Predation by seals on salmonids in two Scottish estuaries

Detailed observations of the behaviour of harbour seals, Phoca vitulina L., at sites within the estuaries of the Rivers Dee and Don, in north-eastern Scotland, were made over two full years between 1993 and 1996. Small numbers of grey seals, Halichoerus grypus Fab., were also present. The presence of seals within the estuaries was strongly related to season, with maximum numbers observed in winter and early spring; seals were virtually absent in June and July. The River Don was used largely as a haul-out site, while the River Dee was used predominantly as a foraging site, although it was not possible to determine whether the same seals were using the two estuaries. More seals were hauled-out on the River Don during twilight and dark than in daylight. The seals were observed to eat mostly salmonids, Salmo salar L. and S. trutta L., unidentified roundfish and flounder, Pleuronectes flesus L. The otoliths identified in scats collected at the mouth of the River Don belonged to marine species indicating that the seals were also feeding outside the estuaries. A minimum estimate is given of the numbers of large salmonids eaten in each river during the course of the year. Although no information was available on the numbers of salmonids using the rivers or the reproductive status of the fish eaten by the seals, as a cause of mortality, seal predation on large salmonids in estuaries is apparently an order of magnitude less important than mortality caused by angling within the river.     

Relationships among long'term fisheries abundances, hydrographic variables, and gross pollution indicators in northeastern U.S. estuaries

Categorical time series regression was applied to 55 fish stocks in the Potomac, Hudson, Narragansett, Delaware, and Connecticut estuaries for the period 1929–1975. Interannual variability in catch per unit effort (CPUE) was related to CPUE, hydrographic variables, and pollution variables, lagged back in time to represent the conditions contributing to the multiple ages comprising each fishery. Hydrographic variables included water temperature and flow in the estuary– and, for offshore spawning stocks, wind direction and magnitude–during the months of spawning and early life stage development. Pollution variables included measures of dissolved oxygen conditions in the estuaries, volume of material dredged, and sewage loading (or human population). Lagged CPUE, hydrographic variables, and pollution variables all played important roles in explaining historical variability in CPUE. Lagged CPUE was significant in 45 of 55 stocks generally accounting for 5–35% of the variability. Lagged hydrographic variables were significant in 53 of 55 stocks, explaining an additional 5–40% of the variability unaccounted for by lagged CPUE. Lagged pollution variables were significant in 35 of 55 stocks, generally accounting for an additional 5–30% of the variability not explained by lagged CPUE and hydrographic variables. Results did not exhibit expected patterns of consistency in the importance of lagged CPUE for a species across estuaries or consistency in the importance of pollution variables across estuaries. Results did exhibit the expected north-to-south longitudinal pattern in the importance of timing of the hydrographic variables, the months of importance being one or two months later in more northerly estuaries. Higher-order interaction effects were important in almost all stocks that were well-modeled by categorical time series regression. Of the 30 stocks with final regression models having R² > 0.55, 26 stocks involved significant interaction effects, five had only significant interaction effects (no significant main effects), and 20 stocks had significant interactions involving variables not significant as main effects. The difficulties involved in analyzing long-term trends in fish populations and partitioning variability between natural and anthropogenic sources are discussed.     

Novel insights into the marine phase and river fidelity of anadromous twaite shad Alosa fallax in the UK and Ireland

