PFRP Pelagic Fisheries Research Program Comparative Trophic Ecology of Yellowfin and Bigeye Tuna Associated with Natural and Man-made Aggregation Sites in Hawaiian Waters
T. obesus
T. albacares Dean Grubbs and Kim Holland Hawaii Institute of Marine Biology Pelagic Fisheries Research Program University of Hawaii What we know!
The formation of aggregations, groups of fishes attracted to a common resource (Freeman and Grossman 1992), is prevalent among tropical tunas.
These aggregations are usually associated with physical entities (seamounts, floating debris, cetaceans, vessels, buoys, FADs).
The majority of tropical tunas harvested commercially and recreationally are “associated.”
What we don’t! Underlying biological significance of aggregation behavior is poorly understood. Pros and cons of association: Pros:
1) ☯ Forage 2) \ Predation 3) ☯ Reproductive Success
Cons:
1) ☯ Competition interspsecific and intraspecific 2) ☯ Susceptibility to modern fishing gear. Distributions of bigeye and yellowfin are vertically distinct. BUT, this pattern is known to collapse when associated. OBJECTIVES:
Compare feeding ecology of yellowfin and bigeye tuna within and between various mixed aggregations (using unassociated samples as controls).
a) Stomach Fullness b) Feeding Strategy c) Prey Composition d) Depth of Feeding e) Timing of Feeding
Evaluate potential trophic benefit of aggregating.
Evaluate the effect of man-made aggregating structures on trophic biology.
(depth 4700m)
UNASSOCIATED SAMPLES (LONGLINE) METHODS: 1) Port Sampling a) Samples obtained directly from returning vessels b) Samples obtained from seafood buyers at UFA
2) Field Sampling a) Sampling at sea on commercial troll/handline vessels. b) Sampling at sea aboard project vessels.
Association Bigeye Yellowfin
Unassociated 47 37
Cross Seamount 389 116
Offshore Weather Buoys 177 87
Nearshore FADs 11 93
Dolphin Pods 0 2
TOTAL 624 335 560 228 Total Analyzed (90%) (68%) Results
Prey Composition Depth
YF Epipelagic Zone 200 meters BE Mesopelagic Zone
1000 meters
Bathypelagic Zone
4000 meters Abyssopelagic Zone Abyssal Plain
Hadal Zone Prey Diversity (Fishes)
PHYLUM: CHORDATA SUPERORDER SCOPELOMORPHA ORDER DACTYLOPTERIFORMES SUBPHYLUM: VERTEBRATA (CRANIATA) ORDER MYCTOPHIFORMES 33 FAMILY DACTYLOPTERIDAE CLASS: TELEOSTOMI (OSTEICHTHYES) 17 FAMILY MYCTOPHIDAE ORDER SCORPAENIFORMES SUBCLASS: ACTINOPTERYGII SUPERORDER LAMPRIDIOMORPHA 34 FAMILY SCORPAENIDAE INFRACLASS: NEOPTERYGII ORDER LAMPRIDIFORMES ORDER PERCIFORMES DIVISION: TELEOSTEI 18 FAMILY LOPHOTIDAE 35 FAMILY PERCICHTYIDAE SUBDIVISION: ELOPOMORPHA 19 FAMILY TRACHIPTERIDAE 36 FAMILY PRIACANTHIDAE ORDER ANGUILLIFORMES SUPERORDER PARACANTHOPTERYGII 37 FAMILY ECHENEIDAE 1 FAMILY OPHICHTHYIDAE ORDER OPHIDIIFORMES 38 FAMILY CARANGIDAE 2 FAMILY SERRIOVOMERIDAE 20 FAMILY OPHIDIIDAE 39 FAMILY BRAMIDAE SUBDIVISION: EUTELEOSTII ORDER GADIFORMES 40 FAMILY CHAETODONTIDAE SUPERORDER STENOPTERYGII 21 FAMILY BREGMACEROTIDAE 41 FAMILY POMACENTRIDAE ORDER STOMIIFORMES ORDER LOPHIIFORMES 42 FAMILY