22 
occur given the mobility of shortnose sturgeon and the availability of suitable 
habitat. Therefore, no lethal take is expected to occur. 
The probability of lack of attainment of dissolved oxygen levels protective of short- 
nose sturgeon when the 2010 sediment and nutrient reduction goals are met has been 
modeled by EPA (U.S. EPA 2003c) and was the basis for determining the extent of 
take anticipated. As such, take levels can be determined for each of the designated 
uses where take is anticipated (open water, deep-water and deep-channel). As indi¬ 
cated in the biological opinion, take is likely to occur only in the summer months 
(June 1-September 30). Based on the analysis documented in the accompanying 
biological opinion, the area of the Bay designated uses that fail to meet a 5mg liter 1 
monthly average dissolved oxygen level can be used as a surrogate for take of short- 
nose sturgeon by harassment. As shortnose sturgeon are benthic fish, the modeling 
runs done for the bottom layer of the Bay have been used to determine the extent of 
take. To further refine this analysis, the “tolerate” habitat threshold has been used; 
that is, the estimate of area that will have temperatures <28°C, salinity <29 ppt and 
depth <25 meters which can be reasonably expected to be the areas of the Bay where 
shortnose sturgeon may be present in the summer months (U.S. EPA 2003c). 
Despite the use of the best available scientific and commercial data, NOAA Fisheries 
cannot quantify the precise number of fish that are likely to be taken. Because both 
the distribution of shortnose sturgeon throughout the Bay and the numbers of fish 
that are likely to be in an area at any one time are highly variable, and because inci¬ 
dental take is indirect and likely to occur from effects to habitat, the amount of take 
resulting from harassment is difficult, if not impossible, to estimate. In addition, 
because shortnose sturgeon are aquatic species who spend the majority of their time 
on the bottom and because shortnose sturgeon are highly mobile while foraging in 
the summer months, the likelihood of discovering take attributable to this proposed 
action is very limited. In such circumstances, NOAA Fisheries uses a surrogate to 
estimate the extent of take. The surrogate must be rationally connected to the taking 
and provide an obvious threshold of exempted take which, if exceeded, provides a 
basis for reinitiating consultation. For this proposed action, the spatial and temporal 
extent of the area failing to meet dissolved oxygen standards protective of shortnose 
sturgeon provides a surrogate for estimating the amount of incidental take. 
EXTENT OF TAKE FROM 2004-2009 
Using data provided by EPA, the extent of take occurring from the time of the adop¬ 
tion of the guidance 3 could be estimated. As habitat conditions in the Bay are 
expected to improve over time as interim measures are achieved before the 2010 
goals are met, it is reasonable to assume that this surrogate level of take will decrease 
3 Adoption of the guidance by the states and District of Columbia and approval by EPA is expected to 
occur in 2004 and 2005. 
chapter iv 
Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion 