1. Most research on anadromous fishes has been invested in their freshwater life‐phases, resulting in a relatively sparse understanding of their spatial ecology during marine life‐phases. However, understanding the marine dispersal of anadromous fishes is essential to identify threats and to implement conservation measures that fully encompass their lifecycle.
2. The twaite shad Alosa fallax is an anadromous fish increasingly imperilled across its range due to pollution, harvesting, and impediments to freshwater migration, but little is known about its distribution and movements during its marine life‐phase. Here, the application of acoustic telemetry provided novel insights into the coastal dispersal of twaite shad in the UK and Ireland during 2018–2019, and the freshwater entry of individuals during the 2019 spawning season.
3. Of 73 twaite shad acoustic‐tagged during their upstream migration in the River Severn in May 2018, 58 emigrated from the river. Twelve were subsequently detected 200 km to the south‐west at the Taw–Torridge Estuary between July 2018 and April 2019, where estuarine movements up to 5.8 km inland occurred in summer, winter, and spring. One was subsequently detected in the Munster Blackwater Estuary (Ireland) and then in the River Severn, indicating a minimum movement distance of 950 km. Thirty‐four (59%) of the emigrating individuals from 2018 re‐entered fresh water in the rivers Severn (n = 33) and Wye (n = 2) in April and May 2019.
4. These results suggest year‐round use of estuarine and nearshore habitats by at least a subset of the twaite shad population during their marine phase, providing evidence of potential range overlap between populations that spawn in different areas in the UK and Ireland, which may be facilitated by substantial dispersal. The results also highlight the potential of telemetry for estimating freshwater and marine mortality, and the benefits of sharing detection data across networks.

     

Disentangling the identities and distribution patterns of the introduced beachfleas Orchestia gammarellus and Platorchestia platensis (Crustacea: Amphipoda: Talitridae) in South Africa

Two introduced beachfleas, Orchestia gammarellus and Platorchestia platensis, have been recorded from South Africa, but have been misidentified by some earlier researchers and, prior to this study, each was also known from just a few, scattered observations, such that their true distributions remained obscure. We illustrate both species to clarify the features that identify and distinguish them and determine their true distributions by re-examining historical samples and by collecting new material from estuaries and lagoons along the west and south coasts of South Africa. Adult males of O. gammarellus have slender antennae and characteristic expanded, flattened, oar-like distal segments on pereopod 7. Adult males of P. platensis have the peduncle of antenna 2 strongly swollen and have bulbous, but not flattened, distal segments on pereopod 7. Both species occur under wrack and other debris along the banks of estuaries and sheltered lagoons. Orchestia gammarellus is found only along the south-west coast, in the Berg River Estuary, Langebaan Lagoon and the Diep River Estuary. Previous records from Knysna were misidentifications of P. platensis. Platorchestia platensis is found at one west coast site, Langebaan Lagoon, but is widely distributed from Cape Point eastwards to at least Algoa Bay. Both species share the same habitats as several other native beachfleas and competitive interactions between native and introduced species merit investigation.     

Reactions of phosphorus with sediments in fresh and marine waters

Abstract. The interactions of P with soils and sediments are examined in the context of transport processes from land, through rivers to estuaries and coastal waters. In soil erosion, selective size fractionation and preferential sorption to finer solids is crucial in the transport of P to water courses. Problems in quantifying the sorption affinity and equilibrium phosphate concentration (EPC) of mixtures of different soils and sediments are identified. Riverine transport of P by suspended solids is usually very important and examples of the changes in the amount and composition of particulate P (PP) concentration during storm events are discussed. Increased P content of solids during the first autumn storms, probably reflect the resuspension of accumulated stream bed-deposits. The fate of P in estuaries and their importance as possible long-term sinks of P are discussed. The relatively high concentrations of dissolved P associated with riverine inputs are to some extent buffered by the relatively high concentrations of suspended sediments resulting from tidal flows. Phosphorus may be released during transport to the sea due to decreases in the EPC, increases in salinity and release from bottom sediments as a result of low oxygen conditions.     

Key factors influencing transport of white shrimp (Litopenaeus setiferus) post-larvae into the Ossabaw Sound system, Georgia, USA

We examined conditions under which white shrimp (Litopenaeus setiferus) post‐larvae enter an estuarine channel receiving high freshwater discharge and one receiving negligible discharge in the Ossabaw Sound system of Georgia, USA, during 1997 and 1998. We used surface nets to collect plankton over several 14‐day periods, during which consecutive tows were made at night against the flooding current at stations in the inlet channels. During these sampling periods, additional intensive periods of around‐the‐clock surface and near‐bottom (using a bottom sled) plankton tows were made. Data on oceanographic conditions were obtained from moored instrument arrays and shipboard sampling. We identified three key factors that influenced the densities of post‐larval white shrimp in time and space within the Ossabaw inlet system. The first factor was a critical minimum temperature of coastal waters of 27–28°C. Once the threshold temperature was reached, lunar tidal stage became a key factor when the full duration of the flood tide coincided with darkness during peak ingress. This peak also coincided with an increase in water level within the system by more than 0.2 m, which induced an additional influx of water that reinforces the flood current over the ingress period. Our results suggest that the direction of subtidal currents (into or out of the system) becomes a significant factor in post‐larval ingress when influx of water coincides with the time of favorable temperature conditions and nighttime flood tides.     

