Composition, distribution, and diversity of pelagic ...

Marine Biology Research, 2009; 5: 328
344

ORIGINAL ARTICLE

Composition, distribution, and diversity of pelagic fishes around the Canary Islands, Eastern Central Atlantic

RUPERT WIENERROITHER1*, FRANZ UIBLEIN1, FERNANDO BORDES2 & TERESA MORENO2 Institute of Marine Research, Bergen, Norway; 2Instituto Canario de Ciencias Marinas, Telde, Gran Canaria, Spain

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1

Abstract Oceanic islands of volcanic origin have a narrow shelf and a steep slope that should lead to considerable spatial overlap among coastal and oceanic fauna. During six pelagic surveys in the Canarian archipelago, Eastern Central Atlantic, over 65,000 fishes belonging to 211 species were collected at depths between 8 and 1035 m. The mesopelagic families of the lanternfishes (Myctophidae) and the bristlemouths (Gonostomatidae) accounted for about 50% of all specimens. By multivariate classification and ordination methods four different assemblages associated with mesopelagic, epipelagic
oceanic or coastal habitats could be identified. Two of these assemblages were coastal, differing in the proportion of meso- and epipelagic species. These data indicate intense horizontal migrations of mesopelagic fishes (mainly Myctophidae) into the neritic realm and increased interactions between coastal and oceanic habitats. Alpha diversity indices were higher and dominance was lower in oceanic habitats compared to the coastal realm. No marked differences among oceanographically similar areas of the entire archipelago were found. Beta diversity as a measure of similarity among sites or samples revealed variabilities between areas south of Gran Canaria and Fuerteventura islands. A considerable heterogeneity in species distribution was found off SE Fuerteventura in an area with high hydrographic variability. Therefore, both topography and hydrography are important factors influencing the distribution and abundance of pelagic fishes in this oceanic archipelago.

Key words: Atlantic, Canary Islands, diel migrations, diversity, mesopelagic fishes, myctophidae

Introduction Apart from continents, shallow seamounts, or oceanic islands, the vast pelagic realm actually lacks any physical structure which could serve as a distribution barrier. Nevertheless, many of its inhabitants have well-defined regions of occurrence, sometimes being limited to relatively small areas. Conditions in the horizontal strata are spatially homogenous with patterns of seasonal and latitudinal variability (Robison 2004). Topographic and meso-scale hydrographic features proved to be the most influential for species distribution for islands of volcanic origin, like the Canarian archipelago, in the Eastern Central Atlantic. The special topographic conditions around such islands should intensify the interactions among coastal, oceanic, benthic, and benthopelagic organisms (Uiblein & Bordes 1999). This hypothesis was

supported by Bordes et al. (1999), who reported the occurrence of two typical shelf-dwelling species (Scomber colias Gmelin, 1789 and Sardinella aurita Valenciennes, 1847) in oceanic waters together with mesopelagic fishes (e.g. Lampanyctus alatus Goode & Bean, 1896, Lobianchia dofleini (Zugmayer, 1911)), and Wienerroither (2003), who found numerous lanternfishes (e.g. Diaphus dumerilii (Bleeker, 1856), Hygophum hygomii (Luetken, 1892), Lobianchia dofleini) in coastal waters. In addition, the Canarian archipelago shows a particular hydrology. The islands lie in the southward-directed Canary Current and are also under the influence of deep-water masses from the North Atlantic, the Mediterranean, and the Antarctic (Mittelstaedt 1983). Topologically induced deep water meanders (Longhurst 1998) and eddies

*Correspondence: Rupert Wienerroither, Institute of Marine Research, P.O. Box 1870, Nordnes, 5817 Bergen, Norway. E-mail: [email protected] Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark (Accepted 9 September 2009; Printed 23 June 2009) ISSN 1745-1000 print/ISSN 1745-1019 online # 2009 Taylor & Francis DOI: 10.1080/17451000802478055

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Pelagic fishes around the Canary Islands (Arı´stegui et al. 1994, 1997) as well as seasonally varying upwellings (Uiblein et al. 1998), offshore water filaments, eddies, and island wakes (Barton et al. 1998) lead to a high complexity and small-scale hydrographic variability both horizontally and vertically. These influence chlorophyll values and primary production and hence the distribution of fishes. The structure of mesopelagic micronekton assemblages has been the subject of several investigations (Hulley 1992; Gonza´lez & Sa´nchez 2002; Fock et al. 2004; Pusch et al. 2004a), revealing a close relationship to physical and trophic conditions. The decreasing water depth around seamounts reduces density and diversity of mesopelagic fish (Pusch et al. 2004b), which respond in different ways to the impingement with the demersal fauna (Porteiro & Sutton 2007). Auster et al. (1992) ascribe the aggregation behaviour of myctophid fishes with other pelagic fauna to predation risk reduction and more profitable search for prey. In a study using acoustics and a deployed camera for in-situ identification of pelagic fauna off Hawaiian Islands, BenoitBird & Au (2006) observed a highly dynamic use of adjacent oceanic and coastal habitats by mesopelagic fishes. They ascribed their findings to horizontal migrations of certain faunal groups including myctophid fishes, and found in an earlier study (BenoitBird & Au 2003) large differences in the overall distribution patterns and densities of mesopelagic animals, but did not investigate spatial distribution, assemblage structure, and diversity patterns at high taxonomic resolution. The understanding of the relationship between species richness and its spatial change is fundamental to the assessment of spatial diversity patterns (Koleff & Gaston 2002). To our knowledge few studies have been undertaken so far to thoroughly understand the shallow and deep pelagic fish assemblage structure of oceanic islands. In the present study we further examine earlier hypotheses (see Bordes et al. 1999; Uiblein & Bordes 1999; Wienerroither 2003) that the narrow shelf and the steep slope around oceanic islands facilitate the use of the productive coastal zone by vertically migrating mesopelagic fishes and the increased abundance of the coastal fauna in the epipelagic oceanic realm. The objective of this study is to identify the species composition and distribution of pelagic fishes in the immediate surroundings of the Canary Islands in order to determine (1) overall and local diversity, and (2) the faunal change between individual stations, different habitats, and areas within the islands. The influence of sampling depth, bottom depth, and time of day as important ecological factors on species composition, distribution, and diversity are also discussed.

329

Material and methods Six pelagic trawling surveys with the vessel B/E ‘La Bocaina’ were carried out within the Canarian Archipelago between 1997 and 2002 (month and year follow the acronym for each cruise): ‘La Bocaina 11/97’ (B), ‘ECOS 04/99’ (C), ‘Mesopelagic 05/99’ (D), ‘Pelagic 01/00’ (E), ‘Pelagic 11/00’ (F), and ‘Bocaina 03/02’ (G). The trawl tows were conducted horizontally during day and night, at different depths (epipelagic: 8
219 m; mesopelagic: 215
1009 m) and above different bottom depths from coastal (min. bottom depth 40 m) to oceanic (max. bottom depth 2525 m) waters. Exact data concerning duration, location, trawling and bottom depth, of all surveys and tows are given in Table I. The maps of the surveys and the single sampling stations, indicating the type (coastal, epipelagic or mesopelagic), the length, and the direction of the trawls are shown in Figures 1 and 2. Trawl tows overlapping the 200 m depth line which demarcates the epi- and mesopelagic realm were considered as epipelagic. Trawl tows overlapping the 200 m bottom depth line demarcating the coastal and oceanic realm were considered as coastal if the range of the bottom depth during the haul was less than 200 m and as epipelagic if the range was more than 200 m. A commercial trawl with 80 m maximum horizontal opening was used (average vertical opening during tows 6.6 to 16.5 m). Cod-end mesh size was 2 mm and the opening of the cod-end was strengthened by a steel ring of 1.5 m diameter. Samples were scaled to a trawling time of 1 h. Characteristics of the vessel and the net, as well as a description of the fishing operations are given in Bordes et al. (1999) and Wienerroither (2003). The fishes were fixed in 7% formalin and later transferred to 70% ethanol. The specimens of the surveys ‘La Bocaina 11/97’ and ‘ECOS 04/99’ have been included into the collections of the Zoological Museum of the University of Copenhagen (ZMUC), Denmark, and of the Instituto Canario de Ciencias Marinas (ICCM), Telde, Gran Canaria, Spain. Specimens of the remaining surveys are all deposited at ICCM. Species identification is based on the following literature: Badcock (1982), Bigelow et al. (1964), Hulley (1981), Johnson (1974), Krefft (1970, 1971), Nafpaktitis et al. (1977), Nakamura & Parin (1993), Nelson (2006), Nielsen & Smith (1978), Nielsen & Bertelsen (1985), Rofen (1966), and Whitehead et al. (1984
1986). The occurrence of species in Canarian waters and general distribution have been checked using Badcock (1970), Badcock & Merrett (1976), Bordes et al. (1999), Brito et al. (2002), Hureau & Monod (1979), Kotthaus (1972),

330

R. Wienerroither et al.

Table I. Characteristics of trawl tow stations of all surveys. Epipelagic stations in normal, coastal stations in italics, and mesopelagic stations in bold letters. Stations B4, B7, B10, C1, C3, C11, C20, E4, F4, G9, and G11 were without result. See text for further explanations.

