Simultaneous high resolution sampling of predator behavior and habitat characteristics is often difficult to achieve despite its importance in understanding the foraging decisions and habitat use of predators. Here we tap into the biosonar system of Blainville's beaked whales, Mesoplodon densirostris, using sound and orientation recording tags to uncover prey-finding cues available to echolocating predators in the deep-sea. Echolocation sounds indicate where whales search and encounter prey, as well as the altitude of whales above the sea-floor and the density of organisms around them, providing a link between foraging activity and the bio-physical environment. Tagged whales (n = 9) hunted exclusively at depth, investing most of their search time either in the lower part of the deep scattering layer (DSL) or near the sea-floor with little diel change. At least 43% (420/974) of recorded prey-capture attempts were performed within the benthic boundary layer despite a wide range of dive depths, and many dives included both meso- and bentho-pelagic foraging. Blainville's beaked whales only initiate searching when already deep in the descent and encounter prey suitable for capture within 2 min of the start of echolocation, suggesting that these whales are accessing prey in reliable vertical strata. Moreover, these prey resources are sufficiently dense to feed the animals in what is effectively four hours of hunting per day enabling a strategy in which long dives to exploit numerous deep-prey with low nutritional value require protracted recovery periods (average 1.5 h) between dives. This apparent searching efficiency maybe aided by inhabiting steep undersea slopes with access to both the DSL and the sea-floor over small spatial scales. Aggregations of prey in these biotopes are located using biosonar-derived landmarks and represent stable and abundant resources for Blainville's beaked whales in the otherwise food-limited deep-ocean.

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A total of 168 bottom longline operations were carried out at depths between 72 and 1102 m during four cruises off Lanzarote and Fuerteventura, Canary Islands. One hundred and twenty-eight operations were successful, resulting in the capture of I167 fishes belonging to 55 species. Clear variations in fish total weight and number, species richness and diversity, and the relative abundance of single species occurred among five different depth zones between 100 and 1100 m. The particular platform topography of the Canary Islands may affect the density and diversity of slope-dwelling fishes. Whereas fish body length and weight showed an overall increase with depth, no such trends were found at the level of individual species. One species, Lepidopu.~ caudatus, even revealed a bigger-shallower trend. Among three species of trichiurids, depth distribution patterns were detected that may reflect vertical space partitioning. In October 1995, an unusually high number of Mora moro with advanced gonadal maturity were collected off eastern Fuerteventura at 997 m depth. At lesser depths and during other seasons, only a few individuals of this species were caught in the same area. This indicated a seasonal variability in local abundance that is most probably related to reproduction. Mora moro has an excellent flesh and may represent a valuable fisheries resource. Open problems requiring further research in the study area such as selectivity effects of the fishing gear and possible influences of ecological factors on geographical distribution of the deep-water ichthyofauna, as well as important aspects of the future demersal fisheries management in the Canarian archipelago are briefly outlined. $?) 1996 The Fisheries Society of the British Isles

Oceanic islands of volcanic origin have a narrow shelf and a steep slope that should lead to considerable spatial overlap among coastal and oceanic fauna. During six pelagic surveys in the Canarian archipelago, Eastern Central Atlantic, over 65,000 fishes belonging to 211 species were collected at depths between 8 and 1035 m. The mesopelagic families of the lanternfishes (Myctophidae) and the bristlemouths (Gonostomatidae) accounted for about 50% of all specimens. By multivariate classification and ordination methods four different assemblages associated with mesopelagic, epipelagicÁ oceanic or coastal habitats could be identified. Two of these assemblages were coastal, differing in the proportion of meso-and epipelagic species. These data indicate intense horizontal migrations of mesopelagic fishes (mainly Myctophidae) into the neritic realm and increased interactions between coastal and oceanic habitats. Alpha diversity indices were higher and dominance was lower in oceanic habitats compared to the coastal realm. No marked differences among oceanographically similar areas of the entire archipelago were found. Beta diversity as a measure of similarity among sites or samples revealed variabilities between areas south of Gran Canaria and Fuerteventura islands. A considerable heterogeneity in species distribution was found off SE Fuerteventura in an area with high hydrographic variability. Therefore, both topography and hydrography are important factors influencing the distribution and abundance of pelagic fishes in this oceanic archipelago.

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