Early Life Stages of Fishes in Lake Taal, Philippines: Assessment and Implications for Biodiversity Management and Conservation
Total Page：16
File Type：pdf, Size：1020Kb
Philippine Journal of Science 150 (3): 619-630, June 2021 ISSN 0031 - 7683 Date Received: 05 Oct 2020 Early Life Stages of Fishes in Lake Taal, Philippines: Assessment and Implications for Biodiversity Management and Conservation Ma. Lourdes D. Merilles, Charmane B. Nochete, Benjie D. Tordecilla, and Maria Theresa M. Mutia* Freshwater Fisheries Research and Development Center National Fisheries Research and Development Institute Butong, Taal, Batangas, Philippines Lake Taal is the third largest lake in the Philippines and its fisheries provide livelihood to thousands of locals in its coastal areas. This study was conducted to recommend possible strategies and measures to conserve and protect the population of fishes, especially of the early life stages (ELS). The composition, abundance, and distribution of ELS and the environmental factors affecting these were investigated through monthly ichthyoplankton surveys and monitoring of water parameters, phytoplankton, and zooplankton abundances in 12 equidistant stations from January 2015 to December 2018. A total of 26,345 fish eggs and 9,140 fish larvae were collected, of which 88.9% of the fish larvae were morphologically identified into eight families, while the rest were unidentified. Families Terapontidae (44.5%) and Gobiidae (37.0%) numerically dominated the identified larvae catch. Distribution of the egg, yolk sac, and pre-flexion stages (ELS) significantly varied across stations. Three stations on the northern basin of the lake showed the highest fish egg abundance (731.82, 246.47, and 381.28 ind 100 m–3) while stations on the west, northwest, and eastern bay of the lake showed the highest abundance of fish larvae (153.76, 121.28, and 94.64 ind 100 m–3). The temporal distribution of ELS was highly associated with zooplankton, green algae, and salinity while spatial distribution was highly associated with the majority of the water parameters and chlorophyll a. Seasonal and annual distribution of ELS showed significant variation, which reveals possible spawning patterns of the identified fish larvae and the influence of varying environmental conditions to the distribution of ELS. Based on these, the identified possible spawning and larval foraging grounds are recommended as protected zones. Reduction of nutrient inputs to minimize changes in the lake trophic condition is also recommended. Keywords: fish eggs, fish larvae, fish sanctuary, ichthyoplankton, spawning, water quality INTRODUCTION alarmingly increasing number of introduced fish species. The lake has a total area of 236.9 km2, a maximum depth Lake Taal, a tropical freshwater lake that is the third of 198 km, and an average depth of 60 km (Castillo and largest and one of the deepest lakes in the Philippines, Gonzales 1976). Along the perimeter of the lake are 38 boasts of a diverse array of ichthyofauna – from a single tributary rivers some of which are spring waters in origin. endemic to a few native to several migratory and an The only drainage of the lake is the 8.2-km Pansipit River located at the southern portion of the lake, which *Corresponding Author: [email protected] 619 Philippine Journal of Science Merilles et al. Early Life Stages of Vol. 150 No. 3, June 2021 Fishes in Lake Taal empties into Balayan Bay. Many studies conducted in distribution of ELS of fishes in the lake; 2) determined the lake accounted for the diversity of fish species in the the environmental factors affecting the temporal and lake (Herre 1927; Villadolid 1937; Mercene and Alzona spatial distribution of ELS of fishes; and 3) recommended 1990; Mercene 1997; Pagulayan et al. 1999; Aquilino et possible strategies and measures to conserve and protect al. 2011; Corpuz et al. 2016; Mutia et al. 2018a). Given the population of fishes especially of ELS. the diversity of fishes in the lake, biodiversity conservation and lake management are crucial, especially in the light of many anthropogenic problems that threaten its ecosystem. The current total fish production trend shows a continuous MATERIALS AND METHODS decline from 8,792 metric tons (MT) in 1992 to 882 MT in 2000 and 460 MT in 2011 (Mutia et al. 2018a). Study Area and Sampling Factors attributing to the decline include illegal fishing, Ichthyoplankton survey was conducted in Lake Taal once overfishing, pollution, and the expansion of aquaculture a month for 48 mo (from January 2015 to December activities in the lake (Mutia et al. 2018a). 