Fish as Bio-indicators

Long term observations of fish populations can be a valuable way to assess the environmental health of local waterways. One value in keeping SAV records and fish records is that certain fish species are quite dependent upon healthy SAV beds for spawning and for protection, particularly during the juvenile stages of certain species. Since fish are in direct contact with the aquatic environment, problems in the water can directly impact fish populations. Some of the more common problems for fish species include low oxygen levels, excessive sedimentation, thermal pollution, acid rain and barriers to spawning sites. Natural changes in a waterway can also be reflected in the types of fish observed in a study site. During periods of drought, the salinity, or salt level in the water increases. The allows the fish in the saltier Chesapeake Bay to make their way up into the Patuxent River. Species such as bluefish, spot and weakfish have been captured in the seine nets as far up the river as King's Landing Park.

Natural changes in fish populations can also be observed by long term monitoring. Fisheries scientists measure the spawning success of species such as rockfish by measuring a young of the year index. The techniques used by the scientists are very similar to those employed by our seventh grade students, in fact, quite often our student data will stay in line with the results reported by the fisheries scientists. It is not always simple to assign a reason for declines in populations of certain species. An example of this can be observed in the Blue Crab data collected during the Fall of 2000. Reports of extremely low crab harvests were reported widely across the Chesapeake Bay during this season. Our seventh grade seine survey results also indicated that crabs were extremely low, perhaps the lowest ever. Possible causes for this decline include a natural cyclical downturn, overharvesting, increases in predatory species such as rockfish or water pollution. Studies are underway to determine the cause or causes for this decline. Scientific data collection, as well as the reports of harvests of particular species can be a way to establish the baseline data that is needed to investigate the causes for crab declines.

The student generated data have helped the CHESPAX staff in observing the seasonal and yearly changes in populations. The on-going study helps to determine the relative abundance of different species as well as helping to document the appearance of new and unusual species. Every single seine haul brings us a better understanding of the fish populations of the Patuxent River.

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