Distribution and Relative Abundance of Spawning American Shad (Alosa sapidissima) in the St. Johns River, Florida
The American shad (Alosa sapidissima) is a member of the herring family. American shad ascend rivers from the ocean in order to spawn. Juveniles spend their first growing season in the river of their birth and then swim to the ocean in the fall to grow and mature. They remain in the ocean for two to six years before they mature and return to spawn in the river in which they originally hatched.
American shad range along the Atlantic coast, from Florida to Canada. The St. Johns River harbors the southern-most spawning population. Shad that spawn in rivers south of Cape Hatteras, North Carolina die after spawning. However, those spawning in rivers north of Cape Hatteras often survive to spawn in subsequent years. Populations from all rivers mix in the ocean and migrate between the coastal Atlantic and adjacent bays of Canada in the summer and the Atlantic off the southeast coast of the U.S. in the winter. As the offshore stock reaches the southern end of its migration, it enters the St. Johns River beginning in December. Spawning activity peaks in February and March in the St. Johns River between Deland and Cocoa.
Historically, shad had been an important food source in North America since the colonial era. Shad have been important to recreational anglers in the modern era; however, recreational angling peaked in the St. Johns River during the 1950s and 1960s. Atlantic coast commercial landings peaked at the turn of the twentieth century but have declined dramatically along with most of the shad's range. Obstruction of spawning runs, pollution, and high harvest rates have all taken a toll on abundance, prompting the Atlantic States Marine Fisheries Commission (ASMFC) to mandate protective measures that include a directive to monitor existing populations and rebuild stocks where necessary.
Commercial landings in the St. Johns River also peaked in the early 1900s and declined significantly throughout the century. Recreational effort and landings have also decreased markedly in recent years. The net ban in 1995 eliminated most of what remained of Florida's commercial American shad fishery. Later in 2005, a commercial fishery off the coast of the mid-Atlantic states was terminated, so directed fisheries, other than a small in-river recreational fishery, should no longer be impacting the stock.
There is hope that as commercial harvest is eliminated, the stock will rebuild and this will be reflected in improved recreational catch rates and renewed recreational interest in the species. So far, the resurgence in the recreational fishery has not been observed. Angler catch rates have fluctuated annually with no apparent trend, and the number of recreational anglers continues to decline as of the last angler survey in 2005. Are there too few fish making the run to interest anglers? Will increased angling be detrimental to the recovery of American shad on the St. Johns River? This study should provide information to help answer these questions.
Since 2002, researchers have sampled American shad at three sites on the St. Johns River to monitor the abundance and distribution of spawning individuals. Scientists from the DeLeon Springs Freshwater Fisheries Field Lab collect adult shad by electrofishing every other week from January to May of each year. Shad are counted, sexed (or have the sex of the fish recorded), measured, and released. Samples are collected between Lake Monroe and Iron Bend including an area known as "Shad Alley." This area is generally considered the heart of the shad spawning grounds, and most of the recreational fishing effort for this species has historically occurred there.
Two additional sites upstream of "Shad Alley" in the vicinity of Puzzle Lake and State Road 50 are also sampled. No trend in average electrofishing catch rate has been observed over the six years of monitoring. Low water conditions of 2006 and 2007 reduced available spawning habitat to small sections of the river upstream of Lake Harney. Dense concentrations of spawning shad were found in these locations, but the overall survey catch rates did not increase because shad were scarcer in other locations than in years with higher flows. These findings indicate that the population has remained unchanged, neither increasing nor declining. Without substantial fishing pressure, there may be other factors hindering the population from rebounding as expected. An annual survey of abundance of juvenile American shad was initiated in 2006 to monitor the success of spawning from year to year and determine whether poor recruitment is slowing the recovery of the stock.