SARSIA high-occurrence season

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					Feeding of capelin (Mallotus villosus) in Newfoundland waters
Richard L. O’Driscoll, Morag J.D. Parsons & George A. Rose

SARSIA                  O’Driscoll RL, Parsons MJD, Rose GA. 2001. Feeding of capelin (Mallotus villosus) in Newfound-
                        land waters. Sarsia 86:165-176.

                        The diet of capelin (Mallotus villosus Müller) from six areas off the Newfoundland and Labrador
                        coast was compared over three seasons (January, May-June, August-September) in 1999. A total of
                        1247 stomachs were examined. Of these, 837 (67 %) contained food. The proportion of empty stom-
                        achs was higher in winter (55 %) than in spring (28 %) or autumn (20 %). Copepods were the major
                        prey over all areas and seasons, occurring in 90 % of non-empty stomachs. Hyperiid amphipods,
                        euphausiids, larvaceans and chaetognaths were also important, occurring in 30 %, 11 %, 9 % and 7 %
                        of non-empty stomachs respectively. The importance of these other prey groups increased with in-
                        creasing capelin size. Larger capelin contained larger prey. There were also spatial and temporal
                        differences in diet. Capelin from Placentia Bay, southeastern Newfoundland, consumed smaller
                        copepods and a higher proportion of amphipods than capelin from other areas. Diet composition,
                        particularly the incidence of lipid-rich Calanus species, may influence capelin growth.

                        Richard L. O’Driscoll*, Morag J.D. Parsons, & George A. Rose, Fisheries Conservation, Fisheries and
                        Marine Institute, Memorial University of Newfoundland, P.O. Box 4920, St. John’s NF, Canada A1C 5R3.
                        *Present address: National Institute of Water and Atmospheric Research (NIWA), PO Box 14-901,
                        Kilbirnie, Wellington, New Zealand.

                        Keywords: Capelin; Mallotus villosus; diet; feeding; growth; Newfoundland.

                                                               sons. This is the most extensive quantitative account of
                                                               the diet of capelin from Newfoundland waters to date.
Capelin (Mallotus villosus Müller) are an important            Such information is important for understanding the role
component of many northern marine ecosystems. In               of capelin in the Northwest Atlantic ecosystem and al-
waters off Newfoundland and Labrador capelin are a             lows comparison with recent feeding studies from other
key forage species for many species of marine mam-             northern regions (e.g. Iceland, Astthorsson & Gislason
mals (e.g. humpback whale Megaptera novaeangliae               1997; Barents Sea, Ajiad & Pushchaeva 1992; Bering
Borowski, harp seal Phoca groenlandica Fabricius),             Sea, Naumenko 1984).
seabirds (e.g. murres Uria spp., Atlantic puffin Frater-
cula arctica L.) and fish (e.g. Atlantic cod Gadus             MATERIAL AND METHODS
morhua L., Greenland halibut Reinhardtius hippo-
glossoides Walbaum), as well as supporting a moder-            SAMPLE COLLECTION
ate (quota ~30 000 tons in 1999) commercial fishery.           Capelin were sampled using either a Campelen 1800
  Despite their central role as a link between zoo-            bottom-trawl or an International Young Gadoids Pelagic
plankton production and higher trophic levels (Bundy           Trawl (IYGPT) mid-water-trawl during acoustic-trawl
& al. 2000), relatively little is known about feeding of       research surveys in winter (January), spring (May-June)
capelin in the Northwest Atlantic. Several studies             and autumn (August-September) 1999. Both trawls
(Templeman 1948; Kovalyov & Kudrin 1973; Chan &                were fitted with a cod-end liner with a mesh size of 13
Carscadden 1976; Marchand & al. 1999) describe                 mm. Fishing times were between 15-30 min. Tow depth
capelin diet in general terms, but only Vesin & al. (1981)     ranged from near surface (~20 m) to 300 m.
and Gerasimova (1994) provide quantitative accounts              Samples were collected at sites across the Northeast
of prey composition across a range of capelin sizes.           Newfoundland and Labrador Shelf and within major
These two studies were restricted spatially (western Gulf      bays on the northeast and southeast coast (Fig. 1). Six
of St. Lawrence, Vesin & al. 1981; Grand Banks,                key areas were identified corresponding to the location
Gerasimova 1994) and the work of Gerasimova (1994)             of acoustically detected concentrations of capelin (Fig.
was only in the spring (April-May).                            1). Two areas (Northeast Grand Bank and Labrador)
  In this paper we present information on capelin diet         were sampled in all three seasons, two areas (Trinity
over a broad geographical area and across three sea-           Bay and Placentia Bay) were sampled in winter and
166                                             Sarsia 86:165-176 – 2001

