Geology Reports⌕ Search

Geology topics

Research about Canada, United States

Source-linked reports with geographic coverage including Canada, United States.

At least 469 records · Page 26Linked to original sources
USGS2021

Toward an integrative geological and geophysical view of Cascadia subduction zone earthquakes

The Cascadia subduction zone (CSZ) is an exceptional geologic environment for recording evidence of land level changes, tsunamis, and ground motion that reveals at least 19 great megathrust earthquakes over the past 10 kyr. Such earthquakes are among the most impactful natural hazards on Earth, transcend national boundaries, and can have global impact. Reducing the societal impacts of future events in the U.S. Pacific Northwest and coastal British Columbia, Canada requires improved scientific understanding of megathrust earthquake rupture, recurrence, and corresponding hazards. Despite substantial knowledge gained from decades of research, large uncertainties remain about the characteristics and frequencies of past CSZ earthquakes. In this review, we summarize geological, geophysical, and instrumental evidence relevant to understanding megathrust earthquakes along the CSZ and associated uncertainties. We discuss how the evidence constrains various models of great megathrust earthquake recurrence in Cascadia and identify potential paths forward for the earthquake science community.

British Columbia, Oregon, Washington↗
USGS2021

Climate impacts on the Gulf of Maine ecosystem: A review of observed and expected changes in 2050 from rising temperatures

The Gulf of Maine has recently experienced its warmest 5-year period (2015–2020) in the instrumental record. This warming was associated with a decline in the signature subarctic zooplankton species, Calanus finmarchicus . The temperature changes have also led to impacts on commercial species such as Atlantic cod ( Gadus morhua ) and American lobster ( Homarus americanus ) and protected species including Atlantic puffins ( Fratercula arctica ) and northern right whales ( Eubalaena glacialis ). The recent period also saw a decline in Atlantic herring ( Clupea harengus ) recruitment and an increase in novel harmful algal species, although these have not been attributed to the recent warming. Here, we use an ensemble of numerical ocean models to characterize expected ocean conditions in the middle of this century. Under the high CO 2 emissions scenario (RCP8.5), the average temperature in the Gulf of Maine is expected to increase 1.1°C to 2.4°C relative to the 1976–2005 average. Surface salinity is expected to decrease, leading to enhanced water column stratification. These physical changes are likely to lead to additional declines in subarctic species including C. finmarchicus , American lobster, and Atlantic cod and an increase in temperate species. The ecosystem changes have already impacted human communities through altered delivery of ecosystem services derived from the marine environment. Continued warming is expected to lead to a loss of heritage, changes in culture, and the necessity for adaptation.

Maine, Massachusetts, New Brunswick, New Hampshire↗
USGS2021

Limited co-existence of native unionids and invasive dreissenid mussels more than 30 Y post dreissenid invasion in a large river system

There are serious concerns for native freshwater mussel survival (Bivalvia: Unionidae) in the Laurentian Great Lakes region after populations were seemingly pushed to the brink of extirpation following the introduction of dreissenid mussels ( Dreissena polymorpha and D. rostriformis bugensis ) in the mid-1980s. The Detroit River was the first major river system in North America to be invaded by dreissenids, and unionids were considered extirpated from the river by 1998. Since then several unionid refuges (areas with relatively low dreissenid impact and surviving unionids) have been found in coastal areas of lakes St. Clair and Erie, but no documentation exists in the Detroit River. To assess dreissenid presence and potential unionid persistence, a mixture of stratified random, historical, and potential refuge sites were surveyed during summer 2019 in the Detroit River. Unionid and dreissenid habitat use was further investigated with analysis of variance and classification tree analyses. Of the 56 sites surveyed, only five sites had live unionids totaling 220 animals of 11 species. More than 2000 unionid shells of 31 species were collected from 39 sites, confirming the large and diverse unionid populations that existed prior to the dreissenid invasion. Ninety-eight percent of live unionids found showed evidence of past or present dreissenid attachment. Estimated dreissenid densities were highly variable with river location and ranged from 0 to 5673 live individuals per m 2 , with the largest densities concentrated in the upstream half of the Detroit River. Despite their previously assumed extirpation from the Detroit River, live unionids were found during this comprehensive survey. Although only 40% of the historical species within the unionid assemblage remains, our results suggest, in the right conditions, some coexistence is possible among some species of unionids and dreissenids in this large river system.

