Sedimentation of organic detritus in Lochs Etive and Creran,Argyll, Scotland

The rates of sedimentation of organic detritus were measured at 3 stations in two Scottish sea lochs, Loch Etive and Loch Creran, using sedimentation jars exposed at various depths. Details are given of the seasonal and depth distribution of sedimenting material, and its composition for a 1-year period. Differences in the pattern of sedimenting material collected at different depths and in the seasonal patterns of sedimentation at the different stations suggested that, in each case there were differences in the relative importance of detritus from various sources. At all stations, phytoplankton production made a relatively small contribution to the total detritus collected, either directly as dead cells, or indirectly as the faeces of zooplankton organisms. Near the head of Loch Etive there were contributions by filamentous algae and Enteromorpha sp., but a major source of detritus was terrestrial debris, mainly carried into the loch in the waters of the River Etive. In the lower basin of Loch Etive, terrestrial detritus also contributed to the total sedimenting near the surface, but at greater depths much of the material collected in the sedimentation jars probably resulted from short-term resuspension and re-deposition of bottom material, reflecting a net transport of fine sediment from the shallower to the deeper areas of the loch. Secondarily resuspended material was also a major source of material collected in the jars exposed in Loch Creran.     

Community structure of the benthos in Scottish Sea-lochs. IV. Multivariate spatial pattern

Most studies of spatial patterns of invertebrates in soft sediments have concentrated on populations of individual species. Those that examined patterns in communities have tended to employ categorical analytical techniques. Using macrofaunal abundance data from van Veen grab samples collected 20 to 100 m apart in known spatial arrangements from Scottish sea-lochs, the relationships between patterns in macrobenthic species composition and distances between samples were explored using matrix correlations in a non-parametric framework. Using a simple definition of spatial structure, i.e. that intersample distances are monotonically correlated with intersample species-similarity, spatial structure at each of seven stations was assessed using non-parametric Mantel tests based on rank-correlations. Changes in community structure were positively correlated with distance at all sites in Loch Etive, on both current-swept muddy sands and soft deep muds. Different components of the macrobenthos contributed to spatial pattern at each site. Simple spatial structure was also detectable at a muddy-sand site in Loch Creran, but neither on soft mud, nor at the soft mud site in the Firth of Lorne. The concept of rank-correlograms was introduced. These were used to examine the extent and form of spatial structure in different components of the macrobenthos at each site. Relationships between similarity and distance were neither simple nor consistent. Results were compared to previous studies which used the same data, and it was concluded that studies carried out at a particular scale, or on a particular component of the benthos, are unlikely to be successful in predicting spatial relationships at other scales or for other components of the benthos. Correlational rather than categorical analyses are recommended for exploratory studies of spatial relationships in the benthos. Analyses of the spatial structure at these seven sea-loch sites suggests that by ensuring that samples are at least 40 m apart an investigator is unlikely to underestimate variability or otherwise invalidate statistical analyses based on the use of the samples as replicates. Spacing samples up to 100 m apart may increase variability estimates, further reducing the chance of concluding that a difference exists when one does not. Received: 4 May 1999 / Accepted: 8 March 2000     

Growth,mortality and shell morphology of cultivated mussel (Mytilus edulis) stocks cross-planted between two Scottish sea lochs

One-year-old rope-grown blue mussels (Mytilus edulis L.) were held in experimental lantern nets and cross-transplanted between two sea lochs (Lochs Etive and Leven) on the west coast of Scotland. Growth and mortality were monitored from May 1991 to May 1992, as well as shell morphology in native and transplanted mussels. There were highly significant differences (P0.001) in growth rates between lochs; both native and transplanted mussels performed better in all shell and tissue growth-parameters in Loch Etive than in Loch Leven. Stock also had a significant (P0.05) influence on shell length and live weight, but its contribution to total variance was considerable only in the latter case. Wet and ash-free dry meat weights were governed mainly by site and to some extent by site x stock interaction. Mortality rates were quite low (6 to 7% yr^-1) and did not show any significant variation either between sites or stocks. There were significant morphological differences (ratios of shell length, height and width) between the Loch Etive and Loch Leven populations (P0.001) which persisted for one year after transfer. Stock appeared to be the main factor affecting shell morphology, as opposed to site. Linear regressions of shell height and width on length were significantly different between the native stocks, but became indistinguishable from those of the recipient populations one year after reciprocal transfer. This did not, however, conceal the effect of stock origin on dimensional ratios. It is concluded that site differences related to environmental factors, notably chlorophyll a levels and currents, and also possible stress caused by high levels of Zn and Cu, are major determinants of growth, which are of main interest to aquaculture, while morphological differences most probably result from genotypic variation.     

