Kona Coast Research Articles

Raman analysis of octocoral carbonate ion structural disorder along a natural depth gradient, Kona coast, Hawai‘i

Abstract Both environmental and physiological factors cause carbonate ion structural disorder in biogenic Mg-calcites. A major component of this disorder is driven by the incorporation of Mg through environmental forcing and growth rate kinetics although non-Mg factors (e.g., other cation/anion impurities, organic molecules) also contribute. Understanding the drivers of Mg content in biogenic calcite and its effects on disorder has implications for octocoral Mg paleo-proxies and the stability and diagenetic alteration of their calcitic skeletons. However, prior studies of biogenic Mg-calcites have often been complicated by sampling inconsistencies over space and time and potential intra-sample Mg variability. This study aims to analyze the relative contributing factors of octocoral Mg-calcite structural disorder along gradients of both depth and growth rate. Calcitic octocorals (Coralliidae and Keratoisididae, N = 28) were collected from 221–823 m depths across a natural gradient in biogeochemical parameters (pH: 7.4–7.9, T: 5–16 °C) off the Kona coast of Hawai‘i Island and were analyzed using Raman spectroscopy. Samples were collected during the same month, controlling for potential seasonal variability. Raman spectral parameters from the ν1 peak quantified total carbonate ion structural disorder (full-width at half maximum height [FWHM] of ν1) and Mg content (ν1 position, Raman shift). The total structural disorder was then partitioned into Mg-driven and non-Mg driven components (residual ν1 FWHM). The total structural disorder and Mg content decreased significantly with increasing depth, correlating with temperature and carbonate system parameters. The Mg-temperature relationships from this study were also consistent with prior studies. Non-Mg structural disorder did not correlate to any environmental parameters. When measured across an intra-sample gradient of ontogenetic growth rate, total structural disorder, Mg content, and non-Mg structural disorder increased with growth rate for all but one taxon, demonstrating the kinetic effect of growth rate as well as potential taxon-specific physiological effects. These results provide insight into how environmental and growth rate kinetic effects independently affect different components of carbonate ion structural disorder (Mg content and non-Mg factors). These findings also suggest that Raman spectroscopy may be helpful in quantifying solubility within biogenic calcites.

Mountain-to-sea ecological-resource management: Forested watersheds, coastal aquifers, and groundwater dependent ecosystems

Improving the understanding of connections spanning from mountain to sea and integrating those connections into decision models have been increasingly recognized as key to effective coastal resource management. In this paper, we aim to improve our understanding of the relative importance of linkages between a forested watershed, a coastal groundwater aquifer, and a nearshore marine groundwater-dependent ecosystem (GDE) using a dynamic groundwater optimization framework and simple ecosystem equations. Data from the Kīholo aquifer on the Kona Coast of Hawai‘i Island are used to numerically illustrate optimal joint management strategies and test the sensitivity of those strategies to variations in physical and behavioral parameter values. We find that for a plausible range of watershed management costs, protecting part of the recharge capture area is always optimal. Without watershed protection, maintaining a safe minimum standard growth rate for a GDE-dependent marine indicator species, reduces net present value non-trivially, but optimal investment in watershed conservation offsets that potential reduction by 75 %. In general, we find that optimal watershed management and groundwater pumping are most sensitive to changes in water demand growth and parameters that describe nearshore salinity.

Combined passive acoustic and video monitoring of coral reefs to better understand reef soundscapes and multi-species interactions

A detailed understanding of ecological soundscapes provides a window into ecosystem state that might otherwise go undetected. Rather than consider acoustic emissions of a particular species, a top down ecosystem acoustics point of view gives potentially valuable insights to reef ecosystem function. Simultaneous passive acoustic and video data were collected from coral reefs off the Kona Coast of Hawaii in January 2019 during a soundscape experiment. Frequent interactions between fish species as well as collective behaviors are identified and tracked by applying computer vision to video data. Comparison relating video data to acoustic data allows assessment of the same behaviors as simultaneously reflected in directional passive acoustic data. Collective consideration of acoustics and video offers insight into acoustic signatures of particular soniferous communities and behaviors amongst and between reef species. Machine learning applications match patterns between fish trajectories in videos and the sound field as received by a directional antenna. The relative level of biological activity and presence or absence of particular behaviors provides key data in the effort to understand coral reef ecosystem state.

