Scottish East Coast Research Articles

Multistate capture–recapture models for irregularly sampled data

Multistate capture-recapture data comprise individual-specific sighting histories, together with information on individuals’ states related, for example, to breeding status, infection level, or geographical location. Such data are often analysed using the Arnason–Schwarz model, where transitions between states are modelled using a discrete-time Markov chain, making the model most easily applicable to regular time series. When time intervals between capture occasions are not of equal length, more complex time-dependent constructions may be required, increasing the number of parameters to estimate, decreasing interpretability, and potentially leading to reduced precision. Here we develop a multi-state model based on a state process operating in continuous time, which can be regarded as an analogue of the discrete-time Arnason–Schwarz model for irregularly sampled data. Statistical inference is carried out by regarding the capture-recapture data as realisations from a continuous-time hidden Markov model, which allows the associated efficient algorithms to be used for maximum likelihood estimation and state decoding. To illustrate the feasibility of the modelling framework, we use a long-term survey of bottlenose dolphins where capture occasions are not regularly spaced through time. Here, we are particularly interested in seasonal effects on the movement rates of the dolphins along the Scottish east coast. The results reveal seasonal movement patterns between two core areas of their range, providing information that will inform conservation management.

How litter moves along a macro tidal mid-latitude coast exposed to a coastal current

A simplified particle-tracking model with an idealised coastline was used to investigate how the interaction between variable winds and water level (VaWWL) operates spatially along a coast. The model included a constant along-coast current, horizontal diffusion, onshore/offshore wind drift, beach/cliff combinations and point/distributed litter sources. The default model reproduced basic properties of observed beach litter loadings (zero net accumulation, negatively skewed loading distributions) and the observed spatial pattern along the Scottish east coast, with average loadings increasing in the coastal current direction. The VaWWL effect moved the along-coast flux of floating litter offshore as debeaching events occur during offshore winds. Varying diffusion, coastal current speed, windage, beach/cliff combinations and different foreshore boundary conditions were investigated. Reconciling model predictions with previous estimates of plastic inflow suggested sinking rates of up to 90% soon after first entry into the sea. The VaWWL effect offers a realistic boundary condition for particle-tracking models.

Spatial distribution of foreshore litter on the northwest European continental shelf

Foreshore litter data from a UK citizen-science programme, combined with OSPAR data, were analysed for possible spatial patterns around Scottish and North Sea coastlines. Loading distributions were positively skewed, and statistics commensurate with such distributions were used. When considering coast type, litter loadings on Scottish harbour and river foreshores were influenced by local litter sources. When considering exposure to the predominant westerly winds over Scotland, litter loadings on the west coast (i.e. predominant onshore winds) were greater on foreshores on open coasts compared to those within embayments. The opposite was true for the Scottish east coast (i.e. predominantly offshore winds). The north east coast of the UK appeared to have an organised pattern of plastic litter loading, increasing in magnitude (median) and spread (inter quartile range) in the direction of the coastal flow. Four other coastal segments with similar patterns were suggested from the west of Scotland to Denmark.

Broad-scale acoustic monitoring for cetaceans and underwater noise in relation to offshore wind farm construction in Scotland

Marine construction projects, such as offshore wind farms and port developments often use techniques that produce significant levels of noise underwater, which could have effects on marine wildlife. Marine Scotland is the government body responsible for regulating these activities in Scottish waters and for ensuring that wildlife populations are protected in line with legislation. Large scale offshore wind farm construction will begin to take place off the Scottish east coast in 2017, using piled foundations. To monitor for potential broad scale changes in distribution of protected cetacean species during construction activities, Marine Scotland have deployed an array of 30 click detectors and 10 broadband acoustic recorders across the Scottish east coast each summer since 2013. Here we present baseline distributions for dolphins and harbour porpoises, along with ambient noise levels recorded concurrently. Dolphin detections across the monitored area are highly variable, with some locations that are clearly favoured. Harbour porpoise are ubiquitous and in more than 60% of locations are detected on 100% of monitored days. This is likely to mean that there is more power to detect changes in porpoise distribution in relation to offshore wind farm pile driving than for dolphins.

