Rhode Island's Ever-Changing Narragansett Bay
Perry Jeffries, Professor Emeritus
Graduate School of Oceanography
Perry Jeffries earned BS and MS degrees at URI, and a PhD degree at Rutgers University. He came to the Narragansett Marine Laboratory as an Assistant Professor of Oceanography. His research interests include coastal ecosystems (structure and patterns of change), zooplankton distribution and abundance, and fatty acid and amino acid pools in relation to environmental conditions.
It was a cold and stormy night—January 6,
1959— when the Narragansett Marine Laboratory, predecessor to the Graduate
School of Oceanography (GSO), burned to the ground. Everything was lost, including
irreplaceable records and a manuscript that Marie P. Fish had left on her desk
for a final check. Her husband, Charles J. Fish, founder and director of the
lab, moved his staff to the old Washington County Jail in Kingston and started
anew.
As the ashes cooled, a research program on the
bottom fishes and invertebrates in Narragansett Bay and Rhode Island Sound emerged.
Marie Fish needed information about seasonal migrations to correlate with recordings
of underwater sound, a matter of critical interest to the U.S. Navy. Charles
Fish, whose classic dissertation on the plankton of the Woods Hole Region set
the bar for seasonal studies, realized an extra benefit. Long-term changes in
a complex of interacting populations inhabiting coastal waters could be measured
rather than left to anecdotal accounts. When Charles Fish retired in 1966, he
gave me his data, and I have worked to maintain a program designed to perpetuate
his ideas.
Every week since January 1959, a trawler has
left Wickford Harbor and made a 30-minute otter tow in mid-Narragansett Bay
and in Rhode Island Sound. The net collects animals (three inches and larger)
living on and just above the bottom. We measure water temperature and count
and weigh each species. Winter flounder are given special attention: individuals
are measured and sex is noted.
Because we do the same thing week after week,
we can observe gradual and long-term changes. No record comparable to this 42-year-old
data set exists for any coastal area; thus the data become more valuable every
year.
Annual abundance is the total of average monthly
catches for a species. Thus, for a year-round species, up to 52 samples reduce
to a single estimate of abundance. Sampling was less frequent during the early
days but now, thanks to Captain Tom Puckett's dedication aboard the trawler
Cap'n Bert and several generations of outstanding graduate assistants,
we rarely miss a week. The record is available for management purposes and,
since 1999, all have had access to it.
The local scientific community requests specimens
from the trawl, and surprising uses have been found for our temperature data.
I could hear a sigh of relief when I gave bottom water temperatures to the engineers
of the Jamestown Verrazano Bridge who needed to take temperature into consideration
before mixing and pouring concrete in the middle of winter.
The winter flounder confounds me as I attempt
to explain the changes that occur among the 24 species that make up 99 percent
of the year-round catch. Winter flounder once made up 50 percent of the inshore
fisherman's income, but the population is now a mere vestige of its former glory.
Intuition tells me that an 80 percent decline from the first to the fourth decade
of our program is not entirely due to overfishing and pollution—two common
explanations for problems in coastal waters.
After the flounder population reached a low point
in 1976, I published a paper with Bill Johnson, a GSO graduate student in 1980
who assisted with the trawl, reporting a correlation between warmer winters
and the flounder's 86 percent decline from a peak in 1968. But correlation does
not prove causation, and warming from 1971 through 1975 amounted to about 2°C,
which seemed insufficient to produce a major biological effect (see Figs. 1
and 2). Besides, there was little ancillary information for corroboration, and
back then no one was talking about climatic warming in coastal waters.
I learned from Candace Oviatt, director of the
Marine Ecosystem Research Laboratory, that sand shrimp raised havoc in outdoor
aquaria by eating anything they could get their claws on. Was this inch-long
terror, previously capable of feeding only during warmer months, now able to
feed in winter? If so, the flounder's reproductive efforts would be disrupted.
After the flounder population recovered briefly
(1978–1983), I proposed a theory in a paper with Mark Terceiro, a GSO doctoral
student in 1985, who used part of the trawl record for his dissertation. We
combined warming and predation to explain the flounder's behavior. Winter flounder
have an unusual ability to repopulate in estuaries at extremely low temperatures,
a time when predators are either offshore or inactive. Shrimp have adapted,
and since 1970, following warmer winters have invaded the flounder's refuge,
devouring its eggs and larvae. Extrapolating Sandra Whitehouse's 1994 GSO dissertation
results on shrimp feeding rates, I calculated that predation might well destroy
all the young flounder produced during a single winter in Narragansett Bay.