Numerical Simulations of Seasonal Variations of Rainfall over the Island of Hawaii

AbstractThe seasonal variations of rainfall over the island of Hawaii are studied using the archives of the daily model run from the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) from June 2004 to February 2010. Local effects mainly drive the rainfall on the Kona coast in the early morning and the lower slopes in the afternoon. During the summer, the incoming trade winds are more persistent and moister than in winter. The moisture content in the wake zone is higher than open-ocean values because of the convergent airflow associated with dual counterrotating vortices. As the westerly reversed flow moves toward the Kona coast, it decelerates with increasing moisture and a moisture maximum over the coastal area, especially in the afternoon hours in summer months. The higher afternoon rainfall on the Kona lower slopes in summer than in winter is caused by a moister (>6 mm) westerly reversed flow bringing moisture inland and merging with a stronger upslope flow resulting from solar heating. Higher nocturnal rainfall off the Kona coast in summer than in winter is caused by the low-level convergence between a moister westerly reversed flow and offshore flow. On the windward slopes, the simulated rainfall accumulation in winter is higher because of frequently occurring synoptic disturbances during the winter storm season. Nevertheless, early morning rainfall along the windward coast and afternoon rainfall over the windward slopes of the Kohala Mountains is lower in winter because the incoming trades are drier.

Near shore distributions of phytoplankton and bacteria in relation to submarine groundwater discharge-fed fishponds, Kona coast, Hawai‘i, USA

Phytoplankton are important components of coastal marine ecosystems that are strongly influenced by freshwater inputs from land, including submarine groundwater discharge (SGD). Although SGD generates sharp onshore – offshore gradients in physical and chemical conditions at several locations around Hawaii Island little is known about the biotic responses of water column microbes to these conditions. We studied the distributions of phytoplankton and bacteria at two contrasting sites with SGD-fed fishponds, Kiholo and Kaloko Bay, including the full range of salinity extending from the fishponds to the coastal ocean. We addressed the hypotheses that (1) SGD-fed fishponds support a higher biomass and different composition of phytoplankton than the adjacent ocean, and (2) phytoplankton biomass and composition are related to SGD-driven salinity gradients in the coastal ocean. Phytoplankton biomass in fishponds was elevated (10–100-fold) and accompanied by higher average cell size pico- and nano-phytoplankton (2–6 μm) relative to sites outside the fishpond. General additive models (GAMs) showed elevated biomass and average cell size at mid-range salinities and declining biomass at salinity < 20 outside the fishponds. Multivariate RDA showed significant, site-specific relationships between surface phytoplankton biomass (Chl a), cell counts, and environmental parameters. Analysis of surface vs. deep samples from outside the fishponds showed elevated phytoplankton biomass at the surface, except in Kiholo lagoon where phytoplankton was elevated beneath the SGD-driven pycnocline. This study shows structuring of coastal phytoplankton through SGD inputs and suggest that changes in SGD due to coastal development or climate change can impact coastal marine ecosystems through effects on phytoplankton communities.

