Interactions between seals and atlantic salmon (Salmo salar) in rivers and estuaries of Newfoundland and Labrador

The causes for the decline in some Atlantic salmon (Salmo salar) stocks in eastern Canada are uncertain but many resource users consider predation by seals in rivers and estuaries to be a contributing factor. During the 1990s, the Department of Fisheries and Oceans (DFO) received reports from resource users of increased seal-salmon interactions on several rivers in Newfoundland and Labrador. To address these concerns, semi-directed interviews (n=57) were conducted from 2004 to 2006 with resource users on 29 rivers throughout the Province. Respondents were requested to comment on any changes in the relative abundance, timing of migration, habitat use and foraging behavior of seals frequenting the area during the last 5 years (2000-2005), during the 1990s, and 1980-1990. Starting in the mid 1990s, harp seals (Pagophilus groenlandicus) increased their residency time in some rivers and estuaries by 1-3 months. Potential harp seal predation on salmon was considered to be high for half of the 16 rivers frequented by harp seals on the northeast coast of Newfoundland and southern coast of Labrador. In 6 of these rivers, the reported increase in the occurrence and relative abundance of seals was concurrent with the migration or spawning of pelagic forage fish (e.g. capelin) in the area. One river was influenced by variable local ice conditions during late spring, and one river was affected by both of these conditions. The presence and relative abundance of harbor seals (Phoca vitulina) in some rivers and estuaries increased during the 1990s; potential predation was considered to be high on 10/24 of these rivers. In the case of grey seals (Halichoerus grypus), relative abundance has increased in some Labrador rivers since 2000, with 3 rivers considered to have high potential predation. -- A directed harp seal diet study was carried out in 2005 and 2006 on the Campbellton River, one of the rivers considered to have high potential for predation during the smolt salmon run. A total of 122 seal stomachs were analyzed and no evidence was found that seals were feeding on salmon. Capelin, an energy-rich forage fish, was the major prey component in both years. Although information from resource users suggested that the potential for harp seal predation on salmon had increased since the mid-to late 1990s, the diet component of the project indicated that they were not necessarily feeding on salmon when these species co-occurred. Similar investigations on other seal species and rivers with high potential will be necessary before it can be concluded that harp, grey or harbour seal predation of salmon stocks is not occurring

Metabolome Analysis Reveals Betaine Lipids as Major Source for Triglyceride Formation, and the Accumulation of Sedoheptulose during Nitrogen-Starvation of Phaeodactylum tricornutum.

Oleaginous microalgae are considered as a promising resource for the production of biofuels. Especially diatoms arouse interest as biofuel producers since they are most productive in carbon fixation and very flexible to environmental changes in the nature. Naturally, triacylglycerol (TAG) accumulation in algae only occurs under stress conditions like nitrogen-limitation. We focused on Phaeodactylum strain Pt4 (UTEX 646), because of its ability to grow in medium with low salinity and therefore being suited when saline water is less available or for wastewater cultivation strategies. Our data show an increase in neutral lipids during nitrogen-depletion and predominantly 16:0 and 16:1(n-7) accumulated in the TAG fraction. The molecular species composition of TAG suggests a remodeling primarily from the betaine lipid diacylglyceroltrimethylhomoserine (DGTS), but a contribution of the chloroplast galactolipid monogalactosyldiacylglycerol (MGDG) cannot be excluded. Interestingly, the acyl-CoA pool is rich in 20:5(n-3) and 22:6(n-3) in all analyzed conditions, but these fatty acids are almost excluded from TAG. Other metabolites most obviously depleted under nitrogen-starvation were amino acids, lyso-phospholipids and tricarboxylic acid (TCA) cycle intermediates, whereas sulfur-containing metabolites as dimethylsulfoniopropionate, dimethylsulfoniobutyrate and methylsulfate as well as short acyl chain carnitines, propanoyl-carnitine and butanoyl-carnitine increased upon nitrogen-starvation. Moreover, the Calvin cycle may be de-regulated since sedoheptulose accumulated after nitrogen-depletion. Together the data provide now the basis for new strategies to improve lipid production and storage in Phaeodactylum strain Pt4.Open-Access-Publikationsfonds 2016peerReviewe