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to be those initiated by PICES, with the first one in Dalian, China in 2008
(http://www.pices.int/publications/pices_press/volume19/v19_n1/pp_30-31_Kobe-WS_f.pdf).
To evaluate the potential effect of search effort, we calculated the relative percent of
nonindigenous fouling organisms to non-fouling invaders in each ecoregion (Figure 59). Foulers
were defined as barnacles, tunicates, bryozoa, hydroids, and serpulid polychaetes. Because of
their economic importance to shipping and aquaculture, a reasonable effort appears to have been
put into their enumeration on all coasts. Additionally, fouling invaders are more obvious than
cryptic guilds of invaders, such as infaunal species, and are more likely to be detected and
reported. We assume, therefore, that fouling invaders are less likely to be underreported
compared to non-fouling invaders. Thus, the relative percent of foulers to non-foulers should be
higher in less well surveyed regions. The two most intensively studied locations, Hawaii and the
NEP, have similar relative percentages of foulers (27.6% versus 26.5%). In comparison, in the
least studied location, the NCIP, foulers constitute about half of the non-foulers (49%). The
NWP has an intermediate value (32.5%). While not conclusive, this increase in the relative
percent of nonindigenous foulers relative to other types of invaders supports the contention that
differences in search effort was an important factor contributing to lower number of NIS in the
NWP and NCIP. It is important to note that the lesser search effort appears to vary substantially
among taxa. Macroalgae have been extensively studied in Japan and China (e.g., Lewis and
Norris, 1987; Yoshida and Yoshinaga, 2010) which may partially explain why there are a
relatively large numbers of nonindigenous brown and green macroalgae reported from the NWP
(Figures 29 and 31).
3) Differences in the application of criteria used to classify species as nonindigenous. Except in
cases of stocked species, classifying a species as nonindigenous usually requires a judgment call
based on incomplete data. We suggest that researchers in the United States and Canada may be
more likely to classify a species as nonindigenous than their Asian counterparts. One indicator of
such an effect is the regional difference in the number of provisional species (species not yet
identified to species) classified as nonindigenous. There were 31 provisional species classified as
NIS in the NEP (8.4% of total NIS) and 22 provisional species classified as NIS in Hawaii (6.3%
of total NIS). In comparison, there were only two provisional species classified as NIS in the
NWP (0.95% of total NIS). This disparity in the number of species with unknown identities and
origins classified as nonindigenous is suggestive of a different viewpoint as to what constitutes
sufficient information to classify a species.
4) Differences in the number of taxonomic groups evaluated in detail for nonindigenous species.
A factor related to search effort is the difference in the number of taxonomic groups that have
been evaluated in detail for the presence of NIS. In the NEP, nearly every taxonomic group has
been evaluated for nonindigenous species to some degree. It is our impression that in Asia most
of the effort has focused on larger taxonomic groups, especially those with economic value.
Support for this theory comes from the observation that groups with a relatively large number of
NIS in the NWP include taxa important to aquaculture (brown and green macroalgae and fishes,
Figures 29, 31, and 57) or have direct negative economic impacts (barnacles, Figure 52). In
comparison there are relatively few nonindigenous polychaetes reported from the NWP (Figure
42). Although there have been a number of studies on Japanese polychaetes (e.g., Imajima and
Hartman, 1964) our evaluation of this literature is that it focused on the taxonomy and natural
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