Ecopath model of the pelagic ecosystem of the WCPO and related projects. ALLAIN V.

Transcription

1 SCTB1 Working Paper INFO-ECO-1 Ecopath model of the pelagic ecosystem of the WCPO and related projects. ALLAIN V. Oceanic Fisheries Programme Secretariat of the Pacific Community Noumea, New Caledonia July

2 Introduction With the final objective of managing the fisheries resources through ecosystem-based management, the emphasis has been put lately on the development of ecosystem modelling as a result of FAO, UNEP and EU incentives (UNEP, 2001; Browman and Stergiou, 2004; Pikitch et al., 2004). If the different modelling tools have not yet proved themselves as management tools, they help understanding ecosystem resources interactions that are sometimes more important than the impact of fisheries (Christensen and Pauly, 1), and are paving the way to future implementation of ecosystem-based management of fisheries. In the Pacific Ocean several models have been developed to try and understand the interactions between the different components of the pelagic ecosystem: Seapodym (Lehodey, 2001, 2004), IBM (Kirby, 2004) in the western Pacific, Ecopath/Ecosim models in the western Pacific (Godinot and Allain, 2003), in the central Pacific (Kitchell et al 1, 2002) and in the eastern Pacific (Olson and Watters 2003). These models are more or less advanced and they have some limitations, but they allow highlighting the data gaps that need to be filled to improve the accuracy and the confidence in the model. They also offer an easily accessible view of the system and a powerful tool to aggregate ecosystem data from different sources; it is a necessary framework for the refinement of input parameters and it allows testing hypotheses about ecosystem functions, policy screening of proposed ecosystem management strategies and better understanding of the possible impacts of long-term regime shifts (Gibbons-Fly, 2000). The Ecopath/Ecosim model developed for the western and central Pacific, detailed in Godinot and Allain (2003, SCTB BBRG5), was built with special interest in tuna. The three species of tropical tuna are considered as different groups and 1 other functional groups are included in the model: detritus, phytoplankton, zooplankton, crustacea, cephalopods, epi- and meso-pelagic fish, small top predators and adult top predators. Data inputs for each group are Biomass, Prodution, Consumption, Ecotrophic efficiency, catch and diet matrices. The major weakness of our Ecopath model is the uncertainty of most parameters and diets. Most species are poorly known, and input parameters used are usually not based on local data. This leads to great uncertainty in the estimation of the data input values, as biological factors and abundance can vary strongly with the area. Moreover many functional groups were not included or over-aggregation due to the lack of information. A major modification recommanded to improve the model was the replacement of current data with local data both on target and bycatch species as well as on nonexploited species. Another factor for improvement is the comparison of this model with other to try to better understand the functioning of the ecosystem and of the model. With these recommendations in mind, new data were collected, progress were made in existing projects and new collaborations were implemented to develop an improved Ecopath model and acquire a better knowledge of the ecosystem. These data, projects and collaborations are presented here for information. 2

3 1. The UNDP/GEF project: Food web study of the western and central Pacific Ocean tuna ecosystem In February 2000 a five-year UNDP GEF Strategic Action Programme for International Waters of the Pacific Island Region was signed to focus on the threat of the unsustainable exploitation of living and non-living resources in this region. The project identifies the Westren Pacific Warm Pool Ecosystem is the defining feature of the region, with boundaries that coincide with western and central Pacific Ocean tuna fishery. This project has two main components: oceanic and coastal and the Food web study is part of the first one. The oceanic component focuses on the management and conservation of tuna stocks in the western central Pacific and its objective is to enable conservation and sustainable yield of ocean living resources. The oceanic component is to be implemented by the Forum Fisheries Agency (FFA) and the Oceanic Fisheries Programme (OFP) of the Secretariat of the Pacific Community (SPC). Biological research on the Warm Pool Ecosystem, and more specifically the food web study of this area are an important part of Activity 3.5 of this UNDP/GEF project: Improved scientific advice relating to regional tuna stocks, non-target species and the oceanic ecosystem available to support management decision-making. The work aims at providing an initial characterization of the Western Pacific Warm Pool Large Marine Ecosystem. In particular, trophic relationships among major components are determined by conducting biological sampling, and the establishment of databases will be essential for more detailed ecosystem modelling in the future. Simulations using the biodynamic models that are under development should allow exploring the impact on the different components of the ecosystem, of environmental changes such as El Niño Southern Oscillation, as well as fishery exploitation variations. To study the trophic relationships between the different species of the pelagic ecosystem, two types of biological sampling are carried out sampling of the stomach contents of tuna and by-catch species captured by purse seine and longline fisheries in the region; and tissue samples (muscle and liver) from tuna, by-catch and forage species for stable isotope analyses used to estimate trophic level. Samples are collected by observers from the different national observer programmes in the area on fishing vessel (mainly longline and purse seine). Since the beginning of the programme in January 2001, 4 sampling trips have been done, 3 on longline boats and on purse seine vessels. Sixteen sampling trips were organised in French Polynesia, in New Caledonia, three in Federated States of Micronesia, three in Papua New Guinea, in Solomon Islands and two in Cook Islands (See map p.6). samples have been collected so far, from which 4 stomachs have been examined (51 different species, cf Table) and 2 muscle and liver samples of predators and 42 prey items have been isotopically analysed. Diet of mahi mahi, wahoo, lancetfish and yellowfin have been partially analysed with the data available (Allain 2003, Allain 2004). 3

