A standard, universally useful classification scheme for deepwater habitats needs to be established so that descriptions of these habitats can be accurately and efficiently applied among scientific disciplines. In recent years many marine benthic habitats in deep water have been described using geophysical and biological data. These descriptions can vary from one investigator to another, which makes it difficult to compare habitats and associated biological assemblages among geographic regions. Using geophysical data collected with a variety of remote sensor systems and in situ biological and geologic observations, we have constructed a classification scheme that can be used in describing marine benthic habitats in deep water. 0 1999 Ifremer / CNRS / IRD / Editions scientifiques et medicales Elsevier SAS habitat / universal classification / benthic I fisheries management Resume .-Une classification des habitats benthiques profonds. Un systeme de classification des habitats benthiques profonds, pour avoir valeur de reference g&r&ale, doit pouvoir etre mis en pratique avec precision et efficacite dans les disciplines scientifiques. Ces dernieres an&es, les habitats marins benthiques profonds ont tte decrits a partir de dontrees geophysiques et biologiques ; les descriptions varient d'un chercheur a l'autre, rendant la comparaison difficile entre les habitats et les populations de differentes regions geographiques. Des donnees geophysiques obtenues par plusieurs systemes de detection a distance, et des observations biologiques et geologiques in situ, ont permis d'etablir une classification qui est proposee pour decrire les habitats marins benthiques en eau profonde. 0 1999 Ifremer / CNRS / IRD / Editions scientifiques et medicales Elsevier SAS habitat I classification universelle I benthique I gestion des pecheries

It is often assumed that visual survey data provide more accurate fish counts than conventional extractive gear. As a result, use of underwater vehicles to assess the abundance and distribution of fishes has increased rapidly over recent years. However, a review of observations reported for 48 demersal marine fish taxa showed that almost all respond in some way to underwater vehicles. Whether or not movements or changes in behavior affect survey bias is more difficult to assess. A simple conceptual model is presented to evaluate relationships between stimulus intensity, distances from the vehicle where reactions occur, and survey bias. Largest bias is caused by attraction or avoidance that occurs outside the field of cameras or observers. While light level and vehicle speed have been explored experimentally in a few cases, much remains to be learned about how bias varies among species, age groups, different vehicles, and operating conditions. Given poor understanding of survey bias, we recommend that surveys be conducted with minimum possible variation in operations and that vehicle time is devoted to experimental evaluation of methods. There is no good substitute for direct observations on fish behavior, distribution, and abundance; and survey design can be improved through experimentation.