To strengthen our theory, we needed evidence
that shrimp thrived during winter. Soon thousands of shrimp appeared, entangled
in the trawl's manila ropes. Our skeptics would not be stilled until measurements
were made of shrimp feeding rates at low temperatures. Some biologists insist
that fishing pressure is the controlling factor. This cannot be true because
the flounder population recovered in the late 1970s, only to collapse again
as the warming trend recurred (compare Figs. 1 and 2).
Studies on plaice in the North Sea bolstered
the shrimp theory. Plaice belong to the same genus as winter flounder, and they
prosper following cold winters. North Sea shrimp belong to the same genus as
sand shrimp, and they fare well during warm winters, feeding on plaice eggs
and larvae. The predator-prey genera are the same, only the species differ.
I call it a congeneric correspondence: Similar species interact in the same
way on both sides of the North Atlantic.
From the early 1980s on, when the flounder population
collapsed a second time, unusual events took place among the Bay's crabs: Sand
crabs appeared in January and commenced to shed. Previously, this species and
the related Jonah crab, along with other invertebrates, waited until spring
to begin their migration from the ocean.
The flounder population entered the new millennium
at less than 10 percent of the total catch. Against a background of warmer winters,
the winter flounder's future is not promising.
It follows that the myriad bottom foods in Narragansett
Bay once supporting winter flounder have become available for others, which
may explain increases of migratory lobsters, crabs, squid, butterfish, and scup.
Outsiders, chiefly warm water visitors to the Bay, have taken over bottom habitats.
Note how scup filled in the gaps left by winter flounder (see Fig. 2). In 1995,
it looked as if invertebrates would overrun both the Bay and Rhode Island Sound.
Recently, however, their numbers have fallen off. Body size is small and the
species are less desirable, so commercial value is less than it was during the
flounder's halcyon days (see Fig. 3).
One exception is lobster, which defies all explanation.
How long can that population endure? Several years ago, I saw three offshore
trawlers at the mouth of the Bay, dragging the bottom with their huge nets;
a fourth was leaving. What were they after? Not fish. The catch would not have
been enough to cover fuel costs. It must have been lobsters, whose numbers had
reached an all-time high in 1992 (see Fig. 4). Then came an oil spill that killed
millions of lobsters.
I wonder when outdated fishery economics, ineffective
management, and perhaps even greed will catch up with our splendid crustacean.
The population is unstable; its numbers in the Bay dropped one-half in a single
year (1998–99), and it remained there through 2000. Perhaps its limit has
been reached (see Fig. 4).
A major conclusion emerges: The winter flounder's
rise and fall are part of a bigger whole that changes continuously. Prior to
1970, the controlling dynamics were Bay-centered. The balance shifted to Rhode
Island Sound in the early 1970s, went back to the Bay after two cold winters,
and finally returned to R.I. Sound in the early 1980s, where it has remained
ever since. Reflecting this dynamic balance, the 24 major species fall into
five groups for the 1959–1998 period:
Group 1. Progressive increases: butterfish, lobster, squid, Atlantic herring,
little skate, striped sea robin, fourspot flounder;
Group 2. Multimodal (several) increases: cancer crabs, conch, spider crab, Mantis
shrimp, scup;
Group 3. Indeterminate: horseshoe crab, starfish, fluke, ocean pout, red hake;
Group 4. Multimodal declines: winter flounder, windowpane flounder, silver hake;
Group 5. Progressive decreases: cunner, tautog, northern sea robin, longhorn
sculpin.
The Bay's winter flounder population established
a pattern that others seemed to follow. Flounder thrived twice following cold
winters, but each time, winters soon warmed, and the populations waned. During
the flounder's first collapse, scup, a warm-water species, migrated more strongly
into the Bay to take its place. Invertebrates and butterfish, another warm-water
migrant, characterized the aftermath of the flounder's second collapse.
For migrating bird populations, the eminent ecologist
Robert MacArthur would have called this Bay-Sound relation an expression of
his Principle of Equal Opportunity—go to the habitat where the getting
is good. We now know that that principle applies to fish and bottom invertebrates
as well as to birds. You might say that the Bay has less control of its destiny
as warm water visitors take over.
Group 5 has the big losers in the numbers game.
Cunner and tautog are related, though the former is a pest for recreational
fishermen and the latter is a commercially valuable species. Longhorn sculpin
reproduce during winter, so their eggs and larvae may also fall prey to shrimp.
The demise of the cunner and northern sea robin is a mystery.
Deciphering the information presented by the
trawl data provides me with more than statistics and ecological theory. Its
patterns unveil the whole that every oceanographer knows is the proper way to
study an issue. This was Charles Fish's credo. He rebuilt a laboratory to support
a graduate program that embodies this ideal, making certain that the message
is clear for generations to come. Credit also goes to the administration of
the Graduate School of Oceanography and to the state of Rhode Island for supporting
this study.