Database Characterization
The Nonindigenous Aquatic Species (NAS) Database contains (as of
April 01, 2024) 718,735 spatially-referenced biogeographic records of
introductions and/or observations of 1,406 species of aquatic organisms,
including fishes, mammals, reptiles, amphibians, invertebrates, and
plants. Each specimen record within the database represents an
individual observation of a nonindigenous aquatic species in the
wild (e.g., angler catching a
red-bellied pacu Piaractus brachypomus in Missouri) or
documented release/introduction (e.g., intentional stocking of Brown
Trout Salmo trutta by natural resource agencies for fisheries
enhancement). Species introductions come in a variety of forms including
accidental (e.g., transport in ballast tanks of shipping vessels; escape
from pond or enclosure during flooding) and intentional releases, both
authorized (e.g., stocking of fishes for sport) and illegal (e.g.,
dumping of aquaria into local waterways). Specimen records are derived
from a variety of sources, including (but not limited to): scientific
publications, news reports, museum collection databases,
partnerships/data exchanges with other researchers or state/federal
agencies, agency stocking reports, and direct reports of observations
through a sighting report form.
The information and charts on this page were generated from specimen
records originating within the United States between 1800 and 2023, and
do not include Lionfish
(Pterois volitans and P. miles) records from other
countries or specimen records of species formerly tracked by the NAS
Database (i.e., marine invertebrates).
Database overview
Figure 1 shows the number of individual specimen records, and the
number of unique species comprising those records, recorded for each
decade since 1800:
Although the NAS database contains specimen records dating back to
1790, the majority of records are reports of introductions within the
last ~40 years. This does not indicate an increase in the rate of
species introduction in recent years: species introduction,
detection/observation of non-native species, and documentation of a
non-native species occurrence are all independent events, and it is
difficult to derive or estimate introduction rates from rates of
observation or documentation. Increased numbers of reports within the
last ~40 years could result from an increased awareness of impacts
associated with non-native species and the growth of research in
invasion biology, and/or increasing rates of communication of non-native
species occurrences. Similarly, a low number of specimen records prior
to ~1900 could be due difficulty in documenting historical records of
species introductions and observations of non-native species (e.g., no
available documentation or problems accessing literature sources;
missing or ambiguous species or locality descriptions).
Temporal Accuracy of Specimen Records
During entry of specimen records into the NAS database, any temporal
information contained within source material is used to identify or
assign a date of observation/introduction to a record. Additionally,
each record is scored on the degree of uncertainty in the assigned date
(to year), using the following categories of temporal accuracy:
- Actual: Record indicates actual year of
introduction/observation.
- Estimated: Actual year of introduction/observation
is unknown, but approximate range is given. Year is estimated as
midpoint of approximate range. For example, if a report indicates that a
species was introduced “in the 1980s”, the year of introduction would be
estimated as 1985.
- Publication Year: No year given in record source.
Publication date of record source is used as a proxy for
introduction/observation year
Figure 2 shows the number of specimen records within the NAS database
assigned to each class of temporal accuracy, for each decade. Figure 3
shows an expanded view of the temporal accuracy of specimen records in
the NAS database with an introduction date within the last 50 years:
A majority of the specimen records within the database include the
actual year of observation/introduction (i.e., when a species was
collected or reported), including most records for observations within
the last 50 years. Publication of books of state fish distributions
(e.g., Rohde et al.’s Freshwater
fishes of South Carolina), and fish stocking information released by
state agencies (e.g., Washington Department of Fish and Wildlife’s Warmwater
fishes of Washington) or collated by other sources (e.g., DeLorme
state gazetteer for Arizona),
containing many reports lacking an observation/introduction year
resulted in large spikes in specimen records with a temporal accuracy of
“Publication Year” in 1998-2001, 2005, and 2009.
Geographic Accuracy of Specimens
Specimen records within the NAS database are also classified by the
degree of spatial uncertainty in the assigned geographic location
associated with each specimen record. Spatial uncertainty is represented
by three separate categories:
- Accurate: Locality description indicates a specific
site, and/or site is unique. Geographic coordinates can be easily
inferred from locality description (e.g., Santa Fe River, 100 m
downstream of boat ramp at US 27, High Springs, FL), or are directly
provided by the source. No other water body with the same name exists in
the state and/or county. Size of water body is small relative to
dispersal capabilities of reported species.
- Approximate: Locality description indicates a
general area, and/or site is potentially ambiguous. Geographic
coordinates cannot be easily inferred from locality description (e.g.,
near Gainesville, FL), or locality description only indicates the name
of a large body of water (e.g., Lake Okeechobee).
- Centroid: Geographic location is the calculated
center point of a specified geographic polygon. Used for records
indicating presence within or throughout a specific county or HUC (e.g.,
Alachua County, FL).
Figure 4 examines the geographic accuracy of specimen records within
the NAS database. Numbers above the points indicate the number of
specimen records in each category:
Most records within the NAS database are assigned to a specific
geographic location, due to either direct reporting of geographic
coordinates or a robust description of the collection location that
allows for geolocation. “Other” on this graph represents specimen
records that do not fall into any of the three defined classes, and are
primarily historic records or those that are extremely ambiguous in
their geographic description, including some state non-specific records
or records where geographic coordinates could not be assigned. We are
currently working to assign a more specific class to these records.
References
The NAS reference database comprises all literature sources
(including books, news stories, articles from scientific journals,
agency reports, etc.) that are used as documentation for specimen
records, as well as references containing supplementary information used
to create species-specific fact sheets: written summaries of a species’
biology, ecology, current known native and introduced range, impacts,
and management. Fact sheets exist for the majority of species within the
NAS database, and are continually updated and expanded. Species-specific
fact sheets can be found through a search page.
Figure 5 shows the distribution of references in the NAS reference
database by publication date:
A large increase in the number of references after ~1990 is due to
the increasing importance and use of internet-associated sources (e.g.,
news websites, online state agency stocking reports, museum collection
databases) of species occurrence data, and the increase of research
efforts in invasion biology.