Molecular discrimination of toxic and non-toxic Alexandrium species (Dinophyta) in natural phytoplankton assemblages from the Scottish coast of the North Sea

Molecular methods provide promising tools for routine detection and quantification of toxic microalgae in plankton samples. To this end, novel TaqMan minor groove binding probes and primers targeting the small (SSU) or large (LSU) ribosomal subunit (rRNA) were developed for two species of the marine dinoflagellate genus Alexandrium (A. minutum, A. tamutum) and for three groups/ribotypes of the A. tamarense species complex: Group I/North American (NA), Group II/Mediterranean (ME) and Group III/Western European (WE). Primers and probes for real-time quantitative PCR (qPCR) were species-specific and highly efficient when tested in qPCR assays for cross-validation with pure DNA from cultured Alexandrium strains. Suitability of the qPCR assays as molecular tools for the detection and estimation of relative cell abundances of Alexandrium species and groups was evaluated from samples of natural plankton assemblages along the Scottish east coast. The results were compared with inverted microscope cell counts (Utermöhl technique) of Alexandrium spp. and associated paralytic shellfish poisoning (PSP) toxin concentrations. The qPCR assays indicated that A. tamarense (Group I) and A. tamutum were the most abundant Alexandrium taxa and both were highly positively correlated with PSP toxin content of plankton samples. Cells of A. tamarense (Group III) were present at nearly all stations but in low abundance. Alexandrium minutum and A. tamarense (Group II) cells were not detected in any of the samples, thereby arguing for their absence from the specific North Sea region, at least at the time of the survey. The sympatric occurrence of A. tamarense Group I and Group III gives further support to the hypothesis that the groups/ribotypes of the A. tamarense species complex are cryptic species rather than variants belonging to the same species.

Diet and feeding niches of juvenile Gadus morhua, Melanogrammus aeglefinus and Merlangius merlangus during the settlement transition in the northern North Sea

A study on the feeding ecology of juvenile cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangus during the pelagic to demersal transition was carried out on fishes sampled throughout their settlement season at a local nursery ground in the north-western North Sea, off the Scottish east coast. A comprehensive quantitative taxonomic analysis of the diets, as described in the paper, showed the emergence of distinctive feeding niches, minimizing the potential for competition between species and size categories. The diet of the juveniles changed with fish size, water depth, time of year and distance offshore. Small G. morhua were present in the study area earlier in the season, settled further inshore and ate a higher proportion of pelagic prey (copepods) and as size increased they moved into deeper waters and targeted larger, more benthic prey. As M. aeglefinus grew larger and moved into deeper waters, a diet of largely copepods, amphipods, pelagic Ammodytes spp., cyprids and pelagic gastropods evolved to one dominated predominantly by fishes and benthic invertebrates. In the case of M. merlangus, widespread ages and sizes throughout the sampling season, a consequence of their more protracted spawning season, resulted in dietary changes which were more likely to be influenced by seasonal changes in the prey field, in addition to developmental (size) changes, than the diets of the other two species.

Spatiotemporal coupling/decoupling of planktonic larvae and benthic settlement in decapods in the Scottish east coast

Settlement patterns and the relationship between meroplanktonic larvae and settlement in decapods were studied on the Scottish east coast. Artificial settlement substrates (ASS), deployed at two locations (sandy vs. rocky sea substrates), were employed to collect megalopae and newly settled juveniles. Abundance of meroplanktonic larvae was used as an indicator of larval supply. The results showed a clear seasonality in settlement rates, and in some cases, significant differences between sites were detected. Nevertheless, the interference of the ASS with the surrounding habitat limits the study of spatial variability in settlement rates. Significant cross-correlation was found between the abundance of megalopae and juveniles in the collectors and planktonic larval abundance a month earlier. For individual species, this relationship was observed only in Pisidia longicornis. Complexities caused by the great variety of pre- and post-settlement processes, alongside effects of secondary dispersals of early juveniles may have obscured the relationship between meroplanktonic larvae and juveniles in other species.

