Toxics in Harbor Seals
This indicator describes the presence and effect of persistent bioaccumulative toxics (PBTs) in harbor seals and in the fish they eat. PBTs are chemicals that dissolve easily in animal fat and do not break down readily, causing them to build up or bioaccumulate in the food web.

What is happening?

In 2002, we highlighted the incidence of polychlorinated biphenyls (PCBs), dioxins and furans in harbour seals in the transboundary Puget Sound Georgia Basin Ecosystem.⁸ We focus this indicator on PBDEs, another type of persistent bioaccumulative toxic, or PBT, which has lately been the subject of much public and regulatory interest, as well as PCBs in their food sources. Research indicates that the level of PBDEs in harbor seals will eclipse that of PCBs in the not-too-distant future, based on current production and consumption patterns in North America.

Methodology

PBDEs at Different BC and Washington Sites

During 2003 PBDE levels were measured in harbor seals in four locations: Fraser River estuary, Vancouver, BC; Hornby Island, Strait of Georgia, BC; Smith Island, eastern Juan de Fuca Strait, WA; and Gertrude Island, South Puget Sound, WA.

Blubber tissue samples were taken from three-and-a-half to five week old pups. Eight seals per site were weighed, identified by sex, flipper-tagged for identification and then released. Samples were stored until analysis for PBDEs at AXYS Analytical Services in Sidney, BC. The results are expressed as the amount of PBDEs in micrograms (ug) per kilogram (kg) of lipids or fats in the blubber.

Seals from Gertrude Island, Puget Sound, were approximately twice as contaminated as their counterparts to the north, indicating that they are exposed to higher levels of PBDEs in their diet. This may be attributed to either higher relative contamination of Puget Sound, or differences in what the seals eat amongst study sites.

Bar Chart Comparing PBDE Concentrations from Harbor Seals in BC and Washington

Source: Department of Fisheries and Oceans Canada

Flame Retardants (PBDEs) in Harbor Seal Fat

Location	PBDEs in Fat
WA: Gertrude Island	1,064 µg/kg of lipid (fat tissue)
WA: Smith Island/ eastern Juan de Fuca Strait	720 µg/kg of lipid
BC: Vancouver, BC/Fraser River	497 µg/kg of lipid
BC: Hornby Island (NW Strait)	589 µg/kg of lipid

Source: Department of Fisheries and Oceans Canada

PBDEs in Puget Sound harbor seals over time

An analysis of harbor seal samples collected between 1984 and 2003 revealed that PBDE concentrations in harbor seals from Gertrude Island, South Puget Sound, increased from 15 to 1064 micrograms of pollutant per kilogram of fat – a meteoric increase of 1500 percent.⁹ Emerging concerns include increasing levels of flame retardants in the marine ecosystems of Puget Sound and Strait of Georgia.¹⁰

Increase in Flame Retardants in Harbor Seal Fat, South Puget Sound, 1984-2003

Source: Department of Fisheries and Oceans Canada

Contaminants in the Food Web

The Harbor Seal Diet and the Food Basket Approach

The primary route of exposure to PBDEs for harbor seals is through their diet. "Food basket" studies, typically used to assess human diets, were used to assess contaminant intake by harbor seals in the Strait of Georgia and Puget Sound. Techniques used to identify what the seals were eating include visual observations, stomach content analysis, scat (fecal) analysis and fatty acid signatures.

Between August 2000 and August 2001, harbor seal prey (food) items were collected from Puget Sound and the Strait of Georgia. In Puget Sound, of the 25 prey items identified, the Pacific tomcod and Pacific herring constitute the largest percentage of the diet at 37.7 percent and 19.1 percent, respectively. In the Strait of Georgia, of the 16 prey items identified, Pacific hake and Pacific herring dominated the harbor seal diet at 44.2 percent and 33.6 percent, respectively.¹¹

Contamination of Harbor Seal Food Basket with PBTs

This study revealed that the Puget Sound harbor seal food basket was seven times more contaminated with PCBs (2.90 mg/kg lipid) than the Strait of Georgia food basket (0.41 mg/kg lipid). This is consistent with previous observations that Puget Sound harbor seal pups are seven times more contaminated than those inhabiting the Georgia Strait.¹² Differences in prey consumed did not explain the differences in contamination between the two harbor seal populations, but was rather attributed to an effect of local contamination within Puget Sound.¹³

PBDE concentrations were almost five times higher in the Puget Sound seal food basket, suggesting again that this basin is more contaminated with PBT contaminants than the Strait of Georgia. While increased level of industrialization and local sources may partly explain these observations, Puget Sound is also known to be a more vulnerable receiving environment than the Strait of Georgia.

