Pomatoschistus minutus

Pomatoschistus minutus is sometimes considered to form a species complex with Pomatoschistus norvegicus and Pomatoschistus lozanoi. Pomatoschistus lozanoi is morphologically intermediate between the other forms and may interbreed with them in the wild (Webb, 1980). However, evidence suggests that back-crossing of the resultant hybrids does not occur and Pomatoschistus lozanoi is genetically distinct from the other forms (Webb, 1980).

• The sand goby usually remains inactive, except when feeding (Fonds & Veldhuis, 1973). Pomatoschistus minutus feeds on small polychaetes, cumaceans, amphipods and mysids. Depending on the bottom type, it has been noted to show colour adaptations (Aquascope, 2000b), and has also been noted to burrow into the sediment to avoid predators (Magnhagen & Forsgren, 1991).
• The sand goby is a small goby, reaching a maximum of 10 cm in length. Males are generally longer than females (Quignard et al., 1983). Growth is slower in winter in the Atlantic, and slower in the summer in the Mediterranean (Quignard et al., 1983). Larvae gradually spend more and more time on the bottom, and at a length of approximately 17-18 mm they are usually fully adapted to the benthic way of life.
• Although of no commercial importance itself, it is incidentally caught in abundance in French Mediterranean lagoons (Quignard et al., 1983).

• The sand goby is considered to be an abundant species, found along all coasts of the British Isles. It can tolerate a wide range of temperatures and salinities, shown by its distribution from Norway and the Baltic Sea to the Mediterranean, and the fact that it resides in brackish and fully saline waters. It is usually found in deeper waters and at higher salinities than Pomatoschistus microps.
• Fonds (1973) showed that adult sand gobies tolerate salinities between 0.9 psu and 45 psu and that they survived and remained in good condition at a temperature as low as 2 °C. However, in the Thames estuary they preferred high salinity and high suspended solids concentrations (Araújo et al., 2000).
• Pomatoschistus minutus is a migratory species of semi-enclosed lagoon-like environments (Pampoulie et al., 1999). It has been noted to undertake spawning migrations in the Mediterranean Sea (Bouchereau et al., 1989) and thermal migrations in the North Sea and the Baltic Sea (Fonds, 1973; Hesthagen, 1977). Thermal migrations occur when temperatures decrease below 4-5 °C (Fonds, 1973) or increase above 19 °C (Hesthagen, 1977). In the Thames estuary an increase in numbers has been noted during autumn and winter (Araújo et al., 2000). In the Severn estuary, however, goby numbers declined in winter. This was suspected to have reflected a movement away from the shallows and towards deeper, warmer water (Claridge et al., 1985). Healey (1971) observed a scarcity of sand gobies in the Ythan estuary from February to June and, after eliminating decreased temperature, a change in salinity or a change in food supply as a cause, suggested that it was a result of a seasonal migration. Healey (1971) hypothesized that the gobies migrated out to sea so that eggs could develop, however, the hypothesis was subsequently rejected.

• The sand goby becomes sexually mature at about 7 months to a year old (Miller, 1986; Bouchereau et al., 1990). At this time, individuals measure approximately 4 cm (Bouchereau et al., 1990). Reproduction involves repeat spawning between February and May in Britain, and March to July in the Baltic Sea (Miller, 1986). The female usually lays her eggs under empty bivalve shells and the male proceeds to guard them. Males care for approximately 2 egg batches at the same time, belonging to different females (Kvarnemo, 1994), and females respawn with an interval of about 1 to 2 weeks (Kvarnemo, 1998). Fecundity is reported as between 2,878 - 3,000 eggs by Miller (1986) and between 998 and 5100 by Bouchereau et al. (1990).
• Pomatoschistus minutus spawns at 8 to 15 °C, lower than that of the Pomatoschistus microps (Wiederholm, 1987). In the Atlantic reproduction is protracted (Bouchereau & Guelorget, 1998; Rogers, 1989) and in the Mediterranean it is contracted (Bouchereau & Guelorget, 1998).
• The lifespan of the sand goby is approximately 1.3 to 2 years (Miller, 1986). Quignard et al. (1983) recorded lifespans of the sand goby as 12 to 14 months in the Mediterranean and up to 22 months in the Atlantic.