Research and Monitoring

Biologists from the Division of Fish and Wildlife keep track of the state’s fish populations. They work on Delaware’s rivers, ponds, estuaries, the Delaware Bay, and coastal waters and study how different species are faring.

What Fisheries Biologists Do

Recording information and releasing
Fisheries Biologist John Clark captured and tagged this striper (48.5 inches long and weighing 54.8 lbs.) on the spawning grounds in the Delaware River, during the annual spring electrofishing survey – used to assess the spawning population.

Fisheries biologists use different types of sampling gear to check fish populations. Their methods depend on the habitat (pond, river, estuary, tidal stream, etc.) and the kind of fish involved.

Some fish, like largemouth bass or striped bass, are best collected using electrofishing. Fish in deeper waters, such as weakfish and croaker in the Delaware Bay, are more easily collected by trawling.

Once collected, fish are weighed and measured. Scale samples or other aging structures may be removed to help determine the age and growth of the fish. Finding a variety of sizes and ages indicates a healthy fish population.

Sometimes, fisheries biologists need to gather other information. They’ll design and carry out special studies needed to help manage healthy fish populations.

For example, one study of striped bass food habits in the Delaware Bay uses a small pump to flush out the contents of of fishes’ stomachs. The fish are released, hungry but healthy, and biologists study what they’ve eaten.

How is this Information Used?

Biologist catches a fish
Fisheries Biologist Cathy Martin, with a 6.5 lb largemouth bass taken by electrofisher in Broad Creek on the Nanticoke River.

Fish biology studies help scientists identify and plan ways to deal with a variety of local and regional problems.

These may include pond-specific issues such as over-crowding of smaller fish or poor growth. There may be habitat issues, such as the destruction of shoreline structures or run-off affecting water quality.

For species like the striped bass, management must be at the regional or coastal level. Striped bass move into the Delaware River during the spring to spawn upstream of the Delaware Memorial Bridge. They can go into Pennsylvania waters. When the adults move out into coastal waters, they may migrate between New England and North Carolina.

All coastal states gather and share information about shared species. The US Fish and Wildlife Service and other inter-state agencies lead management for these species.

Research Reports