ICES mar. Sei. Symp., 199: 209-221. 1995

Decapod in the diets of demersal fish in the Cantabrian Sea

I. Olaso and E. Rodriguez-Marin

Olaso, I., and Rodriguez-Marin, E. 1995. Decapod crustaceans in the diets of demer­ sal fish in the Cantabrian Sea. - ICES mar. Sei. Symp., 199: 209-221.

The diets of 14 species of demersal fish, representing 81% of the fish biomass of the Cantabrian Sea (ICES Division VIIIc), were determined in the spring and autumn of 1988 from the analysis of 6536 stomachs. Decapod crustaceans represented 54.3% of the diet of these fish in frequency of occurrence and 22.1% in percentage by volume. The main prey taxa were: Solenocera membranacea, Alpeus glaber, the Crangonidae and families within the Natantia, the Paguridae and Galatheidae families within the Anomura, and Goneplax rhomboides and the family within the Brachyura. Predator-prey linkages were described and each predator was assigned to the size group that would best demonstrate any size-related feeding pattern.

I. Olaso and E. Rodriguez-Marin: Instituto Espanol de Oceanografia, Laboratorio Oceanogrâfico de Santander. Apdo240, 39080 Santander, Cantabria, Spain [tel: (+34) 42 2740431275033, fax: (+34) 42 275072],

Introduction Studies of size, distribution, and abundance of prey and diet selection by predators were conducted because The Bay of Biscay forms a well-defined unit because of these parameters play a fundamental role in the selec­ its geographical location and semi-enclosed nature. The tion of diet and have the advantage of being easily southern part of this gulf, called the Cantabrian Sea, is a quantified (Murdoch and Oaken, 1975; Vince et al., transition zone and its fish and inhabitants 1976). The large majority of demersal fish are opportun­ are a mixture of tropical, subtropical species and boreal istic feeders and it is also known that prey size in relation species (Garaa-Raso et al., 1987; Olaso, 1990; Sanchez, to the size of the fish is a determining factor in the food 1990). In this area, seasonal reproductive and feeding composition of such feeders (Daan, 1973) and that migrations of commercial species (such as anchovy, differences in diet are influenced by preference for mackerel, red sea bream, hake, and tuna) take place, certain prey. Considering these principles and the ab­ and these migrations support intense fishing activity sence of such studies in this area, we were interested in throughout the year by a large and diversified fleet. determining some of the qualitative aspects of the inter­ In view of the economic importance of these fisheries, action between demersal and benthic fish. Hence, in the a series of research cruises were begun in 1980 to investi­ present article the role of decapod crustaceans as prey, gate the demersal fisheries and to provide information and the trophic linkages and differences in prey size on the distribution and abundance of the megabenthos selection are reported. (Olaso, 1990; Sanchez, 1990). In these cruises the analy­ sis of fish stomach contents was used to determine the alimentary habits of the fish and the relationship be­ tween the invertebrate megabenthos and demersal fish. Materials and methods In previous studies in this area it was determined that crustaceans are the most important prey group in terms The stomach contents of 14 species of demersal fish, of percentage of frequency (Olaso and Pereda, 1986; obtained from stratified random bottom trawl surveys in Sorbe, 1981). These authors noted the importance of the Cantabrian Sea in the spring and autumn of 1988, are crustaceans in the food of small-sized fish, while the rest given in Table 1. These species were selected because of the invertebrate groups were not very significant; they form a significant part (81%) of the fish biomass however, and molluscs are important to (Sanchez, 1990) and/or are known predators of decapod specific species of predators (Olaso, 1990). crustaceans. Furthermore, these fish were sufficiently 210 /. Olaso and E. Rodriguez-Marin ices,™ , sd. symp , 199(1995)

Table 1. List of predator species whose stomach contents were analysed. N = total number; %E = emptiness percentage.

Spring Autumn Total Year

Species N % E N % E N %E

Aspitrigla cuculus 65 35.4 140 54.3 205 48.3 Aspitrigla obscura 36 16.7 35 54.3 71 35.2 Conger conger 134 41.0 216 39.8 350 40.3 Galeus melastomus 14 35.7 40 10.0 54 16.6 Lepidorhombus boscii 367 32.7 803 45.6 1170 41.5 Lepidorhombus whiffiagonis 484 44.4 696 51.0 1 180 48.5 Lophius piscatorius 89 80.8 141 69.5 230 73.9 434 57.8 760 53.4 1 194 55.0 Micromesistius poutassou 326 55.8 561 77.0 887 69.2 Mullus surmuletus 215 35.3 55 5.5 270 29.3 Phycis blennoides 121 27.3 121 27.3 Raja clavata 42 9.5 61 14.8 103 12.6 Scyliorhinus canicula 220 25.5 336 23.2 556 24.1 Trisopterus luscus 90 23.3 55 20.0 145 22.1