Azadinium obesum (Dinophyceae), a new nontoxic species in the genus that can produce azaspiracid toxins

Tillmann U., Elbrächter M., John U., Krock B. and Cembella A. 2010. Azadinium obesum (Dinophyceae), a new nontoxic species in the genus that can produce azaspiracid toxins. Phycologia 49: 169–182. DOI: 10.2216/09-35.1The novel dinoflagellate taxon we describe here as Azadinium obesum sp. nov. was isolated as clone 2E10 from the North Sea along the Scottish east coast, the same locality as for Azadinium spinosum Elbrächter et Tillmann, the type and formerly only species for this genus. In contrast to A. spinosum, a known producer of azaspiracid (AZA) toxins, the isolate of A. obesum produces no known AZA analogues detectable by liquid chromatography coupled with tandem mass spectrometry. Azadinium obesum is a small (13–18 µm length; 10–14 µm width) photosynthetic dinoflagellate with a thin theca exhibiting the Kofoidean plate tabulation: Po, cp, X, 4′, 3a, 6″, 6C, 5?S, 6′″, 2″″. This species is morphologically distinguished from A. spinosum by slightly larger mean cell size, consistent absence of an antapical spine, the lack of a stalked pyrenoid and several details of the plate configuration. Among these thecal features, the first precingular (1″) plate of A. obesum does not touch the first epithecal intercalary plate and is four sided rather than five sided as in A. spinosum. Furthermore, in A. obesum the lower half of the first apical (1′) plate is very narrow and tongue-like, and precingular plates 1″ and 6″ are very close together, whereas these diverge in A. spinosum. DNA sequence and phylogenetic analysis elucidates and supports the separation (but close affinity) of A. obesum and A. spinosum, as well as the description of the former as a distinct species. Phylogenetic interpretation of the four genes analysed – internal transcribed spacer, 18S rDNA, 28S rDNA (D1/D2) and cytochrome oxidase I – further validates the recently erected genus Azadinium Elbrächer et Tillmann but does not clarify the position of the genus with respect to higher taxonomic levels within the subclass Peridiniphycidae.

Assessing nursery contribution to recruitment: relevance of closed areas to haddock Melanogrammus aeglefinus

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 400:221-232 (2010) - DOI: https://doi.org/10.3354/meps08384 Assessing nursery contribution to recruitment: relevance of closed areas to haddock Melanogrammus aeglefinus P. J. Wright*, D. Tobin, F. M. Gibb, I. M. Gibb Marine Scotland, Marine Laboratory, 375 Victoria Road, Aberdeen AB11 9DB, UK *Email: p.wright@marlab.ac.uk ABSTRACT: Closing areas where juveniles aggregate has often been assumed to benefit recruitment since it reduces mortality of undersized individuals. However, the number of juveniles per unit area that recruit to an adult population may vary due to a combination of factors. Consequently, more appropriate nursery definitions have been based on measures of juvenile contribution to an adult population, either as overall contribution (essential juvenile habitat hypothesis) or recruits per area (the nursery role hypothesis). Nonetheless, these definitions do not explain why nursery contribution differs. In the present study, the nursery contribution of areas in the North Sea and west of Scotland was examined for haddock Melanogrammus aeglefinus. Elemental concentrations in the equivalent parts of the otolith of juvenile and adult fish were compared from the same year-class. Discriminant analysis indicated that 4 discrete 0-group regions around the Scottish coast could be distinguished with a classification accuracy of 83 to 89%. In contrast, the elemental signatures from adult cores sampled in adjacent spawning areas indicated high levels of mixing throughout the study region. The Scottish east coast region accounted for the highest overall contribution in 2003, and this was related to the high 0-group density in that region. While 0-group densities in this area have been consistently high since 2001, previous large year-classes have been characterised by high densities further north and east. Therefore, if 0-group density is always a good indicator of nursery contribution, temporary area closures that vary in relation to juvenile settlement concentrations may have more benefit to recruitment than permanent closures. KEY WORDS: Nursery value · Haddock · Connectivity · Otolith microchemistry · North Sea · West of Scotland Full text in pdf format PreviousNextCite this article as: Wright PJ, Tobin D, Gibb FM, Gibb IM (2010) Assessing nursery contribution to recruitment: relevance of closed areas to haddock Melanogrammus aeglefinus. Mar Ecol Prog Ser 400:221-232. https://doi.org/10.3354/meps08384 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 400. Online publication date: February 11, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Using T‐PODs to assess variations in the occurrence of coastal bottlenose dolphins and harbour porpoises

