University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Publications, Agencies and Staff of the U.S. Department of Commerce U.S. Department of Commerce 3-2008 Diet of the Striped Dolphin, Stenella coeruleoalba, in the Eastern Tropical Pacific Ocean William F. Perrin Kelly M. Robertson William A. Walker Follow this and additional works at: https://digitalcommons.unl.edu/usdeptcommercepub Part of the Environmental Sciences Commons Perrin, William F.; Robertson, Kelly M.; and Walker, William A., "Diet of the Striped Dolphin, Stenella coeruleoalba, in the Eastern Tropical Pacific Ocean" (2008). Publications, Agencies and Staff of the U.S. Department of Commerce. 23. https://digitalcommons.unl.edu/usdeptcommercepub/23 This Article is brought to you for free and open access by the U.S. Department of Commerce at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Publications, Agencies and Staff of the U.S. Department of Commerce by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. NOAA Technical Memorandum NMFS T O F C E N O M M T M R E A R P C E E D MARCH 2008 U N A I C T I E R D E M ST A AT E S OF DIET OF THE STRIPED DOLPHIN, Stenella coeruleoalba, IN THE EASTERN TROPICAL PACIFIC OCEAN William F. Perrin Kelly M. Robertson William A. Walker NOAA-TM-NMFS-SWFSC-418 U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Marine Fisheries Service Southwest Fisheries Science Center The National Oceanic and Atmospheric Administration (NOAA), organized in 1970, has evolved into an agency which establishes national policies and manages and conserves our oceanic, coastal, and atmospheric resources. An organizational element within NOAA, the Office of Fisheries is responsible for fisheries policy and the direction of the National Marine Fisheries Service (NMFS). In addition to its formal publications, the NMFS uses the NOAA Technical Memorandum series to issue informal scientific and technical publications when complete formal review and editorial processing are not appropriate or feasible. Documents within this series, however, reflect sound professional work and may be referenced in the formal scientific and technical literature. NOAA Technical Memorandum NMFS ATMOSPH ND E This TM series is used for documentation and timely communication of preliminary results, interim reports, or special A RI C C I A N D purpose information. The TMs have not received complete formal review, editorial control, or detailed editing. A E M I C N O I S L T A R N A T O I I O T A N N U . E S C . R D E EP M AR OM MARCH 2008 TMENT OF C DIET OF THE STRIPED DOLPHIN, Stenella coeruleoalba, IN THE EASTERN TROPICAL PACIFIC OCEAN William F. Perrin11, Kelly M. Robertson , and William A. Walker2 1NOAA, National Marine Fisheries Service Southwest Fisheries Science Center 8604 La Jolla Shores Drive La Jolla, California, USA 92037 Email: [email protected] 2NOAA, National Marine Fisheries Service National Marine Mammal Laboratory Alaska Fisheries Science Center 7600 Sand Point Way, N.E., Seattle, Washington USA 98115 NOAA-TM-NMFS-SWFSC-418 U.S. DEPARTMENT OF COMMERCE Carlos M. Gutierrez, Secretary National Oceanic and Atmospheric Administration VADM Conrad C. Lautenbacher, Jr., Undersecretary for Oceans and Atmosphere National Marine Fisheries Service James W. Balsiger, Acting Assistant Administrator for Fisheries ABSTRACT crab Portunis xanthusii made up 46%. The rest Knowledge of the trophic ecology of pelagic was composed of the remains of several small dolphins is important to understanding the fishes of the families Myctophidae, ecosystem of the eastern tropical Pacific. Gonostomatidae, Phosichthyidae, Mesopelagic species predominated in the diet of Scopelarchidae, Evermannellidae, Paralepididae 131 striped dolphins; the myctophid and Bathylagidae and cephalopods of the Lampanyctus parvicauda, a melamphaeid families Ommastrephidae, Onychoteuthidae, Melamphaes sp., and the enoploteuthid squid Enoploteuthidae, Mastigoteuthidae and Abraliopsis affinis were the most numerous and Octopoteuthidae. No data were provided on most prevalent. Composition varied among four frequency or prevalence of occurrence regions; fish predominated in three southerly regions, and fish and cephalopods occurred in The present study aimed to describe and about equal numbers in a region close to the compare diets of cetacean predators in the northern tropical convergence. Prey for which pelagic ecosystem of the ETP, with an ultimate length could be estimated ranged from about 2 to goal of providing input for an accurate functional 17 cm in length. Most feeding occurred at night model of the system (see Cox et al. 2003; Olson or early in the morning. Species composition and Watters 2003; Watters et al. 2003). We also was similar to those for striped dolphins taken compare the diet of the species in the ETP with pelagically in other parts of the world in that in other regions and with the diet of other representing mainly mesopelagic species but dolphins of the