Räime Clupea harengus membras varajaste elustaadiumide ökoloogia Läänemere kirdeosas

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Läänemeres elav räim (Clupea harengus membras) on Atlandi heeringa (Clupea harengus L.) kääbustunud vorm, kes on kohastunud elama riimveelise Läänemere väga varieeruvates keskkonnatingimustes. Morfoloogiliste tunnuste alusel eristatakse Läänemere räimel kahte erinevat sesoonset kudemistüüpi – kevad ja sügiskudu räim. Käesolevas töös on analüüsitud räimevastsete toitumisaktiivsuse ja nende sooltorust leitud saakloomade dünaamikat ning leitut on seostatud valitud eluta- ja eluskeskkonna teguritega. Räimevastsete toidus oli valdavaks liigiks aerjalgne Eurytemora affinis, kusjuures kõikide teiste liikide isendeid leiti vaid juhuslikult. Räimevastete toitumisaktiivsus seostus erinevate keskkonnateguritega, ning seosed varieerusid sõltuvalt räimevastse arengust. Kalade varajaste elustaadiumite arvukuse dünaamika uuringute üks praktilisi väljundeid on juba möödunud sajandist alates seostunud kalavaru täiendi suuruse hindamisega. Vaatamata järjepidevatele pingutustele ei ole selles valdkonnas väga suuri edusamme saavutatud. Me leidsime, et suurte räimevastete arvukus seostus usaldusväärselt räimevaru täiendi arvukusega, ja on seega oluline kalandusandmetest mitte-sõltuv lisategur hindamaks kujuneva räimevaru suurust lähitulevikus. Käesolevas töös käsitletud üheksateistkümne Liivi lahe kevadräime varajaste elustaadiumidega seonduva teguri pika-ajalisel analüüsil (perioodil 1957-2010) selgitasime a) kas ja millal on toimunud radikaalsed pöördumatud muutused (ehk nn. režiiminihked), b) millised tegurid või nende kombinatsioon mõjutavad nimetatud muutusi ning c) kas režiiminihked süsteemis toimusid sünkroonselt räime varajaste elustaadiumidega. Leitu põhjal võib järeldada, et ökosüsteemis saab eristada kahte erinevat seisundit. Esimene neist kestis perioodil 1957–1985, millele järgnes sujuv, pikka aega kestnud üleminek (1986–1991) uude seisundisse, alates 1992 kuni tänapäevani. Sealjuures, tugevaim signaal keskkonnaseisundi muutustele pärines eluta keskkonnast ning seostus mere termilise režiimi muutusega. Analüüsi kaasatud fenoloogiliste ning eluskeskkonna komponente koondavate aegridade olulisus režiiminihkele oli seega vähemtähtis.Baltic herring (Clupea harengus membras) is Atlantic herring (Clupea harengus L. 1758) sub-species that is adapted to the prevailing spatio-temporally varying heterogeneous environmental conditions of the Baltic Sea. On the basis of morphometric and meristic characters, two groups – spring and autumn spawners – were distinguished in the Baltic Sea. In the present thesis, feeding ecology of the larval spring-spawning herring was studied in relation to selected abiotic and biotic parameters. The copepod Eurytemora affinis was the strongly dominating dietary item during all years while other prey was ingested only sporadically. Feeding activity of herring larvae was affected by different environmental variables and the relationships varied among the size classes of herring larvae. We have found that the abundance of large larvae correlated well with the year class strength of the Gulf of Riga (GoR) spring spawning herring population. This should be considered as an important fisheries independent finding in practical terms as it allows preliminary estimations to be made much earlier than the availability of the stock assessment results. The multivariate shiftogram approach by pooling nineteen different herring early life-history stages relevant variables was applied to identify a) whether and when the abrupt changes (also called as regime shifts) take place in the herring-relevant data series in the GoR ecosystem, b) which factors or their combination are responsible for the observed ecosystem-level changes and c) whether changes at the ecosystem level appeared synchronously with those observed in phenology and abundance-related single time series of larval herring. It appeared that two distinct ecosystem states of the GoR could be identified. The first state occurred between 1957–1985, followed by a smooth transition period, lasting from 1986–1991 and has resulted in a new ecosystem phase since 1992 onwards. The GoR ecosystem seem to be mainly regulated by abiotic conditions, especially those related to the thermal regime (sea surface temperature in spring and summer, winter air temperature and timing of ice retreat) while phenological and biotic time-series (timing of maximum abundance of herring larvae, onset of herring larvae and mean abundance of Eurytemora affinis adults) had a substantially minor role