                                                                  Stomach contents from formaldehyde-preserved sam-
                                                                ples were washed and then examined under a dissect-
                                                                ing microscope. Contents were sorted into major taxo-
                                                                nomic groups (usually class or order, e.g. copepods,
                                                                amphipods, euphausiids, larvaceans, pteropods, chaeto-
                                                                gnaths, fish larvae, etc) and counted. The prey group
                                                                that contributed the greatest volume of the diet (meas-
                                                                ured by displacement) of each individual was noted.
                                                                Weights of stomach contents were not recorded because
                                                                a suitably sensitive balance was not available. Intact
                                                                prey items were measured to the nearest 0.1 mm. Total
                                                                lengths were measured for all groups except copepods
                                                                where prosome length was measured. It was impossi-
                                                                ble to obtain sizes for some groups (e.g. larvaceans,
                                                                pteropods) because of digestion and distortion. When
                                                                more than 50 intact copepods were present in the stom-
Fig. 1. Location of trawl stations where capelin samples were
collected in winter (squares), spring (circles) and autumn      ach a random sample of 50 was selected and measured.
(stars) 1999. Six key areas are indicated.                        Approximately 10 % of stomach samples were se-
                                                                lected based on the prey composition and degree of di-
                                                                gestion (only relatively undigested samples were se-
spring only, and the remaining two areas (Avalon Pe-            lected) for more detailed identification. In these sam-
ninsula and Funk Island Bank) were only sampled in              ples, prey items were identified to the lowest possible
one season (spring and autumn respectively). Samples            taxonomic level (usually genera). The range of sizes of
from four other sites outside these key areas were also         each taxon present in the stomach contents was re-
examined (Fig. 1).                                              corded.
   A random sample of 200 capelin was measured from
                                                                STATISTICAL ANALYSIS
each trawl. From this sample a subsample of up to five
fish per 10-mm length class was selected for stomach            It was difficult to formally compare capelin diet between
analysis. Because of spatial differences in length com-         seasons and locations because of differences in the size
position of catches, it was seldom possible to obtain           of fish from different areas. Differences in capelin size
five fish from each available length class in every catch.      will confound seasonal and spatial patterns because of
In winter and autumn, the abdominal wall of each                length related selectivity of prey (see Results).
capelin selected for stomach analysis was slit and then            We used diet information from all samples combined
the whole fish was preserved in 4 % formaldehyde-               and observed length frequency distributions to calcu-
seawater solution for later dissection and analysis. In         late the expected proportion of stomachs from each area/
spring, stomachs of selected fish were dissected at sea         season containing a prey group. For example, over all
and preserved in 4 % formaldehyde-seawater solution.            areas 30 % of non-empty stomachs from capelin 130-
A further subsample of up to five fish per 10-mm length         139 mm in length contained hyperiid amphipods. Four-
class from each trawl was frozen for subsequent otolith         teen capelin with non-empty stomachs from Trinity Bay
removal and ageing.                                             spring samples were in this length range. If diet was
                                                                similar over all areas and locations we would expect
SAMPLE ANALYSIS                                                 0.3(14) = 4 capelin in the 130-139 mm length class from
Total length, weight, sex, maturity and stomach full-           Trinity Bay spring samples to contain hyperiids. Math-
ness (on a scale of 0-4 where 0 is empty and 4 is full,         ematically, expected occurrence of prey group f in area
Chan & Carscadden 1976) were assessed for all sub-              a and season s, Efsa was calculated as:
sampled capelin (i.e. up to ten fish per 10-mm length
class). Where appropriate total length (from tip of the                                       x
mandible to the end of the ventral lobe of the tail) was                           E fsa =          p fi nasi
corrected for shrinkage during preservation or freez-                                        i =1
ing. Thawed lengths of frozen fish were converted to
fresh lengths by multiplying by a factor of 1.03 (Win-          Where pfi was the overall proportion of stomachs in 10
ters 1982). Lengths of whole fish preserved in formalin         mm length class i (i = 1,2,3 … x) that contain prey group
where multiplied by a factor of 1.05 (our unpublished           f and nasi was the number of capelin samples from fish
data).                                                          in length class i from area a and season s. The pfi was
                                             O’Driscoll – Capelin feeding                                             167