Long-term characterization of the marine soundscape in Kona, Hawaii

Soundscape analysis of marine environments is still a new field of inquiry, with the majority of studies focusing on individual species or acoustic functional groups. Additionally, the challenges of making long term acoustic recordings in marine habitats, particularly in deep water, have limited the duration of many analyses. The Pacific Islands Fishery Science Center has been collecting passive acoustic data at a depth of 630 m off the Kona coast of the Island of Hawaii since 2007, and has recently begun a soundscape analysis effort to characterize the contributors to the local acoustic environment. This project seeks to examine not only low frequency noise patterns, below 1 kHz, but also higher frequency sounds that may overlap in frequency with the signals of many cetacean species. We have begun by identifying the relative contribution of odontocete echolocation, and also close approaches of boats and the presence of echosounders. The temporal patterns in these signals reveal daily and seasonal cycles in biological and anthropogenic sounds, which provide both detailed insight into the interactions between humans, animals and their environment, and long term trends in activity of those sound sources.Soundscape analysis of marine environments is still a new field of inquiry, with the majority of studies focusing on individual species or acoustic functional groups. Additionally, the challenges of making long term acoustic recordings in marine habitats, particularly in deep water, have limited the duration of many analyses. The Pacific Islands Fishery Science Center has been collecting passive acoustic data at a depth of 630 m off the Kona coast of the Island of Hawaii since 2007, and has recently begun a soundscape analysis effort to characterize the contributors to the local acoustic environment. This project seeks to examine not only low frequency noise patterns, below 1 kHz, but also higher frequency sounds that may overlap in frequency with the signals of many cetacean species. We have begun by identifying the relative contribution of odontocete echolocation, and also close approaches of boats and the presence of echosounders. The temporal patterns in these signals reveal daily and seasonal cycles ...

Deep sea animal density and size estimated using a Dual-frequency IDentification SONar (DIDSON) offshore the island of Hawaii

Pelagic animals that form deep sea scattering layers (DSLs) represent an important link in the food web between zooplankton and top predators. While estimating the composition, density and location of the DSL is important to understand mesopelagic ecosystem dynamics and to predict top predators’ distribution, DSL composition and density are often estimated from trawls which may be biased in terms of extrusion, avoidance, and gear-associated biases. Instead, location and biomass of DSLs can be estimated from active acoustic techniques, though estimates are often in aggregate without regard to size or taxon specific information. For the first time in the open ocean, we used a DIDSON sonar to characterize the fauna in DSLs. Estimates of the numerical density and length of animals at different depths and locations along the Kona coast of the Island of Hawaii were determined. Data were collected below and inside the DSLs with the sonar mounted on a profiler. A total of 7068 animals were counted and sized. We estimated numerical densities ranging from 1 to 7 animals/m3 and individuals as long as 3 m were detected. These numerical densities were orders of magnitude higher than those estimated from trawls and average sizes of animals were much larger as well. A mixed model was used to characterize numerical density and length of animals as a function of deep sea layer sampled, location, time of day, and day of the year. Numerical density and length of animals varied by month, with numerical density also a function of depth. The DIDSON proved to be a good tool for open-ocean/deep-sea estimation of the numerical density and size of marine animals, especially larger ones. Further work is needed to understand how this methodology relates to estimates of volume backscatters obtained with standard echosounding techniques, density measures obtained with other sampling methodologies, and to precisely evaluate sampling biases.

Natural and anthropogenic events influence the soundscapes of four bays on Hawaii Island

The soundscapes of four bays along the Kona Coast of Hawaii Island were monitored between January 2011 and March 2013. Equivalent, unweighted sound pressure levels within standard 1/3rd-octave bands (dB re: 1μPa) were calculated for each recording. Sound levels increased at night and were lowest during the daytime when spinner dolphins use the bays to rest. A tsunami provided an opportunity to monitor the soundscape with little anthropogenic component. We detected a decrease in sound levels and variability in one of the busiest bays. During the daytime in the 3.15kHz 1/3rd octave band, we detected 92 loud outliers from vessels, aquaculture, and military mid-frequency active sonar. During one military mid-frequency active sonar event sound levels reached 45.8dB above median ambient noise levels. The differences found in the bays illustrate the importance of understanding soundscapes to effectively manage noise pollution in marine ecosystems.

