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NOAA Technical Memorandum NMFS-AFSC-346

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Migration patterns of adult male California sea lions (Zalophus californianus)

Preface

This report presents the results of the first satellite tracking study of adult male California sea lions (Zalophus californianus) and it is the first to fully describe the species’ migration in terms of timing, distance, duration, and the diving and swimming behavior of individuals. Earlier reports or studies on the movements or migration of California sea lions did not utilize satellite or VHF telemetry data so the results were not definitive or detailed. Several more recent studies, as cited later in this report, have utilized satellite tracking to investigate the movements of male California sea lions, however these studies did not focus on migration and describe only short-distance movements during the non-migration period (Weis et al. 2006, Wright et al. 2010). Another study completed in 2016 involved satellite tracking of adult male sea lions captured in Puget Sound, Washington, as part of a U.S. Navy funded effort to investigate the abundance and movements of sea lions around U.S. Navy facilities. The study in 2016 did not document migration and the results have not yet been published.

In our study, nine satellite instruments were attached to adult male sea lions from 1995 to 2000. The primary objective of the study was to document the southbound migration of California sea lion males. Seven of the instruments deployed were also dive recorders. The instruments were all deployed in late March to early June, just prior to the southbound migration, in order to maximize the likelihood that the instruments would stay attached during the full southbound migration period. Eight of the nine sea lions completed the full southbound migration to rookeries off southern California. One also completed a full northbound track. These data allowed us to calculate for the first time average daily swimming distances, maximum 24-hour travel distances, and resting and diving activity.

The data provided in this paper answer many of the basic life history questions for this species which prior to this study had only been inferred. For example, the route taken by this species during the migration demonstrates the coastal migration route along the continental shelf. Other questions such as how fast do they swim, how far can they swim per day, how deep do they dive, and do they feed during the migration are answered in this report and no longer need to be left to speculation. This report provides a reference for future researchers conducting studies on this species, or other migratory species where satellite telemetry is utilized. Finally, the information in this report is important for resource management agencies, conservation organizations, and even defense agencies who are in constant need of accurate data in order to make informed decisions concerning the environment and human activities. Even though this study was completed in 2000, the information that we present is still timely and important to future researchers because the results of this study have not been presented before.



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