A CODED ACOUSTIC TELEMETRY SYSTEM FOR HIGH-PRECISION MONITORING OF FISH LOCATION AND MOVEMENT - APPLICATION TO THE STUDY OF NEARSHORE NURSERY HABITAT OF JUVENILE ATLANTIC COD (GADUS-MORHUA)

Biological telemetry is a powerful technique that provides continuous and simultaneous monitoring of fish in their natural environment, in b oth space and time, enabling researchers to study fish without constra ints associated with many study techniques in use today. This paper de scribes a new acoustic telemetry technology which relies on an advance d coding and modulation scheme to provide precise localization of fish in high noise marine coastal environments. The coding scheme enables discrimination of a large number of individual fish without use of mul tiple frequency channels. Innovations in telemetry receiver technology permit simultaneous code searching of large numbers of transmitters t o minimize data loss and enhance temporal resolution of positioning fo r individual tags. This system was used to study movement and position of juvenile Atlantic cod (Gadus morhua), on both diel and seasonal sc ales, in, inshore/nearshore habitats in Newman Sound, Newfoundland, Ca nada. Telemetered data was coupled to high resolution habitat mapping and bathymetry to permit association of position with components of ha bitat. Diel patterns in juvenile cod habitat use are evident in the Su mmer months but not in the Fall. Spatial density of detections suggest ed different diel levels of activity. Patterns in movement of an indiv idual fish clearly demonstrated directed and relatively rapid movement between habitat areas. The frequency of occurrence of fish at various depth strata indicated a Summer nocturnal movement to shallow inshore areas which was not evident in the Fall. These results indicate the p otential of advanced telemetry systems, with high spatial and temporal resolution positioning, in the study of habitat requirements and use by juvenile fife stages of fish.