Northern Pike Monitoring and Telemetry
Utah Lake, Utah

Utah Lake is home to the only known endemic population of June Sucker (Chasmistes liorus).  The species was abundant in the 19th century; however, populations rapidly declined in the 20th century due to habitat loss, introduction of nonnative fishes, and overharvesting (Andersen et al. 2007).  Steep decline of the June Sucker population led U.S. Fish and Wildlife Service (USFWS) to list June Sucker as endangered in 1986 (USFWS 1999).  Extensive recovery efforts by the interagency group “June Sucker Recovery Implementation Program” (JSRIP), led to June Sucker being reclassified from endangered to threatened on February 3, 2021 (USFWS 2021).  Threats that impact the existence of June Sucker population in Utah Lake include declining water levels, habitat loss, and introduced fish species.  The recovery plan for June Sucker includes securing water rights, habitat restoration, and annual stocking of thousands of fish from hatcheries and refuge populations.  These recovery efforts have resulted in a seemingly stable population of June Sucker.  However, the illegal introduction of Northern Pike (Esox lucius) into Utah Lake in early to mid-2000s may jeopardize JSRIP recent success. Presence of Northern Pike in Utah Lake was confirmed in sampling by Utah Division of Wildlife Resources (UDWR) in 2011.  The Northern Pike population in Utah Lake is currently at a low level (BIO-WEST 2020).  However, Northern Pike are voracious predators and could decimate both stocked June Sucker and naturally produced young-of-year in Utah Lake (Reynolds 2017).  Because of the substantial threat Northern Pike poses to recovery, it was determined that research and monitoring for Northern Pike in Utah Lake should be initiated to a) identify Northern Pike spawning sites and aggregations during other times of the year; b) identify the best capture methods, and ultimately, control measures; and c) evaluate potential impact of Northern Pike on the June Sucker population.

A three-year research project was initiated in 2021 by Marsh & Associates (M&A) using a combination of acoustic and radio tracking, larval trapping, seining, and observation to describe Northern Pike movement, habitat use, congregational behavior, and spawning behavior in Utah Lake. The overall goal of this project is to “provide the JSRIP information on location and timing of Northern Pike congregations in Utah Lake so that the effectiveness of targeted netting and electrofishing efforts to remove Northern Pike is maximized.  Where possible, this information includes physical and other biological characteristics associated with Northern Pike movements and congregations.”  The nine primary objectives of this work are: contact Northern Pike using submersible ultrasonic receivers at fixed and random sites within Utah Lake. conduct active telemetry of Northern Pike implanted with radio-equipped tags in tributaries of Utah Lake, perform targeted sampling for larvae and early juvenile Northern Pike employing passive lighted trap and, possibly, active lighted net techniques, assimilate data from remote PIT scanners with data from other detection sources, conduct two prolonged monitoring trips (total 20 workdays) during the Northern Pike spawn, conduct one prolonged post-spawn (10 workdays) monitoring trip., conduct approximately three (total 15 workdays) non-spawn monitoring trips, aid Utah Department of Wildlife Resources (UDWR), as needed, and assess temporal and spatial distribution patterns of Northern Pike and identify areas of concentrated and/or frequent use and summarize habitat use, as data allows.

Primary objectives were accomplished in the first year of this project by a combination of on-site fieldwork on Utah Lake, Provo, UT, and data processing and analysis at M&A offices in Tempe, Arizona.  Fieldwork was partitioned into three categories based upon the timing of Northern Pike life history functions: spawn-trips, when adults were assumed to be in reproductive mode and adults, larvae, and early juveniles may be aggregated; post-spawn trips, when fish were expected to be actively dispersing; and non-spawn trips, when fish of all life stages likely were dispersed.  Post-spawn field trips were not conducted in this first year because the project was initiated after conclusion of Northern Pike spawning and post-spawning periods in Utah Lake. 

M&A conducted three, 5-day non-spawn field trips.  The first non-spawn trip was conducted July 12 to 16, 2021, second September 13 to 17, 2021, and third November 15 to 19, 2021.  Based on rising water temperatures, ice off, and consultation with UDWR and Central Utah Water Conservancy District (CUWCD) staff in January, M&A initiated spawning season sampling on Monday February 22, 2022.  Spawning season sampling includes 5-day work weeks (20 work-days total, 10 workdays per trip) of intensive sampling.  The first spawn-trip occurred from February 22 to March 4, 2022, and the second was scheduled on March 21 through April 1, 2022. A three-part telemetry approach was implemented: 1) deployment of SURs1 at “fixed” sites within Utah Lake, 2) random deployment of SURs in Utah Lake within areas that contain desirable habitat characteristics (objective 1), and 3) active manual tracking of radio-equipped tags mainly within major tributaries of Utah Lake (objective 2).  We supplemented this telemetry with targeted sampling for larval and early juvenile Northern Pike to identify adult spawning areas. Apart from larval trapping, all methods for contacting Northern Pike have had at least some success (radio, acoustic, PIT, and angler capture).  Based on mortality estimated in the literature, less than half of Northern Pike tagged since 2020 may be alive.