expressed as a proportion of non-empty stomachs ex-            (Table 3). Hyperiid amphipods (Themisto spp.),
cept for empty stomachs (pempty,i) where it was the pro-       euphausiids (Thysanoessa spp.), larvaceans (Oikopleura
portion of total stomachs in length class i.                   sp.) and chaetognaths (Sagitta sp.) were also important
  Expected values of prey occurrence Efsa were com-            in capelin diet, occurring in 30 %, 11 %, 9 % and 7 %
pared to observed values using a two-sided binomial            of non-empty stomachs respectively (Table 2). Several
test of proportions (Freund 1988). The null hypothesis         other groups were present in a small proportion (< 5 %)
that diet was similar over all areas and seasons was re-       of stomachs (Tables 2-3).
jected if a prey group was observed significantly more
                                                               LENGTH RELATED SELECTIVITY OF PREY
or less frequently than expected. The test assumes that
individual capelin stomachs were statistically independ-       Capelin lengths ranged from 72-193 mm. There was
ent samples. This assumption may be violated where             strong evidence for differences in selectivity of prey
capelin were taken from the same trawl catch, so p-            related to capelin length (Fig. 2). Larger prey items such
values should be treated with caution.                         as hyperiid amphipods, mysids, larvaceans, pteropods
  To examine seasonal and spatial variation in the size        and fish larvae occurred more frequently in the stom-
composition of copepods in capelin diet, copepod sizes         achs of larger capelin. Smaller prey like molluscan lar-
were first standardised by capelin length. A linear re-        vae, fish eggs and diatoms were eaten by smaller
gression was fitted to a plot of log-transformed copepod       capelin. Copepods and euphausiids were consumed by
prosome lengths as a function of log-transformed               all lengths of capelin (Fig. 2). Both copepods and
capelin length. Residuals about this fitted regression         euphausiids occurred in a wide range of sizes in the
provided a standardised measure of copepod size inde-          diet (Table 3) due to the presence of different species of
pendent of capelin length. Non-parametric Mann                 copepods and different developmental stages of cope-
Whitney and Kruskal Wallis tests (Freund 1988) were            pods and euphausiids. There was also evidence for se-
then used to compare standardised copepod sizes be-            lection within prey groups, with larger capelin eating
tween areas and seasons. Kruskal Wallis tests were also        larger individuals. This selectivity was particularly clear
used to compare the size (length-at-age) of capelin be-        for copepods (Fig. 3).
tween areas.                                                   SEASONAL AND SPATIAL DIFFERENCES IN DIET
                                                               There were spatial and seasonal differences in capelin
RESULTS                                                        diet (Fig. 4). In general the proportion of empty stom-
DIET COMPOSITION                                               achs was lower in spring (28 %) and autumn (20 %)
                                                               than in winter (55 %), but in some areas (Labrador and
A total of 1247 stomachs from 48 trawl samples were
examined (Table 1). Of these 837 (67 %) contained food.
Copepods were the dominant prey over all capelin
                                                               Table 2. Frequency of occurrence and importance of prey
lengths, sites and seasons, occurring in 90 % of non-          groups from the stomachs of capelin caught in Newfoundland
empty stomachs and being the major prey by volume in           waters in winter, spring and autumn 1999. Occurrence is the
69 % of non-empty stomachs (Table 2). The most com-            number of non-empty stomachs that contained a prey group.
mon genera of copepods identified from a subset of             Dominance is the number of stomachs in which the prey group
capelin stomachs were Calanus, Metridia, and Temora            contributed the highest volume of stomach contents. Total
                                                               number of stomachs examined (Table 1) was 1247.
                                                                   Prey Group              Occurrence     Dominance
Table 1. Summary of samples used to examine seasonal and           Copepods                   753            578
spatial differences in capelin diet in Newfoundland waters.        Hyperiid Amphipods         248            145
First number in each cell is the number of individual stom-        Euphausiids                 95             42
achs analysed. Second number (in parentheses) is the number        Larvaceans                  79             31
of trawl sets from which stomach samples were taken. Area          Chaetognaths                61              9
locations are shown in Fig. 1.                                     Molluscan larvae            42              0
                                                                   Pteropods                   33              7
                          Winter       Spring      Autumn
                                                                   Fish larvae                 21             14
Labrador                  70   (9)    102   (3)     90   (2)       Cirripedian larvae          19              0
Funk Island Bank           0            0           90   (3)       Mysids                      15              5
Trinity Bay               31   (1)    126   (4)      0             Brachyuran larvae            8              0
Avalon Peninsula           0           55   (2)      0             Cladocerans                  7              2
Northeast Grand Banks     63   (2)     90   (3)     29   (1)       Fish eggs                    7              0
Placentia Bay            107   (3)    298   (11)     0             Diatoms                      6              0
Other                     37   (1)      0           59   (3)       Empty                      410            410
168                                           Sarsia 86:165-176 – 2001

