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Ocean Tracking Network Raises Marine Animal Tracking to a New Level

To the naked eye, a salmon or cod cruising Canada’s coastal waters might look like any other fish of its kind. If one could peak inside, however, it would quickly become evident that some individuals have gone high-tech. An increasing number of fish in Canadian waters and around the world have been implanted with acoustic tags or transmitters. In the case of marine mammals such as seals, tags are larger and often attached to their fur or skin.

Each acoustic tag transmits a unique sound pulse that can be detected by an acoustic receiver (a hydrophone) or listening station, which records the presence of the fish when it’s within range (~400 m). The larger tags (in larger species), akin to mini hard-drives, also gather other valuable data that enable scientists at Fisheries and Oceans Canada (DFO) and other organizations around the world to explore unanswered questions about the lives of marine species.

These tagging efforts are also becoming an integral part of the Ocean Tracking Network (OTN), a $168-million international conservation project that is developing a global network of underwater acoustic receivers to track thousands of marine animals over increasingly larger expanses of ocean, while also collecting climate change data. This comprehensive examination of the movement and migration of marine life and related ocean conditions will provide valuable information about marine food webs that is essential for ecosystem-based management (EBM) of fisheries and other sensitive components of the marine world.

Seeking new insights into migration patterns

Fisheries and Oceans Canada Mechanical Design Technologist Jason Burtch and Mechanical Engineering Technologist Jay Barthelotte of the Bedford Institute of Oceanography prepare an acoustic receiver assembly for deployment on the Halifax Line.

Photo: S. Kirchhoff, Ocean Tracking Network, Dalhousie University

“The Ocean Tracking Network will help answer a big unknown in fisheries research…what triggers migration patterns and why fish follow certain routes,” says Dr. Peter Smith, Fisheries and Oceans Canada physical oceanographer at the Bedford Institute of Oceanography (BIO). “We know where many stocks spawn and when they migrate, but we have little information about what conditions trigger migration, what routes are followed and why.”

Dr. Smith is one of many leading scientists around the world who are collaborating on the Ocean Tracking Network. In addition to the Bedford Institute of Oceanography, Fisheries and Oceans Canada scientists at the Institute of Ocean Sciences, the Pacific Biological Station in Nanaimo, British Columbia, the Maurice Lamontagne Institute in Mont-Joli, Quebec, and the Freshwater Institute in Winnipeg are collaborating on the Ocean Tracking Network with university researchers across the country and around the world.

Headquartered at Dalhousie University, the project builds on the Pacific Ocean Shelf Tracking (POST) project, which gathers data on the movements of tagged salmon and other marine animals along the west coast of Canada and the United States using a series of acoustic lines or “curtains”. With more lines in place or planned around the world, the Ocean Tracking Network is expanding on the Pacific Ocean Shelf Tracking technology as a pilot project of the United Nations Intergovernmental Oceanographic Commission’s Global Ocean Observing System (GOOS), the marine component of the Global Earth Observing System of Systems (GEOSS).

Ocean Tracking Network Technology

A receiver assembly in the water just after deployment.

Photo by: S.Kirchhoff, Ocean Tracking Network, Dalhousie University

Receivers are deployed in lines stretching across the continental shelves - shallow, submerged plateaus that form the edge of continental landmasses. Using coded pulses of sound from the tags, the receivers record when and where tagged animals cross the line. The acoustic pulses also allow scientists to obtain original tagging information including the species and when and where the individual was tagged.

Nearly 75 percent of pelagic marine animals are large enough to carry an acoustic tag that will report physiological and/or environmental data to a submerged hydrophone and therefore doesn't require the animal to surface for satellite communication or to be recaptured in order to provide data to the archive.

Ocean Tracking Network Canada

Canada’s Natural Sciences and Engineering Research Council (NSERC) provided $10 million in funding for tagging studies as part of Ocean Tracking Network Canada, which Fisheries and Oceans Canada is supporting in-kind with expertise and vessel time1. When complete, Ocean Tracking Network Canada will encompass a large number of acoustic curtains in the Atlantic, Arctic, Indian, Southern and Pacific oceans, plus the Mediterranean Sea.

Ocean Tracking Network Canada will investigate the movements of continental shelf marine animals, how these movements affect species interactions, and what the consequences of human activities and environmental variability and change are on the distribution and abundance of species. Key questions being explored include:

  • What are the physical, chemical and biological oceanographic linkages that determine the population structure, dynamics, movement and critical habitat of marine organisms?
  • How will climate variability/change and anthropogenic activities affect the distribution and abundance of marine organisms?
  • What are the implications of Ocean Tracking Network findings on the social, economic and legal dimensions of ocean governance?

