Recruitment variability in vendace, Coregonus albula (L.), and its consequences for vendace harvesting
DisciplineLimnologia ja hydrobiologia
Timo Marjomäki tutkii väitöskirjassaan muikun rekryyttimäärän (=vuosiluokan runsaus ensimmäisen elinvuoden syksyllä tai talvella) vuosien välisen runsaudenvaihtelun ominaispiirteitä ja syitä sekä tarkasteli vaihtelun vaikutuksia kalastukseen ja sen säätelyyn ja toisaalta kalastuksen heijastumista vuosiluokkavaihteluun.This thesis analyses the characteristics and causes of interannual variability in vendace recruitment and its consequences for, and interactions with, vendace harvesting. The interannual variability of prerecruit mortality was high. The daily mortality during the stage 1-3 weeks after hatching was about 10% and in stage 3 weeks - recruitment about an order of magnitude lower. Yet, the stagespecific total mortalities and their variability were of the same order of magnitude. Thus, both stages had potential for determination of the year-class strength. The variability was largely caused by factors external to the population. The synchrony found in the population dynamics of proximal lakes supported this conclusion. Sparse evidence of compensatory density dependence in mortality was found between hatching and recruitment, but good evidence for compensation was found when the whole period from spawning to recruitment was studied.Considerable model and parameter uncertainty concerning the spawning stock-recruitment relationship existed and methodological biases handicapped the analysis. High larval abundance was required to produce an abundant year-class indicating a positive association between the spawning stock and recruitment in low stock level. Symptoms were found of delayed density dependent mortality induced by a previous year-class causing two year cyclicity. However, tendency for two year cyclicity was also detected for a simulated vendace population under high mortality without delayed density dependence. Observations and conceptual modelling revealed that fulltime commercial fishers diminish interannual yield and income variability by increasing fishing effort during stock decline. Fishing was stopped when the revenue per unit effort went below a certain minimum level. Simulation showed that the strategy of moderately adjusting fishing effort gained compromises of almost as high annual revenue as a constant effort strategy but with lower annual variation and lower risk to spawning stock than the strategy aiming at constant revenue. Successful reduction of variability requires lower mean fishing effort than that producing maximal sustainable revenue. No detrimental effects on pelagic fish stocks associable with fishing were found in a case study comparing zones of a lake with different intensities of trawl fishing. The results thus support high compensation capacity in vendace population dynamics. Means for regulating the number of fishing enterprises based on stock productivity was considered to be a precondition for successful attenuation of yield and revenue variability. Threshold control to secure a spawning stock sufficient to ensure sustainable fisheries was also considered necessary. ...
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Lifting the Vendace, Coregonus albula, on the Life Table : Survival, Growth and Reproduction in Different Life-Stages during Very High and Low Abundance Regimes Marjomäki, Timo J.; Valkeajärvi, Pentti; Karjalainen, Juha (Finnish Zoological and Botanical Publishing Board, 2021)We analyzed the variability in vendace population parameters in the context of a life table. Parameters related to growth, fecundity and survival were estimated for post-recruitment (age > 1 growing season) life stages of ...
Genetic-based evaluation of management units for sustainable vendace (Coregonus albula) fisheries in a large lake system Karjalainen, Juha; Sjövik, Rosanna; Väänänen, Tuula; Sävilammi, Tiina; Sundberg, Lotta-Riina; Uusi-Heikkilä, Silva; Marjomäki, Timo J. (Elsevier, 2022)The goal of the processing industry, trade and consumers is to get eco-labelled freshwater fish products from sustainable fisheries into the market as soon as possible. The fourth largest natural lake system in Europe, the ...
Karjalainen, Juha; Tuloisela, Markus; Nyholm, Kristiina; Marjomäki, Timo J. (Finnish Zoological and Botanical Publishing Board, 2021)Depending on their reproductive strategy, different fish species either aggregate or disperse eggs and larvae in their reproductive habitat. Because yolk-sac larvae of vendace (Coregonus albula) disperse widely across the ...
Karjalainen, Juha; Marjomäki, Timo (Wiley-Blackwell Publishing, Inc., 2018)Mating in nature is rarely random, and most fish species have refined mating systems. The vendace (Coregonus albula) is a short‐lived, small‐sized, cold‐water‐adapted pelagic schooling species that is known to spawn in ...
Planktivorous vendace (Coregonus albula) utilise algae-derived fatty acids for biomass increase and lipid deposition Strandberg, Ursula; Hiltunen, Minna; Taipale, Sami; Yeung, Sean; Kankaala, Paula (Wiley-Blackwell Publishing, Inc., 2018)Spatial and seasonal variation in the abundance and composition of phytoplankton and other basal resources (bacteria, terrestrial detritus) influence the availability of essen-tial polyunsaturated fatty acids (PUFA) for ...