Tiit Raid
University of Tartu
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Featured researches published by Tiit Raid.
Population Ecology | 2011
Michele Casini; Georgs Kornilovs; Massimiliano Cardinale; Christian Möllmann; Wlodzimierz Grygiel; Patrik Jonsson; Tiit Raid; Juha Flinkman; Valeriy Feldman
For the first time an international acoustic survey dataset covering three decades was used to investigate the factors shaping the spatial and temporal patterns in the condition of sprat and herring in the Baltic Proper. Generalized additive models showed that the spatial and temporal fluctuations in sprat density have been the main drivers of the spatio-temporal changes of both sprat and herring condition, evidencing intra- and inter-specific density dependence mediated by the size and distribution of the sprat population. Salinity was also an important predictor of herring condition, whereas temperature explained only a minor part of sprat model deviance. Herring density was an additional albeit weak significant predictor for herring condition, evidencing also intra-specific density dependence within the herring population. For both species, condition was high and similar in all areas of the Baltic Proper until the early 1990s, coincident with low sprat densities. Afterwards, a drop in condition occurred and a clear south–north pattern emerged. The drop in condition after the early 1990s was stronger in the northern areas, where sprat population increased the most. We suggest that the increase in sprat density in the northern areas, and the consequent spatial differentiation in clupeid condition, have been triggered by the almost total disappearance of the predator cod from the northern Baltic Proper. This study provides a step forward in understanding clupeid condition in the Baltic Sea, presenting evidence that density-dependent mechanisms also operate at the spatial scale within stock units. This stresses the importance of spatio-temporal considerations in the management of exploited fish.
Hydrobiologia | 2004
Jonne Kotta; Mart Simm; Ilmar Kotta; Inga Kanošina; Kalle Kallaste; Tiit Raid
Phytoplankton, mesozooplankton, mysids and fish larvae were studied during 15–29 annual cycles measured weekly to monthly in Parnu Bay, the Gulf of Riga. The monthly variability of the biological data was related to temperature, ice conditions, salinity, influx of nutrients, the North Atlantic Oscillation (NAO) index, cloudiness and solar activity. Phytoplankton development was mainly a function of the NAO index. For the whole study period the abundance of zooplankton increased with increasing water temperature and solar activity. Significant correlations between phytoplankton and zooplankton densities were found until 1990. After the invasion of the predatory cladoceran Cercopagis pengoi in 1991, the zooplankton community was likely to be regulated by the introduced species rather than phytoplankton dynamics. The increased abundances of rotifers and copepods triggered the increase in mysid densities. The development of herring larvae was positively affected by the high density of copepods and rotifers but also by increased eutrophication. Until 1990 there was no significant relationship between the density of zooplankton and herring larvae. A negative relationship between the density of zooplankton and herring larvae in the 1990s suggests that the major shift in zooplankton community resulted in food limitation for herring larvae. The results indicated that (1) atmospheric processes in the northern Atlantic explain a large part of the interannual variation of the local phytoplankton stock, (2) trophic interactions control the development of pelagic communities at higher trophic levels, and (3) the introduction of an effective intermediate predator has repercussions for the whole pelagic food web in Parnu Bay.
Annales Zoologici Fennici | 2011
Leili Järv; Jonne Kotta; Ilmar Kotta; Tiit Raid
To date the studies that link community structure of benthic invertebrates with fish feeding are rare as well as factors that are behind this feeding selectivity are poorly known. In this study, we related invertebrate species composition, their dominance structure and fish biological characteristics to the feeding selectivity and overlap of the native flounder, perch and the invasive round goby in Muuga Bay, the Baltic Sea. Species composition and proportion of benthic invertebrates in the diet of fishes differed from what was available in the field. Except for the round goby, the studied fishes preferred small and mobile invertebrates over large bivalves. However, diet of the studied species, namely the round goby and flounder overlapped. Besides, perch preyed on young stages of the round goby indicating that the introduction of round goby may negatively affect flounder but positively perch.
