of fisheries Small-scale San Miguel Bay, Philippines: biology and stock assessment Edited by t Daniel Pauly Antonio N. Mines2 1982 1International Center for Living Aquatic Resources Management, MCC P.O. Box 1501, Makati, Metro Manila, Philippines. 2 Institute of Fisheries Development and Research, College of Fisheries, University of the Philippines in the Visayas, Quezon City, Philippines. Small-scale fisheries of San Miguel Bay, Philippines: biology and stock assessment EDITED BY D. PAULY A.N. MINES 1982 Published by the Institute of Fisheries Development and Research, College of Fisheries, University of the Philippines in the Visayas, Quezon City, Philippines; the Internptional Center for Living Aquatic Resources Management, Manila, Philippines; and the United Nations University, Tokyo, Japan. Printed in Manila, Philippines Pauly, D. and A.N. Mines, Editors. 1982. Small-scale fisheries of San Miguel Bay, Philippines: biology and stock assessment. ICLARM Technical Reports 7, 124 p. Institute of Fisheries Development and Research, College nf Fisheries, University of the Philippines In the Visayes, Quezon City, Philippines; International Center for Living Aquatic Resources Management, Manila, Philippines; and the United Nations University, Tokyo, Japan. Cover: Upper: Abo (Otolithes ruber, the most important demersal fish of San Miguel Bay. VPhoto, N. Navaluna]. Lower: satellite view of the Bay, to the right of center. [Photo, NASA, U.S.A.]. ISSN 0115-5547 ICLARM Contribution No. 92 Preface The research project "Small-Scale Fisheries of San Miguel Bay: A Multidisciplinary Analysis" was conducted jointly by the Institute of Fisheries Development and Research (IFDR) of the College of Fisheries, University of the Philippines in the Visayas and the International Center for Living Aquatic Resources Management (ICLARM), both based in Metro Manila, Philippines. In addition to funding from IFDR and ICLARM the project received grants from the United Nations University (UNU), Tokyo, Japan and the Philippine Council for Agriculture and Resources Research and Development (PCARRD), Los Baios, Laguna, Philippines. I FDR and ICLARM are both grateful for -his support because completion of this research project would have been impossible without it. The project has produced four technical reports which cover the biological, economic and sociological aspects of th2 San Miguel Bay fisheries. A fifth report synthesizes these complementary aspects and discusses their implications for managing the San Miguel Bay fisheries. In this technical report the bio!ogical aspects of the fisheries of San Miguel Bay are analyzed. It represents the results of data collection and analysis over approximately a two-year period, 1979-1981. DR. I.R. SMITH PROF. A. MINES Director Project Leader and Director Traditional Fisheries Program Institute of Fisheries Development ICLARM and Research (IFDR) e.III Table of Contents Preface ..................................................................... The Assessment of the Fisheries: Objectives and Methodology. A.N. MINES ............................................................. The Physical Environment. A.N. MINES, D.PAUL', N.A. NAVALLINA, AND J.M. VAKILY ......................................................... The Fishes and their Ecology. D. PAULY ........................................... 15 Length-Weight Relationships of Fishes. E. CINCO .................................... 34 Morphometrics, Biology and Population Dynamics of the Croaker Fish, Otolithes ruber. N.A. NAVALUNA .................................. 38 Catch and Effort in the Small-Scale Fisheries. D. PAULY, 56 A.N. MINES AND N.A. NAVALUNA ............................................. Catch and Effort in the Trawl Fishery. J.M. VAKILY ................................. 65 History and Status of the San Miguel Bay Fisheries. D. PAULY .............................................................. 