(Draft) Trophic levels of multi-species in the Gulf of Thailand 01. Ratanawalee Poonsawat 1 Mala Supongpan 2 Villy Christensen 3

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1 (Draft) Trophic levels of multi-species in the Gulf of Thailand 01 Ratanawalee Poonsawat 1 Mala Supongpan 2 Villy Christensen 3 Abstract Catches by species groups in the Gulf of Thailand and diet composition of each species were analyzes in this study. Results show the mass balance of the multi-species in the Gulf of Thailand. The trophic levels of fish group were ranging Shark was the top predator, following by large piscivore, coastal tuna, Scomberomorus and Saurida. Food chain and food web of all species groups and some certain species has been shown. Since all fish groups, pelagic fish, demersal fish and invertebrate groups in the Gulf of Thailand are already fully exploited, over exploited and nearly full exploited resources resulted less balance of the resources in the system. This study provides background of the interaction of the multi-species groups that has unbalance in nature. It was propose to enhance some potential fish, invertebrate species to make the ecosystem fruitful and balance of the system at large. 1 Fishery Biologist, Upper Gulf Fisheries Research and Development Center, Bangpoeng, Praviriyapon Road, Prapradaeng, Samuth Prakarn Province BKK Consultant on Marine Fisheries, Chulabhon Building, 2 nd Floor, Kasetsart University Campus, Bangkok Professor, University of British Columbia; North Sea Center, Canada 1

2 Introduction Fisheries not only affect populations but also alter the energy flows and species interactions in marine food webs and communities simply because all fish species are components of food web and interact with other species through predation, competition and prey. The mass-balance trophic models allowed to describe the species structure and energy flows within each habitat and whole system, and to do some preliminary impact analysis by mixed trophic impact. Thus, any alteration of a stock biomass or size and age structure also alters food-web structure, energy flow, and species interaction as well as the strength of this interaction in marine ecosystem. Some responses can be compensatory in nature. Fisheries also influence nontargeted as well as targeted species. Some of the non-targeted species are part of the by-catch, but others have been affected profoundly by the complex interactions in food webs initiated by fisheries that reduce the abundance of their predators or prey. It was believed that moving from a single-species approach toward a food-web management approach is an important step forward in achieving an ecosystem approach to fisheries management. The following output results will explain what food webs are and how they are viewed and analyzed, reviews information on trophic levels in food webs, and considers top-down (consumer-control) and bottom-up (resource-control) effects on species in the multi-species ecosystem. Objectives 1. To analyze the mass balance for multi-species fisheries in the Gulf of Thailand. 2. To analyze the trophic level of the multi-species in the Gulf of Thailand. 3. To analyze mixed trophic impact. 4. To analyze food chain and food web of multi-species. 5. To propose some possible predator and prey enhancement to make mass balance in the natural resource. 2

3 Materials and Methods Materials 1. Data for fish groups were collected from the research vessel from 1973 to 2005 and were grouping into 40 groups (Appendix 1 and 2). (Apendix 1 new data Mala-ewe6-1.csv; Appendix 2 Thai Gulf biomass-new 1.csv) 2. Diet composition was accessed from review literature and Fish-based. 3. The analysis was done by using the computer software EWE versions 5.1 and Material and methods 2.1. Study site Gulf of Thailand is the study site (Fig. 1), it has 304,000 km 2 of surface area within EEZ zone Figure 1. Gulf of Thailand and EEZ zones 3

4 2.2 Method Research vessels have conducted routine surveys in the Gulf of Thailand at depth 10 to 50 meters since 1973 up to present time. Time series of CPUEs (catch per unit effort) of marine resources are using as data input in the Ecopath. The marine resources are categorized into 40 fish groups, some small quantity are combine and fish larvae are also separated from the adult fish. 2.3 Model description The Ecopath from EWE version 5.1 and 6 are used to analyze for this study. The first Ecopath equation describes how the production term for each group (i) can be split in components. This is implemented with the equation, Production = catches + predation mortality + biomass accumulation + net migration + other mortality.. Eq. 1 or, more formally, P i = Y i + B i.m2 i + E i + BA i + P i (1 - EE i )...Eq. 2 where P i is the total production rate of (i), Y i is the total fishery catch rate of (i), M2 i is the total predation rate for group (i), B i the biomass of the group, E i the net migration rate (emigration immigration), BA i is the biomass accumulation rate for (i), while M0 i = P i (1-EE ) i is the other mortality rate for (i). On the need for input parameters Not all parameters used to construct a model need to be entered. The Ecopath model links the production of each group with the consumption of all groups, and uses the linkages to estimate missing parameters, based on the mass-balance requirement of equation (1) that production from any of the groups has to end somewhere else in the system. This can be expressed, where there is not accumulation of biomass as 4