Outlier Loci Detect Intraspecific Biodiversity amongst Spring and Autumn Spawning Herring across Local Scales

Herring, Clupea harengus, is one of the ecologically and commercially most important species in European northern seas, where two distinct ecotypes have been described based on spawning time; spring and autumn. To date, it is unknown if these spring and autumn spawning herring constitute genetically distinct units. We assessed levels of genetic divergence between spring and autumn spawning herring in the Baltic Sea using two types of DNA markers, microsatellites and Single Nucleotide Polymorphisms, and compared the results with data for autumn spawning North Sea herring. Temporally replicated analyses reveal clear genetic differences between ecotypes and hence support reproductive isolation. Loci showing non-neutral behaviour, so-called outlier loci, show convergence between autumn spawning herring from demographically disjoint populations, potentially reflecting selective processes associated with autumn spawning ecotypes. The abundance and exploitation of the two ecotypes have varied strongly over space and time in the Baltic Sea, where autumn spawners have faced strong depression for decades. The results therefore have practical implications by highlighting the need for specific management of these co-occurring ecotypes to meet requirements for sustainable exploitation and ensure optimal livelihood for coastal communitie

Essential coastal habitats for fish in the Baltic Sea

Many coastal and offshore fish species are highly dependent on specific habitat types for population maintenance. In the Baltic Sea, shallow productive habitats in the coastal zone such as wetlands, vegetated flads/lagoons and sheltered bays as well as more exposed rocky and sandy areas are utilized by fish across many life history stages including spawning, juvenile development, feeding and migration. Although there is general consensus about the critical importance of these essential fish habitats (EFH) for fish production along the coast, direct quantitative evidence for their specific roles in population growth and maintenance is still scarce. Nevertheless, for some coastal species, indirect evidence exists, and in many cases, sufficient data are also available to carry out further quantitative analyses. As coastal EFH in the Baltic Sea are often found in areas that are highly utilized and valued by humans, they are subjected to many different pressures. While cumulative pressures, such as eutrophication, coastal construction and development, climate change, invasive species and fisheries, impact fish in coastal areas, the conservation coverage for EFH in these areas remains poor. This is mainly due to the fact that historically, fisheries management and nature conservation are not integrated neither in research nor in management in Baltic Sea countries. Setting joint objectives for fisheries management and nature conservation would hence be pivotal for improved protection of EFH in the Baltic Sea. To properly inform management, improvements in the development of monitoring strategies and mapping methodology for EFH are also needed. Stronger international cooperation between Baltic Sea states will facilitate improved management outcomes across ecologically arbitrary boundaries. This is especially important for successful implementation of international agreements and legislative directives such as the Baltic Sea Action Plan, the Marine Strategy Framework Directive, the Habitats Directive, and the Maritime Spatial Planning Directive, but also for improving the communication of information related to coastal EFH among researchers, stakeholders, managers and decision makers. In this paper, efforts are made to characterize coastal EFH in the Baltic Sea, their importance and the threats/pressures they face, as well as their current conservation status, while highlighting knowledge gaps and outlining perspectives for future work in an ecosystem-based management framework. (C) 2018 Elsevier Ltd. All rights reserved.Peer reviewe

Dual impact of temperature on growth and mortality of marine fish larvae in a shallow estuarine habitat

High individual growth and mortality rates of herring Clupea harengus membras and goby Pomatoschistus spp. larvae were observed in the estuarine habitat of the Gulf of Riga, Baltic Sea. Both instantaneous mortality (0.76–1.05) as well as growth rate (0.41–0.82 mm day-1) of larval herring were amongst highest observed elsewhere previously. Mortality rates of goby larvae were also high (0.57–1.05), while first ever data on growth rates were provided in this study (0.23–0.35 mm day-1). Our study also evidenced that higher growth rate of marine fish larvae did not result in lower mortalities. We suggest that high growth and mortality rates primarily resulted from a rapidly increasing and high (> 18 °C) water temperature that masked potential food-web effects. The explanation for observed patterns lies in the interactive manner temperature contributed: i) facilitating prey production, which supported high growth rate and decreased mortalities; ii) exceeding physiological thermal optimum of larvae, which resulted in decreased growth rate and generally high mortalities. Our investigation suggests that the projected climate warming may have significant effect on early life history stages of the dominating marine fish species inhabiting shallow estuarie

