Ichthyoplankton Surveys: The Rodney Dangerfield of Fishery Science
Grace Klein-MacPhee, Associate Marine Research Scientist
Graduate School of Oceanography
Grace Klein-MacPhee earned a BA and an MA in biology from Boston University and a PhD in biological sciences from URI. She has worked for the Environmental Protection Agency in Narragansett and taught at the University of Alaska in Juneau. She has specialized in the biology of flatfishes and the early life history of northwest Atlantic fishes since coming to GSO in 1986. Her most ambitious work is the revision, with co-editor Bruce B. Collette, of Bigelow and Schroeder's Fishes of the Gulf of Maine, to be published by the Smithsonian Institute Press in 2002.
An ichthyoplankton survey is being conducted
in Narragansett Bay to identify spawning areas and seasons for major recreational
fish species, estimate the numbers of spawning stock for management purposes,
and de termine any changes in abundance or distribution of species since the
last survey was conducted in 1990. Plankton are floating or drifting organisms
with limited powers of locomotion that are transported primarily by water movement.
Zooplankton are the animal component of the plankton, and ichythyoplankton are
the zooplankton comprising the eggs and young stages (larvae) of fishes. Ichthyoplankton
surveys are collections of these organisms made at a number of sampling locations
using nets with a mesh size small enough (200–500 microns) to retain fish
eggs and larvae. The nets also collect other zooplankton such as copepods, larval
crab and shrimp, jellyfish, and other young invertebrates.
Ichthyoplankton surveys date back to the 1900s
when cod eggs were discovered to be planktonic. Up until the 1950s, collections
were used to learn about the early life history of different fishes, particularly
the commercially valuable species, and to determine their horizontal and vertical
distribution. In the 1950s, ichthyoplankton work expanded to include systematics
and taxonomy, geographical distribution, stock recruitment relationships, and
spawning stock biomass. Systematics is the naming, description, and classification
of organisms that shows patterns of relationships among species. Taxonomy is
the theory and technique of describing, naming, and classifying organisms. Prior
to the 1950s, very few fish eggs and larvae had been identified. Often the larval
stages do not resemble the adults, especially in the case of eels and flounders.
Before one determines geographic distribution, stock recruitment relationships,
or stock biomass, one must first identify the early life stages of fishes.
Large surveys were initiated on the West Coast
to find the causes for the decline in the commercially important sardine population
(California Cooperative Oceanic Fisheries Investigations, or CalCOFI) and on
the East Coast to study the commercially valuable herring population (Marine
Resource Monitoring Assessment and Prediction, or MARMAP). A wealth of information
was gathered from these studies. However, several objectives of the surveys
were not as successful as researchers had hoped. For example, estimates of spawning
stock biomass is most accurate for fish that spawn only once a season and are
relatively confined geographically. Ichthyoplankton surveys should be supplemented
with adult surveys to obtain an age distribution as different size (age) fish
produce different numbers of eggs. Stock recruitment relationships can't consistently
be determined from survey data because large numbers of eggs do not necessarily
mean large numbers of recruits, and sometimes modest numbers of larvae produce
a large year class.
Sea sampling, such as the CalCOFI and MARMAP
programs, is expensive and requires ship time and manpower. Large open-water
surveys are difficult to fund and are often perceived as "kill 'em and
count 'em" science, routine and repetitive in nature, and yielding little
new information. Thus, like Rodney Dangerfield, ichthyoplankton surveys get
no respect.
In the 1980s and early 1990s, funding for surveys
decreased. Because students were no longer trained in survey techniques and
identification and archiving of ichthyoplankton samples, it became difficult
to find experienced technicians and researchers. It also became more difficult
to publish results of surveys in peer- reviewed journals. One group, however,
remained active in conducting surveys. Operators of power plants are typically
required to monitor flora and fauna adjacent to their facilities to assess the
effects of the power plants on local species. They maintain valuable long-term
data sets and publish annual reports. However, the circulation of most of these
reports is restricted and they can be difficult to obtain.
