Conclusions and future research

In conclusion, the present work illustrates the importance of lipids and stable isotopes as sources of information related to marine food webs of West Greenland.

Remarkably little work has been done on the role of lipids in the West Greenland marine ecosystem despite their fundamental role in ma-rine animals and the Arctic mama-rine food web. Most of what is cur-rently known represents work performed in the Canadian Arctic, Svalbard and Northern Norway and by a few research groups from countries with a long tradition within marine lipid research.

Pres-35 ently, however, research projects are emerging which include at least aspects of lipids in the West Greenland ecosystem. It is my hope that with this study awareness on the importance and potential use of lipids will add to this positive trend.

Combining stable isotopes and lipid biomarkers with other and more conventional tools will add new dimensions to the information level needed for a sustainable exploitation and management of the West Greenland marine ecosystem and its resources. At times where global change is at work and affecting the system to an unknown degree this approach is likely to give valuable new information on changes in food web structure, trophic relations, productivity and food quality of particular importance to the wealth and health of the Greenland population.

Evidence that the marine food web of West Greenland is similar in structure to that of Arctic food webs (Paper 1) may infer a number of similarities between these systems, however small deviations from that of high-Arctic polyneas are apparent, and may add significant new information to our basic understanding of these systems. Hence the fact that some higher level predators seem to feed at compara-tively low trophic levels in the West Greenland system may prove essential. This is currently being investigated by the delineation of trophic relations through the combined use of our isotopic food web model and fatty acid biomarkers and is expected to give additional information on species-specific feeding strategies and diet. We sug-gest the marine isotopic food web model of West Greenland be used in future modelling of e.g. contaminant transfer, energy-flow and carbon-flux. Further development of the model aiming to include ideally all species (but especially invertebrates) is encouraged.

In order to exploit the marine resources of West Greenland in a sus-tainable way it is important to manage these on scientific based ad-vice. On this basis, populations of large whales inhabiting Greenland waters have been managed for some time now where subsistence hunting has long been an important issue to the local populations inhabiting these areas. The International Whaling Commission (IWC) communicated the need for improved management tools in the man-agement of the North Atlantic minke whale (Balaenoptera acutoros-trata), currently being exploited by subsistence Norwegian and Greenlandic hunters. Conventional methods have failed to give sig-nificant new information and a search for new tools was encouraged.

In this study we investigated the use of fatty acids and showed that blubber fatty acid signatures are a valid tool in stock discrimination in a large migratory whale like the North Atlantic minke whale (Pa-per 2). We recommend, however, that fatty acids be included in a multi-component approach (Paper 3) in order to ensure a more solid scientific basis for future advice. Apart from information on stock structure additional information can be gained from the use of these fatty acid signatures, due to the role and dietary origin of fatty acids.

This combined potential deserves more attention in the future.

The role of marine species is essential in the traditional Greenlandic diet which is characterised by a high content of n-3 PUFA. Scientific evidence has established that marine related lipids and especially the

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long-chained n-3 PUFAs EPA (20:5n-3) and DHA (22:6n-3) have a preventive effect on several of the pathologies related to the meta-bolic syndrome. However, compared to 30 years ago the Greenland diet of today has changed along with a more western-like lifestyle (Paper 5) and is no longer in agreement with international dietary recommendation. Fat intake is above recommendations and saturated fatty acids have increased at the expense of the nutritional desirable unsaturated fatty acids. This development has however resulted in a decrease in diet related contaminant exposure (Paper 6) but diseases related to the more western-like diet and sedentary lifestyle is likely to be the trade off. In fact an increase in type-2 diabetes and metabolic syndrome has already been observed in the Greenland population.

This “Arctic dilemma” makes dietary advice quite difficult to give.

Presently, a preliminary advice is that an increase in marine con-sumption should be avoided until contaminant levels have decreased to a safe level. Hence an increased frequency of life-style related dis-eases is expected among the Greenland population.

Both the fatty acid composition and the contaminant levels vary in marine species and in principle it should therefore be possible to compose a diet where the benefits and risks are better balanced. In order to do so marine species with a high lipid quality contrasting low contaminant levels needs to be identified.

From this study, information on the nutritional lipid quality of ma-rine key species has been made available. Based on lipid quality components (LQCs) a number of best sources have been appointed after having been correcting for Hg and PCBs respectively. These contaminant-corrected LQCs can be used in giving a balanced dietary advice, where at the same time, contaminant exposure levels are re-duced and the intake of healthy marine related lipids is increased, thereby circumventing the “Arctic dilemma”. We suggest that con-taminant-corrected LQC and other nutritional relevant parameters should be combined in a future dietary model for the Greenland population. Contaminants and nutritional parameters should be graded relative to their health risk/benefits in relation to public health. Finally a model should include specific information on dietary recommendations related to population groups and diseases.

Marine tissues and species not of quantitatively major importance to the current Greenland diet may prove as healthy alternatives and therefore serves more attention.

The health implications from a marine based diet is not one-sided and in this context lipids normally considered health may have nega-tive effects on public health if total amounts are exaggerated. Apart from marine mammals blubber most marine food components are considered lean and would not challenge the recommended lipid energy percentage in the diet. Amounts of PUFA could however lead to an increased risk of peroxidation if antioxidant intake is not ade-quate. Evidence is increasing on the importance of balance between individual and classes of fatty acid in the diet. The anti-inflammatory effect of EPA can be advantageous to balance the immune system but if its counter-balance in the form of AA (20:4n-6) is low it may lead to impairment of the immune response. Contaminants and other

nutri-37 ents affect the immune response in a similar way and we have in fact shown that a marine based diet can impair the immune response of a predatory mammal. To what extend this was due to the high content of contaminants, EPA or low content of AA is not clear but most likely a combined effect of this cocktail is responsible for the effect. In order to investigate this further each factor has to be isolated and this will result in a daunting task but however more importantly contri-bute with a very significant peace of information.