Vol.3, No.4, 295-298 (2013) Open Journal of Animal Sciences
Composition and distribution of the European green
crab in Prince Edward Island, Canada
Mary A. McNiven1*, Pedro A. Quijon2, Alfred W . Mitchell1, Aaron Ramsey3, Sophie St-Hilaire1
1Atlantic Veterinary College, University of PEI, Charlottetown, Canada; *Corresponding Author: mmcniven@upei.ca
2Deptartment of Biology, University of PEI, Charlottetown, Canada
3PEI Department of Fisheries, Aquaculture & Rural Development, Montague, Canada
Received 25 July 2013; revised 26 August 2013; accepted 15 September 2013
Copyright © 2013 Mary A. McNiven et al. This is an open access article distributed under the Creative Commons Attribution Li-
cense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The European green crab (Carcinusmaenas) is a
non-native invasive species to North America
which has been found in the north-western At-
lantic Ocean since the nineteenth century. In
Prince Edward Island Canada, this species has
been steadily increasing over the last 10 years,
especially in estuaries found on the eastern and
southern coasts. Our chemical analysis of the
whole green crab determined that it was high in
protein and ash, and low in lipid content. We
also found the chemical composition varied only
slightly for different sized crabs (40 to 70 mm)
over the six-month sampling period, suggesting
this species could be harvested any time be-
tween May and Oct ober.
Keywords: European G reen Crab; Catch Per Day;
Chemical Analysis; Invasive Species
The European green crab (Carcinusmaenas) is a non-
native invasive species to North America which has been
found in the north-western Atlantic Ocean since the nine-
teenth century [1]. The green crab has flourished in
North America because it is able to tolerate a wide range
of water temperatures and salinities and live in many
types of marine habitats [2]. This species of crab is a
voracious predator that feeds on a variety of prey in-
cluding soft shell clams, quahogs, mussels, and oysters
[3,4]. In addition, the green crab competes with other
crustaceans for nutrient resources and habitat [5,6], and
damages the ecosystem by digging in sediment around
eelgrass beds and disturbing the root systems [7,8].
Culling efforts to control this invasive species have not
been successful to date likely because the efforts were
not sustained, or due to the difficulty in removing all life
stages of the crab by trapping [4,9]. An effective control
of green crab populations on the east coast of Canada
will require intensive trapping over a large spatial scale
for a period of several years. From an economic point of
view, this is not feasible unless potential uses for this
species are identified and the crab can indeed be sold to
subsidize or cover the cost of fishing. Unfortunately,
there is currently no market for the European green crab
in North America although it is a popular food in south-
ern Europe [9]. It is a relatively small crustacean and
although there is an ample supply, it is difficult to eco-
nomically extract the meat so it has not been successfully
marketed in North America.
As crustacean meat extraction technology improves
and its cost decreases, it may be possible to identify mar-
kets for this species. For instance, green crab meat may
be sold for human consumption [10] or be used as a paste
for flavouring in soups, sauces and dips [11], which
would utilize the whole crab eliminating the cost of meat
extraction. It may also be possible to develop non-human
food markets such as the pet or zoo food industry, the
aquaculture feed industry, or as bait for commercial fish-
eries. The potential use of a species for these or other
markets requires information such as body chemical
composition and the distribution of harvestable popula-
tions, none of which is readily available for green crab.
The chemical composition of marine species destined
for human consumption is influenced by nutritional pref-
erences, age, sex, seawater temperature and salinity
[12,13]. For this reason, it is important to document how
the chemical composition of green crab changes over the
course of the season when this species could potentially
be harvested. In addition to the consistency of product
quality, commercial markets require a constant (seasonal)
supply of substantial quantities of crab for which har-
vestable areas must be identified. Hence, the objectives
of our study were to assess the chemical composition of
Copyright © 2013 SciRes. OPEN ACCESS
M. A. McNiven et al. / Open Journal of Animal Sciences 3 (2013) 295-298
the European green crab over a six-month period and to
estimate the distribution of these populations around
Prince Edward Island (PEI), Canada.