4 SHARKS Scientific name Common name Total nb of samples Micronesia AREA New PNG - Caledonia Solomon Elasmobranchii sharks (unidentified) 1 1 Alopias superciliosus bigeye thresher shark 1 1 Alopias vulpinus thresher shark (vulpinas) 1 1 Carcharhinus falciformis silky shark Carcharhinus leucas bull shark 1 1 Carcharhinus longimanus oceanic white-tip shark Isurus oxyrhinchus short finned mako shark 1 Isurus paucus long finned mako shark 3 3 Prionace glauca blue shark Sphyrna lewini scalloped hammerhead 1 1 Sphyrna spp. hammerhead sharks 1 1 RAYS Dasyatis violacea pelagic sting-ray 6 Mobula japanica manta ray 3 3 BILLFISH Istiophorus platypterus sailfish (indo-pacific) 2 1 Makaira indica black marlin Makaira mazara blue marlin Tetrapturus angustirostris short-billed spearfish 6 4 Tetrapturus audax striped marlin 1 5 Xiphias gladius swordfish 25 TUNA Katsuwonus pelamis skipjack Thunnus alalunga albacore Thunnus albacares yellowfin Thunnus obesus bigeye LARGE PREDATORS Acanthocybium solandri wahoo Alepisaurus ferox longsnouted lancetfish Coryphaena hippurus mahi mahi / dolphinfish Lampris guttatus moonfish / opah Sphyraena barracuda great barracuda Sphyraena genie blackfin barracuda 1 1 Sphyraena spp. barracudas (unidentified) SMALL PREDATORS Aluterus monoceros filefish (unicorn leatherjacket) Auxis thazard frigate tuna 5 5 Balistidae oceanic triggerfish 3 3 Chiasmodontidae chiasmodontidae 1 1 Decapturus macarellus mackerel scad / saba Desmodema polystictum dealfish 1 1 Elagatis bipinnulata rainbow runner Gempylidae snake mackerels /escolars 5 5 Gempylus serpens snake mackerel Gnathanodon speciosus golden trevally Kyphosus cinerascens drummer (blue chub) 1 1 Lepidocybium flavobrunneum escolar 1 Lobotes surinamensis triple-tail 1 1 Lophotus capellei crestfish/unicornfish 1 1 Melichthys niger black triggerfish Platax teira longfin batfish Promethichthys prometheus roudi escolar 1 1 Ruvettus pretiosus oilfish Scombrolabrax heterolepis black mackerel Taractichthys longipinnis big-scaled pomfret 2 2 Taractichthys steindachneri sickle pomfret 6 6 unspecified 5 5 Number of analysed stomachs in the western and central Pacific area. Shaded cells represent species with more than samples. Polynesia 4

