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Federal Register / Vol. 86, No. 8 / Wednesday, January 13, 2021 / Rules and Regulations threats are likely. In other words, the foreseeable future is the period of time in which we can make reliable predictions. Reliable does not mean certain; it means sufficient to provide a reasonable degree of confidence in the prediction. Thus, a prediction is reliable if it is reasonable to depend on it when making decisions.
It is not always possible or necessary to define foreseeable future as a particular number of years. Analysis of the foreseeable future uses the best scientific and commercial data available and should consider the timeframes applicable to the relevant threats and to the species likely responses to those threats in view of its life-history characteristics. Data that are typically relevant to assessing the species biological response include speciesspecific factors such as lifespan, reproductive rates or productivity, certain behaviors, and other demographic factors.
In considering the foreseeable future as it relates to the status of the Interior least tern, we consider the factors affecting the species and historical abundance trends. Our period of record for monitoring the species and its associated habitat is over three decades, which, when combined with our knowledge of factors affecting the species, allows us to reasonably predict future conditions. We think it is reasonable to define the foreseeable future for the Interior least tern to be 30
years based on analysis of these factors and as presented in more detail under Future Conditions and Species Viability, below.
When the Interior least tern was listed as endangered in 1985, the identified threats factors influencing its status were the modification and loss of habitat and curtailment of range Factor A, predation and disturbance of local colonies Factor C, and the inadequacy of State or Federal mechanisms to protect its habitat at that time Factor D.
The following analysis, based on an assessment of the Interior least tern, evaluates these previously identified threats, any other threats currently facing the species, and those threats that are reasonably likely to affect the Interior least tern in the foreseeable future following the delisting and the removal of the Acts protections.
Habitat Loss and Curtailment of Range The primary threats identified for the Interior least tern in the 1985 final listing rule were associated with the destruction and modification of habitat due to channel engineering practices on large rivers of the Interior Basin i.e., damming, channelization, and channel
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stabilization 50 FR 21784, May 28, 1985, pp. 2178921790; Service 1990, pp. 2223. Reservoirs had inundated hundreds of miles of historical or potential tern riverine habitat in many Mississippi River Basin drainages, and reduced sediment input into channels below dams had caused channel degradation, constriction, and loss of potential nesting habitats.
Channelization, channel training structures dikes, and bank stabilization in the Missouri, Mississippi, and Ohio Rivers prevented natural geomorphic response to loss of sediments, resulting in deepened and narrowed channels, and loss or terrestrialization vegetation encroachment of potential nesting sandbars and islands. Reservoir releases for hydropower, navigation, and flood control also were found to adversely affect Interior least tern populations surviving below these same dams Service 1990, p. 22. These trends of habitat degradation were also expected to continue throughout most of the terns fragmented range Smith and Stuckey 1988, entire.
New information on the species response to the threats identified at the time of listing indicate that anthropogenic changes in some river channels supporting the Interior least tern have also benefited the Interior least tern in ways that may have compensated for historical impacts to its habitat. For example, in the Lower Mississippi River where tern numbers have increased by an order of magnitude, and which currently supports more than 60 percent of the Interior least tern nesting population, channel engineering, including the construction of channel training dikes, resulted in higher sandbars as well as earlier and shorter spring and summer high water events in this portion of the range Schramm 2004, pp. 306, 322;
USACE 2013, p. 60. Such changes have reduced egg and chick flood-related mortality events, extended the nesting season, and increased re-nesting opportunities, all of which may explain the Interior least tern population increase in the Lower Mississippi River over the past four decades.
Anthropogenic habitats are also now known to provide significant opportunities for Interior least tern nesting and recruitment. High flows in the Platte River have historically peaked after most nesting has been initiated within the river channel, flooding nests and hatchlings, and limiting re-nesting opportunities Farnsworth et al. 2017, p.
3587. Models now suggest least tern nesting success would only have occurred during 32 percent of years, an inadequate success rate to have
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maintained the species within the Platte River. It is now hypothesized that offchannel mining habitats were, and continue to be, critical to the success of the Interior least tern in the central and lower Platte River Farnsworth et al.
2017, p. 3588. Similar observations have been proposed for some reaches of the Missouri River e.g., Jorgensen 2009, entire. In Texas and Colorado, foraging and nesting habitats created by dam construction have provided for Interior least tern colonization of arid regions historically unsuitable for the species Service 2013, pp. 2627.
Although river channel engineering, including reservoirs, channelization, channel training structures, and bank stabilization, continues to alter the Interior least terns habitats, as outlined above, these habitat modifications have also created additional habitat opportunities for this species. The Interior least terns known range has increased significantly; the reported numbers of nesting Interior least terns have expanded by almost an order of magnitude from fewer than 2,000 in 1985, to approximately 18,000 in 2005
Lott 2006, p. 10, and currently more than 480 Interior least tern colonies are known to occur in four major drainages with 16 primary subpopulations Lott et al. 2013, pp. 36163617. Most of these subpopulations have been stable or increasing over the past two decades Lott et al. 2013, p. 3620; Lott and Sheppard 2017a, pp. 5152. Thus, the negative impacts of river channel engineering on the tern appear to have been initially overestimated.
Loss of some historical Interior least tern summer nesting habitat likely occurred on a local or regional scale prior to listing; however, we have found no evidence that nesting habitat loss is currently limiting the Interior least tern on a rangewide scale. The Interior least tern continues to nest in all habitat types and drainages identified in 1985, and there is no evidence of significant regional decline or extirpation from any drainage since listing Service 2013, p.
10. As previously noted, the Interior least tern uses a variety of anthropogenic habitats such as navigation systems, reservoirs, sand mines, and so forth, allowing the Interior least tern to not only survive, but also to thrive in some drainages, and even expand its range into areas without historical records.
While future conditions within some portion of the Interior least terns range may deteriorate due to natural or anthropogenic changes for example, climate change may increase the likelihood of heavy rainfall events or human demands e.g., water extraction
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