Skates leave the seabed at night

Although skates are often regarded as sedentary bottom-dwelling fish, Eleanor Greenway's PhD research shows that they lead a far more dynamic life than previously thought. During the day they generally rest on the seabed, while at night they actively swim through the water column. These daily vertical movements were observed throughout the year.

The findings suggest that these movements are primarily linked to foraging behaviour, with skates likely following their prey. In some cases, the movements were also associated with fishing activity and tidal cycles. Greenway found evidence of selective tidal transport, which had not previously been observed in these species. This suggests that skates may use tidal currents as part of different movement strategies.

“It was an amazing experience to work at sea and study these animals in the wild. I was particularly fascinated to find that skates actively swim through the water column at night. This goes against what we traditionally thought about skate behaviour,” says Eleanor Greenway.

In addition to studying skate behaviour, Eleanor Greenway investigated how their diet changes as they grow. Juveniles of all three species feed largely on the same prey, mainly shrimp. As they increase in size, however, clear differences emerge. Blonde skates specialise primarily on fish, thornback skates on crabs, while spotted skates adopt a more mixed diet.

These dietary shifts mean that, as adults, the three species fulfil different ecological roles and together form a network of predators within the North Sea ecosystem.

Based on age data and comparisons with historical records, the three species studied appear to reach smaller maximum sizes than those reported in the past. They also mature at a smaller body size. In all three species, reproductive output increased with body length. Observations of egg cases and females that had recently laid eggs further suggest that some species may reproduce throughout much of the year.

To uncover the hidden lives of skates, Eleanor Greenway combined several research methods. She examined stomach contents and chemical "fingerprints" of diet using stable isotope analysis, estimated age from vertebrae, and tracked skates using electronic tags.

These tags recorded information such as depth and temperature. The data only became available once the tags had been recovered and returned by fishers and beachcombers. In the end, around one-third of the tags were recovered. For her age analyses, Greenway examined almost 400 skates, ranging from newly hatched individuals to animals approximately six to seven years old.

Sharks, skates and rays grow relatively slowly, produce few offspring and their populations recover only gradually after declines. As a result, they are particularly vulnerable to human pressures such as fishing. Although populations of skates in the North Sea and other parts of the north-east Atlantic have shown signs of recovery in recent decades, much remains unknown about their ecology, growth and reproduction. This knowledge is essential for the sustainable management of these species.

Marine ecologist Eleanor Greenway was awarded her PhD by Wageningen University & Research on 10 July 2026. Her thesis is entitled ‘Of Shadows and Wings: Ontogenetic Ecology and Life-History Traits of Three Skate Species in the Northeast Atlantic’.