Description: Atlantic herring (Clupea harengus), an ecologically and economically important species in the northern hemisphere, shows pronounced seasonal migratory behaviour. To follow distinctive migration patterns over hundreds of kilometers between feeding, overwintering and spawning grounds, they are probably guided by orientation mechanisms. We tested whether juvenile spring-spawning Atlantic herring, caught in the western Baltic, use a sun compass for orientation just before they start leaving their hatching area. Fish were randomly divided into two groups, one of them clock-shifted 6 h backwards, to investigate whether they shift their orientation direction accordingly. Individual fish were placed in a circular bowl and their orientation was tested multiple times with the sun as a sole visual orientational cue. Our results show for the first time that juvenile Atlantic herring use a time-compensated sun compass during their migration. Their swimming direction was impaired, but still present, even when the sky was very cloudy, indicating additional orientation capabilities.

Description: In the coming decades, environmental change like warming and acidification will affect life in the ocean. While data on single stressor effects on fish are accumulating rapidly, we still know relatively little about interactive effects of multiple drivers. Of particular concern in this context are the early life stages of fish, for which direct effects of increased CO2 on growth and development have been observed. Whether these effects are further modified by elevated temperature was investigated here for the larvae of Atlantic herring (Clupea harengus), a commercially important fish species. Over a period of 32 days, larval survival, growth in size and weight, and instantaneous growth rate were assessed in a crossed experimental design of two temperatures (10°C and 12°C) with two CO2 levels (400 μatm and 900 μatm CO2) at food levels mimicking natural levels using natural prey. Elevated temperature alone led to increased swimming activity, as well as decreased survival and instantaneous growth rate (Gi). The comparatively high sensitivity to elevated temperature in this study may have been influenced by low food levels offered to the larvae. Larval size, Gi and swimming activity were not affected by CO2, indicating tolerance of this species to projected "end of the century" CO2 levels. A synergistic effect of elevated temperature and CO2 was found for larval weight, where no effect of elevated CO2 concentrations was detected in the 12°C treatment, but a negative CO2 effect was found in the 10°C treatment. Contrasting CO2 effects were found for survival between the two temperatures. Under ambient CO2 conditions survival was increased at 12°C compared to 10°C. In general, CO2 effects were minor and considered negligible compared to the effect of temperature under these mimicked natural food conditions. These findings emphasize the need to include biotic factors such as energy supply via prey availability in future studies on interactive effects of multiple stressors. © 2018 Sswat et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Description: How fisheries will be impacted by climate change is far from understood. While some fish populations may be able to escape global warming via range shifts, they cannot escape ocean acidification (OA), an inevitable consequence of the dissolution of anthropogenic carbon dioxide (CO2) emissions in marine waters. How ocean acidification affects population dynamics of commercially important fish species is critical for adapting management practices of exploited fish populations. Ocean acidification has been shown to impair fish larvae’s sensory abilities, affect the morphology of otoliths, cause tissue damage and cause behavioural changes. Here, we obtain first experimental mortality estimates for Atlantic cod larvae under OA and incorporate these effects into recruitment models. End-of-century levels of ocean acidification (~1100 μatm according to the IPCC RCP 8.5) resulted in a doubling of daily mortality rates compared to present-day CO2 concentrations during the first 25 days post hatching (dph), a critical phase for population recruitment. These results were consistent under different feeding regimes, stocking densities and in two cod populations (Western Baltic and Barents Sea stock). When mortality data were included into Ricker-type stock-recruitment models, recruitment was reduced to an average of 8 and 24% of current recruitment for the two populations, respectively. Our results highlight the importance of including vulnerable early life stages when addressing effects of climate change on fish stocks.

