Electronic Tagging of Pacific Salmon – Coastal working group

Chair: David Welch
Rapporteur: Ric Brodeur/Jen Zamon
Participants: Jesse Ausubel, Ric Brodeur, Cynthia Decker, John Ferguson, Mike Field, Sandy Johnston, Gilles Lacroix, Dave Meerburg, Jennifer Nielsen, Gus Rassam, Alan Ruger, Bruce Ward

Introduction

The Continental Shelf Working Group (COSWG) sought to identify priority research projects in which the use of electronic tags would 

1. make significant contributions to resolving issues regarding habitat use and survival of salmon in the ocean and
2. demonstrate proof-of-concept within local pilot studies that could be integrated into longer-term projects with substantially larger spatial, temporal, and stock-specific coverage.

The acoustic array concept had been distributed via email prior to the meeting. Prior to the start of detailed discussions in the start of the shelf working group meeting, participants were initially canvassed to see if alternative tracking technologies that either complemented or competed with the acoustic array could be identified. Alternative tracking technologies with the necessary spatial resolution for shelf-based work that either complemented or competed with the acoustic array were not identified. Discussion within the group therefore assumed that the array could be built and all projects discussed were predicated on the assumption that some form of array technology would be available for use.

(Subsequent to the Vancouver meeting, this array was dubbed POTENT- the Pacific Ocean Tracking and Evaluation NeTwork. This name was chosen in order to free up the acronym POST (Pacific Ocean Salmon Tracking) for the overall CoML project , since the concept of two postal codes for the salmon applies equally to both the offshore and shelf studies).

Although discussion centered around the use of an acoustic array, significant time was also spent on the discussion of archival tags as a source of important information. The use of archival tags is more fully described in the offshore WG report; however, it was generally viewed by the Shelf working group that archival tags would provide important long-term information on the behavioural patterns of salmon similar to what would be obtained in the offshore, with the exception that geoposition data would be too coarse to reliably establish the location of the salmon on the shelf. However, in this case the information obtained from an acoustic array would provide this information.

The Shelf WG also thought that important additional information would be obtained from double-tagging salmon in the offshore with both an archival tag and an acoustic tag. In this case the movements of the salmon onto the shelf could be tracked from the acoustic array, and the river that an archivally tagged salmon entered could be determined by placing acoustic array elements in the mouths of key rivers. Using this approach, the migration track of salmon from specific rivers could be tracked back to their river of origin. Because archival tags are passive devices and send out no signal of their own, recovery of such salmon is normally dependent on recapture in commercial fisheries. However, harvest rates for salmon range from 50-70%, implying that one-third to half of the returning salmon bearing archival tags will not be intercepted and would be lost up the rivers. If elements of the array were placed within key river systems this would substantially increase the probability of recovering archival tags within the river system, as well as providing important information on the in-river behaviour of the migrating salmon. It was the consensus of the group that important synergies between the acoustic array and archival tag technologies are therefore possible, and need to be more fully developed during the planning phase.

Habitat use and survival of salmon in the ocean: what information gaps can be filled by a continental shelf tagging research program?

The shelf working group agreed that a continental shelf array would provide data on the direction, speed, and timing of individual salmon movements for acoustically tagged individuals. In some cases, these arrays may also provide information on the spatial and temporal distribution of mortality and mortality rates.

When compared to what is known about the freshwater life history phases of Pacific salmon, very little is known about their marine life history. The COSWG identified several general questions which need to be answered, and which could be addressed with tagging/array methods. The length of the list made it clear just how many gaps exist in our knowledge of salmon biology. If the ultimate goal is wise use of Pacific salmon resources, there is a need to fill in these information gaps and develop a better understanding of the ocean biology of Pacific salmon. Each of the questions listed below could be addressed if the acoustic array POTENT could be built.