Northeast Grand Banks) the level of feeding remained          tion of independent samples (see Material and Meth-
low (> 50 % of stomachs empty) in spring. Copepods            ods), Table 4 provides useful information about spatial
were an important prey in all areas and all seasons, but      and seasonal variation in diet taking into account dif-
other groups contributed a higher volume of the diet at       ferences in capelin size. For example, capelin from
specific times and locations. For example larvaceans          Labrador in winter had a relatively high proportion of
were the dominant prey in 49 % of capelin stomachs            empty stomachs (Table 4). In non-empty stomachs the
from the Avalon Peninsula in spring (Fig. 4).                 occurrence of copepods and larvaceans in Labrador
   Table 4 compares expected values of prey occurrence        winter samples was lower than expected, while the pro-
(Efsa) to observed values. Although significance levels       portion containing euphausiids was higher than expected
should be treated with caution because of the assump-         (Table 4). In contrast, capelin from the Avalon Penin-
                                                              sula in spring had lower proportions of empty stom-
                                                              achs and stomachs containing euphausiids than ex-
                                                              pected, but relatively high occurrence of copepods,
Table 3. Taxa identified from each of the prey groupings in
                                                              larvaceans and pteropods (Table 4).
Table 2. The season (W = winter, S = spring, A = autumn) in
which each genera was recorded and range of sizes found in
                                                                 There was also seasonal and spatial variation in the
capelin stomachs are also given.                              size composition of copepods in capelin stomachs. Fig-
                                                              ure 5 shows the linear regression between log-trans-
Prey group                      Season    Size range (mm)
                                                              formed copepod prosome lengths and log-transformed
Copepods                                                      capelin lengths used to standardise copepod size and
   Calanus spp.                 W,S,A          1.5-7.2*       account for length related selectivity (Fig. 3). Residuals
   Centropages sp.              A              0.8-1.0*
                                                              about this fitted regression were used to examine sea-
   Euchaeta sp.                 S              -
   Metridia sp.                 W,S,A          1.0-2.7*       sonal and spatial patterns in copepod size independent
   Microcalanus sp.             S              0.5-0.9*       of differences in capelin length (Fig. 6).
   Paracalanus sp.              S              0.9-1.2*          In the two areas which were sampled in all three sea-
   Pseudocalanus sp.            S,A            0.6-2.0*       sons (Labrador and Northeast Grand Banks) there were
   Temora spp.                  W,S,A          0.5-1.1*       significant seasonal differences in the size of copepods
Hyperiid Amphipods                                            in capelin stomachs (Kruskal Wallis tests: Labrador, χ2 =
   Themisto spp.                W,S,A          1.5-18.2       9.2, d.f = 2, p = 0.01; Northeast Grand Banks, χ2 = 14.0,
                                                              d.f = 2, p = 0.001). The decrease in the size of copepods
   Thysanoessa spp.             W,S,A          1.7-27.3
Cladocerans                                                   in capelin stomachs between winter and spring in these
   Podon sp.                    A              0.8-1.1        two areas and also in Trinity Bay (Fig. 6) was largely
Mysids                                                        due to transition in the diet from large overwintering
   Unidentified                 W,S            5.5-22.6       Calanus spp. (copepodite V-VI) to smaller, earlier de-
Brachyuran larvae                                             velopmental stages (copepodite I-V) of the next Calanus
   Unidentified                 S,A            -              generation.
Cirripedian larvae                                               Capelin from Placentia Bay fed on smaller copepods
   Unidentified cyprids         W,S            -
                                                              during the winter than capelin from other areas (Fig. 6,
   Unidentified nauplii         S              0.4-0.5
Larvaceans                                                    Kruskal Wallis test, χ2 = 48.2, d.f = 3, p < 0.001). Ex-
   Oikopleura sp.               S              -              amination of identified samples showed Temora spp.
Pteropods                                                     and Metridia spp. were much more abundant than
   Limacina sp.                 S,A            -              Calanus spp. in the winter diet of Placentia Bay capelin.
Molluscan larvae                                              The proportion of Calanus in the diet of capelin in
   Unidentified Prosobranchs    W,S,A          0.2-0.6        Placentia Bay increased in the spring, and this was re-
   Unidentified Lamellibranch   A              0.2            flected in the increased size of copepods observed in
                                                              stomachs in spring compared to winter (Fig. 6, Mann
   Sagitta sp.                  W,S,A          19.0-30.0
Fish larvae                                                   Whitney U test, U = 924, Z = –5.56, p < 0.001). De-
   Ammodytes sp.                S              32.4-46.9      spite the increase of importance of Calanus in spring,
   Gadus morhua L.              S              12.2-20.0      the diet of capelin in Placentia Bay still consisted of
Fish eggs                                                     smaller copepods than in other areas (Fig. 6, Kruskal
   Unidentified                 S,A            -              Wallis test χ2 = 71.5, d.f = 4, p < 0.001). This was be-
Diatoms                                                       cause few large Calanus (copepodite V) were observed
   Unidentified                 W,S,A          0.1-0.2        in capelin stomachs from Placentia Bay in spring and
*Copepod lengths are prosome lengths only. Lengths of all     there was a higher proportion of smaller species such
other prey items are total lengths.                           as Metridia, Temora and Pseudocalanus than in other
                                           O’Driscoll – Capelin feeding                                                 169