Sediment Dynamics and Pollutant Mobility in Rivers (SEDYMO): Assessing Catchment-Wide Emission-Immission Relationships from Sediment Studies. BMBF Coordinated Research Project SEDYMO (2002–2006)

-  DOI: http://dx.doi.org/10.1065/jss2005.11.002 Background and Scope. Apart from their function as indicator or memory for local pollutant inputs, sediments, and especially sediment cores, can be used as a tool for assessing emissionimmission relationships of contaminants on a river-basin scale. Methods. In the framework of the SEDYMO program, source effects, i.e. intensity of sediment erosion under different shear stress, were investigated using a combination of core profile or sampling box studies in laboratory flumes and a mobile in-situ testing device for sediment stability. Results. Calculations of immission risks on downstream areas, e.g., from a three-step approach (substances of concern, areas of concern, areas of risk; Heise et al. 2004), may be directly confirmed from sediment core data, specifically from flood layers, at the target site.     

Effects of hot dry summers on the loss of Atlantic salmon, Salmo salar, from estuaries in South West England

Salmon, Salmo salar L., were radio tagged in four estuaries in South West England. At medium to high summer flows, most salmon entering the river did so within 10 days of tagging. Lower flows were associated with an increased tendency for fish to remain in tidal water for a protracted period, and for those delayed fish to fail to enter the river. The delay was correlated with low freshwater flow, but it was concluded that high water temperature, and in some situations low dissolved oxygen, were likely to be the major influences. The causes of failure to enter the river by the delayed fish include lethally low levels of oxygen in some situations, but a major factor may be missed physiological opportunity. Implications in terms of water resource management, fisheries management and climate change are discussed.     

Description and ecology of larvae of Glossogobius callidus and Redigobius dewaali (Gobiidae) from temperate South African estuaries

This paper describes the morphology and ecology of the larvae and early juveniles of two common gobiids in warm temperate South African estuaries. The early developmental stages of Glossogobius callidus and Redigobius dewaali were collected during plankton surveys in seven permanently open and five intermittently open estuaries along southeastern South Africa. Larval G. callidus have a characteristic ventral row of pigment that extends from the cleithral symphysis along the ventral midline of the tail to the end of the caudal peduncle; notochord flexion takes place at the yolk-sac stage, between 3 and 4 mm BL. Larval R. dewaali are characterized by having two very large stellate melanophores on the ventral surface of the trunk and tail, and internal pigment between the snout and hindgut; notochord flexion takes place between 4 and 6 mm. Body lengths at settlement for G. callidus and R. dewaali are 13 mm and 16 mm, respectively. G. callidus and R. dewaali dominate the larval gobiid catch in warm temperate estuaries. Estuary type and freshwater input played a defining role in the occurrence of larvae of these, often sympatric, species in temperate estuaries. Larval G. callidus occurred in both permanently open and intermittently open estuaries, and were most abundant in mesohaline regions over the spring/summer period. By contrast, larval R. dewaali occurred exclusively in permanently open estuaries and were more prevalent in the fresh and oligohaline regions in autumn. Larvae of both species were more prevalent in freshwater-rich estuaries. Densities of G. callidus and R. dewaali peaked at 101 and 3829 larvae per 100 m³respectively. The usefulness of using the early stages of these gobiids as indicators of estuarine health based on their specific and often prolific estuarine occurrence is discussed.     

江苏省盐城市沿海河口地区水环境调查及对策研究

对盐城入海河口水质进行采样调查,分析排海污染物的类型及其分布状况,严格加强污染物的控制与排放;调整产业结构,促进产业转型;加强相关法规制度的建设与完善;加强科研投入,完善治理技术。