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Fall Water Temps Help Rockfish Choose Habitat

It’s October, and the striped bass—or rockfish—are starting their long trip home! While some rockfish (Morone saxatilis) can be found year-round in the Chesapeake Bay, most leave after spawning in springtime in the Bay’s tributaries for cooler waters up north along the Atlantic coast and join the rest of the “coastal stock” of striped bass. Water temperature plays a large role in helping these fish select their habitat as they move through the year.

As fall arrives, these trophy-sized migratory striped bass are quite large, sometimes over 50 pounds. They head back into the Bay for one last feeding stop before they move to their winter grounds off the coast of Virginia and North Carolina. In many cases, coastal water temperatures trigger this southward migration of mature striped bass, forcing them to leave their “summer in the Hamptons” off New England as waters cool. Coastal communities along the Atlantic coast enjoy productive fishing for striped bass as they head south toward the Chesapeake Bay with the onset of fall temperatures. Once in the Chesapeake, rockfish primarily feed on menhaden with a few other prey items mixed in. Because the mainstem of the Bay is nearly 200 miles long, distributions of both the forage fish and the striped bass are closely linked to the changing conditions in each region. Water temperatures and location of forage fish help rockfish select more precisely where they prefer to be in the Bay.

Striped bass are not the only ones keenly aware of the changes that drive their choice of habitat: Recreational and commercial fishermen on the Bay look forward to the return of migratory rockfish as well. Monitoring parameters tracked by the NOAA Chesapeake Bay Interpretive Buoy System, including water temperature and salinity, can help fishermen track how far up the Bay the migratory rockfish are likely to be found, and where the hot spots may be. As this graph from 2011 at the NOAA CBIBS Gooses Reef buoy shows, water temperatures generally drop significantly in October, encouraging rockfish to move up the Bay.

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In many cases, a warm fall can make for challenging fishing, with rockfish concentrated in the lower portions of the Chesapeake Bay. A cooler fall can mean a banner year for striped bass fishing in the Maryland portion of the middle and sometimes upper Bay. Thousands of fishermen from around the country will be out on the Bay participating in the annual fall run of these trophy-sized striped bass and competing in several rockfish tournaments in October and November. The success for fishermen this fall will largely be determined by how well they match up where they fish with where the migratory fish are. What will 2012 bring? Only time will tell, but real-time conditions as observed by CBIBS can provide tools for a potential sneak preview.

Water temperatures can also affect rockfish in another way: spawning success. In general, warm winters and dry springs—as the Chesapeake experienced in early 2012—don’t encourage a successful spawning season for striped bass returning to the freshwater reaches of Chesapeake Bay tributaries. Recently, the Maryland Department of Natural Resources announced that the 2012 striped bass juvenile index—basically a survey of how many rockfish were spawned this spring—was the lowest on record.

Striped bass reproduction is highly variable; successful years can be followed by below-average years, and vice versa. While scientists will continue to monitor future years’ juvenile index closely, there is no immediate cause for concern.

 

 

 

 
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