                                               Fig. 2. Length related selectivity of prey groups by capelin. Length frequency
                                               of capelin from which stomachs were analysed is shown in the top left panel.
                                               Percentage occurrence of empty stomachs (second panel in left column) is
                                               the proportion of all stomachs within a 10-mm length class that contained no
                                               food. In all remaining panels percentage occurrence is the proportion of non-
                                               empty stomachs within a length class that contained a particular prey group.

areas. Perhaps because of the paucity of large copepods,      winter capelin from Labrador were larger than fish from
larger capelin from Placentia Bay fed mainly on hyperiid      Trinity Bay, Northeast Grand Banks and Placentia Bay
amphipods in spring. Fifty six percent of non-empty           (Fig. 7). By the spring, capelin from Labrador, Trinity
stomachs from large (> 140 mm) capelin sampled in             Bay, Northeast Grand Banks and the Avalon Peninsula
Placentia Bay in spring were dominated by amphipods           were similar in length (Fig. 7), indicating more rapid
compared to 20 % of stomachs where copepods were              growth in Trinity Bay and the Northeast Grand Banks
dominant. In other areas copepods remained important          than in Labrador or movement of larger fish into these
for larger capelin. For example, in Trinity Bay in spring     areas from the north. Capelin from Placentia Bay were
copepods were the dominant item in 70 % of non-empty          generally similar in size to fish from Trinity Bay and
stomachs from capelin > 140 mm.                               the Northeast Grand Banks in winter, but were signifi-
                                                              cantly smaller than capelin from all other areas in spring
SEASONAL AND SPATIAL DIFFERENCES IN CAPELIN SIZE              (Fig. 7). Autumn age data are not presented because
There were spatial differences in length-at-age of capelin    sample sizes were small and it was difficult to separate
(Fig. 7). In all areas size of capelin increased between      immature, maturing and recovering (spent) fish in au-
winter and spring, consistent with growth (Fig. 7). In        tumn samples.
170                                            Sarsia 86:165-176 – 2001

Fig. 3. Length related selectivity of copepods by capelin. Eight panels show percentage occurrence of eight 1-mm size classes
of copepods based on measurements of prosome length. Occurrence of each copepod size class is expressed as a percentage of
stomachs within a 10-mm capelin length class that contained copepods of any size (Fig. 2).


