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American Fisheries Society Symposium 69:311–320, 2009© 2009 by the American Fisheries Society

Tracking Diadromous Fishes at Sea: The Electronic Future Using Hybrid Acoustic and Archival Tags

Michael J. W. StokeSbury*The Ocean Tracking Network, Faculty of Science, Dalhousie University

Halifax, Nova Scotia B3H 4J1, Canada

Michael J. DaDSWellBiology Department, Acadia University, Wolfville, Nova Scotia B4P 2R6, Canada

kiM N. hollaNDUniversity of Hawaii, HIMB, Kaneohe, Hawaii 96744, USA

GeorGe D. JackSoNInstitute of Antarctic and Southern Ocean Studies, University of Tasmania

Private Bag 77, Hobart, Tasmania 7001, Australia

W. DoN boWeNFisheries and Oceans Canada, Bedford Institute of Oceanography

Marine Fish Division Dartmouth, Nova Scotia B2Y 4A2, Canada

roNalD k. o’DorConsortium for Ocean Leadership

4th Floor, New York Avenue NW, Washington, D.C. 20005, USA

Abstract.—Tagging fish with electronic tags can provide information on movement, migration, behavior, and stock structure while diadromous species are at sea. The state of the art technology for tracking fishes in the marine environment includes two families of tags. Archival tags store data and either relay them to satellites or require recapture for interrogation. Low return rates for diadromous species make these tags very expen-sive to use. A second type, acoustic tags, sends signals to passive receivers. Information is collected from the fish only when it is within range of a receiver. Technology is now being developed to mesh these tags into a fully integrated tag that will permit archived data to be transmitted acoustically over multiple frequencies to receivers allowing data retrieval without recapturing the animal. The new technology includes a “business card” tag that is a miniaturized receiver coupled with a coded pulse transmitter. These tags will exchange and record individual-specific codes when two animals carrying them come within acoustic range of each other, which will allow data from many animals to be moved ashore through few animals. These devices would be ideal for quantifying the de-gree of school fidelity (or, conversely, mixing) or the degree of at sea interaction of fishes from different river systems and provide ecological information to enhance management in an ecosystem approach to fisheries.

* Corresponding author: mstokesb@dal.ca

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IntroductionRecent advances in tagging of aquatic animals with electronic tags has led to critical information in the areas of animal movement and migration (Block et al. 2001, 2005; Boustany et al. 2002; Lacroix et al. 2005), behavior (Austin et al. 2006; James et al. 2006a; Teo et al. 2007), natural history (Stokesbury et al. 2005; Weng et al. 2005, James et al. 2006b), management (Comeau et al. 2002; Welch et al. 2004; Block et al. 2005), and conservation (Block et al. 2005; Heide-Jørgensen and Reeves 2006; James et al. 2006c). Electronic tag technology used to track animals in the marine environment includes two families of tags: archival tags and acoustic tags.

Archival tags store data collected by sensors in the tag. To access the stored information, the data can be relayed from the tag to a satellite system such as ARGOS or Iridium. Data are transmitted direct-ly, if the animal is at the surface of the water for long enough (Block et al. 2005; Weng et al. 2005; James et al. 2006a), or by disengagement of the tag, which then ascends to the surface and downloads its information (Block et al. 1998; Lutcavage et al. 1999; Stokesbury et al. 2004). Data from archival tags can also be downloaded if the animal is cap-tured and the tag removed and returned to the re-searcher (Block et al. 2005). A new type of archival sonic tag downloads data when cued by an acoustic receiver. This tag is called a communicating histo-gram archiving transmitter (CHAT), and the con-cept has been tested successfully with tiger sharks Galeocerdo cuvier (Holland et al. 2001). However, in that prototype, data download over the acoustic link required a long time and mobile animals could move out of the receiver range prematurely.

Other than CHAT tags, acoustic tags do not store data but continuously transmit acoustic sig-nals that are received only when the animal is within range (approximately 500 m) of submerged hydro-phones—either mounted on a tracking vessel or on a mooring. Consequently, data are collected only while the fish is within range of a receiver (Lacroix and McCurdy 1996; Lacroix et al. 2005, Stokesbury et al. 2005). This technology is more cost-effective in some designs and, due to the generally smaller size of the tags, is often more useful for smaller fishes than archival technology. It is used mostly for animals that are not at the surface long enough to contact satellites.

