Oberflächennahes Ichthyoplankton der Kanarenstrom-Region

Surface-living plankton of the subtropical NE-Atlantic (from 22° to 33° N and 28° W to the African coast) has been collected in winter 1970. Near the coast additional deeper hauls down to 50 m have been made. A modified David-Neuston sampler with two nets (300 or 500 μ mesh size) and a modified Gulf V sampler ("Langhai") with 300 μ were used. This paper deals with the ichthyoplankton only. A total of 14863 fishes or fish larvae were caught. They belonged to 51 different taxa. Between the neritic area (reaching to 130 nautical miles from the coast) and the oceanic area, great differences in the composition of ichthyoplankton were observed. The 27 neritic neuston samples yielded 110 less than 35 of the 51 taxa, while the 32 oceanic neuston samples had but 22 taxa, where of only 6 had not been caught in the first section. The average concentration of 190 fishes in 100 m3 of water filtered in the former area was significantly higher than in the oceanic area (112 individuals in 100 m3). The higher number of species near the coast is due to the fact that besides young stages of bottom-living and neritic pelagic fishes, mesopelagic species were caught. The neritic area showed higher surface temperatures, which normally brings a higher number of species. The species composition was not distinctly different with the results obtained in other seasons, but the percentage and the length distribution varied. The reason seems to be that the spawning of many species took place in this season. Young larvae of Macrorhamphosus, Scombridae, Carangidae and Sparidae have been caught in higher numbers. The following ecological aspects were observed in a part of the material. The distribution of some fishes, e.g. Mugilidae, indicate a preference to surface temperatures higher than 19°C. Sparids probably have the same temperature range. A large number of the ichthyoplankton showed a preference to the immediate surface for certain hours or even the whole day. For these species the daily rhythm was noted and an ecological grouping of the groups "euneuston", "daytime facultative neuston", "nighttime facultative neuston" and "pseudoneuston" was made. The "euneuston" includes all stages of Scomberesox, Mugilidae, Sparidae and the juvenile Carangidae. The "daytime facultative neuston" includes the juveniles of Macrorhamphosus and Scombridae together with the larvae of Ceratoscopelus. "Nighttime facultative neuston" are the young larvae of Macrorhamphosus and several genera of adult Mytophidae. "Pseudoneuston" includes mainly larvae of mesopelagic species as well as the larvae of Scombridae. For some taxa, a change in behaviour is probable. So early larval stages of Macrorhamphosus (up to 3 mm) and small Belone belong to the "nighttime facultative neuston", while elder stages should be regarded as "daytime facultative neuston" or "euneuston" in Belone. A change probably occurs in Scombridae and Carangidae too. Corresponding with this behavioural change in Macrorhamphosus a change in pigmentation from brown-white to blue seems to appear. A similar change may be assumed for Scombridae and Carangidae, but was not found in Belone