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ANNUAL STRIPER REPRODUCTION RESULTS

It’s official; the 2019 striped bass YOY indexes are in for Maryland and Virginia, but what does this mean?
By Toby Lapinski  |  October 17, 2019
ANNUAL STRIPER REPRODUCTION RESULTS
Scientists carefully conduct a seine net survey along the Chesapeake Bay during the summer. (Image courtesy of MD DNR)

First off, before I go any further, let me be clear that the annual Young of the Year (YOY) index is not the end all be all of the striped bass population as a whole. A great many factors can go into an exceptionally high or low score from year to year. Further, excessive mortality can wipe out a good year just as easily as a really bad year can be “corrected” by a high survival rate of those juvenile fish.

Each year there are two surveys completed in the Chesapeake Bay, one by the Maryland Division of Natural Recourses (MD DNR) and one by the Virginia Institute of Marine Science (VIMS). Together, these two surveys provide us with an idea of how successful the year’s spawn was in the Chesapeake Bay which is the primary nursery ground for Atlantic striped bass.

What follows are the announcements by the MD DNR and VIMS as well as their YOY indexes for 2019. As you will see, Maryland’s number is down, around one-half the 66-year average of their study, and Virginia is a little bit above its average. This does not mean that we should be running to hills, screaming for a striped bass moratorium, nor does it in any way, shape or form say that things are just fine. It is simply a snapshot of the amount of juvenile fish which have been surveyed in the Bay this year. We have seen both good and bad surveys when the population was up as well as when it is down, so it is only one of many small pieces which collectively come together to form the Atlantic striped bass population as a whole. However, one thing that can’t be done is that you can’t make more baby striped bass once the year’s spawning cycle is complete until the next go-round. In other words, each year you start off with a finite number of fish in a given year-class, and you can only go down from there through natural and man-made mortality.

MARYLAND
The Maryland Department of Natural Resources announced the results of the young-of-year striped bass survey, which tracks reproduction of the species in Chesapeake Bay. The 2019 juvenile striped bass index is 3.4, below the 66-year average of 11.6.

The young-of-year striped bass survey measures the annual spawning success of the state fish, commonly known as rockfish. The index represents the average number of recently hatched striped bass captured in samples taken during the survey.

During this year’s survey, biologists collected more than 51,000 fish of 54 different species, including 445 young-of-year striped bass. While the abundance of some important forage species like silversides, spot, and menhaden increased in Maryland waters, the survey showed that white perch and yellow perch experienced below-average reproduction.

Weather, river flows, and availability of food for newly hatched fish are all important factors in the spawning success of fish such as striped bass. Although the specific cause of this year’s poor spawning has not yet been determined, large variations in annual reproductive success are normal for the Bay’s striped bass population. Typically, several years of average reproduction are interspersed with high and low years. While three of the past five years have produced strong numbers of young-of-year striped bass, the department is recommending continued monitoring and conservation measures.

“The Chesapeake Bay spawning stock is still capable of high reproductive success under the right conditions,” Assistant Secretary for Aquatic Resources Bill Anderson said. “We will continue to work with our partners along the Atlantic coast and implement measures to responsibly manage the Chesapeake Bay striped bass population.”

Beginning in 2018, the department launched initiatives aimed at reducing striped bass mortality during the fishing season. Those measures included new regulations on size limits and mandatory circle hooks, plus an education campaign on safe catch-and-release practices that now includes an advisory system on optimal conditions for fishing.

The department has monitored the reproductive success of striped bass and other fish species in Maryland’s portion of the Chesapeake Bay since 1954, making this one of the oldest fish surveys in the country. Twenty-two survey sites are located in the four major spawning areas: Choptank, Nanticoke, and Potomac rivers and the Upper Chesapeake Bay. Biologists visit each site three times per summer, collecting fish with two sweeps of a 100-foot seine net. After each observation, scientists safely and carefully return the fish to the water.

The index number is the result of averaging the number of recently hatched striped bass caught in each of these samples.

VIRGINIA
Preliminary results from an ongoing long-term survey conducted by researchers at the Virginia Institute of Marine Science suggest an average year class of young-of-year striped bass was produced in Virginia tributaries of the Chesapeake Bay in 2019. The 2019 year class represents the group of fish hatched this spring that will grow to fishable sizes in three to four years.

The program, formally known as the Juvenile Striped Bass Seine Survey, recorded a mean value of 9.54 fish per seine haul in the Virginia portion of the Chesapeake Bay, which is similar to the historic average of 7.77 fish per seine haul. The 2019 value—which scientists call a recruitment index—was also similar to indices observed in the past six years. Although there can be considerable variation in striped bass recruitment among years, the average indices observed in recent years suggests that abundance of juvenile striped bass has been stable.

Striped bass play an important role as a top predator in the Chesapeake Bay ecosystem and are a valuable resource for commercial and recreational anglers. "Professor Mary Fabrizio, who directs the Juvenile Striped Bass Seine Survey at VIMS, notes that the economic and ecological value of striped bass lends significant interest to the year-to-year status of their population. ”By estimating the relative number of young-of-year striped bass," she says, "our survey provides an important measure of annual and long-term trends in the Bay's striped bass population."

The VIMS Juvenile Striped Bass Seine Survey currently samples 18 index stations in the Rappahannock, York, and James River watersheds. Biologists sampled each site 5 times from mid-June to late August in 2019, deploying a 30.5 m-long (100-foot) seine net from the shore. Each fish captured in the net is counted, measured, and returned to the water. These young striped bass usually measure between 40 and 100 mm (1.5-4 inches) long. Survey scientists in Virginia measured 1,624 juvenile striped bass at these stations in 2019. VIMS has been conducting the survey annually since 1967 for the Virginia Marine Resources Commission (VMRC). The Maryland Department of Natural Resources conducts a similar survey in the northern portion of the Bay, and this year documented a below-average index.

The striped bass population in Chesapeake Bay has rebounded from historic lows in the late 1970s and early 1980s, after fishing bans were enacted in Delaware, Maryland, and Virginia in the mid- to late-1980s. Since then, the population increased to the point that striped bass in the Bay and elsewhere were considered recovered. In 2019, scientists determined that the striped bass population was overfished and that mortality due to fishing was higher than what the population can withstand in the long term. Monitoring of juvenile striped bass recruitment will continue next year to provide managers with crucial information to sustainably manage this important species.

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