Decades ago, yellow perch spawned successfully in upper portions of the Severn, including the fresh waters of Severn Run — so much so that the state of Maryland once boasted a very popular hatchery there.
But since the 1980’s, yellow perch spawn rates in the Severn River (and other urban freshwater rivers, streams and creeks) have been declining precipitously.
Margaret McGinty, an official with the Maryland Department of Natural Resources, offered answers and explanations last month during the John Wright Speaker Series.
Causes: Stormwater runoff (silt, sediment, nutrients) from development, an increase in the river’s temperature and salinity, as well as reductions in oxygen levels and loss of habitat have all factored in the decline of the perch’s mature offspring.
And while no remedies are yet at hand, they are being sought. New research is hoping to pinpoint exactly why and when in the yellow perch’s reproductive cycle the failures occur.
McGinty explained that for the last 20-30 years, in an effort to promote sound management of the yellow perch fishery, the state has been studying how land use is affecting their stock, habitat and procreation.
In response to plummeting catch numbers, they closed a number of rivers to perch fishing in 1989 and then reopened them in 2009 after fisherman reported increased catch rates. They hoped a recovery had occurred. It hadn’t, at least not in larval perch survival rates.
New studies undertaken by state agencies showed that salinity levels were exceeding ideal spawning levels from 66-100% of the time, eggs were being smothered from sedimentation, and dissolved oxygen levels were too low to support larval survival.
But even when eggs were taken from adult Severn River perch to hatch elsewhere, the eggs were in poor shape, McGinty pointed out.
She said that they’re hatching no more than 20% of the time. Acid rain studies done back in the 1980s showed contaminants as a factor in larval survival, as well, and in 1995, the Severn River Commission corroborated that habitat-related effects were severely limiting larval survival rates.
Eventually, scientists began focusing on the possibility of some type of endocrine disruptor affecting reproduction, prompting a 2009-2011 joint USGS, FWS and DNR study that looked specifically at reproductive health in several historically important yellow perch spawning areas, the Severn among them.
That study observed a number of biological effects related to yellow perch reproductive health, including that the eggs weren’t developing normally.
Alex MacLeod, a PhD student at the University of Maryland and fellow presenter with McGinty, is using those results to focus his three-year dissertation study (2017-2019) on yellow perch reproductive health in the Severn, Choptank and Mattawoman Rivers.
Specifically, MacLeod is looking at the fish’s genetics, hormones and histopathology to ascertain healthy reproductive patterns.
His task: “To determine at what reproductive stage and in what manner yellow perch populations from developed watersheds (impacted) deviate from normal reproductive development.”
If it isn’t likely that yellow perch spawning will return to historic levels, McGinty, MacLeod and others hope that by understanding precisely why yellow perch are failing to reproduce in adequate numbers, that appropriate steps can be taken to target restoration and management of critical spawning habitats, allowing the yellow perch to once again thrive in the Severn and other Bay tributaries.
– by Lucie Lehmann
Photos: Lucie Lehmann