TOTAL 2516 43.0 4020 49.3 6536 46.9

abundant for analysis; a minimum of 50 stomachs of prey, and Nt is the total number of stomachs contain­ each species were analysed. ing the food analysed. The study area corresponds to ICES Division VIIIc, 2. The volumetric method. The volume of the stomach and is made up of sandy and muddy bottoms. Samples contents was measured applying the ecological feed­ were collected at depths of between 30 and 500 m. Fish­ ing method developed at Woods Hole (Bowman, ing was based on daytime trawling, with trawls of 30 min 1982), in which a “trofometro” is used, a piece of duration, using a trawl gear with a mesh size of 20mm. equipment comprising several different sized half­ Sampling was randomly stratified. The methodology cylinders built into a tray in such a way that they form used to select the stations was described by Sanchez and horizontal half-cylindrical moulds (Olaso, 1990). Olaso (1987). Percentage by volume, V: In each haul a maximum of 10 stomachs per length range of the more abundant fish species were sampled. V = v/V,*100 Fish with regurgitated food in their oral cavity were where v is the volume of a specific prey and V, is the rejected, whereas fish with empty stomachs but without total prey volume. apparent indications of regurgitation were not. The stomach contents were analysed on board ship. Examin­ ation involved separation of food items into taxonomic Each method has both advantages and limitations in categories. Fish, decapod crustaceans, and cephalopod evaluating the importance of a prey group. Frequency of molluscs were identified by species, but other groups occurrence produces a bias, overvaluing small and nu­ were combined into higher order taxa. merous prey. On the other hand, the volumetric method To evaluate the importance of the stomach contents overestimates the importance of large organisms (Hys­ two methods were used: lop, 1980). In this study the decapod crustacean prey are of relatively small size, and so both methods have been taken into account. 1. The frequency o f occurrence method. This was used The following information was collected for each prey to characterize fish feeding, and only stomachs con­ species: percentage in relation to the volume of stomach taining food were used for estimation (Dunn, 1954; contents, number of specimens per stomach, state of Kennedy and Fitzmaurice, 1972). This method does digestion and prey length. The prey which were undi­ not give quantitative information, but is rapid and gested and whose size coincided with those found in the requires a minimum of apparatus, giving a somewhat codend of the net were not considered, since predators qualitative picture of the food spectrum (Hyslop, could have fed while they were concentrated in the net 1980). Frequency of occurrence (percentage), F: during the haul (Brown and Cheng, 1946; Bowman, F = n/Nt*100 1986; Klemetsen, 1982). Measurements were taken from decapod crustaceans where n is the number of stomachs with a specific as follows: for the Natantia, the Macrura Reptantia ICES mar. Sei. Sym p., 199 ( 1995) Decapod crustaceans in the diets of demersal fish in the Cantabrian Sea 211 group and the Galatheidae family, total length was Table 2. List of prey groups found in stomachs of 14 demersal fish species. F = frequency of occurrence percentage; V = measured (distance from the post-orbital edge to the percentage by volume. telson apex, with the abdomen extended); for