EPA's Vessel General Permit and Small Vessel General

metabolism of organic chemicals. While organic loading from the many land-based sources are
orders of magnitude larger than that from vessels, vessel discharges pose yet another incremental
source to those land based loadings. Data are not available to place vessel organic loading in
context of consequences for our species. We review the effect of low dissolved oxygen on listed
resources and their surrogates to acknowledge the potential effects of this discharge constituent
on listed resouces.
Intergravel dissolved oxygen concentrations for survival of embryo and larval salmonids need to
be at least 8 mg/L dissolved oxygen, which requires dissolved oxygen levels of 11 mg/L in
overlying water. Other salmonid lifestages require 8 mg/L in the water column, with
impairments to productivity occurring when levels decline to 6 mg/L or lower (LD and CA
20056). Sturgeon basal metabolism, growth, consumption and survival are all very sensitive to
changes in oxygen levels, which may indicate their relatively poor ability to oxyregulate. Based
on bioenergetics and behavioral responses of young of the year juveniles aged 30 to 200 days,
productivity losses occurred at oxygen saturation levels below 60 percent, which corresponds to
5 mg/liter at 25 o C (Wirth et al. 2000). Accordingly, dissolved oxygen levels of 5 mg/L and
above are also considered protective of sturgeon (Southworth et al. 2011).
Marine mammals and marine turtles are air-breathing organisms and are not expected to be
directly affected by increased BOD or associated decline in dissolved oxygen. Johnson’s
seagrass is tolerant of low dissolved oxygen. Reported effects of low dissolved oxygen on
abalone species include mortality, immune suppression (Sturgeon 1954), and reduced growth
rate (Movahedinia et al. 2012). Holding conditions specified in the recovery plan for this species
require dissolved oxygen levels to be maintained at or within 10% of saturation. However,
intertidal species like black abalone are tolerant to extremes in environmental conditions such as
fluctuations in dissolved oxygen (Alam et al. 2000). Searches of the open literature and the
NMFS status review for coral species did not identify issues with depletion of dissolved oxygen
or BOD.
Direct linkage of BOD with adverse effects on listed species is complicated by extrapolating the
organic loading represented by BOD to actual levels of the proximate stressor, low dissolved
oxygen. The VGPs limit discharges into impaired waters and discharges of high BOD waste
streams in protected areas. The VGPs also require BOD monitoring of graywater in new build
vessels. These restrictions lead NMFS to conclude that BOD contributions from vessels
compliant with the VGPs are not likely tip the balance between neutral and harmful levels of
organic loading to waters where our species occur.
Total Residual Chlorine (TRC)
Chlorine gas released into water first dissolves and then undergoes immediate conversion into
two forms of free chlorine: hypochlorous acid (HOCl) and the hypochlorite ion (OCl-). If the
water contains ammonia, the solution will likely also contain two forms of combined chlorine:
monochloramine and dichloramine. Because all four of these forms of chlorine can be toxic to
aquatic organisms, the term “total residual chlorine or TRC” is used to refer to the sum of free
chlorine and combined chlorine in fresh water. However, because salt water contains bromide,
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