CIRRHITIDAE 3 FAMILY STOMIIDAE 22 FAMILY OGCOCEPHALIDAE 43 FAMILY CHIASMODONTIDAE 4 FAMILY MELANOSTOMIIDAE SUPERORDER ACANTHOPTERYGII 44 FAMILY BLENNIIDAE 5 FAMILY CHAULIODONTIDAE ORDER BELONIFORMES 45 FAMILY ACANTHURIDAE 6 FAMILY IDIACANTHIDAE 23 FAMILY EXOCOETIDAE 46 FAMILY SCOMBROLABRACIDAE 7 FAMILY ASTRONESTHIDAE 24 FAMILY HEMIRAMPHIDAE 47 FAMILY MALACANTHIDAE 8 FAMILY GONOSTOMATIDAE ORDER GASTEROSTEIFORMES 48 FAMILY TRICHIURIDAE 9 FAMILY PHOTICHTHYIDAE 25 FAMILY FISTULARIIDAE 49 FAMILY GEMPYLIDAE 10 FAMILY STERNOPTYCHIDAE 26 FAMILY SYNGNATHIDAE 50 FAMILY SCOMBRIDAE SUPERORDER CYCLOSQUAMATA SERIES PERCOMORPHA 51 FAMILY ISTIOPHORIDAE ORDER AULOPIFORMES ORDER STEPHANOBERYCIFORMES 52 FAMILY NOMEIDAE 11 FAMILY PARALAPEDIDAE 27 FAMILY MELAMPHEIDAE 53 FAMILY ARRIOMATIDAE 12 FAMILY SCOPELARCHIDAE ORDER BERYCIFORMES 54 FAMILY LUTJANIDAE 13 FAMILY EVERMANNELLIDAE 28 FAMILY ANOPLOGASTRIDAE 55 FAMILY TETRAGONURIDAE 14 FAMILY OMOSUDIDAE 29 FAMILY BERYCIDAE ORDER TETRAODONTIFORMES 15 FAMILY ALEPISAURIDAE 30 FAMILY DIRETMIDAE 56 FAMILY BALISTIDAE 16 FAMILY NOTOSUDIDAE 31 FAMILY HOLOCENTRIDAE 57 FAMILY MONOCANTHIDAE 32 FAMILY TRACHICHTHYIDAE 58 FAMILY TETRAODONTIDAE 59 FAMILY OSTRACIIDAE 60 FAMILY MOLIDAE Authors Area Species (N) Fish Families Reintjes & King 1953 Central Pacific Yellowfin (1067) 38 Ronquillo 1953 Western Pacific Yellowfin 36 King & Ikehara 1956 Central Pacific Yellowfin (439) 48 Watanabe 1958 Indian Ocean Yellowfin 37 Alverson 1963 Eastern Pacific Yellowfin (3763) 42 Kornilova 1981 Indian Ocean Yellowfin (445) 23 Borodulina 1982 Gulf of Guinea Yellowfin (67) 20 Borodulina 1982 Western Pacific Yellowfin (31) 30 Brock 1985 Hawaii Yellowfin (201) 27 Maldeniya 1996 Sri Lanka Yellowfin (4181) 44 Kim et al. 1997 Western Pacific Yellowfin (181) 13 Current Study Hawaii Yellowfin (228) 34
King & Ikehara 1956 Central Pacific Bigeye (166) 35 Borodulina 1974 Gulf of Guinea Bigeye (143) 23 Kornilova 1981 Indian Ocean Bigeye (534) 19 Kim et al. 1997 Western Pacific Bigeye (170) 13 Current Study Hawaii Bigeye (560) 52 Prey Diversity Comparisons
Prey Diversity (Shannon's Reciprocal Index) 8 Bigeye Yellowfin 7 6 5 4 3 2
Shannon's Reciprocal 1 0 Unassociated Seamount Weather Buoy Results
Stomach Fullness Mean Stomach Fullness 8 7 Bigeye Yellowfin 6 5 4 3 2 1 0 Seamount Offshore Buoy Unassociated Mean Stomach Fullness 8 Bigeye Yellowfin 7 6 5 4 3 2 1 0 Seamount Offshore Buoy Unassociated
ANOVA: F=0.453, D=0.363
Yellowfin Mean Stomach Fullness 8 Bigeye Yellowfin 7 6 5 4 3 2 1 0 Seamount Offshore Buoy Unassociated
ANOVA: F=40.272, D<0.0001
Bigeye Dietary Overlap Morisita’s Index % Overlap (sign. at 0.6) (sign. at 60%)
Bigeye 0.27 25% Unassociated vs. Seamount
Bigeye 0.27 26% Unassociated vs. Buoy
Bigeye 0.19 18% Seamount vs. Buoy
Yellowfin 0.12 14% Unassociated vs. Seamount
Yellowfin 0.22 27% Unassociated vs. Buoy
Yellowfin 0.22 25% Seamount vs. Buoy Mean Stomach Fullness 8 Bigeye Yellowfin 7 6 5 4 3 2 1 0 Seamount Offshore Buoy Unassociated
