A survey is given of the fish eggs, postlarvae and young fish occurring in the macroplankton catches at lightvessel Texel. Fishing in the tidal current at the surface with a course mesh net (2 x 2mm meshsize) during day and night is a very selective way of sampling small fish. Most fish larvae stay at greater depth (10-20),only come to the surface at night, or avoid the net during the day. The monthly mean catches only give a general picture of "relative abundance" of a selected group of "surface dwelling" fish larvae and young fish. Due to the large meshsize of the net, only postlarvae were caught (> 5 mm) and large eggs (2 mm): plaice eggs in winter, pilchard eggs in summer. The monthly average numbers per haul of allfish together show two periods with relatively high number: a) Winter, January to May: mainly herring, plaice, elvers, sandeels, gobies and small pipe fish. b) summer, July to October: mainly horse-mackerels, sprat, pilchard, gobies, dwarf soles=solenettes, lesser weever and many other species. The catches were relatively low in May-June and in November-December. The change in relative abundance of the different fish species, and of all larvae together in Winter and summer from 1962 to 1964, suggests that the winterspecies declined in numbers while the summerspecies increased in numbers. Such changes may have been due to changes in the food supply (Copepods) and/or predation (Medusae) of fish larvae, following the severe Winter of 1962/63. For some selected species some observations are given of the food composition in the stomachs, and of the growth rate estimated from the changing length-distribution. |
