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Federal Register / Vol. 86, No. 8 / Wednesday, January 13, 2021 / Rules and Regulations
since 1995 17,591 birds rangewide; 62
percent occurring along the Lower Mississippi River, equaling or exceeding least tern population estimates along the U.S. Gulf Coast Lott 2006, p. 50. Since 2006, the majority of Interior least terns continue to be reported from the Lower Mississippi River Service 2013, p. 11. As did Kirsch and Sidle 1999, p. 478, Lott 2006, p. 52 also hypothesized a wider least tern metapopulation, which included Gulf Coast and interior subpopulations, and the possibility of a shift of birds from the Gulf Coast to inland habitats due to the presence of better nesting conditions, particularly on the Lower Mississippi River.
However, there are few data directly supporting the Kirsch and Sidle 1999, pp. 473477 or the Lott 2006, p. 52
immigration hypotheses as a factor in the 20-year increase in Interior least tern counts. There has not been a complete or organized rangewide count since 2005; however, some geographic segments continue to be annually monitored, including portions of the Missouri USACE in litt. 2017, entire, Platte Keldsen and Baasch 2016, entire, Red Stinson in litt. 2017, entire, Arkansas Cope in litt. 2017, entire; Nupp 2016, entire, and Wabash Rivers Mills 2018, entire. These partial counts indicate that we continue to exceed the recovery goal of 7,000 birds Service 2013, pp. 1112.
Numerical Population Targets In addition to the numerical population targets identified in the recovery plan for five major river drainages throughout the terns range see above, sub-drainage targets were also identified for the Missouri and Arkansas River drainages Service 1990, pp. 2829. Drainage and sub-drainage numerical targets were based upon the opinions of technical experts and State and Federal resource agencies of the potential for population increase at the time Service 1990, p. 28. The drainage system population size targets have been exceeded in three of the five targeted drainages Lower Mississippi more than 25 years, Red more than 15
years, and Arkansas Rivers more than 10 years see Service 2013, pp. 2226.
As to the Rio Grande drainage, it is now recognized that the subpopulations found within the drainage represent recent exploitation of anthropogenic habitats i.e., salt flats and reservoirs and are not historical habitats; thus, these areas were inappropriately designated as essential segments of the terns ecosystem in the recovery plan Service 2013, pp. 2627.
Therefore, numerical targets originally
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set for the Rio Grande drainage are no longer considered necessary for this species recovery.
As to the Missouri River drainage, the Interior least tern population size has remained relatively stable approximately 1,600 birds over the 29
years since recovery criteria were identified Service 2013, p. 11, and neither the drainage population target 2,100 nor many of the targets identified for Missouri River drainage segments have been consistently met Service 2013, pp. 1421. However, since the tern was listed, the Missouri River system has received a significant commitment of conservation attention and resources USACE 2017a, pp. 117, particularly in comparison to other drainages that have experienced increases in tern populations. Based on the lack of increase in population, in light of the substantial commitment of resources, we conclude that that the Missouri River drainage is likely at the carrying capacity of the available habitat Service 2013, pp. 1421, and the recovery goal of 2,100 birds is not achievable. Periodic downward trends observed in a few Missouri drainage subpopulations have been reversed by habitat improvement following major floods Pavelka 2012, p. 2, or offset by upward trends in other subpopulations Pavelka 2012, pp. 78; Lott and Sheppard 2017a, pp. 4953, indicating that the Missouri River drainage Interior least tern population is sustainable and recovered.
In short, some drainage population targets identified in the 1990 recovery plan have not been fully met, as the Rio Grande was inappropriately considered essential see above and the Missouri River drainage appears to be at carrying capacity and incapable of reaching the 2,100 target identified in the recovery plan. However, the inability to meet these drainage and sub-drainage targets have been offset by large increases in the Interior least tern populations within the Arkansas, Red, and Lower Mississippi Rivers, and by the discovery of numerous subpopulation segments throughout the Interior Basin that were either unrecognized or not occupied at the time of listing and recovery plan development, increasing the number of known breeding colonies from a few dozen at listing to more than 480 Lott 2006, p. 10; also see Service 2013, pp.
3133.
Habitat Criteria Recovery plan delisting criteria required the protection, enhancement, and restoration of essential Interior least tern breeding habitats Service 1990, pp.
2829. Beyond the identification of
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specific river reaches as essential, habitat parameters were not defined, nor were specific objective and measurable criteria for their protection identified.
The recovery plan outlined several tasks to protect and enhance Interior least tern habitats, including managing water flows, modifying construction activities, and protecting all areas identified as essential across the species range through acquisition, easements, or agreements Service 1990, pp. 2950.
Recovery tasks identified for managing water flows are primarily relevant to portions of the Missouri, Red, and Arkansas River drainages, which cumulatively encompass about 20 percent of the Interior least tern breeding population. The majority of the remainder of the species range occurs along unimpounded sections of the Mississippi River not subject to flow management. Over the past two decades, protective flow management actions have been identified and incorporated by USACE Northwest Division into their Missouri River Bank Stabilization and Navigation Project and operations of the Missouri River Reservoir System, including seasonal reservoir flow management to reduce nesting mortalities, and for sandbar augmentation and modification, vegetation management, predation control, human restriction measures, and water-level management for reservoir nesting areas USACE 2017a, pp. 139143. In the Southern Plains, USACE Southwest Division civil works projects in the Arkansas, Canadian, and Red River systems within Arkansas, Oklahoma, and Texas use reservoir storage and operation to reduce flooding; minimize land bridging, predation, and human disturbance during Interior least tern nesting season;
and enhance nesting habitats at other times of the year USACE 2002, pp. 3
4; 2016, pp. 1820. These water management practices have been adopted by the respective USACE
Divisions and Districts as best management practices BMPs and with commitments to continue into the future regardless of the future status of the Interior least tern under the Act USACE
2016, pp. 2, 24; 2018, pp. 413417.
Recovery tasks for modifying construction activities within river channels have been successfully implemented across Interior least tern habitats that are managed under USACE
programs in jurisdictional waters categories of waters defined under the Clean Water Act 33 U.S.C. 1251 et seq.
that include navigable waters, interstate waters, tributaries, impoundments, etc..
Construction practices critical to maintaining and protecting nesting
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