Rockfish leave Chesapeake Bay at a specific length

A new study on striped bass in the Potomac River is providing new insight into rockfish migration. Researchers at the University of Maryland Center for Environmental Science have discovered that when rockfish reach 32 inches in length they leave Chesapeake Bay and head out to the ocean. 

The study also revealed that the smaller fish which remained in the bay had higher mortality rates compared to the ocean migrators.

“Knowing the size at which they leave, we can do improved management that is tailored better to commercial and recreational fishing sectors those related to catch and size limits,” said study co-author Professor Dave Secor. “It allows us to bring different parts of the fishery into an assessment model to evaluate stock health and test how effective regulations will be.”

The team tagged 100 striped bass, also known as a rockfish, to monitor their movements in and out of the Chesapeake Bay. The larger fish were found to migrate to ocean waters at a length of 32 inches, regardless of their gender.

“By our best estimates they are in the Chesapeake Bay for 9 years, and when they reach 32 inches they head north,” said Professor Secor.

Migrating striped bass spend the summer and fall seasons in Massachusetts, where they contribute to important recreational fisheries. In the late fall, they migrate south and then journey back to the Chesapeake Bay in the springtime to spawn. A few weeks after spawning, the bass return to the ocean. 

The mortality rate of the small resident striped bass that remain in the Chesapeake Bay is 70 percent, which is nearly twice as high as the larger fish that migrate to the ocean. 

The researchers surgically implanted small acoustic transmitters inside of the fish to track their migrations. 

“Biotelemetry has allowed us to move beyond the question of whether Potomac River striped bass leave the Chesapeake Bay, to where do they go when they leave? All arrows point to Massachusetts,” said Professor Secor. “There is a remarkable connection between fisheries in Potomac and Massachusetts Bay and Cape Cod.”

By quantifying the exact size that striped bass reach before leaving the Chesapeake Bay, assessment models can be improved to inform both anglers and fisheries managers. 

“An improved understanding of differential migration allows fisheries managers to specify stock assessments according to different population sub-components, and tailor reference points and control rules between regions and fishing stakeholder groups,” said Professor Secor.

The study is published in the journal PLOS ONE.

—

By Chrissy Sexton, Earth.com Staff