The rise of low-cost, small, and efficient microcontrollers and single-board computers (e.g., Arduino1, Raspberry Pi2, Nvidia Jetson3) has catalyzed a vibrant, user-led community that focuses on the ...development of useful or fun "do-it-yourself (DIY) projects. The utility of these "tiny computers" as backbones for low-cost oceanographic sensor systems has not been lost on the marine science community, particularly for applications that do not need the endurance, accuracy, or ruggedness provided by commercial oceanographic products. Additionally, open-source oceanographic tools bolster the goals of the United Nation's Decade of Ocean Science for Sustainable Development to encourage a more inclusive and participative approach to ocean science, to better predict ocean phenomena, and to democratize access to the ocean.
Passive acoustics is a tool to monitor behavior, distributions, and biomass of marine invertebrates, fish, and mammals. Typically, fixed passive acoustic monitoring platforms are deployed, using a ...priori knowledge of the location of the target vocal species. Here, we demonstrate the ability to conduct coastal surveys of fish choruses, spatially mapping their distributions with an autonomous surface vehicle. For this study, we used an autonomous Liquid Robotics Wave Glider SV3 equipped with a Remora-ST underwater acoustic recorder and hydrophone. The exploratory 15-day deployment transited through three marine reserves, resulting in approx. 200 hours of passive acoustic recordings, and revealed five distinct fish choruses from La Jolla to Capistrano Beach, CA (approx. 80 km separation), each with unique acoustic signatures. Choruses occurred in the evening hours, typically in the 40 to 1000 Hz band. There was a lack of both temporal and frequency partitioning amongst the choruses, but some choruses exhibited distinct spatial niches by latitude and water temperature. These results suggest that the mobility of the Wave Glider allows for persistent surveys and studies that otherwise may be too challenging or costly for stationary or ship-based sensors; a critical consideration for documenting biological activity over large spatiotemporal scales, or sampling of nearshore marine reserves.
Soundscape ecology is a relatively new field that can provide insights into the structure and health of marine habitats. Though this field is growing, the acoustics of many marine habitats, including ...the giant kelp forests off Southern California, remain poorly studied. Here, we examine the diel and seasonal periodicity of kelp forest soundscapes within a protected and unprotected site off San Diego, CA. Singular value decomposition was used to identify frequency bands of interest, enabling tracking of these bands through seasons to examine their variability. Four frequency bands were identified: (1) 60–130 Hz, which encompassed a putative fish chorus, (2) 300–500 Hz, which encompassed a different putative fish chorus, (3) a band that encompassed humming generated by Plainfin Midshipmen
Poricthys notatus
(fundamental frequency: 85–95 Hz, and two subharmonics 175–185 Hz and 265–275 Hz), and (4) a band that encompassed the snaps of snapping shrimps from 2.5 to 7.5 kHz. Overall, kelp forest soundscapes exhibited diel and seasonal variability. In particular, the two putative fish choruses dominated the dusk soundscapes during late spring and summer, and the Midshipmen hums persisted throughout nights in summer. Snapping shrimp sounds exhibited stereotypic crepuscular activity, with peaks in acoustic energy in the 2.5–7.5 kHz band occurring at dusk and dawn. In addition, vessel noise was identified and found to exhibit strong seasonal and spatial variation. Vessel noise was greatest during August and September at the protected site and was generally lower during the winter and spring months. These findings help establish reference acoustic indices for the kelp forests off Southern California, within and outside of a protected area, and can provide resource managers with information on how well a marine reserve protects a species of interest, as well as the putative human visitation of these protected areas.
•Large Atlantic bluefin tuna tagged off the coast of Ireland utilize the warm North Atlantic Current to access foraging areas in the North Atlantic Ocean.•Five hotspots of Atlantic bluefin tuna occur ...in the central and eastern North Atlantic Ocean. Each are in regions with long-lived, quasi-stationary anticyclonic features (i.e., eddies or recirculation).•Daily maximum depth and time at mesopelagic depths (i.e., greater than 200 m) are positively correlated with absolute dynamic topography in the open ocean.•In the Winter, a majority of Atlantic bluefin tuna tagged in Irish waters travel to the Newfoundland Basin, a region with intense mesoscale eddy activity and high mesopelagic fish biomass.•Some Atlantic bluefin tuna migrated in the Spring to the Mediterranean Sea, an important spawning ground for this species.
Electronic tagging of Atlantic bluefin tuna (ABT; Thunnus thynnus) has shaped our understanding of their movements and migrations throughout the Atlantic basin. In this study, we used pop-up satellite archival tagging data to examine the movements of 51 large (CFL µ ± σ: 215 ± 15 cm) ABT tagged off the coast of Ireland. When combined with satellite oceanographic data, we found that ABT take advantage of the warm North Atlantic Current to access foraging areas in the North Atlantic Ocean. We identified four potential foraging regions: (1) off the coast of Ireland, (2) the Bay of Biscay, (3) the Newfoundland Basin, and (4) the West European Basin. In addition, 14 ABT migrated to their spawning grounds in the Mediterranean Sea, entering by May 16 and exiting by July 7, on average. In all five regions, anticyclonic ocean features (i.e., eddies or recirculation) were present. In the open ocean, these features often co-occurred with areas where the daily maximum depth of tuna exceeded 400 m and tuna spent extended time at mesopelagic depths (i.e., greater than 200 m). We hypothesize that ABT exploit anticyclonic structures to forage on the abundant mesopelagic fish communities. Additionally, our results suggest that ABT are travelling across the North Atlantic Ocean in a directed migration to the Newfoundland Basin to reach what may be one of the best mesopelagic feeding grounds in the world.
The Southern California Bight (SCB) is a highly productive ecosystem and thus, attracts a variety of cetaceans, including Bryde’s whales (Balaenoptera edeni). It also has areas of high human activity ...where ocean noise includes by sound from commercial shipping as well as from sonar activity. Several encounters of Bryde’s whales were tracked in this area using a large-aperture seafloor array of five High-frequency Acoustic Recordings Packages (HARPs), deployed from December 2010 to February 2011. Bryde’s whale Be4 calls were manually detected. Time-difference-of-arrivals (TDOAs) of a call between each hydrophone pair were computed by cross-correlating time series waveforms. A 10 km × 10 km area with 25-m grid spacing and homogeneous sound speed was used to calculate sets of modeled TDOAs for each grid point. To localize each whale call, the grid point with the smallest total least-squares difference between the set of measured and modeled TDOAs was used. Successive locations provide tracks from which sound source levels, swimming speeds, and calling rates can be estimated. These preliminary results provide a quantitative foundation required for sound impact studies as well as a population density estimate of this species in the SCB.
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