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FINAL PROGRAMMATIC BIOLOGICAL OPINION ON U.S. NAVY ACTIVITIES IN THE HAWAII RANGE COMPLEX 2008-2013 For several years, <strong>NMFS</strong>’ biological opinions have established that most loggerhead sea turtles populations face high probabilities of extinction as a result of both environmental and demographic stochasticity. Demographic stochasticity, which is chance variation in the birth or death of an individual of the population, is facilitated by the increases in mortality rates of loggerhead populations resulting from the premature deaths of individual sea turtles associated with human activities (either removal of eggs or adult females that are killed on nesting beaches or that die as a result of being captured in fisheries) or incidental capture and mortality of individuals in various fisheries. The information available suggests that loggerhead sea turtles have high probabilities of becoming extinct in the Pacific Ocean unless they are protected from the combined threats of entanglements in fishing gear, overharvests, and loss of their nesting habitat. The limited data available suggests that nesting aggregations of loggerhead sea turtles in the Pacific Ocean exist at sizes small enough to be classified as “small” populations (that is, populations that exhibit population dynamics that increase the extinction probabilities of the species or several of its populations) as evidenced by biases in the male to female ratios in the Pacific. These small sizes would increase the extinction probability of these nesting aggregations. The status of loggerhead sea turtles in the Atlantic Ocean remains uncertain and controversial. For years, the south Florida nesting aggregation, which is the only major nesting aggregation in the western Atlantic Ocean, had been assumed to be stable or increasing. However, more recent data demonstrate that this nesting population is currently declining and probably has been declining for several years. Between 1998 and 2007, nest counts of loggerhead sea turtles in the State of Florida have declined by almost 50 percent to the lowest levels in the 19 years of Florida’s monitoring program (Fish and Wildlife Research Institute 2007). Given that (1) the nesting aggregations that account for almost 90 percent of loggerhead nesting in the western Atlantic Ocean are declining, (2) the other nesting aggregations in the western Atlantic Ocean are substantially much smaller, and (3) large numbers of sea turtles from these smaller populations are captured or killed in commercial and other fisheries in the United States each year, we suspect that the extinction probabilities of loggerhead sea turtle populations in the Atlantic Ocean are only slightly lower than those of populations in the Pacific Ocean. The principle difference between the Atlantic and the Pacific may be this: loggerhead sea turtle populations in the Atlantic Ocean may currently be large enough to avoid the small population dynamics we have discussed previously, but the intensity of the anthropogenic pressure on their populations (in the form of numbers captured and killed in fisheries alone) appear to be large enough to accelerate the extinction probabilities of these populations. Diving and Social Behavior Studies of loggerhead diving behavior indicate varying mean depths and surface intervals, depending on whether they were located in shallow coastal areas (short surface intervals) or in deeper, offshore areas (longer surface intervals). The maximum recorded dive depth for a post-nesting female was 211-233 meters, while mean dive depths for both a post-nesting female and a subadult were 9-22 meters. Routine dive times for a post-nesting female were between 15 and 30 minutes, and for a subadult, between 19 and 30 minutes (Sakamoto et al. 1990 cited in Lutcavage and Lutz 1997). Two loggerheads tagged by Hawai’i-based longline observers in the North Pacific and attached with satellite-linked dive recorders were tracked for about 5 months. Analysis of the dive data indicate that most of the dives were very shallow - 70% of the dives were no deeper than 5 meters. In addition, the loggerheads spent approximately 40% of their time in the top meter and nearly all of their time at depths shallower than 100 meters. On 136
FINAL PROGRAMMATIC BIOLOGICAL OPINION ON U.S. NAVY ACTIVITIES IN THE HAWAII RANGE COMPLEX 2008-2013 5% of the days, the turtles dove deeper than 100 meters; the deepest daily dive recorded was 178 meters (Polovina et al. 2003). Polovina et al. (2004) reported that tagged turtles spent 40 percent of their time at the surface and 90 percent of their time at depths shallower than 40 meters. On only five percent of recorded dive days loggerheads dove to depths greater than 100 meters at least once. In the areas that the loggerheads were diving, there was a shallow thermocline at 50 meters. There were also several strong surface temperature fronts the turtles were associated with, one of 20°C at 28°N latitude and another of 17°C at 32°N latitude. Vocalizations and Hearing The information on loggerhead turtle hearing is very limited. Bartol et al. (1999) studied the auditory evoked potential of loggerhead sea turtles that had been captured in pound nets in tributaries to the Chesapeake Bay in Maryland and Virginia and concluded that loggerhead sea turtles had most sensitive hearing between 250 and 1000 Hz, with rapid decline above 1000 Hz (Bartol et al. 1999). This is similar to the results produced by Ridgway et al. (1969) who studied the auditory evoked potentials of three green sea turtles (in air and through mechanical stimulation of the ear). They concluded that the maximum sensitivity of green sea turtles occurred from 300 to 400 Hz with rapid declines for tones at lower and higher frequencies. They reported an upper limit for cochlear potentials without injury of 2000 Hz and a practical limit of about 1000 Hz. These hearing sensitivities are similar to the hearing sensitivities reported for two terrestrial species: pond turtles (Pseudemys scripta) and wood turtles (Chrysemys inscuplta). Pond turtles are reported to have best hearing responsiveness between 200 and 700 Hz, with slow declines below 100 Hz and rapid declines above 700 Hz and almost no sensitivity above 3000 Hz (Wever and Vernon 1956) the latter has sensitivities up to about 500 Hz, followed by a rapid decline above 1000 Hz and almost no responses beyond 3000 or 4000 Hz (Peterson 1966). 137
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