95 iv The Assessment of the Fisheries: Objectives and Methodology A.N. MINES Institute of Fisheries Development and Research College of Fisheries University of the Philippines in the Visayas Quezon City, Philippines MINES, A.N. 1982. The assessment of the fisheries: objectives and methodology, p. 1-4. In D. Pauly and A.N. Mines (eds.) Small-scale fisheries of San Miguel Bay, Philippines: biology and stock assessment. ICLARM Technical Reports 7,124 p.Institute of Fisheries Development and Research, College of Fisheries, University of the Philippines in the Visayas, Quezon City, Philippines; Inter­ national Center for Living Aqudtic Resources Management, Manila, Philippines; and the United Nations University, Tokyo, Japan. Abstract San Miguel Bay is a major fishing ground on the Pacific coast of the Philippines. The Bay is exploited by trawler operators and small-scale fishermen competing for t. - same resources. A multidisciplinary research project involving fishery biologists, economists and sociologists was conducted from 1979 to 1981 to obtain a factual base from which options for the management of the Bay's fishery-including the allocation of its catch-could be derived. This paper, which presents the objectives and methodology of the biological section of the project, serves as a background to seven other papers, which discuss aspects of the Bay, its fishes and fisheries. Introduction In 1979, the Institute of Fisheries Development and Research (I FDR) of the University of t1e Philippines in the Visayas, College of Fisheries (UPV-CF) and the International Center for Living Aquatic Resources Management (ICLARM) joined hands in a concerted effort to conduct an in-depth analysis of the socioeconomic conditions of small-scale fishermen in the Philippines. San Miguel Bay in the Bicol Region, one of the country's most productive fishing grounds, was selected as the study area. Besides being an important fishing ground for shrimps, avariety of fish species, such as croakers, herrings, mullets, juvenile Spanish mackerels, anchovies and crevalles ar.­ also commonly caught in the Bay by fishermen using a variety of fishing gear, e.g., stationary fish traps, gill-nets, fish corrals, beach seines, liftnets and trawls. In the Philippines, fisheries regulations and statistics distinguish between the commercial sector, which uses vessels of more than 3 gross tons (GT), and the municipal sector, which uses smaller boats and may operate in inshore waters. The latter are under the jurisdiction of the munici­ palities, while the commercial sector is regulated at the national level. During the 1970s, there arose conflicts among fishermen in the Bay, especially between the gill­ netters and the operators of commercial trawlers. The gill-netters sought the help of the authorities concerned to ban commercial trawlers from fishing inside San Miguel Bay, since under existing legis­ 2 lations, most of the fishing area in the Bay is within municipal waters. In 1978, aworkshop conducted by the Bureau of Fisheries and Aquatic Resources (BFAR) and the South China Sea Fisheries Devel­ opment and Coordinating Programme (SCSP) using secondary catch data, concluded that San Miguel Bay was overfished (Simpson 1978). This was contested by certain fishermen in the area. The primary objective of the research project envisioned by IFDR and ICLARM was to con­ duct a multidisciplinary study in San Miguel Bay to examine the problems of the municipal fishery and the fishing communities around the Bay. It was recognized that biological, technological, economic and sociological factors all influence the income of municipal fishermen, and in order to understand fully the problems of these fishermen, the interrelationships of these factors must be determined. Because a multidisciplinary approach has not been applied before to fisheries research in the Philippines, an underlying rationale for the project was to develop such an approach which could also be used in other areas. It was envisioned that the results of this study should serve as a basis for government policymakers and planners to include the fisheries sector of San Miguel Bay in the integrated area development plan coordinated by the Bicol River Basin Development Program (BRBDP). The three distinct, but complimentary components or modules of this IFDR/ICLARM project were: Biology (fish stock assessment); Economics; and Sociology (including mobility). While each of these modules had its own specific research objectives, the overall goal was to determine options for improving the household incomes of the small-scale fishermen in the area. Objectives of the Biology Module The specific objective of the biology module was to assess the status of the fishery resources of San Miguel Bay, that is, to assess (i) whether the Bay as awhole is overfished or not, and (ii) the performance of the various parts of the fishery. This entailed the estimation of catch by gear type, species group, the seasonality of the total catch and of the catch per unit of effort of the various gears to describe the major biological characteristics of the fishery. Methodology In the following, a summary review is given of the methods used to achieve these