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Federal Register / Vol. 86, No. 8 / Wednesday, January 13, 2021 / Rules and Regulations provided counts for 21 populations or population segments that were unknown at the time of listing, which collectively support more than 2,000
terns.
Population Trends The Interior least tern has demonstrated a positive population trend, increasing by almost an order of magnitude or 10 times what it was prior since it was listed in 1985. After it was listed, researchers increased survey effort and the geographical extent of the area surveyed, producing sufficient Interior least tern count data to analyze population trends for several river reaches that support persistent breeding colonies. Kirsch and Sidle 1999, p. 473 reported a rangewide population increase to over 8,800 adults in 1995, and found that 29 of 31 Interior least tern locations with multi-year monitoring data were either increasing or stable. Lott 2006, p. 50 reported an increase to over 17,500 adult birds in 2005, forming 489 colonies in 68
distinct geographic sites. While some proportion of the rangewide increase in adult bird counts and number of nesting colonies are likely attributable to increased survey efforts and improved survey techniques, both Kirsch and Sidle 1999, p. 473, and Lott and Sheppard 2017a, pp. 5052
documented multiple drainage population increases using multi-year counts.
Lott 2006, p. 92 conceptualized the Interior least tern functioning as a large metapopulation a regional group of connected populations of a species, which might also include least terns on the Gulf Coast. Using available information on dispersal of least terns, Lott et al. 2013, pp. 36163617 defined 16 discrete breeding populations of Interior least tern, with 4 major geographical breeding populations population complexes accounting for more than 95 percent of all adult birds and nesting sites throughout the range.
Portions of these four population complexes have experienced multi-year monitoring to different degrees. While some local colony, subpopulation declines have been documented, the Interior least tern has experienced a dramatic increase in range and numbers since listing and development of the recovery plan e.g., Kirsch and Sidle 1999, p. 473; Lott 2006, pp. 1049.
There has been no reported extirpation of any population or subpopulation since the species was listed in 1985.
Recovery Criteria Section 4f of the Act directs us to develop and implement recovery plans
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for the conservation and survival of endangered and threatened species unless we determine that such a plan will not promote the conservation of the species. Recovery plans must, to the maximum extent practicable, include objective, measurable criteria which, when met, would result in a determination, in accordance with the provisions of section 4 of the Act, that the species be removed from the list.
Recovery plans provide a roadmap for us and our partners on methods of enhancing conservation and minimizing threats to listed species, as well as measurable criteria against which to evaluate progress towards recovery and assess the species likely future condition. However, they are not regulatory documents and do not substitute for the determinations and promulgation of regulations required under section 4a1 of the Act. A
decision to revise the status of a species, or to delist a species is ultimately based on an analysis of the best scientific and commercial data available to determine whether a species is no longer an endangered species or a threatened species, regardless of whether that information differs from the recovery plan.
There are many paths to accomplishing recovery of a species, and recovery may be achieved without all of the criteria in a recovery plan being fully met. For example, one or more criteria may be exceeded while other criteria may not yet be accomplished. In that instance, we may determine that the threats are minimized sufficiently and the species is robust enough that it no longer meets the definition of an endangered species or a threatened species. In other cases, we may discover new recovery opportunities after having finalized the recovery plan. Parties seeking to conserve the species may use these opportunities instead of methods identified in the recovery plan.
Likewise, we may learn new information about the species after we finalize the recovery plan. The new information may change the extent to which existing criteria are appropriate for identifying recovery of the species.
The recovery of a species is a dynamic process requiring adaptive management that may, or may not, follow all of the guidance provided in a recovery plan.
The Service approved the Interior Least Tern Recovery Plan on September 19, 1990 Service 1990, entire. The objective of the recovery plan was to establish standards for recovery that may lead to delisting the Interior least tern. Recovery criteria are the values by which it is determined that a recovery
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plan objective has been reached.
Recovery criteria identified in the recovery plan were designed to assure the protection of essential habitat by removal of threats at that time and habitat enhancement, establish agreedupon management plans, and attain a rangewide population of 7,000 birds at the levels listed below for five major river drainages throughout the Interior least terns range:
1 Adult birds in the Missouri River system will increase to 2,100, and remain stable for 10 years.
2 Current numbers of adult birds 2,2002,500 on the Lower Mississippi River will remain stable for 10 years.
3 Adult birds in the Arkansas River system will increase to 1,600, and remain stable for 10 years.
4 Adult birds in the Red River system will increase to 300, and remain stable for 10 years.
5 Current numbers of adult birds 500 in the Rio Grande River system will remain stable for 10 years.
Primary recovery tasks conducted to achieve the recovery objective and drainage population targets included:
1 Determining the distribution and population trends of the Interior least tern;
2 Determining habitat requirements and status;
3 Protecting, enhancing, and increasing Interior least tern populations; and 4 Preserving and enhancing the terns habitats.
These are briefly reviewed below.
Rangewide Population Criterion to Delist The Interior least tern rangewide numerical recovery criterion 7,000
birds has been met and has been exceeded since 1994 see Service 2013, pp. 7127. Using rangewide seasonal count data from 1984 722 terns through 1995 8,859 terns, Kirsch and Sidle 1999, pp. 473477 demonstrated achievement of the numerical recovery criterion and a positive population growth trend. They noted that most of the Interior least tern increase had occurred on the Lower Mississippi River, observed that population increases were not supported by fledgling success estimates available at that time, and hypothesized that Interior least tern increases were possibly due to immigration surges from a more abundant least tern population inhabiting the Gulf Coast Kirsch and Sidle 1999, p. 478.
Lott 2006, entire organized, compiled, and reported a synchronized rangewide count for Interior least tern in 2005, finding tern numbers had doubled
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