Members of the Predation Group attending the September 1998 SI
Data Workshop were Steve Bollens, Larry Madin and Barbara Sullivan.
Heidi Franklin from the University of Maine (working part time with
Bollens) joined on Saturday to work with us on Matlab programming.
The following topics were
1. Review of progress on analysis of samples.
All of the Broadscale Survey MOC-10 samples from 1995 and 1996, and
a small proportion of those fom 1997 and 1998, have been analyzed in
BollensÕ lab, including identification and enumeration of all
specimens, and measurement for length of up to 50 individuals of
each species per net. Work will continue in BollensÕ lab on
remaining 1997 and 1998 samples, and 1999 samples from Phase III.
Representative plots of seasonal abundance for some larger organisms
are attached to this report.
The number of MOC-10 samples from the Process cruises, 1994-1997
is shown below. All samples are given rough counts immediately
after collection and before preservation. Lab counts have been
completed on a subset of the preserved samples that represent
replicated sampling in regions of interest. Remaining samples will
be completed in 1998 and 1999, according to priorities established
by the Predation Group. (See Figure A
and Figure B.)
Number of MOC-10 samples collected:
|Year ||Cruise ||# of tows|
|1994 ||AL9403 ||21|
|1995 ||EN268 ||22|
|SJ9503 ||6 |
|SJ9505 ||5 |
|1997 ||EN298 ||24 |
|Total || ||113|
MOC-1 samples from process cruises in 1994, 1995 and 1997 have
been analyzed in Sullivan's lab for identification and enumeration
of invertebrate predators. Predators >10 mm in length are
counted from the whole sample; smaller, more numerous predators are
counted from subsamples. Predators are placed in size categories:
1-3 mm, 3-10mm, >10mm. Bongo net samples from April and May
process cruises collected by R.G. Lough 1993-1997 have been counted
for hydroids. Analysis of 1994 and 1995 MOC-1 samples is completed.
Analysis of 1997 samples is in progress and has been done in
cooperation with K. Wishner. A representative plot of vertical
distribution of a small but ubiquitous and abundant predator of
copepods collected during 1997 is available as
Number of MOC-1 and bongo net samples processed:
|Year ||MOC-1 ||Bongo|
|1993 ||NA ||47|
|1994 ||16 ||62|
|1995 ||148 ||96|
|1997 ||91 ||66|
2. Review of Predator List
We created a revised list of predators on Georges Bank, based on
data from MOC-1 and MOC-10 collections. A comprehensive list of
about 40 species will be narrowed to a short list of the most
abundant predators, which we expect to number 10-15 species. The
status of information on feeding rates and selectivity, including
functional responses and temperature effects was also reviewed for
each species. We have our own data on feeding rates or selection
for about 10 species, and expect to use values from the literature
for about another 10-15. Additional data on predation rates by
copepods and other small predators will be obtained on Process
cruises in 1999.
Clytia gracilis (hydroids)
3. Matrix for calculation and plotting of predator and prey
distributions, and predation related mortality.
We discussed the structure of a general matrix for calculating
predation mortality and mapping it in time and space, based on
distributional data for predators and prey, and appropriate feeding
rate information. Distribution data will come mainly from the
Broadscale MOC-1 and MOC-10 collections, supplemented in some places
with data from Process cruises (MOCNESS or bongo tows). Rate data
will be from a combination of our own measurements, from feeding
experiments or gut contents analysis, and comparable results from
the literature for other species. All rate data will be normalized
to an arbitrary temperature (i.e. 10°C), and then adjusted to
ambient temperatures for different seasons and locations. The
calculation matrix includes:
- abundance of predator species as numbers per m2 or m3 (for depth
- feeding rates for each predator species, as number of prey
consumed per day
- abundance of all prey species, from Broadscale data
- proportion of prey species made up by target species of
copepods or fish
- functional response equations relating predator feeding rates to
- Q10 functions to correct predation rates for temperature
- selectivity functions to represent possible deviation from
non-selective feeding on target species
The expected output of the matrix is an estimated predation
mortality for each predator-prey pair, at each Broadscale station.
The matrix should allow depth-specific calculations if desired. It
will then be possible to sum the effects of all predators on a given
target species, to map the total predation mortality for that
species in space and time on Georges Bank. These values can be
compared to demographic estimates of mortality, and incorporated
into models of population dynamics.
