1. Variability in the diet of common dolphins (Delphinus delphis) and prey availability along the Portuguese continental coast
Ana Marçalo1,2, Lidia Nicolau1,2, Marisa Ferreira1,3, José Vingada1,2,3, Alexandra Silva4, Graham J. Pierce5
1. Sociedade Portuguesa de Vida Selvagem, Universidade do Minho, Portugal;
2. Centre for Environmental and Marine Studies (CESAM), Dep Biology, Universidade de Aveiro, Portugal.
3. CBMA/Dep Biology, Universidade do Minho, Portugal.
4. IPMA-Instituto Português do Mar e da Atmosfera, Lisboa, Portugal.
5. University of Aberdeen, Ocean Lab, UK.
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INTRODUCTION
METHODS
Necropsy of stranded dead animals
Tissue and stomach sampling, sex, maturity, fishery interactions assessment
Stomach washing, prey extraction, identification and quantification (hard parts – bones, otoliths), beaks)
Numerical importance (% N) and numerical occurrence (% F), otolith and beak measurement
Descriptive analysis of interannual, regional, (North vs South), sex, size and cause of death/fisheries interaction variation in the diet N
To date, only one study is available on common dolphin, Delphinus delphis, diet along the Portuguese continental coast, which indicated that sardine, Sardina pilchardus, was the most important prey species (Silva, 1999). Recent biomass assessments indicate a decrease in sardine abundance off Portugal, which triggered the adoption of regulatory measures such as landings and days at sea limits, especially for the purse-seining fishery that targets the species. In this study we describe the diet of common dolphins in Portuguese continental waters, from animals recently stranded dead between 2010 and 2012.
OPORTO
LISBON
FARO
Fig 1. Map of Portuguese coast showing the location of the strandings of common dolphins, Delphinus delphis, from which stomach contents were analyzed in this study (n = 92).
RESULTS AND DISCUSSION A
Family N %N F %F
Clupeidae
Sardina pilchardus
908
17,9 76
82,6
Engraulidae
Engraulis encrasicolus 95
1,9 25
27,2
Gadidae
Micromesistius poutassou 27
0,5 6
6,5
Gadiculus argenteus
103
2,0 1
1,1
Trisopterus sp.
126
2,5 18
19,6
Merluccidae
Merluccius merluccius
162
3,2 30
32,6
Macroramposidae
Macroramphosus sp. 85
1,7 28
30,4
Belonidae
Belone belone 23 3
3,3
Carangidae
Trachurus sp.
370
7,3 46
50,0
Sparidae
Boops boops 74
1,5
29,3
Pagrus pagrus
0,0
Sparidae sps. 2
Centracanthidae
Spicara smaris 9
0,2
2,2
Ammodytidae
Gymnammodytes sp.
0,6
Scombridae
Scomber colias
410
8,1 41
44,6
Scomber scombrus
Atherinidae
Atherina sp.
174
3,4
Sternoptychidae
Maurolicus muelleri
Gobiidae
Gobiidae sp.
477
9,4
Citharidae
Citharus linguatula 7
0,1
Soleidae
Soleidae sp. 44
0,9
Unidentified Fish 26 11
12,0
Total (fish group)
3252
64,1 92
100,0
Sepiidae
Sepia spp.
Sepiolidae
Sepiola atlantica
1010
19,9 35
38,0
Sepiolid sp.
Loliginidae
Alloteuthis sp.
764
15,1 33
35,9
Loligo sp. 31 14
15,2
Ommastrephidae
Illex coindentii 10
7,6
Octopodidae
Eledone cirrhosa
Total (cephalopoda group)
1818
35,8 48
52,2
Crustacea NI 5
Total
5075 B B
Table 1. Number (N), and frequency of occurrence (F) of the prey items identified in the stomach contents. In red the 6 most important species found in the diet.
Fig 2. Numerical importance (A) and occurrence (B) of the main prey families identified from the stomachs analyzed and comparing with Silva ,1999.
Fig 3. Numerical importance of the main prey families identified from the stomachs analyzed by area (A) and incidental capture by seining (purse seine or beach seine) vs other gears (net and trawl) (B). A
Fig 5. Evolution of landings of the main small pelagic species landed in continental Portugal (Bars; DGRM 2011, 2012, 2013) and their numerical importance in the stomachs during the period of this study (Lines; ).
Fig 4. Numerical importance of the prey identified from the stomachs analyzed by sex (X2= 0,43; df= 1; P > 0,05; A) and size of the animals (small - <150 cm; medium – cm; large - > 191 cm) (X2= 39,4; df= 2, P < 0,05, B) and considering prey habitat preferences.
Our results suggest that common dolphin diet has changed in response to changes in the pelagic fish community, particularly the decline of sardine and the increase of chub mackerel (Scomber colias).
REFERENCES
Silva, Diet of common dolphins, Delphinus delphis, off the Portuguese continental coast. JMBAUK, 79:
DGRM (2011, 2012, 2013). Datapescas Nº 87, 91 and 95.
A.M. is financed by a pos doc grant SFRH/BPD/64889/2009 from the Science and Technology Foundation (FCT)