P.S.Z.N.: Marine Ecology, 19 (I): 5 3 4 6 (1998) 0 1998 Blackwell Wissenschafts-Verlag, Berlin ISSN 01 73-9565 Accepted: January 16, 1998 Spatial Distribution of Shelf- and Slope- Dwelling Fishes Collected by Bottom Longline off Lanzarote and Fuerteventura, Canary Islands FRANZ UIBLEIN', FERNANDO BORDES~, RICARDO CASTILLO~ & ANTONIO G. RAMOS~ ' Institut fiir Zoologie der Universitat Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria. E-mail: franz.uiblein@sbg.ac.at 'Institute Canario de Ciencias Marinas, Aptdo. de Correos 56, E-35200 Telde, Gran Canaria, Spain. 'Departamento de Biologia, Faculdad de Ciencias del Mar, Universidad de Las Palmas de Gran Canaria, P.B. 550, Las Palmas de Gran Canaria, Spain. With 6 figures and 2 tables Key words: Depth distribution, depth-size, spawning aggregation, reproductive timing, Mora moro, topography, hydrography, local upwelling, satellite imagery. Abstract. A total of 1789 fish belonging to 38 families and 73 species were collected at depths between 18 and 1 102 m during 216 bottom longline operations off Lanzarote and Fuerteventura, Canary Islands, between February 1994 and December 1995. For each species the depth distribution is provided. Length-weight and depth-size relationships are reported for three shelf-dwelling species. The bigger- deeper relationship found in two of them contrasts with the bigger-shallower pattern of the deeper living trichiurid Lepidopus caudurus. In November 1997, nine additional bottom longline operations were carried out of€ eastern Fuerteventura at depths between 805 and 1217 m. In this area, after earlier studies in October 1995, a spawning aggregation of the morid Mom moro was encountered for the second time. The catches of 1997 revealed a strongly male-biased sex ratio. Also, the males showed a significantly lower gonadosomal index than two years earlier. These findings indicate slight interannual variations in reproductive timing and an earlier arrival of male Mora moro at the spawning grounds. Clear variations in the number of fish collected at adjacent sites possibly reflect a preference for distinct microhabitats. Preliminary evidence of local upwelling of cold water above the spawning grounds is provided by satellite imagery. Problem The Canary Islands region, situated in the northernmost part of the Eastern Central Atlantic, shows distinctive topographic and hydrographic conditions which may affect the spatial distribution of both shallow- and deep-water fishes to a con- siderable extent. The rather narrow shelf and the steep upper slope, typical for oceanic islands of volcanic origin, set spatial limits to the demersal fish assemblage. The hydrography of this region is characterized by countercurrents at different U. S. Copyright Clearance Center Code Statement: 0173-9565/98/1901-0053!$14.00/0