Synopsis of Higher Trophic Level
Meeting, Miami, FL
February 23-24, 2000
Introduction
The
focus of the meeting was inform new Florida Bay Science Panel member Ed Houde
regarding higher tropic level research in Florida Bay, review progress on upper
trophic level research, and to continue discussing performance measures (mid
and long term). Nancy Thompson acted as
chair for the meeting.
March 21, 1998 Report of the HTL organizing group
Recommendations
1. Focus on salinity and its effects upon
upper trophic level organisms.
2. Recognize regional differences.
3. Synthesize existing information in
relation to Science Question #5 and, specifically, “How are higher trophic
levels affected by freshwater inflow, particularly as it affects salinity?
Response
Synthesis projects were sponsored by FDEP,
ENP, and NMFS.
Directive of the June, 1999, HTL Meeting
PMC Directive
Focus on performance measures.
Response of HTL Researchers.
Florida Bay performance measures have thus
far been developed for pink shrimp, the American crocodile, and the spiny
lobster. A crocodile performance
measure based on simulated salinities in Little Madeira Bay and a pink shrimp
performance measure linked to water releases into Everglades National Park were
used in the C&SF Restudy.
Progress Reports
1.
Darlene Johnson- Synthesis study using existing data to examine salinity
effects upon forage fish/macroinvertebrate and mollusc communities
Synthesis Study
Twenty-four indicator species of fish and
macroinvertebrates have been selected.
Existing data on forage fish and macroinvertebrates has been acquired
and a data base is being developed to accommodate data sets and merge them
together. Data exists for the 70's,
80's, and 90's.
Preliminary analyses of data has begun. Pink
shrimp was selected as the first species to be analyzed based on economic and
ecological importance (everybody eats pink shrimp). Preliminary pink shrimp analyses and statistical models were
presented for 1994-1997 FMRI data Three
other data sets (Thayer & Powell, Sogard & Matheson) will be integrated
into the model in the future. Strong
basin effects and month (spatial and temporal) were found along with bottom
type (obtained from USGS bottom type studies), percent of basin with depths
less than one, tidal amplitude, and salinity (lagged 3 months). Jim Colvocoresses recommended that the data
be converted to density using information available for each gear. Jim Colvocoresses noted model results were
being affected by inaccuracies in USGS bottom type information. The bottom-type information did not match
observed bottom vegetation at fixed stations. It was suggested we put together
an improved seagrass map based on a coverage residing at FMRI (see Frank
Sargent) developed from aerial survey data and groundtruthed by Jim
Fourqurean. This could be
augmented/fine-tuned/corrected by data collected by Durako and Hall (FMRI) for
10 Florida Bay basins. In addition,
recorded observations on vegetation at fixed stations could also be used to
improve the map. Observations were made
on only about half of the Colvocoresses samples, however data collected by
Thayer & Powell and Sogard & Matheson contain quantitative seagrass
information for all stations.
Ehrhardt’s presentation (see later notes) suggested that integrating sea
level data into the model might be useful for explaining temporal variation in
densities of some species.
Community Study
Community analyses of FMRI forage fish and
mollusc data sets using cluster analysis and non-metric multidimensional scaling
showed that distinct animal communities resided in the Bay and were affected by
salinity. Larger molluscs were
structured by minimum salinities that occurred during the previous twelve
months while smaller molluscs responded to maximum salinities. Summer fish and macroinvertebrate
communities were structured by habitat factors such as depth and summer
temperatures. Differing salinities did
not change clusters at the outer edges of Florida Bay.
2.
Allyn Powell- forage fish and ichthyoplankton
A summary of
80's and 90's research was presented.
Bay anchovies were found to be up in 1994-1995, up in some areas in
1996, and down again in 1997. Spotted
seatrout distribution expanded in the 90's from the 80's, especially in central
regions. 1994 and 1995 were wet years
even though in some areas salinities were higher.
A bioenergetic model is being developed for
spotted seatrout. They are currently
working on growth using otoliths. The
growth information will be integrated into the bioenergetic model. Studies are being conducted on the effects
of salinity and temperature on growth using otoliths. About 347 fish are being sampled. No statistical differences have been found in growth between
regions. They have a Ph.D. student who
will be doing the bioenergetic model.
Gray snapper work is also being done. Based on growth, there seem to be 2 cohorts-
one in late spring/summer and a different one in the late fall. Growth rates seem to vary. It is uncertain if peaks are due to distinct
spawning peaks or differential survival.
What goes on outside the Bay may be more important than what goes on
inside the Bay.