“Fisheries and Oceans Canada research projects to tag and track various marine species will feed into the Ocean Tracking Network and vice versa,” says Dr. Smith. “For example, research scientists at the Bedford Institute of Oceanography will be using data from the Halifax Line to learn more about species such as salmon, haddock, sturgeon, seals, sharks and cod.”

Edmund Halfyard, a PhD candidate in marine biology at Dalhousie University, implants an acoustic tag into a salmon smolt from the West River in Nova Scotia. The tagged salmon are among many species of marine animals that have been tagged and have the potential to be detected by Oceans Tracking Network acoustic curtains.

Photos by: Edmund Halfyard/G. Ferguson

The Halifax Line

Alongside a wharf at the Bedford Institute of Oceanography (BIO), Fisheries and Oceans Canada physical oceanographer Dr. Peter Smith of BIO, and Dan Jackson and Duncan Bates of Ocean Tracking Network Headquarters prepare to depart for the first deployment of acoustic receivers on the Halifax Line, one of several acoustic "curtains" in place or planned around the world by the Ocean Tracking Network (OTN).

Photo: S. Kirchhoff, OTN, Dalhousie University

Fisheries and Oceans Canada is involved in the development of at least five acoustic curtains, including the Halifax Line (see map below), an oceanographic transect off the coast of Halifax, Nova Scotia, along which Fisheries and Oceans Canada has collected oceanographic data since 1950. One acoustic curtain is being positioned roughly along the same transect, which will enable researchers to compare new data with historical temperature and salinity data.

In collaboration with Dalhousie University, the first acoustic receivers were deployed on the inner portion of the Halifax line in the spring of 2008. "This pilot line also incorporates Acoustic Doppler Current Profilers concentrated inshore of the 200-metre isobath2 to measure variations in the dominant current on the Scotian Shelf off the coast of Nova Scotia. Data on the strength of the current at various depths will help interpret detections along the line," says Dr. Smith. "Some of the moorings also house sensors to measure oceanographic parameters including temperature, salinity, pressure and oxygen, providing insight into what factors in the physical environment may prompt various species to migrate and when."

"Our goal is to install the rest of the Halifax Line by the end of March 2012 and operate it continuously for five years thereafter," says Dr. Smith "However, the original plan for the Halifax Line -266 instruments stretching about 200 kilometres directly across the shelf to the 200-metre isobath - is being modified to avoid conflict with silver hake fishers, who conduct a bottom trawl fishery in waters deeper than 200 metres, which has the potential to damage the hydrophone moorings. There is also an active pollock fishery on the shelf, so we are considering further modifications to the line to avoid interactions with their fishing lines on the Sambro Bank."

The above map of the Halifax Line includes initial modifications to avoid conflict with the silver hake fishery in waters deeper than 200 metres. The route of the entire line has not been finalized, and additional smaller deviations are being considered to account for the pollock fisheries on Sambro Bank and the outer shelf.

Image by: Dr. Peter Smith, Fisheries and Oceans Canada

Early findings

The Halifax pilot line has already provided some insights into the migratory habits of at-risk Atlantic Salmon. "Early results reveal that 34 salmon tagged in the Bay of Fundy, Gulf of Maine and the LaHave River (west of the line) moved eastward across the inner part of the line between the spring and July of 2008. All but one of the detections occurred in June, and one salmon crossed the curtain in May," says Dr. Smith. Current metres along the line revealed what was happening when the fish crossed the curtain. The fish appeared to choose the path of least current resistance, migrating eastward when opposing currents were weakest in May-June and crossing inshore of the mooring site at the end of the pilot line where currents are generally weaker than at the site itself.

"The Nova Scotia Current, which flows from the northeast to the southwest throughout the year, reaches its maximum in late fall/early winter, is at its weakest in the May/June period, and starts to strengthen again in July," says Dr. Smith. "So one hypothesis is that salmon may time their migrations from the Gulf of Maine, Bay of Fundy and LaHave River such that the countervailing currents are minimal. That is one example of the type of hypothesis that we can explore once the entire curtain is in place and we have a better indication where most of the fish are crossing the line and when."

Red circles on the left side of the image above represent the locations at which 34 Atlantic Salmon were detected moving eastward across the Halifax pilot line from the Gulf of Maine and Medway River, N.S., during April to July of 2008

Red circles on the chart (right) indicate the timing of the detections (e.g. 080602 refers to June 02, 2008) versus the position (hydrophone mooring site number) at which the fish crossed the line.

Image by: Ocean Tracking Network Group, Dalhousie University


1 The Canadian Foundation for Innovation (CFI) also provided $35 million for infrastructure (e.g., moorings, hydrophones) to support a number of "acoustic curtains" worldwide. Fisheries and Oceans Canada is also supporting the deployment and maintenance of this infrastructure with technical expertise and vessel time.

2 An isobath is a contour line of equal depth.