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Survey/ Station B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12 B13 B14 B15 B16 B17 B18 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 D1 D2 D3 D4 D5 D6 E1 E2 E3 E4 E5 E6 E7 E8 E9 E10 E11 F1 F2 F3 F4

Date

Time

Initial latitude, longitude

Final latitude, longitude

Trawl depth (range, in m)

Bottom depth (range, in m)

09 Nov 97 10 Nov 97 10 Nov 97 10 Nov 97 12 Nov 97 13 Nov 97 14 Nov 97 15 Nov 97 15 Nov 97 16 Nov 97 16 Nov 97 16 Nov 97 18 Nov 97 20 Nov 97 20 Nov 97 21 Nov 97 23 Nov 97 24 Nov 97 08 Apr 99 09 Apr 99 10 Apr 99 10 Apr 99 11 Apr 99 12 Apr 99 13 Apr 99 14 Apr 99 14 Apr 99 15 Apr 99 15 Apr 99 22 Apr 99 23 Apr 99 23 Apr 99 23 Apr 99 24 Apr 99 25 Apr 99 26 Apr 99 26 Apr 99 30 Apr 99 30 Apr 99 30 Apr 99 01 May 99 11 May 99 11 May 99 11 May 99 12 May 99 12 May 99 12 May 99 19 Jan 00 19 Jan 00 22 Jan 00 22 Jan 00 25 Jan 00 25 Jan 00 26 Jan 00 26 Jan 00 27 Jan 00 27 Jan 00 27 Jan 00 10 Nov 00 12 Nov 00 12 Nov 00 14 Nov 00

20:35
21:35 17:20 18:18 20:12
21:12 11:50
12:24 06:40
07:10 06:25
06:52 14:15
15:15 10:20
11:00 19:25 20:25 00:10
01:23 03:05
04:05 23:25
00:35 06:05
07:05 19:45 20:45 23:50
00:50 21:20
22:20 22:08
23:08 00:25
01:00 19:23
20:50 21:17
22:00 05:13
06:00 21:28
23:30 09:45 11:40 22:13
23:41 21:51
22:55 05:38
06:45 21:20
22:15 10:35 12:25 15:02
15:55 22:35
23:25 01:05
02:05 16:55 18:40 21:50
22:45 00:00
01:20 22:40
23:45 01:01
02:09 12:10 13:50 07:06
08:00 17:13 18:20 21:52
23:50 21:15
23:10 05:55
07:05 08:35 09:40 22:15
23:15 09:05 10:05 21:35 22:35 23:45
00:45 18:30 19:55 22:10
23:10 14:35 15:50 23:15
23:45 16:25 18:00 20:21
21:15 15:20 16:40 20:15
21:35 15:25 16:55 20:15
20:45 21:45
22:45 20:38
21:28 18:28
19:17 21:59
22:46 11:00
11:52

28807,46? N 14802,48? W 28806,38? N 13857,83? W 28810,04? N 14809,46? W 28810,23? N 14805,19? W 28802,50? N 14826,28? W 28851,55? N 13854,29? W 28855,23? N 13834,57? W 28858,67? N 13828,74? W 29823,12? N 13812,23? W 29820,42? N 13821,88? W 29822,50? N 13833,36? W 28850,06? N 13853,01? W 28807,95? N 14801,63? W 27838,30? N 15837,64? W 27840,99? N 15844,21? W 28807,23? N 15847,59? W 27 850,20? N 15819,27? W 27 851,58? N 15818,71? W 28851,75? N 13844,02? W 28850,30? N 13851,52? W 28849,69? N 13852,47? W 28810,07? N 14800,31? W 28807,29? N 14803,65? W 28805,76? N 14803,85? W 28808,43? N 14812,47? W 28807,85? N 14802,32? W 28849,61? N 13845,97? W 28849,82? N 13837,89? W 28851,30? N 13841,63? W 27842,78? N 15849,74? W 27 846,05? N 15848,70? W 27838,99? N 15839,43? W 27843,08? N 15843,70? W 27 843,78? N 15847,00? W 28811,38? N 16850,51? W 28807,60? N 16846,16? W 28810,71? N 16853,77? W 28804,60? N 17821,20? W 28818,98? N 17806,61? W 28806,84? N 17823,31? W 28841,90? N 17859,46? W 28839,50? N 13826,49? W 28834,57? N 13831,57? W 28849,29? N 15822,68? W 28848,30? N 15823,67? W 29804,05? N 16856,10? W 29802,45? N 16858,18? W 27856,97? N 15816,52? W 28800,05? N 15820,45? W 28812,13? N 15831,58? W 28811,49? N 15838,13? W 27841,51? N 15831,39? W 27844,58? N 15824,40? W 28804,16? N 15855,10? W 28805,24? N 15849,56? W 27849,08? N 15854,01? W 27 841,65? N 15842,91? W 27 841,82? N 15843,27? W 28810,69? N 15831,73? W 28803,04? N 15821,37? W 28803,38? N 15820,70? W 27 859,53? N 15820,53? W

28805,96? N 14805,92? W 28805,17? N 14800,42? W 28809,72? N 14804,70? W 28810,02? N 14807,18? W 28802,21? N 14824,23? W 28850,16? N 13854,51? W 28854,25? N 13838,19? W 28856,98? N 13830,11? W 29820,37? N 13811,96? W 29816,58? N 13823,92? W 29819,72? N 13833,59? W 28847,27? N 13852,11? W 28806,34? N 14804,23? W 27836,98? N 15839,98? W 27843,36? N 15846,66? W 28805,07? N 15850,17? W 27852,80? N 15818,27? W 27849,87? N 15818,71? W 28849,01? N 13846,02? W 28847,30? N 13852,67? W 28847,29? N 13852,89? W 28809,57? N 14807,11? W 28805,62? N 14809,88? W 28804,43? N 14808,34? W 28805,15? N 14815,71? W 28806,33? N 14806,65? W 28846,41? N 13847,25? W 28845,50? N 13841,62? W 28848,16? N 13843,95? W 27839,77? N 15848,58? W 27844,15? N 15846,49? W 27836,21? N 15843,42? W 27841,13? N 15842,58? W 27841,37? N 15843,46? W 28807,53? N 16847,98? W 28810,95? N 16850,31? W 28805,89? N 16851,04? W 28802,37? N 17819,43? W 28818,09? N 17803,89? W 28802,36? N 17819,96? W 28834,61? N 17856,36? W 28836,90? N 13829,24? W 28831,85? N 13834,12? W 28846,86? N 15824,52? W 28846,40? N 15825,80? W 29802,46? N 16858,30? W 29800,60? N 17800,20? W 28800,37? N 15818,07? W 28803,48? N 15821,56? W 28812,62? N 15835,50? W
27840,27? N 15834,77? W 27843,82? N 15828,42? W 28802,39? N 15856,49? W 28802,71? N 15853,57? W 27851,64? N 15856,73? W 27842,36? N 15844,61? W 27843,23? N 15846,05? W 28810,60? N 15834,48? W 28800,52? N 15820,28? W 28800,94? N 15820,73? W 27857,86? N 15821,14? W