Consistent with these findings, are the studies conducted by the Washington Department of Ecology (Ecology) and the Washington Department of Fish and Wildlife (WDFW) which demonstrate elevated PBT contamination of sediments and bottom fishes in the urbanized bays of central Puget Sound compared to southern Puget Sound and the Georgia Basin.¹⁴

Pacific Herring and PBTs

Herring and Zooplankton
Herring range over wide geographic regions and feed on zooplankton (pronounced zo-plankton), including krill, copepods and amphipods. Zooplankton are tiny, microscopic animals that drift with the currents and are the first consumers, or link, in the marine food chain. Typically 0.2 inches, or 5 millimeters, in length, they include larvae and come from the Greek word for wanderer or drifter.

Herring is a food source for many animals that are higher in the food chain or food web. Juvenile and adult herring inhabit the "water column" – the part of the water located between the surface and the bottom – and are eaten by seals, diving birds, and many marine fish species including Chinook and Coho salmon. When adult herring move inshore to spawn, their eggs are eaten by wading and shore birds, many fish species and crabs. Once the eggs hatch and the larvae move offshore into the water column, they fall prey to many other animals that eat plankton, including jellyfish. Accordingly, the health of these predators depends on the health of the herring as one of its food sources.

Methodology

Between 1999 and 2003, 1,055 three-year old male herrings were sampled in six of 14 major Puget Sound Georgia Basin stocks, including: Squaxin, Port Orchard, Semiahmoo (1999-2004), Cherry Point (1999 and 2003), Denman/Hornby Island (1999) and Quartermaster Harbor (2003). Total PCBs in whole bodies of herring from Port Orchard and Squaxin (central and southern Puget Sound, respectively) were four to nine times higher than those from the Georgia Basin.¹⁵

Results

The elevated levels of PCBs in Puget Sound herring are similar to levels measured in herring from the Baltic Sea in Northern Europe, one of the more highly contaminated marine ecosystems in the world.

For the three sites that have been sampled annually – Semiahmoo, Port Orchard and Squaxin Pass, PCBs did not decline in herring between 1999 and 2004 (Washington Department of Fish and Wildlife, unpublished data). This data is collected by the Puget Sound Ambient Monitoring Program, or PSAMP.¹⁶

Pacific herring sampled in Puget Sound in 2004 also have elevated PBDE levels, almost three times higher than herring from the southern Georgia Basin.¹⁷ Although trend data is not yet available for PBDEs in Pacific herring, data from other west coast fish studies show that unlike PCBs, PBDEs are rapidly increasing in the marine food web.

Herring Sampling Locations, Puget Sound Ambient Monitoring Program

Source: Washington State Department of Fish and Wildlife, West et al.

Polychlorinated Biphenyls (PCBs) in Adult Herring, 1999-2004

Source: Washington State Department of Fish and Wildlife, West et al.

PBDEs in Herring from Three Sampling Locations

Source: Washington State Department of Fish and Wildlife, O'Neill et al.

Other Circulation and Food Web Implications

With each successive or higher feeding level in the marine food chain, the more contaminated that consumer becomes. For example, contaminants in the water column can move into plankton, and then into herring and other fish like Pacific salmon, and then to harbor seals that eat the herring and to Killer Whales that eat salmon (primary prey for southern resident Killer Whales) or the seals (important prey for marine mammal-eating transient killer whales). The differences observed in PCB and PBDE contamination in Puget Sound compared to Strait of Georgia herring also reflects contaminant patterns in herring predators: Chinook salmon, Coho salmon and harbor seals and in resident southern and killer whale pods that feed predominantly on salmon in the summer months.

Puget Sound Circulation Model

Click on the image below to view a larger version

Source: Hardistry and Miamoto, "The Sound: Puget Sound Multimedia CD-ROM," 1997. WA Sea Grant and Applied Physics Lab, University of Washington.

Chinook salmon from Puget Sound are approximately three times more contaminated with PCBs than other northeastern Pacific Chinook populations because of their increased residence time of some stocks or individuals in Puget Sound.¹⁸ Wild Coho salmon from Puget Sound also have higher PCB levels than Coho from the southern Georgia Basin, likely associated with their longer residence in Puget Sound.¹⁹ Puget Sound Resident salmon sampled in 2003 and 2004 had PBDE at 40 µg/g, almost 28 times higher than those levels reported for Chinook salmon returning to northern British Columbia.²⁰ Similarly Hites et al. documented very low levels of PBDEs in wild Chinook salmon fillets from Alaska and British Columbia.²¹

High concentrations of PCBs²² and PBDEs²³ have been found in free-ranging killer whales in BC and Washington. These studies indicate that the southern residents are more contaminated than their northern counterparts, and highlight the potential importance of local sources within the industrialized Puget Sound and/or Strait of Georgia.

 

 

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