objectives (see Table 1). * Catch and effort data: It was considered a primary task to obtain a reliable estimate of the present combined catches of all San Miguel Bay fishermen. This was accomplished by making an estimate of the total number of the different types of fishing gear used in the Bay. The catch per unit of effort by gear, by month and species groups over a 12-month period was then determined. The total catch from the Bay was estimated by multiplying the total effort by the catch per effort figures by gear, month and species group. Catch per unit of effort by gear type was obtained by direct monitoring of the fishing activities of the particular gear at selected landing places. A team of research assistants assigned to the module boarded trawlers twice a month to gather catch data during operations of the trawlers around San Miguel Bay to supplement available data on this particular type of fishing gear. Counts of the number of larger gears (fixed gears, trawlers, etc.) were made along the beaches and offshore. The number of smaller gears (push nets, handlines, etc.) was obtained in the course of the household survey conducted by the sociology module of the project. The average catch per unit of effort of these gears was estimated either by direct monitoring or from recall interviews of respondent fishermen. The results of these computations are reported by Pauly et al. (this report) for the small­ scale fishery and by Vakily (this report) for the trawl fishery. Throughout this report, what are usually called "baby trawlers" (generally 2 to 3 t) and larger 3 trawlers (of up to 117 t) are grouped into asingle trawl fishery, while all other gears belonging to the municipal sector are considered parts of the small-scale fishery. Pauly (this report) gives a rationale for the separation of the San Miguel Bay fishery into these two categories. * Biological and oceanographic data: Little emphasis was given to purely biological work on the fishes of San Miguel Bay. However, Navaluna (this report) collected morphometric, meristic and fecundity data on the croaker Otolithesruber in the course of his investigation on the population dynamics of what turned out to be the most important finfish of San Miguel Bay. Cinco (this report) studied length-weight relationships of a number of fish species. Based on earlier records in the taxonomic literature (notably Herre 1953), Pauly (this report) compiled a list of the fish of San Miguel Bay which was augmented by 28 new records obtained in the course of the project. Biological characteristics of these fishes (188 species in all) were obtained from the available literature, which allowed grouping the species into various feeding guilds arid building amodel of the trophic interrelationships in the Bay. Crude assessments were then made of the potential impact of the selected exploitation of the various groups of species on the multispecies stock as awhole (Pauly, this report). Also, the list ef species was divided into different groups depending on the reported extent of their ability to with­ stand salinity fluctuations. This made it possible to characterize San Miguel Bay fauna 9s typically estuarine, markedly separate from the hard bottom/reef fish fauna occurring off the mouth of the Bay. Collection of oceanographic data was very limited. However, available secondary data on tidal amplitudes, river runoff into the Bay, rainfall, wind run and some salinity measurements were combined to provide acoherent picture of the Bay's water budget and to describe the Bay's estuarine character (Mines et al., this report). A bathymetric survey of the Bay was conducted using a portable echosounder. The results were used to deduce a minimum rate of siltation in the Bay (using the chart of the Bureau of Coast and Geodetic Survey as reference) which has implications both to the biological productivity of the Bay and to the accessibility of certain parts of San Miguel Bay to fixed and mobile fishing gears, hence to fishery managerr 9nt issues (Mines et al., this report). * Length-frequency data: These data were collected in order to compare the sizes of fish caught by the small-scale fishery with those caught by the trawl fishery, and to estimate the va!ues Table 1. Major data sources and sampling methodology used for the assessment of the San Miguel Bay fisheries. Phase Duiation Data collected Sampling methodology Sample size I a) Catch and effort 2 years catch, effort and catch/effort - small-scale fisher';; actual gear very large, i.e., giving annual data for all gears counts