Abstract Assessments of anthropogenic impacts on cetaceans are often constrained by limited data on the extent to which these species use particular areas. Timing porpoise detectors (T‐PODs) are autonomous data recorders for detecting cetacean echolocation clicks, potentially providing cost‐effective opportunities for monitoring cetacean occurrence. The performance of T‐PODs was assessed in three areas off the Scottish east coast, where the relative occurrence of bottlenose dolphins and harbour porpoises was known to differ. Land‐based observations in one area compared visual and acoustic detections of dolphins, while direct hydrophone recordings of dolphin echolocation clicks were compared with T‐POD detections during boat surveys. Land‐based surveys recorded 89 groups of dolphins within 900 m of the T‐POD. All groups spending >30 min in the area were detected on the T‐POD, and the probability of detection declined in relation to distance from the recording site. The number of dolphin clicks recorded on the independent hydrophone system was significantly related to the number detected by a T‐POD. Between pairs of T‐PODs, there was also significant correlation with the numbers of clicks recorded in each hour, both for channels set to detect bottlenose dolphins and for channels set to detect harbour porpoises. Year‐round deployments of paired T‐PODs detected significant geographical variation in detections for both bottlenose dolphins and harbour porpoises. This pattern reflected published data from visual surveys, where dolphins occurred most regularly within the Moray Firth Special Area of Conservation, and porpoises were sighted more regularly in offshore waters. T‐PODs do not detect all cetaceans in the area, and care must be taken when interpreting data from mixed species communities. Nevertheless, these results confirm that T‐PODs provide an effective method for monitoring the occurrence of bottlenose dolphins and harbour porpoises, and provide excellent potential for collecting baseline data from poorly studied areas and monitoring long‐term temporal change in key areas of interest. Copyright © 2009 John Wiley & Sons, Ltd.

Unambiguous identification of pectenotoxin-1 and distribution of pectenotoxins in plankton from the North Sea

Lipophilic phycotoxins in size-fractionated plankton net tows (20 μm mesh-size) were measured on-board during a month-long oceanographic cruise in North Sea coastal waters. Tandem mass spectrometry coupled to liquid chromatography (LC–MS/MS) was employed for the detection and quantification of a broad spectrum of known and putative phycotoxins. For pectenotoxins (PTXs) the following ion masses ([M + NH 4] +) were monitored: m/ z 876 for PTX-2, m/ z 892 for PTX-11 and PTX-13, and m/ z 874 for PTX-12 and PTX-14. The PTX levels in net plankton were highest along the Danish north coast, but levels over 50 ng per net tow were also detected on the southern Scottish East coast and in the northern Skagerrak. Abundance of PTXs was highly correlated with the occurrence of the marine dinoflagellate Dinophysis spp. Whereas in the eastern North Sea PTX-2 was the most abundant PTX, in the western North Sea PTX-1 was the major component, but it was also present in lower proportions in the Norwegian and Danish waters than in the western North Sea. Isobaric PTX-11 was absent or only detected at trace levels throughout the entire cruise, and PTX-13 and PTX-14 were not detected at all. The identity of PTX-1 was confirmed by comparison of retention time and mass spectrum of the North Sea phytoplankton sample to PTX-1 previously isolated from shellfish. Statistical analysis showed the best correlation between the occurrence of PTX-1 and Dinophysis acuminata cell concentration. Nevertheless, we could not rule out the possibility of metabolic transformations of PTXs by organisms that have grazed upon Dinophysis. Such biotransformations could conceivably occur in heterotrophic dinoflagellates or ciliates, or even via oxidation in copepod fecal pellets. In any case, this study confirmed the presence of PTX-1 in the plankton and is the first definitive report of this toxin in the North Sea.

Seasonal distribution of white-beaked dolphins (Lagenorhynchus albirostris) in UK waters with new information on diet and habitat use

The white-beaked dolphin, Lagenorhynchus albirostris, is commonly found throughout the North Sea and shelf waters of the North Atlantic. Little is known about the behaviour and ecology of this species, especially in British coastal waters. In this paper we present details of the seasonal and geographical distribution of white-beaked dolphins around the UK, along with new information on their diet and habitat use. Analysis of historical stranding records show a segregation of the sexes, with a significant difference between when males and females strand in UK waters. There has been a steady decline in reported strandings since the 1970s and seasonal differences in the distribution of strandings suggest that sea temperature may limit white-beaked dolphin distribution around the British coast. Stomach contents' analysis, from dolphins stranded mainly on the Scottish east coast, identified haddock and whiting as the predominant fish species being taken. Boat surveys were performed along the north-east Scottish coast to examine relationships between topography, environmental conditions, dolphin presence and group size. Dolphin presence was related to seabed slope and aspect while variation in temperature explained almost 45% of variation in observed group size, with smaller groups associated with higher sea temperatures.

