It is scarcely possible to exaggerate the importance of the sandeel to the seas around our coastline. As a group they are abundant, producing immense numbers of young fish each year, and both adults and young spend much of their lives near the sea’s surface.
As a result they are important as a food for a wide range of fishes living in the upper layers of water. They are even more crucial to seabirds, since the peak abundance of young sandeels coincides with the period when terns, puffins, guillemots and others are feeding their young. Because the sandeels are plentiful inshore, their value is enhanced for adult birds, which don’t have to fly far to find food.
Telling them apart
There are five species of sandeel in British waters, two large and three small, and identification can be difficult between them unless you count the number of vertebrae. Greater sandeel (Hyperoplus lanceola-tus) At up to 35cm (14in) long, this is the largest of the sandeels. Also known as the launce, it is easily identifiable by the black spot on either side of the snout.
Corbin’s sandeel (Hypewplus immoxula-tus) Up to 30cm (12in) in length, this specimen is distinguished from the other sandeels by its uniformly dusky snout. Like that of the greater sandeel, its top jaw is only slightly extendible. Cuvier’s lesser sandeel (Ammodytes tobianus) Up to 20cm (8in) long, with scales over the entire body in regular rows and in patches on the base of each tail fin lobe, this sandeel has a maximum of 56 rays in the dorsal fin. It is found in water up to 30m (100ft) deep. This is the species that is collected on the beach for bait. Raitt’s lesser sandeel (Ammodytes mari- nus) Up to 25cm (10in) in length, this species has irregular rows of scales and none on the tail fin lobes. There are a minimum of 55 rays in the dorsal fin. It is found in water over 30m (100ft) deep. Smooth sandeel (Gymnammodytes semi-squamatus) Up to 23cm (9in) long, with no scales on the front part of the body, this species has unevenly spaced pores above and below the lateral line. The dorsal fin has two distinct depressions along its length. It is found in water over 20m (66ft) deep, over shell and gravel bottoms.
The five types of sandeel breed throughout the year, depending on location and water temperature. They all bury their eggs in sand or shell gravel. The fry hatch quickly and live near the surface, feeding on plankton, fish eggs and larvae.
As they grow larger they eat crustaceans and young fish – young herring are particularly vulnerable to sandeel attack, just as young sandeels are to adult herring. Sandeels alternate between living near the surface during the day and hiding in bottom sand at night or when they are alarmed.