genus Stenella in the ETP. differed from that for striped dolphins inhabiting more coastal regions, indicating flexibility in the Methods and materials trophic ecology of the species. The diet in the ETP resembled that of the pantropical spotted The material examined is a heterogeneous dolphin, S. attenuata, in the same region, assemblage of samples collected and processed although the latter may occasionally take larger opportunistically during two decades of research prey. Overlap with the diet of the spinner with other primary objectives in the eastern dolphin, S. longirostris, in the same region is tropical Pacific. U.S. Government technicians less; it may feed deeper, to 400m. aboard commercial tuna seiners collected carcasses/stomachs of 128 striped dolphins killed incidentally during fishing operations Introduction (Gerrodette 2002) during the period 1973--1989 (Table 1, Figure 1). Two of these (CJD0001-2) The striped dolphin is a pelagic inhabitant of were taken accidentally in a set on tuna tropical and warm-temperate waters around the associated with a "log" (floating object); the globe (Jefferson et al. 1993, Archer and Perrin remainder were killed incidentally in deliberate 1999, Archer 2002). It ranks third in abundance sets on dolphin schools. The number of dolphins among dolphin species in the offshore eastern sampled from a single set of the net ranged from tropical Pacific (ETP) (Ballance and Pitman 1 to 13. Stomachs were also collected from two 1998). In other parts of its range it is the most striped dolphins collected and donated by a abundant dolphin (e.g., Mediterranean – Aguilar fishing vessel in 1973 (WFP0268 and 0269). A 2000), of intermediate rank (second among all subsample of cephalopod beaks was collected cetaceans in the tropical Indian Ocean – Ballance from an additional dead dolphin found floating at and Pitman 1998; fifth in the Gulf of Mexico – sea in 1986 (MAW0045). The total number of Ballance and Pitman 1998), or uncommon collections (schools sampled) was 34. The (Philippines – Heaney et al. 1998; Dolar et al. samples came from four regions in the eastern 2006). tropical Pacific (Fig. 1): off Mexico (20 The only previously-available stomachs), far offshore to the west (36), in the information on prey of striped dolphins in the Costa Rica Dome and to the west (48), and near ETP is data on five dolphins in the unpublished the Galapagos Islands (27). The dolphins from doctoral thesis of Galván Magaña1, taken in tuna the tuna fishery were taken in association with purse seine sets on yellowfin tuna in the region yellowfin tuna (Thunnus albacares) and (in two of the Costa Rica Dome. The stomach contents cases) skipjack tuna (Katsuwonus pelamis) and totaled 125g, of which the remains of the pelagic with other dolphins (pantropical spotted dolphin, Stenella attenuata, in 13 of the net sets and 2 spinner dolphin, Stenella longirostris, in 10). In number of samples (beaks or otoliths) were lost 10 cases, the tuna (unidentified) escaped the net in storage; these samples were included in the set that killed the dolphins. analyses of total forestomach content by mass When collected at sea, the stomachs but not in the analyses of occurrence and were tied off at the upper esophageal and lower prevalence; complete data for these analyses duodenal ends and frozen for return to the were available for forestomachs from 104 laboratory. Most carcasses were returned frozen specimens (92 containing otoliths from 11,671 whole to the Southwest Fisheries Center fish and beaks from 5,222 cephalopods; 12 (SWFSC) and the stomachs collected there. After empty). Crustacean remains were uncommon total volume or mass was measured in the (present in only 13 of the 105 specimens) and laboratory, the contents were stored in 70% ethyl usually of very small volume and well-digested. alcohol. They were rough-sorted in various ways Their rareness may be due to a small role in the and volumes or weights of components measured diet or to more rapid digestion of remains than at the SWFSC over a period of several years. for fish and squid. In most cases it was not Extracted beaks and otoliths were stored in 70% possible to determine the number of prey items alcohol. During and after identification, the represented, and the taxon was recorded only as otoliths were stored dry. Varying amounts of "present." Therefore, the calculations of data were available for the 131 stomach samples; prevalence were based only on the fish and the most complete suite included collection data cephalopod remains. (date, location, collector, time of day the dolphin Cephalopod beaks were identified by chase started (or, in the case of the "log" set, WAW by comparison with a private collection of time net was let go), associated cetacean beaks from the eastern Pacific. Identification species), total volume or mass of stomach and enumeration were based almost entirely on contents; volume or mass of contents of the lower beaks.