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Lake Victoria provides important ecosystem services including transport, water for domestic and industrial uses and fisheries to about 33 million inhabitants in three East African countries. The lake plays an important role in modulating regional climate. Its thermodynamics and hydrodynamics are also influenced by prevailing climatic and weather conditions on diel, seasonal and annual scales. However, information on water temperature and circulation in the lake is limited in space and time. We use a Regional Oceanographic Model System (ROMS) to simulate these processes from 1st January 2000 to 31st December 2014. The model is based on real bathymetry, river runoff and atmospheric forcing data using the bulk flux algorithm. Simulations show that the water column exhibits annual cycles of thermo-stratification (September-May) and mixing (June-August). Surface water currents take different patterns ranging from a lake-wide northward flow to gyres that vary in size and number. An under flow exists that leads to the formation of upwelling and downwelling regions. Current velocities are highest at the center of the lake and on the western inshore waters indicating enhanced water circulation in those areas. However, there is little exchange of water between the major gulfs (especially Nyanza) and the open lake, a factor that could be responsible for the different water quality reported in those regions. Findings of the present study enhance understanding of the physical processes (temperature and currents) that have an effect on diel, seasonal, and annual variations in stratification, vertical mixing, inshore-offshore exchanges and fluxes of nutrients that ultimately influence the biotic distribution and trophic structure. For instance information on areas/timing of upwelling and vertical mixing obtained from this study will help predict locations/seasons of high primary production and ultimately fisheries productivity in Lake Victoria.

Background: Whilst there is a body of scientific literature relating to the epibiotic macrofauna on large whales, there is little information on the cetaceans in Icelandic waters. Common minke whales, Balaenoptera acutorostrata Lacépède, 1804, are a common sighting between the months of April to November, however, the migration and distribution of the population in winter requires establishing. The present study provides baseline information on the species composition, geographic distribution and abundance of the epibiotic macrofauna on minke whales landed in Icelandic waters and comments on their acquisition., Methods: The epibiotic macrofauna and skin lesions on 185 and 188 common minke whales respectively, landed in Icelandic waters between April to September 2003-2007 were determined. For each whale, the fluke and one lateral side was examined., Results: A total of seven epibiotic species were found: the caligid copepod Caligus elongatus (prevalence (P) = 11.9%, mean intensity (M.I) = 95.5); the pennellid copepod Pennella balaenopterae (P = 10.3%, M.I = 1.6); the cyamid amphipod Cyamus balaenopterae (P = 6.5%, M.I = 37.0); the lepadid cirripedes Conchoderma virgatum (P = 0.5%, M.I = 4.0) and Conchoderma auritum (P = 0.5%, M.I = 1.0), the balanid cirriped Xenobalanus globicipitis (P = 1.6%, M.I = 5.3) and the sea lamprey Petromyzon marinus (P = 2.7%, M.I = 1.0). In addition, the hyperparasitic monogenean Udonella caligorum was found on C. elongatus (P = 6.6%) on 8 of the 22 whales infected with the copepod. No significant relationship was observed between parasite intensity and host body length for either C. balaenopterae or C. elongatus, while the proportion of infected hosts was higher in August-September than earlier in the summer for C. balaenopterae (χ2 = 13.69; p<0.01: d.f.=1) and C. elongatus (χ2 = 28.88; p<0.01: d.f.=1)., Conclusions: The higher prevalence of C. balaenopterae on male whales (χ2 = 5.08; p<0.05: d.f.=1), suggests possible different migration routes by the sexes. A likely explanation of the occurrence of P. marinus attached to the minke whales may be due to the gradually rising sea temperature in the area in recent years. This study represents the first known record of C. elongatus on a cetacean host.

The intense fishing mortality imposed on Atlantic cod in Icelandic waters during recent decades has resulted in marked changes in stock abundance, as well as in age and size composition. Using a molecular marker known to be under selection (Pan I) along with a suite of six neutral microsatellite loci, we analysed an archived data set and revealed evidence of distinct temporal changes in the frequencies of genotypes at the Pan I locus among spawning Icelandic cod, collected between 1948 and 2002, a period characterized by high fishing pressure. Concurrently, temporal stability in the composition of the microsatellite loci was established within the same data set. The frequency of the Pan I(BB) genotype decreased over a period of six decades, concomitant with considerable spatial and technical changes in fishing effort that resulted in the disappearance of older individuals from the fishable stock. Consequently, these changes have likely led to a change in the genotype frequencies at this locus in the spawning stock of Icelandic cod. The study highlights the value of molecular genetic approaches that combine functional and neutral markers examined in the same set of individuals for investigations of the selective effects of harvesting and reiterates the need for an evolutionary dimension to fisheries management.