and beachside sampling mean catch/effort for some, of catch-per-trip data and on monthly basis for (Ilost gears - trawl fishery; sampling on about 2 trips per month board trawler, c.omplemented with in-depth analysis of adjusted catch statistics b) Length-frequency data 2 years length-frequency data on measurement of length-frequency about 2,500 fish measured 15 different species of fish samples on board trawlers 11 Bathymetric survey 1 day present depth contours of echosounding of Son Miguel Bay transects used for drawing San Miguel Bay with portable echosounder fitted isolines covering 40%of on small boat the Bay III Survey of previous 2 years list of fish species occurring scanning of all likely sources o! literature and historical in and general hydrography primary and secondary data, includ­ data of San Miguel Bay. Previous ing files containing unanalyzed data, estimates of effort and of theses, published and unpublished catch/effort of trawlers, reports, etc. Early catch composition and anecdotal information on changes in the Day's fishery 4 of the growth and mortality parameters of the fish population in San Miguel Bay. These data were gathered mainly on board trawlers during fishing operations but also from the different landing places around the Bay. * Yield-per-recruit analyses: The yield-per-recruit models of Beverton and Holt (1957, 1966) were used to demonstrate the impact of the use of very fine mesh nets to trawl for anchovies, as well as to identify optimal fishing mortalities for penaeid shrimps (Pauly, this report) and for the croaker, Otolithes ruber. The yield-per-recruit model was also used to estimate absolute recruitment into the stock of 0. ruber (Navaluna, this report). e Historical data: Because of the importance of time series data in stock assessment, special efforts were exerted to secure historical data on the resources of San Miguel Bay. These sources include unpublished reports, theses and raw data on files at various institutions. The data were used after thorough checking and standardization to complement the original data and those available in the published literature. Acknowledgements I would like to thank all those researchers who contributed directly to this study, notably Dr. Pauly, ICLARM, the members of the biology module, Estrella Tulay, Noli Navaluna, E. Cinco and M. Vakily, the members of the economics and sociology modules, as well as the officers of the Research Division of the Bureau of Fisheries and Aquatic Resources, Manila, whose historical data on San Miguel Bay proved crucial in our study of the present condition of the Bay. References Beverton, R.J.H. and S.J. Holt. 1957. On the dynar.,;cs of exploi:*.d fish populations. Fish. Invest. Min. Agric. Fish. Food (G.B.) Ser. II.19. 533 p. Beverton, R.J.H. and S.J. Holt. 1966. Manual of methods for fish stock assessment. Part 2. Tables of yield functions. FAD Fish. Tech. Pap. 38 (Rev. 1). 67 p. Herre, A.W. 1953. Check list of Philippine fishes. U.S. Fish and Wildl. Serv. Res. Rep. 20. 977 p. Simpson, A.C. 1978. Report of the BFAR/SCSP workshop on the fishery resources of the Pacific Coast of the Philippines, 18-22 September 1978, Naga City, Philippines. SCS/GEN/78/19. 48 p.South China Sea Fisheries Development and Coordinating Programme, Manila. San Miguel Bay Fishing Gear and Catch k7 2 / 1. The most simple fishing gear is the hook and line. It accounts for about 0.15% of the Bay's total catch. 2. Dug-out, non-motorized bancas are widely used by • - small-scale fishermen. There are about 150 such boats in the Bay. 3. The scissor net is used in shallow waters, pushed ahead of the fisherman. Main catch isbalao (small ser­ gestid shrimp' and oth,, small shrimp. About 500 tonnes of these shrimp are caught annually by this gear. 4. The scissor net can be used in deeper water with the help of a banc. 3 5. A large fish trap. About 100 are used in the Bay, mostly smaller than the one shown. Together they catch low 50 tonnes of fish annually. V. .......... 5 4 6 , - " .. . *l- -a''--' . " ' ' 76 6. A specialized gear, the crab trap, used for catching swimming crabs. 7. Hauling in a beach seine. A dozen operate around the Bay. S8. A gill-netter, the major gear of the Bay's small­ /4 scale fisheries, accounting for half the small-scale catch, or about one-quarter of the whole San Miguel Bay fishery. 9. Medium-sized trawler under construction. . .. 10. A large trawler. They generally do not operate in­ side the Bay, although their home port is several kilo­ .meters upstream on the Bicol River. A - ,.. 10,1-­ g '10