each locality showed some gonad development, only at three localities did spawning occur. At these places, populations had the broadest age and size distributions and were in deep water that experienced medium to high wave energy. Since spawning grounds and nursery areas are up to several hundred kilometres apart, the processes of larval advection and adult movement are implicated as obligate processes of the life history.

Spatial implications of a temperature-based growth model for Atlantic cod (Gadus morhua) off the eastern coast of Canada

Lengths at age of Atlantic cod (Gadus morhua) off the eastern coast of Canada vary up to three-fold among geographic regions, with Georges Bank and the southern Gulf of St. Lawrence being the regions of fastest and slowest growth, respectively. Colour-coded contour maps of length at ages 2–8 (n = 59 518) based on research vessel surveys between 1971 and 1992 clearly showed the spatial variations in size at age. Corresponding maps of July–September bottom water temperature appeared to reflect relative growth rate, whereas those for depth did not. A polynomial expansion of a temperature-based von Bertalanffy growth model appeared to fit the data well, with no residual patterns across most ages, lengths, temperatures, or years. Model predictions were also consistent with reported lengths at age for cod in other regions and countries. Declines in bottom water temperature over the past 5–10 years appear to be at least partly responsible for observed declines in size at age of the cod stock on the eastern Scotian Shelf.