Characterizing Winter Flounder (Pseudopleuronectes americanus) Nursery Areas Using Otolith Microstructure and Microchemical Techniques
|Elizabeth Fairchild||UNH - Department of Biological Sciences||Principal Investigator|
|Linda Kalnejais||UNH - Department of Earth Sciences||Collaborator|
|Scott Elzey||Massachusetts Division of Marine Fisheries||Collaborator|
|Vincent Manfredi||Massachusetts Division of Marine Fisheries||Collaborator|
|Jason MacNamee||Rhode Island Dept. of Environmental Management||Collaborator|
|Stephen Dwyer||Millstone Power Station||Collaborator|
|Dr. Chris Chambers||National Oceanic and Atmospheric Administration||Collaborator|
Favorable winter flounder nursery habitats identified using fish growth and condition indices
Winter flounder populations on the eastern seaboard of the U.S. have reached historically low levels, despite increasing fishing regulations intended to preserve the species. Little is known about the quality of nursery habitats for winter flounder and how variations in quality affect recruitment into the adult populations. In 2013, N.H. Sea Grant-funded researchers calculated flounder growth and condition indices to indirectly evaluate the quality of twelve nursery areas ranging from New Jersey to New Hampshire. The data indicated that two sites — Boston Harbor, Mass., and Great Bay, N.H. — serve as the best nursery sites, while the Niantic River in Connecticut ranked as the worst nursery site. This research will help resource managers and scientists to better understand the effectiveness of indirect measurements like fish growth and condition to determine nursery quality for winter flounder recruitment.
Researchers identify two indices that most accurately assess winter flounder habitat quality
Following the recent collapse of the winter flounder fishery on the U.S. east coast, researchers are trying to determine how variations in the fish nursery habitat affect recruitment into the adult population. Because of the cost and time-intensive requirements of direct measurements such as otolith microchemistry analyses, it is likely that resource managers will only have access to indirect measurements, such as fish growth and condition. In 2013, N.H. Sea Grant-funded researchers evaluated four different indirect indices — length day-1, weight day-1, Fulton’s K and relativized weight — to assess the differences in winter flounder habitat quality in twelve locations ranging from New Jersey to New Hampshire. Based on these calculations, researchers determined that two indirect indices — length day-1 and Fulton’s K — most effectively and accurately determine the quality of winter flounder nursery habitats. These results provide resource managers with guidelines for the most effective tool choice to determine which sites that are most suitable for focusing their winter flounder population management efforts in the future.
Otolith microchemistry helps researchers trace adult winter flounder back to their natal nurseries
In light of historically low winter flounder populations on the U.S. east coast, scientists are seeking methods of assessing flounder nursery habitat quality to determine their contribution to the overall population. In 2013, N.H. Sea Grant-funded researchers conducted the first in a series of studies to determine if adult flounder found in offshore waters can be linked back to their natal estuarine nurseries solely based on unique estuarine water chemistry markers incorporated into the fish’s otoliths. The researchers developed a technique using solution-based inductively coupled mass spectrometry (ICP-MS) to more accurately analyze winter flounder otoliths. The results indicate that otolith elemental signatures are site-specific and vary on a small spatial scale (5-10 km). In addition, juvenile winter flounder can be classified with 73% accuracy to their natal nursery using this technique. This level of accuracy provides justification for further development of winter flounder otolith microchemistry as a tool to assess population connectivity and help resource managers identify and protect the most productive flounder nurseries.
Winter flounder are an important commercial and recreational species; unfortunately populations have experienced drastic reductions throughout their range. Despite ever increasing fishing regulations, winter flounder populations are not rebounding. Therefore, the viability of winter flounder as a marine resource not only depends on the enforcement of regulated fishing practices but the protection of their habitat as well (Pereira et al, 1999). That is why the concept of Essential Fish Habitat (EFH) was incorporated into the 1996 Sustainable Fisheries Act. EFH is defined as “those waters and substrates necessary to fish for spawning, breeding, feeding or growth to maturity” (Pereira et al, 1999). Certain estuaries and embayments that serve as winter flounder spawning and nursery areas have been classified as EFHs and are extremely important to population sustainability. EFHs are critical for winter flounder because they can support the tenuous maturation beyond early life stages where the mortality rate can reach 99% (Pearcy 1962). The year class strength of winter flounder is determined primarily during these early life stages (Sogard, 1991). Therefore, it is critical that methods for determining the most productive nursery areas (sites that contribute the greatest number of recruits into the adult population) be identified, so these areas can be researched and protected. We will test a fairly modern technique (otolith microchemistry) that has not been used on winter flounder to determine if a unique chemical imprint due to natal nursery (estuary) ground is discernible in juvenile winter flounder otoliths. In addition, we will utilize otolith microstructure analyses to learn more about latitudinal variations in winter flounder stocks and populations.