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Satellite Tracking

Why did animal X stop transmitting?

Salish sea harbor seal foraging study 2014

A project of Washington Department of Fish and Wildlife Marine Mammal Investigations in conjunction with the partners and sponsors detailed below.

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NameSpeciesLife StageRelease DateLast LocationDays Transmitted
ID# 12 BL1915 137175 Harbor SealAdult2014-04-282014-10-01156
ID# 3 BL1911 137166 Harbor SealAdult2014-04-042014-08-04122
ID#1 BL1910 137164 Harbor SealAdult2014-04-032014-09-05155
ID#10 YL1693 137173 Harbor SealAdult2014-04-212014-09-17149
ID#11 BL1914 137174 Harbor SealAdult2014-04-282014-09-12137
ID#2 BL1909 137165 Harbor SealAdult2014-04-042014-09-04153
ID#4 BL1912 137167 Harbor SealAdult2014-04-142014-09-13152
ID#5 BL1913 137168 Harbor SealAdult2014-04-182014-06-2366
ID#6 YL1689 137169 Harbor SealAdult2014-04-212104-09-1833022
ID#7 YL1690 137170 Harbor SealAdult2014-04-212014-09-02134
ID#8 YL1691 137171 Harbor SealAdult2014-04-212014-09-18150
ID#9 YL1692 137172 Harbor SealAdult2014-04-212014-09-18150

Click on an animal's name for maps and more information.


Project Overview

The Washington Department of Fish and Wildlife is coordinating a comprehensive research effort to determine where and why juvenile steelhead are dying in the Puget Sound marine environment. This is a collaborative effort involving NOAA Fisheries, US Geological Survey, the Puget Sound Partnership, Puget Sound Treaty Tribes and the non-governmental organization, Long Live the Kings. Eleven studies are evaluating a variety of hypotheses. This particular study attempts to determine whether predation by harbor seals is playing a role. Several factors may be at play including steelhead condition and inability to avoid predators, decreases or shifts in food webs, and/or increases or changes in seal abundance or distribution.

Increases in harbor seal populations in Puget Sound and concomitant declines in a number of harbor seal prey species (e.g., Puget Sound herring and hake) have occurred during a period of reduced marine survival and abundance of Puget Sound steelhead. While this alone does not implicate Harbor seals as a predator, it does warrant further investigation. There is suggestive evidence based on previous acoustic telemetry tagging that steelhead smolts with tags were eaten by seals or other marine mammals. This is based on changes in tag movement patterns in localized regions of the Salish Sea (Melnychuck et al. 2013, Moore et al. 20013). Since predation events are difficult to observe and quantify, primarily because steelhead do not travel in schools like herring or hake, diet-based scat studies are difficult to do. Therefore, study utilizes acoustic telemetry (pinging tags in steelhead and detector arrays in seals) to evaluate potential encounters between juvenile steelhead and harbor seals.

Twelve adult harbor seals were captured and outfitted with a telemetry package consisting of a Wildlife Computers ARGOS-linked GPS dive computer (SLASH10-F), VEMCO Mobile Transceiver (VMT-35) and an Advance Telemetry Systems radiotag (MM-430) attached to a floatation pack. Floatation packs were glued to the fur on the seal’s upper back to allow antennae transmissions when a seal was on the surface or hauled out. When the packs fall off during the seal’s annual molt in late summer they need to be located and retrieved to download archived data.

Seals were captured in April and May at central Puget Sound haulout sites located on Blakely Rocks (1), Orchard Rocks (4), Klas Rocks (1), Snake Island (2) and Colvos Rocks (4). At the same time, out migrating juvenile steelhead (smolts) were implanted with VEMCO V7 acoustic tags and released in the Nisqually, Green and Skagit Rivers. The ARGOS-linked GPS tag provides detailed positions of harbor seals throughout the study. The VEMCO VMT-35 transceiver will detect steelhead smolts with pinging V7 acoustic tags within a range of approximately 200 m, and it will transmit an identifying signal that can be detected by other transceivers on other seals and on fixed telemetry receivers. Reference acoustic tags were also deployed near each capture location. The inferred track of each seal can be interpolated between successive GPS locations to provide a fairly accurate estimate of the distance between the seal and the reference tag location to provide direct information on the ranges at which V7 transmitters can be detected by each seal-mounted VMT-35 transceiver.

The study attempts to quantify spatial and temporal overlap of harbor seals and steelhead smolts to measure predation by harbor seals.

1. Spatial overlap will be evident from detections of seals and steelhead on the same fixed telemetry receivers regardless of when those detections occur, and will provide information on whether or not steelhead and seals occupy similar course-scale habitats in Puget Sound.

2. Spatial and temporal overlap will be evident from concurrent detections on fixed receivers or detections of steelhead on seal-mounted VMT receivers. The number of different steelhead detected by VMT receivers and the frequency with which each steelhead was detected on one or more VMT receivers will indicate the degree of spatial-temporal overlap.

3. Predation events will be presumed from 1) recurring continuous pings (hours to days) on seal-mounted receivers indicating ingestion and retention of the tag in seal digestive tract (strong evidence), and 2) stationary tags indicating a tag on the seafloor within a seals foraging area (weaker evidence). Concurrent pings and the GPS-locations will also help to identify where harbor seals are encountering steelhead smolts.

4. GPS tags will provide precise locations and therefore habitat use of seals, when the seals surface, which we will use to make statistical estimates of the foraging areas for each seals.

This study and the other Puget Sound steelhead research are components of the Salish Sea Marine Survival Project, a massive international research effort to determine the primary factors affecting juvenile salmon and steelhead survival in Puget Sound and the Strait of Georgia.

For more information about the project, go to

Harbor seal research activities occur under NMFS permit #13430.

Project Partners

Washington Department of Fish and Wildife

NOAA Northwest Fisheries Science Center

Long Live the Kings



  • The presentation of data here does not constitute publication. All data remain copyright of the project partners. Maps or data on this website may not be used or referenced without explicit written consent.
  • For more information please visit the project website.

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