Active acoustic telemetry tracking and tri-axial accelerometers reveal fine-scale movement strategies of a non-obligate ram ventilator

Abstract

Background: California horn sharks (Heterodontus francisci) are nocturnally active, non-obligate ram ventilating sharks in rocky reef habitats that play an important ecological role in regulating invertebrate communities. We predicted horn sharks would use an area restricted search (ARS) movement strategy to locate dense resource patches while minimizing energetic costs of travel and nighttime activity. As ectotherms, we predicted environmental temperature would play a significant role in driving movement and activity patterns. Methods: Continuous active acoustic tracking methods and acceleration data loggers were used to quantify the diel fine-scale spatial movements and activity patterns of horn sharks. First passage time was used to identify the scale and locations of patches indicative of ARS. Activity was assessed using overall dynamic body acceleration (ODBA) as a proxy for energy expenditure. Behavior within a patch was characterized into three activity patterns: resting, episodic burst activity, and moderate, consistent activity. Results: After resting in daytime shelters, individuals travelled to multiple reefs throughout the night, traversing through depths of 2-112 m and temperatures of 10.0-23.8°C. All sharks exhibited area restricted search patch use and arrived at their first patch approximately 3.4 ± 2.2 h (mean ± SD) after sunset. Sharks exhibited moderate, consistent activity in 54% of the patches used, episodic burst activity in 33%, and few (13%) were identified as resting at night. ODBA peaked while sharks were swimming through relatively deeper (~30 m), colder channels when traversing from one patch to the next. There was no consistent pattern between ODBA and temperature. Conclusions: We provide one of the largest fine-scale, high-resolution paired data sets for an elasmobranch movement ecology study. Horn sharks exhibited ARS movement patterns for various activity patterns. Individuals likely travel to reefs known to have profitable and predictable patches, potentially tolerating less suitable environmental temperatures. We demonstrate how gathering high-resolution information on the movement decisions of a community resident enhances knowledge of community structure and overall ecosystem function.

Diverse Activity Rhythms in Sharks (Elasmobranchii)

“…This is consistent with data obtained from video and accelerometry data from captive animals, which exhibited late-evening activity peaks and daytime troughs. A similar pattern has also recently been reported in the closely related horn shark ( Heterodontus francisci ), with wild sharks resting in shelters throughout the day and becoming active at night (Meese and Lowe, 2020). Whether these activity patterns are endogenous or regulated by external cues is unknown.…”

Determining Stingray Movement Patterns in a Wave-Swept Coastal Zone Using a Blimp for Continuous Aerial Video Surveillance

“…The stingrays in our study generally exhibited straight movements even at fine spatial scales, except when swimming in the northern headland, where the sinuosity increased significantly. Sinuous movement has been related to searching behaviours in other stingray species and demersal elasmobranchs-with animals seeking to locate resource patches, including foraging opportunities, shelter, or potential mates [19,[44][45][46]. Our findings are consistent with stingrays using the central, sandflat area of the bay for transiting between locations in their home range and the northern headland for exploring resource patches.…”

Intraspecific variation in diel patterns of rocky reef use suggests temporal partitioning in Port Jackson sharks

“…Further, with fewer remaining males, females are less likely to be sexually harassed later in the breeding season, which may also prolong female residency events on the subtidal rocky reefs. Sexual segregation on a spatial scale is a common behaviour observed across many species of elasmobranchs (Wearmouth and Sims 2010), including other horned sharks (Meese and Lowe 2020). It is thought to result from intraspecific competition, differences in pre-and post-copulatory reproductive strategies or differences in habitat or energetic requirements between the sexes (Sims 2003;Wearmouth and Sims 2008;Jacoby et al 2010).…”