4 research outputs found
First insights into the vertical habitat use of the whitespotted eagle ray Aetobatus narinari revealed by pop‐up satellite archival tags
The whitespotted eagle ray Aetobatus narinari is a tropical to warm‐temperate benthopelagic batoid that ranges widely throughout the western Atlantic Ocean. Despite conservation concerns for the species, its vertical habitat use and diving behaviour remain unknown. Patterns and drivers in the depth distribution of A. narinari were investigated at two separate locations, the western North Atlantic (Islands of Bermuda) and the eastern Gulf of Mexico (Sarasota, Florida, U.S.A.). Between 2010 and 2014, seven pop‐up satellite archival tags were attached to A. narinari using three methods: a through‐tail suture, an external tail‐band and through‐wing attachment. Retention time ranged from 0 to 180 days, with tags attached via the through‐tail method retained longest. Tagged rays spent the majority of time (82.85 ± 12.17% S.D.) within the upper 10 m of the water column and, with one exception, no rays travelled deeper than ~26 m. One Bermuda ray recorded a maximum depth of 50.5 m, suggesting that these animals make excursions off the fore‐reef slope of the Bermuda Platform. Individuals occupied deeper depths (7.42 ± 3.99 m S.D.) during the day versus night (4.90 ± 2.89 m S.D.), which may be explained by foraging and/or predator avoidance. Each individual experienced a significant difference in depth and temperature distributions over the diel cycle. There was evidence that mean hourly depth was best described by location and individual variation using a generalized additive mixed model approach. This is the first study to compare depth distributions of A. narinari from different locations and describe the thermal habitat for this species. Our study highlights the importance of region in describing A. narinari depth use, which may be relevant when developing management plans, whilst demonstrating that diel patterns appear to hold across individuals
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Breaking bags and crunching clams: assessing whitespotted eagle ray interactions with hard clam aquaculture gear
Shallow coastal waters are commonly used in shellfish aquaculture for 'grow-out' of bivalves like the hard clam Mercenaria mercenaria. These locations have substantially higher clam densities than the surrounding environment and attract molluscivores, requiring clammers to incorporate anti-predator materials into their grow-out gear to protect their product. However, the effectiveness of these materials against larger predators like rays remains untested. Inspired by clammer reports of predator-inflicted damage to grow-out gear, we assessed the capacity of the whitespotted eagle ray Aetobatus narinari to interact with clams housed within a suite of industry standard anti-predator materials. Mesocosm experiments were conducted where rays were exposed to unprotected clams (control), clams inside polyester mesh clam bags (dipped in a latex net coating and non-dipped), and under high density polyethylene (HDPE) or chicken wire cover netting. Gear interactions were quantified from video footage throughout the course of the experiment (5 h), and clam mortality was assessed after the completion of each trial. While rays were capable of consuming clams through bags, anti-predator treatments reduced clam mortality 4- to 10-fold compared to control plots. Double-layered (i.e. bags with cover netting) treatments had the lowest clam mortality (0.6 +/- 0.1%; mean +/- SE), highlighting the utility of this type of protection in limiting ray impacts. Though not significantly greater, we noted relatively high levels of interactions with HDPE netting over other materials, which was facilitated by the material ensnaring the lower dental plate of the rays. Clammers should consider adopting multi-layered anti-predator gear; however, resecuring materials periodically remains imperative at reducing ray interactions
Visitation patterns of two ray mesopredators at shellfish aquaculture leases in the Indian River Lagoon, Florida.
The Indian River Lagoon is a primary location of field-based "grow-out" for bivalve shellfish aquaculture along Florida's Atlantic coast. Grow-out locations have substantially higher clam densities than surrounding ambient sediment, potentially attracting mollusk predators to the area. Inspired by clammer reports of damaged grow-out gear, we used passive acoustic telemetry to examine the potential interactions between two highly mobile invertivores-whitespotted eagle rays (Aetobatus narinari) and cownose rays (Rhinoptera spp.)-and two clam lease sites in Sebastian, FL and compared these to nearby reference sites (Saint Sebastian River mouth, Sebastian Inlet) from 01 June 2017 to 31 May 2019. Clam lease detections accounted for 11.3% and 5.6% of total detections within the study period, for cownose and whitespotted eagle rays, respectively. Overall, the inlet sites logged the highest proportion of detections for whitespotted eagle rays (85.6%), while cownose rays (11.1%) did not use the inlet region extensively. However, both species had significantly more detections at the inlet receivers during the day, and on the lagoon receivers during the night. Both species exhibited long duration visits (> 17.1 min) to clam lease sites, with the longest visit being 387.5 min. These visit durations did not vary substantially between species, although there was individual variability. Based on generalized additive mixed models, longer visits were observed around 1000 and 1800 h for cownose and whitespotted eagle rays, respectively. Since 84% of all visits were from whitespotted eagle rays and these longer visits were significantly longer at night, this information suggests that observed interactions with the clam leases are potentially underestimated, given most clamming operations occur during daytime (i.e., morning). These results justify the need for continued monitoring of mobile invertivores in the region, including additional experimentation to assess behaviors (e.g., foraging) exhibited at the clam lease sites