11-08-2012, 12:10 PM
August is an important month on Lake Erie for the Division of Wildlife. In August, a trawl survey is used to anticipate the future population size of Lake Erie fish, especially walleye and yellow perch. Why not use the trawl data from previous months? While adult fish are easily caught in May, June, and July trawls, catches of spring-hatched fish during these months aren't reliable. By August, these "age-0" fish have grown large enough to be captured in the trawl; they are too big to slip through the mesh of the net. In addition, August trawl data is more reliable for forecasting fish populations. By then, fish hatched earlier in the year have run the survival gauntlet and are less susceptible to changes in weather, water temperature, and food availability. This reliability allows biologists to use August trawl data from adult, yearling, and age-0 fish to project future population sizes and make meaningful comparisons to previous years.
2012 marks the 43rd year of the western basin survey and 22nd year of the central basin survey. The western basin is surveyed at 41 sites between the Michigan border and Huron, Ohio, while the central basin survey consists of 57 sites from Huron to the Pennsylvania border. One 10-minute tow of the trawl is made along the bottom at each site, and the area sampled and the numbers of fish captured are recorded from each tow. The same trawls and sites are used each year to allow comparisons from one year to the next. Following the survey, results are standardized to the number of fish captured "per hectare" (1 hectare equals about 2 ½ acres).
2012 Survey Highlights
In the western basin, the 2012 survey resulted in more age-0 walleye and age-0 yellow perch than in the 2011, but the numbers both species were well below the long-term average for the survey (see Figure 1 below). Abundances of yearling and adult yellow perch were both below average as well. Also noteworthy, age-0 emerald shiners, age-1 and older emerald shiners, age-0 and age-1 white perch abundances were at or near all-time highs.
In the central basin, the survey is split into two halves; a west-central survey conducted from Huron to Fairport Harbor, and an east-central basin survey conducted from Fairport Harbor to the Pennsylvania border. Few age-0 walleye are collected in central basin surveys as most walleye spawning takes place in the shallower, warmer waters of the western basin. However, yellow perch data from the central basin surveys are important for managing this species. In 2012, age-0 and yearling yellow perch numbers were below average in both halves of the central basin, but catches of adult yellow perch were average in the west-central and well above average in the east-central (Figure 2). Also of note, catches of age-0 white bass, age-0 white perch, and age-0 emerald shiners were high in 2012, similar to the western basin.
So what happens next?
During the months ahead, results from Ohio surveys will be combined with surveys conducted in Ontario, Michigan, Pennsylvania, and New York to estimate population sizes and determine how many walleye and yellow perch can safely be harvested from Lake Erie. This harvestable portion is called the Total Allowable Catch (TAC), and when the TAC is finalized, each state and province is issued their 'slice of the pie'. In Ohio, the daily bag limits are set for walleye and yellow perch based on our portion of the TAC. The TAC is announced every March at the Lake Erie Committee meeting, which is why Ohio bag limit changes on Lake Erie don't become effective until May 1st each year.
We are still learning what makes a strong or a weak walleye or yellow perch hatch. But our August trawl survey allows us to track differences in hatches from year to year, anticipate population sizes in the future, and gain invaluable information for managing Ohio's largest fisheries.
2012 marks the 43rd year of the western basin survey and 22nd year of the central basin survey. The western basin is surveyed at 41 sites between the Michigan border and Huron, Ohio, while the central basin survey consists of 57 sites from Huron to the Pennsylvania border. One 10-minute tow of the trawl is made along the bottom at each site, and the area sampled and the numbers of fish captured are recorded from each tow. The same trawls and sites are used each year to allow comparisons from one year to the next. Following the survey, results are standardized to the number of fish captured "per hectare" (1 hectare equals about 2 ½ acres).
2012 Survey Highlights
In the western basin, the 2012 survey resulted in more age-0 walleye and age-0 yellow perch than in the 2011, but the numbers both species were well below the long-term average for the survey (see Figure 1 below). Abundances of yearling and adult yellow perch were both below average as well. Also noteworthy, age-0 emerald shiners, age-1 and older emerald shiners, age-0 and age-1 white perch abundances were at or near all-time highs.
In the central basin, the survey is split into two halves; a west-central survey conducted from Huron to Fairport Harbor, and an east-central basin survey conducted from Fairport Harbor to the Pennsylvania border. Few age-0 walleye are collected in central basin surveys as most walleye spawning takes place in the shallower, warmer waters of the western basin. However, yellow perch data from the central basin surveys are important for managing this species. In 2012, age-0 and yearling yellow perch numbers were below average in both halves of the central basin, but catches of adult yellow perch were average in the west-central and well above average in the east-central (Figure 2). Also of note, catches of age-0 white bass, age-0 white perch, and age-0 emerald shiners were high in 2012, similar to the western basin.
So what happens next?
During the months ahead, results from Ohio surveys will be combined with surveys conducted in Ontario, Michigan, Pennsylvania, and New York to estimate population sizes and determine how many walleye and yellow perch can safely be harvested from Lake Erie. This harvestable portion is called the Total Allowable Catch (TAC), and when the TAC is finalized, each state and province is issued their 'slice of the pie'. In Ohio, the daily bag limits are set for walleye and yellow perch based on our portion of the TAC. The TAC is announced every March at the Lake Erie Committee meeting, which is why Ohio bag limit changes on Lake Erie don't become effective until May 1st each year.
We are still learning what makes a strong or a weak walleye or yellow perch hatch. But our August trawl survey allows us to track differences in hatches from year to year, anticipate population sizes in the future, and gain invaluable information for managing Ohio's largest fisheries.