Community structure of the benthos in Scottish sea-lochs. III. Further studies on patchiness

Large-scale patchiness in the distribution of the benthic fauna was investigated in Loch Etive (Scottish west coast) by two series of van Veen grab hauls. Each series was taken along a traverse across the width of the loch, with sampling points about 100 m apart. One sample series was taken on sandy mud and the other, at a greater depth, on soft mud. Two approaches in data processing were applied: (1) The variance: mean ratio and the Morisita I tests for significant aggregation were applied to the species abundances in the sample series; (2) 3 measures of sample homogeneity, each involving the calculation of an index of faunal similarity, were applied to the separate samples. The results, however, could not show significant differences between the two series of samples. These findings were compared to results obtained from (a) a previous study, where differences in patchiness between areas were shown for a smaller scale of sampling design in Loch Etive and neighbouring areas, and to which the I method is also applied here; and (b) the results of applying the variance: mean ratio and I tests to data published by Holme (1953). The present results indicate greater aggregation at the present scale of sampling than for the previous, smaller scale of sampling, or for the comparable scale of Holme's sampling. The degree of concordance shown by the values of I for the circular-design sampling to the values of the 3 measures of patchiness applied previously, and to the means of the species abundances, was measured by Spearman's rank correlation coefficient. The results clearly demonstrated the I values, unlike the others measured, to be almost completely independent of the mean. It was concluded that, for comparing the pattern from benthic samples using standard-size bottom samplers, where the mean may vary widely between each set of samples, the I method is probably most useful.     

Reproductive cycle of the brachiopodTerebratulina retusa on the west coast of Scotland

The reproductive cycles of two populations of the Recent articulate brachiopodTerebratulina retusa (Linnaeus) are described, based on samples taken between October 1985 and October 1986. Stereological analysis of the gonads revealed a single synchronised spawning event between late November and the end of January in the Firth of Lorn. In a second population, in Loch Fyne, spawning took place repeatedly throughout the spring and summer, with greatest spawning activity occurring in the late autumn.T. retusa from Loch Fyne were approximately three times more fecund than those from the Firth of Lorn. Productivity in the Clyde Sea area is approximately five times higher than in Firth of Lorn and higher fecundities and spawning frequencies of the Loch Fyne population are attributed, in part, to greater food availability. The initiation of gametogenesis appears to be mediated by the mobilisation of reserves stored in the outer mantle epithelium during the winter. Primary productivity increases dramatically in the spring and gametogenesis shows a corresponding increase.     

Community structure of the benthos in Scottish sea-lochs. II. Spatial pattern

Spatial pattern in the distribution of the macrobenthos was studied from series of van Veen grab samples taken in a systematic pattern in Lochs Etive and Creran, W. Scotland. Each series was collected in a circular pattern at 7 stations. Plots of the variances of the numerical occurrences of the species in the samples against their means revealed greater deviation from the random expectation in the case of the 2 muddy sand stations than for the soft-mud stations, with only 1 exception. Two tests of goodness-of-fit to the Poisson distribution were also applied. The degree of concordance between the 3 measures of non-randomness applied was measured. The best correlation was found between values of the ratio of variance: mean and the test statistic D of the Kolmogorov-Smirnov goodness-of-fit test. It was not possible to discuss the biological basis for the pattern measured, except for a few species shown to be markedly aggregated. No clear trend emerged from attempts to detect differences in pattern with various ecological groupings of the macrobenthos. However, from the use of the test values as sample statistics illustrative of overall community pattern, it was possible to conclude that the fauna of the shallow, usually current-swept areas of muddy sand in the sea-lochs investigated was more aggregated than that on the, usually deeper, soft-mud sediments in quieter water.     

