Nutritional value of fish & squid reduced by warm water events

The nutritional quality of fish and squid deteriorates under warm water events, with implications for the marine environment, marine predators and fisheries/food for humans.

The research led by the University of Sydney shows that under warm water events the nutritional balance of fish and squid changes, and is of lower quality, while under cold water events it is higher quality.

The research was conducted in New Zealand using a highly successful marine predator seabird, the Australasian gannet, as a biological monitor of the marine environment and food sources. The team combined miniature bird-borne GPS loggers, fish and squid nutritional analysis and nutritional modelling, and quantified colder and warmer water events by comparing the mean sea surface temperature with 10 years of data. Fish and squid captured by gannets were found to have a significantly lower ratio of healthy oils to protein during warm water events.

The research was published in the Journal of Animal Ecology. Lead author Dr Gabriel Machovsky-Capuska, said “Marine mammals and seabirds such as gannets eat similar foods as humans, namely fish and squid.

All capture prey in similar areas, and inevitably all are impacted by nutritional changes to this food source. “During warm water events gannets had to work harder for their food as they expanded their foraging habitat and increased their foraging trip duration, while at the same time consuming prey and diets with lower content of energy-providing oils.

Our approach can be used to understand and ultimately protect travelling routes for migratory species, and could support the conservation of endangered species in terms of food quality and habitat suitability.”

Co-author Professor David Raubenheimer of the University of Sydney said the research used a novel method: “Our approach allows us to associate the nutritional quality of marine resources with geographic location, water depth and environmental conditions such as sea surface temperature and chlorophyll levels.

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