the Bra- chyura infraorder, carapace length was determined (dis­ Crustacea F V tance from the foremost part to the end of the carapace) ; for the Paguridae family, céphalothorax length was Anomura Family Galatheidae measured (distance from the post-orbital edge to the Galalhea spp. 1.18 0.12 post-dorsal edge of the céphalothorax). Munida intermedia 0.26 0.12 If the stomach contents were in an advanced state of Munida perarmata 0.03 0.00 digestion or the prey was incomplete, the length of its Munida sarsi 0.43 0.19 Munida spp. 3.03 2.59 hard structure was measured - carapace or propodus Family Paguridae length in decapod crustaceans. In the laboratory, from Pagurus bernhardus 0.12 0.05 the material collected and preserved in 70% alcohol, Pagurus prideauxi 1.87 2.15 regression functions of size-weight, chela length- Pagurus variabilis 0.06 0.02 0.63 size, céphalothorax length-size, etc., were obtained, Other Paguridae 0.92 Other Anomura 0.17 0.01 from which total length and weight were estimated Total Anomura 7.72 5.88 (Rodriguez-Marin, 1993). Brachyura Atelecyclus rotundatus 0.63 0.78 Corystes cassivelaunus 0.23 0.81 Results Goneplax rhomboides 3.80 1.22 From the demersal fish selected, 6536 stomachs were Inachus leptochirus 0.06 0.01 Family Portunidae analysed (Table 1). The high average percentage of depurator 3.69 3.35 empty stomachs, 46.9% (43% in spring and 49.3% in Liocarcinus holsatus 0.20 0.02 autumn), found particularly in Merluccius merluccius, Liocarcinus puxillus 0.06 0.00 Micromesistius poutassou, Lophius piscatorius, and Macropipus tuberculatus 0.09 0.01 0.66 1.90 Lepidorhombus whijfiagonis, may be considered a Polybius henslowii Other Portunidae 4.47 0.49 normal feature of the diurnal feeding periodicity of fish, Other Brachyura 2.48 0.54 since sampling was carried out during daylight, and Total Brachyura 15.64 9.13 many authors have provided evidence of feeding activity Macrura during darkness (Kruuk, 1963; de Groot, 1964; Bowman Nephrops norvegicus 0.06 0.06 and Bowman 1980). Sorbe ( 1980) presented values of up Scyllarus sp. 0.43 0.04 to 80% of empty stomachs for M. poutassou on the Other Macrura 1.01 0.17 Total Macrura 1.50 0.27 French continental shelf, and Bowman and Bowman (1980) estimated nearly 40% for silver hake. Natantia 5.50 2.28 The prey species found in the fish stomachs are listed Solenocera membranacea Alpheus glaber 6.40 1.34 in Table 2, and the mean number of prey per stomach Chlorotocus crassicornis 0.35 0.06 containing food was 5.2. Of the 18193 prey analysed, Pasiphaea sivado 0.78 0.19 84% were crustaceans. Plesionika heterocarpus 0.03 0.00 Family Processidae Processa canaliculata 0.09 0.03 Diet composition Processa spp. 9.31 1.45 Differences in diet composition between spring and Family Crangonidae Philocheras bispinosus 0.06 0.00 autumn are shown in Figure 1. In frequency of occur­ Philocheras echinolatus 0.46 0.05 rence the decapod crustaceans make up the most im­ Philocheras sculptus 0.20 0.01 portant prey group (F = 54.3%), while in volume (V = Pontophilus spinosus 1.56 0.14 22.1%) they are considerably less significant than fish (V Other Crangonidae 2.02 0.15 8.61 0.95 = 70.6%). Decapod crustaceans have higher values in Other Natantia Total Natantia 31.11 6.66 the diet of fish in spring (F = 56.8% and V = 26.9%) 1.09 0.15 than in autumn (F = 52.7% and V = 19.1%). Other Other Decapoda crustaceans have lower values, and these are also lower in autumn than in spring.