Seasonal variation in some population parameters of Euchaeta species (copepoda: Calanoida)

Studies of the biology of oceanic copepods are few relative to those of coastal species. Females of the genus Euchaeta have spermatophores attached to the genital somite by the male and carry their broods of eggs attached to this somite, so defining the breeding season. Populations of E. norvegica in the fjordic environment of Loch Etive (collected between 1971 and 1974 and from 1978 to 1979), Scotland and in the marginal oceanic region of the Rockall Trough, northeastern Atlantic Ocean (collected between 1973 and 1976) and of a further eight species of Euchaeta in the Trough are examined. Seasonal changes in the incidence of egg masses and spermatophores attached to the females, sex ratio and population numbers are determined. Sampling errors in the estimation of these parameters are larger in the oceanic Rockall Trough. The Loch Etive populations of E. norvegica produce two generations per year with a proportion, variable between years, of the population producing a third generation. This species produces a single annual generation in the Rockall Trough as do E. acuta and E. pseudotonsa. Two generations per year are probably passed through by E. gracilis in the Trough while the large bathypelagic E. sarsi may produce a single generation in the autumn of every second year. The other bathypelagic species, E. barbata, E. scotti, E. abbreviata and E. longissima, breed continuously throughout the year and no estimate of their generation times is possible. Consequently, this approach to population analysis is useful where breeding is seasonal, but resolving generation time in bathypelagic crustaceans remains a problem.     

Geographic variation,niche breadth and genetic differentiation at different geographic scales in the mussels Mytilus californianus and M. edulis

Genetic differentiation was investigated in the marine mussels Mytilus californianus Conrad and M. edulis Linn. from the west coast of North America. In allopatry with M. californianus, M. edulis occurs throughout the intertidal zone; however, in microgeographic sympatry its ecological range is restricted to above the M. californianus mussel bed and to patches of substratum opened by natural disturbances within the bed. Over the same geographic scale, the broader-niched M. edulis shows greater among-locality genetic difference and greater levels of polymorphism than M. californianus at two enzyme loci. Genetic differentiation on a geographic basis was investigated in M. californianus at a single rock (on a scale of meters), on an island (on a scale of kilometers), throughout a strait (on a scale of 10² kilometers), and along the west coast of North America (on a scale of 10³ km). Differentiation was minimal over the west coast, and could be explained by microhabitat differences in a local area. The minimal differentiation in west coast mussels relative to strong geographic differentiation of M. edulis on the east coast of North America may be related to the steeper latitudinal thermal gradient on the east coast. Local ecologically related microgeographic variation can result in biased and misleading estimates of genetic heterogeneity but microgeographic variation at enzyme loci may not be due to selection at the loci investigated or may even be due to the breeding structure of the mussel populations, as suggested by Tracey et al. (1975).     

Laboratory study of predation by Aurelia aurita on larvae of cod,flounder, plaice and herring: development and vulnerability to capture

Capture success of the medusa Aurelia aurita preying on various developmental stages of fish larvae was measured together with larval reactivity and escape speed after being stung. These experiments were conducted in the spring of 1983 with A. aurita medusae collected from Loch Etive, Scotland and laboratory-reared larvae of Gadus morhua L., Platichthys flesus L., Pleuronectes platessa L. and Clupea harengus L. Capture success of the medusae increased with medusa size, but decreased with advancing larval development. Smaller species of larvae were more vulnerable to capture. Larval reactivity to encounters with medusae increased with advancing development, and larger species of larvae were more reactive to encounters. Larval escape swimming speeds also increased with advancing larval development and size. These results indicate that earlier stages of larvae within a species and smaller species of larvae at a given stage are more vulnerable to predation by medusae since they are less reactive to encounters. Apparently they are more susceptible to the effects of neurotoxins. Predation rates on different developmental stages of herring larvae are documented and compared with rates predicted by a predation model. Predictions fell within the range of observed predation rates, but tended to overestimate rates by larger medusae feeding on larger herring larvae. This indicates the possibility of predator satiation and/or behavioural avoidance.     

The water economy of the sea grass Thalassia testudinum

The osmotic values in the leaves of Thalassia testudinum Banks ex König, collected from the natural habitat, were found to be 32 atm; the relative transpiration was 100%. Electronmicroscopical analysis of the cuticle reveals many perforations. The critical sublethal water deficit lies near 65%. In dense meadows the green surface area of the plants amounts to 18.56 m²/m² bottom area.     

The undulating oceanographic recorder — A new instrument system for sampling plankton and recording physical variables in the euphotic zone from a ship underway

The prototype Undulating Oceanographic Recorder Mark I is an instrumented towed vehicle which can be programmed to undulate between a minimum depth of 8 m and a selected maximum depth between 15 and 70 m, with an undulation length between 3 and 30 km, at any speed between 7 and 15 knots (3.6 to 7.7 m/sec). It takes a continuous series of plankton samples, each integrated over the undulation depth range, and records data on magnetic tape, at a preselected rate between 30/min and 30/h, from which salinity, temperature and depth can be derived with accuracies of ±0.1, ±0.1C° and ±0.5 m, respectively. The instrument is automatic, self-contained and generates its own power supplies. It is towed on about 200 m of unfaired steel cable and can be handled with the winching and lifting equipment found on most research vessels. Examples of processed data from three cruises are presented: temperature and salinity contours on a vertical section through a complex stratified area in the N.W. Irish Sea; results from a survey of the waters over the continental shelf and slope to the north of Scotland, showing the distribution of water masses and associated plankton; and hydrographic data taken in Loch Etive on the west coast of Scotland.     

