HICEAS is primarily a cetacean and ecosystem survey, and much of the sampling uses standardized methodology that is used in many other regions of the world. However, we also will use the opportunity and our extended time at sea to test new assessment tools, conduct special studies for specific species, and offer opportunities to other scientists to conduct their research in concert with our transect survey. The following are a few of the additional projects we commonly conduct during surveys like HICEAS.
Using Unmanned Aircraft Systems (UAS)
Our work to-date has focused on measuring more traditional characteristics of cetacean populations, like their abundance, mortality, structure, and distribution, but we are also interested in tracking the health of these populations and the individuals within them. Oblique, or sidelong, photography of individual cetaceans from ships and small boats is a staple of our assessment methodology and can be used to visually evaluate some features related to individual health, like whether a whale looks too thin or has a sizeable wound or a skin infection. However, taking vertical photographs from the air offers a better vantage point and a way to explicitly quantify and compare measures that directly relate to the health of population and individuals, like how many females in the population are having calves and what is the nutritional status of individuals?
Vertical aerial photography of cetaceans in Hawaiian waters from manned aircraft is cost-prohibitive and logistically infeasible far from the islands. However, the collection of such photographs using UAS flown from a research vessel could be easily integrated into our standard survey operations. During large-scale surveys like HICEAS we fly a hexacopter from either a ship or small boat to collect high resolution vertical aerial photographs of cetaceans. These images are used to evaluate reproductive output, by quantifying the proportion of adult females with calves in a group, and individual size and body condition, by taking photogrammetric measurements of individual length and width. Target species for UAS operations during large-scale surveys often include false killer whales, short-finned pilot whales, sperm whales, and Bryde's whales, although flights may be made during sightings of rare and high profile species, such as killer whales, blue whales, and North Pacific right whales, in order to maximize the information gained from such unique opportunities.
Surveying with Drifting Autonomous Spar Buoy Recorders (DASBRs)
Autonomous (no human intervention needed) stationary acoustic recorders have been broadly used to understand the distribution and seasonality of cetaceans throughout the world's oceans. At PIFSC, we maintain a network of seafloor-anchored passive acoustic listening stations to listen for cetaceans and understand ocean noise. During HICEAS 2017, we used a new type of free-floating autonomous recorder, the DASBR, to listen for cetaceans throughout the main Hawaiian Islands. DASBRs are designed with 2 hydrophones forming a short vertical array at ~150m depth that allows for computing the depth and distance of the sound source. With these measures, we can determine how far the vocal animals are from DASBR, and the collection of those measurements may allow us to estimate the abundance of the species we're acoustically detecting. Because the instruments are drifting, we can deploy them without regard to bottom depth, and we can sample an area in a more random and representative way than is possible with bottom-mounted stationary recorders.
DASBRs were designed by our partners at the Southwest Fisheries Science Center and were used during their PASCAL survey in 2016. We used them during HICEAS primarily to estimate the abundance of beaked whales and Kogia near the main Hawaiian Islands. These species are especially hard to see, particularly during marginal or poor weather, and are often difficult to approach for species identification even when they are seen. Most beaked whales can be identified to species by their characteristic sounds, such that a drifting acoustic array is an ideal way to detect their presence, and ultimately estimate their abundance. We deployed 19 DASBRs over the course of HICEAS, each drifting at sea and collecting data for 10-50 days before being recovered. Each DASBR is tracked using Iridium satellite locators. Although our primary goal is to estimate abundance of deep-diving whales, DASBRs record across a broad frequency range that enable to us to detect the occurrence of most cetacean species, from baleen whales to the highest frequency delphinid sounds.
Identifying Cryptic Cetaceans using Environmental DNA (eDNA)
Some species of cetacean are hard to see, even when conditions are perfect and there's a full team of observers watching for them. Sometimes the observers just get a brief look, or the acousticians detect sounds, but they can't be identified to species. Using new environmental DNA (eDNA) methods, we hope to bring identity to some of these 'unidentified cetaceans.' The name eDNA derives from the collection method, essentially that we are detecting the DNA of an individual as it passes through the environment and sheds small bits of tissue, like sloughed skin. Our "environment" is water, and water samples are collected and frozen, then filtered through a fine mesh polycarbonate membrane. The eDNA is then extracted from the filter and used in standard genetic analyses to determine which species were present. This approach has been used extensively to detect species in freshwater aquatic environments, and more recently researchers have been experimenting with the approach in the marine realm and specifically with cetaceans. Our partners at Oregon State University and Cornell University, with funding from the Office of Naval Research, have been testing this approach with a variety of cetacean species off the U.S. west coast and have had success identifying their target species up to 2 hours after the whale left the area.
During HICEAS 2017 we focused our eDNA sampling efforts on an especially challenging species of beaked whale. Beaked whales are difficult to see unless weather conditions are very good, and even then, many species look similar. Most beaked whale species do, however, produce echolocation clicks that appear to be unique to the species. Passive acoustic datasets from across the Pacific have been analyzed for beaked whale sounds, and while most of the detected signals have been associated with observed animals, there are a few that have yet to be associated with any species at all. One sound type in particular, known among acousticians as 'BWC', was first detected at Cross Seamount in 2005. That unique sound type has since been recorded in other locations throughout the Hawaiian Archipelago and across the central and western Pacific. Most interestingly, the sounds are heard only at night, no matter the recording location, making it quite difficult to associate an acoustic detection with a visually observed whale. This BWC signal is also the only beaked whale sound heard on Cross Seamount, apparently at the exclusion of other common beaked whales in region.
During HICEAS we conducted CTDs over Cross Seamount and at other times when BWC signals were heard on the towed array, collecting water in hopes that the elusive beaked whale left a little piece of itself behind. During HICEAS 2017 we collected 170L of water around Cross Seamount. Our goal will be matching the 'DNA barcode' of a beaked whale species with the acoustic recordings on the CTD, and voilà!, we'll know who's making all this racket! Or maybe, we'll identify a new species of beaked whale.
Refurbishing an Ocean Noise Reference Station
Passive acoustic monitoring of the ocean ambient sound field is a critical aspect of NOAA's mandate for ocean and coastal stewardship. This includes detecting and characterizing sounds produced and used marine mammals and other marine life, natural sources of noise, such as earthquakes and rain, and anthropogenic (human-generated) noise sources that contribute to the overall ocean noise environment. Noise generated by humans (especially commercial shipping and seismic oil & gas exploration) is increasingly being recognized as a potential threat to marine mammals. Increases in ambient and anthropogenic noise can impact marine mammals by hindering communication, altering communication behavior, and inducing stress.
To monitor ocean noise, NOAA has deployed 10 acoustic monitoring stations throughout U.S. waters that together make up the Ocean Noise Reference Station Network. One of these stations is located approximately 100 mi north of Oahu and within our HICEAS study area. Site NRS04 was originally deployed in July 2015 and was ready for recovery and redeployment during HICEAS 2017. On station at the NRS site, the crew aboard the R/V Oscar Elton Sette expertly recovered the oceanographic mooring from ~5000m depth, outfit that mooring with a new recorder, and then redeployed in the same location to allow for 2 more years of monitoring at this site. The data from this site provide a calibrated record of ocean noise that can be compared to the other network recordings and form the start of a long-term record of ocean noise levels in this region. Maintenance of the ONRS Network is an important component of NOAA's Ocean Noise Strategy, a roadmap for reducing ocean noise and better understanding its impact on marine ecosystems.