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$Wetenschap - \Nijverheid- Handel$

this was indeed so (Table 2): in Macoma the ratio was 3.3. Thus, faecal analysis confirmed the visual observations of prey seleciion. Size selection Estimates of prey size made by eye in me field suggesied Knot took Macoma between 3/4 and 2 cm long, but faecal analysis showed that the size range was narrower (0.9 to 1.6 em: Fig. 4). It appears lhat the observers overestimated the sizes of the larger prey and underestimated those of the smaller ones. In order to correct ihe visual estimates, a cumulative frequency distribution was made of the size classes found in the faeces. This allowed the average size of the six categories used for estimating prey size visually in the field to be superimposed on the frequency distribution of the actual size classes taken (inset in Fig. 4). To increase the sample size for the smallest prey categories, the few prey classified in the field as 0.75.1 or 1.25 cm long are combined for purposes of this study. 10 5 5) estimated size (mm) 10 15 shell length (mm) WHY KNOT TAKE MEDIUM-SIZED MACOMA FIELD ESTIMATES n-63 prey FIR. 4. Macoma. Size Ircquency distribution of prey laken hy the same Knot according to A. faecal analysis and B. visual estimates in the field Inset gives the function used lo correct the »isnal estimates ol prey size. 20 274 A quarter of all Macoma handled by Knot were not swallowed. Although occasionally small Macoma were lost during handling, most rejections concerned large prey, refused after a 5 to 6 s frantic handling effort. The larger the prey, the more were rejected (Fig. 5A). Since half of the Macoma 16 mm long were re- • a* / s 40 / - «. / 1 2 20 ^-N. J o V*. y/s lost 3 "40 i i i i i s Q U- 20r- MGr4.M7*aJ s - a * B a g* 4 2 12 ALL PREY .MAKE P.ATE 7 C7-ng s ' 13 —I— 14 — I 15 shell lengih (mm) - © ONLY PREV INGESTED — 1 — 16 Fig. 5. Macoma. The handling ol dillerenl sizes by Knot. A. Percent prev lost or rejected. B. Handling lime of prey swallowed by Knot and lost or rejected. C Ash-free dry weight (AFDW i as determined in 1062 specimens collected, r = 0.999 I). Profitability ling AFDW s ' handling) of prey swallowed. The upper line represents only the prey lhat were swallowed: the lower line reflects ihe profitability after taking into account the lime lost during handling of rejected prey isee panel Al: the intake ratelmg AFDW s 'i during feeding is indicated by grey shading.
fused, specimens larger than this were clearly too large for Knot. Knot handle Macoma w ith a series of 'catch and throw movements' during which the food is transported up the bill (Gerriisen I 988). The larger the prey, the greater the number of catch and throw cycles required, and so handling lime increased with prey si/e (Fig. 5B). The profitability of each prey size, expressed as mg AFDW s' handling, was calculated from the relation between prev size and handling time (Fig. 5B) and between prey size and AFDW (Fig. 5C). As handling time increased disproportionably to the amount of llesh. the profitability decreased in the larger si/e classes (Fig. 51)). This decrease was even larger when the time lost in handling rejected prey finally was taken into account (Fig. 5D). Intake rate During 67 min of feeding. Knot took 63 Macoma whose average weight was 39.6 mg AFDW. The contribution of the three other prey species to die total food intake was only 1%. AFDW of the single 11 mm Cockle laken was 16.2 mg. of ihe three Corophium 3x().4 mg. and of the single 4 em Ragworm 7.6 mg. The total intake rate was 0.63 mg s 1 . excluding 18.8% of the observation time spent preening, usually in short bouts. With this non-feeding time included, the overall intake rate decreased to 0.51 mg s" 1 . Density of available prey Though the Knot fed in a rich area (Fig. 6), not all prey may have been available. Below we attempt to quantify which prey were actually available to Knot. Ingestible prey Though Macoma between 3 and 21 mm were present (Fig. 6). no prey larger than 16 mm long were taken (Fig. 4). Since more than half of Macoma 16 mm long were rejected (Fig. 5A), this is presumably the largest prey that is normally ingested. The same upper size limit was also found by Prater (1972), Goss-Custard el al. 11977b). Nehls (1992) and Piersma et al. (1993b). This limit is probably not determined by length per se. but by the combined effect of shell w idth and height. The "catch and throw movement" made by Knot handling a large shell (Gerritsen 1988) is intended to bring the prev with its longest axis parallel to the bill. Since WHY KNOT TAKE MEDIUM-SIZED MACOMA 275 BOOO - 4000 shell length (mm) P. ulvae 36300 m 2 Fig. 6. Densit*) of each size class ol the Mud Snail Peringia and five bivalve species IMocoma, Cerastoderma, Mya, Scmbicularia and Mytilus) 00 the sue where Knot fed. Note different vertical scales. Large Cerastoderma (23 to 33 mm: 150 specimens m i: A/\
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WADERS AND THEIR ESTUARINE FOOD SUP
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plia^ohi. WADERS AND THEIR ESTUARI
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Waders and their estuarine food sup
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WADERS AND THEIR ESTUARINE FOOD SUP
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figuren: Dick Visser omslagfoto: Ja
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15 Versatility of male curlews (Num
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That science is making progress, ma
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INTRODUCTION The remnants of brushw
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When hcnlhic bivalves extend llien
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the burrow depths and on the fracti
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INTRODUCTION Ms,i invest 409 of (he
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able lo sw itch 10 oiher prey which
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Long-term, broadly-based research c
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Chapter 1 SEASONAL VARIATION IN BOD
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SEASONAL VARIATION IN BODY WEIGHT O
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Tahle 1 Weight loss ('•- ± SE) m
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i 60 50 40 30 20 10 0 • INFESTED
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240- SEASONAL VARIATION IN BODY WEI
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20 10 0 -10 -20h 2 3 4 5 6 7 8 9 se
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a E 400 - S. plana 35 mm 320 240 16
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Chapter 2 HOW THE FOOD SUPPLY HARVE
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FOOD SUPPLY HARVESTABLE BY WADERS H
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Methods The study sites were situat
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less than that of bivalves, partly
