CM 2005/X:07
INCIDENTAL CATCHES OF MARINE MAMMALS IN FISHERIES IN SABAH AND SARAWAK WATERS, EAST MALAYSIA
Saifullah A. JAAMAN1,2, Yuhana U. LAH-ANYI2, and Graham J. PIERCE1
1. Department of Zoology, School of Biological Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, United Kingdom (E-mail: [email protected]). 2. Marine Mammals and Whale Shark Research and Conservation Program, Borneo Marine Research Institute, Universiti Malaysia Sabah, Locked Bag 2073, 88999 Kota Kinabalu, Sabah, Malaysia.
ABSTRACT: The nature and magnitude of incidental catches of marine mammals in fisheries was investigated in Sabah and Sarawak waters, East Malaysia, using a combination of interview survey procedures and observer trips on fishing boats. Between March 1997 and December 2004, we interviewed fishermen working on 753 and 358 boats in Sabah and Sarawak, respectively, who were employing trawl nets, purse seines, gillnets and fish stakes (kelong). They were asked questions about sightings of marine mammals and interactions with fishing. We also followed 36 trawl and 10 purse seine fishing trips in Sabah between June 2003 and December 2004. Fishing was conducted in coastal waters and the methods were briefly described and total annual catches by each method and region were estimated. Marine mammals were reported incidentally caught by 310 (41%) and 99 (28%) fishing boats in Sabah and Sarawak, respectively. Gillnetters, trawlers and fish stakes were reported to catch cetaceans and dugongs, while purse seiners caught only cetaceans. In certain areas, some caught animals were consumed, traded and/or used as shark bait. Overall, the magnitude of incidental catches of marine mammals is significantly greater in gillnets, as compared to other fishing gears. No catches were seen during observer trips. A total of 306 (95% CI = 250 – 369) cetaceans and 479 (95% CI = 434 – 528) dugongs were estimated to be caught annually by fishing fleets in Sabah. The Sarawak fishing fleet is estimated to incidentally catch 221 (95% CI = 189 – 258) cetaceans and 14 (95% CI = 2 – 30) dugongs per year. The estimated number of by-catches, particularly in gillnets, may be unsustainably high. A monitoring and educational program, together with the establishment of MPAs, is paramount to minimise the threat.
KEYWORDS: conservation; cetacean; Dugong dugon; fisheries; by-catch; Malaysia; Sabah; Sarawak
1 1. INTRODUCTION
The countries of Southeast Asia are dominated by coast, making fishing an integral part of the industry and culture of their people (Dolar, 1994). East Malaysia, which comprises the states of Sabah and Sarawak, and the Federal Territory of Labuan, occupies the northern one-third of the island of Borneo (Figure 1). It is surrounded by the South China Sea to the north and west, the Sulu Sea to the northeast and the Celebes Sea to the east. The East Malaysian territorial waters, including the 200-nautical mile (nm) Exclusive Economic Zone (EEZ), cover an area of about 330,800 km2 and the total length of its coastline is approximately 2,607 km (MOSTE, 1997). The seas are significant because of the continental shelf, which is extremely nutrient rich and able to support a remarkable diversity of species (MOSTE, 1997; Oakley et al., 2000).
Although predominantly small-scaled and coastal, with more than 70% of the catches taking place within 30 nm from shore, the fisheries sector is an important source of employment in East Malaysia and plays a significant role in the Sabah and Sarawak economy (DoFS, 2004; DoMFS, 2004). Fish constitutes 60-70% of animal protein intake, with an average annual consumption of 47.8 kg per person. The fishing industry involves multi-gear fisheries and hence the catch is normally made up of a large variety of marine species, of which prawns are the most important commercially valuable species. Between 25-50% of the amount of fish landed in 2002, particularly from trawlers, is by-catch or incidental catch of miscellaneous fishes (trash fish) including undesirable size or age classes of the target species (DoFS, 2004; DoMFS, 2004). Unfortunately, other non-target species, such as marine mammals and turtles, are also occasionally caught in fisheries (Jaaman et al., 2000; Jaaman and Lah-Anyi, 2002, 2003; Jaaman, 2004).
By-catch of marine mammals in fisheries is often a controversial issue and of major concern to scientists and resource managers worldwide (Northridge, 1984; Lien et al., 1994; Perrin et al., 1994; 1996; In press; Tregenza et al., 1997; Morizur et al., 1999; Northridge and Hofman, 1999; Silvani et al., 1999; Marsh et al., 2002; López et al., 2003; Reeves et al., 2003; Tudela et al., 2005). Perrin et al. (In press) stated that the by-catch in fisheries in Southeast Asia is even greater than previously supposed, and there is no indication that this problem has been addressed in a meaningful or satisfactory way anywhere in the region. The distinction between catch and by-catch is often not clearly expressed, since that fisheries have multiple target species and almost anything that is caught has value (whether for commercial sale, use as bait, or domestic consumption).
In East Malaysia, many fishermen regarded cetaceans and dugongs as fish species and incidentally caught animals are known consumed, traded or used as fishing bait, particularly in Sabah, where some fishermen opportunistically hunt the animals during fishing trips (Jaaman et al., 2004). Despite federal and state legislation that protects the species, directed fisheries or incidental catches of cetaceans and dugongs in fisheries are apparently not being monitored and documented. This study represents a first attempt to determine the nature and magnitude of by-catches of marine mammals and estimate the associated level of mortality in fisheries in East Malaysia. It is part of a long-term study on the distribution, abundance and conservation status of marine mammals in Malaysia.
The study was based on an interview survey and on-board observation. While interview surveys are not necessarily a reliable source of quantitative data on marine mammal catches (see Lien et al., 1994 for a detailed critique), especially if fishermen wish to conceal the occurrence of such mortality, interview survey offers a means of obtaining a minimum
2 estimate for numbers of animals killed (López et al., 2003). In contrast, the placement of observers on-board fishing boats is considered the most reliable method for collecting information regarding marine mammal catches (Perrin et al., 1994; Tregenza et al., 1997; Morizur et al., 1999; Silvani et al., 1999). The combination of these two methods has proved useful in estimating by-catch of cetaceans from a large fleet of small scale or artisanal fisheries, coupled with the diversity of fishing areas and gears, such as in Galicia, Spain (López et al., 2003) and could be used in Southeast Asia (Perrin et al., In press).
