Biological variation of Greenland halibut – Optimizing sustainability, quality and commercial value (Qaleralik)
BACKGROUND
Greenland halibut, qaleralik in Kalaallisut (Greenlandic), is one of Greenland’s most important natural resources. It is a slow-growing, bottom-dwelling flatfish inhabiting the fjords and open seas in and around Greenland, where it supports a large commercial fishery.
Greenland halibut is a fatty white fish with a fat content above 10%, and it is exported world-wide from Greenland. Fish and shellfish generally make up more than 90% of Greenland’s exports, and Greenland halibut products alone account for roughly one third of all exported seafood. As the world’s largest supplier of Greenland halibut, maintaining consistent quality in exported batches is extremely important.
However, ‘mushy halibut’ with watery, jelly-like fillets appear in catches, and ‘Mushy halibut syndrome’ (MHS) constitutes a challenge due to the low quality of mushy fillets. On top of that, sorting the mushy halibut from the normal ones before the fish is filleted is difficult because they look alike at capture, and there are no effective methods for early detection. As a result, resources are spent on processing and distributing fish products that end up being downgraded or even discarded.
MHS is under-investigated, and many gaps in knowledge persist. The cause and extent of its occurrence is unknown, just as details of its characteristics and effects on halibut product quality are unclear. However, with growing global emphasis on food waste and sustainable fisheries, addressing quality issues such as MHS becomes increasingly important, to help reduce raw material losses and improve utilization of harvested marine resources.
PURPOSE
This PhD thesis investigated aspects related to the quality and biology of Greenland halibut affected by MHS. The aim was to characterize MHS using relevant product quality parameters and explore possible causes, while laying a foundation for potential detection and mitigation strategies.
A multidisciplinary approach was adopted, and Greenland halibut from the commercial Greenlandic fishery underwent both sensory evaluation, histological examination (microscopic tissue studies), physicochemical analyses such as texture assessment and processing yield, hyperspectral imaging trials and biological assessments.
The research was structured into five work packages with the following objectives:
1. Review and document the occurrence of MHS in Greenland halibut from commercial catches in Greenlandic waters
2. Characterize and compare the sensory, physicochemical and histological attributes of normal Greenland halibut fillets to fillets affected by MHS
3. Evaluate non-invasive detection techniques, with emphasis on hyperspectral imaging, for their potential to differentiate fish affected by MHS in commercial catches
4. Investigate biological health and possible biometric factors associated with the occurrence of MHS, to identify common denominators of affected fish and plausible causes, and assess whether MHS constitutes a pathological condition or natural variation
5. Explore the presence and prevalence of zoonotic nematode larvae in the flesh of Greenland halibut, and their possible association with MHS
RESULTS
Chemical analysis showed marked reductions in the dry matter and fat content of fillets affected by MHS, and both chemical constituents decreased with increasing MHS severity.
The average fat content of normal fillets was 10.4%, while for fillets severely affected by MHS, average fat content was only 2%.
Overall fatty acid and mineral content of the fillets also differed between normal and severely affected fish; Compared to normal fillets, fillets severely affected by MHS contained less saturated fatty acids and more polyunsaturated fatty acids. Sodium (Na) was almost three-fold increased while potassium (K) content was halved. Lastly, processing trials showed that the cooked yield of fillets affected by MHS was 20% lower compared to normal fillets.
Trials with the hyperspectral fish scanner The Maritech Eye™ showed that fat and dry matter content could be used to sort normal and mushy fillets. This scanning technology showed potential as a non-invasive detection modality, to support early identification of affected fish and optimized grading.
No signs of disease were observed, but mushy halibut were in poorer condition compared to normal halibut, with higher reproductive maturity and parasite load. While the findings did not reveal one single cause of MHS, the results indicate that MHS is linked to food intake and spawning status, although the possible influence of factors such as depth of capture and genetics were not investigated in this PhD study.
The project has improved the understanding of MHS and generated knowledge for future studies and fisheries optimization.
FUTURE PERSPECTIVES
This research lays a foundation for a more complete understanding of MHS, and for developing technologies and management strategies to reduce losses related to its occurrence, and support sustainable fishery practices.
Future studies should prioritize expanding spatio-temporal sampling coverage for more robust analyses and refining commercial detection tools for early identification of affected fish products, and explore value-adding processing strategies to optimize product utilization.
Genetic variability, viral presence and pollutants could be a focus for future research diving deeper into the mechanisms behind MHS, and surveillance of parasite prevalence and distribution can provide valuable indicators of foods safety, ecosystem dynamics and stock health – all of which can support responsible and informed management of Greenland’s important natural resources.
Relevant links:
Paasisavut (Kalaallisut / Dansk / English), KNR 13.11.2024 | KNR