General Questions

• Do different salmon stocks form stock-specific aggregations in the ocean, have stock-specific migration pathways, or use stock-specific foraging areas at sea, much as they do in freshwater? There is growing suspicion that the migration pathways of salmon at sea are sharply defined. Salmon may move back and forth between their freshwater spawning grounds and marine feeding areas, using specific pathways and migration behaviours, much as many “northern” birds move from well-defined summering grounds to tropical or sub-tropical overwintering grounds. Marine animals may be equally faithful to specific areas, but the lack of appropriate technology may have hampered our ability to recognise this. The “two postal codes” concept discussed more fully in the Planing Proposal, is an expression of this possibility.
• If so, what are the boundaries of these areas, what are the conditions defining the boundaries (spatial, temporal), and what are the residence times of fish in these areas?
• Do salmon distribution and movement/migration patterns change with longer-term changes in ocean productivity or ecology (e.g. El Niño vs. La Niña conditions)?
• How well does the timing and direction of out-migrating smolts match the timing and location of spring blooms in shelf waters? How often and under what ocean conditions do matches vs. mismatches of smolts and blooms occur?
• What are the winter movements and habitat use of salmon?
• Are there differences in the movement patterns of wild vs. hatchery fish?
• Is there any evidence for competition or density-dependent mortality in wild vs. hatchery stocks in the ocean?
• Are specific post-smolt migration behaviors associated with changes in year class success? If so, could post-smolt behavior and ocean conditions forecast year-class strength?
• Is there stock-specific, life-stage specific, or location-specific mortality in the ocean?
• Would it be possible to follow individual salmons’ movements over a complete life history cycle (e.g., by creating jacks from large smolts)?

Answering these general questions would help freshwater managers to determine what type of actions could enhance ocean survival (e.g. timing and location of smolt releases to coincide with favorable ocean conditions, whether reduction in hatchery output would enhance ocean survival of wild fish, and whether or not such actions should be applied on a stock-specific basis.). These answers would also help governments develop policies that would enhance survival in marine habitat (e.g. better forecasting of adult returns or changing timing and location of open fisheries as appropriate to ocean conditions for a specific brood year).

The COSWG also identified important groups of related specific hypotheses which could be addressed with an acoustic array:

• “Smolt Highway Hypotheses” – Is there a well-defined migration corridor along the west coast of North America? If so, what is the spatial extent of this “highway”? How quickly are individuals moving along this route? Where and when does mortality occur?
• “Plume-Transport Hypotheses” – Are smolts from the Columbia River system actively using the Columbia plume for transport or feeding purposes? Are smolts being advected within the plume (either cross shore or alongshore) or are their swimming directions and rates independent of plume direction and strength? Do different Columbia stocks use the plume differently?

The analysis of movement patterns would pinpoint the location of salmon habitat for process-oriented studies, including truly longitudinal studies of salmon growth and mortality with “aquaria trawls” to recapture and resample tagged fish.

Priority research projects

Although specific pilot projects still need to be fleshed out and prioritized, COSWG members identified several species of concern. These species were included because they are all species of significant concern and all have smolts large enough (> 14 cm) to accept the current generation of acoustic tags.

• Chinook ­ Sacramento & Klamath (Ca), Columbia River, Puget Sound, Fraser R (B.C.), Kodiak & Cook Inlet (Ak)
• Coho – Columbia River, Cook Inlet
• Steelhead – Columbia River, East Coast/West Coast Vancouver Island, Rogue River half-pounder returns, Hood River summer/winter runs; Mad River

Pilot projects under discussion included the following, all of which would form building blocks for a larger continental shelf array if built.

• Columbia River plume study – to investigate the relationship between fish movement, plume strength, and cohort strength
• Keogh River vs. Waukwass River steelhead study – model system in which to compare east coast vs. west coast Vancouver Island differences in ocean mortality for smolts and kelts

There was also discussion of projects involving Yukon River and Alaska stocks, but specific initial studies that would strengthen the CoML were not identified.It was agreed that the existence of a tracking array would assist in resolving a number of important management questions. In general, most managers wanted to know – where does my stock go, how long does it stay there, and does that affect growth and mortality?

Longer-term goals

It was the consensus of the participants that pilot projects should strive to provide both proof-of-concept and preliminary results to initiate multi-national, process-oriented, fishery-independent research. The eventual expansion of pilot studies into a full acoustic array would allow monitoring salmon movements and habitat use along coastal North America from California to the Aleutian Islands year-round. POTENT would also be able to integrate with research projects carried out by the Offshore Working Group (to integrate continental shelf and open-ocean movements of salmon and aid in the recovery of archival tags) and with an eventual Tagging of Pacific Pelagics (TOPP) program. (TOPP deals with non-salmonid marine organisms.).