Mercury concentrations in the surface sediments of the intertidal area along the west coast of Peninsular Malaysia

Total mercury (Hg) levels in the intertidal surface sediments along the west coast of Peninsular Malaysia were analysed by using heat vaporization method. Total Hg levels in these sediments ranged from 3.00 to 201?µg?kg^?1 dry weight with a mean concentration of 60.0?µg?kg^?1 dry weight. More than 90% of the samples studied have the total Hg concentrations less than 150?µg?kg^?1 dry weight. Compare with the regional data and sediment quality guidelines, the Hg contamination in the intertidal area along the west coast of Peninsular Malaysia was not serious, except for a few sites that might have received anthropogenic Hg in the samples collected between 1999 and 2000. It is suggested that a similar study of heavy metals in the sediments of the west coast of Peninsular Malaysia be conducted regularly.     

Precision of the mean and the design of benthos sampling programmes: caution advised

To calculate the number of samples required to estimate population density to a specified precision, a prior estimate of the sample variance is needed. Using data from the freshwater benthic literature, Downing (1979, 1980a) calculated a regression equation to predict sample variance from sampler size and population density. He used predicted sample variance to calculate the number of samples, of a range of sizes, required to estimate a range of population densities to a specified precision. He concludes that massive savings (1300 to 5000%) of total surface area sampled may be achieved by using sample units of small surface area. These conclusions are misleading. The data set used for the regression does not adequately cover the combination of a low-density population sampled by a device of small surface area. The benthic community of Belhaven Bay, East Lothian, Scotland was sampled in 1982 with a 0.1 m² grab and a 0.0018 m² corer, providing 112 sets of replicate data which were used to test the hypothesis that for a specified precision of the mean a considerable saving of total area sampled may be obtained by sampling with a device of small surface area. The benthos of Loch Creran, Argyll, Scotland was sampled with contiguous corer samples on four occasions in 1980 and 1981, providing 234 independent sets of replicate data. Contiguous samples were grouped to form several simulated series of samples of increasing surface area. A sampler of small surface area provided a saving of total area sampled of about 20%. Whether such a small saving is justifiable will depend on the extra field expenses incurred by taking many small samples.     

Surf-zone fish assemblages in south-western Australia: do adjacent nearshore habitats and the warm Leeuwin Current influence the characteristics of the fish fauna?

Nearshore fish faunas from 32 sites along 1500 km coastline of temperate south-western Australia were sampled by seine net between 1991 and 1992 to examine the species composition in sandy surf zones along this region, and to determine whether it is influenced by adjacent nearshore habitats and the warm southward flowing Leeuwin Current. Although the ichthyofauna was diverse, with 95 species from 47 families recorded, it was numerically dominated by only a few species. Species of Atherinidae, Mugilidae, Tetraodontidae, Clupeidae and Pomatomidae, such as Atherinomorus ogilbyi, Leptatherina presbyteroides, Mugil cephalus, Aldrichetta forsteri, Torquigener pleurogramma, Hyperlophus vittatus, Spratelloides robustus and Pomatomus saltatrix, were often common to these surf zones. When the species composition of the surf zones was compared with that found in adjacent nearshore habitats, 38 and 42% of the species were shared with reefs and seagrass beds, respectively, and 22% were present in all three habitats. Classification and ordination demonstrated that the faunal composition on the west coast was distinct from that on the south coast, and within each of these regions there were discrete assemblages. There was a marked decline in the number of species on the south coast, with 20 to 66 species reported from the six west-coast assemblages and 11 to 16 species collected from the four south-coast assemblages. A high proportion of resident species was found in the surf zones on both coasts; however, there was a smaller contribution of transient species on the south coast than on the west coast. This decline in transient species was associated with the absence of tropical species on the latter coast. Benthic invertevores were dominant on both coasts, while trophic diversity decreased and the proportion of zooplanktivores increased on the south coast. These differences in the characteristics of the fish fauna between the two coasts can be related to the presence of seagrass beds and limestone patch reef adjacent to sandy surf-zone areas on the west coast which provide more microhabitats for fish. The presence of inshore limestone reefs along the west coast moderates wave energy, producing more sheltered and temporally stable surf zones. The lower number of species on the south coast can also be attributed to the reduced influence of the Leeuwin Current. This southward flowing current acts as a mechanism for the dispersal of tropical species which display no regular association with the surf zones on the lower west coast.     

