Comparative Trophic Ecology of Yellowfin and Bigeye Tuna Associated with Natural and Man-made Aggregation Sites in Hawaiian Waters

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) ॐ 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 47m)

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 2 TOTAL Total Analyzed 624 56 (9%) 335 228 (68%)

Results Prey Composition

Depth 2 meters BE YF Epipelagic Zone Mesopelagic Zone 1 meters Bathypelagic Zone 4 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 2 FAMILY OPHIDIIDAE 39 FAMILY BRAMIDAE SUBDIVISION: EUTELEOSTII ORDER GADIFORMES 4 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 1 FAMILY STERNOPTYCHIDAE 26 FAMILY SYNGNATHIDAE 5 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 3 FAMILY DIRETMIDAE 56 FAMILY BALISTIDAE 16 FAMILY NOTOSUDIDAE 31 FAMILY HOLOCENTRIDAE 57 FAMILY MONOCANTHIDAE 32 FAMILY TRACHICHTHYIDAE 58 FAMILY TETRAODONTIDAE 59 FAMILY OSTRACIIDAE 6 FAMILY MOLIDAE

Authors Area Species (N) Fish Families Reintjes & King 1953 Central Pacific Yellowfin (167) 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) 2 Borodulina 1982 Western Pacific Yellowfin (31) 3 Brock 1985 Hawaii Yellowfin (21) 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 (17) 13 Current Study Hawaii Bigeye (56) 52

Prey Diversity Comparisons Shannon's Reciprocal 8 7 6 5 4 3 2 1 Prey Diversity (Shannon's Reciprocal Index) Bigeye Yellowfin Unassociated Seamount Weather Buoy

Results Stomach Fullness

8 7 6 5 4 3 2 1 Mean Stomach Fullness Bigeye Yellowfin Seamount Offshore Buoy Unassociated

8 7 6 5 4 3 2 1 Mean Stomach Fullness Bigeye Yellowfin Seamount Offshore Buoy Unassociated ANOVA: F=.453, =.363 Yellowfin

8 7 6 5 4 3 2 1 Mean Stomach Fullness Bigeye Yellowfin Seamount Offshore Buoy Unassociated ANOVA: F=4.272, <.1 Bigeye

Dietary Overlap Morisita s Index % Overlap (sign. at.6) (sign. at 6%) Bigeye.27 25% Unassociated vs. Seamount Bigeye.27 26% Unassociated vs. Buoy Bigeye.19 18% Seamount vs. Buoy Yellowfin.12 14% Unassociated vs. Seamount Yellowfin.22 27% Unassociated vs. Buoy Yellowfin.22 25% Seamount vs. Buoy

8 7 6 5 4 3 2 1 Mean Stomach Fullness Bigeye Yellowfin Seamount Offshore Buoy Unassociated t-test: t=.39, =.7

Unassociated Tuna: Frequency of Occurrence of Prey Fish Families 1 Major Families of Prey Fishes % of samples 8 6 4 2 mesopelagics Bigeye Yellowfin epipelagics Paralapedidae Myctophidae Omosudidae Chiasmodontidae Scopelarchidae Scorpaenidae Gempylidae Anoplogasteridae Astronesthidae Sternoptychidae Alepisauridae Molidae Thunnidae Ostraciidae Engraulidae

Unassociated Tuna: Frequency of Occurrence of Invertebrate Prey 1 Major Taxa of Invertebrate Prey % of samples 8 6 4 2 mesopelagics epipelagics Bigeye Yellowfin Cephalopoda Peneidae Euphausiacea Sergestidae Oplophoridae Megalopae Stomatopoda Amphipoda Thaliacea

Feeding Strategies (Costello 199) Percent Abundance 1 8 6 4 2 Rare Prey Specialized Feeding Strategy 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence Dominant Prey Percent Abundance 1 8 6 4 2 Generalized Feeding Strategy Wide Diet Breadth 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence

Unassociated Percent Abundance 1 8 6 4 2 Bigeye Tuna Feeding Strategy Molidae Cephalopoda Peneidae 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence Percent Abundance 1 8 6 4 2 Yellowfin Tuna Feeding Strategy Thaliacea Cephalopoda Engraulidae Amphipoda 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence

Unassociated 1 Bigeye Tuna Feeding Strategy Percent Volume 8 6 4 2 Molidae Mesopelagic Aggregate 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence Cephalopoda 1 Yellowfin Tuna Feeding Strategy Percent Volume 8 6 4 2 Scombridae Engraulidae Thaliacea Cephalopoda 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence

Dietary Overlap Morisita s Index % Overlap (sign. at.6) (sign. at 6%) Bigeye vs. Yellowfin.42 27% Unassociated

8 7 6 5 4 3 2 1 Mean Stomach Fullness Bigeye Yellowfin Seamount Offshore Buoy Unassociated t-test: t=3.5, =.31 NOAA Weather Buoy

Weather Buoy Tuna: Frequency of Occurrence of Prey Fish Families 1 Major Families of Prey Fishes % of samples 8 6 4 2 mesopelagics epipelagics Bigeye Yellowfin Bramidae Lophotidae Gempylidae Thunnidae Ostraciidae Tetraondontidae Balistidae Dactylopteridae Molidae Exocoetidae Chaetodontidae Syngnathidae Alepisauridae

Weather Buoy Tuna: Frequency of Occurrence of Invertebrate Prey 1 Major Taxa of Invertebrate Prey % of samples 8 6 4 2 mesopelagics epipelagics Bigeye Yellowfin Cephalopoda Gymnosomata Phyllosomes Euphausiacea Heterocarpus Sergestidae Enoplemetophidae Isopoda Amphipoda Thaliacea Stomatopoda Megalopae

