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A Summary of Acoustic Tagging and Juvenile Salmon Acoustic Telemetry System Program in the Northwestern United States

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By Brenna Bales, SRC intern

Before the existence of satellite and acoustic tracking technologies, the most we knew about a certain marine species’ range was from either visual observations or catch data. By developing these systems and scientists cooperating globally by sharing their data, we have learned that some “tropical” species like tiger sharks are not tropical at all but can in fact go as far north as Maine or Canada and out thousands of miles into the mid-Atlantic on a single migration from Florida (sharktagging.com). In 1999, an estimated 11,800 electronic tags (both satellite and acoustic) were placed on marine mammals, fish, invertebrates, reptiles, and birds around the world (Stone et al, 1999). There is a major difference between these two technologies, however. While satellite tags will track an animal wherever it goes as long as it can communicate with a satellite (meaning the tag must hit the surface to be detected), acoustic tags (Image 1) must be within range to an underwater hydrophone for the signal to be detected. This enables acoustically tagged animals to be tracked on a much finer scale without the need for the animal to come to the surface.

Image 1: Differently sized acoustic tags that would be used internally to monitor movements of animals.

A research organization may set up a hydrophone array over a certain area to pinpoint their tagged animals’ locations; however, this array may also detect other animals that have been acoustically tagged by different research organizations. This can be helpful to everyone, as only one hydrophone is needed to track all kinds of animals and their tags, such as sawfish, sharks, and marine mammals; however, private interests may hinder this (Grotheus 2009). Lastly, acoustic tagging has benefits in that it can be used to track multiple individuals within a population in one location versus a small number of animals tracked over different time scales and locations (Huepel et al, 2006).

In 2001, the U.S. Army Corps of Engineers Portland District decided that they wanted to track juvenile salmon in the Columbia river basin through their migration to the Pacific Ocean. There were several goals to the JSATS (Juvenile Salmon Acoustic Telemetry System) project, including 1) assessment of survival and habitat use of juvenile salmonids migrating through the estuarine environment 2) estimation of route-specific dam passage survival of juvenile salmonids 3) determination of fish survival and migration behavior, and 4) to determine effects of water temperature stratification and dissolved gas (https://waterpower.pnnl.gov/jsats/). By 2008, 4,140 JSATS  and 48,433 passive integrated transponder (PIT)- tagged yearling Chinook salmon (Oncorhynchus tshawytscha) had been tagged (McMichael et al, 2010). The dams are shown in Image 2 along with the route that the salmon migrated towards the Pacific Ocean.

Image 2: Study area used in JSATS in the Snake and Columbia river basins in 2008. Red circles demarcate the hydrophone array locations and the star marks the release location of the tagged yearling Chinook salmon.

The researchers on the project concluded that the JSATS tags gave more survival location data with higher precision than the PIT tags (McMichael et al, 2010). The JSATS tags also transmitted every 5 seconds, which is optimal for the current study in tracking such small-scale movements around the local dams. All components of the system were non-proprietary, unlike many other arrays currently established. A major outcome from this was the competitive nature in which the U.S. Army Corps of Engineers bid for reductions in sizing and pricing for these tags, leading to many advances in the technology. The study is on-going, and research is being conducted on the biological effects of tagging and how the environment is affecting the receivers and their detection capability. This telemetry system has been designed extremely efficiently and should be used as a model for other up and coming acoustic tagging endeavors.

Literature Cited

Grothues, T.M., 2009. A review of acoustic telemetry technology and a perspective on its diversification relative to coastal tracking arrays. In Tagging and tracking of marine animals with electronic devices (pp. 77-90). Springer, Dordrecht.

Heupel, M.R., Semmens, J.M. and Hobday, A.J., 2006. Automated acoustic tracking of aquatic animals: scales, design and deployment of listening station arrays. Marine and Freshwater Research, 57(1), pp.1-13.

McMichael, G.A., Eppard, M.B., Carlson, T.J., Carter, J.A., Ebberts, B.D., Brown, R.S., Weiland, M., Ploskey, G.R., Harnish, R.A. and Deng, Z.D., 2010. The juvenile salmon acoustic telemetry system: a new tool. Fisheries, 35(1), pp.9-22.