5 2. PFRP project: collaboration for a Pacific wide project, This project funded by the Pelagic Fisheries Research Program PFRP is entitled Trophic structure and tuna movement in the cold tongue-warm pool pelagic ecosystem of the equatorial pacific. Principal investigators are Valerie Allain (SPC), Robert Olson (IATTC), Felipe Galván-Magaña (CICIMAR Mexico), Brian Popp (University of Hawaii) with the participation of Brittany Graham (University of Hawaii) and Brian Fry (Louisiana State University). More details on the study can be obtained at and Recent modeling (Lehodey, 2001) suggests that tuna productivity in the western and central Pacific Ocean is tied to upwelling along the equator in the central and eastern Pacific. The project proposes to test this hypothesis by combining diet analysis, stable isotopic compositions, food-web modeling, and stable isotope markers to trace tuna movements and trophic-level variation in the equatorial Pacific. The hypothesis predicts that tunas that reside near equatorial upwelling fronts feed at relatively low trophic levels. Opposite trends are expected in equatorial regions with little upwelling, such as the warm pool of the western Pacific, where tunas are expected to feed at higher trophic levels and move extensively, searching for less-abundant prey. The main objectives of the study are: 1. to define the trophic structure of the pelagic ecosystems in the western, central and eastern parts of the tropical Pacific Ocean (diet and isotope analysis, Ecopath modelling), 2. to establish an isotope-derived (upwelling-related) biogeography of the pelagic tropical Pacific ecosystems (isotope analysis), and 3. to characterize large-scale tuna movements related to upwelling regions along the equator (isotope analysis). Results of this study should help define ecosystem linkages leading to tuna production and the effect of climate variability on the systems. This information is important for both fisheries production and ecosystem modeling of the equatorial Pacific Ocean. Sampling of predators and preys Predators are sampled onboard fishing vessel by observers. In the western and central Pacific the sampling programme is detailed in paragraph 1. In the eastern Pacific samples from 1 purse-seine trips were collected during the period covered by this report. These included trips from Ecuadorian ports and trips from Mexican ports. Set locations were widely distributed, from 25º N to º S and from 6 º W to 1 º W (see map). 246 specimens of 1 different species were collected (see table) of which 00 stomachs have been examined. Part of the data have been partially analyzed in the western Pacific only. 5

6 Scientific name Common name Total nb of samples SHARKS Alopias sp. thresher shark 1 Carcharhinus falciformis silky shark 1 Carcharhinus longimanus oceanic white-tip shark 2 BILLFISH Makaira mazara blue marlin Tetrapturus angustirostris short-billed spearfish 1 TUNA Katsuwonus pelamis skipjack 4 Thunnus albacares yellowfin 555 Thunnus obesus bigeye 23 LARGE PREDATORS Acanthocybium solandri wahoo 231 Coryphaena hippurus mahi mahi / dolphinfish 203 SMALL PREDATORS Black skipjack tuna 5 Auxis thazard frigate tuna Balistidae and Monacanthidae oceanic triggerfish and filefish 32 Chiasmodontidae jacks Kyphosidas and Lobotidae Kyphosids and lobotids 252 MARINE MAMMALS Spinner dolphin 1 Number of sampled stomachs in the eastern Pacific. Shaded cells represent species with more than samples. Distribution of the yellowfin sampled for stomach examination and isotope analysis in the different areas of the Pacific Ocean. Preys and plankton are collected on ships of opportunity. In the western and central pacific, during 2 exploratory trips in the EEZ of New Caledonia and one scientific cruise onboard the Shoyo-Maru, a Japanese research boat cruise of the Fishery Agency of Japan, in the equatorial Pacific, 46 samples of particulate organic matter, 6

7 6 samples of zooplankton and 235 forage preys were collected. In the eastern Pacific samples were collected by the U.S. National Marine Fisheries Service onboard two NOAA research ships, David Starr Jordan and McArthur II under the direction of the Stenella Abundance Research Project (STAR - a multi-year study to assess the status of dolphin stocks): 1 samples of particulate organic matter, 6 samples of zooplankton and >400 forage preys were collected. Stable isotope analysis Stable isotope analysis has advanced on 3 separate fronts: (1) analysis of predators and preys collected from the western and central Pacific, (2) a continuation of analysis of tuna caught around Oahu - Hawaii, and the most intense effort has focused on (3) laboratory experiments on captive tuna. First results of isotope analysis were received for the western and central Pacific: samples of muscle and liver of different pelagic top predators and preys were analysed for carbon and nitrogen isotopes. Several factors could explain the tendencies observed in the isotope values. Location seems an important factor: fish of the same species but from different locations have different values. Length may be another contributing factor. Nitrogen isotope values of predators also appear related to depth. More samples are needed to try to explain the values observed and are in the process of being analysed. d1 5N 1 YELLOWFIN HAWAII MICRONESIA EASTERN PACIFIC NEW CALEDONIA dc 1 YELLOWFIN dc dn 1 BIGEYE dc dn 1 SKIPJACK dc δn vs. δ3c values for yellowfin, bigeye and skipjack tuna in different areas of the Pacific Ocean