t-test: t=0.39, D=0.7000 Unassociated Tuna: Frequency of Occurrence of Prey Fish Families Major Families of Prey Fishes 100
80 Bigeye Yellowfin
60 mesopelagics epipelagics 40
% of samples 20
0
Molidae Thunnidae Ostraciidae MyctophidaeOmosudidae Gempylidae Engraulidae Paralapedidae Scorpaenidae Alepisauridae Scopelarchidae Astronesthidae Chiasmodontidae Anoplogasteridae Sternoptychidae Unassociated Tuna: Frequency of Occurrence of Invertebrate Prey Major Taxa of Invertebrate Prey 100
80 Bigeye Yellowfin
60 mesopelagics epipelagics 40 % of samples 20
0
Peneidae Megalopae Thaliacea Sergestidae Amphipoda Cephalopoda Euphausiacea Oplophoridae Stomatopoda Feeding Strategies (Costello 1990) Specialized Feeding Strategy 100 80 Dominant Prey 60 40 Rare Prey 20
Percent Abundance 0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence
Generalized Feeding Strategy 100 80 Wide Diet Breadth 60 40 20
Percent Abundance 0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence Unassociated
Bigeye Tuna Feeding Strategy 100
80
60
40 Molidae Cephalopoda 20 Peneidae Percent Abundance 0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence
Yellowfin Tuna Feeding Strategy 100
80
60
40 Thaliacea Cephalopoda Engraulidae 20 Amphipoda Percent Abundance 0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence Unassociated
Bigeye Tuna Feeding Strategy 100
80 Molidae 60
40 Mesopelagic Aggregate
Percent Volume 20 Cephalopoda 0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence
Yellowfin Tuna Feeding Strategy 100
80
60
40 Scombridae Engraulidae Thaliacea Cephalopoda
Percent Volume 20
0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence Dietary Overlap
Morisita’s Index % Overlap (sign. at 0.6) (sign. at 60%)
Bigeye vs. Yellowfin 0.42 27% Unassociated Mean Stomach Fullness 8 Bigeye Yellowfin 7 6 5 4 3 2 1 0 Seamount Offshore Buoy Unassociated
t-test: t=3.05, D=0.0031
NOAA Weather Buoy Weather Buoy Tuna: Frequency of Occurrence of Prey Fish Families Major Families of Prey Fishes 100
80 Bigeye Yellowfin
60 mesopelagics epipelagics 40 % of samples 20
0
Molidae Bramidae Thunnidae Balistidae Lophotidae Gempylidae Ostraciidae Exocoetidae SyngnathidaeAlepisauridae Tetraondontidae Dactylopteridae Chaetodontidae Weather Buoy Tuna: Frequency of Occurrence of Invertebrate Prey Major Taxa of Invertebrate Prey 100
80 Bigeye Yellowfin
60 mesopelagics epipelagics 40
% of samples 20
0
Isopoda Thaliacea Megalopae Sergestidae Amphipoda Cephalopoda Phyllosomes Gymnosomata Euphausiacea Heterocarpus Stomatopoda Enoplemetophidae Offshore Weather Buoy Associated
Bigeye Tuna Feeding Strategy 100
80 Cephalopoda 60
40
20 Megalopae Percent Abundance 0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence
Yellowfin Tuna Feeding Strategy 100
80 Megalopae 60
40 Cephalopoda 20
Percent Abundance Stomatopoda 0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence Offshore Weather Buoy Associated
Bigeye Tuna Feeding Strategy 100
80
60 Bramidae 40 Cephalopoda Lophotidaedae
Percent Volume 20
0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence
Yellowfin Tuna Feeding Strategy 100