During the Workshop we worked on programming the structure of the
matrix in Matlab. Initial runs can be tried in the near future.
Data will be mapped using the Matlab contouring and mapping routines
under development in the Georges Bank program.
4. Gut Contents Analysis
We still need to complete a large number of microscopic gut-content
analyes for the major predators. While we have considerable data
for Crangon and Pleurobrachia, Sagitta and
hydroids, and some for Themisto and Bolinopsis,
there are many samples of other predators remaining to be done.
Recent examinations by Sullivan of small Themisto, for
example, showed that copepod remains were identifiable in the guts.
Existing and additional data on gut contents will be used with our
own and other rates of gut passage to estimate in-situ feeding
5. Antibody and DNA probes for gut contents.
The antibody reagents we have developed over the last 4 years have
recently been shown to be less specific to Calanus than
earlier thought. Specificity appears to depend on carefully
controlled dilutions and other conditions, which cannot always be
met with field-collected samples. We plan now to use the antibody,
which is specific to copepods, to detect the presence of copepods in
the guts of predators, such as euphausiids, mysids and gammarid
amphipods, whose diet we know little about. This will enable us to
limit our list of predators on target species.
Support for use of DNA probes to identify cod, haddock,
Calanus and Pseudocalanus remains in predator guts was
cut from our Phase III proposal. However, Madin has a new student,
Annette Frese, who has experience with these techniques, and is
interested in applying DNA probes to the analysis of gut contents.
We anticipate cooperation with Ann Bucklin in this work, and will
probably be obtaining samples during the 1999 Process cruises.
6. Use of Process cruise samples.
Sampling with the MOC-1 and MOC-10 on Process cruises has generally
been directed at specific questions about the distribution of
predators or prey relative to stratification, source and loss
regions, or frontal processes. The samples are therefore analyzed
so as to address these questions, and not necessarily with the same
protocol as the Broadscale samples. In cases where sample analysis
is comparable (some MOC-10 hauls), the data will be used to
supplement Broadscale data. Sampling on process cruises provides
specific information on predator-prey co-occurrence as a function of
depth, on size relationships between predators and prey, and is a
source of specimens for gut contents analysis and laboratory
Process MOC-1 samples will continue to be analyzed in Sullivan's
lab, and future MOC-10 samples will be sorted in Bollens' lab.
7. Postdoctoral Investigator.
We agreed to advertise immediately for a postdoctoral
investigator who will work during Phase III on small predators. The
postdoc will be responsible for conducting feeding experiments on
process cruises and in the lab.
8. Cruise Plans
Preliminary discussions about cruise plans for 1999 were held with
Ted Durbin, Greg Lough and Karen Wishner, followed by more planning
on Monday with Dian Gifford and Karen. Our proposal originally
included time on 4 process cruises, but budget cuts now limit us to
three. During the Durbin cruise in April, we intend to concentrate
on the role of small predators, and compare our predation estimates
to Calanus mortality measured by Durbin, Runge and Ohman.
Our objectives for the cruise in May with Lough are to sample
predators of larval fish across the tidal mixing front, using the
MOC-10 and LAPIS video systems. The time series analysis of
abundance and distribution of hydroids,
predators of both copepods and larval fish, will be continued on
this cruise, using counts from bongo net tows in the vicinity of the
larval fish patch.
On the cruise in June with Wishner and Gifford, we plan to do
similar replicated sampling for large and small predators across the
tidal front, using the same equipment. It was decided on Monday
that three additional days would be needed on the June cruise with
Gifford and Wishner to accommodate the MOC-10 sampling. These days
may be available from time on Durbin's cruises in March and April.
List of figures
Figure A: Abundance of Clupea harengus
on Georges Bank, collected with the MOC-10. Each month represents
the mean of all Broad-scale stations sampled. (n=1080 fish)
Figure B: Abundance of Salpa spp.
on Georges Bank, collected with the MOC-10. Each month represents mean of
all Broad-scale stations sampled. (n=36,093)
A representative sample of the amphipod, Themisto gaudichaudi.
These predatory amphipods consume copepods when young (1-3mm) and
copepods and larval fish when greater than 6mm long. Small
juveniles are very abundant (up to 130,000/1000m³) in the
upper water column; larger individuals are common in both the upper
water column and at mid-depth.