Sturgeon spawning

At seven and a half feet long, the fish took up most of the circular 12-foot tank she was slowly circumnavigating, the rows of thorny scales lining her back and her pointed snout giving her the appearance of a dinosaur. She was an Atlantic sturgeon, caught in the Chesapeake Bay at the mouth of the Choptank River in the spring of 2007, and the lab where I worked at the time, the University of Maryland’s Horn Point Laboratory, was buzzing with the news of her arrival.

Atlantic sturgeon, a ‘prehistoric’ species more than 120 million years old that can grow up to 14 feet long, were fished down to a fraction of their former population in the 1800s and 1900s, primarily because of the profits to be made by selling their eggs as caviar. Since 1998 there has been a moratorium on harvesting the fish on the U.S. Atlantic coast, but fish that are caught accidentally in the Chesapeake Bay can be turned in for a reward (pdf); these days, they are generally tagged and released back into the water where they were caught.

The fish that I saw at Horn Point was there because she was a mature female, full of eggs – the lab is involved in sturgeon restoration efforts, and planned to fertilize her eggs and, eventually, release her progeny back into the Chesapeake Bay.

In order for restoration efforts to succeed, it’s necessary for scientists to learn as much as they can about how Atlantic sturgeon spawn and reproduce in the wild – and new research recently published in the journal PLoS ONE suggests that the timing of sturgeon spawning might be more variable than previously thought.

Atlantic sturgeon are anadromous, like salmon – they are born in freshwater, migrate to estuaries or the ocean to grow, then return to the streams where they were born to spawn. (Unlike some species of salmon, sturgeon typically make several spawning trips during their lifetime.) Previous research documented Atlantic sturgeon returning to freshwater in the spring and summer.

A team of scientists monitored Atlantic sturgeon in the James River, which empties into the Chesapeake Bay, during the spring and fall between 2008 and 2014. They documented four adult sturgeon during the spring, and 369 adults during the fall sampling trips.

The scientists implanted tags into some of the fish, which allowed them to follow their movements throughout the river. They identified two predominant patterns: the one fish that they were able to tag in the spring swam upstream – presumably to the spawning grounds – in May, then quickly left the river. The fish tagged in the fall typically swam into the lower river in June for an ‘extended staging period,’ then swam upstream in September and October, apparently to spawn, suggesting that the Atlantic sturgeon in the James River have two spawning runs, one in the spring and one in the fall.

The scientists note that further study of the timing and location of the two spawning groups “is required to develop informed sampling and tagging protocols to better estimate population size,” a number that sturgeon researchers and managers are very interested in getting right. The discovery of a previously overlooked fall spawning run is also important for fish conservation; “i.e., dredging moratoria in the spring alone cannot be effective when most of the population is in the spawning reaches in the late summer and fall.”

The Atlantic sturgeon I saw at Horn Point in 2007 was part of a much larger conservation and restoration effort, one that continuing research on the timing of sturgeon spawning can’t help but improve.

As a species, Atlantic sturgeon were swimming under the waves when dinosaurs walked the Earth, more than 120 million years ago. 

(Image by Mauro Orlando via Flickr/Creative Commons license)