Stone, G., Schubel, J. and Tausig, H., 1999. Electronic marine animal tagging: New frontier in ocean science. OCEANOGRAPHY-WASHINGTON DC-OCEANOGRAPHY SOCIETY-, 12, pp.24-27.

Image 1 source: https://commons.wikimedia.org/wiki/File:Example_of_Acoustic_Telemetry_Tags_for_Fisheries_Research.jpg

Image 2: McMichael, G.A., Eppard, M.B., Carlson, T.J., Carter, J.A., Ebberts, B.D., Brown, R.S., Weiland, M., Ploskey, G.R., Harnish, R.A. and Deng, Z.D., 2010. The juvenile salmon acoustic telemetry system: a new tool. Fisheries, 35(1), pp.9-22.

Investigating Atlantic Salmon Dive Behavior in the Norwegian and Barents Seas

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By Grant Voirol, SRC Intern

Atlantic salmon, Salmo salar, are both an economically and ecologically important organism. An anadromous fish, Atlantic salmon spend most of their lives at sea before swimming into freshwater rivers to spawn. While at sea, Atlantic salmon periodically migrate to depths deeper than 10 meters. One proposed model of their diving behavior is that the salmon dive to deeper colder waters to feed before returning to shallower warmer water to digest. In this way, they can maximize their energy conservation (Reddin et al 2004). However, in colder waters of the most northern Atlantic, temperatures of shallower water are not significantly warmer than the depths that salmon can reach. So what factors govern Atlantic salmon diving behavior in these colder waters?

Picture 1

Atlantic salmon are both popular sport fish throughout the Atlantic as well as important predators and prey. Photo: Hans-Petter Fjeld (CC-BY-SA).

A recent study sought to find out. To do so, researchers studied post-spawning Atlantic salmon in the Norwegian and Barents Seas over season and daily timescales. Three populations from the three rivers Orkla, Alta, and Neiden, were caught and tagged using pop-up satellite archival tags (PSATs) and data storage tags (DSTs). PSATs measure temperature and depth and are attached externally to the salmon. They release themselves from the fish if a predetermined period of days goes by, the fish dives to a depth that will harm the tag (1200 meters), or the tag registers a constant depth, usually meaning the fish has died. Once they release themselves, the tags send a signal to satellites where the data collected as well as its position can be downloaded. DSTs are inserted internally in the salmon and measure temperature and depth at a much higher resolution. However, since the tags are inserted into the salmon, these salmon must be recaptured in order to retrieve the data. Recapture was dependent on fishers who would receive a reward for returning the tags to the researchers.

The findings show that the three groups of salmon displayed similar patterns of dive behavior during the sampled period. On the seasonal time scale, salmon went to deeper depths during winter and spring following the depth of the mixed layer (Figure 1). On daily timescales, the salmon occupied greater depths during daylight hours and returned to nearer to the surface during nighttime hours (Hedger et al. 2017).

Figure 1

Median dive depth per month. Solid line shows depth of the mixed layer. Increases in dive depth occur during the months of November to May. (Hedger et al. 2017)

A better understanding of the distribution and behavior of different populations of Atlantic salmon is important in order to know if different management practices need to be employed in different areas. Furthermore, this information gives us a better picture of the role that Atlantic salmon play in the Northeast Atlantic as both a predator and prey species.

Works Cited

Hedger RD, Rikardsen AH, Strøm JF, Righton DA, Thorstad EB, Næsje TF (2017) Diving behaviour of Atlantic salmon at sea: effects of light regimes and temperature stratification. Mar Ecol Prog Ser 574:127-140.

Reddin DG, Friedland KD, Downton P, Dempson JB, Mullins CC (2004) Thermal habitat experienced by Atlantic salmon (Salmo salar L.) kelts in coastal Newfoundland waters. Fish Oceanogr 13: 24−35.

