Post-stocking fate of June sucker in Utah Lake 2015 Final Annual Report

June sucker Chasmistes liorus is an endangered species endemic to Utah Lake, Utah. Historically, Utah
Lake supported a unique fish assemblage representing 13 native fishes. Impacts from anthropogenic
disturbances and the introduction of non-native fish species have altered the fish assemblage and only
two native fishes remain, June sucker and Utah sucker Catostomus ardens. June sucker was once
abundant in the lake, but a substantial population decline caused by multiple factors including
overharvest, habitat degradation, river and stream impoundments, and negative interactions with nonnative species reduced the population to less than 1,000 wild individuals in the latter 1990s.
Propagation and population augmentation is a primary recovery strategy for June sucker, although poststocking mortality of hatchery-reared June sucker is poorly understood. In this study, we examined
immediate post-stocking mortality and spatial distribution of hatchery-reared June sucker.
In 2015, the third year of this study, 24 June sucker were surgically implanted with acoustic tags. An
additional 1,180 PIT tagged fish were released in open water from a boat during two separate stocking
events in early summer (June) and early autumn (August). Active tracking was conducted using a
programmable acoustic tracking receiver and both directional and omni-directional hydrophones.
Submersible ultrasonic receivers (SURs) were strategically placed throughout the study area for
continuous passive tracking. Different SUR arrangements were used for both tracking events to respond to a decline in water levels in early autumn. Portable remote PIT scanning antennas were deployed at locations of temporal June sucker aggregations in the lake proper based on past observations, and randomly deployed throughout the study area to examine spatial distribution and survival of PIT tagged fish. Kaplan-Meier survival estimates were derived from the final fate of each acoustic tagged June sucker. Active and passive tracking records were used to assess spatial distribution with ArcGIS®. Survival was estimated at 0.88 through week 2, and 0.68 through week 3 and for the remainder of the 60-day tracking period for early summer fish. Survival was not estimated for the early autumn tracking period because 7 of 14 fish had an unknown fate (lost contact). Portable remote PIT scanning antennas recorded a total of 2,274 contacts representing 773 unique PIT tags over the five-month study. Since 2007, average size at stocking for June sucker has been 220 mm; however, average release size of June sucker contacted through PIT scanning in 2015 was 307 mm.

Our results revealed that survival was higher for the 2015 early summer (0.68) tracking period compared to the 2014 early summer (0.00) tracking period. In contrast, lack of survival and a large proportion of lost contacts during early autumn in 2015 were consistent with 2014 results. Past observations of immediate post-stocking avian predation suggest this mortality factor may be playing a role, especially in early autumn. Few immediately stocked fish were contacted with portable remote PIT scanning antennas in the lake proper. Cohorts that had the most contacts were released at an average length greater than 220 mm. Increasing size at release of hatchery fish may increase survival and accelerate augmentation of the population with hatchery-reared fish, a primary recovery strategy. Post-stocking survival of fish allowed to grow an additional year at the hatchery (larger fish) will be assessed in 2016.

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