Description: Herring larvae were sampled during the lllLS in the ICES area IVa from 1990 to 1997. Larval growth was determined based on otolith microstructure analysis from larvae of 7-25mm standard length. The data were correlated to the North Atlantic Oscillation (NAO) and the intlow of Atlantic water (AW) at the same period. The study showed a strong correlation between positive NAO years with a higher inflow of AW and subsequently higher larval growth rates. which could be an indication of favorable growth conditions

Description: The usefulness of multivariate morphometrics to distinguish between fed and starved fish larvae was tested on laboratory reared herring larvae (Clupea harengus ). Linear Discriminant Analysis was used to obtain a linear function which separates the two groups of larvae maximally. The calculations were based on twelve morphometric characters, taken individually by means of an image analysing system. A statistically significant separation of fed and starved larvae was obtained. The most important characters and the number of characters necessary for separation are outlined.

Description: One of the effects of fishing is a reduction in average age and size in exploited fish stocks, leading to an increasing proportion of recruit spawners in the stock. Current management practice assumes equal viability of offspring from first time spawners and from repeat spawners, despite the fact that that first time spawners often produce smaller eggs than older spawners. The aim of this EU-project is to follow offspring from families of first time spawning and older cod, reared under identical and semi-natural conditions in marine enclosures (mesocosms). The parental origin of the larvae is identified using microsatellite DNA methodology. The advantage of this approach, compared to traditional laboratory rearing, is that rearing conditions are close to natural conditions, and all larvae are reared in the same environment. This eliminates the tank-to-tank variability often observed in traditional rearing experiments. The fish are reared from hatching, through the larval and juvenile stages, until sexual maturity. Growth rates, survival and nutritional condition will be measured using methods such as RNA/DNA ratio and otolith micro increment analysis. The results will be related to parental origin and quality measures of the eggs. It is intended to incorporate the results into management models for improvement of fishery management strategies. In this paper we will focus on a description of the project

Description: Growth rate has been shown to effect survival and recruitment of marine fishes. How growth rates in the field are affected by larval development and environmental variability is poorly understood. Recent growth rates of sprat larvae, a key species in the Baltic Marine ecosystem, were determined by converting RNA/DNA ratios determined from individual larvae into recent growth based on a laboratory calibrated RNA/DNA temperature growth model. Several factors (larval size, temperature and photoperiod) that may contribute to the observed variability in recent growth sampled in the spawning seasons 2002 through 2004 were analyzed with a variety of models. Best fit was found for the Generalized Additive Models (GAMs). Larval size (dry weight), photoperiod and temperature terms explained 29 % and 36 % of the variability observed in recent growth of sprat larvae in the Baltic Sea, respectively.

Description: To estimate the importance of starvation induced mortality for recruitment of marine fish larvae three distinct methods were applied to determine the nutritional condition of fish larvae in situ. In addition to highly sensitive fluorescence techniques for analysing RNA/DNA ratios and tryptic enzyme activities histological standard methods were used to compare the nutritional status of fish larvae of the genus Vinciguerria (Photichthyidae) caught in two ecologically different areas of the Indian Ocean: In the central Arabian Sea and on the continental shelf of Pakistan. A comparison of the results elaborated by the distinct methods shows a trend towards better nutritional conditions for fish larvae from the offshore region.

Description: Atlantic herring (Clupea harengus), an ecologically and economically important species in the northern hemisphere, shows pronounced seasonal migratory behaviour. To follow distinctive migration patterns over hundreds of kilometers between feeding, overwintering and spawning grounds, they are probably guided by orientation mechanisms. We tested whether juvenile spring-spawning Atlantic herring, caught in the western Baltic, use a sun compass for orientation just before they start leaving their hatching area. Fish were randomly divided into two groups, one of them clock-shifted 6 h backwards, to investigate whether they shift their orientation direction accordingly. Individual fish were placed in a circular bowl and their orientation was tested multiple times with the sun as a sole visual orientational cue. Our results show for the first time that juvenile Atlantic herring use a time-compensated sun compass during their migration. Their swimming direction was impaired, but still present, even when the sky was very cloudy, indicating additional orientation capabilities.