VIMS Juvenile Fish and Blue Crab Trawl Survey

The Virginia Institute of Marine Science (VIMS) has played an important part in the preservation of the Chesapeake Bay. One data set that has played an integral part in this process for over 40 years is the VIMS Juvenile Trawl Survey. This project began in sampling in 1955 and continues in similar fashion today. The primary objective of the trawl survey is to monitor trends in seasonal distribution and abundance of juvenile fish of about twenty recreationally, commercially, and ecologically important finfish and invertebrates. Most species targeted by this survey are available to the survey nets for a limited amount of time during the year, because of seasonal abundance and migrations out of the Bay. Further, many species have a limited geographic range within the Bay and its tributaries. For each species then, only three or four months of highest abundance are used in computation of the index; and only the areas in which each species is most plentiful are included for the index. For some species this is all river and Bay segments, for others only the Bay or subsections of the Bay are used, and for still others only the rivers or river segments are used. For most target species, individuals become susceptible to, or can be caught by, the survey nets several months after hatching, when they are referred to as Age 0 (young-of-the-year) or "juvenile" fish. Some species are also (or exclusively) caught as older individuals. For some species, this group of older fish is only one year class and for other species it is several. Indices are also calculated for these older groups. Where these indices clearly represent only one year class, they are labeled as "age 1"; where they include several year classes, they are referred to as "Age 1+". Juvenile indices serve several purposes. Most importantly, they serve as an annual indication of recruitment success or failure, for example, providing an "early warning" of year class failure. They allow us to monitor the pulse of the Bay. These indices can also be an indication of the success or failure of a management plan or regime, and serve as the data for input to stock assessment models used by the managers. In addition, the length of the time series allows an analysis of the possible causes driving year class success or failure, and allows us to see long-term changes in populations that may be caused by over-harvesting, pollutants, or climate change. Finally, the data provide a valuable information base for student research on age and growth, pollutant body burdens, climate interactions, stock identification, and population dynamics of the various species. Indeed, the VIMS Trawl Survey is just one element of a VIMS comprehensive fish monitoring program which includes beach seine surveys targeting striped bass, white perch, and bluefish; surveys which sample juvenile shad much farther upriver than the Trawl Survey; and pound net and gill net surveys which sample adult fish of several species. Because most of these species are migratory, the VIMS surveys are elements of multi-state monitoring efforts which support interstate fishery management plans. When combined with other surveys which sample fish, a comprehensive picture of the relative condition of a fish population can be compiled. Several Maryland-Virginia bistate fishery management plans call for a continuation of the VIMS trawl survey to make annual estimations of recruitment success. Further, Atlantic States Marine Fisheries Commission and Mid-Atlantic Fisheries Management Council interstate and regional fishery management plans cite the need for monitoring and support for annual recruitment of juvenile finfishes. The trawl survey and seine surveys provide these data.