2.1. Chemical Composition over Time
In order to assess potential temporal changes, green
crabs were captured in estuaries in eastern PEI on a
monthly basis from May to October 2012 by deploying
five Fukui traps in habitats known to contain green crabs.
Traps were baited with approximately 100 g of mackerel.
After collection, crabs were transported in coolers to the
University of Prince Edward Island, where they were
frozen at 20˚C until chemical analysis was done. All
animal procedures were done in accordance with the
Canadian Council of Animal Care.
Crabs were sorted by carapace size based on the cate-
gories most likely to be fished (40 - 50 mm, 50 - 60 mm,
or 60 - 70 mm). Samples of crabs were prepared by
thawing the samples overnight. The pooled samples of
crabs (five crabs/sample, three replicate samples) were
weighed and dried in an oven at 60˚C until the weight
remained constant (~72 h). Samples were reweighed and
ground using a centrifugal grinder (Retsch, ZM100) with
a 1 mm screen. Samples were analyzed for dry matter,
ash, nitrogen, and lipid as described by AOAC proce-
dures [14]. All reagents were of analytical grade (Fisher
Scientific, Ottawa, ON, Canada). The proportions of true
protein and chitin were estimated using equations based
on the nitrogen stoichiometric content of chitin and pro-
tein and the measured percentage values of total nitrogen
and non-nitrogen compounds [15]. Results were ana-
lyzed using a two-way analysis of variance with month
of capture and carapace size as the main effects [16].
Differences between means with a P value less than 0.05
were considered to be significant.
2.2. Assessment of Harvestable Populations
In order to document the spatial distribution of poten-
tially harvestable populations, the most recent data from
the PEI Department of Fisheries, Aquaculture, and Rural
Development [17] was compiled and analyzed to esti-
mate catch per unit effort (CPUE). Data came from sam-
ples collected with sets of three cylindrical 61 × 38 cm
coated wire mesh traps with a 5 cm catch opening at 27
sites around PEI between late August and mid October
2012. Traps were placed overnight in estuarine areas 1.5
to 2.5 m deep using herring as bait. Total number of
crabs caught after a three day period was used to calcu-
late CPUE (catch per trap per day).
3.1. Chemical Composition
The actual levels of ash, lipid, and total nitrogen as
well as estimated true protein and chitin levels of green
crabs based on carapace size and month of harvest are
shown in Tabl e 1. In general, differences in composition
Ta b l e 1 . Chemical composition of whole green crab samples (50 - 70 mm carapace width) collected once per month from May to
October 2012. (Means within column and month with different superscripts are significantly different, P < 0.05).
Carapace mm Ash % DM Lipid % DM Nitrogen % DM Protein (est.) % DM Chitin (est.) % DM
40 32.9c 4.67a 5.98a 18.4a 44.0
50 36.1b 3.43b 5.63ab 16.0b 44.5
60 38.0c 3.23b 5.04b 14.8b 43.9
40 34.3b 4.15a 5.66a 15.6a 45.9b
50 38.2a 3.11b 5.25b 13.2a 45.5b June
60 39.5a 2.71b 4.75c 8.44b 49.3a
40 37.9b 2.69a 5.22a 12.3a 47.1b
50 36.6b 3.03a 5.46a 14.3a 46.1b
60 40.3a 1.86b 4.76b 8.52b 49.3a
40 35.9 3.51a 5.37 13.1 47.5
50 36.6 3.37a 5.09 10.5 49.5 August
60 37.2 2.36b 5.26 12.0 48.4
40 35.0b 3.92a 5.36a 12.6a 48.4b
50 36.2b 3.28a 5.42a 13.7a 46.8b
60 40.7a 1.86b 4.52b 6.18b 51.3a
40 36.7 4.26a 5.07 10.9 48.2
50 37.6 2.80b 5.30 13.1 46.4
60 38.6 2.80b 5.03 10.8 47.8
SEM 0.77 0.297 0.13 1.07 0.82
Copyright © 2013 SciRes. OPEN ACCESS
M. A. McNiven et al. / Open Journal of Animal Sciences 3 (2013) 295-298 297
between the sizes of crab were greatest for the first three
months, after which differences due to size were no
longer apparent for the ash, total nitrogen and estimated
protein contents, but remained for the lipid content.