Michigan↗
USGS2021

Estimating trends of common raven populations in North America, 1966—2018

Over the last half century, common raven ( Corvus corax; raven) populations have increased in abundance across much of North America. Ravens are generalist predators known to depredate the eggs and young of several sensitive species. Quantifying raven population increases at multiple spatial scales across North America will help wildlife resource managers identify areas where population increases present the greatest risk to species conservation. We used a hierarchical Bayesian modeling approach to analyze trends of standardized raven counts from 1966 to 2018 using Breeding Bird Survey data within each Level I and II ecoregion of the United States and Canada. We also compared raven abundance within and outside the distributions of 9 sensitive or endangered species. Although we found substantial evidence that raven populations have increased across North America, populations varied in growth rates and relative abundances among regions. We found 73% of Level I (11/15) and II (25/34) ecoregions demonstrated positive annual population growth rates ranging from 0.2–9.4%. We found higher raven abundance inside versus outside the distributions of 7 of the 9 sensitive species included in our analysis. Gunnison sage-grouse ( Centrocercus minimus ) had the highest discrepancy, with 293% more ravens within compared to outside of their range, followed by greater sandhill crane ( Antigone canadensis tabida ; 280%), and greater sage-grouse ( C. urophasianus ; 204%). Only 2 species, least tern ( Sternula antillarum ) and piping plover ( Charadrius melodus ), indicated lower raven abundance within relative to outside their distributions. Our findings will help wildlife resource managers identify regional trends in abundance of ravens and anticipate which sensitive species are at greatest risk from elevated raven populations. Future research directed at identifying the underlying regional drivers of these trends could help elucidate the most appropriate and responsive management actions and, thereby, guide the development of raven population management plans to mitigate impacts to sensitive species.

Human-Wildlife Interactions↗
USGS2021

Migration phenology and patterns of American woodcock in central North America derived using satellite telemetry

American woodcock Scolopax minor (hereafter woodcock) migration ecology is poorly understood, but has implications for population ecology and management, especially related to harvest. To describe woodcock migration patterns and phenology, we captured and equipped 73 woodcock with satellite tracking devices in the Central Management Region (analogous to the Mississippi Flyway) of North America and documented migration paths of 60 individual woodcock and 87 autumn or spring woodcock migrations during 2014–2016. Woodcock migration at the scale of the Central Management Region was more synchronous in spring than in autumn, but unlike most other migratory birds, average duration of autumn migration (31 days) was shorter than duration of spring migration (53 days). This difference in migration duration resulted from woodcock making more close-together migratory stopovers during spring migration, not because woodcock had individual stopovers of longer duration. During autumn migration, the number of days, the number of stopovers, migration end date and net migration displacement were negatively related to initiation date and rate of migration, and the number of stopovers and the net migration displacement were negatively related with migration end date. Spring migration duration, end date, the number of stopovers and net migration displacement were negatively related to migration rate and initiation date was positively related to migration rate, suggesting that woodcock that initiated spring migration later had faster migration rates. Juvenile female woodcock began spring migration later than adult female woodcock. Our results provide a basis for comparing current harvest seasons with presence of migrating woodcock during autumn and provide insight into differential harvest of migratory versus local woodcock on breeding areas.

central North America↗
USGS2021

Secretive marsh bird habitat associations in the Mississippi Flyway: A meta-analysis