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I Fig. 3). Peak condition was reach
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total biomass since most of those t
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on the basis of the preceding and t
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However, for obvious reasons, we ma
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prey. A decrease in the prey densit
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Tahle 2. The intake rate ol < lyste
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* ' % -. . ; a X - . - * • ^ •
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(Zwarts & Wanink 1989). In quiet we
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general law relating handling time
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nearly twice as much time (0.79 s).
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4 5 6 7 8 9 size class of Corophium
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and annually. Second, the lower siz
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Prey switching Waders feeding on ti
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autumn and spring, and the contrary
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where they switch to surface-living
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Chapter 3 BURYING DEPTH OF THE BENT
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DEPTH AND SIPHON CROPPING IN SCROBI
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I DEPTH AND SIPHON CROPPING IN SCRO
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DEPTH AND SIPHON CROPPING IN SCROBI
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Table 3. Three-Way analysis Of vari
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Chapter 4 SIPHON SIZE AND BURYING D
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15 20 size (mm) Fig. 3. Cerasioderm
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10 size (mm) SIPHON SIZE AND DEPTH
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o, 7 01 5 | * CL 5- SIPHON SIZE AND
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4 Q) Si •a a. 16- 20- A predator:
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prey risk for an animal al a depth
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Table 6. Size al which there is a m
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* ' 1 /-/ "».-^*«C
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face and so expose themselves to a
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surface in die containers was varie
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50 OOF 310.00 I 5.00 ^ 1.00 3=" 0.5
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Tahle 1. Macoma and Scrobicularia.
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siphon would not have to reach the
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known siphon weight and burying dep
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ACCESSIBLE PREY ARE OFTEN IN POOR C
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1 2 3 4 burying depth (cm) Kin. I.
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I—1 • • : : : : ! - ! -|-r 0
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Chapter 7 DOES AN OPTIMALLY FORAGIN
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OPTIMAL FORAGING AND THE FUNCTIONAL
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100 200 300 prey density (n-m-2) Fi
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Table I. Results of five one way an
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Table 2. Results of eight iwo-wav a
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prey density II III Fig. 12. Freque
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PREY SIZE SELECTION AND INTAKE RATE
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Predicted 'passive size selection'
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lig. 2. Larger Mussels are less ava
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Fig. 5. Scrobicularia plana. Size c
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and maiiv are too thick-shelled to
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The measurements of handling time i
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1 2 3 4 5 6 7 probing depth (cm PRE
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valves may vary by a factor of two
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optimal foraging model, the minimum
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their gut is full? Do they reduce t
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PREY PROFITABILITY AND INTAKE RATE
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catchers to take only certain prey
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licult error of estimate arose if p
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Counts of feeding and non-feeding b
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20 30 40 50 shell length (mm) PREY
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Nereis Arenicola tipuia earthwo'm M
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take rate. We might therefore expec
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prey species, using parallel slopes
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5.0 4.0 1-3.0 a & • % * • * •
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time during the feeding period. As
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winter. Similarly, handling time in
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5.0 - f-4.0 S 3.0 in I 20 a 2 a | 1
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situation arrived in the western pa
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• ' • 14 PREY PROFITABILITY AND
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Notes lo appendix: PREY PROFITABILI
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Chapter 10 WHY OYSTERCATCHERS HAEMA
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2 4 6 8 10 time on feeding area (h)
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80- 60- o 80 60- 40- 20- INTAKE RAT
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est of bod\ behind: an estimated 22
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INTAKE RATE AND PROCESSING RATE IN
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Wanink 1993). The energy content of
Page 220 and 221: (7) Age All studies dealt with adul
Page 222 and 223: irds over long periods. As an examp
Page 224 and 225: Discussion There is no difference i
Page 226 and 227: comparison between the weight of ih
Page 228 and 229: . 1', L ! •
Page 230 and 231: Introduction PREDICTING SEASONAL AN
Page 232 and 233: PREDICTING SEASONAL AND ANNUAL FLUC
Page 240 and 241: 1000 r 1 II" 1 - r^Jan'80 PREDICTIN
Page 252 and 253: IOO BO 60 40 20 0 PREDICTING SEASON
Page 265 and 266: WHY KNOT TAKE MEDIUM-SIZED MACOMA W
Page 267 and 268: in Zwarts & Esselink 1989). The len
Page 269: shell length (mm) FIR. 3. Peringia.
