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October 22, 2008

2008 Maryland Young-Of-Year Striped Bass Survey shows below average reproduction

DNR biologists have monitored the reproductive success of striped bass and other species in Maryland's portion of the Chesapeake Bay annually since 1954

The Maryland Department of Natural Resources Fisheries Service recently finalized the 2008 striped bass (rockfish) juvenile index, a measure of striped bass spawning success in Chesapeake Bay. The 2008 index is 3.2, below the long-term average of 11.7. During the survey DNR biologists collected 422 young-of-year (YOY) striped bass.

"Healthy striped bass populations are known for such highly variable spawning success," said Eric Durell, DNR Fisheries Biologist. "This is just the third time in the past decade that striped bass reproduction in Maryland's Chesapeake Bay has been below average."

Two of the most successful spawning years ever documented (2001 and 2003) also occurred during this period. Typically, several years of average reproduction are interspersed with occasional large and small year-classes.

Poor reproduction was also observed for other spring-spawning species such as white perch and American shad, leading biologists to suspect that large-scale environmental factors may be responsible. Heavy rains in early May resulted in decreased water temperatures on major striped bass spawning grounds.

"This spring water temperatures fell below levels known to be lethally cold to striped bass eggs and larvae," explained Durell. "Survival of these sensitive life stages is a major determinant of spawning success."

DNR biologists have monitored the reproductive success of striped bass and other species in Maryland's portion of the Chesapeake Bay annually since 1954. Twenty-two sites were surveyed in the four major spawning systems: Choptank, Potomac, and Nanticoke Rivers, and the Upper Chesapeake Bay. Biologists visit each site monthly from July through September, collecting fish samples with two sweeps of a 100-foot beach seine. The index is calculated as the average catch of YOY fish per sample.

For more information visit www.dnr.maryland.gov/fisheries/juvindex/index.html.