Secretive marsh birds, including rails and bitterns, have experienced widespread population declines due to the loss of wetland habitat on which they depend. Because of their cryptic behavior, secretive marsh birds are challenging to study and information on their habitat requirements is limited, especially across the full annual cycle. Quantifying habitat associations throughout the annual cycle and at broad geographic scales can advance a more comprehensive approach for secretive marsh bird conservation. The goal of this study was to quantitatively synthesize results from empirical studies that examined species-habitat relationships of secretive marsh birds in the North American Mississippi Flyway to identify general patterns and information gaps that can guide future management and conservation efforts. We performed a meta-analysis and incorporated results from 40 studies that quantitatively assessed habitat associations of American Bittern ( Botaurus lentiginosus ), Least Bittern ( Ixobrychus exilis ), King Rail ( Rallus elegans ), Sora ( Porzana carolina ), Virginia Rail ( Rallus limicola ), and Yellow Rail ( Coturnicops noveboracensis ). Most studies examined breeding season habitat, whereas only 13% reported on habitat use during migration and none during winter. At landscape scales, breeding marsh birds were positively associated with amount of wetlands, especially in the Great Lakes region, and negatively associated with amount of urban land cover, particularly for American Bittern. At the local scale, breeding marsh birds were positively associated with cattail coverage ( Typha spp) and other robust emergent vegetation. Overall, marsh birds were negatively associated with woody wetland vegetation, although effects were weaker in the Prairie region and varied among species. During autumn migration, moist-soil vegetation coverage was important for rails in the lower Midwest. The habitat use patterns we identified across studies provide a general characterization of marsh bird breeding habitat to aid in landscape-level multi-species conservation efforts. Our study also highlights the immediate research needs for full annual cycle conservation of secretive marsh bird habitat in North America: specifically, information during winter and migration.

Avian Conservation and Ecology↗
USGS2021

Fisheries research and monitoring activities of the Lake Erie Biological Station, 2020

This report presents biomass-based summaries of fish communities in the West Basin of Lake Erie derived from USGS bottom trawl surveys conducted from 2013 to 2020 during June and September. The survey design provided temporal and spatial coverage that did not exist in the interagency trawl database, and thus complemented the August ODNR-OMNRF effort to reinforce stock assessments with more robust data. Analyses herein evaluated trends in: total biomass, abundance of dominant predator and forage species, non-native species composition, biodiversity and community structure. Data from this effort can be explored interactively online (https://lebs.shinyapps.io/western-basin/), and are accessible for download (https://www.sciencebase.gov/catalog/item/6013031fd34e162231fed756, Keretz et al. 2021). Annual survey data are added to these sources as the data become available.

