EPA's Vessel General Permit and Small Vessel General

which makes it potentially vulnerable to Allee effects (e.g., inbreeding depression) that could
cause further population decline or preclude a substantial increase in abundance (see NMFS
2008f). The intensity of factors affecting the species is increased by stochastic events such as the
small number of reproductive age males and high mortality rates for this group and is a major
reason that the SRKW was listed as endangered rather than threatened (NMFS 2008f).
Using data from 1974–2003, Krahn et al., (2002, 2004) further analyzed the population
dynamics of the species to identify demographic factors contributing to the latest decline in
abundance. Changes in survival were not related to stochastic variation caused by the SRKW
community’s small size, such as random patterns in births or deaths or to annual fluctuations in
survival. Rather, the survival patterns were more likely influenced by external causes, such as
changes in prey availability etc.
Threats
Natural Threats. The population of SRKWs has declined recently. The recent decline and
unstable population structure make it difficult for SRKWs to recover from natural spikes in
mortality (NMFS 2008f). Although disease outbreaks have not been identified in this population,
increased contaminant loading may increase the susceptibility of individuals to disease.
Anthropogenic Threats. Salmon is the primary prey of killer whales and has been severely
reduced due to habitat loss (NRC 1996, Slaney et al. 1996, Gregory and Bisson 1997,
Lichatowich 1999, Lackey 2003, Pess et al. 2003, Schoonmaker et al. 2003). A 50% reduction in
killer whale calving has been correlated with years of low Chinook salmon abundance (Ward et
al. 2009).
Contaminants entering SRKW habitat in Puget Sound and its surrounding waters accumulate in
water, benthic sediments and in prey organisms (Krahn et al. 2009). SRKWs bioaccumulate
these toxins in their tissues which may lead to numerous adverse physiological changes (Krahn
et al. 2009). The greatest contaminant threats are from organochlorines (e.g. PCBs, pesticides,
dioxins, furans and DDT) (Ross et al. 2000, CBD 2001, Krahn et al. 2002, Cullon et al. 2009,
Krahn et al. 2009). These chemicals bioaccumulate in fatty tissues, persist and can be transmitted
from mother to offspring (Haraguchi et al. 2009, Krahn et al. 2009).
Vessel activity has also been identified as a threat to SRKWs. In 2005, a U.S. vessel participating
in sonar exercises apparently caused significant behavior changes in killer whale activity , such
that the whales vacated the area (NMFS 2005a). Additionally, the increase in “background
noise” resulting from vessel traffic has the potential to influence or disrupt the ability of SRKWs
to navigate, communicate and forage (Bain and Dahlheim 1994, Gordon and Moscrop 1996,
Erbe 2002, Williams et al. 2002a, Williams et al. 2002b, Holt et al. 2009).
Critical Habitat
NMFS designated critical habitat for Southern Resident killer whales on November 29, 2006 (71
FR 69054). Three specific areas were designated; (1) the Summer Core Area in Haro Strait and
waters around the San Juan Islands; (2) Puget Sound; and (3) the Strait of Juan de Fuca, which
comprise approximately 6,630 square kilometers of marine habitat. Three primary constituent
elements exist in these areas: water quality to support growth and development, prey species of
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