5 Production = Catch + biomass accumulation + predation mortality + net migration + other mortality where the predation mortality term is the parameter that links the groups with each other. Ecopath balances the system using one production equation for each group in the system. For a system with three groups three production equations like the one above are used, i.e., Eq. 15 where, P i is the total production of group i; Y i is the catches of group i, E i is the net migration of i, and BA i the biomass accumulation. DC ij is the proportion of the diet predator group i obtains from prey group j. Bi is the biomass of group i; Q/Bi is the consumption/biomass ratio of group i. P/B i is the production/biomass ratio of group i; EE i is the ecotrophic efficiency, i.e. (1 - other mortality), of group i. Y i, E i, BA i, and DC ij must always be entered, while entry is optional for any of the other four parameters (B i, Q/B i, P/B i, EE ). i The above set of linear equations can be solved even if, for any of the groups, one or more of these four parameters is/are unknown (see below). It is not necessary that the same parameter is unknown for all groups, as the program can handle any combination of unknowns. The algorithms involved in the estimation of missing parameters are described in detail in Appendix 4 in the Help system. A number of algorithms have been incorporated, to estimate more than one missing parameter for each group, which takes advantage of the fact that most entries in the diet composition matrix will be zero. In some cases it may thus be possible to estimate the value of Q/B in addition to i, P/B, or EE of a group. However, it is generally not possible to estimate the biomasses or P/B of apex predators from which there is no exports, or more specifically no fishery catches. Moreover, if too many input parameters are missing when estimating 5

6 the basic parameters, a message to this effect will be displayed and the program will be aborted. In such cases, the data set will need to be complemented with additional inputs. Results and Discussion in 1. The mass balance for multi-species fisheries in the Gulf of Thailand. After input the group name, relative cpue kg/hr) of each fish group, the production per biomass (PB ratio=z) and ecotrophic efficiency less than 1 into the EWE software program, the Ecopath part of the program will run automatically and input some values that needed to fill out. The output mass balance for multi-species fisheries in the Gulf of Thailand is shown in Table 1. Since all fish groups, pelagic fish, demersal fish and invertebrate groups in the Gulf of Thailand are already fully exploited, over exploited and nearly full exploited resources (Contribution: Marine Fisheries, 2008). If the fish has been taken from nature, each group will effect to another group and the balancing species in nature is destroyed, the fisheries will be not in the sustainable manner. 2. The trophic level of the multi-species in the Gulf of Thailand. Trophic level has developed as a very general collective term, describing groups of species that are similar distance in terms of energy transfers from the photosynthetic base. Fig.1 shows trophic level of all groups. The trophic levels of each group are ranging 1 to 4.8 which shark is the top predator in this case. The top five predators in ordering are shark, large piscivore, coastal tuna, Scomberomorus and Saurida. The average trophic level is 3, the fish groups which the trophic level ranging 2.20 to 2.95 are Rastrelliger, small pelagic fish, crab and lobster, trash fish, shellfish and pony fish 6

7 3. Mixed trophic impact It becomes possible to assess the effect of trophic that changes the biomass of a group will have on the biomass of the other groups in the ecosystem as well as the catch from fishing gear will have on the catch of others. The bars pointing upwards indicate positive impacts, while the bars pointing downwards show negative impacts (Fig. 2). The impacts are relative and comparable between groups and gear. In this case, the apex predators (shark) will have a negative impact on their preferred preys. Most groups have a negative impact on themselves, interpreted here as reflecting increased within-group competition for resources. If a group cannibalizes itself the impact of a group on itself may be positive. The mixed trophic impact routine as a tool for indicating the possible impact of direct and indirect interactions (including competition) in a steadystate system, not as an instrument for making predictions of what will happen in the future if certain interaction terms are changed. The major reason for this is that changes in abundance may lead to changes in diet compositions, and this cannot be accommodated with the mixed trophic impact analysis. All groups are impacted each other and the types of fishing gear in capturing different fish groups are also impacted to other (Fig. 2), e.g. trawling fisheries are targeting to demersal fish (large piscivore, Saurida, Nemipterus, shark and rays) and catching some other pelagic fish as by catch (Lutjianus, Plectorhyncus, Ariidae-Spelling check) and it is effected to the fish that eat demersal fish as well as purse seine fisheries are targeting to pelagic fish (coastal tuna, carangid, anchovy) and it is effected to pelagic fish eaters. If the ecosystem looses its balance of fish species resulting to the fishery system will not sustain. The system will be develop in a peculiar way, e.g. in the Gulf of Thailand the demersal fish was overexploited it means less demersal fish to eat squid eggs (unbalance of the ecosystem) then the squid population was bloomed. Another case, at first the demersal fish has been over exploited, then the fishers targeting to pelagic fish that was still abundance at that time by increasing number of purse seine boats up to three 7