Decapod crustaceans as prey taxa Of the four decapod groups, Natantia, Brachyura, Ano- mura, and Macrura, only the first three represent an 212 I. Olaso and E. Rodriguez-Marin ICES mar. Sei. Symp., 199 (1995)

FREQUENCY OF OCCURRENCE 60 n

50

40 - □ DECAPOD ■ OT. CRUST. 30 EID FISH ■ I OT. INVERT. 20 m m 1 1 SPRINGI AUTUMN TOTAL Fig. la

PERCENTAGE BY VOLUME 80

60

□ DECAPOD ■ OT. CRUST. 40 1 1 FISH WM OT. INVERT.

20

SPRING AUTUMN TOTAL

Fig. lb

Figure 1. Main food items - fish, decapod crustaceans, other crustaceans, and other invertebrates- in the diet of 14 demersal fish species in the spring and autumn, and the total, expressed as frequency of occurrence (a) and percentage by volume (b). ICES mar. Sei. Symp., 199 (1995) Decapod crustaceans in the diets o f demersal fish in the Cantabrian Sea 213 appreciable percentage in volume, in either the spring or PERCENTAGE BY VOLUME autumn, while Macrura are only rarely found in the diet (Fig. 2). Thirty-eight prey taxa of decapod crustaceans were found in the stomachs, of which 13 were Natantia, 11 Brachyura, 10 Anomura, 3 Macrura and one that was □ BRACHYURA □ ANOMURA unidentified (Table 2). Many of these taxa were weakly 15 represented, showing low percentages of frequency and ■ MACRURA volume; hence only the data of the species and families ■ ■ NATANTIA which were most abundant have been used: Solenocera membranacea, Alpheus glaber, Crangonidae, Processi- dae, Paguridae, Galatheidae, Goneplax rhomboides, and Portunidae. In these families different prey taxa AUTUMN have been grouped together because identification of Figure 2. Decapod crustacean groups in the diet of demersal the species was not always possible, while the genus or fish expressed as percentage by volume for spring and autumn. family was identifiable. This grouping has also facilitated more representative numbers for data analysis; the eight groups selected are well represented. The frequency most important predators are P. blennoides (F = values are more significant than those of volume since 34.3%), Mullussurmuletus (F = 26.3%), L. boscii (F = most of them are small-bodied, with the exception of the 17.2%), and Trisopterus luscus (F = 16.9%). taxa Munida spp. within the Galatheidae, Pagurus pri- deauxi within Paguridae, and Liocarcinus depurator and Polybius henslowii within Portunidae. Anomura infraorder: The Galatheidae Family, which ranges from 8 to 79 mm, is preyed on by five fish species. It is an important prey for A. cuculus (F = 20.9%) and of Predator-prey relationship and prey size Scyliorhinus canicula (F = 12.7%.) preference The Paguridae Family was prey for three species. As the first step in establishing the predator-prey link­ Among the cartilaginous fish, R. clavata (F = 16.9%) age, the size ranges of the selected prey were related to and 5. canicula (F = 15.6%) were the most important. the size range of their predators, since the relative im­ portance of the prey taxa generally varies according to Brachyura infraorder: Goneplax rhomboides of a size fish size (Table 3). The measurement of feeding between 2 and 18 mm was found in the stomachs of four tendency was based on the frequency of occurrence fish species. The major predators were T. luscus (F = value (F) obtained for each prey taxon in each size range 16.7%) and C. conger (F = 12.4%). The Portunidae of each predator. The following are the most relevant family is consumed in a wide size range (3-37 mm) by data in Table 3: eight species. It is mainly present in the stomachs of A. obscura (F = 56.1%), R. clavata (F = 51.3%), and A. Natantia group: Solenocera membranacea is consumed cuculus (F = 34.5%). It is of relative importance to L. in a size range between 12 and 79 mm by six fish species. boscii, M. surmuletus, and T. luscus. Specimens greater Two of these fish are large species, M. merluccius and than 15 mm are only eaten by large-sized species such as Conger conger, and feed on S. membranacea when the R. clavata and S. canicula. fish are small; however, it is prey to all size ranges of the Ivlev (1961) considered that prey size relative to that other four fish predators. The most significant predator of the predator is a good criterion by which to determine is Raja clavata (F = 31.7%). the selectivity of food. He considered the ratio of sizes Alpheus glaber is preyed on in a size range from 8 to more important than their absolute values. To obtain an 46 mm. Its main predators are Phycis blennoides (F = overall picture of this ratio the values of average size of 21%) and Lepidorhombus boscii (F = 15%). each prey taxa against average predator size are pre­ The Crangonidae family appears in the stomach con­ sented in Figure 3. It can be seen that there is a tendency tents of four species whose size is no greater than 32 cm. for prey size to increase as predator size increases. To The prey size varies from 8 to 46 mm, but the average determine the characteristics of the predator-prey re­ value is low. The gurnards Aspitrigla obscura (F = lationships, linear regressions between the size of each 45.7%) and Aspitrigla cuculus (F = 21.7%) are notable predator and each of their prey taxa were done (Table predators of this family. 4). The aim of the analysis was to divide each predator A wide size range (8 to 67 mm) of the Processidae into the length group that would best indicate any size- Family is eaten by a large number of fish species; the related feeding pattern. It can be appreciated that there 214 I. Olaso and E. Rodriguez-Marin ICES mar. Sei. Symp., 199 (1995)

Table 3. Composition of prey sizes in relation to predator lengths, x = average; S.d. = standard deviation; No. prey = number of prey; No. stom. = number of stomachs; F = frequency of occurrence for each predator length range.

Prey size No. Predator length No. range (mm) X S.d. prey Predator range (cm) X S.d. stom. F

Solenocera membranacea 30-75 52 11.6 14 C. conger 25-51 44 6.9 13 8.6 15-65 39 12.9 63 L. boscii 14-33 22 4.8 51 7.8 12-77 46 10.7 89 L. whifßagonis 19-41 33 4.2 49 9.2 33-55 42 7.1 18 M. merluccius 11-24 15 3.6 17 5.1 34-61 46 6.5 43 R. clavata 35-99 58 14.4 26 31.7 30-79 49 11.8 20 S. canicula 19-59 42 11.8 18 4.6

Alpheus glaber 25-45 32 4.4 24 C. conger 30-61 46 7.9 22 10.8 8-46 30 5.8 109 L. boscii 15-32 24 4.1 95 15.0 25-37 31 3.7 19 L. whiffiagonis 19-39 27 5.3 19 3.6 19-37 25 5.5 21 P. blennoides 13-25 19 3.4 17 21.0 21-40 34 5.3 42 S. canicula 24-65 46 11.0 35 8.7 21-34 28 5.0 22 T. luscus 16-39 26 6.6 17 15.0