2. BACKGROUND
2.1 East Malaysian fishing industry
In general, East Malaysian waters are shallow (< 200 m, mostly less than 100 m). The continental shelf is relatively wide (over 100 km) along the Sarawak coast, between 30-100 km on the west and northeast and becomes very narrow (< 30 km) on the east of Sabah. Fishing is controlled by three acts, namely the Fisheries Act 1985 (up to the EEZ boundaries), Fisheries Regulations 1964 (within the territorial waters of Sabah) and Fisheries (Maritime) Regulations 1976 (within the territorial waters of Sarawak). The management authorities in Sabah and Sarawak are the Department of Fisheries Sabah (DoFS) and the Department of Marine Fisheries Sarawak (DoMFS), respectively.
There are four fishing zones that have been established through a licensing scheme, whereby zones are designated for specific fishing gear, classes of vessels and ownership. The four management zones attempted to provide equitable allocation of resources and reduce conflict between traditional and commercial fishermen. Basically, the four zones are: 1) Zone A (< 5 nm from shore), is reserved solely for small-scale fishers using traditional fishing gear, gillnet and owner-operated vessels, 2) Zone B (> 5 nm), where owner- operated commercial fishing vessels of less than 40 Gross Registered Tonnage (GRT) using trawl nets and purse seine nets are allowed to operate, 3) Zone C (> 12 nm), where commercial fishing vessels of more than 40 GRT are allowed to operate, and 4) Zone C2 (> 30 nm), where deep-sea fishing vessels of 70 GRT and above are allowed to operate.
The marine capture fisheries are characterised by various types of fishing gears used to harvest a large variety of species (DoFS, 2004; DoFMS, 2004). The fishing gear is classified into commercial (i.e., trawl nets, purse seines and gillnets) and traditional. The otter bottom trawl is the main fishing gear used to harvest demersal finfish and prawn resources and the purse seine is used to exploit the pelagic fish resources. Two main types of purse-seines are employed; the fish purse seine, which is used to catch pelagic fishes [e.g., fringescale sardine (Sardinella fimbriata), longtail tuna (Thunnus tonggol), Indian mackerel (Rastrelliger kanagurta), scads (Selar spp., Decapterus spp.) and squids (Loligo spp.)] and the anchovy purse-seine, which is used to fish for anchovies (Stolephorus spp.). Gillnets (including driftnets) are another category of important fishing gear used to harvest coastal fisheries resources. The finfish gillnets and driftnets mainly target high-valued pelagic fish species, such as, pomfrets (Formio niger, Pampus spp.), treadfins (Polynemus spp., Eleutheronema tetradactylum), longtail shad (Shad hilsa macrura) and Spanish mackerel (Scomberomorus spp.). However, the bottom set gillnets are also used by coastal fishermen to catch demersal fish species, such as, marine catfish (Tachysurus spp. and Arius spp.) and jewfish (Decapterus spp.). The crustacean gillnets are actually trammel nets, and are employed to catch the more valuable crustacean species, such as, the Penaeus shrimps, blue crab (Portunus pelagicus) and Indo-Pacific swamp crab (Scylla serrata).
3 Figure 1: East Malaysia, with main fish landing points (towns) and surrounding seas.
Figure 2: A fish stake, or locally known as kelong or belat, set near mangroves in Cowie Bay, Sabah.
4
Traditional fishing gears include fish stakes, portable traps, hook-and-line, bag nets and lift nets (DoFS, 2004; DoFMS, 2004). These are passive fishing gears that are operated by fishermen using non-powered and outboard-powered boats or sometimes small inboard- powered boats, mainly in Zone A fishing area. They harvest a large number of demersal, as well as pelagic fish species, crustaceans and molluscs. A type of fish stake, or locally known as kelong or belat (Figure 2), is commonly operated in sheltered and shallow areas with large tidal fluctuations to catch commercial species, such as, mangrove snapper (Lutianus johni), groupers (Epinephelus spp., Plectropornus spp.), treadfins (Polynemus spp., Eleutheronema tetradactylum), rays (Gymnura spp., Dasyatis spp.), blue crab (Portunus pelagicus), yellow prawn (Metapenaeus brevicornis) and squids (Loligo spp.). Sharks, which are highly priced for their fins and mainly caught in trawls and drifnets (DoFS, 2004; DoFMS, 2004), are also one of the main target species of longline fishermen in Sabah and Sarawak (pers. obs.). Furthermore, fishermen, particularly those using non- or outboard-powered boats, often have more than one gear, such as a set of gillnet and longline, or other traditional gears, and use them alternately or simultaneously, depending on locality and season (pers. obs.).
There are 16 fishing districts along the coast of Sabah. These districts can be divided into three regions: Western (Kota Belud, Tuaran, Kota Kinabalu, Papar, Beaufort, Kuala Penyu and Sipitang), Northeastern (Sandakan, Beluran, Pitas, Kota Marudu and Kudat) and Eastern (Tawau, Semporna, Kunak and Lahad Datu), which represent fishing in the South China Sea, Sulu Sea and Celebes Sea, respectively. According to the Summary of Annual Fisheries Statistics Sabah (DoFS, 2004), the total landings from the marine fishery sector in 2002 were 175,122 metric tons (mt) with a wholesale value of about RM584 millions (US$154 millions). Of these, commercial and traditional gears contributed 130,331 (74%) and 44,792 (26%) metric tons, respectively.
Based on listing made in 1998, there were a total of 20,845 registered fishermen in Sabah (DoFS, 2004). Of these, 8,091 (39%) were traditional fishermen, 6,134 (29%) gill-netters, 5,123 (25%) trawl-netters and 1,497 (7%) seine-netters. The fishing fleet consists of a total of 10,456 boats, of which 2,524 (24%) were non-powered, 4,653 (45%) outboard- and 3,279 (31%) inboard-powered. Almost all (99%) of the non-powered and outboard-powered boats and 1,032 (41%) of the small (< 40 GRT) inboard-powered boats were engaged in gillnet and traditional fishing. Only 52 (1.6%) and 2 (0.1%) of the total inboard-powered boats were between 40 – 69 GRT and above 69 GRT, operating in Zone C and Zone C2, respectively. Although there were a relatively higher number of commercial gears used in the Western and Northeastern regions than the Eastern region, the highest amount of landings (78,583 mt) came from the latter region.