71
78 500 523 34
69 22
35 40
44 28
43 13
42 53
83 527 557 20
64 34
46 31
43 90
107 592 603 28
63 42
66 30
52 116
146 28
39 8
39 25
39 19
50 382 511 23
52 19
40 47
67 18
33 258 600 12
40 38
49 33
53 480 694 24
40 18
61 25
47 45
71 553 716 34
52 255 535 25
70 18
42 38
40 495 561 42
47 517 591 448 526 48
66 467 566 17
50 356 402 37
66 490 510 10
70 578 610 40
45 493 503 25
34 41
64 55
90 17
45 43
90 37
64

1360
1413 1067 1390 617
1457 49
85 130
530 656
860 128
217 101
120 1280 1350 94
144 586
692 70
115 1183
1442 1638 1667 116
344 104
112 136
231 181
260 117
220 79
99 98
112 102
695 1264 1351 1400
1544 67
314 1254
1359 87
165 1031 1077 756
770 1145
1315 82
90 1069 1384 57
115 100
123 74
132 75
176 1213 1409 90
107 944 1283 110
118 96
784 1327
1349 1287 1306 1646
1782 1940 2525 1660 2120 1463
2119 765 845 105
294 949 1455 60
122 950 1260 76
186 1239 1644 101
280 767 1096 75
86 75
92 132
853 103
263 98
414 102
240































































Pelagic fishes around the Canary Islands

331

Table I (Continued)

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Survey/ Station F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 G1 G2 G3 G4 G5 G6 G7 G8 G9 G10 G11 G12 G13 G14 G15 G16 G17 G18 G19 G20 G21 G22 G23 G24 G25 G26 G27

Date

Time

Initial latitude, longitude

Final latitude, longitude

Trawl depth (range, in m)

Bottom depth (range, in m)

14 Nov 00 15 Nov 00 15 Nov 00 17 Nov 00 19 Nov 00 19 Nov 00 19 Nov 00 20 Nov 00 20 Nov 00 21 Nov 00 21 Nov 00 21 Nov 00 21 Nov 00 22 Nov 00 22 Nov 00 07 Mar 02 08 Mar 02 09 Mar 02 09 Mar 02 10 Mar 02 10 Mar 02 11 Mar 02 12 Mar 02 13 Mar 02 13 Mar 02 14 Mar 02 14 Mar 02 14 Mar 02 14 Mar 02 15 Mar 02 15 Mar 02 15 Mar 02 15 Mar 02 15 Mar 02 16 Mar 02 16 Mar 02 16 Mar 02 17 Mar 02 17 Mar 02 17 Mar 02 17 Mar 02 18 Mar 02

22:33
23:13 21:20
22:03 23:04
23:53 17:21 18:39 11:00 12:14 13:28 14:38 18:24
20:04 18:28 19:35 21:16
22:18 12:08 13:23 15:01 16:01 18:36
19:10 21:30
22:34 11:53 12:53 14:50 15:55 22:34
23:52 19:54
20:59 17:35 19:00 21:55
23:03 00:10
01:12 10:39 11:05 21:20
21:54 20:35 21:35 13:18
14:00 16:18 17:20 10:05
10:40 14:01 15:05 16:56 18:20 21:30
22:00 10:55
11:30 12:52
13:30 15:06 15:45 16:50 17:45 21:09
21:45 13:18 14:35 20:10
20:52 22:14 22:50 00:24 01:05 02:47 03:40 19:56
20:48 22:03
23:35 00:46 02:00

27 844,96? N 15826,21? W 27 841,04? N 15842,19? W 27 842,21? N 15844,79? W 27838,12? N 15847,02? W 27837,49? N 15845,05? W 27840,32? N 15848,57? W 27 841,39? N 15843,84? W 28802,70? N 15856,76? W 28803,32? N 15851,38? W 27837,21? N 15839,71? W 27836,26? N 15840,36? W 27833,81? N 15821,66? W 27837,91? N 15838,55? W 27836,13? N 15848,77? W 27836,01? N 15846,38? W 28806,91? N 14813,87? W 28809,49? N 14800,21? W 28804,15? N 14814,83? W 28808,22? N 14803,44? W 28804,46? N 14814,80? W 28808,50? N 14802,93? W 28809,89? N 14801,28? W 28808,54? N 14806,45? W 28809,46? N 14810,29? W 28807,78? N 14806,21? W 28807,30? N 14801,00? W 28804,74? N 14801,90? W 28804,17? N 14800,61? W 28808,76? N 14812,22? W 28804,08? N 14809,47? W 28803,70? N 14809,75? W 28802,72? N 14810,50? W 28803,37? N 14809,79? W 28803,69? N 14809,38? W 28803,42? N 14815,01? W 28811,42? N 13859,82? W 28803,20? N 14810,10? W 28803,08? N 14810,24? W 28802,86? N 14810,33? W 28810,48? N 14802,56? W 28804,36? N 13858,91? W 28804,56? N 13859,73? W

27 844,22? N 15828,23? W 27 841,85? N 15844,83? W 27 843,75? N 15846,99? W 27839,52? N 15850,05? W 27839,54? N 15847,82? W 27841,92? N 15851,22? W 27 844,76? N 15848,54? W 28801,24? N 15858,53? W 27 859,90? N 15853,30? W 27835,82? N 15842,30? W 27837,30? N 15838,11? W 27832,73? N 15819,18? W 27836,44? N 15841,52? W 27835,26? N 15846,87? W 27837,05? N 15848,94? W 28803,95? N 14816,75? W 28810,33? N 14803,85? W 27859,83? N 14817,44? W 28807,31? N 14807,31? W 28802,18? N 14817,21? W 28807,89? N 14805,88? W 28809,79? N 14803,55? W 28807,36? N 14808,74? W 28809,23? N 14807,76? W 28808,34? N 14803,69? W 28807,29? N 14803,49? W 28803,75? N 13859,02? W 28802,22? N 13857,74? W 28807,43? N 14813,26? W 28802,02? N 14811,03? W 28801,63? N 14811,07? W 28800,98? N 14812,46? W 28805,29? N 14808,10? W 28801,49? N 14811,04? W 28800,26? N 14816,79? W 28809,35? N 14801,68? W 28801,27? N 14811,37? W 28800,83? N 14811,73? W 28800,79? N 14811,80? W 28809,90? N 13859,80? W 28803,31? N 14803,46? W 28804,00? N 14803,56? W

20
48 37
64 47
71 434 606 622 813 310 530 24
57 444 900 37
46 495 1009 592 637 29
31 31
37 464 924 496 630 24
60 13
54 440 665 22
130 34
123 617 915 98
219 269 529 19
31 429 572 31
140 323 570 632 1035 15
43 30
99 185
211 311 378 470 695 30
139 308 498 15
33 215 261 310 427 565 980 20
33 25
62 310 525

59
75 98
202 92
112 927 1653 928 1287 1174 1650 98
228 1634 1765 88
117 1344 1620 1316 1688 2189
2438 1305
1603 1440 1690 1358 1564 140
284 217
606 1107 1327 1000
1211 747
1006 980 1162 137
464 656 1026 40
77 959 1198 1246
1347 1406 1447 1447 1529 96
211 1439
1677 1461
1680 1000 1690 1364 1491 1462
1672 1262 1592 43
570 1499 1701 1505 1750 1523 1750 51
529 1374
1577 1364 1548
























Lloris et al. (1991), Que´ro et al. (1990), Rodrı´guez (2000), Rudyakov (1979), Whitehead et al. (1984
1986), and FishBase (http://www.fishbase.org). Multivariate community analysis Epipelagic trawl stations conducted during the day (i.e. G15 and G16) as well as singletons with respect to the whole data set (station B8) were excluded a priori. Hierarchical agglomerative clustering with group-average linking, based on the Bray
Curtis Similarity measure, was used to delineate groups with distinct community structure (Field et al. 1982). The normal or q-type analysis uses all species and treats samples as individual observations, each being composed of a number of attributes (i.e. the















































various taxa collected per tow). The analysis was done based on root
root transformed densities using the PC-ORD software package. The transformation down-weights the more abundant species and is invariant to scale range (Field et al. 1982). The specification of the similarity level for cluster separation was chosen to be data-driven. To compensate for possible misinterpretations derived from the exclusive use of dendrograms in community studies (Field et al. 1982), non-metric multidimensional scaling (MDS) was adopted. This method produces an ordination of the stations or species in two dimensions. Indicator species values were calculated using the method of Dufrene & Legendre (1997) to detect and describe the value of different species for

