Has the Mt. Hope Bay Fish Assemblage
Changed More Than Narragansett Bay Assemblages?
Figure 1: The
greater Narragansett Bay region including Mt. Hope Bay and the Sakonnet River,
with identification of areas used for further analysis
- Previously, research
has focused on comparing winter flounder abundance in the Massachusetts portion
of Mt. Hope Bay to abundances for the entire Narragansett Bay and coastal
ignores strong spatial patterns in winter flounder catches due
to location effects. Estuarine ecologists have long known
that fish abundance is strongly affected by location within
partially account for these biases, we conducted an analysis
of winter flounder and fish species
assemblages based on Rhode Island Department of Environmental Management
(RIDEM) Seasonal Trawl Survey data. We divided this data into 9 area
sectors within the greater Narragansett Bay.
- The RIDEM Seasonal
Trawl Survey data base was chosen for this analysis because it is the only
data set that has good spatial coverage of the entire greater Narragansett
Bay Estuary and covers a 23 year period, including years before and after
the collapse of winter flounder stocks.
Winter Flounder Abundance
2: Annual mean winter flounder catch, segregated into the 9 areas
shown in Figure 1, plotted against time. The line referred to as 0 (dark
blue) is the mean of all data pooled together and represents the trend for
the greater Narragansett Bay region.
3: Same as Figure 2, but data has been aggregated into 5 year
periods, and some areas have been dropped for clarity. As above, the line referred
to as 0 (dark blue) represents the trend for the greater Narragansett Bay
- Figures 2 and 3
indicate that the abundance of winter flounder has decreased in all areas
of the greater Narragansett Bay region over the last fifteen to twenty years.
decline in catches within Mt. Hope Bay appears to be similar
to declines in most
other areas within the greater Narragansett Bay region.
Figure 4: Same
as Figure 3, but for hogchoker.
Figure 5: Same
as Figure 3, but for Windowpane.
Figure 5: Same
as Figure 3, but for Scup.
4 through 6 show plots of mean catch (within the entire greater
Narragansett Bay region)
for three other species. Two of these species (hogchoker and windowpane)
show declines during the last fifteen years, similar to winter flounder.
The mean catch for scup shows an increase over the same period.
- A total of 29 species
were analyzed across the entire region, with 10 showing a decline, 14 showing
an increase, and 5 exhibiting no identifiable trend over the last 20 years.
- Data analysis is
ongoing for individual subareas, including Mt. Hope Bay.
Figure 7: Canonical
plots for fish assemblages in Mt. Hope Bay and Narragansett Bay showing
changes in assemblage over the last two decades.
plots in Figure 7 show similar trends in both Mt. Hope Bay and
the entire greater Narragansett
- A shift
from benthic, or bottom dwelling, fishes (e.g. winter flounder)
towards pelagic, or water
column fishes (e.g., herring) has occured in both Mt. Hope Bay and greater
Narragansett Bay over the last 20 years.
- In all cases, trends
observed in Mt. Hope Bay appear to be similar to the other areas.
a Narragansett Bay-Wide Pattern
changes in winter flounder and other fish abundances in Mt. Hope
Bay appear to mirror
something happening throughout the greater Narragansett Bay system.
research will examine potential causes of the observed fish assemblage
shift in detail.
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