Lake Erie’s hatch numbers below average in 2012

1/8/2013

Lake Erie is a big, wet place. By surface area, it is the 11th largest lake on the planet, stretching some 241 miles by 57 miles.

With an average depth of around 60 feet and a maximum depth of 210 feet, Erie is a puddle by Great Lakes standards, but it still contains 116 cubic miles of water. That’s not a phrase we throw around too often — “cubic miles of water.”

In that often murky world under the surface of Lake Erie is a lot of fish. Conducting a census of those residents is a fundamentally difficult task, flush with challenges.

“Counting fish is just like counting trees — except that they are invisible and keep moving,” John Sheperd of the University of South Hampton in the United Kingdom once said.

If hyperbole was his intent, he probably missed the mark. Fish roll calls are that tough, but we still do them, utilizing the best tools available and a meticulous approach.

The biologists charged with monitoring Lake Erie’s fish population were out on the water late in the summer, doing their annual head count of young-of-the-year walleye and perch.

This study of the “hatch” takes place in August because surveys done earlier in the year tend to miss the spring-hatched fish due to their tiny size. By the end of the summer, these fish have grown to the point that they can be captured in the mesh trawl nets used by the fisheries folks.

Fish from the spring hatch that have lived to this point have demonstrated an ability to thrive and are much more likely to survive changes in water temperature and the availability of food. The data from August netting surveys in the Western Basin of Lake Erie give biologists the best information to use to estimate the success of the hatch, and project future populations of Erie’s most-coveted gamefish.

The 2012 August trawl showed the walleye hatch in Ohio’s portion of the western end of the lake was below average, with about two young-of-the-year fish per hectare. A hectare is roughly equal to 2.5 acres.

On average, about nine walleye from the hatch are netted per hectare. The lower 2012 numbers are similar to those from 2011, 2009, and 2008. The 2008 and 2009 walleye hatches contributed an estimated 3 million to 4 million fish to the Lake Erie population by the time those fish reached 2 years of age. An average hatch would contribute about 10 million of these fish by age 2.

“The 2012 hatch was below average, but it was not a bust,” said Jeff Tyson, fisheries Biologist Supervisor for the Division of Wildlife’s Lake Erie Fisheries Research Unit in Sandusky.

“Obviously, the strength of our fishery is not determined by a single hatch. There are still a lot of fish from that strong 2003 class out there, so there is a relatively high probability of catching trophy size walleye. And there’s also a broad distribution of fish size.”

The August survey in the Ohio waters of the Western Basin netted about 23 young-of-the-year yellow perch per hectare, about a third of the average of 70 per hectare. Tyson said the perch hatch appears to be similar to those from the 2006 and 2009 classes, which added about 8 million to 9 million fish to the population by the time they reached 2 years of age.

The 2012 yellow perch hatch will not impact the formula for allocating total harvest numbers until 2014, but the most recent trend has been down, with the 2010 and 2011 hatches worse than 2012’s.

The survey trawl is conducted from a large research vessel with a captain and crew of four biologists. A 30-foot wide by 7-foot tall funnel-like net is pulled through the water near the lake floor for about 10 minutes. The catch is then pulled up by a hydraulic lift, and the fish are emptied into sorting trays and catalogued by species and age group.

“We will see anywhere from a few hundred to several thousand fish in each haul,” Tyson said, adding that trawls are conducted from 40 different Western Basin locations by the Ohio crew, with Ontario biologists sampling a similar number of sites on the Canadian side of the lake’s western end.

“The most abundant fish in our surveys are white perch,” Tyson said about the non-native species that was originally found in the brackish waters along the Atlantic coast. They have been found in Lake Erie dating back nearly 60 years, and are believed to have entered the lake through the Erie Canal or the Welland Canal.

While the walleye and yellow perch hatches appear to be under the long-term average, the August trawls revealed a population of emerald shiners — a forage fish important in the diet of yellow perch and walleye — that is approaching a record high.

Tyson said that in the coming months, survey numbers from all the Ohio sections of the lake will be joined with those from Ontario, Michigan, Pennsylvania, and New York, and an estimate on the total populations of walleye and yellow perch in Lake Erie will be reached. A harvest target, or Total Allowable Catch (TAC), will be determined, and each state or province will set its bag limits based on its portion of the TAC.

The TAC is announced in March by the Lake Erie Committee. Any changes in Ohio’s bag limits would then become effective on May 1.

Contact Blade outdoors editor Matt Markey at: mmarkey@theblade.com or 419-724-6068.