Crangonidae (Philocheras echinolatus, Philocheras sculptus, Pontophilus norvegicus, Pontophilus spinosus, and other Crangonidae) 8-28 14 4.2 111 A . cuculus 9-28 22 2.8 23 21.7 9-18 12 2.4 120 A . obscura 13-30 22 5.3 21 45.7 8-46 17 7.2 104 L. boscii 11-32 20 4.5 60 8.9 12-23 15 3.4 33 P. blennoides 15-30 18 2.4 11 14.3

Processidae (Processa canaliculata, P. modica, P. nouveli, and Processa spp.) 21-53 32 8.2 22 C. conger 32-57 44 6.8 18 9.2 8-66 23 10.3 229 L. boscii 11-35 20 4.4 117 17.2 15-59 34 11.3 28 L. whiffiagonis 16-37 25 4.7 22 3.8 14-58 32 10.8 46 M. merluccius 11-24 14 2.8 30 9.1 8-38 19 6.6 128 M. surmuletus 9-34 23 4.5 50 26.3 13-50 21 5.1 73 P. blennoides 14-20 18 1.4 24 34.3 20-67 38 13.8 25 S. canicula 25-62 46 12.3 19 4.9 12-31 24 4.2 71 T. luscus 23-39 29 2.8 15 16.9

Paguridae (Pagurus bernhardus, Pagurus prideauxi, Pagurus variabilis, and other Paguridae) 24-48 -- 17 R. clavata 41-72 62 11.7 10 16.9 13-50 26 11.8 84 S. canicula 17-65 47 11.6 65 15.6 11-17 15 2.4 18 T. luscus 21-34 26 4.2 10 10.2

Galatheidae (Galathea intermedia, Munida intermedia, Munida sarsi, and Munida perarmata) 8-56 18 10.6 49 A . cuculus 17-35 25 5.1 18 20.9 13-60 36 10.9 24 C. conger 29-78 49 8.4 18 8.7 5-25 15 4.4 50 L. boscii 14-31 22 4.2 37 5.7 18-46 31 8.8 29 L. whiffiagonis 17-38 28 5.4 20 3.5 16-70 41 9.2 76 S. canicula 23-61 43 11.7 49 12.7

Goneplax rhomboides 6-17 11 2.3 30 C. conger 40-60 51 5.3 22 12.4 2-13 9 9.7 85 L. boscii 15-35 25 4.4 75 11.7 9-18 12 2.4 10 S. canicula 25-61 43 10.8 10 2.7 3-13 8 2.6 26 T. luscus 23-34 28 3.9 14 16.7

Portunidae (Liocarcinus depurator, Liocarcinus holsatus, Liocarcinus puxillus, Macropipus tuberculatus, Polybius henslowii, and other Portunidae) 4-25 7 4.2 81 A . cuculus 18-39 26 5.0 30 34.5 4-7 5 0.7 193 A . obscura 16-28 26 2.1 23 56.1 3-17 7 2.5 193 L. boscii 11-35 21 4.9 100 14.7 3-15 6 1.9 73 L. whiffiagonis 13-37 25 5.7 40 6.8 3-7 5 0.9 66 M. surmuletus 9-34 22 4.4 27 14.2 6-37 21 7.6 147 R. clavata 41-99 65 12.1 40 51.3 11-32 24 6.1 31 S. canicula 27-65 45 11.0 30 7.8 5-31 14 6.5 23 T. luscus 17-39 29 6.7 15 13.4 ICES mar. Sei. Sym p., 199 ( 1995) Decapod crustaceans in the diets o f demersal fish in the Cantabrian Sea 215