332

R. Wienerroither et al.

(a)

10 9

11

Type, length, and direction of trawl Coastal Epipelagic Mesopelagic

Azores Madeira

Canary Islands Africa 2000

Cape 1000

Verde

Tenerife

15 N 20 N 25 N 30 N 35 N

Europe

Lanzarote 6

Isobaths (100, 500, 1000, 2000, 3000 m)

29 N

8

7 12

28 30’N

Fuerteventura 4

-25 W -20 W -15 W -10 W

3

13 2

1

16

28 N

5

Gran Canaria 17 18

15 14

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0

27 30’N

50 km

16 30’W

16 W

15 30’W

15 W

14 30’W

14 W

13 30’W

(b) D6 D5

Lanzarote C2C1 C11 C3 C9 C10

D3 C23

D4

La Palma

29 N

D1

D2 C21 La Gomera C17 Tenerife C22 C19 C18 C20

El Hierro

28 30’N

Fuerteventura

Gran Canaria C13 C16 C15 C12 C14

C4 C7 C8 C5 C6

0

28 N

27 30’N

50 km

18 W

17 30’W

17 W

16 30’W

16 W

15 30’W

15 W

14 30’W

14 W

13 30’W

Figure 1. Map of survey (a) ‘La Bocaina 11/97’ (B1
B18), and (b) ECOS 04/99’ (C1
C23) and ‘Mesopelagic 05/99’ (D1
D6) (legend as in Figure 1a). Station numbers refer to Table I. Insert in Figure 1a: the Canarian Archipelago, situated in the Eastern Central Atlantic.

the clusters derived by the classification and ordination method (McCune & Grace 2002). Information on the concentration of species abundance in a particular group is combined with the fidelity of occurrence of a species in a particular group, whereupon perfect indication means that the presence of a species points to a particular group without error, at least with the data set at hand. The statistical significance is evaluated by a randomization test (Monte Carlo Test, 1000 runs) which allows estimating exact significance without relying on the assumptions required for the standard asymptotic method.

Ecological diversity The diversity and abundance of species was analysed using a representative set of indices (Magurran 2004) including total number of species and total number of individuals, species richness (Shannon
Wiener H’ and Simpsons D Index), evenness (Equitability J), and dominance (Berger
Parker). The hypotheses were tested that there are differences in diversity among (1) the principal clusters obtained from the multivariate analysis (result-driven data selection) and (2) areas within the Canarian archipelago (a-priori data selection). For comparison among areas epi- and mesopelagic tows south of

Pelagic fishes around the Canary Islands

(a)

28 15’N E3 E4

E7

F1

E8 E2 F13

F3 F2

F12

Gran Canaria

F4

28 0’N E1

E9 F11 F10 F8 F18

F7

F5

27 45’N

E6

E11 E10 E5

F6 F17 F9 F19 F15 F14

F16

0

10

20

333

Results From a total of 104 trawl tows (35 coastal, 32 epipelagic and 37 mesopelagic), 93 resulted in the capture of 65,815 adult or juvenile fishes (14,609 epipelagic, and 51,206 meso-, bathy-, benthopelagic, or bathydemersal fishes). These belong to 19 orders, 51 families, 123 genera, and 211 species. Thirteen species are new records for the area. An overview of all species, indicating number of individuals and the survey in which they were captured is provided in Table II.

km

16 0’W

(b)

15 45’W

15 30’W

15 15’W

15 0’W

Multivariate community analysis Type, length, and direction of trawl Coastal Epipelagic Mesopelagic

Fuerteventura 21

25

Isobaths 100, 500, 1000, 2000, 3000 m

9

14

8 10

7 6 4

28 10’N 2 11

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1

3

20

17

28 5’N

27

15 18 16 19 22 23

5

12 26 13 0

24

5

10

28 0’N

km

14 20’W

14 15’W

14 10’W

14 5’W

14 0’W

Figure 2. Map of survey (a) ‘Pelagic 01/00’ (E1
E11) and ‘Pelagic 11/00’ (F1
F19) (legend as in Figure 2b) and (b) ‘Bocaina 03/02’ (G1
G27). Station numbers refer to Table I.

Gran Canaria (epipelagic stations: B15, C12, F 17; mesopelagic stations: B14, C14, E5, F8, F9, F10, F14, F15, F18, F19) and south of Fuerteventura (epipelagic stations: B1, B3, B13, C4, C5, C6, C7, C8, G2, G4, G5, G7, G15, G16, G19, G21, G25, G26; mesopelagic stations: B2, G3, G6, G8, G10, G12, G13, G17, G18, G20, G22, G23, G24, G27), were grouped. Mean and confidence intervals for indices of clusters and areas were calculated and pairwise t-tests were used for additional statistical examination. Beta diversity investigates the degree of association or similarity of sites or samples and is higher, the fewer species the different communities share (Magurran 2004). It was used to find possible differences (1) between the areas south of Gran Canaria and Fuerteventura and (2) variations among three selected groups of mesopelagic tows from survey 03/02 off SE Fuerteventura (Figure 2b; group 1: G6, G8, G10; group 2: G22, G23, G24; group 3: G12, G13; G27) to study small-scale discontinuities. Two indices, recorded to be the best to determine the degree of turnover in species composition, Whittaker bW and Wilson & Shmida bT (Wilson & Shmida 1984; Magurran 2004), were used based on presence and absence data.

The dendrogram resulting from the Bray
Curtis analysis of the 90 trawl stations is shown in Figure 3. Most of the stations are allocatable to four main clusters (1
4). One smaller cluster (cluster 5) is formed by four trawl stations. Two stations deviate in species composition from all others. The results of multidimensional scaling (MDS) using the same similarity matrix as above, delineating groups of stations from the dendrogram is shown in Figure 4. This analysis gives essentially the same picture as the dendrogram. The principal factor of association was the trawling depth in combination with the bottom depth. Mesopelagic tows are found in cluster 2 and the smaller cluster 5, whereas coastal tows are represented in cluster 3 and 4. Epipelagic oceanic tows formed the cluster 1 and are distributed in all other clusters except cluster 5. On account of the many stations no fixed similarity level for cluster separation was defined, therefore clusters vary from 45.8% (cluster 2) to 14.2% (cluster 4) similarity. Figure 5 illustrates epipelagic and coastal tows around Gran Canaria and Fuerteventura and their affiliation to the clusters, showing also the spatial overlap between cluster 3 and 4. Below is a detailed characterization of each of the five clusters. . Cluster 1, similarity level 41.1%, 13 stations, mean water depth 1427 m, habitat epipelagic
oceanic: it comprises only epipelagic tows, characterized by a high variability in abundance of vertically migrating mesopelagic species and by three epipelagic species (Sardinella aurita, Scomber colias, Trachurus picturatus). Indicator species for this group are myctophids (Table III), known for their intense daily vertical migration behaviour. All tows are restricted to the oceanic realm (Figure 5). . Cluster 2, similarity level 45.8%, 33 stations, mean water depth 1388 m, habitat mesopelagic: with the exception of one far-offshore epipelagic trawl station (D6), cluster 2 is composed of mesopelagic tows exclusively. The relatively

334

R. Wienerroither et al.

Table II. List of species encountered in the six surveys, with indication of number of specimens per survey. New records for the area are emphasized in bold, systematic order is according to Nelson (2006). Order

