Papers by Timo J Marjomäki
Ecology of Freshwater Fish, Apr 26, 2022
This is a self-archived version of an original article. This version may differ from the original... more This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details.
Ices Journal of Marine Science, Dec 31, 2021
Perch (Perca fluviatilis) is an important prey species of the great cormorant (Phalacrocorax carb... more Perch (Perca fluviatilis) is an important prey species of the great cormorant (Phalacrocorax carbo sinensis) in the coastal waters of the northern Baltic Sea. The annual predation mortality caused by cormorants was estimated based on the consumed numbers of perch in relation to the abundance of perch in vulnerable age groups in the sea. We used existing stock assessment data (Archipelago Sea) or a simple population model in other areas (Gulf of Finland, Bothnian Sea, and Quark), based on commercial and recreational perch catches, and estimated fishing and natural mortalities, with distributions describing our understanding about the likelihood of different values for every variable. The median predation mortality was -% annually, depending on the sea area. The area-specific % likelihood limits ranged from to % annually. Compared to a recent perch tagging study in the Quark, the cormorant-induced mortality estimates were considerably lower, but the likelihood distributions partly overlapped. The results were sensitive to the estimated number of vulnerable perch in the population, which in turn largely depends on the natural mortality in young perch age groups.
Aquatic Conservation: Marine and Freshwater Ecosystems
The decline of endangered freshwater pearl mussel (FPM, Margaritifera margaritifera) has been att... more The decline of endangered freshwater pearl mussel (FPM, Margaritifera margaritifera) has been attributed to juvenile mortality caused by low concentrations of dissolved oxygen in the stream substrate resulting from fine sediments (siltation) that impede water exchange in the interstitial microhabitat of juveniles. If low oxygen concentration causes recruitment failure of FPMs, knowledge on the oxygen tolerance of juvenile FPMs is essential for the conservation of the species, as it will justify conservation efforts improving water exchange in the bottom gravel. However, the tolerance of low oxygen of FPM juveniles has not been directly studied. Juvenile FPMs (9–11 months old) were exposed in individual chambers equipped with optical oxygen measurement spots to different levels of dissolved oxygen at 19 °C and their viability was monitored for 10 days to assess the acute oxygen tolerance of juvenile FPMs. Oxygen concentration ranged between 8.8 and 6.2 mg L−1 in the high oxygen treat...
Riista- ja kalatalouden tutkimuslaitos, 1997
ICES Journal of Marine Science, 2020
The number of cormorants has rapidly increased in the northernmost Baltic Sea. In 2018, 50 km × 5... more The number of cormorants has rapidly increased in the northernmost Baltic Sea. In 2018, 50 km × 50 km ICES catch rectangle 55H1 had 3140 breeding pairs. To estimate the predation effect of cormorants on perch populations, we Passive Integrated Tags tagged 1977 perch and 9.9% of tags were found. The median instantaneous cormorant-induced mortality during the breeding time, with consumption by non-breeding individuals, was estimated at 0.23 and at 0.35 during the whole residing period. We estimated with a yeild-per-recruit model that the long-term maximum loss of perch yield of tagged sub-population would be at 80% probability interval 32–67%, and when extended to the entire 55H1, 10–33%, respectively. The cormorants’ share of the >2-year-old perch biomass and production would be 8%, while that of other natural mortality would be 63% and that of fishing 29% in 55H1. The yield-per-recruit-results should be interpreted as an estimate of maximum cormorant effect because the dependence...
Hydrobiologia, 2016
Hatching time (HT) of autumn-spawning fishes depends strongly on the egg incubation temperature a... more Hatching time (HT) of autumn-spawning fishes depends strongly on the egg incubation temperature and especially on the warming of water in spring, which synchronizes the hatching with ice-out despite the large inter-annual variability in spring phenology. However, the relative roles of genetic and environmental effects on the HT have rarely been explored. We studied experimentally the parental effects on the HT and size of vendace (Coregonus albula (L.)) and whitefish (C. lavaretus L.) larvae under short and long winter conditions using a full-factorial breeding design. Both parents significantly affected the HT of vendace, mostly by additive genetic effects, and the difference between short and long winter treatment was also significant. In whitefish, the female × male interaction was significant, implying non-additive genetic effects. The maximum range of the HT of eggs between parent pairs within certain winter condition was 3 weeks and was clearly lower than the potential range for the temperature-adjusted HT. The size of eggs or hatched larvae did not correlate with the HT in either of the species. The variation in HT between eggs from different parents creates a basis for genetic adaptation to climate change and for local adaption of populations in their thermal environments.
Jyväskylän yliopiston bio- ja ympäristötieteiden laitoksen tiedonantoja, 2020
Riista- ja kalatalouden tutkimuslaitos, 1997
Boreal Environment Research, 2004
We studied the swimming speed and vertical distribution of fish under ice from March to April and... more We studied the swimming speed and vertical distribution of fish under ice from March to April and in open water in August. Fish were surveyed with a downward facing stationary 120 kHz split beam echo-sounder in a boreal lake. A commercial trace tracking software was used to estimate the depth, speed and size of fish. Most fish in the study area were smelt (Osmerus eperlanus) and vendace (Coregonus albula). In March and April, fish were detected under the ice around the clock, whereas in August only a few fish were detected during daytime. Fish were typically detected between 12 and 19 m depth and they swam from 5 to 50 cm s-1 i.e. 0.5 to 3 body lengths s-1. The effect of sunrise and sunset on the under-ice swimming depth and speed became more marked with increasing day length. In summer, the effect on depth was not so evident. In March-April there was a shift towards day activity, which persisted in August. Changing illumination seemed to account for most variation in the swimming depth and speed of fish.
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Papers by Timo J Marjomäki