How many fish are in the sea? For obvious reasons, it’s difficult to estimate fish populations. But Patrick Lynch and Mark Henderson are trying to figure it out.
This fall, Virginia Sea Grant awarded Population Dynamics Fellowships to Lynch and Henderson, both graduate students at Virginia Institute of Marine Science (VIMS). The fellowship, co-funded by National Marine Fisheries Service and Sea Grant, provides financial assistance and career-building opportunities for Ph.D. students studying better ways to estimate fish populations by improving our understanding of the effects of fishing mortality, growth, recruitment, and natural mortality. This understanding is a key to maintaining productive fisheries, and this year’s Population Dynamics Fellows believe their research will help to close gaps of uncertainty and enable better management of Virginia’s fisheries.
Populations of Large Atlantic Fishes
Current models estimate fish populations based on reported catch. However, for bycatch species such as blue and white marlins, whose catches have been poorly reported, these data may not reliably predict populationtrends. By basing models on environmental and habitat data, Patrick Lynch believes some of these uncertainties might be overcome. To do this, Lynch will analyze data obtained from satellite tags and fishermen about the areas and habitats where blue and white marlins occur.
“The most exciting thing for me is the ability to use catch information to determine the status of a population and to see the results used in managing stocks,” Lynch says.
Lynch is conducting his research under Dr. Robert Latour (VIMS Dept. of Fisheries Science) and Dr. Kyle Shertzer (National Marine Fisheries Service). Lynch joined the VIMS Dept. of Fisheries in 2005 as a masters student, focusing on the feeding ecology of Atlantic menhaden. He holds a bachelors in bioengineering from Syracuse University (New York).
Distinguishing Populations of Summer Flounder
The U.S. Atlantic coast summer flounder population doesn’t seem to be rebuilding very quickly, given measures taken to protect the fish in the 1990s and 2000s. Mark Henderson suspects that this could be because there is more than one stock of summer flounder in the Chesapeake Bay.
Uncertainty about the number of stocks could hinder rebuilding efforts, because different stocks, even of the same species, can have different rates of maturity and mortality. Henderson believes his study may uncover two distinct stocks of flounder that migrate along different routes and spend different amounts of the life cycle in the Chesapeake Bay.
Henderson will use three different types of tags to track flounder mortality and movement in the Bay.
“Mortality rates are notoriously difficult to estimate,” says Henderson, but his study could help to resolve some of this uncertainty.
Henderson is conducting his research under Dr. Mary Fabrizio (VIMS Dept. of Fisheries Science) and Dr. Steven Cadrin (National Oceanic and Atmospheric Administration). Henderson holds a masters in aquatic and fishery science from the University of Washington and a bachelors in biology from the State University of New York at Geneseo.