Diet composition of capelin from Newfoundland wa-               1997; this study) and may also vary interannually
ters in 1999 was broadly similar to that reported in pre-       (Gerasimova 1994), seasonally (Vesin & al. 1981;
vious feeding studies in the Northwest Atlantic                 Astthorsson & Gislason 1997; this study) and spatially
(Templeman 1948; Kovalyov & Kudrin 1973; Chan &                 (Naumenko 1984; this study).
Carscadden 1976; Vesin & al. 1981; Gerasimova 1994;                Euphausiids were less important in this study than
Marchand & al. 1999) and in other northern regions              previously reported, occurring in only 11 % of non-
(Naumenko 1984; Ajiad & Pushchaeva 1992; Huse &                 empty capelin stomachs. This proportion was lower than
Toresen 1996; Astthorsson & Gislason 1997). In this             in earlier studies of capelin diet in Newfoundland wa-
study, as in previous work, the diet was dominated by           ters. Kovalyov & Kudrin (1973) recorded euphausiids
copepods particularly Calanus spp. Other groups were            in 44 % of stomachs with food in March-June 1972,
also present including hyperiid amphipods, euphausiids,         while Gerasimova (1994) found euphausiids in 11-28 %
larvaceans and chaetognaths. The contribution of these          of non-empty capelin stomachs from the Grand Banks
other groups appears to increase with capelin size (Vesin       in April-May 1987-1990. In other areas euphausiids
& al. 1981; Ajiad & Pushchaeva 1992; Gerasimova                 seem to play an even more important role in capelin
1994; Huse & Toresen 1996; Astthorsson & Gislason               diet, making up 80-90 % of the diet (by weight) in parts
                                              O’Driscoll – Capelin feeding                                               171

Fig. 4. Seasonal and spatial differences in importance of major prey groupings from six areas in Newfoundland waters. Area
locations are shown in Fig. 1 and sample sizes are provided in Table 1. Missing bars indicate no samples were collected.
Percentage dominance is the proportion of stomachs in which the prey group contributed the highest volume of stomach contents.

of the Bering Sea (Naumenko 1984) and over 95 % of              foundland waters by Kovalyov & Kudrin (1973), but
the stomach content weight of large (12-14.9 cm) cape-          higher than previously observed on the Grand Banks
lin in the Barents Sea (Ajiad & Puschaeva 1992). Con-           (5-15 % of non-empty stomachs, Gerasimova 1994) and
versely, hyperiid amphipods were a relatively impor-            also higher than in other northern regions (e.g. Iceland,
tant contributor to the diet of capelin in this study, oc-      Astthorsson & Gislason 1997).
curring in 30 % of non-empty stomachs. This was simi-              Previous studies in Newfoundland waters (Temple-
lar to the proportion reported for capelin from New-            man 1948; Kovalyov & Kudrin 1973; Gerasimova 1994)
172                                             Sarsia 86:165-176 – 2001

Fig. 5. Relationship between log-transformed copepod length
and log-transformed capelin length.

have reported cannibalism of capelin eggs and larvae.
For example, Templeman found capelin eggs made up
~90 % of the diet of spawning and post-spawning
capelin sampled near-shore. No identifiable capelin eggs         Fig. 6. Seasonal and spatial variation of copepod sizes in
or larvae were observed in capelin stomach contents              capelin stomachs. Standardised copepod sizes are residuals
examined in this study. Cannibalism is probably only             about the fitted regression in Fig. 5 and so are corrected for
                                                                 capelin length selectivity. Boxes show 25th to 75th percen-
important in spawning areas during or immediately fol-
                                                                 tiles divided by the median. Whiskers show the range of sizes.
lowing spawning.                                                 W = winter, S = spring and A = autumn.
  The seasonality of capelin feeding observed in New-
foundland waters in 1999 was consistent with previous
reports (Chan & Carscadden 1976; Vesin & al. 1981;               sonal pattern in capelin feeding was probably related to
Astthorsson & Gislason 1997). Levels of feeding were             seasonal patterns in abundance of zooplankton prey.
lower in winter than in spring and autumn. The sea-              Continuous plankton recorder (CPR) records from the

