Using animal telemetry, it is now possible to record the ocean environment and fine-scale behavior of individuals even in the most remote regions of the world’s oceans, great lakes, and connecting channels. Animal telemetry is the process of obtaining data remotely (via a tag secured to the animal) and can be conducted in real time with radio and acoustic telemetry, or in ‘archival mode’ where logged data are stored, or downloaded from static acoustic detectors, tracks and ocean profiles are reconstructed from time-series data that are either transmitted on a time-delayed basis to satellites, or analyzed when the animal is recaptured and the tag physically returned [1–6]. Passive acoustic systems are also operational, detecting whales and dolphins based on their natural vocalizations.

Over the past two decades, thousands of animals have been tagged and released worldwide to investigate how animals use their three-dimensional world and to quantify important physical and biological aspects of their environments while in transit [7]. The tags animals carry record data at rates that may exceed one measurement per second including location, depth, temperature, light, salinity, acceleration, speed, acoustics, and physiological parameters (heart rate, oxygen, and body temperature). Animals are sensitive indicators of environmental trends and current oceanic conditions. Animal telemetry provides the opportunity to monitor these sentinels to assess current conditions and predict climate trends.

Using animals as ocean observing platforms

In the last 25 years, technological advances have made it possible to use animals as ocean observing platforms to carry remote-sensing devices [i.e., Animal-Borne Sensors (ABS)] [3, 30–32]. ABS are mobile, autonomous platforms that are relatively inexpensive to deploy (compared to ocean gliders or AUVs), provide important insights into US coastal and EEZ areas, and are particularly useful in the open oceans that are difficult and expensive to monitor (e.g., Arctic and Antarctic regions, gyre regions). Animals are adept at finding areas of particular interest to oceanographers, including surface and sub-surface fronts, eddies, and confluences that aggregate prey. Data collected by ABS include oceanographic-quality water column profiles (temperature, conductivity, light level, oxygen, and tag-derived variables such as chlorophyll proxies from light extinction) as well as behaviors in foraging “hotspots,” ecological interactions, migration routes and habitat utilization patterns. ABS complement gliders and other autonomous vehicle products to provide unique and cost-effective data from poorly sampled ocean regions, and are rapidly becoming an integral component of the Global Ocean Observing System (GOOS), especially at high latitudes. Tagged animals routinely provide vertical oceanographic profiles (Fig. 1) throughout the upper 1500 m of the water column and in some cases deeper (2000 m). Animals travel to regions that are relatively inaccessible to other ocean observing technologies, such as the polar oceans beneath seasonal or permanent sea ice [3, 30–32] or remote atolls such as those in the Northwest Hawaiian Islands. Additionally, animals move into locations and sample where Argo floats are often pushed away (upwelling zones) and across political boundaries. These data can be used to improve ocean forecasting systems by reducing initial condition errors in ocean models.

The animal telemetry community is internationally recognized and organized, and large-scale global animal telemetry programs have emerged (Australian Animal Tagging and Monitoring System (AATAMS), Global Tagging of Pelagic Predators (GTOPP), Ocean Tracking Network (OTN), Southern Elephant Seals as Oceanographic Samplers, Southern Ocean Observing System). Autonomous platforms are the backbone of the global in situ ocean observing system. An observing system that can track aquatic animals and their habitats is critical for the conservation and sustainable management of commercially harvested species, protected species and other marine resources.

Federal, state, academic and commercial organizations routinely collect animal telemetry data in the United States, but a unified, national network does not exist. Current projects range in scale from neritic to ocean basins. In the past decade, regional networks collecting data in US waters have emerged, including the Atlantic Coastal Telemetry Network, Florida Atlantic Coast Telemetry, Great Lakes Acoustic Telemetry Observation System, Pelagic Fisheries Research Program in Hawaii, Ocean Biogeographic Information System-SeaMap, Pacific Ocean Shelf Tracking, and Tagging of Pelagic Predators. Inclusion of biological resources in ocean observation is critical to advancing National Ocean Policy priority objectives, particularly Ecosystem-Based Management and Coastal and Marine Spatial Planning. Many of the existing programs already have the capability to provide live updates on animal movements, behavior, and oceanographic environment data. Importantly, demonstration projects have indicated that animal-borne sensors are reliable, inexpensive platforms for delivering high quality oceanographic data. National and international programs have succeeded in delivering these oceanographic data to the U.S. IOOS and GOOS.