8 Overall, the data collected from Hawaiian waters illustrates a distinct and rapid ontogenic shift in both yellowfin and bigeye tuna. The ontogenic shift, documented in both liver and white muscle tissues, will be modeled to provide estimates of tissue turnover in wild tuna. Aptly, these values will be compared to data collected in the diet experiments with captive tuna. BET = δ N ( ) 6 6 YFT = Fork Length (cm) Ontogenic trophic shift observed on isotope values of liver and white muscle samples of yellowfin and igeye tuna from Hawaii. A tuna tank was constructed at the HIMB facilities in Hawaii, under the guidance of Dr. Kim Holland. Shortly after the construction of the tank was completed, tuna were placed in the tank and serendipitously provided an ideal diet shift experiment to base future work on. More specifically, the diet fed to the tuna once in the tank (i.e. a mixture of squid and smelt) was isotopically distinct from the wild diet. A more rigorous diet shift experiment began in Feb and is nearly complete. Overall, the tissue turnover rates of captive tuna are similar to those recorded f for mammals. Not only is the scientific community interested in the uses of stable isotopes to determine tissue turnover rates, but the results of these experiments will also enable us to better assess tuna migration and are at the foundation of future work. Ecosystem modeling In the western and central Pacific the model developed in 2003 will be improved: the diet matrix will be modified using data collected in the area by the observer programmes. In the Eastern Pacific a trophically-explicit, spatially-aggregated ecosystem model of the pelagic eastern tropical Pacific, developed previous to this project, using Ecopath with Ecosim, was published in 2003 (Olson, R.J., and G.M. Watters A model of the pelagic ecosystem in the eastern tropical Pacific Ocean. Inter-Am. Trop. Tuna Comm., Bull. 22 (3): 3-21). The model will be reformulated based on new data describing trophic connections (diet data) and trophic structuring (stable isotope data) forthcoming from this project. Substantial improvements are expected because the

9 existing model contains a paucity of information about the forage fishes and cephalopods at middle trophic levels, whereas this project will measure trophic positions of these taxa relative to those of the predators, based on stable isotope analysis. This PFRP project is included in the OFCCP-GLOBEC program. The Oceanic Fisheries and Climate Change project (OFCCP-GLOBEC) will investigate the effect of climate change on the productivity and distribution of oceanic tuna stocks and fisheries in the Pacific Ocean with the goal of predicting short- to long-term changes and impacts related to climate variability and global warming. The ultimate goal of the project is to conduct simulations with ecosystem models that include the main tuna species, using an input data set predicted under a scenario of climate change. Four major components have been identified: - 1. Monitoring the upper trophic levels of the pelagic ecosystem - 2. Food web structure in pelagic ecosystems - 3. Modelling from ocean basin to individual scale - 4. Socio-economical impacts. The PFRP Trophic structure and tuna movement in the cold tongue-warm pool pelagic ecosystem of the equatorial pacific project is part of the component 2 of the OFCCP-GLOBEC project. 3. CLIOTOP project: collaboration and comparison with other oceans The general objective of CLIOTOP (CLimate Impacts on Oceanic TOp Predators ) is to organize a large-scale worldwide comparative effort aimed at identifying and elucidating the key processes involved in open ocean ecosystem functioning. In particular, CLIOTOP aim at determining the impact of both climate variability at various scales and fishing on the structure and function of open ocean pelagic ecosystems and their top predator species. The ultimate objective is the development of a reliable predictive capability of the dynamics of top predator populations and ecosystems that are combining both fishing and climate (environmental) effects. CLIOTOP is organized around five working groups: WG 1 Early life history WG 2 Physiology, behaviour and distribution WG 3 Trophic pathways in open ocean ecosystems WG 4 Synthesis and modeling WG 5 Socio-economic aspects and management strategies Under the WG 3 Trophic pathways in open ocean ecosystems, the key questions are 1. What are the main trophic pathways of oceanic top predators and how do they differ among and within oceans? 2. Is there evidence of change in trophic pathways over time and space consistent with climate scale variability can seasonal and spatial variability be used to explore the impacts of climate variability? 3. What is the spatial distribution of forage organisms and how does hydrodynamics drive this from small to large scales? What is the impact of climate variability on this distribution? 4. Is it possible to identify indicators, such as prey species or size spectra, that would highlight significant changes in trophic pathways?

