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Feeding Ecology of Small Deep-Water Lanternsharks (Etmopterus Spinax and Etmopterus Pusillus) Off the Algarve Coast

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Feeding Ecology of Small Deep-Water Lanternsharks (Etmopterus Spinax and Etmopterus Pusillus) Off the Algarve Coast UNIVERSIDADE DO ALGARVE Faculdade de Ciências e Tecnologia, Campus de Gambelas Centro de Ciências do Mar (CCMAR) FEEDING ECOLOGY OF SMALL DEEP-WATER LANTERNSHARKS (ETMOPTERUS SPINAX AND ETMOPTERUS PUSILLUS) OFF THE ALGARVE COAST Laura Nuño Muñoz (a50744) Master's thesis Master integrated in Marine Biology Work performed under the guidance of: Dr. Jorge M.S. Gonçalves Dra. María Esmeralda S.L.C. Costa da Fonseca FARO 2015 i FEEDING ECOLOGY OF SMALL DEEP-WATER LANTERNSHARKS (ETMOPTERUS SPINAX AND ETMOPTERUS PUSILLUS) OFF THE ALGARVE COAST Declaração de autoria de trabalho: Declaro ser autor deste trabalho, que é original e inedito. Autores e trabalhos consultados estão devidamente citados no texto e constam da listagem de referências incluida. ii “Ignorance more frequently begets confidence than does knowledge: it is those who know little, not those who know much, who so positively assert that this or that problem will never be solved by science.” Charles Darwin, The Descent of Man. iii iv INDEX Chapter 1 – INTRODUCTION 1.1. General introduction …………………………………………………….................2 1.2. Description of studied species ……………………………………………………...3 1.2.1. Taxonomic classification …………………………………….....................4 1.2.2. Etmopterus spinax (Linneaus, 1758) ……………………...........................4 1.2.2.1. General diagnosis ………………………………………………....4 1.2.2.2. Biological characteristics …………………………………………5 1.2.2.3. Distribution and habits …………………………………………....5 1.2.3. Etmopterus pusillus (Lowe, 1839) ……………………………...................6 1.2.3.1. General diagnosis …………………………………………………6 1.2.3.2. Biological characteristics ………………………………………....6 1.2.3.3. Distribution and habits …………………………………………....7 1.2.4. Feeding ecology of both species of lantern sharks ………………………...7 1.2.4.1. Main prey items…………………………………………..……...8 1.2.4.1.1. Euphausiids …………………………………………...8 1.2.4.1.2. Natantid decapods ………………………………..…...8 1.2.4.1.3. Teleost fish …………………………..………………..8 1.2.4.1.4. Cephalopods ……………………………..……………9 1.2.5. Economic and conservation value in fisheries ………………….…..…..10 1.3. Objectives of the study …..………………………………………………..............11 Chapter 2 – MATERIALS AND METHODS 2.1. Geographical location of studied area …………………………………………....13 2.2. Characterization of sample ……………….………………………………………13 2.3. Laboratory procedure …………………………………………………………….15 2.4. Representativeness of sample …………………………………............................17 2.5. Univariate statistical analyses …………………………………………................18 2.5.1. Quantitative analyses ………………………………………………….…18 2.5.1.1. Numeric method …………………………………………………18 2.5.1.2. Gravimetric method ……………………………………………..18 2.5.1.3. Frequency of occurrence ……………………..………………….18 2.5.2. Mixed analyses ……………………………………………………...…...19 i 2.5.2.1. Index of Relative Importance (IRI) ………...........…...………….19 2.5.2.2. Weighted Food Index (IPO2) ……………………………………20 2.5.3. General classification methods prey ……………………………………..20 2.5.4. Vacuity Index (VI) …..…………………………………………………..20 2.5.5. Comparing the diets between species …………………………………….21 2.5.5.1. Feeding overlap (Schoener Index) ……………….………….…...21 2.5.5.2. Trophic level (TL) ………………………………….……………21 2.5.5.3. Diversity, Richness and Evenness Indices ……………………….21 a) Diversity Index (H’) ……..……………………………...…..22 b) Richness Index (R1) …………………………………………23 c) Evenness Index (J’) …………………………………………23 2.6. Multivariate statistical analysis .……………………………………...…..............24 2.6.1. CLUSTER analysis ………………………...…………………………….24 2.6.2. Multidimensional Scaling analysis (MDS).……………...........................24 2.6.3. ANOSIM analysis ..……………………………………...........................24 2.6.4. SIMPER analysis ..………………………………………………………25 Chapter 3 –RESULTS 3.1. Etmopterus spinax (Linnaeus, 1758) …….………………………………………..27 3.1.1. Representativeness of the sample………………………………………..27 3.1.2. General composition of the diet…...……………………………………27 3.1.2.1. Prey classifications……………………………………………....30 3.1.2.2. Diversity indices…………………………………………………32 3.1.3. Relationship between sex and diet composition………………………….32 3.1.3.1. Diversity indices…………………………………………………34 3.1.3.2. Multivariate statistical analysis…………………………………..34 3.1.4. Relationship between maturity and diet………………………………….36 3.1.4.1. Diversity indices…………………………………………………39 3.1.4.2. Multivariate statistical analysis…………………………………..39 3.1.5. Relationship between season and diet…………………………………….41 3.1.5.1. Diversity indices………………………………………………....43 3.1.5.2. Multivariate statistical analysis……………………………….