We contend that aquatic resources of the U.S. would be well served by a national ATN, and that an efficient path toward developing such a network is through the U.S. IOOS. The U.S. IOOS is a national–regional partnership working to provide new tools and forecasts to improve safety, enhance the economy, and protect our environment. IOOS is a partnership of 18 Federal agencies, 11 Regional Associations (RAs), the Alliance for Coastal Technologies, and the U.S. IOOS Coastal and Ocean Modeling Test bed. The list of the U.S. IOOS federal agencies and RA partners can be found at http://www.ioos.noaa.gov.

The development of U.S. IOOS initially focused on the acquisition and integration of physical and chemical oceanographic data. With this system now operational, it is important for U.S. IOOS to add the acquisition of relevant biological data, and to enhance the acquisition of physical and chemical oceanographic data with ABS. Animal telemetry is a mature technology, provides essential information on marine resources and environmental data and is ready to be integrated within IOOS.

In the past two decades, rapid advances in animal transmitters and data storage tags have made it possible to collect high-quality biological and oceanographic observations from animals in their habitats [7, 33, 34]. Currently, a plethora of tag types exists with distinct position and sensor capabilities. Sharks, tunas, salmon, sturgeon, marine mammals, reptiles and seabirds have been tagged routinely with sophisticated instruments that sample biological behaviors (diving), oceanographic variables (pressure, light, temperature, salinity), position (GPS, ARGOS, Geolocation) and biology/physiology (body temperature, heart rate, blood or tissue oxygen saturation, tail-beat, sound) (Fig. 2). Some of these electronic tags report profiles of the water column to satellites in near-real time. When animals predictably return to specific locations (e.g., marine mammal haul out sites), where exploitation rates are high (e.g., tunas), or where aggregation occurs around buoys (e.g., fish aggregation devices), entire archived time series can be downloaded from recovered tags. Together, these technologies provide the means to track animals for multiple years, providing seasonal, annual and climatological data. Animal telemetry provides unique datasets for resource management and ocean modelers and enables IOOS to conduct analyses that can advance many of the United States National Ocean Policy Priority Objectives.

In addition to electronic tags that record data from environmental sensors, some tags transmit acoustic data to underwater receivers. This results in a cable-free underwater network for recording animal movements and is particularly useful for studying small species, and aquatic species that do not surface often, making radio telemetry difficult to employ [5]. Decreasing size, longer battery life, and increasing sophistication of acoustic transmitters [6] provide a mechanism for monitoring the behavior of a wide range of species across great distances, using networks of underwater receivers that span multi-national boundaries. Complementing these networks is the emerging use of satellite-enabled acoustic receivers and unmanned mobile gliders or mobile marine mammals fitted with acoustic receivers. For cetaceans that vocalize, passive receivers on moorings use hydrophones to listen for whales. By investing and maintaining fixed underwater receiver networks (passive and active), and mobile receiver platforms that uplink to Iridium satellite receivers or cell networks, the opportunity for long-term monitoring has emerged. Monitoring marine species is valuable not only in terms of increasing the perceived value of protected and exploited resources and minimizing human impacts, but also for the data those species deliver as roving reporters about the oceans, our changing climate and by extension our terrestrial weather. Several nations have increased the priority of using these operational technologies with substantial government and private investments (Australia: AATAMS, Canada: OTN).

Significant infrastructure costs are required for large-scale acoustic telemetry. Other Nations have recognized the need for National investment in ocean infrastructure for biological monitoring and have incorporated these infrastructure costs into their growing IOOS equivalent capacities (Australia, Canada). We envision that the ATN efforts in the US would require a combination of acoustic, satellite and archival technologies deployed simultaneously that would assure complete monitoring of coastal and pelagic marine ecosystems within and beyond the EEZ. Importantly, US scientists are proven leaders in ATN and have organized and carried out some of the largest telemetry programs in global ocean waters [5, 22, 35].

The challenges lie in defining what biological ocean observing data will best meet the needs of multiple users, and discerning the most economical acquisition and delivery of ATN data to IOOS. Importantly, the technical achievements of the past decade make biological ocean observation of animals a reality, and a US operational capacity only requires stable investments in existing technology across American waters. We envision national IOOS and RA coordination and investments are required to make an ATN operational in US waters. However, due to the existence of a large number of animal telemetry regional projects, in US waters, and the coordination exemplified by ATN members at workshops to date, we believe that the rapid assembly of a unified US network is possible.

Stronger ATN ocean observing capabilities would augment our knowledge and understanding of ocean ecosystems and our ability to engage in science-based decision-making and ecosystem-based management. By developing, maintaining and disseminating an integrated data display and storage of animal and telemetry data gathered by private, academic, local, state and federal institutions, IOOS has the capacity to lead and strengthen our national ocean observing capabilities in this area. The ATN is currently a grassroots organization at a national level and IOOS is poised to take a leadership role nationally and internationally.