Family/Sub-family

Squaliformes

Dalatiidae

Albuliformes Anguilliformes

Halosauridae Derichthyidae Nemichthyidae

Serrivomeridae Saccopharyngif. Clupeiformes

Argentiniformes

Saccopharyngidae Eurypharyngidae Engraulidae Clupeidae

Opisthoproctidae

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Microstomatidae

Platytroctidae

Alepocephalidae

Stomiiformes

Diplophidae Gonostomatidae

Sternoptychidae

Phosichthyidae

Astronesthinae

Species Etmopterus pusillus (Lowe, 1839) Squaliolus laticaudus Smith & Radcliffe, 1912 Aldrovandia affinis (Guenther, 1877) Derichthys serpentinus Gill, 1884 Avocettina infans (Guenther, 1878) Nemichthys curvirostris (Stroemman, 1896) Nemichthys scolopaceus Richardson, 1848 Serrivomer beanii Gill & Ryder, 1883 Serrivomer lanceolatoides (Schmidt, 1916) Saccopharynx ampullaceus (Harwood, 1827) Eurypharynx pelecanoides Vaillant, 1882 Engraulis encrasicolus (Linnaeus, 1758) Sardina pilchardus (Walbaum, 1792) Sardinella aurita Valenciennes, 1847 Sardinella maderensis (Lowe, 1838) Dolichopteryx longipes (Vaillant, 1888) Opisthoproctus grimaldii Zugmayer, 1911 Opisthoproctus soleatus Vaillant, 1888 Bathylagus greyae Cohen, 1958 Dolicholagus longirostris (Maul, 1948) Melanolagus bericoides (Borodin, 1929) Nansenia groenlandica (Reinhardt, 1840) Barbantus curvifrons (Roule & Angel, 1931) Holtbyrnia macrops Maul, 1957 Maulisia mauli Parr, 1960 Searsia koefoedi Parr, 1937 Bathytroctes microlepis Guenther, 1878 Rouleina maderensis Maul, 1948 Xenodermichthys copei (Gill, 1884) Diplophos taenia Gu¨nther, 1873 Manducus maderensis (Johnson, 1890) Bonapartia pedaliota Goode & Bean, 1896 Cyclothone braueri Jespersen & Ta˚ning, 1926 Cyclothone livida Brauer, 1902 Cyclothone microdon (Guenther, 1978) Cyclothone pallida Brauer, 1902 Cyclothone pseudopallida Mukhacheva, 1964 Gonostoma denudatum Rafinesque, 1810 Margrethia obtusirostra Jespersen & Ta˚ning, 1919 Sigmops bathyphilus (Vaillant, 1884) Sigmops elongatus (Guenther, 1878) Argyropelecus aculeatus Valenciennes, 1850 Argyropelecus affinis Garman, 1899 Argyropelecus gigas Norman, 1930 Argyropelecus hemigymnus Cocco, 1829 Maurolicus muelleri (Gmelin, 1789) Sternoptyx diaphana Hermann, 1781 Sternoptyx pseudobscura Baird, 1971 Valenciennellus tripunctulatus (Esmark, 1871) Ichthyococcus ovatus (Cocco, 1838) Vinciguerria attenuata (Cocco, 1838) Vinciguerria nimbaria (Jordan & Williams, 1895) Vinciguerria poweriae (Cocco, 1838) Astronesthes gemmifer Goode & Bean, 1896 Astronesthes indicus Brauer, 1902 Astronesthes leucopogon Regan & Trewavas, 1929 Astronesthes macropogon Goodyear & Gibbs, 1970 Astronesthes micropogon Goodyear & Gibbs, 1970 Astronesthes neopogon Regan & Trewavas, 1929 Astronesthes niger Richardson, 1845 Borostomias antarcticus (Loennberg, 1905) Borostomias elucens (Brauer, 1906) Borostomias mononema (Regan & Trewavas, 1929)

11/97 04/99 05/99 01/00 11/00 03/02 1 1 1 1 1 1 62 3 1

2 5 3 66 1

34 4

6354 43

5 37 1

1 35

33

1 3

1

1 3

2 1 7 256 111 1 23 12 4 24 4

7

3 4 1 2

1 4 1 100 17 1 13 1 3 160 1 1 2 2 26 2 1 3

8

12 1 8

8 1

1 8 1

3 3270

6 2569

682

788

820 6 3

1 1 13 1 1281

4 34 11 5 8 2 3 41 15 8 58 1328 57

1 2 1 3 586 5 9 113 1 5 2 30 4 3 23 5 7 4 2 71 260 22 1

2 4 3 804

954 2

34 3 2

11 23 8 1

7 5 3 6 44

8 5 1 7 52

17 5

235 40 46 1 94 9

26 32

15 387

2

1

53

1 1 6 674 103 2 1

4 2 749 59 70

160 5 4 6 136 4 6 5 1 1 2 2

1 1 1 2 1 4

10 19 425 97 7 2 3 1 1 5 2

1 1 3

1

Pelagic fishes around the Canary Islands

335

Table II (Continued) Order

Family/Sub-family

Stomiinae

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Melanostomiinae

Idiacanthinae Malacosteinae Aulopiformes

Synodontidae Notosudidae Scopelarchidae

Evermannellidae Alepisauridae Paralepididae

Myctophiformes

Myctophidae

Species Neonesthes capensis (Gilchrist & von Bonde, 1924) Rhadinesthes decimus (Zugmayer, 1911) Stomias boa (Risso, 1810) Stomias brevibarbatus Ege, 1918 Stomias longibarbatus (Brauer, 1902) Chauliodus danae Regan & Trewavas, 1929 Chauliodus sloani Bloch & Schneider, 1801 Bathophilus brevis Regan & Trewavas, 1930 Bathophilus digitatus (Welsh, 1923) Bathophilus longipinnis (Pappenheim, 1914) Bathophilus pawneei Parr, 1927 Bathophilus vaillanti (Zugmayer, 1911) Chirostomias pliopterus Regan & Trewavas, 1930 Echiostoma barbatum Lowe, 1843 Eustomias acinosus Regan & Trewavas, 1930 Eustomias bigelowi Welsh, 1923 Eustomias braueri Zugmayer, 1911 Eustomias fissibarbis (Pappenheim, 1912) Eustomias longibarba Parr, 1927 Eustomias melanostigma Regan & Trewavas, 1930 Eustomias obscurus Vaillant, 1884 Eustomias schmidti Regan & Trewavas, 1930 Eustomias simplex Regan & Trewavas, 1930 Eustomias tetranema Zugmayer, 1913 Flagellostomias boureei (Zugmayer, 1913) Leptostomias bilobatus (Koefoed, 1956) Leptostomias gladiator (Zugmayer, 1911) Leptostomias longibarba Regan & Trewavas, 1930 Melanostomias bartonbeani Parr, 1927 Melanostomias biseriatus Regan & Trewavas, 1930 Melanostomias tentaculatus (Regan & Trewavas, 1930) Photonectes braueri (Zugmayer, 1913) Photonectes dinema Regan & Trewavas, 1930 Photonectes margarita (Goode & Bean, 1896) Photonectes parvimanus Regan & Trewavas, 1930 Idiacanthus fasciola Peters, 1877 Malacosteus niger Ayres, 1848 Photostomias guernei Collett, 1889 Synodus synodus (Linnaeus, 1758) Scopelosaurus lepidus (Krefft & Maul, 1955) Benthalbella infans Zugmayer, 1911 Rosenblattichthys hubbsi Johnson, 1974 Scopelarchus analis (Brauer, 1902) Evermannella melanoderma Parr, 1928 Alepisaurus ferox Lowe, 1833 Omosudis lowii Guenther, 1887 Anotopterus pharao Zugmayer, 1911 Arctozenus risso (Bonaparte, 1840) Lestidiops affinis (Ege, 1930) Lestidiops jayakari (Boulenger, 1889) Lestidiops sphyrenoides (Risso, 1820) Macroparalepis affinis Ege, 1933 Macroparalepis brevis Ege, 1933 Magnisudis atlantica (Kroeyer, 1868) Paralepis brevirostris (Parr, 1928) Paralepis coregonoides Risso, 1820 Stemonosudis intermedia (Ege, 1933) Sudis hyalina Rafinesque, 1810 Benthosema suborbitale (Gilbert, 1913) Bolinichthys indicus (Nafpaktitis & Nafpaktitis, 1969) Bolinichthys supralateralis (Parr, 1928) Centrobranchus nigroocellatus (Guenther, 1873)

11/97 04/99 05/99 01/00 11/00 03/02

8 3 58 17

5 137 1 4 196 34 1 1

72 1

1 22

15 3

1 2 96

88 30

1 67 66

288 69

1 91 63

1

1

2

2

3

13 5

24

2 14

1 23

1 8 4 7 1

1 1 1 2 39

16 1 1

2

1 2 17

2

1

4

1 1 1

2

2 1

5

1 1

1 1 2 1 3

1 2 6

1 64

115

62

24

43 1

51

5

1

2

1

3 40 3 16

5 1 2

3 1

29 3 44

1 1 2 1 2

1 90 6 25

1 1

1 2 2 11 12

20 293 1 1

166 48

7 84

1

2 3 1 22 2

94 295

2 2 896 139

1

2

336

R. Wienerroither et al.

Table II (Continued) Family/Sub-family

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Order

Lampriformes Gadiformes Lophiiformes

Beloniformes Stephanoberycif.

