Passage II

As fish mature, their diet often changes. Researchers investigated this phenomenon in 2 groups of winter flounder at a location in the Hudson River estuary where there is significant mixing of river water with ocean water. All the flounder were between 2 mo and 5 mo old and at least 20 mm long.

Study 1

Each June of 1996, 1997, and 1998, 100 flounder were captured and placed in cages that were sitting on the bottom of the estuary. Each cage was lined with a mesh bag that had square openings 3 mm in diameter. At the end of 10 days, the fish were removed from the cages and sorted into 4 classes based on length. The stomach contents of the fish in each class were analyzed to determine the percent by mass of each type of prey. The results, averaged over the 3 years, are shown in Figure 1. The percent of fish in each class with empty stomachs is shown in Table 1.

Study 2

In June of 1998, 30 more flounder were captured, removed from the river, and sorted into 4 classes based on length. Immediately after the fish were sorted, their stomach contents were analyzed to determine the percent by mass of the same types of prey identified in Study 1. The results are shown in Figure 2. The percent of fish in each class with empty stomachs is shown in Table 2.

Tables and figures adapted from D. N.Vivian et al., "Feeding Habits of Young-of-the-Year Winter Flounder, Pseudopleuronectes americanus, in the Hudson River Estuary, U. S. A." @2000 by the New Jersey Academy of Science.