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Status of Lake Ontario Alewife and 2019 NYSDEC Stocking Plans

Background:

  • Lake Ontario supports a world class fishery for trout and salmon and in years of good growth produces the largest Chinook salmon in the Great Lakes, with some individuals exceeding 40 pounds.
  • The primary prey fish in Lake Ontario is the alewife, a type of herring native to the Atlantic Ocean that invaded the Great Lakes over 100 years ago.
  • Lake Ontario Chinook salmon feed almost exclusively on alewife, requiring large numbers of alewife to support a voracious appetite that allows a salmon to grow to over 30 pounds in four years.
  • In 2016, Lake Ontario fisheries management agencies were concerned about declining numbers of adult alewife in future years due to consecutive, poor alewife reproduction in 2013 and 2014. These poor year classes will continue to affect the overall stability of Lake Ontario's alewife population for several more years.
  • In 2016, the Lake Ontario Committee (New York State Department of Environmental Conservation [DEC] and the Ontario Ministry of Natural Resources and Forestry [OMNRF]) announced that stocking levels for Chinook salmon and lake trout would be adjusted down 20% in 2017 to reduce predator demand on adult alewife in order to protect the valuable fishery.
  • Chinook salmon and lake trout stocking targets remained at the 20% reduced level for 2018.

The 2018 Alewife Bottom Trawl Survey

  • The Lake Ontario alewife population is assessed by the U.S. Geological Survey (USGS), DEC, and OMNRF using a collaborative survey design that provides a whole lake estimate of alewife abundance.
  • The alewife population is assessed with bottom trawls in early spring, largely before alewife leave their over-wintering habitat (near bottom in deep water).
  • Alewife were not distributed evenly around the lake in spring 2018, with more alewife in Ontario than in NY waters (Figures 1 & 2; larger circles=larger catches).
  • Growth and condition of alewife declined across all age classes, meaning less energy transferred to predators for every alewife eaten.
  • The relative numbers of alewife at a given size and age (color) in 2018 are presented in Figure 3. Please note that each color represents the same "year class" in all three graphs. A year class is those fish produced in a given year, and they will always belong to that year class. For example: the 2015 year class is yellow when measured at age 1 in the top graph of Figure 3, and remains yellow as age 2 fish in 2017 (middle graph) and as age 3 fish in 2018 (bottom graph).
  • A large number of alewife were produced in 2016 and first measured as age 1 fish in 2017 (2016 year class; green bars in middle graph of Figure 3). This was great news and a good start towards population recovery. Their abundance at age 2 in 2018 (green bars in bottom graph), however, indicates a marked decline in their numbers, likely due to heavy predation.
  • A below average year class was produced in 2017 (age 1 fish in 2018; dark blue bars in bottom graph in Figure 3). Their numbers will likely decline markedly by spring 2019.
  • In 2018, "larger" size alewife that support both alewife spawning and food for large Chinook salmon are primarily composed of age-2 (2016 year class, green bars), age 3 (2015 year class, yellow bars), and age 6 fish (2012 year class, black bars). Alewife numbers in these year classes will decline markedly by spring 2019.
  • As expected, catches of age 4 (2014 year class; red bars) and age 5 (2013 year class; light-blue bars) alewife were poor. The extremely long, cold winters of 2013/2014 and 2014/2015 contributed to the poor 2013 and 2014 year classes, and these poor year classes will continue to affect the overall stability of Lake Ontario's alewife population for several more years.
  • The adult alewife population in 2019 will be composed primarily of alewife ages 2, 3, and 4, and will likely experience additional stress over the next several years. The Lake Ontario Committee (LOC) remains committed to maintaining a high-quality Chinook salmon fishery. While there is hope that a relatively strong 2018 alewife year class will be detected in 2019, concerns regarding instability in the adult alewife population have increased.

New York State Department of Environmental Conservation 2019 Stocking Plans

  • In response to intensified concerns regarding Lake Ontario's alewife population, DEC must take additional action to protect the long-term sustainability of the trout and salmon fishery.
  • Failure to act will serve to extend the severity and duration of adult alewife population instability, with greater potential impacts to the sportfishery. When the adult alewife population is comprised of a broader number of age classes we will consider adjusting stocking back to normal levels.
  • DEC will further reduce Chinook salmon stocking by an additional 20% in 2019. On average, approximately 50% of Lake Ontario's Chinook salmon originate from natural reproduction ("wild" fish).
  • Approximately 50% of Chinook salmon will be raised by sportsmen in nets pens, which increases fish survival on average by 2 times.
  • Lake trout stocking in 2019 will remain at the 20% reduced level. Due to hatchery production issues, lake trout stocking was 23% below target in 2016, and 50% below target in 2017. Also, unlike Chinook salmon that are to be stocked in 2019 and are not yet in the hatchery, lake trout planned for stocking in 2019 are already in the hatchery and six months old.
  • Combined salmon and trout stocking by DEC in Lake Ontario in 2019 will still exceed 2.7 million fish (Table 1). Given favorable wind and water temperature patterns, excellent fishing should continue in 2019.
Table 1. Anticipated NYSDEC 2019 stocking targets for Lake Ontario.
Species Life Stage NYSDEC Stocking Policy
2019
Chinook Salmon* Spring Yearlings 1,056,960
Lake Trout Yearling equivalents 400,000
Rainbow Trout Spring Yearlings 615,700
Brown Trout Spring Yearlings 400,000
Atlantic Salmon Spring Yearlings 50,000
Coho Salmon Fall Fingerlings 155,000
Spring Yearlings 90,000
2,767,660

* Many Chinook salmon will be raised by sportsmen in "net pens," which increases their survival by approximately 2X.

Map showing adult (Age 2+ and older) alwewife bottom trawling sites.
Figure 1. Maps showing adult (Age 2+ = 2 and older) Alewife bottom trawling sites and catch level for 2016, 2017 and 2018.
Larger circles represent larger catches of Alewife; "X" = no Alewife caught at that trawl site. Image credit: Dr. Brian Weidel, USGS,
Oswego, NY.
Map showing Age 1 alewife bottom trawling sites.
Figure 2. Maps showing Age 1 Alewife bottom trawling sites and catch level for 2016, 2017 and 2018.
Larger circles represent larger catches of Alewife; "X" = no Alewife caught at that trawl site. Image credit: Dr. Brian Weidel, USGS,
Oswego.
Lake-wide age structure of Alewife for 2016, 2017 and 2018
Figure 3. Lake-wide age structure of Alewife for 2016, 2017 and 2018. Higher bar height = more fish of that size. The color representing an alewife year class remains the same in successive years. For example the 2015 year class is yellow in 2016 when they were age 1 (top graph), and remains yellow as age 2 in 2017 (middle graph) and age 3 in 2018 (bottom graph). Image credit: Dr. Brian Weidel, USGS, Oswego, NY

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