Stylephoridae Regalecidae Melanonidae Melanocetidae Oneirodidae Ceratiidae Lynophrynidae Scomberesocidae Melamphaidae

Rondeletiidae Cetomimidae

Species Ceratoscopelus maderensis (Lowe, 1839) Ceratoscopelus warmingii (Luetken, 1892) Diaphus adenomus Gilbert, 1905 Diaphus dumerilii (Bleeker, 1856) Diaphus effulgens (Goode & Bean, 1896) Diaphus holti Ta˚ning, 1918 Diaphus lucidus (Goode & Bean, 1896) Diaphus metopoclampus (Cocco, 1829) Diaphus mollis Ta˚ning, 1928 Diaphus perspicillatus (Ogilby, 1898) Diaphus problematicus Parr, 1928 Diaphus rafinesquii (Cocco, 1838) Diaphus splendidus (Brauer, 1904) Diaphus termophilus Ta˚ning, 1928 Diaphus vanhoeffeni (Brauer, 1906) Diogenichthys atlanticus (Ta˚ning, 1928) Gonichthys cocco (Cocco, 1829) Hygophum benoiti (Cocco, 1838) Hygophum hygomii (Luetken, 1892) Hygophum reinhardtii (Luetken, 1892) Hygophum taaningi Becker, 1965 Lampadena chavesi Collett, 1905 Lampadena speculigera Goode & Bean, 1896 Lampadena urophaos Paxton, 1963 Lampanyctus alatus Goode & Bean, 1896 Lampanyctus crocodilus (Risso, 1810) Lampanyctus festivus Ta˚ning, 1928 Lampanyctus nobilis Ta˚ning, 1928 Lampanyctus photonotus Parr, 1928 Lampanyctus pusillus (Johnson, 1890) Lepidophanes gaussi (Brauer, 1906) Lepidophanes guentheri (Goode & Bean, 1896) Lobianchia dofleini (Zugmayer, 1911) Lobianchia gemellarii (Cocco, 1838) Myctophum nitidulum Garman, 1899 Myctophum punctatum Rafinesque, 1810 Myctophum selenops Ta˚ning, 1928 Nannobrachium atrum (Ta˚ning, 1928) Nannobrachium cuprarium (Ta˚ning, 1928) Nannobrachium lineatum (Ta˚ning, 1928) Notolychnus valdiviae (Brauer, 1904) Notoscopelus bolini Nafpaktitis, 1975 Notoscopelus caudispinosus (Johnson, 1863) Notoscopelus elongatus (Costa, 1844) Notoscopelus resplendens (Richardson, 1845) Symbolophorus veranyi (Moreau, 1888) Taaningichthys bathyphilus (Ta˚ning, 1928) Taaningichthys minimus (Ta˚ning, 1928) Stylephorus chordatus Shaw, 1791 Regalecus glesne Ascanius, 1772 Melanonus zugmayeri Norman, 1930 Melanocetus johnsonii Guenther, 1864 Oneirodes anisacanthus (Regan, 1925) Ceratias holboelli Kroeyer, 1845 Haplophryne mollis (Brauer, 1902) Scomberesox saurus (Walbaum, 1792) Scomberesox simulans (Hubbs & Wisner, 1980) Melamphaes typhlops (Lowe, 1843) Poromitra capito Goode & Bean, 1883 Poromitra megalops (Luetken, 1878) Scopelogadus beanii (Guenther, 1887) Rondeletia loricata Abe & Hotta, 1963 Cetomimus hempeli Maul, 1969 Cetostoma regani Zugmayer, 1914

11/97 04/99 05/99 01/00 11/00 03/02 61 158 132 41

24 153 2 24

2 47

1 72 24

15 24 1

1 1 1 12 29 3

19

65

20

2 1 23

17

3

336 372 32 44

2

6 35 955 52 13 1 4

247 5 1 1462 143 56 3 1 10 78 1 4 2 16 114 113 364 29 6 107 14 56 6 1 10

63 5

86 21

1

3

16 39 1 37

177 1544 2 2584

3

7

9 65 15

645 53

99

12 1 13 97 15 3 1

14 1 14 2 125 4 5 2320 45 23 7

207 21 25 1332 134 96 4

30 2 2

3 109 1 15

464 5 24

299 56

5 267 184

294 118 10

1144 34 22

3 2

13 16 3 3 29

68 145 11 1115 138 1 1 3 56 2 12 12 137 106 1517 51 1 4 1 52 2 1 4 7

2

290 32

11 4

1

612 170 1 23 1 201 3 18 32 43 1 355

168 6 4

1

1 2 1

1

1

20 634 189 1 1772 156 14 12 184 5 31 8 2 5 335 17 1 1 1 1 1 1 1 1

2 3

5

10 1

1 1

1 112

1 1 1

11 2 3 11 1 1

Pelagic fishes around the Canary Islands

337

Table II (Continued) Order

Family/Sub-family

Beryciformes

Anoplogasteridae Diretmidae Zeiformes Grammicolepididae Gasterosteiformes Macroramphosidae Scorpaeniformes Scorpaenidae Perciformes Percichthyidae Carangidae Caristiidae Sparidae

Chiasmodontidae Gempylidae

Trichiuridae

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Scombridae Nomeidae Caproidae

Species

11/97 04/99 05/99 01/00 11/00 03/02

Anoplogaster cornuta (Valenciennes, 1833) Diretmus argenteus Johnson, 1864 Grammicolepis brachiusculus Poey, 1873 Macroramphosus scolopax (Linnaeus, 1758) Setarches guentheri Johnson, 1862 Howella brodiei Ogilby, 1899 Trachurus picturatus (Bowdich, 1825) Trachurus trachurus (Linnaeus, 1758) Platyberyx opalescens Zugmayer, 1911 Boops boops (Linnaeus, 1758) Pagellus acarne (Risso, 1827) Pagellus erythrinus (Linnaeus, 1758) Pseudoscopelus altipinnis Parr, 1933 Diplospinus multistriatus Maul, 1948 Nealotus tripes Johnson, 1865 Promethichthys prometheus (Cuvier, 1832) Benthodesmus simonyi (Steindachner, 1891) Lepidopus caudatus (Euphrasen, 1788) Auxis rochei (Risso, 1810) Scomber colias Gmelin, 1789 Cubiceps gracilis (Lowe, 1843) Capros aper (Linnaeus, 1758)

high similarity (32.3%) of clusters 1 and 2 indicates a close relationship among the stations of these groups. In fact they share many vertically migrating species, but not the nonor little migratory species (found only in the mesopelagic tows), which delineate the two clusters. MDS (Figure 4) plots the stations of clusters 1 and 2 very closely, but also indicates the high similarity of the stations within and between the clusters. Non-migrating species like Serrivomer beanii and Sigmops elongatus, among others, are the best indicators for this group (Table III). . Cluster 3, similarity level 17.0%, 12 stations, mean water depth 327 m, habitat coastal: this cluster comprises six coastal and six epipelagic samples, composed of several epipelagic species, mainly in low numbers, and vertically migrating myctophids, partly rich in individuals. Diaphus dumerilii is the best indicator species. The mesopelagic species in this cluster obviously perform an intense horizontal migration from the oceanic realm towards the islands (Figure 5). . Cluster 4, similarity level 14.2%, 26 stations, mean water depth 205 m, habitat coastal: the cluster includes most of the tows taken above the continental shelf (coastal) plus eight oceanic epipelagic tows. It is characterized by the highest number of epipelagic species and individuals. As opposed to cluster 3, mesopelagic fishes (in terms of species and individuals) were less frequent in these trawl stations. Among the epipelagic species caught during the six surveys,

1 8

9

2 6

16

1

4 1

1 96

1 116 4

2

1 7

183

1 2 47

1401

1 870

3

17

2

9

5

11 5

5

4 35

2022 5 6

1 2 1

482 428 4 195 17 11 13

2

28 122

6

44 106

385 8

22 324

1166

only Scomber colias and Trachurus picturatus showed up regularly and are indicator species. . Cluster 5, similarity level 44.3%, 4 stations, mean water depth 1294 m, habitat mesopelagic: the mesopelagic tows in this small cluster have a strong affiliation to cluster 2, the stations are partly overlapping (Figure 4), but differ in a slightly lower number of species.