Lake Erie↗
USGS2021

Status of Cisco in Lake Superior in 2017

This report describes the status of fish species and their habitat in Lake Superior during the reporting period of 2012-2016 in response to achievement of fish community objectives (FCOs) established by fishery managers for the lake. The overarching goal for the FCOs continued to be met as the fish community remained diverse, self-regulating, dominated by indigenous species, and able to support sustainable fisheries, although further rehabilitation of certain fish is required. The Lake Superior Lakewide Action and Management Plan classified all habitat indicators for Lake Superior as good. Primary production and zooplankton abundance were stable during the reporting period and unchanged from the two previous reporting periods, indicating the lower food web is healthy. Abundance of the invertebrates Mysis diluviana and Diporeia spp. were stable during the reporting period, and Diporeia spp. density exceeded target levels defined in the Great Lakes Water Quality Agreement. Lake Whitefish (Coregonus clupeaformis) abundance was lower than during the previous reporting period but was within the FCO target. Abundance of lean, siscowet, and humper forms of Lake Trout (Salvelinus namaycush) remained stable at levels seen in previous reporting periods. The FCO for non-indigenous salmonids was met as Chinook Salmon (Oncorhynchus tshawytscha), Coho Salmon (O. kisutch), and steelhead/Rainbow Trout (O. mykiss) were being sustained by natural reproduction, and their abundance remained stable or increased from previous reporting periods. The FCO for Walleye (Sander vitreus) was not met, although populations showed signs of improvement since the previous reporting period. The fish community in littoral areas and embayments continued to be diverse and composed mostly of indigenous species. No new invasive species were found in Lake Superior during the reporting period. Degraded embayment and tributary habitats continued to prevent achievement of the FCOs for Brook Trout (S. fontinalis) and Lake Sturgeon (Acipenser fulvescens). Barriers created for hydroelectric generation either blocked Lake Sturgeon from historically important spawning grounds or reduced stream flows necessary for its reproduction. In tributaries without man-made barriers, Lake Sturgeon was relatively abundant and appeared healthy. Attainment of the FCOs for Brook Trout and Lake Sturgeon will be challenging and can only be attained through development of large-scale management actions like those implemented for Lake Trout rehabilitation and Sea Lamprey (Petromyzon marinus) control. Sea Lamprey-control expenditures doubled in 2016 from past levels and should result in suppression of the population closer to its FCO after 2016. The prey-fish FCO appears to have been met, but biomass of nearly all prey-fish species declined from that reported for the previous reporting period and has been on a downward trajectory since 2000. Predation by Lake Trout is probably to blame for the declining biomass of prey fish. Poor recruitment by Cisco (C. artedi) over the last 15 years is exacerbating the declines in prey-fish biomass because Lake Trout must compensate for the loss of Cisco by consuming other, less-abundant prey fish.

Lake Superior↗
USGS2021

State of Lake Superior ecosystem in 2017

This report describes the status of fish species and their habitat in Lake Superior during the reporting period of 2012-2016 in response to achievement of fish community objectives (FCOs) established by fishery managers for the lake. The overarching goal for the FCOs continued to be met as the fish community remained diverse, self-regulating, dominated by indigenous species, and able to support sustainable fisheries, although further rehabilitation of certain fish is required. The Lake Superior Lakewide Action and Management Plan classified all habitat indicators for Lake Superior as good. Primary production and zooplankton abundance were stable during the reporting period and unchanged from the two previous reporting periods, indicating the lower food web is healthy. Abundance of the invertebrates Mysis diluviana and Diporeia spp. were stable during the reporting period, and Diporeia spp. density exceeded target levels defined in the Great Lakes Water Quality Agreement. Lake Whitefish (Coregonus clupeaformis) abundance was lower than during the previous reporting period but was within the FCO target. Abundance of lean, siscowet, and humper forms of Lake Trout (Salvelinus namaycush) remained stable at levels seen in previous reporting periods. The FCO for non-indigenous salmonids was met as Chinook Salmon (Oncorhynchus tshawytscha), Coho Salmon (O. kisutch), and steelhead/Rainbow Trout (O. mykiss) were being sustained by natural reproduction, and their abundance remained stable or increased from previous reporting periods. The FCO for Walleye (Sander vitreus) was not met, although populations showed signs of improvement since the previous reporting period. The fish community in littoral areas and embayments continued to be diverse and composed mostly of indigenous species. No new invasive species were found in Lake Superior during the reporting period. Degraded embayment and tributary habitats continued to prevent achievement of the FCOs for Brook Trout (S. fontinalis) and Lake Sturgeon (Acipenser fulvescens). Barriers created for hydroelectric generation either blocked Lake Sturgeon from historically important spawning grounds or reduced stream flows necessary for its reproduction. In tributaries without man-made barriers, Lake Sturgeon was relatively abundant and appeared healthy. Attainment of the FCOs for Brook Trout and Lake Sturgeon will be challenging and can only be attained through development of large-scale management actions like those implemented for Lake Trout rehabilitation and Sea Lamprey (Petromyzon marinus) control. Sea Lamprey-control expenditures doubled in 2016 from past levels and should result in suppression of the population closer to its FCO after 2016. The prey-fish FCO appears to have been met, but biomass of nearly all prey-fish species declined from that reported for the previous reporting period and has been on a downward trajectory since 2000. Predation by Lake Trout is probably to blame for the declining biomass of prey fish. Poor recruitment by Cisco (C. artedi) over the last 15 years is exacerbating the declines in prey-fish biomass because Lake Trout must compensate for the loss of Cisco by consuming other, less-abundant prey fish.