Fishing in Sarawak is conducted exclusively in the South China Sea and the industry is relatively more commercialised and modernised than in Sabah. Overall, there are 15 coastal fishing districts, which are also divided into 3 regions: Northern (Bintulu, Miri, Limbang and Lawas), Central (Sibu, Mukah, Sarikei, Belawai and Daro), and Southern (Sematan, Santubong, Sadong Jaya, Kuching, Kabong and Sebuyau). In 2002, marine capture fisheries landed a total volume of 169,929 mt with a wholesale value of about RM536 millions (US$141 millions) (DoMFS, 2004). Almost all the catches (159,849 mt, 94%) were from commercial gears and only 6% (10,080 mt) of the total landings were contributed by traditional gears.
5 Figure 3: Types of boat used in fishing in East Malaysian waters: (A) a non-powered boat, (B) outboard-engine boats (gillnets), (C) a pump-boat, and (D) an inboard-engine boat (Zone B trawler).
(A) (B)
(C) (D)
6 There were a total of 13,185 registered fishermen in 2002 and the fishing fleet consists of a total of 4,648 boats (DoMFS, 2004). Of these, 59 (1%) were non-powered, 1,550 (33%) outboard- and 3,039 (66%) inboard-powered boats. All non-powered and outboard-powered boats and about 2,213 (86%) of the small (< 40 GRT) inboard-powered boats were engaged in gillnet and traditional fishing. The number of Zone C and Zone C2 fishing boats is significantly higher than in Sabah. There were 182 (6%) of 40 – 69 GRT boats and 297 (10%) of above 69 GRT boats from the total inboard-powered boats. The number of commercial gears used and the amount of landings in the Central region is relatively higher, as compared to the Southern and Northern regions.
Most of the non-powered and outboard-powered boats used for fishing in East Malaysia measured less than 8 m and are either made of wood or fibreglass (Figure 3A and 3B). Outboard-powered boat fishermen usually use 5 to 60 horse power engines. Nevertheless, all boats powered by pump-engines (or commonly known as ‘pump boats’) in Sabah are made of wood (Figure 3C). Most of the inboard-powered boats are also made of wood (Figure 3D), however, fibreglass or steel hull boats are becoming popular, especially in the 70 GRT and above category in Sarawak.
2.2 Marine mammals potentially at risk
There are at least two species of Mysticeti, 19 Odontoceti, and one Sirenian that have been confirmed either to reside in or travel through East Malaysian territorial and EEZ waters (Jaaman, 2004). Based on species that have been positively identified in neighbouring countries, there may be a further eight species of cetaceans stray into or pass through the waters at least occasionally. Except for the fin whale (Balaenoptera physalus), which is listed as “endangered” and the dugong (Dugong dugon) and sperm whale (Physeter macrocephalus) as “vulnerable” to extinction, the other recorded cetacean species are listed either as “least concern” or “data deficient” by the World Conservation Union (Hilton-Taylor, 2000; IUCN, 2001).
Common species found in coastal waters, especially in major bays and estuaries, are the Irrawaddy dolphin (Orcaella brevirostris) and Indo-Pacific humpbacked dolphin (Sousa chinensis) (Beasley and Jefferson, 1997; Jaaman et al., 2001; Jaaman, 2004). In addition, the Indo-Pacific bottlenose dolphin (Tursiops aduncus), spinner dolphin (Stenella longirostris) and pantropical spotted dolphin (Stenella attenuata) have been reported as the most abundant cetaceans in the open waters of East Malaysia (Beasley, 1998; Jaaman, 2004). Dugong was the most common marine mammal species recorded stranded between 1996 and 2001 (Lah-Anyi and Jaaman, 2002). Other species recorded in strandings were the false killer whale (Pseudorca crassidens), Irrawaddy dolphin, Bryde’s whale (Balaenoptera edeni), sperm whale, Indo-Pacific bottlenose dolphin and Cuvier’s beaked whale (Ziphius carvirostris). In addition, the dugong and spinner, spotted and bottlenose dolphins are known to be hunted occasionally or opportunistically during fishing by fishermen in Sabah for human consumption and used as shark bait (Jaaman et al., 2004).
3. MATERIALS AND METHODS
3.1 Data collection
3.1.1 Interview survey
Semi-structured and informal interviews (following Dolar, 1994; Dolar et al., 1997 and Aragones et al., 1997) were used. Between March 1997 and December 2004, fishing villages, fish markets, fish landing jetties and anchored fishing boats in all 16 fishing districts along the coastline of Sabah were visited. On the other hand, interviews in Sarawak were conducted in two different periods: during November 1999 in Lawas and Limbang in the Northern region and between September and October 2000 in the other 13 fishing districts. During site visits, fishermen, village headmen and/or knowledgeable villagers were interviewed. The fishermen are the skipper and/or crew of Zone A or Zone B class boats, employing gillnets, trawl nets, purse seines and traditional gears. Respondents were asked questions about sightings of marine mammals, the incidence and frequency of by-catches and the species involved. Respondents were also asked if they utilised the caught animals. All interviews were conducted by SAJ and YUL, assisted by officers from relevant local authorities (Department of Wildlife Sabah, Department of Fisheries Sabah, Sabah Parks, Department of Fisheries F. T. Labuan, Department of Marine Fisheries Sarawak, and National Parks and Wildlife Division of Sarawak Forest Department) who have extensive knowledge of the community, area and the fishing sector.
Any indication of marine mammal by-catch in the area was photographed. Respondents’ independent reviews of illustrations in the field guides (Leatherwood and Reeves, 1983; Leatherwood et al., 1988; Jefferson et al., 1993; Tan, 1995) and a poster called Mamalia Marin Malaysia produced by the Universiti Malaysia Sabah were used to determine the species of marine mammal taken and species identified in the area.
3.1.2 Observer trips
Due to the enormous fishery sector, large study area and a lack of time and trained personnel, only a small proportion of fishing trips in Sabah were observed and none were followed in Sarawak. Between June 2003 and December 2004, SAJ followed a total of 46 fishing trips. Of these, 36 and 10 trips were onboard Zone B trawlers and purse seiners, respectively, and each trip lasted 1-2 days. Although trawlers in each region were sampled (5 Western, 16 Northeastern, 15 Eastern), observation on purse seine fishing was made only in the Eastern region. During the study period, many purse seiners in the Western and Northeastern regions and inboard-powered boats employing gillnets were neither active nor went out fishing. No attempt was made to follow gillnet or traditional fishermen using non- powered or outboard-powered boats because the boats were small and could not accommodate an extra person onboard. SAJ recorded any by-catches of marine mammals as well as noting their presence in the vicinity of the boat.