Spatio-temporal variation and seasonality of Odontocetes' foraging activity in the leeward side of the island of Hawaii

The Kona coast of the island of Hawaii hosts many species of odontocetes. These marine mammals are top predators and their foraging activity plays an important role in the ecosystem dynamics. Three passive acoustics recorders were used to study the temporal and spatial occurrence of the foraging activity of odontocetes (excluding beaked and sperm whales) at three locations along the Kona coast of Hawaii between 2012 and 2013. Echolocation clicks were detected using the M3R11M3R: Marine Mammal Monitoring on Navy Ranges; EAR: Ecological Acoustic Recorder; NK: North Kona; CK: Central Kona; SK: South Kona; CS-SVM: Class Specific Support Vector Machine; GLM: Generalized Linear Model; ANOVA: Analysis of variance. (Marine Mammal Monitoring on Navy Ranges) system, and custom-designed Matlab (MathWorks, Natick, MA, USA) programs were designed to analyze the detected data. A Generalized Linear Model was used to understand the influence of location and month on the foraging activity. Both location and month affected the foraging activity of Odontocetes in Hawaii. In general, the foraging activity was the highest in the north and the lowest in the south part of the study area. The model revealed that, at each location, the foraging activity tended to decrease over the time of the study. A seasonality seems to be seen for the two southernmost locations. At the northernmost location the foraging activity decreased from February 2012 till 11 months later (January 2013). Odontocetes daily foraging activity was higher at night-time at all locations sampled.

Rare earth element behavior during groundwater–seawater mixing along the Kona Coast of Hawaii

Groundwater and seawater samples were collected from nearshore wells and offshore along the Kona Coast of the Big Island of Hawaii to investigate rare earth element (REE) behavior in local subterranean estuaries. Previous investigations showed that submarine groundwater discharge (SGD) is the predominant flux of terrestrial waters to the coastal ocean along the arid Kona Coast of Hawaii. Groundwater and seawater samples were filtered through 0.45μm and 0.02μm pore-size filters to evaluate the importance of colloidal and soluble (i.e., truly dissolved ionic species and/or low molecular weight [LMW] colloids) fractions of the REEs in the local subterranean estuaries. Mixing experiments using groundwater collected immediately down gradient from a wastewater treatment facility (WWTF) proximal to the Kaloko-Hanokohau National Historic Park, and more “pristine” groundwater from a well constructed in a lava tube at Kiholo Bay, were conducted with local seawater to study the effect of solution composition (i.e., pH, salinity) on the concentrations and fractionation behavior of the REEs as groundwater mixes with seawater in Kona Coast subterranean estuaries. The mixed waters were also filtered through 0.45 or 0.02μm filters to ascertain the behavior of colloidal and soluble fractions of the REEs across the salinity gradient in each mixing experiment. Concentrations of the REEs were statistically identical (two-tailed Student t-test, 95% confidence) between the sequentially filtered sample aliquots, indicating that the REEs occur as dissolved ionic species and/or LMW colloids in Kona Coast groundwaters. The mixing experiments revealed that the REEs are released to solution from suspended particles or colloids when Kona Coast groundwater waters mix with local seawater. The order of release that accompanies increasing pH and salinity follows light REE (LREE)>middle REE (MREE)>heavy REE (HREE). Release of REEs in the mixing experiments is driven by decreases in the free metal ion activity in solution and the concomitant increase in the amount of each REE that occurs in solution as dicarbonato complexes [i.e., Ln(CO3)2−] as pH increases across the salinity gradient. Input-normalized REE patterns of Kona Coast groundwater and coastal seawater are nearly identical and relatively flat compared to North Pacific seawater, indicating that SGD is the chief source of these trace elements to the ocean along the Kona Coast. Additionally, REE concentrations of the coastal seawater are between 10 and 50 times higher than previously reported open-ocean seawater values from the North Pacific, further demonstrating the importance of SGD fluxes of REEs to these coastal waters. Taken together, these observations indicate that large-scale removal of REEs, which characterizes the behavior of REEs in the low salinity reaches of many surface estuaries, is not a feature of the subterranean estuary along the Kona Coast. A large positive gadolinium (Gd) anomaly characterizes groundwater from the vicinity of the WWTF. The positive Gd anomaly can be traced to the coastal ocean, providing further evidence of the impact of SGD on the coastal waters. Estimates of the SGD fluxes of the REEs to the coastal ocean along the Kona Coast (i.e., 1.3–2.6mmolNdday−1) are similar to recent estimates of SGD fluxes of REEs along Florida’s east coast and to Rhode Island Sound, all of which points to the importance of SGD as significant flux of REEs to the coastal ocean.