Lake Superior↗
USGS2021

Lake trout rehabilitation in Lake Ontario, 2020

Each year we report on the progress toward rehabilitation of the Lake Ontario lake trout (Salvelinus namaycush) population, including the results of stocking, annual assessment surveys, creel surveys, and evidence of natural reproduction observed from standard surveys performed by USGS and NYSDEC. Response to the COVID-19 pandemic limited survey effort such that spring and summer bottom trawl surveys and the creel survey were not completed in 2020, and sites sampled during the fall gillnet survey were limited to those east of Rochester, NY. The catch per unit effort of adult lake trout in gill nets increased each year from 2008-2014, recovering from historic lows recorded during 2005-2007. Adult abundances declined each year from 2015 to 2017; and in 2017 were about 35% below the 2014 peak and 17% below the 1999-2004 mean. Adult abundance increased in 2018 by 51% over the 2017 value and remained nearly stable between 2018 and 2020. The 2020 rate of wounding by sea lamprey (Petromyzon marinus) on lake trout caught in gill nets was 2.27 A1 wounds (fresh wound) per 100 lake trout and was near target (2 wounds per 100 lake trout). Condition values for adult lake trout, indexed in September from the predicted weight for a 700 mm lake trout from annual length-weight regressions and Fulton’s K for age-6 males, were among the highest levels observed for the 1983-2020 time series. Reproductive potential for the adult stock indexed from the CPUE of mature females ≥ 4000 g was again above the target in 2020 continuing a trend observed in nine of the last ten years. The 2020 catch of young wild lake trout marked the 26th observation in the last 27 years, however the low numbers of native adults observed during that time period continues to indicate substantial restoration impediments still exist.

Lake Ontario↗
USGS2021

Preserving soil organic carbon in prairie wetlands of central North America

Wetlands of the Prairie Pothole Region (PPR) in the Great Plains of central North America are numerous, densely distributed, and have highly productive plant and animal communities (Photo 49). When in a natural, unaltered condition, these wetlands store relatively large amounts of organic carbon in their soils (Photo 50). Human alterations, such as extensive drainage and land-use conversion for agriculture (Figure 7), have been linked with the loss of soil organic carbon (SOC) and associated emission of carbon dioxide (CO 2 ), as well as impacts to other ecosystem services provided by these wetlands, such as wildlife and waterfowl habitat, plant biodiversity, flood mitigation, groundwater recharge, nutrient removal and retention, and recreation (Gleason et al., 2011). It has been estimated that more than half of the wetlands of the PPR have been lost due to drainage and other disturbances, with losses approaching 90 percent in some areas (Dahl, 2014; Serran et al., 2018). The goal of this case study was to identify land-management strategies that are consistent with maintaining and increasing SOC stocks of PPR wetlands. Two overarching strategies generally are promoted to preserve and enhance SOC stocks of PPR wetlands: avoided drainage and rewetting or restoration. Avoided drainage involves protecting natural, unaltered wetlands from impacts of human actives with the purpose of retaining wetland functions and services such as carbon storage. Rewetting or restoration involves reestablishing natural hydrology and land use with the purpose of enhancing wetland functions and services that were previously lost due to human activities. Avoided drainage provides immediate and long-lasting benefits, while replenishing SOC through rewetting and restoration requires many decades. Both strategies are associated with higher methane (CH 4 ) emissions but lower CO 2 and nitrous oxide (N 2 O) emissions.

