Integrating Charting and Acoustic Habitat Research

Sea Technology, Aug 2008 by Lomnicky, Jay, McConnaughey, Robert

NOAA Hydrographers and Fishery Biologists Collaborate on Multi-Mission Projects in Alaska

The National Marine Fisheries Service (NMFS) is the National Oceanic and Atmospheric Administration (NOAA) line office responsible for managing the fishery resources of the United States according to mandates in the Magnuson-Stevens Fishery Conservation and Management Act (MSFCMA).

The MSFCMA and associated legislation emphasize the maintenance of a healthy ecosystem and dictate management of sustainable and economically viable fisheries.

The authorizing legislation also requires that NMFS identify the habitat requirements of all life stages of all managed species living within the U.S. Exclusive Economic Zone (EEZ). Collectively, "those waters and substrate necessary to fish for spawning, breeding, feeding or growth to maturity" are known as Essential Fish Habitat (EFH). The amount of habitat which comes under the purview of management is a staggering 3.4 million square nautical miles. Alaska waters alone represent a striking 950,000 square nautical miles, an area roughly equivalent to one-third of the land area of the entire United States.

The sheer size of this management area presents a strong incentive for collaborative operations that would simultaneously advance multiple NOAA missions in an efficient and cost-effective manner.

It is well known that information about seabed sediments can help to explain the distribution and abundance of commercially important groundfish and crabs. However, traditional seabed sampling methods (e.g., grab samplers) are inefficient when considering large areas.

Theoretical considerations suggest seabed ensonification as an alternative method for characterizing seafloor habitats. While the relationship between acoustic returns (backscatter and bathymetry) and geological properties of the seafloor is reasonably well established, it is generally unknown whether these data describe the specific characteristics that are important to fisheries.

Recent research by the Alaska Fisheries Science Center's (AFSC) Resource Assessment and Conservation Engineering (RACE) division suggests that processed acoustic backscatter may serve as a proxy for direct sediment measurements. For example, a pilot study in Bristol Bay, Alaska, has shown that processed backscatter from an L-3 Klein Associates Inc. (Salem, New Hampshire) 5410 side scan sonar contributes significantly to quantitative habitat models by explaining distributional patterns for a diverse group of benthic fish and invertebrate species, including flathead sole, Pacific cod and red king crab.1 Similarly, processed backscatter from a vertical-incidence split-beam echo sounder shows correlations with groundfish abundance.

Based on these pilot-study experiences, fishery scientists recognize the utility of acoustics for benthic habitat mapping and also the need to partner with an organization that has greater experience and capabilities for collecting these and other environmental data over large areas of the EEZ.

The National Ocean Service (NOS), another NOAA line office, has diverse responsibilities, including promoting safe navigation through production of nautical charts and the acquisition of tidal and current data, as well as the conservation of critical marine habitat though creation of protected areas and marine sanctuaries. Within NOS, the Office of Coast Survey (OCS) routinely conducts hydrographic surveys with various sonar systems for the production of nautical charts. Their expertise in acoustic surveying makes OCS the natural partner for benthic habitat mapping. However, it has been estimated that 545 ship years and $5 billion (acquisition only) are required to completely survey the U.S. EEZ with conventional acoustic systems. Potential collaboration between NMFS and NOS is also constrained by fundamental differences in organizational priorities for charting and fishery management. That is, hydrographically important areas tend to be near the coast, heavily trafficked and relatively shallow. The priority attached to deeper and less-trafficked waters, where federally managed fisheries are generally most productive, tends to be very low. As such, conventional hydrographic surveying in these areas is unlikely to occur on a time scale beneficial to fishery managers.

The convergence of capabilities and directives of NMFS and OCS, bolstered by passage of the Coastal and Ocean Mapping Integration Act of 2004, presents a unique opportunity to leverage the resources of both organizations while simultaneously addressing their unique congressional mandates. Under one scenario, NMFS advances its EFH objectives related to seabed mapping with the support of OCS assets and expertise with acoustic systems.

OCS, in turn, benefits by receiving reliable hydrographic data from out-year survey locations, as well as possible fiscal contributions to expand the operational capabilities of its hydrographic fleet. In the process, this partnering not only produces multi-use data, but does so while making efficient use of limited resources.