Quantifying the influence of sociality on population structure in bottlenose dolphins

1. The social structure of a population plays a key role in many aspects of its ecology and biology. It influences its genetic make-up, the way diseases spread through it and the way animals exploit their environment. However, the description of social structure in nonprimate animals is receiving little attention because of the difficulty in abstracting social structure from the description of association patterns between individuals. 2. Here we focus on recently developed analytical techniques that facilitate inference about social structure from association patterns. We apply them to the population of bottlenose dolphins residing along the Scottish east coast, to detect the presence of communities within this population and infer its social structure from the temporal variation in association patterns between individuals. 3. Using network analytical techniques, we show that the population is composed of two social units with restricted interactions. These two units seem to be related to known differences in the ranging pattern of individuals. By examining social structuring at different spatial scales, we confirm that the identification of these two units is the result of genuine social affiliation and is not an artefact of their spatial distribution. 4. We also show that the structure of this fission-fusion society relies principally on short-term casual acquaintances lasting a few days with a smaller proportion of associations lasting several years. These findings highlight how network analyses can be used to detect and understand the forces driving social organization of bottlenose dolphins and other social species.

The distribution of phosphorus between soluble and particulate phases for seven Scottish East Coast rivers

Phosphorus (P) fractions were quantified in water samples collected on four occasions from sites at the lower tidal limit of seven Scottish East Coast rivers. Individual catchment characteristics ranged from those dominated by semi-natural land use to those where agriculture predominated. Together the rivers displayed attributes ranging from nearly pristine to those impacted by point and diffuse sources of pollutants. Sampling times were chosen to coincide with periods of low river flows where conditions should result in low concentrations of suspended particulate matter (SPM) but favourable for phytoplankton growth. Total phosphorus (TP) concentrations were 90% of TP and dissolved P dominated all samples. The total phosphorus content (TPC) of SMP ranged from 0.1 to 1.1% and was significantly related to SRP. Organic matter was a significant component of SPM and organically bound phosphorus was the dominant form of particulate P. The C/P ratio of organic matter was wide, between 500–1200 for the more pristine systems which narrowed to < 400 for heavily impacted rivers. Exchangeable P increased during the summer but was generally a minor component of TP and therefore likely to be a significant source of SRP only in pristine rivers. Phytoplankton constituted between 5 and 46% of organic matter and concentrations of chlorophyll-a were significantly correlated with both TP and SRP.

Discrimination of the toxigenic dinoflagellates Alexandrium tamarense and A. ostenfeldii in co-occurring natural populations from Scottish coastal waters

Blooms of the toxic dinoflagellate Alexandrium tamarense (Lebour) Balech, a known producer of potent neurotoxins associated with paralytic shellfish poisoning (PSP), are common annual events along the Scottish east coast. The cooccurrence of a second Alexandrium species, A. ostenfeldii (Paulsen) Balech & Tangen is reported in this study from waters of the Scottish east coast. The latter species has been suspected to be an alternative source of PSP toxins in northern Europe. Recent identification of toxic macrocyclic imines known as spirolides in A. ostenfeldii indicates a potential new challenge for monitoring toxic Alexandrium species and their respective toxins in natural populations. In mixed Phytoplankton assemblages, Alexandrium species are difficult to discriminate accurately by conventional light microscopy. Species-specific rRNA probes based upon 18S and 28S ribosomal DNA sequences were developed for A. ostenfeldii and tested by dot-blot and fluorescence in situ hybridization (FISH) techniques. Hybridization patterns of A. ostenfeldii probes for cultured Alexandrium isolates, and cells from field populations from the Scottish east coast, were compared with those of rDNA probes for A. tamarense and a universal dinoflagellate probe. Alexandrium cell numbers in field samples determined by whole-cell in situ hybridization were much lower than those determined by optical microscopy with the Utermöhi method involving sedimentation chambers, but the results were highly correlated (e.g. r 2 = 0.94; n = 6 for A. tamarense). Determination of spirolides and PSP toxins by instrumental analysis on board ship demonstrated the presence of both toxin groups in plankton assemblages collected from surface waters near the Orkney Islands, and confirmed the association of A. ostenfeldii with spirolides in northern Europe. These results show that rRNA probes for A. tamarense and A. ostenfeldii are useful, albeit only semi-quantitative, tools to detect and discriminate these species in field studies.