Ecological diversity Alpha diversity. Only the four main clusters (1
4) derived by classification and ordination methods are considered in the diversity analysis (Figure 6). Clusters formed by stations close to the shelf (3 and 4) tend to be different from clustered stations from oceanic waters (1 and 2). Cluster 2 (mesopelagic tows) has the highest diversity and equitability and the lowest dominance. This is in contrast to cluster 4, which is much less diverse but shows a high level of dominance (with cluster 3). The number of species (Figure 6a) is significantly different between all clusters (F 153.36, pB0.001) except between clusters 3 and 4, whereas there are no significant differences in number of individuals between the clusters. Significant differences in diversity indices (H’ between clusters 1
3, 1
4, 2
3, and 2
4, F 56.12, pB0.001; Simpson D between clusters 1
4, 2
3, and 2
4, F 17.02, pB 0.005), equitability (Evenness J between clusters 1
3, 1
4, 2
3, and 2
4, F 56.14, p B0.001) and dominance (Berger
Parker between clusters 1
4, 2
3, and 2
4, F 14.38, p B0.005) among the clusters

338

R. Wienerroither et al. Distance (Objective Function)

2,3E-02

3E+00

100

75

5,9E+00

8,9E+00

1,2E+01

25

0

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Information Remaining (%) 50

B1 B13 D1 C6 C8 D3 G19 F17 G4 G26 C12 G5 F16 B2 B9 B14 E1 C10 D2 D4 C19 E5 D5 F8 F9 F15 F19 C5 E7 E9 G8 G12 G20 F12 F14 F18 G13 G18 G24 G22 G23 G27 C14 D6 C21 G10 E3 G17 F10 G3 B6 B17 B18 B11 G7 G2 G14 F1 F3 F2 C16 G1 G6 B3 B15 B12 C7 B16 E6 F13 F6 F11 E11 E2 F5 F7 E10 G21 G25 C9 C15 E8 C2 C4 C22 C23 C17 C18 B5 C13

Cluster 1 2 3 4 5 6 7

Figure 3. Dendrogram showing classification of the 90 trawl stations, four main clusters (1
4) can be distinguished. Abundances of species were root
root transformed before comparing stations using the Bray
Curtis measure, and the dendrogram formed by group-average sorting. The distance axis indicates the distance between groups, not expressed as a simple distance measure, but as Wishart’s (1969) Objective Function (which is a measure of information loss as agglomeration proceeds): Cluster 16.95, Cluster 26.40, Cluster 3 9.80, Cluster 410.13. The second axis is based on the same function, but is converted to a percentage of information remaining: Cluster 141.1%, Cluster 2 45.8%, Cluster 317.0%, Cluster 4 14.2%.

were revealed by pairwise t-tests, which coincide with non-overlapping 99% confidence intervals (Figure 6b
d). Examinations based on a-priori data selection to detect differences between richness, diversity, equitability, and dominance between the patches of trawl stations to the south of Gran Canaria and Fuerteventura, epi- and mesopelagic tows were treated separately. Pairwise t-tests revealed no significant differences. Beta diversity. To the south of Fuerteventura beta diversity is considerably higher compared to the south of Gran Canaria (Table IV). The two habitats to the south of Gran Canaria have approximately similar beta diversity, whereas there is a remarkable difference between the epi- and mesopelagic realms south of Fuerteventura. Groups 2 and 3 have similar

beta diversity, whereas group 1 (closer to the coast and the upwelling region off Gran Tarajal) is higher in bW and bT (Table IV). Discussion Multivariate community analysis The dense ordination of mesopelagic trawl stations (cluster 2) reveals that these have the most closely related species composition. Although several tows contain very rare and unique species, the tows are primarily unified by the dominant non- or little migrating fishes (e.g. Serrivomer spp., Cyclothone spp.). The far offshore position and the deep sounding of the only epipelagic station within this cluster might contribute to the species composition resembling the mesopelagic tows.

Pelagic fishes around the Canary Islands G6

Cluster 1 2 3 4 5 6 7

G3 G10 G17 F10 F12 E3

C21 E9

C13

G20 G12 C5 E7

F14

F19 F15

B2

G13 F18 F8 G27 G18 G24 D4 F9 G22 E1 D2 B14 D5 G23 C10C19 D6 C14 E5 B9 G8 G19

C12 G4

D3

339

B1

G26 G5 F16 C6 F17

D1

B13

C8

B18 B11

C18 F1

F3

G7

G14

B17

E8

G1

C7 C4 G2

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C2

B6

B12

B15

B3

C22 C17

F2

F11 C23

C16

G21

C15

E6 E10

F7 F13

G25 F5 E11 E2 C9

F6

B16

B5

Figure 4. Ordination of the 90 trawl stations in two dimensions using multidimensional scaling on the same similarity matrix as Figure 3, final stress 14.99250.

Clusters 1 and 2 showed the closest relationships. Their tows were all made in the oceanic realm and contain a high diversity of myctophids, which is their unifying factor. Lepidophanes gaussi is the main indicator species for cluster 1 and all the other indicator species are lanternfishes too (e.g. Benthosema suborbitale, Ceratoscopelus warminigii, Diogenichthys atlanticus). These inhabit the epipelagic realm during night for foraging reasons and are often encountered at higher densities there than in mesopelagic tows. Possible explanations for this phenomenon might be the limited space in near-surface habitats leading to a denser aggregation of specimens and/or biotic or abiotic factors with effects on spatial preferences. The most abundant species in these clusters are all mesopelagic (mainly myctophids), only the epipelagic Scomber colias was encountered in comparable abundances. This confirms the unusual horizontal migration into oceanic waters of this normally shelf-dwelling species, as indicated by Bordes et al. (1999).

Myctophids are also the most influential group in cluster 3. Although Diaphus dumerilii is the best indicator species, other lanternfish species occur in high numbers in trawl tows of this cluster too (e.g. Hygophum hygomii, Lobianchia dofleini, Notoscopelus resplendens). But the latter are also very abundant in other tows and therefore less appropriate as indicators. Diaphus dumerilii shows its highest abundances in rather shallow depths indicating a certain degree of land association. Cluster 3 combines trawls in and close to the coastal zone. Uiblein & Bordes (1999) ascribe the occurrence of mesopelagic species in such shallow waters to the abrupt changeover of depths around islands of volcanic origin. Nevertheless, the findings of such high numbers (e.g. 1561 D. dumerilii in survey 11/00 tow 3, 43
90 m trawling depth; 888 H. hygomii in survey 11/00 tow 1, 55
90 m trawling depth), differ from the observations by Hulley (1986) and Hulley & Prosch (1987), who recorded in the southern Benguela upwelling region the stock of only one myctophid species above a

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Fuerteventura

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0

20

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km Cluster 1 Cluster 3 Cluster 4 100, 500, 1000, 2000, 3000 m depth Figure 5. Epipelagic and oceanic tows around Gran Canaria and Fuerteventura, indicating their affiliation to clusters in classification (Figure 3) and ordination (Figure 4).

bottom depth of less than 300 m. Several species of Diaphus have been found to show spatial affinities to steep slope bottoms and hence characterized as ‘pseudoceanic’ (Merrett 1985; Hulley & Lutjeharms 1989). Cluster 4 shows the highest heterogeneity, deriving from several epipelagic species, especially the two indicator species Scomber colias and Trachurus picturatus. Surprising is the presence of the myctophid

D. dumerilii in this cluster comprising mostly coastal tows. In tows 5, 6, and 7 of survey 11/00, the abundance of the lanternfish was comparatively high (54, 128, and 1075 individuals) and also Boops boops (393 and 271 individuals in tow 5 and 7) and S. colias (387 individuals in tow 5; all numbers extrapolated) showed relatively high numbers. These three trawl stations were typically coastal, although this habitat is naturally very narrow around islands

Table III. Indicator species for the four clusters (I
IV) derived by the classification and ordination method. Relative abundance (RA) of the species in the group of stations over the average abundance of that species in all stations (in % of perfect indication). Relative frequency (RF) of the species in the trawl stations of the group (in % of perfect indication). Indicator values (IV) range from 0 (no indication) to 100 (perfect indication) and are based on a combination of RA and RF. Monte Carlo test of significance of observed indicator value for the species in the particular group. Only species with an indicator value of more than 50 are listed.