Mean prey length (mm) explanations for the high consumption of decapod crus­ 60 taceans found in this area. The slightly higher presence of decapod crustaceans in the stomach contents in spring should, in theory, be 50 attributable to the seasonal variation in the abundance of decapods. However, the biomass of benthic crusta­ 40- ceans in spring is significantly lower than it is in the autumn (Olaso, 1990), perhaps because the consump­ □ tion of small fish prey increases in the autumn. For Kiel 30- Bay, Artnz (1980) also found that the biomass of the +4* more important demersal fish species was apparently 2 t i a A □ independent of annual fluctuations of their main food, 20 3 ° x the macrobenthos. X A Sedberry (1983), studying a community of fish in the i o H middle Atlantic Bight, observed that crustaceans were % an important source of food for most of the predators, 6 and that there were large overlaps in the species that o appeared in their diets. Something similar occurs in the Cantabrian Sea, since there is one prey group common 0 10 20 30 40 50 60 70 to a large number of predators. It is noteworthy that Mean predator length (cm) prey with higher abundance indices (Liocarcinus depur- Figure 3. Representation of values of average size of each prey ator, Munida sarsi, Munida intermedia and Pagurus pri- taxa against average predator size, i i=15. membranacea, + 2 A . glaber, □ = 3 Processidae, x = 4 Galatheidae, * = 5 G. deauxi), as observed in Olaso (1990), are very common rhomboides, A = 6 Portunidae. prey for the majority of predators, and are captured at different periods of their lives; the adult prey are typi­ cally consumed by cartilaginous fish: rays, dogfishes, etc. Within the Natantia, although we do not have re­ are fish species such as M. surmuletus, A. obscura, R. clavata, and S. canicula, with very low or even negative liable indices of abundance, the species Solenocera correlations, as they do not select prey as a function of membranacea, Alpheus glaber and the families Processi­ size. The regressions for the cases in which the predator dae and Crangonidae represent an important part of the size-prey size relationship is significant (r2 > 0.75) are trophic flux of small-sized fish (gurnards, small flatfish, represented in Figure 4. L. boscii, M. merluccius, C. and such like). conger, P. blennoides, and A . cuculus are the only Availability and preference for a specific food are species in which some prey taxa sizes change ostensibly factors which determine the selection of prey. To satisfy as they grow. Good fits are only obtained with small­ the former there must be overlapping distributions of fish and decapod crustaceans. The prey taxa selected in sized predators. the present work are euribathimetric (Olaso, 1990), and are available to the demersal fish which move within this range of depths. In the selection of prey, size is limiting Discussion for the predator, and there is a size range of potential The invertebrate megabenthos, together with a small prey. Mac Arthur (1972) postulates that small proportion of fish, is the main food resource for demer­ which eat small prey find prey of adequate size with sal fish (Arntz, 1978; Dunn, 1979). Dunn (1979) points much greater frequency than larger animals which feed out that the magnitude of the biomass of benthos could on larger prey. As a consequence, large animals tend to largely determine the production of demersal fish. Arntz accept a wider range of prey sizes, which makes the and Finger (1981) state that the benthic food resource difference in size between one prey and another increase must be considered limited for large fish and, further­ notably as predator size increases. In the Cantabrian more, that there is a distinct change in the composition Sea, these small species, such as A. obscura, A. cuculus, of the diet with increasing predator size (Tyler, 1972; and M. surmuletus, eat small prey such as small Crango­ Werner, 1979; Sedberry, 1983). However, in the fisher­ nidae, Portunidae, Processidae, and Galatheidae. ies of the Cantabrian Sea, predator fish are small and Species which grow to a large size, S. canicula, C. medium-sized and these size-related changes in diet are conger, R. clavata, ingest a wide range of large prey. As only observed in a few species of fish (M . merluccius, for an example, the size composition of Portunidae in the example). The abundance of small-sized fish and the diet of predators is presented in Figure 5; only this group general absence of larger-sized fish may be one of the has been represented for brevity. 216 I. Olaso and E. Rodriguez-Marin ICES mar. Sei. Symp., 199 (1995)

Length of prey (mm) Length of prey (mm) 60 60

50 50

40 40

30 30

20 20

10

0 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 Length of predator (cm) Length of predator (cm)

— L. boscii ~a~ M merluccius L. boscii —®- P. blennoides

Fig. 4a Fig. 4P

Length of prey (mm) Length of prey (mm) 60 60

50 50

40 40

30 30

20

0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 Length of predator (cm) Length of predator (cm)

~ A. cuculus - e~ P. blennoides *— L, boscii M. merluccius

Fig. 4c Fig, 4d Figure 4. Regression lines of predator length and prey length, Solenocera membranacea (Fig. 4a), Alpheus glaber (Fig. 4b), Crangonidae (Fig. 4c), Processidae (Fig. 4d), Paguridae (Fig. , Galatheidae (Fig. 4f), Goneplax rhomboides (Fig. 4g), and Portunidae (Fig. 4h). ICES mar. Sei. Symp., 199 (1995) Decapod crustaceans in the diets of demersal fish in the Cantabrian Sea 217

Length of prey (mm) Length of prey (mm) 60 60

50 50

40

30

20 20

10

0 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 Length of predator (cm) Length of predator (cm)

—1— T, luscus —^ C. conger

Fig 4e Fig. 41

Length of prey (mm) _ Length of prey (mm) 60 6 0 ------

50

40

30

20

10

0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 Length of predator (cm) Length of predator (cm)

L. boscii A . cuculus ° L. boscii

Fig. 4g Fig, 4h Figure 4. Continued. 218 1. Olaso and E. Rodriguez-Marin i c e s mar. sd. symp., 199(1995)

Table 4. Summary of linear regressions between prey and predator lengths (y = a + bx). a = intercept; b = slope; r2 = determination coefficient.