2018). Figure 1 shows the geographic location of the The Lake Taal basin was declared a protected area under sampling stations. Sampling was done for 11 h from Republic Act 7586 or the National Integrated Protected 20:00H to 07:00H of the next day. Twelve (12) equidistant Areas System Act of 1992 and named as Taal Volcano (approximately 4.45 km in between) sampling stations Protected Landscape (TVPL) by Proclamation 906 on scattered across the lake were sampled – namely, N1, N2, 16 Oct 1996 (DENR 2011). TVPL is managed by the N3, N4, N5, N6, N7, N8, N9, N10, N11, and N12. The Protected Area Management Board under the supervision sampling stations were georeferenced using a GPS receiver of the Protected Area Superintendent. A TVPL management (Garmin GPS Map 76CSX), and coordinates were used as plan was approved and serves as the blueprint for lake a reference during samplings. The coordinates and mean conservation (DENR 2011). Paramount to conservation depth for the 12 sampling stations are shown in Appendix I. and management of fishes in the lake is to determine and Ichthyoplankton. Samples were collected using a protect the fishes’ spawning and nursery grounds. plankton net (330-µm mesh size; 0.5-m diameter and 2-m Complete knowledge of the ELS of fishes is key in length), gauged with a Model 2030R standard flowmeter. understanding the ecology of fishes (Ooi and Chong A single horizontal tow was obtained by means of 10- 2011). This knowledge provides substantial scientific min (sub-surface; within upper 1 m) tows at an average information to evaluate larval recruitment and survival, speed of 1.5 knots (Smith and Richardson 1977) for each which in turn estimates the reproduction success of fish sampling station. The samples collected from the plankton populations and community structure (Chesalina et al. net were immediately preserved with ethanol (70% final 2013). The ELS of fishes includes the most vulnerable solution). In the laboratory, ichthyoplankton samples were stages and developments that are extremely influenced immediately sorted for fish larvae following the standard by environmental fluctuations and variability of their procedure for zooplankton biomass measurement and milieu. Thus, information on the environmental variables sorting (Smith and Richardson 1977) using a dissecting TM is valuable in assessing which factors significantly microscope (Nikon Binocular Microscope). The sorted influence the ELS of fishes’ distribution patterns, which fish larvae were morphologically identified up to the may provide insight into the impacts of climate change Family level using key identification guides (Moser 1996; and/or anthropogenic activities. Leis and Carson-Ewart 2004; Richards 2005; Mwaluma et al. 2014; Aya et al. 2016, 2017; Rodríguez et al. 2017). Fish species have different spawning patterns and Using a compound microscope equipped with an ocular reproductive behavior, and studies regarding the distribution micrometer, morphological characteristics such as body of their ELS are often limited. In Lake Taal, the larval length (BL), body depth (BD), and pre-anal length (PAL) distribution of the endemic and recently declared endangered were measured. The number of fish larvae was translated freshwater sardinella Sardinella tawilis (Hata et al. 2018) into density (ind per 100 m3) using the standard procedure has been reported and the information gathered were used from Smith and Richardson (1977). The volume of water to formulate current management policies for the species filtered in every tow was determined using the formula such as the establishment of a Tawilis reserve area (Mutia et derived from the flowmeter’s manual. al. 2017, 2018b). However, there have not been any similar studies conducted for other fish species in Lake Taal. (1) In this study, the distribution and abundance of the fish larvae community were determined. Specifically, where: it 1) determined the composition, abundance, and V = volume of water filtered 620 Philippine Journal of Science Merilles et al. Early Life Stages of Vol. 150 No. 3, June 2021 Fishes in Lake Taal Figure 1. Location Map of Lake Taal showing the designated sampling stations. r = radius of plankton net (2) FMf = final flow meter reading FMi = initial flow meter reading RC = rotor constant (26,873) where: N = number of individuals in 1-ml sample Phytoplankton and zooplankton. Using a 20-µm mesh V1 = total volume of the plankton sample (ml) plankton net (30-cm diameter; 1-m length), phytoplankton V2 = volume of the lakewater filtered by plankton net samples were collected by vertically towing the net from within hauling depth (ml) a depth of five meters up to the surface. The collected samples were placed in a vial and fixed with Lugol’s iodine The mean abundances of each phytoplankton and (APHA 1998). Zooplankton samples were collected by zooplankton group in all the sampling stations were vertical tows (20 m below the surface) using a 64-µm mesh tracked monthly across the four years. plankton net (30 cm diameter; 1 m length). The samples Water quality and nutrients. During plankton tows in each were placed in a vial and preserved with 10% formalin station, water parameters – namely, water temperature (APHA 1998). Phytoplankton and zooplankton samples (◦C), conductivity (mS/cm), total dissolved solids (g/L), were microscopically examined under a compound salinity (ppt), dissolved oxygen (mg/L), pH, turbidity microscope. The species were identified morphologically (NTU), and chlorophyll-a (µg/L) – were measured using into the lowest taxa possible (Zafaralla 1998; Papa et a YSI 6600 V2 Multiparameter Water Quality Sonde al.