Large-Scale Acoustic Tracking on the East Coast of North America

Acoustic receivers can be deployed on a matrix of moorings such as fish aggregation buoys (Dagorn et al. 2007) or as “curtain arrays” (Lacroix and Mc-Curdy 1996; Heupel et al. 2006). In this configura-tion, a line of receivers is deployed across an area in such a way that if an acoustically tagged fish passes through, it will be detected (Figure 1). This proce-dure was first developed and deployed in the Bay of Fundy (Lacroix and McCurdy 1996), and the array design has been used in many areas, including form-ing the basic array geometry of the Pacific Ocean Shelf Tracking system (POST; Welch et al. 2003) and the Ocean Tracking Network (OTN; O’Dor et al. 2007). The OTN will deploy acoustic curtains in 14 ocean areas between the years 2008 and 2012 (Figure 2). There will be several installations in the northwest Atlantic Ocean, including arrays that stretch from shore to the continental shelf slope off of New Jersey, connected to the Long-Term Ecosys-tem Observatory at 15 m (LEO 15), a cabled system operated by Rutgers University and off of Nova Sco-tia on the “Halifax line.” The Halifax line has been traditionally sampled for oceanographic parameters by the Department of Fisheries and Oceans Cana-da. Also, curtain arrays will be deployed across the Cabot Strait, the Strait of Belle Isle, the Bay of Fun-dy, and individual receiver deployments on the Gulf of Maine Ocean Observing System (GoMOOS) buoys (Figure 3). As a result, an extensive system of curtain arrays will be in place to provide informa-tion on acoustically tagged fishes migrating on the continental shelf of eastern North America.

Argument for Using Electronic Tags to Recover Unbiased Fish

Movement Data

In recent decades, the use of conventional external and internal tags has proven less effective. Fishers have become reluctant to return capture informa-tion because of perceived threats of fishery closures and the bycatch of protected species. A case in point is the West Greenland fishery for Atlantic salmon Salmo salar, which took ocean-feeding salmon from virtually every salmon-producing na-

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Figure 1.—Proposed OTN arrays will create an integrated system for collecting physical oceanographic and biological information from oceans throughout the world.

Figure 2.—The OTN’s scheduled deployments in 14 ocean regions giving a global perspective on ocean and animal movements; arrays deployed in 2009 (●) 2010 (●), 2011–2012 (■).

tion, data for which was provided by the return of external tags by the fishers (Jensen 1990). The fish-ery was initiated about 1960, and by 1970, land-ings had grown to more than 2,000 metric tons (mt)/year as it was exploited by both Greenland and international vessels (Shearer 1992). Because of the real threat that this mixed-stock fishery was collapsing home-returns of Atlantic salmon (Palo-heimo and Elson 1974) international pressure was applied to first remove foreign vessels from the fleet (after 1975), impose quotas (1976), and, fi-nally in 2002, close it completely (Atlantic Salmon Federation 2007).

The fishers responded to these threats by re-ducing the number of external tags they returned, and tag return data after 1980 was biased. Between 1966 and 1992, 1.5 million Atlantic salmon smolts were tagged in Maine using external Carlin tags, and 2,155 tags were returned from the West Greenland fishery (Baum 1997). Data from the return of these tags demonstrate that tags were being held back by fishers after management changes to the fishery (Table 1). Between 1969 and 1976 average landings were 2,077 mt/year or about an estimated 700,000 salmon/year, of which an average of 42% were of North America origin (Reddin and Friedland

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Figure 3.—Arrays of acoustic receivers to be deployed by the Ocean Tracking Network in the Gulf of Maine, the Gulf of St. Lawrence and on the Scotian Shelf between the years of 2008 and 20012.

Table l.—Return rates for external Carlin tagged Atlantic salmon smolts from Maine, USA from the com-mercial fishery off West Greenland during 1969–1976 and 1979–1986 (after Baum 1997). Between 1966 and 1992 a total of 1,585,335 smolts were released from Maine and 2,155 tags were returned from off West Green-land. Separation of data was decided on because no tags were applied in 1978 (Baum 1997), foreign vessels were restricted after 1975, and a quota was set in 1976 (Shearer 1992). mt = metric tons.

Average Continental landings/year origin (mean %) Total tags Total tags Return ratePeriod (mt) (NA)b (E)b applied returned %

1969–1976 2,077 42 58 340,895 1,255 0.371979–1986a 920 52 48 557,170 562 0.10a Average quota/year 1979–1986 was 1,090 mt/year (Shearer 1992).b NA = North American origin; E = European origin. Mean cross-validated, misclassified from known origin salmon is 15.9% ± 4.3% (Reddin and Friedland 1999).

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1999). The average return rate of Maine tags during this period was 0.37% (Table 1). During the period 1979–1986, after fishery restrictions had been ap-plied and the annual catch was reduced by half to an average of 920 mt/year, the tag return rate fell to 0.10%, almost a fourfold decrease. The change in return rate happened even though the number of tags released from Maine nearly doubled and the average proportion of North American salmon off West Greenland during the period increased to a mean of 52% a year (Table 1; Reddin and Friedland 1999). For example, of 48,210 tagged smolts re-leased from Maine in 1970, a total of 403 tags were returned from West Greenland (0.83%), compared to 1980 when 49,760 were released but only 49 tags were returned (0.10%; Baum 1997).