Prey Predator a b r2

S. membranacea C. conger 51.72 0.03 0.01 L. boscii 8.33 1.40 0.90 L. whiffiagonis 43.31 0.02 0.02 M. merluccius 27.50 1.05 0.78 R. clavata 33.64 0.59 0.35 S. canicula 18.70 0.61 0.60 A. glaber C. conger 27.06 0.18 0.31 L. boscii 14.77 0.63 0.87 L. whiffiagonis 25.24 0.22 0.61 P. blennoides 14.45 0.60 0.93 S. canicula 24.11 0.18 0.57 T. luscus 16.27 0.35 0.45 Crangonidae A. cuculus -0.62 0.74 0.80 A. obscura 12.40 0.04 0.00 L. boscii 13.54 0.21 0.59 P. blennoides 4.63 0.57 0.98 Processidae C. conger 6.68 0.59 0.54 L. boscii 10.90 0.51 0.75 L. whiffiagonis 1.81 1.38 0.54 M. merluccius 6.93 1.77 0.92 M. surmuletus 7.86 0.42 0.46 P. blennoides --- S. canicula 51.06 -0.15 0.01 T. luscus 51.10 -0.18 0.03 Paguridae S. canicula 5.98 0.40 0.45 T. luscus 5.84 0.27 0.79 R. clavata --- Galatheidae A. cuculus -15.82 1.53 0.64 C. conger 3.44 0.56 0.77 L. boscii 10.31 0.23 0.16 L. whiffiagonis 29.46 0.04 0.00 S. canicula 27.38 0.31 0.32 G. rhomboides C. conger 16.04 -0.12 0.54 L. boscii -2.65 0.50 0.79 S. canicula 5.76 0.14 0.43 T. luscus 13.41 -0.19 0.98 Portunidae A. cuculus -9.02 0.55 0.79 A. obscura 6.10 -0.04 0.13 L. boscii -1.62 0.42 0.81 L. whiffiagonis 3.13 0.07 0.74 M. surmuletus 5.20 0.03 0.02 R. clavata 2.44 0.26 0.51 S. canicula 30.61 -0.10 0.14 T. luscus -1.37 0.54 0.73

In the predator size-prey size relationship we find predators and small-bodied prey with wide prey size significant and non-significant correlations which allow composition (as can be seen in Fig. 5a). the establishment of three predator types. These with The non-significant correlations are found in preda­ good correlations are type 1 ; notable examples being L. tors which, independently of size, ingest a small or wide boscii preying on S. Membranacea, A. glaber, and the range of prey. If the length range is small, the predator is Portunidae; P. blennoides preying on A. glaber and the small, and these form type 2. Within this type we find A. Crangonidae; M. merluccius preying on the Processi­ obscura preying on Crangonidae and Portunidae, T. dae; and A. cuculus preying on the Portunidae and luscus preying on Processidae, and M. surmuletus prey­ Crangonidae. All of these cases concern small-bodied ing on Processidae and Portunidae. If the length range of ICES mar. Sei. Symp., 199 (1995) Decapod crustaceans in the diets o f demersal fish in the Cantabrian Sea 219

% 50 50 L, boscii A obscura

40 N = 193 N = 193

30 30

20 20

10

0 0 5 10 15 20 25 30 35 40 Carapace length (mm) Carapace length (mm) Fig. 5a Fig. 5b