Alberta, Iowa, Manitoba, Minnesota, Montana, North↗
USGS2021

2020 Status of the Lake Ontario lower trophic levels

Significant Findings for Year 2020: Note that due to covid-19 restrictions, offshore sampling was limited in 2020. 1) May – Oct total phosphorus (TP) in 2020 was 10.6 µg/L (offshore) and 7.7 µg/L (nearshore), higher than the long-term (1995-2019) average in the offshore (6.2 µg/L) and close to average in the nearshore (7.8 µg/L); mean TP values for the past decade (2010-2019) were 6.0 µg/L and 7.9 µg/L in the offshore and nearshore, respectively. In 2020, TP concentrations were significantly higher (p=0.03) in the offshore compared to the nearshore. Note that offshore duplicate samples had high relative percent difference (average 54%. 6-117%) making inferences for the offshore in 2020 uncertain. 2) May – Oct epilimnetic chlorophyll-a was similar at nearshore (1.9 µg/L) and offshore (2.1 µg/L) sites. These values were slightly higher than the average for 1995 – 2019 (1.7 µg/L, offshore; 1.5 µg/L, nearshore) and higher than for the last decade (1.4 µg/L, both offshore and nearshore). 3) May – Oct Secchi depth ranged from 3.5 m to 10.4 m (11 ft to 34 ft) at individual sites and was not significantly different between nearshore (6.3 m; 20.7 ft) and offshore (6.5 m; 21.3 ft) locations. Long-term (1995-2019) average was 7.2 m in the offshore and 6.4 m in the nearshore; means for the last decade were 7.8 m in the offshore and 6.2 m in the nearshore. 4) Despite higher TP values in 2020 than in recent years, TP, chlorophyll-a and Secchi depth are indicative of oligotrophic conditions in the offshore of Lake Ontario. 5) Nearshore summer zooplankton biomass was 10.5 µg/L, near the all-time low (9.4 µg/L, 2017) since monitoring began in 1995. Offshore epilimnetic summer zooplankton biomass was 11.7 µg/L. These values are similar to biomass in the last decade (2010-2019). 6) Peak (July) epilimnetic biomass of Cercopagis was 3.0 µg/L in the nearshore and represented 25% of the zooplankton community at that time; Cercopagis was absent from the July offshore epilimnetic samples in 2020 but was present in whole water column samples taken in August by other agencies. Epilimnetic biomass of Bythotrephes peaked in late-September in both the nearshore (1.0 µg/L) and offshore (1.8 µg/L) and represented 10% and 18% of the zooplankton community at those times, respectively. 7) Summer nearshore and offshore epilimnetic zooplankton density and biomass declined significantly 1995 – 2020. The declines were due mainly to reductions in cyclopoid copepods in both habitats.

Lake Ontario↗
USGS2021

Bottom trawl assessment of benthic preyfish community in Lake Ontario

Since 1978, the Lake Ontario benthic preyfish survey has provided information on the status and trends of the benthic preyfish community related to Lake Ontario Fish Community Objectives that include understanding preyfish population dynamics and community diversity. Beginning in 2015, the benthic preyfish survey expanded from US-only to incorporate lake-wide sampling sites which drastically increased the survey’s spatial coverage. In 2020, the collaborative benthic preyfish survey completed 82 bottom trawl tows across main lake and embayment sites at depths from 6 to 226 m. Compared to previous years, the survey was largely confined to ports east of Rochester on the US side, and east of Wesleyville on the Canadian side due to COVID-19 travel constraints. In total, the survey sampled 109,315 fish from 32 species in 2020. Round goby was the most numerically abundant species comprising 59% of total catch, followed by alewife (27%), and deepwater sculpin (7%). Despite being a common species represented in historical catches, slimy sculpin comprised only 0.05% of the total catch, with only 53 fish sampled in 2020. Annual biomass indices were among the lowest reported for slimy sculpin across the entire time series, whereas deepwater sculpin biomass remained high but showed a decrease from values observed in 2019. Deepwater sculpin condition in 2020 was lower than in 2019 but similar to values observed in 2017-2018. Community diversity remained high relative to historically lower values when round goby and deepwater sculpin were not captured in trawl catches. Round goby biomass in 2020 was the highest on the US time series, but not on the lake-wide series, highlighting the need to resume lake-wide sampling to further understand how regional vs lake-wide sampling affects benthic preyfish population estimates.