Table 4. Spatial and seasonal differences in composition of capelin diet in Newfoundland waters. Symbols indicate whether
occurrence of a prey group in capelin stomachs was higher (+), lower (–), or the same (0) as expected occurrence assuming
equal availability of prey across time and space. Expected occurrences were calculated based on overall size selectivity of prey
groups (Fig. 2) and observed length frequencies of capelin in each area and season. Significance levels were based on two-sided
binomial tests of probability (*** = p < 0.001, ** = p < 0.01, * = p < 0.05, NS = p > 0.05). There was no correction applied for
multiple tests.
Area           Season      Empty                Hyperiids             Larvaceans          Molluscan Chaeto-             Fish
                                     Copepods               Euphausiids          Pteropods larvae   gnaths             larvae
Labrador       Winter       + ***      – ***       – NS       + ***       –*         – NS        – NS       – NS       – NS
               Spring       + ***      + NS        + NS       0 NS        –*         + ***       + NS       – NS       0 NS
               Autumn       – ***      +*          + NS       + NS        –*         – NS        – NS       – NS       – NS
Funk Island    Autumn       – NS       + NS        – **        – NS       – **       – NS        + **       + ***      – NS
Trinity Bay    Winter       + ***      – **        + NS       – NS        – NS       0 NS        – NS       – NS       0 NS
               Spring       – NS       + ***       – ***      + NS        + NS       + NS        – NS       –*         + NS
Avalon         Spring       – ***      +*          + NS        – **       + ***      + ***       0 NS       – NS       – NS
NE Grand       Winter       + NS       + NS        –*         – NS        – NS       – NS        – NS       + **       0 NS
Banks          Spring       + ***      + NS        – ***      –*          + NS       – NS        0 NS       0 NS       – NS
               Autumn       0 NS       + NS        + ***      + **        – NS       0 NS        + NS       – NS       0 NS
Placentia      Winter       + ***      0 NS        – NS       – NS        – NS       0 NS        + NS       – NS       0 NS
Bay            Spring       – ***      – ***       + ***      + NS        – ***      – ***       –*         +*         + ***
                                      O’Driscoll – Capelin feeding                                                 173

Fig. 7. Spatial variation in mean length-at-age of capelin in Newfoundland waters in winter (January) and
spring (May-June). Error bars are + 2 SE. Plots are segregated by sex and maturity because there are differences
in size between these groupings (Winters 1982). LA = Labrador, TB = Trinity Bay, NG = Northeast Grand
Banks, AP = Avalon Peninsula, PB = Placentia Bay. Significance levels from non-parametric Kruskal Wallis
tests are shown in the upper right of each plot (*** = p < 0.001, ** = p < 0.01, * = p < 0.05, NS = p > 0.05).
174                                           Sarsia 86:165-176 – 2001

