Background: Great hammerhead sharks (Sphyrna mokarran) routinely swim on their sides and periodically roll from side to side. A previous study used wind tunnel tests with a rigid model hammerhead shark to demonstrate that the rolling behavior could improve swimming efficiency using the tall first dorsal fin as a lift-generating surface. Scalloped hammerhead sharks (Sphyrna lewini) also have proportionally taller dorsal fins compared to pectoral fins than most shark species and similar to that of great hammerhead sharks, and thus might exhibit similar rolling behavior. This was assessed by deploying multi-sensor accelerometer instrument packages on free-swimming adult scalloped hammerhead sharks to directly measure swimming depth, body orientation and swimming performance. Specific objectives were to (1) determine whether scalloped hammerhead sharks exhibit side swimming and rolling behavior, (2) characterize the patterns of these behaviors, and (3) evaluate the purpose of these behaviors. Results: We obtained 196.7 total days (4720 h) of data from 9 free-swimming adult scalloped hammerhead sharks equipped with multi-instrument biologgers with deployment durations ranging from 7 to 29 days. All sharks exhibited rolling behavior throughout the entire period of observation. The roll angle magnitude and periodicity of rolling showed a clear diel pattern. During daytime, the sharks spent an average of 48% of the time swimming at a roll angle > 30°, with an average roll angle of 41° and rolling periodicity of around 4 min. At night, the sharks spent an average 82% of their time at an angle > 30°, with an average roll angle of 60° and rolling periodicity of around 13 min. In addition to an increase in degree of roll and roll duration, overall dynamic body acceleration (ODBA) also increased at night, and tailbeat frequency was more regular and consistent than during daytime. Conclusion: We observed rolling behavior in scalloped hammerhead sharks similar to that observed in great hammerhead sharks. The diel changes in roll angle and periodicity were accompanied by other changes in swimming behavior. These changes are possibly due to interplay between reducing cost of transport and social interactions with conspecifics.

The Huachuca springsnail (Pyrgulopsis thompsoni) is a species of concern inhabiting springs of the Huachuca Mountains in southeastern Arizona, USA. We documented springsnail distribution and examined the major abiotic and biotic factors influencing springsnail abundance at eight spring channels before and after the onset of seasonal summer rains in 2003. Of the abiotic factors examined (total dissolved solids, pH, distance from spring source, spring channel, water temperature, and dissolved oxygen), only spring channel and total dissolved solids were strongly associated with springsnail abundance. However, correlation of total dissolved solids with pH, temperature, dissolved 02, and distance downstream necessitated hrther exploration of these explanatory variables. We found that sampling locations with P. thompsoni were characterized by cooler, more oxygenated, and less-occluded water conditions relative to sampling locations without springsnails. Springsnail abundance was positively associated with abundance of caddisfly larvae (Helicopsyche sp.) but not significantly associated with abundance of a co-occurring snail (Physa sp.). The most important outcomes of this study were the documentation of major factors associated with springsnail abundance, and recovery of springsnails at greater distances downstream than previously documented.

A female scalloped hammerhead shark (Sphyrna lewini) conducted a species record deep dive to 1240 m in coastal‐pelagic waters off Hawaii Island. This extends the deepest known depth range of the species by over 200 m (650 ft) and highlights the question of the extent to which deep‐diving activity is mediated by physiological constraints, such as temperature and oxygen availability.

Fish moving between different thermal environments experience heat exchange via conduction through the body wall and convection from blood flow across the gills. We report a strategy of preventing convective heat loss at the gills during excursions into deep, cold water by the tropical scalloped hammerhead shark ( Sphryna lewini ). Adult scalloped hammerhead sharks dive rapidly and repeatedly from warm (~26°C) surface waters to depths exceeding 800 meters with temperatures as low as 5°C. Biologgers attached to adult sharks show that warm muscle temperatures were maintained throughout the deepest portion of each dive. Substantive cooling only occurred during the latter stages of the ascent phase and, once initiated, was rapid. Heat transfer coefficient modeling indicated that convective heat transfer was suspended, probably by suppressing gill function during deep dives. This previously unobserved strategy has broad similarities to marine mammal “breath hold” diving.