Influence of wave exposure on South African mussel beds and their associated infaunal communities

This study investigates effects of wave exposure on beds of the mussel Mytilus galloprovincialis and the infaunal communities associated with them. Nine sites of varying wave exposure were sampled near Groenrivier, on the west coast of South Africa. Wave exposure was measured using a Palumbi device, and exposure ranged from 7.17×10³ to 18.49×10³ N m^–2. Percentage mussel cover at each site was measured using 50×50 cm quadrats, and three 10×10 cm samples were removed from the mussel beds in the mid-intertidal zones of each site for examination of infauna. Percentage mussel cover, mean mussel length, mussel biomass and mussel bed depth all peaked at intermediate exposures, declining towards both the most sheltered and most exposed sites. Infaunal species diversity and richness both showed the reverse trend, peaking at the most sheltered and most exposed sites, and declining at intermediate exposures. Neither infaunal abundance, nor biomass, was significantly correlated to wave exposure, although abundance was highest at sheltered sites and biomass greatest at the most exposed site, which was dominated by limpets and large robust polychaetes.Communicated by J.P. Thorpe, Port Erin     

Some biologically important low molecular weight organic acids in the sediments of Loch Eil

The isolation of biologically important low molecular weight organic acids from organically enriched sediments in Loch Eil, Scotland, was carried out by extraction of pore water with acidified ethyl acetate. High concentrations of acetic acid, up to 1.8 mg g^-1 dry weight of sediment were found at Station E-24. Propionate, butyrate, valerate, lactate and traces of succinate were also found. Succinate was present in significant amounts, 42.2 g g^-1 dry weight of sediment at Station E-70, which received a higher input of organic matter than E-24. Both propionate and succinate were absent from a control station in the Lynn of Lorne where the sediment was low in carbon compared with Loch Eil. In experimental tanks, acetate levels increased as the input of organic carbon (as cellulose) was increased up to a load level of 1.5 g m^-2 day^-1. Above this, acetate decreased and succinate appeared. Succinate was not detected in low-loaded tanks. Experiments with sieved mud showed a vertical distribution of the different acids with depth. Lactate and succinate reached highest concentration in the 0 to 3 cm layer, acetate at 3 to 6 cm and propionate at 6 to 9 cm. The results are discussed in relation to the role of these acids as food sources and as indicators of biochemical pathways taking place in sediments with different carbon input levels.     

Skeletal growth zones as age-markers in the sea urchinPsammechinus miliaris

Growth of the inshore sea urchinPsammechinus miliaris (Gmelin) was studied in Loch Creran, western Scotland, using the skeletal growth-marker tetracycline in order to test the validity of natural growth-banding in the coronal test plates as annual age-markers. In order to test whether tetracycline affected the growth ofP. miliaris, an injected and a control group of urchins were held in identical conditions in running sea water aquaria for 21 mo from 1989 to 1991 and measured periodically. A small but significant difference in mean size of injected compared to controls was recorded at 12 mo, but none during subsequent measurements. Size measurements during the trial were consistent with an annual growth cycle, with a maximum in spring and slowing or cessation of growth during autumn/winter. Tetracycline-labelled juveniles were recovered up to 18 mo after initial tagging in mark/recapture experiments undertaken from 1987 to 1989 at two intertidal marked quadrats in Loch Creran. Large numbers ofP. miliaris were also marked with tetracycline and held for 1 yr at 10 m depth in seabed cages in Loch Creran during 1988–1990. All of the intertidal recoveries, and about 69% of the caged specimens that had been successfully labelled, showed a consistent relationship between the position of the tetracycline tag and the pattern of natural growth zones. The remainder were mostly large, slow-growing urchins with the tag positioned near the plate margin. In these the outer growth bands were closely spaced and, particularly if major growth bands seemed to be broken up into double or multiple lines, the major bands were impossible to resolve at the margin. The results support the assumption that in wild populations the dark bands visible with reflected light (translucent in transmitted light) after charring the plate are formed when skeletal growth has stopped or slowed in winter. These lie between wider, lighter coloured (opaque in transmitted light) zones of active plate growth in spring/summer. The dark band formed beyond the tag usually was made up of several closely spaced fine lines, or sometimes of two closely spaced dark bands. The wide growth zones beyond the tag, like those formed previously, usually were broken by fine, dark lines that may represent brief discontinuities in growth. From tagging, the double dark bands can be related to growth over one year; but such anomalous bands, along with the general presence of fine, dark lines interrupting the growth zones, make it difficult reliably to estimate age from the closely spaced peripheral banding on older, slow-growing urchins.     