Overall, the groups of crabs sized 40 - 50 mm and 50 -
60 mm were similar in composition, while the larger
crabs, sized 60 - 70 mm, tended to have higher ash and
lower lipid and total nitrogen levels. Differences in the
estimated chitin levels were most pronounced in June,
July, and September only. Generally, the proportions of
total nitrogen, estimated true protein and lipid were
greatest in May, after which they remained relatively
3.2. Assessment of Harvestable Populations
The eastern shore of PEI had the highest green crab
concentration (up to 32 crabs/trap/d) (Figure 1). Al-
though sampling was only conducted on the western part
of the south shore, the catches were higher there than
those on the north shore, but lower than those on the
eastern shore (Figure 1).
The chemical composition of whole green crab sam-
pled from estuaries in eastern PEI (May to October 2012)
suggests that the size of the crabs affects the protein and
fat content more than the month of catch. The larger
crabs had higher levels of ash and lower levels of nitro-
gen and lipid in the first half of the season. These results
may suggest the larger crabs had recently moulted and
had a relatively higher proportion of shell compared to
the smaller crabs, which are consistent with the corre-
sponding estimated chitin content (Tab le 1 ). The chemi-
cal composition, especially fat content, is dependent on
food type and availability [12] and this may vary over
the course of the fishing season.
Figure 1. Green crab daily catch rates (number of crabs/trap/
day) based on three day sampling period for PEI in 2012.
Regardless of the month or size of crab sampled in our
study, the whole crab was generally high in ash and pro-
tein, and low in fat. For most animal feeds, with the pos-
sible exception of poultry feeds, the high ash content of
whole crab may be a limiting factor for use as a primary
feed ingredient. However, the whole crab may be suit-
able for human consumption as nutrient concentration is
less of a concern.
Our assessment of the distribution of green crab and
historical records available [17] suggest that there has
been a large increase in the number of crabs since 1999.
In that year, less than one crab per trap per day was col-
lected in eastern PEI [17]. Using similar gear and tech-
niques, this area is now estimated to have daily catch
rates up to 32 crabs per trap per day. Considering that the
initial invasion of green crabs was detected in this par-
ticular area (Georgetown, PE), our results suggest that
these are well established and still growing populations.
The southern shore of PEI appears to have fewer crabs,
but could still contribute to a commercial fishery. Recent
monitoring of population numbers in the two largest
embayments of this area (Hillsborough and Bedeque
systems) [4] suggests that these populations are increas-
ing in numbers and spreading into areas not previously
colonized. Given the change between 1999 and 2012 in
crab numbers on PEI, and the increase in crabs observed
in other areas of the Canadian Maritime region [2,18],
we anticipate that crab numbers in western and northern
PEI, currently less than one crab per trap per day, will
also increase.
The relatively constant chemical composition during
the six-month fishing season suggests that there is no
ideal time to fish green crab. This makes it possible to
schedule a green crab fishery at a time when seafood
processing plants are idle. However, it may be beneficial
to establish a fishery that enables the removal of some
green crabs earlier in the season before they propagate or
moult. This may maximize the yield of protein and lipid
in crab products and reduce the impact of the crabs on
the environment.
In conclusion, there is a large quantity of green crab
on PEI, particularly along the east coast. The chemical
analysis suggests that whole crab is high in protein and
low in fat. Also, although there were small differences in
protein and fat content over time and by size of crab,
chemical composition can be considered relatively con-
sistent in terms of quality. The whole product is high in
ash, which may limit its utility in some animal feeds, but
may be beneficial for human-grade products such as fla-
vourings for seafood soups, dips and sauces.
We would like to thank Cassandra Mellish and Paula Tumon-Flynn
and the PEI Shellfish Association for their help with the collection of
Copyright © 2013 SciRes. OPEN ACCESS
M. A. McNiven et al. / Open Journal of Animal Sciences 3 (2013) 295-298
green crabs. This project was funded by an Innovation PEI Pilot and
Discovery Grant (2012).
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