50 50 M. surmuletus R. clavata

40 - N = 66 40 - N = 147

30 - 30 -

20 n 20 -

10 - 10 -

0 Ln .EL, fl nn É O 0 0 0 5 10 15 20 25 30 35 40 Carapace length (mm) Carapace length (mm) Fig. 5c Fig. 5d Figure 5. Size distribution of Portunidae found in the stomachs of L. boscii (Fig. 5a), A . obscura (Fig. 5b), M. surmuletus (Fig. 5c), and R. clavata (Fig. 5d). 220 I. Olaso and E. Rodriguez-Marin ICES mar. Sei. Symp., 199 (1995) prey is wide, the predators are large, and are found in the role of macrobenthos in the western Baltic. Rapp. P.-v. type 3, containing S. canicula, R. clavata and C. conger. Réun. Cons. int. Explor. Mer, 173: 85-100. Arntz, W. E. 1980. Predation by demersal fish and its impact on The predator size-prey size relationship seems to the dynamics of macrobenthos. In Marine benthic dynamics, indicate that there is a specialized, or opportunistic, pp. 121-149. Ed. by K. R. Tenore and B. C. Coull. Univer­ feeding method, since the composition of the predator’s sity of South Carolina Press, Columbia. diet depends on relative abundance and the optimum Arntz, W. E., and Finger, I. 1981. Demersal fish in the western Baltic: their feeding relations, food coincidence and food size of prey species in their niche (Armstrong, 1982). selection. ICES CM 1981/J: 6. Armstrong (1982) considers that the majority offish may Bowman, R E. 1982. Preliminary evaluation of the results of be considered opportunistic feeders on a preferred size analysis of the stomach contents of silver hake (Merluccius range on which they can prey, and as long as they are bilinearis) aboard ship and in the laboratory ashore. NOAA efficient avoid excessive use of energy in the search for Tech. Rep., NMFS SSRF-82-25. 13 pp. Bowman, R. 1986. Effect of regurgitation on stomach content food. In our results we observe that the fish of type 2 are data of marine fishes. Env. Biol. Fish., 16: 171-181. specialized to a small size range of prey during a long Bowman, R. E., and Bowman E. W. 1980. Diurnal variation in period of their lives, while in the fish of type 1 this occurs the feeding intensity and catchability of silver hake (M erluc­ over a much shorter period. In the fish of type 3, how­ cius merluccius). Can. J. Fish, aquat. Sei., 37: 1565-1572. ever, the prey range is wide at all predator sizes. Brown, W. W, and Cheng C. 1946. Investigations into the food of the cod (Gadus callarias L.) off Bear Island, and of the cod There are authors who have organized feeding cat­ and haddock (G. aeglefinus L.) off Iceland and the Murman egories using such different characters as stomach mor­ Coast. Bull. Mar. Ecol., 18: 35-71. phology (de Groot, 1971; Tyler, 1973), mouth position, Daan, N. 1973. A quantitative analysis of the food intake of shape, and size (Morris, 1981; Wootton, 1990), diet cod, Gadus morhua. Neth. J. Sea Res., 6: 479- 517. composition (Langton and Bowman, 1980), etc. All de Groot, S. J. 1964. Diurnal activity and feeding habits of things considered, we have summarized the more plaice. Rapp. P.-v. Réun. Cons. int. Explor. Mer, 155: 48- characteristic decapod crustacean prey and predators of 51. the demersal community. The three clear groups of fish de Groot, S. J. 1971. On the interrelationships between mor­ phology of the alimentary tract, food, and feeding behaviour in relation to their shellfish diet are: in flatfishes (Pisces: Pleuronectiformes). Neth. J. Sea. Res., 5: 121-196. 1. Small benthic predators, like the gurnards/1, cuculus Dunn, D. R. 1954. The feeding habits of some of the fishes and and A. obscura, and M. surmuletus, that have ventro- some members of the bottom fauna of Llyn Tegid (Bala Lake), Merionethshire. J. Anim. Ecol., 23: 224-233. terminal mouths, which allow them to dig in the sand Dunn, J. R. 1979. Predator-prey interactions in the eastern and sediment. Their diet also includes polychaetes, Bering Sea. In Predator-prey systems in fisheries manage­ echinoderms, and gastropods, as has been observed ment, pp. 81-91. Ed. by H. Clepperand R. H. Stroud. Sport in Olaso and Pereda (1986). They mainly eat small Fishing Institute, Washington. Garcîa-Raso, J. E., Gonzalez-Gurriarån, E., and Sardâ, F. Crangonidae, Galatheidae, and Portunidae. 1987. Estudio comparativo de la fauna de cruståceos decâpo- 2. Small and medium size predators that have strong dos braquiuros de tres areas de la Peninsula ibérica (Galicia, benthic habits and feed largely on the epifauna, like Mâlaga y Cataluna). Inv. Pesq., 51 (Suppl. 1): 43-55. L. boscii, L. whiffiagonis, small P. blennoides, and T. Hyslop, E. J. 1980. Stomach contents analysis - a review of luscus. They also feed on Processidae, Solenocera methods and their application. J. Fish. Biol., 17: 411-429. Ivlev, V. S. 1961. Experimental ecology of the feeding of fishes. membranacea, Alpheus glaber, Crangonidae, and Yale University Press, New Haven, Connecticut. 302 pp. Goneplax rhomboides. Kennedy, M., and Fitzmaurice, P. 1972. Some aspects of the 3. Medium and large size predators that feed on large biology of gudgeon Gobio gobio (L.) in Irish waters. J. Fish. specimens of Paguridae, Galatheidae, and Processi­ Biol., 4: 425-440. dae, like R. clavata, C. conger, Galeus melastomus, Klemetsen, A. 1982. Food and feeding habits of cod from the Balsfjord, northern Norway during a one-year period. J. and S. canicula. Cons. int. Explor. Mer., 40: 101-111. Kruuk, H. 1963. Diurnal periodicity in the activity of the Finally, there are clearly ichthyophagous species of a common sole Solea vulgaris Quensel. Neth. Sea Res., 2: 1- 28. large size, like M. merluccius and Lophius piscatorius, Langton, R. W., and Bowman, R. E. 1980. 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