Acoustic monitoring of large whales to the west of Britain and Ireland using bottom mounted hydrophone arrays
October 1996 - September 1998
These reports describe the first two years (October 1996 - September 1998) of a study using bottom-mounted hydrophone arrays (used in other circumstances for military undersea surveillance) to monitor vocalisations of fin, blue and humpback whales. This survey covered initially six and then twelve (after the first year) large overlapping regions of the North East Atlantic Margin, from the Faroe-Shetland region in the north, to the Bay of Biscay in the south.
Calls from the different types of whales were identified by their distinctive sound-spectrographic signatures. Minimum daily whale counts and average daily vocal activity scores are reported for successive ten-day periods. The acoustic detections of the fin, blue and humpback whales all displayed distinct patterns of occurance in all of the monitoring regions.
© 2001 K Young/Sea Watch Foundation
Fin whale signals were the most frequently detected calls, occurring in all twelve regions in every month of the year for which data are available. Highest whale counts and highest vocal activity scores occurred in October through January. Fin whale counts and vocal activity declined steadily from February to minimal levels in May through July, and then increased again during August and September.
Blue whales were detected in all latitudes, with peak detection rates off Western Ireland in November and December, declining through late winter and early spring to minimal levels in March through June. Blue whale counts and vocal activity increased gradually from mid-July through September.
The seasonal patterns of calling activity appeared to be synchronous across all of the regions monitored for both fin and blue whales, and did not show any systematic seasonal migration.
Humpback whales were the least frequently detected species overall, occurring only in the four northern monitoring regions, and only from November through April. Also the times of this activity varied across the regions. Data from three of these four regions weakly suggest a north to south progression in peak humpback vocal activity from early January to mid-February to mid-March. This progression, coupled with data on some individual humpbacks whose movements were tracked for periods of several hours, suggests a late-winter/early-spring southward migration of singing humpbacks into and through the northern four monitoring regions. This was the first time that singing humpbacks had been noted in the north-east Atlantic.
Acoustic monitoring, like visual surveys, does not provide a straightforward method of assessing numbers of whales in an area, because the proportion of whales calling and time spent calling are unknown. However, acoustic surveys using bottom-mounted hydrophones can operate in seasons, weather conditions, and times of day that prohibit visual data collection, and can detect whales at much greater ranges than visual methods. Acoustic monitoring can provide a valuable adjunct to visual cetacean surveys such as the AFEN funded JNCC survey which together provide valuable insights into distributions of whales in the NE Atlantic Margin.
The work has been continuous since October 1996, and is planned to continue until December 2001.
Clark, C.W., and Charif, R.A. 1998
Acoustic monitoring of large whales to the west of Britain and Ireland using bottom mounted hydrophone arrays, October 1996 - September 1997
JNCC Report No. 281
Charif, R.A. and Clark, C.W. 2000
Acoustic Monitoring of large whales off North and West Britain and Ireland: a two year study