80 Molidae 60
40 Scombridae
Percent Volume 20
0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence Dietary Overlap
Morisita’s Index % Overlap (sign. at 0.6) (sign. at 60%)
Bigeye vs. Yellowfin 0.42 27% Unassociated
Bigeye vs. Yellowfin 0.40 32% Buoy Associated Mean Stomach Fullness 8 Bigeye Yellowfin 7 6 5 4 3 2 1 0 Seamount Offshore Buoy Unassociated
t-test: t=6.64, D<0.0001
Cross Seamount Depth
YF Epipelagic Zone 200 meters BE Mesopelagic Zone
1000 meters
Bathypelagic Zone
4000 meters Abyssopelagic Zone Abyssal Plain
Hadal Zone Depth
YF Epipelagic Zone 200 meters BE Mesopelagic Zone
1000 meters
Cross Seamount 330m Bathypelagic Zone
4000 meters Abyssopelagic Zone Abyssal Plain
Hadal Zone Holland, Kleiber, and Kajiura 1998
Estimated residence times of bigeye and yellowfin tuna at Cross Seamount
Bigeye: 32 days
Yellowfin: 15 days
DIFFERENCE NOW MAKES SENSE!
Also supports the increased forage theory as explanation of aggregation. Depth of Feeding
72 samples collected from Cross Seamount September 2001
Of 14 yellowfin, 4 captured >120m deep
Of 58 bigeye, 43 captured >120m deep, 28 captured 300m or greater (along with Ruvettus and Eumegistus illustris) Mean Stomach Fullness with Depth Cross Seamount - September 2001 7.00
Bigeye Yellowfin 6.00
5.00
4.00
3.00
2.00
1.00
N=15 N=10 N=15 N=4 N=28 N=0 0.00 0 100-280 300-360 Depth (meters) Cross Seamount Tuna: Frequency of Occurrence of Prey Fish Families Major Families of Prey Fish 100
80 Bigeye Yellowfin 60 mesopelagics epipelagics 40
% of samples 20
0
Balistidae Bramidae Ostraciidae Myctophidae Gempylidae Exocoetidae Paralapedidae Acanthuridae Percichthyidae Scopelarchidae Tetragonuridae Chaetodontidae ChiasmodontidaeGonostomatidae Scombrolabracidae Cross Seamount Tuna: Frequency of Occurrence of Invertebrate Prey Major Taxa of Invertebrate Prey 100
80 Bigeye Yellowfin
60 mesopelagics epipelagics 40
% of samples 20
0
Isopoda Penaeidae Megalopae Sergestidae Pandalidae Amphipoda Cephalopoda Oplophoridae Euphausiacea Stomatopoda
Enoplemetophidae Cross Seamount Associated
Bigeye Tuna Feeding Strategy 100
80
60
40 Oplophoridae Myctophidae Sergestidae 20
Percent Abundance Cephalopoda 0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence
Yellowfin Tuna Feeding Strategy 100
80
60 Sergestidae 40
20 Megalopae
Percent Abundance Cephalopoda 0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence Cross Seamount Associated
Bigeye Tuna Feeding Strategy 100
80
60
40 Oplophoridae Myctophidae
Percent Volume 20 Sergestidae Cephalopoda 0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence
Yellowfin Tuna Feeding Strategy 100
80
60
40 Myctophidae Sergestidae
Percent Volume 20 Oplophoridae Cephalopoda 0 0 10 20 30 40 50 60 70 80 90 100 Frequency of Occurence Dietary Overlap
Morisita’s Index % Overlap (sign. at 0.6) (sign. at 60%)
Bigeye vs. Yellowfin 0.42 27% Unassociated
Bigeye vs. Yellowfin 0.40 32% Buoy Associated
Bigeye vs. Yellowfin 0.66 57% Seamount Cross Seamount: Percent Abundance of Invertebrate Prey