Mercury
Gamefish (adult legal size) have been found
to have elevated levels of methyl mercury, especially those in the central Bay,
closer to land. This indicates that the
food web is contaminated and suggests a water column source. Isotope analyses suggest that
biomagnification and not a phytoplankton source.
3.
Maria Criales- ichthyoplankton and oceanographic dynamics
Studies have been focusing on the links
involving larvae transport. The Loop
Current is a significant variable for larvae transport, especially for those
organisms with a long larvae development such as spiny lobster.
Studies were conducted from June 1997 to July 1999 in Long Key Pass and
Whale Harbor Channel. El Nino and La
Nina events have been hypothesized to affect spiny lobster (9 months
development time), pink shrimp (20 days - development time), and snapper (30
days development time). New moon is
also an important variable, especially for pink shrimp larvae. Lobster recruitment was the same for El Nino
(1997) and La Nina (1998) years at Long Key but higher at Whale Harbor during
El Nino. Inshore intrusion of the loop
current in April 1997 brought in higher numbers of lobster larvae. The current analyses from the current meter
located at Sombrero and Tennessee Reefs (Tom Lee data analyses) showed that the
gyres formed on the southwest part of the Florida Keys have a major effects on
densities and transport of the lobster larvae.
Pink shrimp larvae were higher during La Nina at both sites. Shrimp larvae peaks occurred during March
and May 1999.
4.
Nelson Ehrhardt (RSMAS)
Pink shrimp recruitment from Florida Bay is
year-around but can be divided into two peak recruitment periods, early
(March-August) and late (September-January).
Decadal pink shrimp recruitment
data (from pink shrimp fishery) indicate that late peaks have declined, and it
is hypothesized that this decline is due to deteriorating Florida Bay
environmental conditions. There is a strong relationship between recruits (3
month lag) and the fishery
Early recruitment is weakly correlated to
parent stock abundance but strongly correlated to densities of juveniles (using Mike Robblee’s throw trap data
for Johnson Key). Pink shrimp
recruitment in the first half of the year
seems to be environmentally-driven and correlated to 4-5 month lagged
rainfall and windspeed. In contrast, September-January recruitment was poorly
correlated with 5 environmental variables tested but correlated with both
parent stock and juvenile abundance and with a 4-month lagged sea level (using
the sea level index, Naples Mean High - Key West Mean Low).
Declines in late peaks began in the 1980's
and around 1990 a major decline began.
Late 1987 recruitment was poorly
correlated to juvenile abundance and may have been affected by windspeed
changes associated with El Nino events.
During the 60's-70's, recruitment was highly correlated to sea level,
while during the 70's-80's there was a flat relationship. During the 80's-90's, there was a negative
relationship. Fishery recruitment was
found to be more strongly related to an index of juvenile abundance (throw trap
data from Johnson Key Basin) than to parent stock size.
A 10-15 cm change in sea level seems to be
enough to affect the ecology of the bay.
The exact mechanism of how it is affecting pink shrimp recruitment from
the Bay is uncertain. Sea level seems to be an index of the “slope” between
Florida Bay and the Dry Tortugas .
Sea level differences affect the movement
of juveniles between Bay nursery
grounds and Totugas spawning grounds.
Complicating factors affecting
juvenile densities seems to be the seagrass die off, the closing of the
Buttonwood Canal in the 80's, and the discontinuation of the Florida Bay bait
shrimp fishery.
5. Joan Browder
In-depth studies of pink shrimp have been
organized around a simulation model of pink shrimp recruitment to the Tortugas
grounds. The model concentrates on
growth and survival of young shrimp as a function of temperature and salinity
in Florida Bay. Simulated potential
annual recruitment from a summer cohort of shrimp was compared for two regions
of the Bay. Simulation results suggested that annual recruitment can vary
substantially from year to year on the basis of observed differences in
temperature and salinity–particularly salinity. Model results also suggested that recruitment from the central
Bay could be much more variable than that from the western Bay, probably
because of the predominance of hypersaline conditions in the central Bay in
some years. On the basis of these
results, Browder proposed that the some of the variability in fishing success
in the Tortugas may be due to salinity patterns. Zoula Zein Eldin at the NMFS Galveston Laboratory conducted
laboratory experiments on survival under a range of temperatures and salinities
to obtain the information used in developing the model. Zein-Eldin recently conducted a more
comprehensive series of experiments. The new data confirm and augment the early
work. In these experiments, the optimum
salinity for both growth and survival was 30 ppt. Temperature influenced sensitivity to salinity. At the request of the Science Panel, Browder
examined the statistical relationship between the catch rates of pink shrimp
recruits and salinities in western and central Florida Bay. Significant relationships were found between
monthly recruitment and monthly mean salinity in each area.
