21 
uses was likely to result in take of shortnose sturgeon in the form of harassment of 
shortnose sturgeon, where habitat conditions (i.e., dissolved oxygen levels below 
those protective of shortnose sturgeon) will temporarily impair normal behavior 
patterns of shortnose sturgeon (NO A A National Marine Fisheries 2004). This 
harassment will occur in the form of avoidance or displacement from preferred 
habitat and behavioral and/or metabolic compensations to deal with short-term 
hypoxic conditions. Neither lethal takes (see below) nor harm are anticipated in any 
Bay area due to the extent of available habitat in the Bay with dissolved oxygen 
levels protective of shortnose sturgeon and the demonstrated ability of shortnose 
sturgeon to avoid hypoxic areas and move to areas with suitable dissolved oxygen 
levels. Shortnose sturgeon displaced from hypoxic areas were expected to seek and 
find suitable alternative locations within the Bay. While shortnose sturgeon may 
experience temporary impairment of essential behavior patterns, no significant 
impairment resulting in injury (i.e., “harm”) was likely due to: the temporary nature 
of any effects, the large amount of suitable habitat with adequate dissolved oxygen 
levels, and the ability of shortnose sturgeon to avoid hypoxic areas. 
As outlined in the Biological Opinion, generally shortnose sturgeon are adversely 
affected upon exposure to dissolved oxygen levels of less than 5mg liter 1 and lethal 
effects are expected to occur upon even moderate exposure to dissolved oxygen 
levels of less than 3.2mg liter -1 . Because dissolved oxygen levels are known to be 
affected by various natural conditions (e.g., tides, hurricanes or other weather events 
including abnormally dry or wet years) beyond the control of EPA or the States and 
District of Columbia and can fluctuate greatly within any given period of time, a 
monthly average dissolved oxygen level has been determined to be the best measure 
of this habitat condition within the Bay. As indicated in the Biological Opinion, an 
area that achieves a 5mg liter -1 monthly average will also achieve at least a 3.2mg 
liter -1 instantaneous minimum dissolved oxygen level. As shortnose sturgeon are 
reasonably certain to be adversely affected by dissolved oxygen conditions below 
these levels, these levels can be used as a surrogate for take. As such, for puiposes 
of this Incidental Take Statement areas failing to meet a 5mg liter -1 monthly average 
of dissolved oxygen will be a surrogate for take of shortnose sturgeon. As noted 
above, this take is likely to occur in the form of avoidance or displacement from 
preferred habitat and behavioral and/or metabolic compensations to deal with short¬ 
term hypoxic conditions (defined as harassment in this situation). The amount of 
habitat failing to meet an instantaneous minimum of 3.2mg liter -1 could be used as 
a surrogate for lethal take of shortnose sturgeon; however, due to limitations of the 
model developed by EPA (U.S. EPA 2003c), the amount of habitat failing to reach a 
3.2mg liter -1 instantaneous minimum could not be modeled. However, an analysis of 
the likelihood of lethal take can be based on the amount of habitat failing to reach a 
3mg liter -1 monthly average (which would also likely be failing to meet a 3.2mg 
liter -1 instantaneous minimum). While a small portion of the Bay will fail to meet 
the 3 mg liter -1 monthly average, shortnose sturgeon are likely to be able to avoid 
these areas. Lethal effects are only expected to occur after at least 2-4 hours of expo¬ 
sure to dissolved oxygen levels of less than 3.2mg liter -1 , and this is not likely to 
chapter iv 
Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion 