Shrimp Prey Families Oplophoridae and Sergestdae 60 Bigeye Yellowfin 40
20
Percent of Total 0
Systelaspis Sergia adult Sergia young O. spinacaudaAcanthephyra O. gracilirostris Sergestes adult Sergestes young
0
200
400
600
Depth (meters) 800
1000 Dietary Overlap
Morisita’s Index % Overlap (sign. at 0.6) (sign. at 60%)
Bigeye vs. Yellowfin 0.42 27% Unassociated
Bigeye vs. Yellowfin 0.40 32% Buoy Associated
Bigeye vs. Yellowfin 0.66 57% Seamount
Bigeye vs. Yellowfin 0.56 52% Seamount (cephalopods. oplophorids, and sergestids separated) Timing of Feeding? Need more data! however....
Cross Seamount: Percent Abundance of Invertebrate Prey
Shrimp Prey Families Oplophoridae and Sergestdae 60 Bigeye Yellowfin 40
20
Percent of Total 0
Systelaspis Sergia adult Sergia young O. spinacauda Acanthephyra O. gracilirostris Sergestes adult Sergestes young
0
200
400
600
Depth (meters) 800
1000 PRELIMINARY CONCLUSIONS
Typical Seamount Prey
Typical Offshore Buoy Prey PRELIMINARY CONCLUSIONS
1) Bigeye and Yellowfin are euryphagous predators with generalized feeding strategies when associated with the Cross Seamount. The forage base for both species is extremely diverse, though few taxa are numerically or volumetrically important in the diet.
2) Differences in vertical distribution are reflected in prey composition and may minimize competition between tuna species. Yellowfin tuna fed primarily on mixed-layer prey while bigeye tuna fed on deep scattering- layer prey
3) Association with the Cross Seamount imparts a larger trophic advantage to bigeye than yellowfin due to high abundance of mesopelagic prey. This explains why published residence times on the seamount are longer for bigeye than yellowfin.
4) Associating with offshore weather buoys is of no trophic advantage to either species may be metabolically costly for bigeye tuna. If this cost is detrimental,detailed evaluations of the ecological impact of man-made structures, such as FADs, in tropical waters might be warranted. FUTURE PLANS
Complete lab analysis of collected samples.
Increase samples from unassociated tuna (longline vessels) and nearshore FADs (recreational vessels)
Continue sampling to increase number of yellowfin samples, investigate timing of feeding, get samples from various capture depths.
Stable Isotopes: Brittany Graham and Brian Popp
Investigate seasonal and ontogenetic changes in trophic ecology. Hypothetical shift in Dietary Overlap Bigeye versus Yellowfin 1
0.8
0.6
0.4 Index of Overlap
0.2
0 <50 51-75 76-100 >100 Tuna Fork Length Hypothetical shift in Dietary Overlap Bigeye versus Yellowfin 1
0.8 ?
0.6
0.4 Index of Overlap
0.2
0 <50 51-75 76-100 >100 Tuna Fork Length Feeding Strategies Specialized Predator
Dominant Prey Copyright R. Dean Grubbs 1998 PAU Seamount-associated Tuna Length Frequencies 150
120 Bigeye Yellowfin
90
60 Frequency 30
0 <50 51-60 61-70 71-80 81-90 91-100 101-110 >110 Fork Length (cm)
Offshore Buoy-associated Tuna Length Frequencies 80
Bigeye Yellowfin 60
40 Frequency 20
0 <50 51-60 61-70 71-80 81-90 91-100 101-110 >110 Fork Length (cm)