126
THE ESSEX NATURALIST
the back which give darker patches along the sides. The fish has a row of
small black dots along each flank (J). The first dorsal fin has two black
spots; one at the base on the rear edge of the fin, the second at the top of
the leading edge (K). The Black Goby is an estuarine species and the largest
of those considered here.
Chaparrudo flavescens: The Two-spot Goby is most often found around
seaweed and is less dependent on the bottom than many species. Con-
sequently the eyes are widely spaced, being on the side of the head, with a
definite flat 'forehead' between them (L). The colour is light brown with
a prominent dark spot at the base of the tail (M) and a less obvious
spot beneath the pectoral fin (N).
Gobius paganellus Linnaeus 1758: Only one specimen has been recorded
in the Blackwater (Barron, 1976). It has a short caudal peduncle (P) and
is very dark coloured. It can be distinguished from G. niger by the light
yellow band along the upper edge of the first dorsal fin (Q).
Aphia minuta: This is a pelagic goby with eyes on the side of the head. It is
almost transparent, with its internal structure clearly visible (R). This is
the only species I have not caught in the Blackwater although it does occur
in Davis's (1967) list.
Abundance of Gobies at Decoy Point
During my visits to Decoy Point, only one nest has been found. The
Mya shell with the goby eggs attached was caught in the trawl-net on 8th
April 1974, when the water temperature was 13°C. During the summer of
1974, large numbers of young gobies (8-15 mm) could be found in the
shallow pools left on the mud-flats by the receding tide. They remained
abundant until the beginning of October when the numbers caught rapidly
dropped to zero. This may have been a temperature-effect, since the
temperature of the water in the main channel fell below 10°C early in
October.
Two, Two-spot Gobies were caught in the autumn of 1974 and the first
Rock Goby reported from the North Sea was caught also at this time
(Barron, 1976). Black Gobies have been caught at infrequent intervals. The
largest was on 3rd May 1973 and measured 73 mm. The smallest was
caught on 4th September 1974 and measured 29 mm. Generally the Black
Gobies caught were larger than the Sand Gobies. No Transparent Gobies
have been caught so far; their pelagic nature and preference for water at
least 1 m deep (Wheeler, 1969) does not make this unexpected. Its des-
cription above is included, however, for completeness.
Figure 4 summarises the data recorded during my visits to Decoy Point.
The smallest gobies considered here were 15 mm. Most of the fish data
relate to Common and Sand Gobies except as stated above with further
details given in Table 3. This gives specific data for fishing trips between
April 1974 and July 1975. It was during this period that particular attention
was payed to the different species caught. It should be noted that in Figure