Offshore Weather Buoy Associated 1 Bigeye Tuna Feeding Strategy Percent Abundance 8 6 4 2 Cephalopoda Megalopae 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence 1 Yellowfin Tuna Feeding Strategy Percent Abundance 8 6 4 2 Megalopae Cephalopoda Stomatopoda 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence

Offshore Weather Buoy Associated 1 Bigeye Tuna Feeding Strategy Percent Volume 8 6 4 2 Bramidae Lophotidaedae Cephalopoda 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence 1 Yellowfin Tuna Feeding Strategy Percent Volume 8 6 4 2 Molidae Scombridae 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence

Dietary Overlap Morisita s Index % Overlap (sign. at.6) (sign. at 6%) Bigeye vs. Yellowfin.42 27% Unassociated Bigeye vs. Yellowfin.4 32% Buoy Associated

8 7 6 5 4 3 2 1 Mean Stomach Fullness Bigeye Yellowfin Seamount Offshore Buoy Unassociated t-test: t=6.64, <.1 Cross Seamount

Depth 2 meters BE YF Epipelagic Zone Mesopelagic Zone 1 meters Bathypelagic Zone 4 meters Abyssopelagic Zone Abyssal Plain Hadal Zone

Depth 2 meters BE YF Epipelagic Zone Mesopelagic Zone 1 meters Cross Seamount 33m Bathypelagic Zone 4 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 21 Of 14 yellowfin, 4 captured >12m deep Of 58 bigeye, 43 captured >12m deep, 28 captured 3m or greater (along with Ruvettus and Eumegistus illustris)

Mean Stomach Fullness with Depth Cross Seamount - September 21 7. 6. Bigeye Yellowfin 5. 4. 3. 2. 1.. N=15 N=1 N=15 N=4 N=28 N= 1-28 3-36 Depth (meters)

Cross Seamount Tuna: Frequency of Occurrence of Prey Fish Families 1 Major Families of Prey Fish % of samples 8 6 4 2 mesopelagics Bigeye epipelagics Yellowfin Myctophidae Percichthyidae Chiasmodontidae Gonostomatidae Gempylidae Scopelarchidae Scombrolabracidae Paralapedidae Tetragonuridae Ostraciidae Exocoetidae Balistidae Chaetodontidae Acanthuridae Bramidae

Cross Seamount Tuna: Frequency of Occurrence of Invertebrate Prey 1 Major Taxa of Invertebrate Prey % of samples 8 6 4 2 mesopelagics epipelagics Bigeye Yellowfin Cephalopoda Sergestidae Oplophoridae Penaeidae Pandalidae Isopoda Enoplemetophidae Euphausiacea Amphipoda Stomatopoda Megalopae

Cross Seamount Associated Percent Abundance 1 8 6 4 2 Bigeye Tuna Feeding Strategy Oplophoridae Myctophidae Sergestidae Cephalopoda 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence Percent Abundance 1 8 6 4 2 Yellowfin Tuna Feeding Strategy Sergestidae Megalopae Cephalopoda 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence

Cross Seamount Associated Percent Volume 1 8 6 4 2 Bigeye Tuna Feeding Strategy Oplophoridae Myctophidae Sergestidae Cephalopoda 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence Percent Volume 1 8 6 4 2 Yellowfin Tuna Feeding Strategy Myctophidae Sergestidae Oplophoridae Cephalopoda 1 2 3 4 5 6 7 8 9 1 Frequency of Occurence

Dietary Overlap Morisita s Index % Overlap (sign. at.6) (sign. at 6%) Bigeye vs. Yellowfin.42 27% Unassociated Bigeye vs. Yellowfin.4 32% Buoy Associated Bigeye vs. Yellowfin.66 57% Seamount

Cross Seamount: Percent Abundance of Invertebrate Prey Percent of Total 6 4 2 Shrimp Prey Families Oplophoridae and Sergestdae Bigeye Yellowfin Systelaspis O. gracilirostris O. spinacauda Acanthephyra Sergia young Sergia adult Sergestes young Sergestes adult Depth (meters) 2 4 6 8 1

Dietary Overlap Morisita s Index % Overlap (sign. at.6) (sign. at 6%) Bigeye vs. Yellowfin.42 27% Unassociated Bigeye vs. Yellowfin.4 32% Buoy Associated Bigeye vs. Yellowfin.66 57% Seamount Bigeye vs. Yellowfin.56 52% Seamount (cephalopods. oplophorids, and sergestids separated)

Timing of Feeding? Need more data! however... Cross Seamount: Percent Abundance of Invertebrate Prey Percent of Total 6 4 2 Shrimp Prey Families Oplophoridae and Sergestdae Bigeye Yellowfin Systelaspis O. gracilirostris O. spinacauda Acanthephyra Sergia young Sergia adult Sergestes young Sergestes adult Depth (meters) 2 4 6 8 1

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 scatteringlayer 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.

1 Hypothetical shift in Dietary Overlap Bigeye versus Yellowfin.8 Index of Overlap.6.4.2 <5 51-75 76-1 >1 Tuna Fork Length

1 Hypothetical shift in Dietary Overlap Bigeye versus Yellowfin.8? Index of Overlap.6.4.2 <5 51-75 76-1 >1 Tuna Fork Length

Feeding Strategies Specialized Predator Dominant Prey

Copyright R. Dean Grubbs 1998 PAU

15 12 Seamount-associated Tuna Length Frequencies Bigeye Yellowfin Frequency 9 6 3 <5 51-6 61-7 71-8 81-9 91-1 11-11 >11 Fork Length (cm) 8 Offshore Buoy-associated Tuna Length Frequencies Frequency 6 4 2 Bigeye Yellowfin <5 51-6 61-7 71-8 81-9 91-1 11-11 >11 Fork Length (cm)