Lake Ontario↗
USGS2021

Strong evidence for two disjunct populations of Black Scoters Melanitta americana in North America

Black Scoters Melanitta americana were marked with satellite transmitters on Atlantic and Pacific coasts of North America to examine continental-scale population delineation. Scoters marked on the different coasts did not overlap at any stage of the annual cycle, suggesting that birds in the two regions could be monitored and managed as separate populations: 1) an Atlantic population, which winters along the Atlantic coast and Great Lakes and breeds from northeast continental Canada westward to the Northwest Territories, and 2) a Pacific population, which winters along the Pacific coasts of Alaska, British Columbia and the Pacific northwest states, and breeds in western Alaska. Range maps for Black Scoter could reflect these distributions revealed by satellite telemetry. Our data provide new information on the distribution of Black Scoters in North America, which can be used to improve the design of future surveys.

Alaska↗
USGS2021

Lake Ontario April prey fish survey and Alewife assessment, 2021

The Lake Ontario April bottom trawl survey and Alewife, Alosa psuedoharengus population assessment are conducted annually to track prey fish community status and aid management decisions related to predator-prey balance. No survey was conducted in 2020 due to the Covid-19 pandemic. The 2021 survey included 248 bottom trawls in both U.S. and Canadian waters, from March 30 - May 7 in the main lake and embayment regions, at depths ranging from 5 – 221 m (16 - 729 ft). The survey captured 947,102 fish, from 30 species with a total weight of 9,191 kg (20,220 lbs). Alewife were 89.2% of the catch by number while Rainbow Smelt, Osmerus mordax , Round Goby Neogobius melanostomus , and Deepwater Sculpin Myoxocephalus thompsonii comprised 5.6, 2.3, and 1.7% of the catch, respectively. Rainbow Smelt biomass in 2021 was among the highest values observed since 1997, especially in U.S. waters. The biomass index for Cisco, Coregonus artedii also increased, primarily due to catches and greater survey effort in the Bay of Quinte. Threespine stickleback, Gasterosteus aculeatus and Emerald Shiner, Notropis atherinoides biomasses remain low. No Bloater, Coregonus hoyi were captured during the 2021 survey. In 2021, the lake-wide Alewife biomass index increased substantially from 2019 due to the presence of an exceptionally high catch of age-1 Alewife (2020 year class). The biomass index of adult Alewife (age-2 and up) declined slightly since 2019, which was expected since Alewife reproduction was generally below average from 2016 to 2019. Expanding the survey spatial extent from U.S. waters to a lake-wide survey in 2016 has improved our ability to estimate Alewife survival and has provided more accurate estimates of Lake Ontario Alewife biomass and density. Simulation modeling based on recent estimates of survival, growth, and reproduction suggests the adult Alewife biomass will likely increase in 2022 and 2023. As part of a continued effort to improve prey fish surveys, we employed hydroacoustic sampling during the 2021 April trawl survey to estimate fish densities in open-water, pelagic habitats not sampled by the bottom trawl. We found fish density, in waters above the trawl headline depth (3m off bottom to surface), were approximately ~100 times lower than pelagic prey fish densities from bottom trawls. These results support the idea that at this time of year, when the warmest water is on the lake bottom, Alewife and most other prey fish primarily inhabit deep, near bottom regions and can be effectively sampled with bottom trawls. We were not able to apportion acoustics targets to species, however the low mean target strength (-43 decibels, dB) suggested these were small fishes (e.g., 100 mm). The greatest hydroacoustics densities were found near the Niagara River confluence and future surveys may use midwater trawls to determine which species these were and continue to improve this multi-agency survey.

Lake Ontario↗