….43 ii 3.2. Etmopterus pusillus (Lowe, 1835)………………………………………………….46 3.2.1. Representativeness of the sample………………………………………...46 3.2.2. General composition of the diet…………………………………………..46 3.2.2.1. Prey classifications………………………………………………49 3.2.2.2. Diversity indices…………………………………………………51 3.2.3. Relationship between sex and diet…………………………………….....51 3.2.3.1. Diversity indices…………………………………………………53 3.2.3.2. Multivariate statistical analysis………………………………….53 3.3. Comparison between Etmopterus spinax and Etmopterus pusillus………………..55 3.3.1. Diversity………………………………………………………………….55 3.3.2. Multivariate statistical analysis…………………………………………..56 Chapter 4 –DISCUSSION 4.1. General diet composition …………………………………...................................60 4.2. Diet composition according to sex and maturity stages …………………………..65 4.3. Diet composition of according to the season …………………………………….66 4.4. General conclusions ……………………………………………………………...68 Chapter 5 –REFERENCES …………………………………………………………..70 ANNEXES……………………………………………………………………………..77 iii FIGURES INDEX Figure 1.1: Etmopterus spinax (Linnaeus, 1758) (drawing by @ Laura Nuño Munõz)………………………………………………………………………........... 4 Figure 1.2. Geographical distribution of Etmopterus spinax (Linnaeus, 1758) (source: Global species database of fish species, FishBase (Froese and Pauly, 2015))……………... 5 Figure 1.3. Etmopterus pusillus (Lowe, 1839) (drawing by @ Laura Nuño Munõz)……… 6 Figure 1.4. Geographical distribution of Etmopterus pusillus (Linnaeus, 1758) (source: Global species database of fish species, FishBase Froese and Pauly, 2015)……………….. 7 Figure 2.1: Laboratory procedure carried out for the stomach contents analysis of E. spinax and E. pusillus (photos by @ Laura Nuño Muñoz)………………………………… 15 Figure 2.2: Prey items (cephalopods, crustaceans and fish) found in the stomach contents of E. spinax and E. pusillus in different digestion stages (photos by @ Laura Nuño Muñoz)……………………………………………………………………………………. 16 Figure 2.3: Side and top view of upper part and lower part of cephalopod beak with their different measures (Wolff, 1984)……………………………………………….................. 17 Figure 3.1: Relationship between cumulative number of prey species identified in the stomach contents and cumulative number of stomachs analyzed of E. spinax……………... 27 Figure 3.2: Representation of quantitative methods (IRI, %N, %Wand %FO) of the three main prey groups in the diet of E. spinax…………………………………………………... 28 Figure 3.3: Relative importance by number (%N) of the main groups of prey (left) and of the different orders of prey (right) in the diet of E. spinax (N=97)…………………………. 29 Figure 3.4: Relative importance by weight (%W) of main groups of prey (left) and the different orders of prey (right) in the diet of E. spinax (N=97)…………………………….. 29 Figure 3.5: Frequency of occurrence (%FO) of main groups of prey (left) and the different orders of prey (right) in the diet of E. spinax (N=97)………………………………………. 30 Figure 3.6: Relative importance (%IRI) of main groups of prey (left) and the different orders of prey (right) in the diet of E. spinax (N=97)……………………………………… 30 Figure 3.7: Representation of the quantitative methods of the main groups of prey (left) and the relative importance (IRI) of prey items (right) in the diet of E. spinax female specimens (N=51)…………………………………………………………………………. 33 Figure 3.8: Representation of the quantitative methods of the main groups of prey (left) and the relative importance (IRI) of prey items (right) in the diet of E. spinax male specimens (N=46)…………………………………………………………………………. 33 Figure 3.9: Dendogram representation obtained by CLUSTERS analysis of the relative importance in the diet for both sexes of E. spinax specimens. The eight groups defined at similarity level of 17% are indicated by the dashed line. ( : A, B and C)………………….. 34 Figure 3.10: MDS plot of relative importance in the diet for both sexes of E. spinax specimens. The main five groups defined at similarity level of 17% with superimposed clusters are indicated by the dashed line…………………………………………………. 35 Figure 3.11: Representation of the quantitative methods of the main groups of prey (left) and the relative importance (IRI) of prey items (right) in the diet of immature female specimens of E. spinax (N= 30)…………………………………………………………… 37 Figure 3.12: Representation of the quantitative methods of the main groups of prey (left) and the relative importance (IRI) of prey items (right) in the diet of E. spinax mature female specimens (N=21)…………………………………………………………………. 37 Figure 3.13: Representation of the quantitative methods of the main groups of prey (left) and the relative importance (IRI) of prey items (right) in the diet of E. spinax immature male specimens (N=23)…………………………………………………………………… 38 iv Figure 3.14: Representation of the quantitative methods of the main groups of prey (left) and the relative importance (IRI) of prey items (right) in the diet of E. spinax mature male specimens (N=23)…………………………………………………………………………. 38 Figure 3.15: Dendogram representation obtained by CLUSTERS analysis of the relative importance in the diet for both maturity stages
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