3.2 Analysis of by-catch rates
3.2.1 Interview data
Interview data were analysed to estimate a “minimum” by-catch rate for Sabah and Sarawak. Data were divided into strata on the basis of fishing region and gear-type. Overall,
8 753 and 358 boats in Sabah and Sarawak, respectively, were included in data analysis. These were boats employing trawl nets, purse seines, gillnets and fish stakes, and reported marine mammal by-catch. Boats employing other traditional gears, such as portable traps, hook-and-line (including longline), bag nets and lift nets, were excluded as these categories reported no marine mammal by-catch. In addition, fish stakes are seldom used in Sarawak and there was no fish stake fisherman interviewed during the survey. Within each stratum, the boats sampled are assumed to be representative, i.e. the proportion of boats reporting by-catch and the calculated by-catch rates can be raised to give estimates for the fleets.
The basic question asked to fishermen reporting by-catch was that how many animals were caught in the previous year, but most of them reported zero by-catch. They were then asked to give the number of animals caught in the past 5 or 10 years period. For the variable figures, such as, 1-2, 3-5, 6-10, 11-20 per 5 or 10 years, the mid-point value was taken and standardised into the number of animals taken per year. For answers such as more than 5, 10, 15, or 20 per 5 or 10 years, the minimum figure was taken and divided by the number of years.
The overall mean annual by-catch per boat for each region and gear-type is given by the total number of animals caught per year divided by the number of interviews. Separate totals were estimated for cetacean and dugong and also for Sabah and Sarawak. By-catch rates for the fleets are estimated using the number of boats in each region and gear-type, published in the fisheries statistics of Sabah (DoFS, 2004) and Sarawak (DoMFS) in 2002, as a raising factor.
The number of fishing trips taken monthly is an estimation. Most of the fishermen interviewed said they fish everyday, except Friday (since that most of them are Muslim and they go to the mosque on Friday). Trawl and purse seine fishermen interviewed said they sometimes stayed overnight or the most three days at sea. Therefore, boats employing gillnets and fish stakes are estimated to make an average of 26 trips per month, whereas trawlers and purse seiners could make to an average of 20 trips per month. These data are used to derive expressions of mean by-catch per trip.
Analysis of factors affecting the reported incidence of by-catch of cetaceans and dugongs was based on binomial Generalised Linear Models (GLM), fitted using BRODGAR software (Highland Statistics Ltd.). The response variables were the presence (1) or absence (0) of by-catch of marine mammals (cetaceans or dugongs). Explanatory variables considered were: interview year, region, fishing gear-type and boat-type. The optimal model was identified using stepwise removal of non-significant terms until no further decrease in the Akaike Information Criterion (AIC) value was seen. In the case of dugong by-catch, data from purse seiners were excluded as this category reported no by-catch (i.e. all value for numbers of animals caught were zero). Dugong by-catch was not reported from the Central and Southern regions of Sarawak and these data were also excluded. In analysing the Sarawak data set, interview year was not considered as one of the explanatory variables because there was co-linearity between interview year and region. Categorical explanatory variables were automatically recoded as binomial dummy variables. For example, the fishing gear-types analysed were gillnet, fish stake, trawl net and purse seine. Three dummy variables were thus created, for fish stake, trawl net and purse seine, and a significant coefficient value indicates a difference from the gillnet category.
Similar analyses were carried out on the variation in numbers of cetaceans and dugongs reported caught. In this case, a quasi-Poisson distribution was assumed for the response variables.
9
Since the most frequently reported number of by-catches from a boat was zero, the data are neither normally distributed nor transformable to normal. Confidence limits for numbers of by-catches were therefore estimated using a bootstrap procedure. A purpose-written BASIC programme was used to simulate the data collection procedure, repeatedly re-sampling with replacement from the set of N interviews in a stratum to generate multiple sets of N interviews. In the present application 10,000 repeats were used, each yielding an estimate of the number of by-caught animals in the stratum, raised to the level for the fleet. In each case, the 10,000 estimates are then sorted, and the 251st and 9,750th values represent the 95% confidence limits (i.e. only 5% of values are more extreme). Interviews were stratified by region and gear-type, and confidence limits derived separately for each region and gear- type, and overall for all regions and all gear-types.
Using a version of the bootstrap programme, and actual interview data for the fleets, expected confidence limits for the total number of animals caught annually were simulated for different numbers of interviews (10-500), including extrapolation to larger numbers of interviews than were actually carried out. We also estimate the number of observer trips needed to corroborate the interview findings on the by-catch rate.
3.2.2 Observer data
All fishing trips observed resulted in no marine mammal by-catch. Following López et al., (2003), analysis was conducted only to estimate the 95% confidence limits of the underlying by-catch rate and a restrospective power analysis was carried out to specify requirements for a long-term monitoring programme.
Assuming that catching a single animal in a net can be modelled as a Poisson process, if λ is the mean by-catch per sampled unit of fishing effort and X is the number of by-catch, the probability of seeing r by-catches during a single sampling unit is given by:
== −λ λr rerXP !)(
Since the terms λr and r! are both equal to 1 for X = 0 , the probability of observing at least one by-catch during N observed units of fishing activity is simply:
⎛ ⎞ ⎛ ⎞ ⎜∑ XP > ⎟ 10 ⎜∑ XP =−= ⎟ −= e −λ )(10 N ⎝ N ⎠ ⎝ N ⎠
Based on a bootstrap re-sampling procedure (Buckland, 1984; Efron and Tibshirani, 1993) and assuming a Poisson distribution, confidence limits for observed by-catch were estimated for a range of sample sizes and underlying by-catch rates.
A similar approach is used to assess the number of observer trips needed to test if the by- catch rate exceeds the permitted Potential Biological Removal (PBR) or mortality limit for the population. According to the International Whaling Commission, the anthropogenic removal rate of any cetacean population should not exceed half the maximum net growth rate of the population (IWC, 1995). At the second meeting of the Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas in November 1997, it was agreed that, in general, an anthropogenic removal of more than 2% of the best available cetacean population estimate was an “unacceptable interaction” (ASCOBANS, 1997). In the case of
10 dugong by-catch, the population simulations of Marsh (1995) suggested that the maximum sustainable level of mortality may be as low as 2% of females annually.