Hydrobiologia | 2016
Timo Arula; Tiit Raid; Mart Simm; Henn Ojaveer
Processes occurring during early life-history stages influence the year-class abundance of marine fish. We found that the abundance of 1-year-old spring spawning herring is statistically significantly determined by the number of post-flexion herring larvae in the Gulf of Riga (Baltic Sea). The abundance of consecutive developmental stages of larvae: yolk-sac, pre-flexion, flexion and post-flexion strongly correlated with each other, indicating that factors which already influence the yolk-sac stage are important in determining the abundance of post-flexion herring larvae. Winter air temperature before spawning determined the timing of maximum abundance of pre-flexion herring larvae, but not their main prey: copepod nauplii, implying that different mechanisms governing major preconditions for the formation of year-class strength. The abundance of post-flexion larvae displayed a potential dome-shaped relationship with sea surface temperature experienced after hatching. We suggest that increased summer temperatures, which exceed the physiological optimum negatively, affect the survival of post-flexion herring larvae. Overall, future climate warming poses an additional risk to larval herring survival and this may lead to a reduction in those herring stock which rely on recruitment from shallow coastal areas.
Hydrobiologia | 2006
Tiit Raid; Olavi Kaljuste
The Baltic herring is one of the key elements of the pelagic ecosystem of the Baltic Sea, being of the most important commercial species of the sea. The structure and dynamics of herring populations (stocks) have been assessed and managed on international level since 1970s. Since 1990, all local herring populations have been combined and assessed as one stock (Central Baltic Herring in Sub-divisions 25–29 and 32). However, the continuously decreasing trend in stock biomass throughout almost 30-years period of observations indicates the failure of the stock management implementation of the scientific advice. The separate assessments of different stocks and results of hydro-acoustic surveys of different sub-units (herring in Sub-divisions 25–27, Sub-divisions 28, 29 and 32 and the Gulf of Riga herring) have revealed rather different situation within combined assessment unit: e.g. fishing mortality of the Gulf of Riga herring has decreased while a sharp increase in mortality is observed in the herring stocks of the North-eastern Baltic (Sub-divisions 28, 29 and 32). At the same time stock abundance and biomass of the Gulf of Riga herring have increased to record high in early 2000s allowing also higher catches. It is concluded that only separate analytical assessment of local populations combined with regular acoustical surveys and following different protection measures have proved to be a successful way in managing the herring stocks. Joint assessment and management of several populations with different structure and dynamics as one combined stock do not allow revealing the real situation and trends in its parts.
international geoscience and remote sensing symposium | 2015
Ülo Suursaar; Tiit Raid; Markus Vetemaa; Toomas Saat
Wave action, turbidity-connected light availability and sediment relocation are among the most important factors forming nearshore benthic habitats. Based on long-term wave hindcasts (1966-2014) and empirical waves-turbidity relationships, hydrodynamically induced shallow sea turbidity component was reconstructed in the differently exposed Estonian coastal sections; possible influences on habitats, including spawning and nursery grounds of littoral fish were discussed. Although both wave and turbidity conditions have undergone some cyclic variations and marks of some violent storms can be found in coastal environment, it was not possible to associate any general shifts in the habitats to variations in long-term wind and wave climates.
Canadian Journal of Fisheries and Aquatic Sciences | 2004
Sanna Rönkkönen; Evald Ojaveer; Tiit Raid; Markku Viitasalo
Marine Ecology Progress Series | 2009
Massimiliano Cardinale; Christian Möllmann; Valerio Bartolino; Michele Casini; Georgs Kornilovs; Tiit Raid; Piotr Margonski; Anna Grzyb; Jari Raitaniemi; Tomas Gröhsler; Juha Flinkman
Ices Journal of Marine Science | 2015
Margit Eero; Joakim Hjelm; Jane Behrens; Kurt Buchmann; Massimiliano Cardinale; Michele Casini; Pavel Gasyukov; Noél Holmgren; Jan Horbowy; Karin Hüssy; Eskild Kirkegaard; Georgs Kornilovs; Uwe Krumme; Friedrich W. Köster; Rainer Oeberst; Maris Plikshs; Krzysztof Radtke; Tiit Raid; Joern O. Schmidt; Maciej T. Tomczak; Morten Vinther; Christopher Zimmermann; Marie Storr-Paulsen
Fish and Fisheries | 2016
Didier Gascuel; Marta Coll; Clive Fox; Sylvie Guénette; Jérôme Guitton; Andrew Kenny; Leyla Knittweis; J. Rasmus Nielsen; G.J. Piet; Tiit Raid; Morgane Travers-Trolet; Samuel Shephard