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4 DISCUSSION

But not only neritic larvae accumulate in the southwest of Gran Canaria and especially southeast of Fuerteventura, also the number of oceanic species is high there and they occur even in the neritic realm. Also JOHN et al. (2004b) observed a mixing of oceanic larvae with neritic species onshore due to an onshore transport by an anitcyclonic eddy. Further, few oceanic specimens appear at neritic sites along the flanks of Gran Canaria and at the stagnation point of Fuerteventura and Lanzarote, where the current divides and flow is minimal. This can be explained by the trajectory model of RODRÍGUEZ et al. (2001). This study shows that particles released north of Gran Canaria within the oceanic realm may beach along the flanks (RODRÍGUEZ et al. 2001). Further onshore currents e.g. due to the local upwelling at the western sides of the islands (Figure 1b-c), might transport oceanic larvae into the neritic zone. The north of the islands is known to accumulate neritic larvae (RODRÍGUEZ et al. 2001), especially species with non-pelagic eggs like pomacentrids (LEIS 1986). The hydrographic feature, which is helping the larvae remain close to the islands, is the stagnation point. This is the area where the current divides and no flow is noticeable. A high concentration of neritic larvae and fish eggs north of Gran Canaria in the study of RODRÍGUEZ et al. (2001) shows the stagnation point being a favoured nursery ground for larvae. Also in the present study a high abundance of neritic larvae is found at the stagnation point of the island complex Fuerteventura and Lanzarote. Furthermore, on the eastern and western flanks of Gran Canaria the abundance of larvae was relatively high. But too few stations were taken to get an accurate picture of the distribution there, as well as in the north of Gran Canaria. Usually the flanks of an island are not areas with high larval fish abundance, as a previous trajectory model showed (RODRÍGUEZ et al. 2001). At the flanks of Gran Canaria, especially in the channel between Gran Canaria and Tenerife, a low abundance was found, which is also congruent with the low mesozooplanktonic biomass there (RODRÍGUEZ et al. 2001). The reason for the low abundance is the flank currents, which advect the plankton and prevent it from accumulating (RODRÍGUEZ et al. 2001). The trajectory model also showed particles, which were released along the flanks and transported out of the area, so flanks do not seem to be a preferred spawning area. Due to the very complex hydrographic situation around the Canary Islands with local upwellings and other hydrographic events (e.g. southeast of Fuerteventura), the overall larval distribution based on the hitherto available samples gives no clear picture or trend. A more fine-scale spatial investigation of planktonic communities and ichthyoplankton would be required for an enhanced interpretation in terms of the local physical characteristics (ARÍSTEGUI et al. 1997; HERNÁNDEZ-LÉON 1991; RODRÍGUEZ et al. 2001; SABATES and MASO 1992) and to tackle the question if anomalous local or mesoscale hydrographic events are reflected in changes in larval distribution (SABATES and MASO 1992).

4.3.3. Seasonal occurrence and distribution JOHN et al. (2004b) noted that the offshore spreading of neritic larvae is more an effect of hydrographic variabilities due to local upwellings than a seasonal effect (JOHN et al. 2004b). But the intensity of the upwellings and current strength is seasonally dependent. E.g. the upwelling is lowest in late autumn (Figure 1a and e). Consequently, the spreading of larvae is also lowest then. This is supported by the present study, since most neritic larvae caught in autumn were within the neritic realm. So the differences in spatial distribution are also seasonally caused. No significant seasonal differences in community structure were encountered in this study. Nevertheless, some trends in larval occurrence and distribution depending on the time of the year could be observed: it seems that the months of January and November represent two spawning events for different communities. Although there might be a further spawning event in May attention has to be paid to the area of investigation. During the May cruise only highly oceanic locations were chosen,

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Inf. Téc. Inst. Canario Cienc. Mar. n°13

Spatial and seasonal patterns in species composition of fish larvae in the Canary Islands  

Technical report consisting on a comprehensive annotated larvae taxa list with the most important taxonomic characters of this region

Spatial and seasonal patterns in species composition of fish larvae in the Canary Islands  

Technical report consisting on a comprehensive annotated larvae taxa list with the most important taxonomic characters of this region

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