Page 273 and 274: 50 100- s s I — f = S. plana, n=2
Page 275 and 276: area is twice as large as the touch
Page 277 and 278: 10 15 lower size threshold (mm) Fig
Page 279 and 280: lime (Hughes 1979). This would furt
Page 281 and 282: WHY KNOT TAKE MEDIUM-SIZED MACOMA T
Page 283 and 284: Chapter 13 ANNUAL AND SEASONAL VARI
Page 285 and 286: VARIATION IN FOOD SUPPLY OF KNOT AN
Page 287 and 288: Two sites (N and M in Fig. 2) were
Page 289 and 290: 20 30 VARIATION IN FOOD SUPPLY OF K
Page 291 and 292: 20 l i r'l ' i •o j^y^T n ^ ' " ^
Page 293 and 294: July ' Aug ' Sept Fig. 9. Proportio
Page 295 and 296: available. There must, however, be
Page 297 and 298: Chapter 14 SEASONAL TREND IN BURROW
Page 299 and 300: BURROWING AND FEEDING IN NEREIS SEA
Page 301 and 302: Table 2. Results of a 2-way analysi
Page 303 and 304: June 1981 June 1982 is * N.MUD •
Page 305 and 306: 8 10 I 12 JZ 5. -g 1*» •e o i 16
Page 307 and 308: 6 - n=!080 5 • g 4 CP > i 3 CO CD
Page 309 and 310: 1985) and Curlew (/wails ,v, Lsseli
Page 311: Chapter 15 VERSATILITY OF MALE CURL
Page 314 and 315: Smid! 1951. Muus 1967, Wolff 1973,
Page 316 and 317: 0.6 0.8 1.0 1.2 1.4 1.6 jaw lengih
Page 318 and 319: Na oi both Nrieck Fig. 7. Numenius
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6 8 10 12 14 16 18 worm length (cm)
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too (Fig. 11 A). Indeed, the averag
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VERSATILITY OF CURLEWS FEEDING ON N
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total time spent al the surface. Th
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2 4 . • 2.2 • 30 .-.2.0 to Q. 1
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PREY DEPLETION BY OYSTERCATCHER AND
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the rule: the observed lower limit
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to locate the clams after they had
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Curlew, by bury ing some hundreds o
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PREY DEPLETION BY OYSTERCATCHER AND
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SAMENVATTING 345
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Voorgeschiedenis In 1960 verscheen
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maken. Als gebied A een grotere voe
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omdat ze nog vrijwel niets wegen. l
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kunnen opzuigen. of diep leven en z
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van de uitgerekte sifo over het wad
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het toen niet gemakkelijk hebben ge
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doende nonnetjes van 10 tot 15 mm l
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aangevoerde voedsel en de wulp past
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zijn dan twee jaar en wulpen geen s
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was dan ook dank/ij de inzet van al
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REFERENCES 367
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Allen RL. 1983. Feeding behaviour o
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BreyT. 1989. Der Einfluss physikali
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latie tol chironoiiiiilen en de wai
Page 371 and 372:
huch der Vogel Milteleuropas, Band
Page 373 and 374:
llolmann II. & H. Huerschelmann 196
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l-cndrem D.W. 1984. Flocking, feedi
Page 377 and 378:
Pekkarinen M. 1984. Regeneration of
Page 379 and 380:
lion of Mussels Mytilus edulis hy O
Page 381 and 382:
lulal Dal esiuanes: a comparison of
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