Using acoustics to prioritize management decisions to protect coastal dolphins: A case study using Hawaiian spinner dolphins

For more than a decade, interactions between humans and Hawaiian spinner dolphins in their resting bays have been a concern for members of the general public, managers, scientists, policymakers, and tour operators. Hawaiian spinner dolphins are the target of a large wildlife tourism industry due to their predictable daytime resting behavior and presence in coastal areas. Using results from passive acoustic monitoring between January 2011 and March 2013 on the Kona coast of Hawai‛i Island, USA, the relative importance of four known Hawaiian spinner dolphin resting bays, the contribution of anthropogenic noise including vessel noise to the four bay soundscapes, and the dolphins' response to human activities were assessed. Here the findings are summarized and visualized and recommendations are provided for action to regulate directed dolphin watching and ensuing unauthorized takes under the Marine Mammal Protection Act of 1972. These findings and recommendations have implications for the federal government's ongoing efforts to implement rules that protect Hawaiian spinner dolphins in their resting bays.

Temporal and spatial variation of beaked and sperm whales foraging activity in Hawai'i, as determined with passive acoustics.

Beaked and sperm whales are top predators living in the waters off the Kona coast of Hawai'i. Temporal and spatial analyses of the foraging activity of these two species were studied with passive acoustics techniques. Three passive acoustics recorders moored to the ocean floor were used to monitor the foraging activity of these whales in three locations along the Kona coast of the island of Hawaii. Data were analyzed using automatic detector/classification systems: M3R (Marine Mammal Monitoring on Navy Ranges), and custom-designed Matlab programs. The temporal variation in foraging activity was species-specific: beaked whales foraged more at night in the north, and more during the day-time off Kailua-Kona. No day-time/night-time preference was found in the southern end of the sampling range. Sperm whales foraged mainly at night in the north, but no day-time/night-time preference was observed off Kailua-Kona and in the south. A Generalized Linear Model was then applied to assess whether location and chlorophyll concentration affected the foraging activity of each species. Chlorophyll concentration and location influenced the foraging activity of both these species of deep-diving odontocetes.

Studying deep diving odontocetes potential prey fields' densities and size structure in Hawaii using a DIDSON imaging sonar

Deep diving odontocetesodontocetes feed in the deep ocean on mesopelagic squid and fish. The distribution of these prey are poorly known but does affect the distribution of deep diving odontocete predators. Hence, it is important to collect data on the density and composition of potential prey to identify deep sea habitats that attract deep diving odontocetes. We used a DIDSON imaging sonar to investigate the density and size structure of mesopelagic animals along the Kona coast of Hawaii, where beaked, sperm and pilot whales are regularly seen. Data were collected at multiple stations during three research cruises by lowering the sonar in the water column to sample at different depths and monitoring the mesopelagic biomass with an EK60 38 kHz echosounder. Foraging activity of whales was monitored at few stations using passive acoustic recorders and a towed array of hydrophones. We were able to count and size 7068 pelagic animals. Density and size varied in space, with higher densities and bigger animals at the offshore stations. The DIDSON was effective at detecting targets bigger than 10 cm, a size range that includes potential prey of deep diving odontocetes. Preliminary data suggest differences may exists in habitat selection by each deep diving odontocetes.

Passive acoustic monitoring of coastally associated Hawaiian spinner dolphins, Stenella longirostris, ground-truthed through visual surveys.

