GOBIES IN THE UPPER BLACKWATER ESTUARY 129
Discussion
The occurrence and distribution of gobies in the Blackwater Estuary has
not been fully studied. Since the fish are often found in shallow water,
however, and can be caught without expensive or sophisticated equipment,
data on these fish could be collected by any interested party. Indeed the
capture of rare or large specimens must often be accompanied by good
fortune as much as good practice. It is possible, therefore, that Pomato-
schistus pictus (Malm, 1863), the Painted Goby, could also be recovered
from the Blackwater Estuary, especially as this fish is common in the
southern North Sea and it has been recorded from the Dutch Wadden Sea
by Fonds (1964). Normally, however, this fish is found at depths from 2
to 25 metres and prefers rough or rocky ground.
The movements of the gobies within an estuary are still little understood.
Temperature dictates the main migrations to deep water in autumn,
although this is more important to the Sand Gobies than Common Gobies.
It would appear, though, that the desire to feed may draw fish back to the
mud-flats whenever a rise in temperature permits. Salinity would seem to
have no effect on these more individual migrations, although very low
values are probably found only for short periods around low-water at
Decoy Point. Migration as well as reproductive success, therefore, affects
the abundance of gobies at Decoy Point.
The Blackwater Estuary is used as a nursery ground for some flatfish,
such as Plaice, Sole and Flounder. The life-cycle and abundance of gobies
may affect all these species in some way. For example the goby may form
part of the diet of adult Plaice and Flounder but be a competitor for food
and space with the O-group flatfish. Sand and Common Gobies may also
feed on the larvae of soles and shrimps (Creutzberg and Fonds, 1971;
and de Veen, pers. comm.), which are found in shallow coastal waters. The
goby competes with prawns and shrimps for space and large numbers may
be caught sometimes by shrimp fishermen. The life-style of the goby is thus
associated with several economic species of fish although not often con-
sidered important in its own right.
Acknowledgements
I wish to thank the members of the School of Natural Sciences, The
Hatfield Polytechnic, and especially Mr D. Brookes, for all their assistance
in preparing this manuscript.
References
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