The Pre-Windermere Interstadial (Late Devensian) raised marine strata of eastern Scotland and their macrofauna: a review

Late Devensian raised marine deposits predating the Windermere Interstadial (c. 13–11 ka BP) are found between the Moray Firth and Berwick. The widely distributed, sparsely fossiliferous Errol Clay Formation of the firths of Forth and Tay was laid down in a high-arctic environment immediately following the retreat of the Late Devensian (Dimlington Stadial) ice. In the Tay Estuary, sedimentation took place under distal glaciomarine to marine conditions at a time when there was a fully marine connection between the Scottish east coast and the then high-arctic Norwegian Sea. On the south shore of the Moray Firth, the similar, but undated Spynie Clay Formation seems to have been laid down in a wholly glaciomarine environment. Part of the macrofauna attributed to the St. Fergus Silt Formation of the NE Scottish coast may have been either misidentified, or is not in situ. The preservation of the fauna and of delicate sedimentary structures indicate that the arctic clays as a whole were laid down rapidly. It is suggested that tidal currents were minimal, and that waves were dampened by sea ice for much of the year. Bones of the ringed seal, Phoca hispida, have been recorded from 12 sites in eastern Scotland. About 40 macrofaunal taxa are present in the Errol Clay Formation, a number similar to that recorded in the Danish Younger Yoldia Clay, which is of comparable age. The faunal nomenclature is updated, and three species ( Cylichna occulta, Retusa obtusa and Lyonsia arenosa) are added to the macrofaunal list for the Errol Clay Formation. Reports of in situ boreal molluscs and of one possibly North American species in the otherwise high-arctic assemblage are not supported by specimens in extant collections. Differential decay of the fauna below the zone of weathering in the Errol Clay Formation may have resulted from early diagenesis. Deposition of the Late Devensian, pre-Windermere Interstadial marine sediments as a whole was probably diachronous, beginning after 15–14 ka BP on the outer coast, but was confined to a short interval (c. 13.5–13 ka BP) at the type site in the Tay Estuary. In the Forth Estuary, the high-arctic marine fauna adjacent to the retreating ice-front may have survived the rapid climatic amelioration (c. 13 ka BP) at the beginning of the Windermere Interstadial (marked by the Main Perth Shoreline) for perhaps a few decades.

A Scottish east coast European ferry service: review of the issues

Peripheral regions and nations within the EU generally enjoy a balanced mix of transport alternatives for access to the Continent's economic centre. Unique among peripheral regions and nations in Northern Europe, Scotland has no direct ferry service to the Continent and relies for access on ferry services from remote seaports, resulting in a greater relative dependence on land transport, particularly road. The evidence presented in this paper suggests that Scotland does not enjoy direct ferry access with the Continent due to any geographic or economic reason, rather the explanation is more to do with technological obsolescence of existing seaport infrastructure coupled with the lack of sufficient Government initiative to help promote direct links. Ultimately, a direct ferry service could help reduce the effects of peripherality and bring about further integration. It would also spread increasing transport demand across modes.

Comparison of changes in the annual variability of the seasonal cycles of chlorophyll, nutrients and zooplankton at eight locations on the northwest european continental shelf (1960–1994)

Mean seasonal cycles in time series of salinity, nutrients, chlorophyll and Zooplankton at 8 locations on the Northwest-European shelf were analysed in relation to each other and with respect to their timing and magnitude during a period most of the time series overlap (1980–1984). A relatively late spring bloom in April/May with low chlorophyll values (2–4 mg/m3) is observed in the Irish Sea, off the Scottish east coast and the Channel entrance. An early spring bloom in March/April and relatively high chlorophyll values (7–12 mg/m3) are found in the Southern Bight of the North Sea and in the Skagerrak, whereas a late spring bloom in April/May with chlorophyll concentrations of about 23 mg/m3 is found along the Dutch and Belgian coast. The peak of the phytoplankton carbon cycle in the German Bight (Helgoland) occurs during summer. This is caused by the dominance of large dinoflagellates in this period. The peak in the yearly abundance of copepods shifts from May-June in the south to July-August in the north of the shelf. In the Irish Sea and the Channel entrance two seasonal copepods peaks are observed. The January nitrate values in Irish Sea, the Southern Bight and the Skagerrak are, compared to the Atlantic input signal represented by the data from the Channel entrance and east of Scotland, about 20% higher. The values of dissolved inorganic phosphate in January are comparable to those of the Atlantic input signal. However, the Irish Sea forms an exception, here the level is increased by 10–20%. The January values for nitrate and dissolved inorganic phosphate at the Dutch and Belgium coast are about 10 and 4, and in the German Bight (Helgoland) 4 and 3 times higher then the Atlantic input signal. At most sites changes in the seasonal cycles of chlorophyll coincide with changes in nutrient concentrations, whereas the maximum level of the seasonal signal of chlorophyll is related to nutrient levels.