Effective decision making to protect coastally associated dolphins relies on monitoring the presence of animals in areas that are critical to their survival. Hawaiian spinner dolphins forage at night and rest during the day in shallow bays. Due to their predictable presence, they are targeted by dolphin-tourism. In this study, comparisons of presence were made between passive acoustic monitoring (PAM) and vessel-based visual surveys in Hawaiian spinner dolphin resting bays. DSG-Ocean passive acoustic recording devices were deployed in four bays along the Kona Coast of Hawai'i Island between January 8, 2011 and August 30, 2012. The devices sampled at 80 kHz, making 30-s recordings every four minutes. Overall, dolphins were acoustically detected on 37.1% to 89.6% of recording days depending on the bay. Vessel-based visual surveys overlapped with the PAM surveys on 202 days across the four bays. No significant differences were found between visual and acoustic detections suggesting acoustic surveys can be used as a proxy for visual surveys. Given the need to monitor dolphin presence across sites, PAM is the most suitable and efficient tool for monitoring long-term presence/absence. Concomitant photo-identification surveys are necessary to address changes in abundance over time.

Groundwater-derived nutrient and trace element transport to a nearshore Kona coral ecosystem: Experimental mixing model results

Study regionThe groundwater influenced coastal waters along the arid Kona coast ofthe Big Island, Hawai’i. Study focusA salinity-and phase partitioning-based mixing experiment was constructed using contrasting groundwater endmembers along the arid Konacoast of the Big Island, Hawai’i and local open seawater to better understand biogeochemical and physicochemical processes that influence the fate of submarine groundwater discharge (SGD)-derived nutrients and trace elements. New Hydrological Insights for the RegionTreated wastewater effluent was the main source for nutrient enrichment downstream at the Honokōhau Harbor site. Conservative mixing for some constituents, such as nitrate+nitrite, illustrate the effectiveness of physical mixing to maintain oceanic concentrations in the colloid (0.02–0.45μm) and truly dissolved (<0.02μm) forms. In contrast, the nonconservative behavior of phosphate highlights the importance of surface complexation reactions that can lead to higher concentrations based on conservative mixing alone. Results from this physiochemical mixing experiment demonstrate how relative availability of P can shift with adsorption behavior, affecting the mobility of phosphate in the environment. With a proposed 8-hectare wastewater treatment facility (WWTF) to be constructed upslope of the Kaloko-Honokōhau National Historical Park (NHP), treated effluent is projected to add additional nutrients. Combined with high permeability, rapid discharge, and increased nutrient loading SGD will likely continue to serve as a persistent source of nutrients and potential contaminant to coral ecosystems.

Physicochemical characteristics, community assemblages, and food web structure in anchialine pools along the Kona Coast on the Island of Hawaii, USA

Anchialine pools are unique localized brackish water ecosystems, comprised of fresh groundwater and saltwater from the ocean mixing through subterranean pathways. This study characterized physicochemical properties, biological communities, and food web structures in anchialine pools on Hawaii Island, hypothesizing pronounced differences between pools with and without introduced fishes. Pools varied greatly in size, temperature, salinity, and dissolved oxygen saturation. On average, 46% of observed species were introduced. Native species of high conservation concern such as the shrimp Metabetaeus lohena and Halocaridina rubra were not observed in pools with introduced fishes, where periphytic algal biomass was lower. δ13C and δ15N analyses revealed an unusual food web structure where all animal species (except Gambusia affinis) occupied the same trophic niche, independent of species, size, and sex. These findings illustrate that simple food web structures with opportunistic feeding patterns in all species can occur in ecosystems that have greatly variable physicochemical properties and diverse biological communities. The wide variation in biological communities even in adjacent pools indicates that individual anchialine pools are unique. The high proportion of introduced species and their observed effects on these fragile ecosystems suggest that they pose a serious threat to native biota in Hawaiian anchialine pools.

Characterizing a Foraging Hotspot for Short-Finned Pilot Whales and Blainville's Beaked Whales Located off the West Side of Hawai'i Island by Using Tagging and Oceanographic Data.

