However, while a number of marine mammal populations have rebounded ( IWC, 1998 Summarized in Carretta et al., 2009), there is no obvious increase in basking shark populations in the Pacific Ocean ( McFarlane et al., 2009). Similar to many marine mammals, targeted fisheries for basking sharks in the Pacific Ocean ended decades ago ( McFarlane et al., 2009).
This list includes the second largest shark, the basking shark ( Cetorhinus maximus, Gunnerus, 1765), that can reach 12 m in length and is named for its habit of swimming slowly at the surface ( Compagno, 1984 Priede, 1984 Sims, 2008 McFarlane et al., 2009). Data collected indicate the potential for large-scale movements and the need for international dialogue in any recovery efforts.Ī long history of human interaction has resulted in the decline of many species of marine megafauna including turtles, tunas, cetaceans, rays and sharks ( Springer et al., 2003 Lewison et al., 2004 Marshall et al., 2006 Bradshaw et al., 2008 Dulvy et al., 2008 Croll et al., 2016 ISC, 2016). Movement patterns and shifts in vertical habitat and use are likely linked to shifts in prey availability and oceanography. The shark that moved south along the Baja Peninsula spent progressively more time in deep water but came to the surface daily. The shark that went to Hawaii had a distinct diel pattern, with days spent at ~450–470 m and nights at ~250–300 m and almost no time in surface waters, corresponding with the diel migration of a specific portion of the deep scattering layer. Offshore vertical movements depended on location. Nearshore, most time was spent in the mixed layer but sharks did spend hours in cold waters below the mixed layer. Vertical habitat use was variable both within and among individuals and changed as sharks moved offshore. Offshore their paths diverged and by January one shark had moved to near the tip of the Baja Peninsula, Mexico and the other to the waters near Hawaii, USA. The two sharks with 180 and 240 days deployments left the coast in the summer and fall. Nearshore, sharks tended to move north in the summer and prefer shelf and slope habitat around San Diego, Point Conception and Monterey Bay. The tags provided both transmitted and archived data on habitat use and geographic movement patterns. From 2010 to 2011, four sharks were tagged with pop-off satellite archival tags with deployments ranging from 9 to 240 days. In the eastern North Pacific (ENP) Ocean, the limited information on basking sharks comes from nearshore habitats where they forage. Similar to many megafauna populations, available data suggest that populations are below historic levels. Basking sharks are large filter-feeding sharks that are second in size only to whale sharks. To fill data gaps on movements, behaviors and habitat use, both near- and offshore, two programs were initiated to deploy satellite tags on basking sharks off the coast of California.
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