Understanding the ecological role of sand eels

Top predators such as seabirds and sea mammals are an important focus of Wozep research. Previous studies have shown that top predators depend on forage fish such as herring, sprat and sand eel. In turn, forage fish depend on plankton production. However, there are still knowledge gaps in our understanding of how these three factors interact. That is why Wozep supports the NWO project “FORAGE FISH”.

The NWO “FORAGE FISH” project, which Wozep supports, was set up to remedy those gaps. It will study the sand eel, the key forage fish species. Sand eels are small, slender, semi-pelagic fish that live buried in the seabed for much of the year. In most cases, they live in a specific area on the top of the sandbanks, where they burrow tail-first into the coarse sand. They only emerge from the seabed during short spawning periods and in spring and early summer, when they forage on plankton ranging from small plankton eggs to larger energy-rich copepods.

The spawning periods vary for the three species of sand eel. The great sand eel (Hyperoplus lanceolatus) spawns in April-September, the lesser sand eel (Ammodytes tobianus) in December-January, and small sand eels (Ammodytes marinus) in February-April and September-November. All three species lay their eggs in the sand, where they mature for a few weeks before hatching. The larvae float on the current to other areas where they settle in the seabed again.

3.1 Sand eel on measuring bord
Photo 1: Sand eel (source: NIOZ/WMR).

Extensive developments are planned for the southern North Sea. They include offshore wind farms but also fish farms, sand mining and beach nourishment operations. The proposed sites often overlap the main spawning and feeding grounds of sand eels. Not surprisingly given the complex life cycle of this key species, more knowledge is needed.

“FORAGE FISH” will look at sand eel distribution in relation to their environment, food availability and top predator distributions to see how changes over time in distribution and fish size can be explained by bottom-up (temperature, food availability) and top-down (predation) processes. Data will be used to develop an integrated population-dynamic energy budget model and the data will be included in a 3D ecosystem model (ERSEM-BFM). Scenarios will be simulated to show how lower-level changes in productivity (due to human activities, for example) affect higher levels (top predators). The results of this project will be used in marine spatial planning to prevent any unforeseen, negative effects on sand eels (and other forage fish), as well as to mitigate the associated knock-on effects on a wide range of top predators.
The research will be also be connected to the Wozep study of soft substrate benthos inside and outside existing offshore wind farms, which will involve collecting sand eels.

“FORAGE FISH” is being conducted by NIOZ (the Royal Netherlands institute for sea research) in collaboration with Wageningen University & Research, CEFAS and St. Andrews University and RWS Wozep. More information on the “FORAGE FISH” project.

Read the report about benthic development in and around offshore wind farm Prinses Amalia Windpark