White perch, striped bass, blue catfish, and gizzard shad capture. (Photo: Leonard Machut/VIMS)
Striped bass juvenile index falls below average
Thursday, October 18, 2012, 22:40 (GMT + 9)
The Maryland Department of Natural Resources (DNR) announced that the 2012 striped bass juvenile index – a measure of striped bass spawning success in Chesapeake Bay – is below the long-term average this year.
“While we expect large variation in striped bass reproduction from year to year and do not view this low value as an imminent problem, we will be carefully monitoring the results of future surveys,” said DNR Fisheries Director Tom O’Connell. “Three consecutive years of poor reproduction would be necessary to trigger mandatory conservation measures.”
This year’s striped bass juvenile index came in at 0.9, the lowest on record. Last year’s survey showed the fourth highest result in the 59-year history of the survey. The long-term average is 12.
Striped bass spawning success can vary dramatically from year to year. Typically, several years of average reproduction are mixed with large and small year-classes.
Environmental conditions such as flow rates and water temperature influence spawning success. The highly successful years of 1989, 1996, and 2001 were followed by below-average years.
Other anadromous species (fish that return to fresh water to spawn), such as white perch, yellow perch, and river herring, also experienced low reproductive success this year, likely due to weather conditions. Similarly, a survey conducted by the Virginia Institute of Marine Science (VIMS) documented poor striped bass spawning success in Virginia’s portion of Chesapeake Bay.
“Generally, warm winters and dry springs are unfavourable conditions for fish that return to freshwater to spawn,” said DNR Striped Bass Survey Director Eric Durell. The survey showed increased reproduction of fish species that spawn in higher salinities or offshore, such as Atlantic croaker and bay anchovies.
During this year’s survey, biologists counted more than 31,000 fish of 54 different species at 22 sites in the four major spawning systems—Choptank, Potomac and Nanticoke rivers, and the Upper Bay. DNR biologists visited each site monthly from July through September, collecting fish samples with two sweeps of a 100-ft beach seine. Juvenile indices are calculated as the average catch of young-of-year fish per sample.