Northwest Atlantic show most zooplankton species ex-          larger-at-age in the spring than fish from Placentia Bay.
hibit peak abundance in the spring or autumn, with               Skjoldal & al. (1992) reported an interaction between
greatly reduced abundance during the winter (Myers &          zooplankton biomass (particularly Calanus finmarch-
al. 1994). The timing of seasonal cycles in zooplankton       icus Gunnerus), water temperature and capelin growth
abundance varies between regions (Myers & al. 1994).          in the Barents Sea. Low abundance of C. finmarchicus
The relatively low levels of capelin feeding we observed      in 1984 following an inflow of warm Atlantic water into
off Labrador and on the Northeast Grand Banks in May-         the Barents Sea contributed to low capelin growth rates
June 1999 may reflect delayed development of zoo-             and a decline in capelin abundance. Recovery of zoo-
plankton biomass in these regions relative to areas fur-      plankton abundance in the late 1980s was accompanied
ther inshore and to the south (Trinity Bay, Avalon Pe-        by an increase in capelin growth and biomass (Skjoldal
ninsula and Placentia Bay).                                   & al. 1992).
   Temporal and spatial differences in capelin diet prob-        Similar large-scale fluctuations in growth and abun-
ably reflect the underlying composition of the zoo-           dance of capelin have been observed in Newfoundland
plankton (Astthorsson & Gislason 1997). We did not            waters in the 1990s. Since 1991 the mean length of ma-
collect zooplankton samples, but most common zoo-             ture age 3 and 4 capelin has decreased and the propor-
plankton taxa reported from Newfoundland waters               tion of fish mature at age 2 has increased resulting in a
(Strong 1981) were found in capelin stomachs. An ex-          decrease in the size of spawning capelin compared to
ception was the cyclopoid copepods. Cyclopoids, par-          the 1980s (Nakashima 1994; Carscadden & Nakashima
ticularly Oithona similis Claus, were relatively abun-        1997). This reduction in size in the early 1990s occurred
dant in zooplankton samples collected over the New-           during a period of cooler water temperatures (Naka-
foundland Shelf (Strong 1981; Pepin & Maillet 2000)           shima 1994), but the size of spawning adult capelin has
but were not observed in capelin stomachs during this         remained low in the late 1990s despite warming waters
study. Oithona similis were present in the diet of larval     (DFO 2000). The spatial distribution of capelin off New-
(5-14 mm) capelin from Newfoundland waters (Pepin             foundland also changed dramatically in the early 1990s
& Penney 1997), suggesting that their absence in this         (review by Carscadden & Nakashima 1997). Acoustic
study may be related to the limited length range of fish      surveys, bottom-trawl surveys and cod-stomach-con-
sampled.                                                      tent analysis all showed a shift in the distribution of
   The small size-at-age of capelin from Placentia Bay        capelin towards the south and east. Capelin virtually
and the relatively large size-at-age of capelin from Lab-     disappeared from the northern part of their range off
rador contradict the earlier observations of Winters          Labrador (Carscadden & Nakashima 1997). At the same
(1982) that capelin growth increased with increasing          time capelin increased in areas such as the Flemish Cap
water temperature from north to south. Differences in         and Scotian Shelf where they were not common previ-
length-at-age between Placentia Bay capelin and capelin       ously (Frank & al. 1996). Capelin biomass in acoustic
from other regions may be related to spatial variation        surveys on the Northeast Newfoundland Shelf declined
in diet, particularly in the consumption of Calanus spp.      dramatically in 1990-1991 and has remained low
Calanus species at high latitudes accumulate large re-        (O’Driscoll & al. 2000).
serves of lipids (mainly wax esters) in oil sacs (Sargent        We hypothesise that observed changes in capelin
& Falk-Petersen 1988). Early copepodite stages have           growth in Newfoundland waters may be related in part
relatively low levels of lipid, and most deposition of        to spatial distribution and prey availability. Zooplankton
wax esters occurs during stages IV and V (Sargent &           biomass in autumn is highest over the deep channels
Falk-Petersen 1988). As a result of this accumulation         and shelf break of the northern Newfoundland shelf
of lipid, large late-stage Calanus have a higher energy       (Anderson & Dalley 1997; Dalley & al. 2000). Biomass
content (J g–1) than earlier stages of Calanus (e.g. Comita   is lower to the south, especially on the plateau of Grand
& al. 1966), other copepod species (e.g. Laurence 1976),      Banks (Anderson & Dalley 1997; Dalley & al. 2000).
and other zooplankton groups (e.g. Williams & Robins          The composition of the zooplankton also varies between
1979). In Placentia Bay, where capelin were relatively        areas (Pepin & Maillet 2000). Summer zooplankton
small, few large Calanus were observed in capelin stom-       communities in northern areas tended to contain a higher
achs. Late-stage Calanus spp. are also rare in zooplank-      proportion of Calanus than communities further south,
ton samples collected in Placentia Bay during spring          that were dominated by smaller copepods (Pepin &
and summer (Paul Snelgrove pers. commn). In other             Maillet 2000). A southerly distribution of capelin, as
areas (Trinity Bay, Avalon Peninsula, Northeast Grand         observed in the 1990s, may have resulted in poorer feed-
Banks, Funk Island Bank, Labrador) Calanus with vis-          ing conditions (especially a reduction in the availabil-
ible oil droplets were common, particularly in the diet       ity of high lipid Calanus spp.) and reduced growth. Un-
of larger capelin. Capelin from these other areas were        fortunately no suitable time series of zooplankton abun-
                                               O’Driscoll – Capelin feeding                                                 175

dance are currently available to allow us to test this hy-        ACKNOWLEDGEMENTS
                                                                  We thank all the sea-going scientific staff and crew of the
   Spatial distribution of capelin in Newfoundland wa-            CCGS Teleost, especially John Anderson and Fran Mowbray.
ters appears to be returning to a more northern distribu-         Phil Eustace aged the capelin samples. Gary Maillet, John
tion (DFO 2000). In 1998 and 1999 capelin were ob-                Anderson, Pierre Pepin and three anonymous reviewers pro-
served in significant quantities in spring and autumn             vided useful comments on this manuscript. Funding for this
acoustic surveys off southern Labrador for the first time         work came from the NSERC Industrial Chair in Fisheries
since 1990 (O’Driscoll & al. 2000). We are monitoring             Conservation and from a New Zealand Foundation for Re-
the influence of these changes on capelin biology and             search, Science and Technology Post-Doctoral Fellowship held
                                                                  by the first author.


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Description: SARSIA high-occurrence season