4. RESULTS
4.1 By-catch rates estimated from interview data
4.1.1 Sabah
Of 753 boats sampled in Sabah, fishermen from 310 (41%) boats indicated the occurrence of incidental catches of marine mammals (Table 1). The majority of the boats (188) caught dugongs, 41 (13%) caught cetaceans and 81 (26%) caught both groups of animals. Dugong was not reported caught in purse seines. Cetaceans and dugongs were reported caught in other fishing gear-types, and in all boat-type and interview year categories.
About 45 cetaceans and 69 dugongs were reported caught incidentally in fishing gears per year with an average catch of 0.06 cetaceans (95% CI = 0.039, 0.079) and 0.09 dugongs (95% CI = 0.077, 0.107) per boat (Table 1). The Northeastern region recorded the highest number of boats reporting by-catch, number of animals reported caught, mean annual by- catch per boat, estimated annual by-catch and estimated mean by-catch per 1000 fishing trips. Overall, the gillnet category recorded the highest number of boats reporting by-catch, number of animals reported caught, mean annual by-catch per boat, estimated annual by- catch and estimated mean by-catch per 1000 fishing trips.
There was an overall estimate of around 306 cetaceans (95% CI = 250, 369) and 479 dugongs (95% CI = 434, 528) caught incidentally per year by the Sabah fishing fleet (Table 3). Over half of these figures were from the Northeastern region. The gillnet category formed the majority of the total estimated by-catch.
4.1.2 Sarawak
A total of 358 boats was sampled of which 99 (28%) boats indicated the occurrence of incidental catches of marine mammals (Table 2). In contrast to Sabah, the majority of the boats (94) in Sarawak caught cetaceans, 3 (13%) caught dugongs and 2 (2%) caught both groups of marine mammals. Dugong was not reported caught in purse seines or in the Southern and Central regions. Cetacean by-catch was reported from all regions, fishing gear-types and boat-types.
About 24 cetaceans and 2 dugongs were reported caught incidentally in fishing gear per year with an average catch of 0.07 cetaceans (95% CI = 0.048, 0.088) and 0.01 dugongs (95% CI = 0, 0.011) per boat (Table 1). Dugongs were reported caught only in the Northern region. The Southern region recorded the highest number of boats reporting cetacean by- catch, number of animals reported caught, mean annual by-catch per boat, estimated annual by-catch and estimated mean by-catch per 1000 fishing trips. In all regions, boats employing gillnets recorded the highest number of incidences of cetacean by-catch, number of animals reported caught and estimated annual by-catch, but the highest mean annual cetacean by-catch per boat and estimated mean annual cetacean by-catch per 1000 fishing trips was by purse seiners.
11 There was an overall estimate of around 221 cetaceans (95% CI = 189, 258) and 14 dugongs (95% CI = 2, 30) caught incidentally per year by the Sarawak fishing fleet (Table 3). More than half of the estimated total numbers of cetaceans caught were from the Southern region. As for by-catch in Sabah, boats employing gillnets formed the majority of the total estimated cetacean and dugong by-catches.
12 Table 1: Summary of interview-based estimates of marine mammal by-catch in Sabah.
INTERVIEWS ESTIMATED FISHING TRIPS CETACEAN BY-CATCHES DUGONG BY-CATCHES - - y y boats boats interviews Number of Number Annual total Annual total Fishing gear Fishing gear Monthly total with by-catch with by-catch with by-catch with by-catch with by-catch with by-catch Fishing region catch per boat catch per boat Est. annual b Est. annual Est. annual b Est. annual Total number of caught annually caught annually caught annually caught annually Mean annual by- Mean annual Mean annual by- Mean annual Number of boats of Number Number of boats of Number Number of boats of Number Monthly per boat Monthly per Est. mean annual annual Est. mean Est. mean annual annual Est. mean Number of animals of Number Number of animals of Number catch for fleet total catch for fleet total by-catch/1000 trips by-catch/1000 by-catch/1000 trips by-catch/1000 Gillnet 1743 187 58 26 45318 543816 27 6.8 0.04 63 0.12 41 14.2 0.08 132 0.24 Fish stake 11 0 0 26 286 3432 Western Trawl net 246 22 0 20 4920 59040 0 0 Purse seine 88 6 0 20 1760 21120 0 0 All gears 2088 215 58 52284 627408 27 6.8 0.03 63 0.10 41 14.2 0.07 132 0.21 Gillnet 1981 280 166 26 51506 618072 56 25.0 0.09 177 0.29 160 39.0 0.14 276 0.45 Fish stake 59 6 2 26 1534 18408 0 2 0.4 0.07 4 0.21 Northeastern Trawl net 993 36 2 20 19860 238320 2 0.4 0.01 11 0.05 1 0.2 0.01 6 0.02 Purse seine 26 7 0 20 520 6240 0 0 All gears 3059 329 170 73420 881040 58 25.4 0.08 188 0.21 163 39.6 0.12 285 0.32
Gillnet 632 160 76 26 16432 197184 32 10.3 0.06 41 0.21 63 14.7 0.09 58 0.29
Fish stake 24 4 2 26 624 7488 1 0.2 0.05 1 0.16 2 0.6 0.15 4 0.48 Eastern Trawl net 183 31 2 20 3660 43920 2 0.4 0.01 2 0.05 0 Purse seine 108 14 2 20 2160 25920 2 1.4 0.10 11 0.42 0 All gears 947 209 82 22876 274512 37 12.3 0.06 55 0.20 65 15.3 0.07 62 0.22 Gillnet 4356 627 300 26 113256 1359072 115 42.1 0.07 292 0.22 264 67.9 0.11 472 0.35 All region Fish stake 94 10 4 26 2444 29328 1 0.2 0.02 2 0.06 4 1.0 0.10 9 0.32 Trawl net 1422 89 4 20 28440 341280 4 0.8 0.01 13 0.04 1 0.2 0.002 3 0.01 Purse seine 222 27 2 20 4440 53280 2 1.4 0.05 12 0.22 0 Grand total 6094 753 310 148580 1782960 122 44.5 0.06 306 0.17 269 69.1 0.09 479 0.27