8 folds of the past record. Especially those light luring fishing included anchovy fishing. Recently the pelagic fish is fully exploited and the number of the purse seine boats is gone down as the results. 4. Food chain and food web Food webs are the key function to know about species interactions and therefore display ecological connections. The connection of individual predators to their preys are direct interactions. A food web is the food chain where smaller organisms are successively consumed by larger ones. Thus one reads of primary producers (organisms that are able to create biological energy through photosynthesis), herbivores, and primary and secondary carnivores. Critical linkages in marine ecosystems are sustained by key predatorprey relationships. Large, long-lived predators and small, short-lived prey (e.g., forage fishes) both contribute in major ways to marine fish catches. Heavy fishing may precipitate species replacements, both at lower trophic levels (e.g. anchovy, small shrimp) and at upper trophic levels (e.g. sharks, large piscivore). Loss from ecosystems of large and long-lived predators is of particular concern because they potentially exercise top-down control of processes at lower trophic levels. Global data sets have indicated that the mean trophic level of fish caught declined significantly from (Pauly et al. 1998). Fishing down food webs (i.e., fishing at lower trophic levels) disrupts natural predator-prey relationships and may lead first to increasing catches, but then to stagnating or declining yields. The food chain and food web of all groups in the Gulf of Thailand are somewhat complicated as shown in Fig. 3. The predator and prey relationship among each other is recognized from the line shown in the figure. Top lines beyond the group nodes are predators and line under the group nodes represented preys. Fig. 4 shows the top predation of shark that can eat all 8

9 Table 1. The mass balance of the multi-species fish in the Gulf of Thailand. B P/B Q/B Group name TL HA B in HA ton/km 2 /yr /yr EE P/Q 1 Rasterlliger spp Scomberomorus Carangidae Pomfret Small pelagic fish False trevally Large piscivores Scianidae Saurida spp Lutianidae Plectorhynchidae Priacanthus spp Sillago Nemipterus spp Ariidae Rays Sharks Cephalopod Shrimps Crab, Lobster Trashfish Small demersal fish Medium demersal piscivore Medium demersal benthivore Shellfish Jellyfish Sea cucumber Seaweeds Coastal tuna Sergestid shrimp Mammals Pony fishes Benthos Zooplankton Juvenile small pelagic Juvenile caranx Juvenile saurida Juvenile Nemipterus Phytoplankton Detritus TL HA EE B P Q Trophic level Habitat area Ecotrophic Efficiency Biomass Production Consumption 9

10 Figure 1. The pyramid of trophic levels of fish groups in the Gulf of Thailand. 10

11 Figure 2. Mixed trophic impact to fish groups and catch by fishing gear in the ecosystem. 11

12 Figure 3. Flow diagram of all fish groups. Figure 4. Flow diagram of shark (Predation of all fish and detritus). 12

13 Figure 6. Flow diagram of zooplankton. sizes of fish as well as some sharks dwelling for detritus at the sea bottom. The zooplankton eats some phytoplankton and detritus. Zooplankton is eaten by zooplankton eater fish (Fig. 5). As fisheries develop in an area their target species change. During their initial development, the focus is usually on higher-trophic level species. As these become more scarce attention switches to the more abundant prey species, and ultimately concentrates on lower-trophic level species, e.g. shrimps and squids (Christensen, 1996; Pauly, 1979). This process, now known as fishing down the food web (Pauly et al., 1998), and its global nature have been demonstrated in numerous studies throughout the world References 13

14 Pauly, D. (1979) Theory and Management of Tropical Multispecies Stocks. Manila: ICLARM (International Center for Living Aquatic Resources Management) Studies and Reviews, 1. Christensen, V. (1996) Managing Fisheries Involving Predator and Prey Species, Reviews in Fish Biology and Fisheries 6(4): (Ecosystem Principles Advisory Panel,1996). Pauly, D., V. Christensen, J. Dalsgaard, R. Froese and F. Torres Jr Fishing down marine food webs. Science 279: Fogarty, M. J. and S. A. Murawski Large-scale disturbance and the structure of marine systems: Fishery impacts on Georges Bank. Ecological Applications Supplement 8(1):S6 S22. Ecosystem Principles Advisory Panel,1996 A Report to CongressAs mandated by the Sustainable Fisheries Act amendments to the Magnuson-Stevens Fishery Conservation and Management Act Acknowledgement 14

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