Trawler Engine Size Had No Effect on Baltic Herring Size/Age Structure: An Experimental Study in the Gulf of Riga, Baltic Sea

The Gulf of Riga stock of Baltic herring (Clupea harengus membras L.) has been maintained through several management tools. One such tool is the restriction of vessels’ main engine power (<221 kW). This restriction was implemented in the early 1990s and is based on the vessel types available in the area and on the assumption that the gear size used in trawl fishery depends on the vessel size (power). In the current study, we compared vessels with different engine powers using the same gears currently allowed in the gulf, to identify whether vessel power had any relation to catch structure. The results showed that engine power did not explain the differences in catch structure, which were more dependent on season and depth of water. Easing the power restriction of the trawl vessels in the Gulf of Riga will most likely not have a major negative impact on the sustainable management of the herring population. However, vessels with higher engine power should not use larger trawl gear than is currently used in the gulf

Trawler Engine Size Had No Effect on Baltic Herring Size/Age Structure: An Experimental Study in the Gulf of Riga, Baltic Sea

The Gulf of Riga stock of Baltic herring (Clupea harengus membras L.) has been maintained through several management tools. One such tool is the restriction of vessels’ main engine power (<221 kW). This restriction was implemented in the early 1990s and is based on the vessel types available in the area and on the assumption that the gear size used in trawl fishery depends on the vessel size (power). In the current study, we compared vessels with different engine powers using the same gears currently allowed in the gulf, to identify whether vessel power had any relation to catch structure. The results showed that engine power did not explain the differences in catch structure, which were more dependent on season and depth of water. Easing the power restriction of the trawl vessels in the Gulf of Riga will most likely not have a major negative impact on the sustainable management of the herring population. However, vessels with higher engine power should not use larger trawl gear than is currently used in the gulf

Maturation at a young age and small size of European smelt (Osmerus eperlanus): A consequence of population overexploitation or climate change?

Abstract Age of fish at maturation depends on the species and environmental factors but, in general, investment in growth is prioritized until the first sexual maturity, after which a considerable and increasing proportion of resources are used for reproduction. The present study summarizes for the first the key elements of the maturation of European smelt (Osmerus eperlanus) young of the year (YoY) in the North-eastern Gulf of Riga (the Baltic Sea). Prior to the changes in climatic conditions and collapse of smelt fishery in the 1990s in the Gulf of Riga, smelt attained sexual maturity at the age of 3–4 years. We found a substantial share (22%) of YoY smelt with maturing gonads after the collapse of the smelt fisheries. Maturing individuals had a significantly higher weight, length and condition factor than immature YOY, indicating the importance of individual growth rates in the maturation process. The proportion of maturing YoY individuals increased with fish size. We discuss the factors behind prioritizing reproduction overgrowth in early life and its implications for the smelt population dynamics

Figure 4

<p>Long term dynamics of biotic variables as mean abundance of copepod <i>nauplii</i> (a), mean abundance of adult <i>Eurytemora affinis</i> (b), maximum abundance of female <i>Eurytemora affinis</i> and nauplii (c), number of herring recruitment (d), mean abundance of herring larvae (e). Dotted lines indicate the position of the shift detected in a single variables by shiftogram analyses. Empty dots denote the year when missing value replacement procedure was applied.</p

Reproduction, Ontogeny and Recruitment

This chapter reviews and synthesises knowledge on reproduction and recruitment in estuary-dependent and estuary-associated fishes. Resident and migrating species (anadromous, catadromous and amphidromous) capitalise on estuarine productivity to ensure successful reproduction. The variable estuarine environments are challenging, but many species are adapted to reproduce in and recruit to these rich and productive ecosystems. Modes of reproduction, including utilisation of nursery habitat by early-life stages and behavioural adaptations, are described, as are contributions of adults to recruitment. Scales and patterns of environmental, hydrodynamic and biological processes that control ingress or retention of early-life stages in estuaries are reviewed. Recruitment processes in estuary-associated species are highly dynamic, depend on fish behaviour, are variably dependent on adult abundance and are difficult to predict. Case studies and global examples are presented to highlight the diversity of strategies and factors that ensure reproductive success