13 Table 2: Summary of interview-based estimates of marine mammal by-catch in Sarawak.
INTERVIEWS ESTIMATED FISHING TRIPS CETACEAN BY-CATCHES DUGONG BY-CATCHES -catch -catch y boats boats interviews Number of Number Annual total Annual total Fishing gear Fishing gear for fleet total for fleet total Monthly total with by-catch with by-catch with by-catch with by-catch with by-catch Fishing region catch per boat catch per boat Total number of caught annually caught annually caught annually caught annually Mean annual by- Mean annual Mean annual by- Mean annual Number of boats of Number Number of boats of Number boats of Number Monthly per boat Monthly per Est. mean annual annual Est. mean annual Est. mean Number of animals of Number Number of animals of Number by-catch/1000 trips by-catch/1000 trips by-catch/1000 Est. annual by-catch by-catch Est. annual Est. annual b Est. annual Gillnet 1152 130 51 26 29952 359424 51 13.3 0.10 118 0.33 0 Southern Trawl net 203 13 2 22 4466 53592 2 0.4 0.03 6 0.12 0 Purse seine 16 2 0 20 320 3840 0 0 All gears 1371 145 53 34738 416856 53 13.7 0.09 124 0.30 0 Gillnet 836 75 16 26 21736 260832 16 3.7 0.05 41 0.16 0 Central Trawl net 388 25 6 22 8536 102432 6 1.4 0.06 22 0.21 0 Purse seine 5 2 2 20 100 1200 2 1.4 0.70 4 2.92 0 All gears 1229 102 24 30372 364464 24 6.5 0.06 66 0.18 0 Gillnet 644 81 16 26 16744 200928 14 3.0 0.04 24 0.12 4 1.6 0.02 13 0.06 Northern Trawl net 159 29 6 22 3498 41976 5 1.2 0.04 7 0.16 1 0.2 0.01 1 0.03 Purse seine 4 1 0 20 80 960 0 0 All gears 807 111 22 20322 243864 19 4.2 0.04 30 0.12 5 1.8 0.02 14 0.06 Gillnet 2632 286 83 26 68432 821184 81 20.0 0.07 184 0.22 All region Trawl net 750 67 14 22 16500 198000 13 3.0 0.04 34 0.17 Purse seine 25 5 2 20 500 6000 2 1.4 0.28 7 1.17 Grand total 3407 358 99 85432 1025184 96 24.4 0.07 221 0.22
14 Table 3: Estimated annual numbers of marine mammal by-catches for Sabah and Sarawak fishing fleets, with bootstrap estimates of 95% confidence limitsa.
CETACEAN BY-CATCH DUGONG BY-CATCHES total total 95% CI 95% CI 95% CI 95% CI of boats of boats Estimated Estimated annual by- annual by- Fishing gear Fishing gear (lower limit) (lower limit) (upper limit) (upper limit) Total number catch for fleet catch for fleet catch for fleet Fishing region SABAH Gillnet 1743 63 35 97 132 77 199 Fish stake 11 Western Trawl net 246 Purse seine 88 All gears 2088 63 37 95 132 79 197 Gillnet 1981 177 94 281 276 225 337 Fish stake 59 4 0 8 Northeastern Trawl net 993 11 0 28 6 0 17 Purse seine 26 All gears 3059 188 112 282 285 238 342
Gillnet 632 41 23 64 58 44 74
Fish stake 24 1 0 4 4 0 7 Eastern Trawl net 183 2 0 6 Purse seine 108 11 0 29 All gears 947 55 38 75 62 49 75 Gillnet 4356 292 220 351 472 417 520 All region Fish stake 94 2 0 2 9 3 12 Trawl net 1422 13 7 24 3 0 13 Purse seine 222 12 2 23 Total 6094 306 250 369 479 434 528 SARAWAK Gillnet 1152 118 73 177 0 Southern Trawl net 203 6 0 16 0 Purse seine 16 0 All gears 1371 124 81 178 0 Gillnet 836 41 20 67 0 Central Trawl net 388 22 6 42 0 Purse seine 5 4 2 5 0 All gears 1229 66 46 90 0 Gillnet 644 24 11 41 13 1 33 Northern Trawl net 159 7 1 13 1 0 3 Purse seine 4 All gears 807 30 19 45 14 2 30 Gillnet 2632 184 148 224 All region Trawl net 750 34 23 47 Purse seine 25 7 2 5 Total 3407 221 189 258 a Western total, Northeastern total, Eastern total, Southern total, Central total, Northern total, all region gillnet, trawl net, purse seine are derived from separate runs of the bootstrap procedure and the figure will therefore not necessarily be exactly equal to the sum of figures from runs using data from single regions or gear-types.
15 4.2 Results of GLM Analyses
4.2.1 Sabah
Binomial GLM confirmed the existence of significant effects of region, gear-type and boat- type on the overall reported incidence of marine mammal by-catch in Sabah (Table 4). A higher proportion of boats in the Northeastern and Eastern regions were reported to catch marine mammals as compared to boats in the Western region. A lower proportion of trawlers and purse seiners were reported to catch marine mammals, as compared to boats employing gillnets. A lower proportion of non-powered and inboard-engine boats were reported to catch marine mammals than boats using outboard-engines. There were no effects of interview year on the overall reported incidence of marine mammal by-catch.
In the case of cetacean by-catch, gear-type and boat-type had significant effects (Table 4). A lower proportion of trawlers was reported to catch cetaceans, as compared to boats employing gillnets. A lower proportion of non-powered boats was reported to incidentally catch cetaceans than boats using outboard-engines.
In the case of dugong by-catch, there were significant region, gear-type and boat-type effects (Table 4). As for overall marine mammal by-catch, there was a lower incidence of dugong by-catch in the Western region than in the Northeastern and Eastern regions. A higher proportion of boats employing gillnets was reported to catch dugongs, as compared to trawlers. A higher proportion of boats using outboard-engines was reported to catch dugongs than non-powered and inboard-engine boats.
The quasi-Poisson GLM for variation in numbers of cetaceans or dugongs reported caught included effects of interview year, region, and gear-type. In addition, boat-type had an effect on numbers of dugongs reported caught. However, none of the effects were individually significant in the final models (Table 5).