Some direct observations on the ecology and behaviour of the Norway lobster Nephrops norvegicus

A detailed investigation of a small area of sea bed occupied by the Norway lobster Nephrops norvegicus (L.) was carried out by diving and television observations at depths of 30 m in Loch Torridon, Scotland. The density of burrows was 1/2 m², but only a proportion of these were occupied by N. norvegicus. Although about 70% of the larger burrows were occupied by N. norvegicus, giving a density of 1 lobster/8 m², very few juveniles (carapace length less than 30 mm) were found in the area. Many of the small burrows were occupied by the gobiid fish Lesueurigobius friesii (Collett). There was evidence that N. norvegicus frequently change their burrows, and fighting for burrows was observed. N. norvegicus remain within their burrows during the day, emerge around sunset to forage for food during the night, and then return to their burrows at dawn. This, and other aspects of their burrowing behaviour, have a marked effect on the commercial trawl catches of N. norvegicus which show large seasonal and diurnal variations in size and sex composition.     

Distribution and behaviour of radiocaesium in Scottish freshwater loch sediments

The distribution and behaviour of radiocaesium have been studied in the sediments of two contrasting freshwater lochs: Round Loch of Glenhead, an acidified loch in south-west Scotland, with organic-rich sediments (≈20%C) and Loch Lomond, 35 km north-west of Glasgow, where sediments are low in organic matter (1–6%C, southern basin), but with a relatively high clay content. In the sediments of Scottish freshwater lochs,¹³⁷Cs [half life (t_1/2) = 30.23 yr] originates from fallout from nuclear weapons’ testing (1950s and 1960s) and from the Chernobyl reactor accident in 1986, which is also the source of the shorter-lived¹³⁴Cs [half life (t_1/2) = 2.05 yr]. Use of the characteristic¹³⁴Cs/¹³⁷Cs activity ratio of radiocaesium emitted from Chernobyl enables resolution of sedimentary radiocaesium profiles into the two component sources. In the organic-rich sediment of Round Loch, downward diffusion of radiocaesium in porewaters obscures its pattern of input to the loch. In the more clay-rich sediments of Loch Lomond, separate radiocaesium concentration peaks, related to atmospheric deposition maxima, are clearly discernible, although an influence of partial mixing is apparent. While the derived Chernobyl fallout inventory of radiocaesium in Round Loch sediments is broadly comparable with that for Loch Lomond, the corresponding weapons testing inventory is an order of magnitude lower than in Loch Lomond. Although Round Loch is situated in an area of known elevated Chernobyl deposition, the inventory is much lower than literature values of atmospheric deposition, indicating significant loss of radiocaesium from this loch. The weapons testing inventory in Round Loch is also lower than reported estimates, whereas in Loch Lomond the established inventories from both sources are similar to, or greater than, fallout deposition. The differences between the distribution and inventories in the two lakes confirms that radiocaesium is much less efficiently bound and is correspondingly much more mobile in the organic sediments of Round Loch of Glenhead than in the more clay-rich sediments of Loch Lomond.     

Reactions of fish to sound generated by divers' open-circuit underwater breathing apparatus

Observations were made on the influence of underwater divers on the behaviour of fish in Loch Torridon, on the west coast of Scotland. An electronically scanned sonar and a television camera were used to record the behaviour of 4 species common in the loch. These were the cod Gadus morhua (L), the saithe Pollachius virens (L), the pollack P. pollachius (L) and the common dab Limanda limanda (L). These fish were attracted to divers and to a sound source when the recorded noise from an aqualung and demand valve was transmitted into the water. By analysis and by testing different components of the noise it was shown that low frequencies between 30 and 110 Hz, generated by the release of exhaled air, were responsible for the attraction. It is suggested that the fish associated this noise with the presence of food organisms disturbed from the sea bed by the diver and that they had become conditioned to the noise over a period of time.