Progress on Performance Measures
There was a discussion as to what performance
measures really are. Essentially they are indicators (such as annual
recruitment or cpue) that help explain variability, distribution by size, how
organisms are being affected by salinity.
HTL researchers need to start focusing on the
processes that are being affected, essentially how the system is working. We need to define what we need from the
physical scientists. For instance, we
know that circulation is affecting nutrients but what is it doing to the habitat? Each needs to define for themselves- what
are the performance measures for your project, how can you get there, and how
are other things affected, and what are the problems getting there.
Science Panel Report
Nancy Thompson asked that everyone review
science panel report and respond with comments by mid-March.
Progress reports are to be submitted in
January, 2000. Joan Browder suggested
that we may want to treat them as a collection of papers.
A conceptual model (in response to the
science panel report) will be redeveloped to show where each project fits into
other work. Each person was asked to
develop their own conceptual model by March 30 and give to Joan so a consensus
diagram can be developed . The
conceptual model should be used to direct research and include a list of
biological indicators. It should define
what areas are being affected by salinity and what resources are associated
with that data. The seagrass model
might be a good model to follow (not the structure but the linking of ideas). We need to predict how the Bay responds to
changes in freshwater inflow.
Science Conference Format- presentation/poster
The format for April 2001 Florida Bay Science
Conference was discussed. Individual
projects will be presented during a poster session and then a synthesis of all
projects will be presented for each subgroup.
Agenda
List of Participants
February 24, 2000
Introduction
Higher tropic level project cooperators met to discuss
details of ongoing synthesis project and to discuss conceptual model
development.
Synthesis Project
Darlene Johnson presented model results and
details regarding data components were discussed and evaluated. FMRI data
should use the latitude and longitudes from reports. Gears should be standardized by area swept. This has already been calculated by FMRI and
will be provided.
We may want to use mixed seagrass as a
variable. Bottom types for fixed
stations can be calculated from percent cover variable and categorical variable
for vegetation type (primary and secondary ).
Detailed physical descriptions of each fixed station are in annual
reports which will be sent. Beaufort
data has quantitative seagrass information taken with each sample.
For our vegetation map, we can use Durako
original data for basins. Jim
Fourqurean’s data is from aerial surveys conducted in 1972?, but he did do some
ground truthing. We can use that
information that has been verified.
Frank Sargent (FMRI) also collected data which now is being handled by
Penny Hall. Carlos may have
Fourqurean’s data.
The sampling design for Beaufort data changed
in March 1999. Prior to 1999, a random
fixed sampling design was used and after they began a stratified sampling.
We should come up with a habitat map, one for
84-85 and one for the 90's.
Thayer suggests that we may want to delete
the1994 ichthyoplankton data as there are taxonomic problems with the data-
such as fish are identified to family rather than to species. The usefulness of the data is limited to
fishes that spawn in the Bay. The
sampling was specifically geared towards spawning of spotted seatrout. The biggest value is in seeing general
changes in species composition. For
instance, the peak in anchovies serves as a drive signal.
For mojarras less than 40 mm, Beaufort data
identifies them as Eucinostomus sp.
There are 2 main species which inhabit different habitats- gula and
argenteus. Most of the fishes called
harengulus probably are argenteus. For
first cut, may want to use grouping Eucinostomus sp.
Another variable we may want to use in the
analyses is distance from a key (as distinct from distance from the
mainland). We may be able to get this
off a GIS map. There seems to be an
ecotone effect in the area where the basin and the shore meet.
Use density instead of abundance.
Beaufort gears changed in 1996 from a 1 boat
trawl to a 2 boat trawl. There is a
bottom swept difference. After 1996 the
area swept is already calculated.
Before 1996, the density/hectare must be calculated from the data.
Don’t use turbidity in the FMRI data, use
Secchi disc instead.
Conceptual Model
Each person needs to develop a conceptual
model on how he thinks the Bay works and how organisms respond to freshwater
flow. We might use Zieman’s diagram and build upon it. For instance, bay spawners eggs may be
affected by salinity changes but outside spawners probably won’t be. Commercial fishing was terminated in 1985
which may have an effect.
P33 is used in models to predict salinity but
relationship is poor because water is being pulled out by Miami metropolitan
area and local rainfall is not being considered. Because of this poor predictability, the mangrove model for
forage fish is not being linked to water management model and they are
developing their own scenarios. They
will be presenting model at USGS May meeting.
We need to develop a more hypothesis driven
model showing links to processes such as growth, feeding, recruitment,
salinity, temperature, the role of animals in structuring seagrass systems.