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Eyes on the Bay|
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Eyes on the Bay |
DNR Uses Continuous Monitoring Water Quality Data to Determine Extension of Susquehanna Flats Catch-and-Release Rockfish Season
Each spring, seventy-five percent of all Atlantic rockfish journey to the Chesapeake Bay to their natal spawning grounds. Many reach the northernmost Bay into which the Susquehanna River empties and collectively known as the Susquehanna Flats. Every year since 1990, when a region-wide moratorium on angling for rockfish was lifted, fishermen from across the country and even other parts of the world have set their sites on the Susquehanna Flats as a destination fishery.
This year, the Susquehanna Flats rockfish fishery was catch-and-release between April 21 and May 3. In the salty waters of the lower Chesapeake Bay and Atlantic Ocean, released fish survive well. However, in the nearly fresh water of the Susquehanna Flats, released fish suffer higher mortalities, especially when water temperature is above 65 degrees Fahrenheit (F). During the spring rockfish season, water temperatures rarely reach this threshold. In fact, if temperatures remain below 65 degrees F, the season could be extended. Gaining a clear picture of exactly when the temperature threshold has been exceeded has proven problematic. During past years, managers used measurements taken by Natural Resources Police officers and readings reported by guides and charter captains to monitor temperatures. With so many individual temperature readings collected, discrepancies and disagreements arose. In order to avoid either closing the season unnecessarily early or leaving it open when temperatures would be detrimental to the survival of released fish, a more accurate and timely record of water temperature was needed.
To solve this problem, the Maryland Department of Natural Resources Fisheries Unit (DNR Fisheries), responsible for managing the Chesapeake Bay rockfish fishery, partnered with the DNR Resource Assessment Service (DNR RAS), which is responsible for monitoring water quality in the Bay. For the past five years, DNR RAS has deployed continuous water quality monitors throughout the Chesapeake Bay and its tributaries. These monitors collect water quality data, including dissolved oxygen, salinity, pH, turbidity, chlorophyll, and water temperature, every 15 minutes during most of the year. The data, which in some cases are telemetered for real-time posting on the Internet, are used to assess the local and overall health of the Bay. This year saw the deployment of a near real-time monitor at Havre de Grace, at the mouth of the Susquehanna River (Figure 1) . Now, DNR Fisheries managers have a way to determine when water temperature exceeded the 65-degree threshold on the temporal scale they needed to make decisions about the duration of the fishery.
Figure1. The Susquehanna Flats continuous monitor, deployed on a pier in Havre de Grace.
Using near real-time water temperature data from Havre de Grace, DNR Fisheries managers announced the extension of the rockfish season for an additional week, closing May 10. During the weeks leading up to the original closing date (May 3), water temperatures rose slightly to approximately 54 degrees F according to the continuous monitor. A water quality mapping cruise on April 24, where an instrument similar to the continuous monitor was deployed on a boat traveling throughout the Susquehanna Flats, corroborated these readings over a broad area.
Figure 2. Temperature plot showing revised closing date.
The continuous monitor then showed that water temperature was hovering around 61 degrees F on May 3, well enough below the threshold to protect released rockfish (Figure 2) the following week progressed, water temperature rose steadily, finally hitting sustained temperatures of between 65 and 66 degrees F on May 10. Many anglers and guides reported that the continuous monitor water temperature records corresponded well with their own.
Undoubtedly, the additional week of fishing resulted in unexpected economic gain for area charters, outfitters, restaurants, hotels, and other related industries. Maryland DNR was also able to save money and manpower that normally would have gone to hand sampling water temperature throughout the area by Natural Resource Police officers. But perhaps most importantly, recreational anglers were able to safely enjoy an extra week of spring rockfish season on the Susquehanna Flats.
For more information of DNR continuous monitoring and water quality mapping , please visit:
For more information on DNR Fisheries rockfish management, please visit:
Maryland Department of Natural Resources Fish Facts - Striped bass.
Water quality data, Maryland DNR website: www.eyesonthebay.net .