Increased use of internal (coded wire) tags for diadromous fishes has occurred because of their homing behavior, but these methods are only useful if large-scale monitoring programs and the neces-sary detection systems are available (Russell et al. 1991). Also, internal tags are not often discovered by fishers or the public and valuable data on move-ments is lost. For these reasons, as well as the con-current technical advances for miniaturizing and cost decrease of electronic tags, electronic methods are becoming widely accepted and used (Rassam 2008). The development of new electronic tags has the ability to provide unbiased information on fish migrations, enhance our ability to observe a wide range of fish behavior, determine critical habitat use, and discover sources of exploitation in real time.

Fish Tagging and Population Ecology

Electronic tags provide data only on an individual level. It is inherently difficult to combine data from individuals that were tagged at different times, often in different areas, and with mixed ages to test a pop-ulation level hypothesis. Many animals need to be tagged so that statistically rigorous methods may be used to derive population level characteristics from tagging data (Sibert et al. 2006). This is a lengthy and expensive process.

A move toward an ecosystem approach to fish-eries (Garcia et al. 2003) presents new challenges to the animal researcher (Cury 2004). In addition to the need for population level answers from data

derived on the individual level, it is required that researchers link ecological processes to ecosystem level patterns (Cury 2004). To obtain this objective, a procedure is required that acquires data from in-dividuals when they interact with members of their population. It also requires recording intraspecific interactions and relationships between animals and the physical properties of their habitat. For this, we need to combine some already existing technologies and to develop wholly new ways of acquiring data.

The Fully Integrated TagSeveral studies have combined both archival and acoustic tag technology (Jackson et al. 2005; Stokesbury et al. 2005). Building upon this idea, the OTN has proposed to combine acoustic and archival technologies with a business card (BC) tag to create a fully integrated tag (FIT). The BC tag in-cludes a miniaturized acoustic receiver that records an acoustic code when a fish carrying it comes near another tagged fish. This tag also transmits its own individual code. These tags may help quantify the degree of school fidelity (or conversely, mixing) in schooling fish such as Atlantic salmon, American shad Alosa sapidissima, or striped bass Morone saxa-tilis. The tagged animal becomes a mobile receiver “bioprobe,” moving and recording proximity (with-in 400 m) to others in the ecosystem. Basic research and development of BC tags is being developed in a joint venture between Amirix Systems Inc. and the Pelagic Fisheries Research Program at the University of Hawaii.

The FIT will permit retrieval of high resolution archival data on migrating animals in the ocean, including records of proximity with other tagged animals and information on geolocation that can be downloaded to hydrophones over a very fast spread spectrum acoustic link (Figure 1). Consequently, the tag does not have to be physically recovered and does not have to be downloaded over a slow and/or expensive satellite link. Development of the FIT tag is outlined in O’Dor et al. (2007).

Using FIT Tags to Study Diadromous Fish Interactions and Life Histories

As we move toward managing systems on the basis of large marine ecosystems (Sissenwine and Mu-

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rawski 2004), we need a more complete vision of the ecological interactions between animals at the same and different trophic levels. This is important both to management and understanding system ecology in terms of food webs and energy flows. We envision two arenas where mobile and widely distributed animals move through coastal and oce-anic waters and report movements, environmental preferences, and interactions: the continental shelf region of the northwest Atlantic and the inner Bay of Fundy.

Species that are natural fits for testing the FIT technology in these Arenas are gray seals Halicho-erus grypus and Atlantic sturgeon Acipenser oxy-rinchus. Gray seals return from marine migrations to Sable Island where they move to the land and are accessible to researchers (Bowen and Harri-

son 1994). These animals have been the focus of a large, electronic-tagging research program (n = 70 tagged individuals) conducted by researchers at the Bedford Institute of Oceanography and Dalhousie University (Austin et al. 2006). During the project, researchers deployed tags that link to satellites and archive data.

Gray seals disperse widely along shelf and oceanic water from the Gulf of Maine to southern Labrador, including the Gulf of St. Lawrence (Fig-ure 4; Mansfield and Beck 1977). We can expect considerable overlap in range between gray seals and many of the diadromous species that will be elec-tronically tagged along the Atlantic seaboard. Nu-merous wild Atlantic salmon stocks are endangered on the Atlantic coast of North America (Amiro 2003; Legault 2005). Salmon from North America

Figure 4.—Grey seal (n = 70) movement and percentage use of habitat along the Atlantic seaboard and electronic tagging sites of diadromous species in this region, including Atlantic salmon (●), American shad (○) Atlantic sturgeon (□), and striped bass (■).

