Spatial And Temporal Patterns Of The Fish Assemblages In The Greater Narragansett Bay Estuarine System: Is Mt. Hope Bay Different?

Abstract

Rountree, R.A., and D. Witting. 2003. Spatial And Temporal Patterns Of The Fish Assemblages In The Greater Narragansett Bay Estuarine System: Is Mt. Hope Bay Different? presented at the Special Symposium: Natural and Anthropogenic influences on the Mt. Hope Bay Ecosystem, held at the NEERS/SNECAFS Joint Meeting, May 8-10, 2003, Holiday Inn, Fairhaven, MA, Hosted by, UMass Dartmouth, SMAST.

Abstract - Winter flounder abundances have experienced dramatic declines throughout the greater Narragansett Bay estuarine system, including within Mt. Hope Bay. However, a controversy has developed as to whether or not the decline has been more severe in Mt. Hope Bay. To address this issue, we chose to use data from the long-term Seasonal Trawl Survey conducted by the Rhode Island Department of Environmental Management (RIDEM). This is the only data set that both encompasses a time frame (1979-2001) that includes the period before and after the decline of winter flounder, and has good spatial coverage of all of the greater Narragansett Bay system, including Mt. Hope Bay. We analyzed the RIDEM Seasonal Trawl Survey data to examined time trends in the abundance of winter flounder and 28 other species from 9 different areas within the greater Narragansett Bay system. No significant difference was found in the decline of winter flounder in Mt. Hope Bay compared to other areas. In fact, the trend for Mt. Hope Bay was intermediate to other areas, with several areas exhibiting stronger decline trend. The fish assemblage was observed to have undergone a dramatic shift from benthic to pelagic species in all areas of Narragansett Bay. This pattern is strongest in the shallow embayments (Greenwich Bay, Sakonnet River, Mt. Hope Bay, Wickford Harbor and upper Narragansett Bay), and weakest in the deep central bay areas. In conclusion, we find that changes in winter flounder abundance and in the fish assemblage between 1979 and 2001 in Mt. Hope Bay are similar to those observed in other parts of the greater Narragansett Bay system, and reflect processes operating on a Narragansett Bay-wide scale.

Full text

Spatial and temporal patterns of the fish assemblages in the
greater Narragansett Bay estuarine system:
evidence for widespread impacts of eutrophication?
Rodney A. Rountree
Mt. Hope Bay Natural Laboratory Program
School for Marine Science and Technology

Central Question:
Is the Mt. Hope Bay's fisheries and ecosystem
significantly worse off than comparable
estuaries without a power plant?

Spatial Comparison
Massachusetts
Rhode
Is. Mt. Hope Bay
3
1
2
45
6
7
8
9
3
1
2
4
5
6
7
8
9
Mt. Hope Bay
Greenwich Bay
Upper Narragansett
Middle West Passage
Middle East Passage
Upper Sakonnet
West Passage
East Passage
Lower Sakonnet

Greater Bay vs 9 areas
Narragansett Bay Average
Mt. Hope Bay

Greater Bay vs 3 upper areas
Narragansett Bay Average
Mt. Hope Bay
Upper Narragansett
Greenwich

Data aggregated into 5-year periods
Narragansett Bay Average
Mt. Hope Bay
79-83 84-88 89-93 94-98 99-01

Greenwich and Sakonnet
dropped
Narragansett Bay Average
Mt. Hope Bay
79-83 84-88 89-93 94-98 99-01

Conclusions so far?
1. Declines in Mt. Hope Bay are similar to other “comparable”
areas within the greater Narragansett Bay system
2. Strongest declines in catches occurred in the shallow
embayments
3. Some suggestions of a shrinkage of the population into
the deeper waters of the central bay

Hogchoker
Mt. Hope Bay
Middle West Passage
79-83 84-88 89-93 94-98 99-01

Windowpane
79-83 84-88 89-93 94-98 99-01

Scup

79-83
84-8894-98
89-93
99-01
Benthic fishesPelagic fishes
Fish assemblage shift in Mt. Hope Bay
64%
20%

Benthic fishesPelagic fishes
79-83
84-88
94-98 89-93
99-
01
72%
15%
Assemblage shift in Narragansett Bay

A Bay-Wide Pattern
Temporal changes in winter flounder and other fish
abundances Mt. Hope Bay appear to mirror something
happening throughout Narragansett Bay. What can account for
these dramatic changes?
Climate change ?
Eutrophication ?
Overfishing ?

Cold Neutral Warm
Decline
Increase
NC
0
10
20
30
40
50
60
Comparison of Temporal Trends by
Temperature Preference
Decline
Increase
NC
Climate Warming?

Benthic
Demersal
Pelagic
Decline
Increase
NC
0
10
20
30
40
50
60
70
80
Comparison of Temporal Trend by Habitat Preference
Decline
Increase
NC
Habitat Shifts?

Trophic Shifts?
Benthic Piscivore Zooplankton
Decline
Increase
NC
0
10
20
30
40
50
60
70
80
90
Comparison of Temporal Trend by Food Type
Decline
Increase
NC

Decline in winter flounder abundance, and
shifts in species assemblages in Mt. Hope Bay
are similar to those observed in other parts of
the greater Narragansett Bay system.
Conclusions

Spatial Comparison
Massachusetts
Rhode
Is. Mt. Hope Bay
3
2
45
7
8
9
3
1
2
4
5
6
7
8
9
Mt. Hope Bay
Greenwich Bay
Upper Narragansett
Middle West Passage
Middle East Passage
Upper Sakonnet
West Passage
East Passage
Lower Sakonnet

Winter flounder by season

Winter flounder by stage and season
Juv
Spring Fall

Comparison in shallow strata
areas only