Satellite tagging data for short-finned pilot whales (Globicephala macrorhynchus) and Blainville’s beaked whales (Mesoplodon densirostris) were used to identify core insular foraging regions off the Kona (west) Coast of Hawai‘i Island. Ship-based active acoustic surveys and oceanographic model output were used in generalized additive models (GAMs) and mixed models to characterize the oceanography of these regions and to examine relationships between whale density and the environment. The regions of highest density for pilot whales and Blainville’s beaked whales were located between the 1000 and 2500 m isobaths and the 250 and 2000 m isobaths, respectively. Both species were associated with slope waters, but given the topography of the area, the horizontal distribution of beaked whales was narrower and located in shallower waters than that of pilot whales. The key oceanographic parameters characterizing the foraging regions were bathymetry, temperature at depth, and a high density of midwater micronekton scattering at 70 kHz in 400–650 m depths that likely represent the island-associated deep mesopelagic boundary community and serve as prey for the prey of the whales. Thus, our results suggest that off the Kona Coast, and potentially around other main Hawaiian Islands, the deep mesopelagic boundary community is key to a food web that supports insular cetacean populations.

Impacts of Land-Use Change on Groundwater Supply: Ecosystem Services Assessment in Kona, Hawaii

AbstractPayments for watershed management link upstream inhabitants whose actions affect water resources with downstream water users. This paper evaluates the effect of plausible shifts in watershed land use on hydrologic services on the Kona coast of Hawai’i Island by measuring vegetation effects on hydrologic fluxes, modeling land-use change impact on the water-supply aquifer, and evaluating the local water department’s associated pumping expenses. Transitions between native and plantation forest will have a 25–40% greater impact on the aquifer than the transition from pasture to either forest type. However, for all transitions, the value to the water department is just 2–5% of the opportunity cost to landowners. To provide context for these findings, the effects of these land transitions on carbon storage, provision of native bird habitat, and land stewardship are assessed. Estimates show that delivery of other services does not always increase when water services increase and suggest that the value of...

Deep sea organisms density estimation using a Dual Frequency Identification Sonar (DIDSON)

Estimating the density of organism living in deep sea scatting layers is of key importance for understanding the biomass in the mesopelagic layers. Scientific echosounders are routinely used for this task; however, new imaging sonar technologies pose the opportunity for estimating density of organism, as well as identification at smaller scales. During the 2013 NOAA KONA Integrated Ecosystem, a Dual Frequency Identification Sonar (DIDSON) (SoundMetrics Inc.) was used to estimate the density, length of organisms in the deep sea scattering layers during nighttime and daytime along the KONA coast of the island of Hawaii. At each station, an EK60 38 kHz echosounder was used to find the depth of the deep sea scattering layers, and the DIDSON was lower into the layer (or layers if two were present) (about 500 and 600 m), and underneath the deeper layer (about 800 m). A total of 4621 organisms were counted and sized. We estimated densities ranging from 6 to 1 organism/m3. Density shows some variation between locations and depth and organism as big as 3 m were sighted.

Single-sensor, cue-counting density estimation of highly broadband marine mammal calls

Odontocete echolocation clicks have been used as a preferred cue for density estimation studies from single-sensor data sets, studies that require estimating detection probability as a function of range. Many such clicks can be very broadband in nature, with 10-dB bandwidths of 20 to 40 kHz or more. Because detection distances are not realizable from single-sensor data, the detection probability is estimated in a Monte Carlo simulation using the sonar equation along with transmission loss calculations to estimate the received signal-to-noise ratio of tens of thousands of click realizations. Continuous-wave (CW) analysis, that is, single-frequency analysis, is inherent to basic forms of the passive sonar equation. Considering transmission loss by using CW analysis with the click’s center frequency while disregarding its bandwidth has recently been shown to introduce bias to detection probabilities and hence to population estimates. In this study, false killer whale (Pseudorca crassidens) clicks recorded off the Kona coast of Hawai’i are used to quantify the bias in sonar equation density estimates caused by the center-frequency approach. A different approach to analyze data sets with highly broadband calls and to correctly model such signals is also presented and evaluated. [Work supported by ONR.]