If surveys don't fulfill their goals to everyone's
satisfaction and they are expensive, what is their value and why should we continue
to perform them? When surveys are conducted consistently and for a long time,
they can illuminate population trends—cycles of abundance and changes in
distribution of eggs and larvae. They also can alert us to bioinvasions and
range extensions or contractions. When an unknown species moves into a region
or extends or reduces its range, it can become an important component of fish
fauna. For example, the smallmouth flounder was rarely found in Narragansett
Bay prior to the 1990s, but now appears in significant numbers—a possible
range extension (see Fig. 1). These data were recently collected by the Rhode
Island Department of Environmental Management (DEM)/GSO Survey. Surveys provide
samples of larval forms of other species, such as crab and shrimp, that can
be used by other researchers or archived for use in the future. Surveys give
us information about the spawning areas and critical habitats of fishes, and
in restricted areas such as Narragansett Bay, they can be used to estimate spawning
stock abundance. Surveys also provide baseline data for determining the effects
of environmental pollutants caused by oil spills, dredging, and toxic chemical
releases; biological stressors such as low dissolved oxygen events; and climatological
events such as global warming.
Surveys cannot tell us why there is a change
in distribution, or how change affects the fishes beyond an increase or decrease
in number. Nevertheless, researchers can use the data to form hypotheses and
to investigate the changes. For example, GSO Associate Marine Research Scientist
Aimee Keller, GSO Marine Research Specialist Jean St. Onge Burns, and I conducted
an 18-station ichthyoplankton survey in Narragansett Bay in 1990 and compared
our data to results from an extensive survey that had been done in 1973–74
(see Fig. 2). There had been a decrease in the number of fish eggs and larvae
and a shift in population abundance from the upper bay to midbay. The differences
between winter flounder larval abundance in 1973 and 1990 (see Fig. 3) were
used by Jeremy Collie as the basis of his examination of the reasons for winter
flounder decline in Narragansett Bay.
Although sea sampling is expensive, surveys in
shallower, more enclosed waters, such as bays and estuaries, are less costly
because smaller boats with fewer crew and less sophisticated equipment can be
used. We are conducting an ichthyoplankton survey with DEM that uses their boats
and captains and our students.
It takes time to train students in identification
and sorting. Identification requires a knowledge of taxonomy and the specialized
structures possessed by larval fish. Taxonomy is rarely taught in classes nor
is the early life history of fishes, so few people have the skills necessary
for this work. Identification is an art as well as a skill; unfortunately some
people, no matter how intelligent and hardworking they are, cannot master it.
Sorting, which does not require intensive training, does require patience and
the willingness to spend a lot of time looking into microscopes. I have had
people quit after one day because they found sorting tedious. However, when
we do find an interested and talented student, it works out very well.
Another potential problem with surveys is the
reluctance of agencies to fund them for more than a year or two. This diminishes
the effectiveness of the information we collect because it is difficult to draw
conclusions from short-term observations. In 1990, we collected a large number
of yellowtail flounder larvae, many more than were collected in 1974. We did
not know if this represented the establishment of a new nursery area for yellowtail
or if this was merely an effect of water currents carrying the larvae into the
Bay as a result of a sporadic oceanographic event. The capability to make this
kind of distinction requires several years of data. Our current survey complements
ongoing surveys of juveniles and adult fishes being conducted by state biologists.
It should give us a complete picture of the life cycles of Narragansett Bay
fish populations, particularly those of commercial and recreational importance.
Our goal is to make this long-term ichthyoplankton survey, coupled with juvenile
and adult surveys, shed light on population trends and critical habitat. This
information will be invaluable for management, and it will be worthy of respect.
Dr. Klein-MacPhee's important research on the ichthyoplankton of Narragansett Bay clearly shows the essential role of taxonomy and systematics. Her data on the status and trends of ichthyoplankton have significant bearing on the management of commercial fisheries in the Bay and also reflect on the overall ecological condition of this important estuary. Without scientists like Dr. Klein-MacPhee who are expert in the collection and identification of organisms such as these, we have little hope of being able to manage and monitor whole ecosystems.
Edward O. Wilson
Pellegrino University Professor Emeritus
Harvard University