Evidence for collective navigation in salmon for homeward migration

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By Hanover Matz, RJD Intern

The long migrations undertaken by Atlantic and Pacific salmon to reach their spawning grounds are known by many. Salmon are anadromous; they spend their adult lives foraging at sea, and then return to the freshwater rivers of their births to spawn and reproduce. How this remarkable feat is accomplished by the salmon with such accuracy is believed to be a combination of geomagnetic and olfactory cues. However, Berdahl et al. examined evidence that salmon may also be relying on social interactions and collective behavior in order to navigate to their natal homes. The authors hypothesized that salmon migrating in large groups could more accurately navigate to their spawning grounds by reducing the effect of navigational errors made by individual salmon. In order to determine whether this was the case, Berdahl et al. compiled results from previous studies that indicated a decrease in straying with an increase in abundance, proposed potential benefits of collective navigation for salmon, and used catch size data to better understand how salmon aggregate in the wild.

The basis for collective navigation in migrating animals is that by traveling in relatively large groups, animals can reduce the effect of navigational errors made by individuals in the group by distributing those errors across the decisions of the group as a whole. A school of salmon returning to their home river can more accurately find that river by relying on the collective decisions of the group rather than an individual salmon can by reading cues on its own. Berdahl et al. synthesized results from multiple studies that showed salmon more effectively returned to their natal grounds when they were in higher abundance, indicating the possible role of collective behavior. Figure 1 shows the results taken from several studies, all of which demonstrate that as the run size or abundance of salmon increased, the straying rate of salmon migrating back to their natal rivers decreased. The more salmon present, the less likely individual salmon were to stray from the correct migration path, suggesting the possible role of collective navigation.

Figure 1 salmon paper (1)

Results of several studies indicating a negative relationship between straying rate and run size in salmon

With this evidence for collective navigation in mind, the authors postulate several potential benefits to salmon through such behavior. Not only would collective navigation allow schools of salmon to properly orient themselves when traveling from the high seas to coastal environments, but it would also allow them to pinpoint the proper estuaries and river mouths necessary to reach their natal grounds. When presented with multiple rivers to migrate towards, collective navigation would also allow the group to effectively decide on the correct path, rather than relying only on the abilities of the individual fish. By making orientation and migration decisions based on the collective choices of the group, the salmon can reduce the effect of errors made by individual fish and the school can reach their spawning grounds based on the decisions of only a few informed individuals. Schooling offers many other potential benefits besides collective navigation, such as protection from predators, and it is likely that salmon rely on both visual and pheromone cues in order to migrate as a group. In order to further provide evidence for collective navigation in salmon, the authors collected catch size data to determine the degree to which salmon school in the high seas.  The data revealed that the catch sizes for multiple species varied from the expected Poisson distribution, indicating the salmon likely aggregate in the open sea. It was overall rare to find fish, and when they were found, they were often found in large numbers, suggesting a degree of schooling at sea. This schooling may increase with increasing migratory behavior. Figure 2 shows the results of the catch size data.

Figure 2 salmon paper (1)

Catch size data for multiple salmon species, shown in solid lines, does not follow the expected Poisson distributions, shown in dashed lines, indicating aggregation of the salmon

What does this evidence for collective navigation indicate? The possibility that salmon may rely on collective navigation in order to reach their spawning grounds implies that populations require enough individuals to aggregate and migrate as a group. What this means for salmon fisheries is that even if a fishery is managed to allow for the future reproduction of the salmon, if enough individuals are removed from the fishery so that the remaining fish cannot effectively aggregate, they may not be able to reach their natal rivers to reproduce. The population may be numerically fished so that there are enough individuals remaining to continue reproducing, but they may be distributed in such a way that they cannot school in large enough numbers to migrate. This could potentially lead to detrimental overfishing of salmon stocks. In order to fully understand the degree that social interactions may play in salmon migration and reproduction, future studies will have to be conducted on the role of collective navigation in salmon and other organisms that migrate over long distances.

 

References

1. Berdahl, A., Westley, P. A., Levin, S. A., Couzin, I. D., and Quinn, T. P. 2014. A collective navigation hypothesis for homeward migration in anadromous salmonids. Fish and Fisheries.