Geology topics

Alexander J. Gatch

Publications and source records attributed to Alexander J. Gatch.

4 recordsLinked to original sources

USGS2023

Seasonal habitat utilization provides evidence for site fidelity during both spawn and non-spawning seasons in Lake Ontario cisco Coregonus artedi

The Lake Ontario cisco Coregonus artedi population declined in the 20th century, and restoration of this species is a management objective. Management tools to restore cisco are limited because little is known about cisco spawning behavior and habitat use. We tagged 76 cisco from a remnant population in Chaumont Bay, Lake Ontario with acoustic transmitters and characterized seasonal habitat use from 2016 to 2021. We also used fine-scale acoustic telemetry, coregonine egg collections, and trap net catches to better understand cisco spawning behaviors related to spawn timing and site selection. Network analysis and Bayesian standard ellipse area indicated that cisco utilization of lake regions and bathythermal niche space varied by season. During spawning season, male cisco concentrated in Chaumont Bay over shallow (∼3 m) rocky shoals where cisco egg deposition was the greatest. Spawning site fidelity to Chaumont Bay was observed for all male cisco surviving to successive years (n = 23). Acoustic-tagged females did not survive consecutive spawning seasons, but trap net catches indicated females were less abundant and occupied spawning areas for less time than males. Post spawn, some individual male cisco (n = 5/23) had differential, yet consistent, annual migrations to separate regions of Lake Ontario, suggesting fidelity to feeding sites. Our results reveal seasonal habitats used by male cisco and, importantly, caution that environmental changes to a single spawning site could negatively affect the remnant Chaumont Bay cisco population. Specialized conservation efforts may be necessary when cisco spawning aggregations have diverse post-spawn migratory behaviors but a central spawning ground.

Chaumont Bay, Lake Ontario↗

USGS2023

Field and laboratory validation of new sampling gear to quantify coregonine egg deposition and larval emergence across spawning habitat gradients

The influence of habitat and environmental conditions on Great Lakes coregonine reproduction is not well described, in part, because we lack sampling gears for early life stages that are effective across habitats. We designed new egg and larval emergence traps to quantify coregonine reproductive success across variable depths and substrates and tested them in laboratory and field settings. In the laboratory, our new metal ring egg traps had greater egg retention (94–100%) and faster post-catch processing (5–7 min) relative to a commonly employed fiber mat trap (30–67% and 30–60 min). In Lake Ontario’s Chaumont Bay, egg densities for lake whitefish Coregonus clupeaformis (0–5,832 eggs m −2 ) and cisco Coregonus artedi (0–426,501 eggs m −2 ) measured with metal ring traps (n = 112) varied across habitats but were greatest between 2–5 m on rock and dreissenid mussel substrates. Emergence traps used an inverted cone, fine mesh, and a clear collection chamber to capture positively phototactic emerging larvae. In the laboratory, traps captured 69–80% of emerged larvae. In Chaumont Bay, emergence traps deployed for 21 days after ice out caught only cisco larvae. Emergence rates varied across habitats (0–118 larvae m −2 day −1 , n = 85) but were highest on dreissenid mussel reef substrate. Our samplers improved processing efficiency and facilitated large sample sizes to quantify variability in egg deposition densities and emergence rates across habitats. These methods can advance coregonine conservation by determining how anthropogenic changes to habitat and environmental conditions influence incubation success.

Journal of Great Lakes Research↗

USGS2023

Lake Ontario August gillnet survey and Lake Trout assessment, 2022

Lake Ontario Lake Trout (Salvelinus namaycush) rehabilitation has been annually assessed with fishery independent surveys since 1983, in an effort to evaluate program benchmarks and compare observations with management objectives. These surveys provide information on the abundance, strain composition, and condition of the adult Lake Trout stock, as well as information on levels of natural recruitment, Sea Lamprey (Petromyzon marinus) wounding rates, and abundance indices of other coldwater fish species (Burbot Lota lota, Cisco Coregonus artedi, and Lake Whitefish C. clupeaformis). In 2022, the catch per unit effort (CPUE) of total Lake Trout in gillnets remained high (18.9 fish/lift; highest since 1998) compared to lows observed during 2005–2009 (average = 7.5 fish/lift). The CPUE of immature Lake Trout in the 2022 survey was the highest since 1994. Wild-produced mature Lake Trout remain rare in the adult population (2.4% of adult catch). Strain composition of stocked fish indicated more than half (56%) of all coded-wire tagged Lake Trout captured in 2022 were from the Superior Klondike strain. Sea Lamprey wounding rates were above target levels in 2022 (3.15 A1 wounds per 100 Lake Trout) and were nearly double the 2021 rate. Lake Trout condition (predicted weight at length) was the highest since data collection began in 1983. Overall, the 2022 survey results indicate that adult Lake Trout are abundant and of high condition but composed mostly of hatchery-origin strains, suggesting recruitment of wild-produced offspring to the adult stock continues to be limited.

Lake Ontario↗

USGS2022

Evaluation of post-stocking dispersal and mortality of juvenile lake trout Salvelinus namaycush in Lake Ontario using acoustic telemetry

Wild reproduction by stocked lake trout Salvelinus namaycush in Lake Ontario has yet to produce a self-sustaining population, requiring a reliance on stocking. Once released, age-1 juvenile lake trout are not typically surveyed until age-2, creating a gap in knowledge of fine-scale post-release behaviors. A method to track fine-scale movements and estimate mortality of juvenile lake trout could complement standard survey methods and benefit management decisions regarding stocking locations. We used acoustic telemetry to estimate post-stocking mortality and observe fine-scale spatial and temporal movements of 38 hatchery-reared, age-1 lake trout from an offshore stocking site in the eastern basin of Lake Ontario from 2017 to 2018. Cumulative post-stocking mortality was estimated at 5.3%, 10.5%, and 26.3% after one week, one month and one year, respectively. The majority of lake trout (68.4%) emigrated from the stocking location within two months and entered deep water (∼50 m) once warm-water incursions at the stocking site exceeded lake trout thermal preferences (15 °C). Lake trout made large movements (i.e., median 1.9 km, maximum 12.4 km straight-line distance) within the first hour post-release and had an average swimming speed of 1.64 km‧hr −1 over the first day. There was no statistically significant relationship between total distance traveled and time of day, although distance traveled tended to be greater during crepuscular and dark periods compared to daylight. Our results provide a conservative estimate of post-release mortality and reveal behaviors of hatchery-reared juvenile lake trout that may be helpful when selecting stocking locations beneficial to restoration program goals.

Lake Ontario↗