10 Different approaches are used: Diet analysis, Stable isotope analyses Automated acoustical methods Data recovery, retrospective and comparative analyses Modeling A first meeting of several collaborators from the WG3 of the CLIOTOP project in June 2004 allowed the first comparison of isotope data to try to characterize isotopically each ocean. More collaboration and exchange of data on isotope, diet data and ecosystem modelling are scheduled in the following years. dn 1 YELLOWFIN INDIAN OCEAN ATLANTIC OCEAN NEW CALEDONIA EASTERN PACIFIC dc dn 1 SKIPJACK dc dn 1 BIGEYE δn vs. δ3c values for yellowfin, bigeye and skipjack tuna in the different Oceans dc

11 Bibliography Allain, V BBRG-6. Diet of mahi-mahi, wahoo and lancetfish in the western and central Pacific. SCTB. Mooloolaba, Australia. - July Allain, V BIO 1. Diet of yellowfin tuna in different areas of the western and central Pacific Ocean. SCTB1. Majuro, Marshall Islands. -1 Aug Browman, H.I. and K.I. Stergiou Perspectives on ecosystem-based approaches to the management of marine reources. MEPS 24 : Christensen, V. and D. Pauly. 1. Placing fisheries resources in their ecosystem context. EC Fish. Coop. Bull., : -. Gibbons-Fly, W Chairman s report. IATTC Bycatch Working Group, 2nd meeting, 4-6 April 2000, La Jolla, California, USA: 1 pp. Godinot, O. & V. Allain. BBRG-5. A preliminary Ecopath model of the warm pool pelagic ecosystem. SCTB. Mooloolaba, Australia. - July Kirby, D.S., G.Allain, P.Lehodey, A.Langley ECO 4 Individual/Agent-based Modelling of Fishes, Fishers, and Turtles. SCTB1. Majuro, Marshall Islands. -1 Aug Kitchell, J.F., C.H. Boggs, X. He and C.J. Walters. 1. Keystone predators in the Central Pacific. In Ecosystem approaches for fisheries management. University of Alaska Sea Grant, AK-SG--01, Fairbanks, Kitchell, J.F., T.E. Essington, C.H. Boggs, D.E. Schindler and C.J. Walters The role of sharks and longline fisheries in a pelagic ecosystem of the Central Pacific. Ecosystems, 5: Lehodey, P The Pelagic ecosystem of the tropical Pacific Ocean: dynamic spatial modelling and spatial consequences of ENSO. Progress in Oceanography. 4: Lehodey, P ECO-1. A Spatial Ecosystem And Populations Dynamics Model (SEAPODYM) for tuna and associated oceanic top-predator species: Part I - Lower and intermediate trophic components. SCTB1. Majuro, Marshall Islands. -1 Aug Lehodey, P ECO-2. A Spatial Ecosystem And Populations Dynamics Model (SEAPODYM) for tuna and associated oceanic top-predator species: Part II - Tuna dynamics and fisheries. SCTB1. Majuro, Marshall Islands. -1 Aug Olson, R.J. and G.M. Watters A model of the pelagic ecosystem in the Eastern tropical Pacific Ocean. IATTC Bull., 22: in press. Pikitch, E.K et al Ecosystem-based fishery management. Science. 305 : UNEP Ecosystem-based management of fisheries: opportunities and challenges for coordination between marine regional fishery bodies and regional seas conventions. UNEP Reg. Seas Rep. Stud., : 52 pp.