Cluster 1

Cluster 2

Cluster 3 Cluster 4

Lepidophanes gaussi Diogenichthys atlanticus Benthosema suborbitale Hygophum reinhardtii Serrivomer beanii Sigmops elongatus Cyclothone pseudopallida Bolinichthys indicus Cyclothone braueri Melamphaes typhlops Diaphus dumerilii Scomber colias Trachurus picturatus

RA %

RF %

IV %

p

65 68 64 62 79 81 79 64 59 100 57 70 68

100 92 92 92 91 82 82 88 94 55 92 92 77

65.5 63.2 58.7 56.9 72.2 66.4 64.7 55.9 55.0 54.5 52.4 64.8 52.7

0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.004 0.006 0.001 0.002

Pelagic fishes around the Canary Islands

(a) 50

341

(b) 3.0

45 2.5

35

Shannon-Wiener H’

Number of Species

40

30 25 20 15 10

2.0

1.5

1.0

5 0

.5 Cluster 1

(c)

Cluster 2

Cluster 3

Cluster 4

(d)

.5

Cluster 1

Cluster 2

Cluster 3

Cluster 4

Cluster 1

Cluster 2

Cluster 3

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.8

Berger-Parker Dominance

.7

Eveness J

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.4

.3

.2

.6

.5

.4

.3

.1

.2 Cluster 1

Cluster 2

Cluster 3

Cluster 4

Figure 6. Mean and 99% confidence intervals of diversity and evenness indices (a: Number of species, b: Shannon
Wiener H’, c: Evenness J, d: Berger
Parker Dominance) of the principal clusters (cf. classification and ordination).

of volcanic origin. As proposed by Uiblein & Bordes (1999), close interactions among coastal, oceanic, benthic, and benthopelagic organisms are induced by the abrupt topography with possible predation of epipelagic species on myctophids like D. dumerilii. Impingement of pseudoceanic species may lead to intense spatial and trophic interactions with slope community (Reid et al. 1991; Gordon et al. 1995; Uiblein & Bordes 1999). The more dispersed ordination of the stations of group IV compared to the other large clusters (Figure 4) reflects irregular occurrences of many species.

Clusters 1 and 2 are clearly defined by habitat (oceanic
epipelagic and mesopelagic), whereas there are spatial overlaps between tows affiliated to clusters 3 and 4 (Figure 5). Seasonal effects can be excluded, as coastal tows within surveys show affiliation to different clusters. This suggests that occurrence and abundance of species is locally and temporally limited to a rather small scale instead of showing a constant pattern throughout the study area. The indicator species are not necessarily restricted to a single cluster (Table III). Specifically D. dumerilii and S. colias were found in stations of all

Table IV. Beta diversity, Whittaker bW (S/a) and Wilson & Shmida bT ([g(H)l(H)]/2Sj), of two different areas, habitats, and groups of mesopelagic trawl stations in the south of Fuerteventura (S total number of species recorded, a average sample diversity, g(H) number of species gained, l(H)number of species lost, Sj species richness of sample j).

Epipelagic realm Mesopelagic realm Groups of mesopelagic trawls

Gran Canaria Fuerteventura Gran Canaria Fuerteventura 1 2 3

Whittaker bW

Wilson & Shmida bT

1.263 4.208 1.729 2.550 1.105 0.767 0.774

1.605 3.981 1.620 2.442 0.737 0.688 0.690

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clusters (except S. colias in cluster 2). Although numbers of individuals vary somewhat significantly, this clearly shows an intensified use of coastal habitats by mesopelagic fishes as well as of oceanic habitats by coastal species, respectively. Several authors used a similar approach to investigate mesopelagic nekton assemblages. Hulley & Lutjeharms (1989), for instance, found that in the southern Benguela region the depth of the water column was the reason for a change in the lanternfish fauna and distinguish between oceanic and pseudoceanic species. Depth is also the deciding factor in cephalopod assemblages along the Spanish Mediterranean coast (Gonza´lez & Sa´nchez 2002). Fock et al. (2004) indicate that habitat structure in conjunction with physical and biological features is an important determinant of community structure. Benoit-Bird & Au (2006) found myctophids as the only animals in shallow waters of Hawaiian Islands, migrating actively with a striking horizontal component. Furthermore, these myctophids were of larger size than those found in farther offshore, deeper layers, which they ascribed to differences in swimming speed.

Ecological diversity Alpha diversity. The diversity indices used confirm the often-stated characteristics of the mesopelagic realm, reported to be the most diverse and densely inhabited area of the open oceans (National Research Council 1995). The high species richness and evenness, and the low dominance values obtained in the current study agree with this statement. Quite contrasting are the mainly coastal tows of cluster 4. These stations in shallow bottom depths are characterised by low species richness, an often high number of individuals (and biomass) and one or two dominating epipelagic species. Clusters 1 and 3 are positioned in between. Cluster 1 (epipelagic tows) is in its diversity closer to cluster 2, with high richness and evenness but low dominance. This can be ascribed to the vertical migrants represented in these tows by high numbers (in species and individuals) and the lack of the partly rare non-migrators. Cluster 3 resembles cluster 4, although these tows are a special case: made close to the coast (some of them even coastal), with mesopelagic fishes, remarkably high in individuals but low in species. Beta diversity. Depths of more than 2000 m are encountered close to the investigation area of Gran Canaria, whereas this depth zone is farther away from that of Fuerteventura. The differences in diversity might reflect the prevailing depth zones in the respective areas or general differences in spatial

heterogeneity. The higher oceanic influence and the eddy south of Gran Canaria (Arı´stegui et al. 1994, 1997; Bordes et al. 1999) may have an effect on species distribution. Arı´stegui et al. (1989) found high primary production and large populations of mesozooplankton in coastal waters south of Gran Canaria compared to oceanic waters. Barange et al. (1998) emphasized the intense influences of hydrological features on a pelagic community in general. Even more remarkable is the distinctness between the epi- and mesopelagic habitat off south Fuerteventura. It emphasizes the complex connection of hydrological features and species distribution. Uiblein et al. (1996, 1998) discussed the existence of a seasonally limited local upwelling off Gran Tarajal, southeast Fuerteventura. Within the sub-area groupings of mesopelagic tows the two groups farther away from the coast have similar beta diversity, that clearly differs from group 1 indicating a heterogeneous species distribution at the scale of a few kilometres distance only. The mesopelagic boundary community of Hawaiian Islands shows similar regional differences in taxonomic composition, abundance and diversity (Reid et al. 1991; Benoit-Bird et al. 2001; Lammers et al. 2004). Benoit-Bird & Au (2006) refer the fine scale separation of habitat use to a reduction of competition between individuals in these dense aggregations relative to night time. Heterogeneity in species distribution depending on topography and hydrography seems to be a common feature, as it was also detected between adjacent deep-sea canyons off the Georges Bank, NW Atlantic (Uiblein et al. unpublished data). This study has resulted in the collection of 13 new pelagic fish species for the Canary Islands. Not all islands and habitats have been covered by the surveys. We have presented here clear evidence of considerable variation in local species composition reflecting the influences of topography and hydrography and the interactions between these two variables. Both epipelagic and mesopelagic fishes seem to respond actively to physical heterogeneity at the scale of a few kilometres only, thus inducing patchiness and turnover among close-by areas. The high number of species encountered, the still ongoing discovery of hitherto unknown species, and the finding of distinct, taxonspecific distribution patterns strongly suggest that pelagic fishes are an important component for the assessment and functional understanding of biodiversity around oceanic islands.

Acknowledgements All surveys were carried out in projects supported by the Viceconsejerı´a de Pesca del Gobierno de Canarias. Rupert Wienerroither got financial support

Pelagic fishes around the Canary Islands from the ‘Stiftungs- und Fo¨rderungsgesellschaft der Paris-Lodron Universita¨t Salzburg’. Sincere thanks to all colleagues at the Zoological Museum Copenhagen (ZMUC) and the University of Salzburg, especially A. Lametschwandtner and J. Strobl.

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