Long‐term changes in the sea‐age at maturity and seasonal time of return of salmon, Salmo salar L., to Scottish rivers

Abstract Using catch data, changes in salmon, Salmo salar L., sea‐age and seasonal return time were compared between several Scottish east coast rivers over the last 150–200 years. Parallel long‐term trends were found, suggesting common influences affecting salmon at sea. Long‐term associations with marine environmental factors were investigated by literature review and comparisons with an index of Icelandic sea‐ice abundance. Apparent associations were shown to exist since about 1900, although the cause was not demonstrated. However, over a longer timescale, the same associations were not apparent. Unique gradual marine changes since 1900 may have resulted in perceptible associations with salmon data which may otherwise be imperceptible when short‐term marine environmental variability is greater than long‐term variability. Marine factors must affect salmon, but the complexity of the marine environment and controls on age at maturity and time of return mean that a retrospective analysis cannot be expected to identify the causal factors.

Nutrient Inputs to Estuaries from Nine Scottish East Coast Rivers; Influence of Estuarine Processes on Inputs to the North Sea

Nutrient distributions (nitrate, ammonia, phosphate and silicate) have been determined in the surface waters of nine North Sea estuaries: Tweed, Forth, Tay, Dee, Don, Ythan, Beauly/Inverness Firth, Cromarty Firth and Dornoch Firth. Seasonal variability has been examined by conducting surveys in April, July and September 1991 and February 1992. On each occasion, surveys of all nine estuaries were normally completed in 3-5 days of each other, around high water on spring tides. This intensive and strictly controlled sampling regime ensures a realistic comparison between nutrient concentrations in individual estuaries. Nutrient concentrations in individual rivers and estuaries are demonstrated to be related to land use. River catchments with intensive agriculture and low freshwater input, such as the Don and Ythan, have enhanced nitrate (up to 600 μM) and phosphate (up to 5 μM) concentrations in their estuaries. By contrast, Highland river catchments with mineral-poor soils, low populations and low agricultural intensity (Inverness, Cromarty and Dornoch Firths) generally lead to nutrient concentrations being lower in river water than in coastal seawater. Conservative mixing of dissolved nutrients is demonstrated to be a function of estuarine flushing time which controls the extent to which internal processes (biological and abiological) can modify nutrient inputs. Nutrients tend to behave conservatively in short rapidly flushed estuaries such as the Tweed, Don and Ythan. In contrast, internal processes are shown to be important when estimating riverine nutrient fluxes to the coastal zone from large slowly flushed estuaries such as the Forth, Tay and Dornoch Firth. For these systems, estimates of riverine inputs to the estuary do not provide a good estimate of the load entering the coastal zone. This is primarily due to the cycling of nutrient elements between dissolved and particulate (including sediment) phases. On a regional basis, gross nutrient inputs are dominated by the pattern of freshwater flow rather than by high concentrations in individual rivers. In consequence the Tay is quantitatively the most important riverine source of nutrients to Scottish North Sea coastal waters. For most of the estuaries examined the N:P ratio at high salinity is close to that observed in coastal waters. For the Don and Ythan, however, (and to a lesser extent the Tweed) the ratio is higher, probably reflecting the influence of agricultural nitrogen inputs; possible implications to phytoplankton growth in coastal waters are discussed. In the northern estuaries (Beauly/Inverness, Cromarty and Dornoch Firths), a source of silicate is evident at low salinity, this is attributed to desorption of silicate from estuarine sediments to nutrient-poor river water.