Bioenergetics modeling of the annual consumption of zooplankton by pelagic fish feeding in the Northeast Atlantic

Comparative Analysis of Fatty Acid Bioaccessibility in Commercial Marine Oil Supplements: An In Vitro Integrated Analytical Study

Zooplankton such as copepods and krill are currently used to produce marine oil supplements, with the aim of helping consumers achieve the recommended intake of n-3 long chain polyunsaturated fatty acids (n-3 LC-PUFAs). Oils from lower trophic levels differ from fish oil in the distribution of lipids into different classes, and this can influence the bioaccessibility of fatty acids, i.e., the percentage of fatty acids that are released into the intestine in a form that can be absorbed by enterocytes. We evaluated fatty acid release after in vitro digestion in four commercial marine oil supplements containing fish, krill and Calanus finmarchicus oils using two different analytical approaches, TLC-FID and 1H-NMR spectroscopy. The results clearly indicated that the release of free fatty acids (FFAs) after simulated digestion mainly depends on the oil source and is mainly related to the partitioning of lipids into different classes. In fact, the lowest FFA release was detected in Calanus oils, which contain high amounts of wax esters. The different release of FFAs, which appeared secondarily related to encapsulation, can modulate the absorption and blood concentration of the administered n-3 LC-PUFAs and therefore their efficacy. This may partly explain the inconsistencies in intervention studies using marine oil supplements.

Modelling seasonal and geographical n-3 polyunsaturated fatty acid contents in marine fish from the Northeast Atlantic Ocean

Demand for n-3 polyunsaturated fatty acids (n-3 PUFAs) exceeds supply. Large-scale studies on effects of season and geography of n-3 PUFAs in marine fish from the Northeast Atlantic Ocean (NEAO) may be used to optimize utilization and improve nutrition security. Using a sinusoid model, seasonal cycles of n-3 PUFAs were determined and found to be species-specific and clearly pronounced for the pelagic zooplankton feeding species. The Greenland halibut showed very little seasonal variation. The n-3 PUFA content in North Sea autumn-spawning (NSAS) herring peaked in summer, while Norwegian spring-spawning (NSS) herring and mackerel had their peak in autumn. A time shift of peaks in n-3 PUFAs between the two herring stocks was detected, likely due to different spawning strategies in addition to a delay of n-3 PUFAs flux in the northern regions of the NEAO. This study demonstrates that consideration of nutrient contents, such as n-3 PUFAs, when organizing and structuring fishery approaches may improve overall nutritional yield. Based on total annual Norwegian fish landings and seasonal variation in n-3 PUFA contents, n-3 PUFAs yield could theoretically be increased from 13.79 kilo ton per year from the current fishing tactics, to 15.54 if the pelagic species were only caught during the time of their seasonal n-3 PUFA peaks. Pelagic fish is a good source for dietary n-3 PUFAs, but harvest timing will also influence n-3 PUFAs intake by human consumers. One portion of fatty fish harvested during winter/spring may not meet the weekly intake reference nutritional guidelines for n-3 PUFAs. Marine n-3 PUFAs yields also varied geographically and decreased southwards, with the lowest values in Skagerrak. This study can serve as a model to understand patterns of reproductive cycles and geographical distribution of n-3 PUFAs in fatty fish from the NEAO and the novel approach may be useful to support sustainable, seasonal fishing programmes for optimization of n-3 PUFAs yields.

Biochemical characteristics of zooplankton entering Atlantic mackerel processing plants in Iceland as side-catch

The Northeast Atlantic mackerel (Scomber scombrus) is a zooplanktivorous fish with its main summer feeding grounds in the waters around Iceland. The zooplankton in the stomachs of the caught fish causes several problems during processing due to the high enzyme activity of the zooplankton. The aim of the study was to evaluate the chemical characteristics of zooplankton that accompanies mackerel as a side-catch and stomach fullness as affected by catching year, season, catching zone, and catching method over three mackerel seasons from 2016 to 2018. Species identification by the fatty acid tropic marker method (FATM) was also applied within the zooplankton rich side-stream. FATM analysis indicated that the majority of the zooplankton mass belonged to Calanus finmarchicus. The lipid composition of the zooplankton rich side-stream varied between years but was rich in monounsaturated, as well as polyunsaturated fatty acids (PUFA), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The results suggest that the zooplankton rich side-stream from mackerel caught in Icelandic waters has the potential for further sustainable processing into valuable nutrients.

Diet and feeding strategy of Northeast Atlantic mackerel (Scombrus scomber) in Icelandic waters

Predator-prey relations, as well as the trophic ecology of highly migratory marine species, is important to understand their impact on the ecosystem. Conventional methods were used to study the diet composition and feeding strategy of the Northeast Atlantic mackerel (Scombrus scomber), during their summer feeding migration to Icelandic waters in 2009-2014. In addition, generalised additive modelling (GAM) was used to determine which biological and environmental factors contribute to the variation of their stomach weight in the years 2011-2014. From the dietary analysis, we found that calanoid copepods (especially Calanus finmarchicus) were the most important contributor to the overall diet of mackerel in the years studied. Although in some years and areas, they also preyed heavily on larger prey items such as euphausiids, amphipods and megalopa larvae of crab and shrimp. The GAM showed that temperature and the time the day of sampling were significant explanatory variables for the stomach weight, while zooplankton biomass did not seem to have much influence. The Northeast Atlantic mackerel are ferocious feeders upon copepods, as well as exhibiting an overall opportunistic feeding strategy. During their feeding migration in Icelandic waters, they were found to feed on the most dominant species available to them.