4.2.2 Sarawak
Using binomial GLM, only region had significant effect on the overall reported incidence of marine mammal or cetacean by-catches in Sarawak (Table 6). A higher proportion of boats in the Southern region were reported to catch marine mammals or cetaceans, as compared to boats in the Central and Northern regions. There were no effects of gear-type and boat- type.
The final model of reported incidence of dugong by-catch included only the effect of boat- type, although this effect was not significant (Table 6).
The quasi-Poisson GLM for variation in numbers of cetaceans reported caught had effects of region and gear-type. Only boat-type had an effect on numbers of dugongs reported caught. However, none of the effects were significant in the final models (Table 7).
16 Table 4: Results from binomial GLM for variation in the incidence of by-catch between different categories of boats in Sabah. The table lists all explanatory variables in the final models. (Categorical explanatory variables are automatically recoded as binomial dummy variables. For example, the gear-types analysed were gillnet, fish stake, trawl net and purse seine. Three dummy variables were thus created, for fish stake, trawl net and purse seine, and a significant coefficient value indicates a difference from the gillnet category). Significant terms are indicated in bold face.
Response Explanatory variable Coefficient Z-value P-value variable (and St Err) Marine Region – Northeastern 1.244 (0.208) 5.987 2.14 x 10-9 mammal Region – Eastern 0.765 (0.231) 3.319 9.05 x 10-4 by-catch Fishing gear – fish stake -0.694 (0.700) -0.992 0.321188 Fishing gear – trawl -2.231 (0.549) -4.063 4.85 x 10-5 Fishing gear – purse seine -1.627 (0.766) -2.124 3.37 x 10-2 Boat – non-powered -2.514 (0.488) -5.149 2.61 x 10-7 Boat – inboard-engine -1.253 (0.219) -5.733 9.89 x 10-9
Cetacean Fishing gear – fish stake -0.647 (1.072) -0.603 0.5463 by-catch Fishing gear – trawl -1.339 (0.564) -2.374 1.76 x 10-2 Fishing gear – purse seine -0.808 (0.772) -1.047 0.2953 Boat – non-powered -2.505 (1.017) -2.462 1.38 x 10-2 Boat – inboard-engine -0.393 (0.264) -1.486 0.1372
Dugong Region – Northeastern 1.667 (0.225) 7.416 1.21 x 10-13 By-catch Region – Eastern 0.832 (0.248) 3.360 7.78 x 10-4 Fishing gear – fish stake -0.533 (0.705) -0.756 0.449687 Fishing gear – trawl -3.303 (1.030) -3.207 1.34 x 10-3 Boat – non-powered -2.317 (0.493) -4.704 2.55 x 10-6 Boat – inboard-engine -1.424 (0.238) -5.981 2.22 x 10-9
17 Table 5: Results from quasi-Poisson GLM of variation in numbers of marine mammals reported caught incidentally in Sabah. The table lists all explanatory variables in the final models.
Response Explanatory variable Coefficient Z-value P-value variable (and St Err) Number of Year 1999 -0.694 (0.716) -0.970 0.33243 cetaceans Year 2000 -1.033 (0.920) -1.123 0.26190 reported Year 2001 -17.026 -0.009 0.99274 caught (1871.516) Year 2002 -1.522 (1.380) -1.103 0.27028 Year 2003 -0.387 (0.876) -0.442 0.65851 Year 2004 -0.283 (1.028) -0.275 0.78303 Region – Northeastern 1.139 (0.976) 1.167 0.24354 Region – Eastern 0.658 (1.080) 0.610 0.54202 Fishing gear – fish stake -16.755 -0.003 0.99770 (5812.159) Fishing gear – trawl -17.062 -0.009 0.99262 (1843.022) Fishing gear – purse seine -0.198 (1.267) -0.156 0.87613
Number of Year 1999 -0.505 (0.749) -0.674 0.50027 dugongs Year 2000 -1.477 (1.200) -1.231 0.21879 reported Year 2001 -0.278 (0.935) -0.297 0.76620 caught Year 2002 -0.749 (1.017) -0.736 0.46167 Year 2003 -0.894 (1.005) -0.889 0.37428 Year 2004 0.086 (1.068) 0.081 0.93566 Region – Northeastern -0.224 (0.605) -0.370 0.71118 Region – Eastern -0.912 (0.867) -1.052 0.29305 Fishing gear – fish stake -16.185 -0.004 0.99718 (4582.726) Fishing gear – trawl -16.182 -0.010 0.99213 (1639.094) Boat – non-powered -16.977 -0.008 0.99386 (2206.496) Boat – inboard-powered -1.039 (0.768) -1.353 0.17648
18 Table 6: Results from binomial GLM for variation in the incidence of by-catch between different categories of boats in Sarawak. The table lists all explanatory variables in the final models. Significant terms are indicated in bold face.
Response Explanatory variable Coefficient Z-value P-value variable (and St Err) By-catch of Region – Central -0.627 (0.290) -2.161 3.07 x 10-2 marine Region – Northern -0.846 (0.294) -2.878 4.00 x 10-3 mammals
Catch Region – Central -0.627 (0.290) -2.161 3.07 x 10-2 cetaceans Region – Northern -1.026 (0.305) -3.360 7.80 x 10-4
Catch dugongs Boat – outboard-powered 1.276 (0.938) 1.360 0.174
Table 7: Results from quasi-Poisson GLM of variation in numbers of marine mammals reported caught incidentally in Sarawak. The table lists all explanatory variables in the final models.
Response Explanatory variable Coefficient Z-value P-value variable (and St Err) Number of Region – Northeastern -0.444 (0.889) -0.500 0.6174 cetaceans Region – Eastern -1.114 (1.160) -0.961 0.3373 reported Fishing gear – trawl -16.334 -0.008 0.9934 caught (1969.782) Fishing gear – purse seine 2.092 (1.137) 1.840 0.0666
Number of Boat – outboard-powered 18.780 0.007 0.9940 dugongs (2678.770) reported caught
19 4.3 Observed by-catch
Although cetaceans (Irrawaddy dolphins, Indo-Pacific bottlenose dolphins, Indo-Pacific humpbacked dolphins or spinner dolphins) were often sighted, no marine mammals were incidentally caught during any of the 46 fishing trips observed in Sabah. Assuming the trips to have been representative, we can be 95% certain that the overall by-catch rate is less than 0.05, i.e. less than one occurrence per 20 trips. Since the Sabah fleet is estimated to make almost 1.8 million individual fishing trips each year, this indicates only that there are fewer than 90,000 incidences of marine mammal by-catch annually.