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migrate into the North Atlantic and most do not return (Anderson et al. 2000; Spares et al. 2007). Seals from rookeries in North America also swim into the North Atlantic searching for salmon and other prey (Austin et al. 2004). The Atlantic coast of North America has a very wide continental shelf, and in some places it is not practical to construct a POST-type continental-scale acoustic receiver ar-ray (Welch et al. 2003). However, the new BC and FIT technology can overcome this problem by us-ing seals as mobile acoustic receivers to record where tagged salmon are in the North Atlantic. Besides At-lantic salmon we expect interactions between gray seals and other tagged diadromous species including American shad, alewife A. pseudoharengus, Ameri-can eel Anguilla rostrata, and striped bass, many of which are eaten by this seal (Mansfield and Beck 1977). These tagged seals would provide time-stamped, georeferrenced data on interactions with fishes and measures of the physical environment in which these interactions occurred.

Gray seals, however, forage mainly along the eastern shelf region of Nova Scotia (Figure 4). In order to gain a more inclusive picture of ecological interactions in the Atlantic and the inner Bay of Fundy arenas, we need to complement gray seal tagging with the tagging of a species that is widely distributed along the North American Atlantic coast. Atlantic sturgeon is a species whose life his-tory lends itself to tagging and also to providing information on other animals that occupy the same environments. Since Atlantic sturgeon are a large, long-lived species with adult weights com-monly 200 kg, they represent an excellent chance to utilize a diadromous fish that is capable of per-forming as a mobile platform for multiple and/or FIT tagging.

Electronic tagging of sturgeon is well estab-lished, and the survivorship of sturgeons from the tagging process is high (Welch et al. 2006; Erick-son and Hightower 2007). They are large enough to carry multiple tags with minimal effect on behavior. They migrate on a seasonal basis in a north–south pattern along the eastern seaboard from North Car-olina to the Bay of Fundy and possibly Labrador, with many diadromous fishes such as other sturgeon, Atlantic salmon, American shad, alewife, American eel, and striped bass (Dadswell 2006; Laney et al. 2007). Migration depths are apparently restricted to #200 m, and they enter estuaries and rivers as well

as ranging over the continental shelf (Secor et al. 2000; Stein et al. 2004). As a result, they are target-ing a variety of environments that provide crucial habitat for many diadromous species. In some larg-er river systems, such as the St. Lawrence (Caron et al. 2002) and the Saint John (Dadswell et al. 1984), their spawning distribution is known. Recapturing Atlantic sturgeon in these rivers, especially if they are carrying acoustic tags that will reveal precisely where in the river system they are located, should not be difficult. Also, there are commercial fisheries for Atlantic sturgeon in the St. Lawrence and Saint John rivers (Dadswell 2006), and some tags may be returned through recapture in the fishery.

The Minas Basin and Chignecto Bay provide a unique marine habitat within the inner Bay of Fundy arena. Although these basins have a large tidal range (10–12 m) that is similar to other areas in the Bay of Fundy, they are summer warm enclaves due to shallow water and extensive tide flats (Bousfield and Leim 1958). Both contain seasonal fish faunal ele-ments that are a mix of marine and diadromous spe-cies and which migrate long distances on the Atlantic coast, with their summer migration terminus in the inner Bay of Fundy (Dadswell et al. 1987; Rulifson and Dadswell 1995; Moore 1998; Dadswell 2006; Rulifson et al. 2008). Additionally, the fishes in this region are under continual threat of the development of tidal power, an occurrence that, by virtue of their extensive migrations, could harm diadromous fish stocks and protected species both from Canada and the United States over a wide area (Dadswell and Ru-lifson 1994; Cada et al. 2007).

Atlantic sturgeons are an important part of the inner Bay of Fundy ecosystem (Armitage and Gin-gras 2003), and they have been tagged with both conventional dart tags and acoustic tags in this region when captured as bycatch in local fisheries (Wehrell 2005: M. J. Dadswell, personal commu-nication). For many diadromous species, details of their migration pathways, stock composition, sea-sonal distribution, and interactions with other fishes in the region are poorly known. Because of the con-strained topography of the inner Bay of Fundy with its numerous narrow passageways (Minas Channel, Economy Point, etc.), access to the fish and poten-tial for tracking with a limited number of acoustic receivers is feasible.

We could also test a number of hypotheses on the stock specific nature of the coastal migration of

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different Atlantic sturgeon populations by tagging these fish with FITs in two or three widely separated Canadian or U.S. rivers (Saint John, St. Lawrence, Hudson, etc.) and in the Bay of Fundy. FIT tagged sturgeons would interact with each other, other acoustically tagged fishes, and the various OTN receiver chains that are proposed for the Atlantic coast (Figure 4). Since the Atlantic sturgeon fish-ery in the United States is currently under a mora-torium and sturgeon fishing in Canada is partially restricted (Dadswell 2006), tagged sturgeon will be allowed freedom of movement and protection for themselves and their tags.

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