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Harbour Seals (harbour + seal)
Selected AbstractsHistological Assessment of Selected Blood Vessels of the Phocid Seals (Northern Elephant and Harbour Seals)ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 3 2010H. Smodlaka Summary Phocid seals exhibit vascular adaptations that allow them to undertake prolonged deep dives. These vascular adaptations are either unique to phocids, or are modified vascular equivalents to those present in terrestrial mammals. One such adaptation, the aortic bulb, is a spherical enlargement of the ascending aorta specific to phocid seals. Its histological make-up consists of a reinforced tunica media with circular and longitudinal layers of elastic fibres. This reinforcement enables multi-axial deformation of the aortic bulb, thus complementing its function as a prominent elastic reservoir or ,windkessel'. A second adaptation, the hepatic sinus, is an asymmetrical dilation of the abdominal portion of the caudal vena cava and accompanying hepatic veins. The hepatic sinus is comprised of a relatively thin tunica media, with a scant smooth muscle component. The bulk of the sinus wall is comprised of tunica adventitia. A third vascular adaptation distinctive to the phocids is the pericardial venous plexus, composed of convoluted veins circumnavigating the perimeter of the heart. Microscopically, these veins have a thick tunica media and also contain valves. Smaller arteries, venules and distinct capillary beds are observed interspersed in-between these veins. It can be hypothesized, that in seals, certain vascular embryonic development may be arrested at an earlier embryonic stage, resulting in these unusual vascular formations. These modifications play a vital role in blood pressure regulation and distribution of oxygenated blood during prolonged deep diving. The purpose of this work was to elucidate the histological aspects of these unique vascular modifications and relate them to specific function. [source] Modelling the impacts of removing seal predation from Atlantic salmon, Salmo salar, rivers in Scotland: a tool for targeting conflict resolutionFISHERIES MANAGEMENT & ECOLOGY, Issue 5 2006J. R. A. BUTLER Abstract, Bioenergetics were used to model the potential impacts on adult Atlantic salmon, Salmo salar L., stocks and rod fisheries of removing harbour seals, Phoca vitulina L., from three rivers of different scales in the Moray Firth, Scotland, viz: the Spey (large), Conon (medium) and Moriston (small). Overall, seals had the greatest impact on the Moriston, where removal of a single animal could increase cumulative catch by 17% during the fishing season. On the Conon and Spey the impacts were negligible, and resulted in increased catches of <1% annually. On all rivers eliminating seal predation had the greatest impact during the spring due to the smaller size of spring salmon sub-stocks. A generalised model of seal removal illustrated that stocks and catches increased by >33% in rivers with monthly rod catches ,10 fish, but declined to <10% for rivers with catches >34 fish. The outputs of the models are qualitative, but provide a management tool for targeting action to resolve seal-salmon fishery conflict. Smaller salmon population units, and spring salmon sub-stocks and fisheries in particular, are most vulnerable to predation. The merit of this approach is discussed regarding the management of Special Areas of Conservation for salmon and seals. [source] Predation by seals on salmonids in two Scottish estuariesFISHERIES MANAGEMENT & ECOLOGY, Issue 3 2001T. J. Carter 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. [source] Using quantitative real-time PCR to detect salmonid prey in scats of grey Halichoerus grypus and harbour Phoca vitulina seals in Scotland , an experimental and field studyJOURNAL OF APPLIED ECOLOGY, Issue 2 2008I. Matejusová Summary 1There is considerable debate over the impact of seal predation on salmonid populations in both the Atlantic and Pacific oceans. Conventional hard-part analysis of scats has suggested that salmonids represent a minor component of the diet of grey seals (Halichoerus grypus) and harbour seals (Phoca vitulina) in the UK. However, it is unclear whether this is an accurate reflection of the diet or due to methodological problems. To investigate this issue, we applied quantitative PCR (qPCR) to examine the presence of salmonids in the diet of seals in the Moray Firth, UK, during the summers of 2003 and 2005. 2Two qPCR assays were designed to detect Atlantic salmon Salmo salar and sea trout Salmo trutta DNA in field samples and experimentally spiked scats. The proportion of scats sampled in the field that were positive for salmonid DNA was low (ª10%). However, the DNA technique consistently resulted in more positive scats than when hard-part analysis was used. 3An experimental study using spiked scat material revealed a highly significant negative relationship between Ct values obtained from the Atlantic salmon qPCR assay and the proportion of Atlantic salmon material added to scats. The Ct value denotes the cycle number at which the increasing fluorescence signal of target DNA crosses a threshold value. Ct values from field-collected seal scats suggested they contained a very low concentration of salmonid remains (1,5%) based on an approximate calibration curve constructed from the experimental data. 4Synthesis and applications. The qPCR assay approach was shown to be highly efficient and consistent in detection of salmonids from seal scats, and to be more sensitive than conventional hard-parts analysis. Nevertheless, our results confirm previous studies indicating that salmonids are not common prey for seals in these Scottish estuaries. These studies support current management practice, which focuses on control of the small number of seals that move into key salmonid rivers, rather than targeting the larger groups of animals that haul-out in nearby estuaries. [source] Assessing the potential impact of salmon fisheries management on the conservation status of harbour seals (Phoca vitulina) in north-east ScotlandANIMAL CONSERVATION, Issue 1 2007P. M. Thompson Abstract Conservation efforts are often constrained by uncertainty over the factors driving declines in marine mammal populations. In Scotland, there is concern over the potential impact of unrecorded shooting of seals, particularly where this occurs near Special Areas of Conservation. Here, we show that the abundance of harbour seals Phoca vitulina in the Moray Firth, north-east Scotland, declined by 2,5% per annum between 1993 and 2004. Records from local salmon fisheries and aquaculture sites indicated that 66,327 harbour seals were shot each year between 1994 and 2002. Matrix models and estimates of potential biological removal indicate that this level of shooting is sufficient to explain observed declines. Nevertheless, uncertainty over the number and identity of seals shot means that other factors such as changes in food availability may be contributing. Recent conservation measures markedly reduced the recorded levels of shooting in 2003 and 2004. In 2005, a coordinated management plan was developed to protect salmon fisheries interests while minimizing impacts on local seal populations. Comprehensive monitoring of future population trends and improved regulation of culls are now required to provide more robust assessments of the impact of human persecution on harbour seal populations in the Moray Firth and in other parts of the UK. [source] Harbour seal movements and haul-out patterns: implications for monitoring and managementAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2009Louise Cunningham Abstract 1.Compliance with conservation legislation requires knowledge on the behaviour, abundance and distribution of protected species. Seal life history is characterized by a combination of marine foraging and a requirement to haul out on a solid substrate for reproduction and moulting. Thus understanding the use of haul out sites, where seals are counted, as well as their at-sea movements is crucial for designing effective monitoring and management plans. 2.This study used satellite transmitters deployed on 24 harbour seals in western Scotland to examine movements and haul-out patterns. 3.The proportion of time harbour seals spent hauled out (daily means of between 11 and 27%) varied spatially, temporally and according to sex. The mean haul-out duration was 5,h, with a maximum of over 24,h. 4.Patterns of movement were observed at two geographical scales; while some seals travelled over 100,km, 50% of trips were within 25,km of a haul-out site. These patterns are important for the identification of a marine component to designated protected areas for the species. 5.On average seals returned to the haul-out sites they last used during 40% of trips, indicating a degree of site fidelity, though there was wide variation between different haul-out sites (range 0% to >75%). 6.Low fidelity haul-out sites could form a network of land-based protected areas, while high fidelity sites might form appropriate management units. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||