4.4 Power analysis
The Sabah fishing fleet is estimated to incidentally catch around 306 cetaceans and 479 dugongs annually, i.e. around 0.17 cetacean and 0.27 dugong by-catches per 1000 trips, respectively. Treating results for each region separately and using the actual number of observed trips and estimated cetacean by-catch rates for each region (Table 1), the probabilities of observing any cetacean by-catches during observed fishing trips would have been 0.0005, 0.0034 and 0.005 in the Western, Northeastern and Eastern regions, respectively. With an overall estimate of 0.04 and 0.22 cetacean by-catches per 1000 trips, the probabilities of observing any cetacean by-catches during the 36 trawl and 10 purse seine fishing trips observed in Sabah would have been 0.0014 and 0.0022, respectively. In the case of dugong by-catch, the probabilities of observing any by-catches during observed fishing trips would have been 0.0011, 0.005 and 0.0033 in the Western, Northeastern and Eastern regions, respectively. With an overall estimate of 0.01 by-catches per 1000 trips, the probability of observing any dugong by-catches during the 36 trawl fishing trips observed would have been 0.00036.
The by-catch rates of cetaceans or dugongs for each region and gear-type and the whole fleet in Sabah are estimated to be around 0.1 to 0.3 animals per 1000 fishing trips. As illustrated in Lopez et al. (2003), given that no by-catches were seen during observed trips, between 10000 and 30000 observer trips would be required annually for us to be 95% confident that the by-catch rate is within these figures (Figure 4). Assuming cetacean species caught in the Northeastern region are spinner, spotted and bottlenose dolphins and based on the species’ population estimate in the southern Sulu Sea of a total of 7849 dolphins (Dolar et al., 1997), 2% of the population for maximum acceptable annual by-catch is approximately 157 dolphins (or 0.18 by-catches per 1000 trips). Therefore, as many as 18000 observer trips would be needed to confirm (95% confident) that the by-catch rate did not exceed this number of events.
Previous figures consider the interpretation of seeing zero by-catches. Lopez et al. (2003) considered the number of observer trips required to obtain a reliable estimate of the by- catch rate. Using data from this study, simulation results illustrate the expected findings that (a) low numbers of observer trips tends to underestimate the by-catch rate, and (b) confidence limits get narrower as the number of observer trips increase (see Figure 5). For an underlying by-catch rate of 0.1 events per 1000 trips, the by-catch estimate stabilises after around 8000 trips, while confidence in the estimate continues to increase up to 30000 trips (Figure 5a). For an underlying by-catch rate of 0.5 events per 1000 trips, the by-catch estimate stabilises after around 8000 trips and confidence in the estimate continues to increase up to 27000 trips (Figure 5b). For an underlying by-catch rate of 0.1 events per 1000 trips, the by-catch estimate stabilises from 1000 trips, while confidence in the estimate continues to increase up to 25000 trips (Figure 5c).
20
If the level of variability in reported catches in the actual interviews is realistic, the estimated by-catch and associated 95% confidence limits derived from simulations should have a similar trend as suggested above (Figure 6). With the present data set, the greatest gains in precision and accuracy occur for increases in the number of interviews up to around 200 per sector (dividing boats into categories according to region and gear-type).
It should be noted that such simulations are inevitably less reliable when used for predicting the results from numbers of observer trips/interviews that are markedly greater than the actual number of observer trips/interviews carried out. Generally however, results suggest that the numbers of interviews for boats employing gillnets was adequate, but that more data are needed for boats employing trawl nets, purse seines and fish stakes.
Figure 4: Probability of seeing zero by-catch events as a function of the underlying true rate of by-catch and the number of observer trips, assuming a Poisson distribution of by-catch events. Probabilities of observing no by-catches for underlying by-catch rates of 0-0.5 events per 1000 trips (based on Lopez et al., 2003).
0.20
N = 35000 N = 30000 N = 25000 0.15 N = 20000 N = 15000 N = 10000
0.10
0.05 P (no by-catches observed in N trips)
0.00 0.0 0.1 0.2 0.3 0.4 0.5 By-catch events per 1000 trips
21 Figure 5: Accuracy and precision of marine mammal by-catch estimates from observer trips in relation to number of simulated fishing trips observed. Median estimated marine mammal by-catch rate and 95% confidence limits, in relation to the number of observer trips, for 0.1 – 1 by-catch events per 1000 trips.
(a) 0.1 by-catch events per 1000 trips
0.0010 Median 0.0009 Lower 95%
0.0008 Upper 95%
0.0007
0.0006
0.0005
0.0004 Observed value Observed
0.0003
0.0002
0.0001
0.0000 0 5000 10000 15000 20000 25000 30000 35000 40000 Number of observer trips
(b) 0.5 by-catch events per 1000 trips
0.0020 Median 0.0018 Lower 95%
0.0016 Upper 95%
0.0014
0.0012
0.0010
0.0008 Observed value Observed
0.0006
0.0004
0.0002
0.0000 0 5000 10000 15000 20000 25000 30000 35000 40000 Number of observer trips
(c) 1 by-catch event per 1000 trips
0.0030 Median Lower 95% 0.0025 Upper 95%
0.0020
0.0015 Observed value 0.0010
0.0005
0.0000 0 5000 10000 15000 20000 25000 30000 35000 40000 Number of observer trips
22 Figure 6: Accuracy and precision of marine mammal by-catch estimates from interviews in relation to number of simulated interviews. Median estimated marine mammal by-catch and 95% confidence limits for six of the studied strata, for different numbers of interviews.
(a) Sabah, Western, gillnets, dugongs (b) Sabah, Northeastern, trawls, dolphins
550 45 Median Median 500 Lower 95% 40 Lower 95% 450 Upper 95% Upper 95% 35 Actual value Actual value 400 30 350
300 25
250 20
200 15 150 Estimated annual by-catch Estimated annual by-catch 10 100 5 50
0 0 0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 250 300 350 400 450 500 Number of interviews Number of interviews
(c) Sabah, Eastern, purse seines, dolphins (d) Sarawak, Southern, gillnets, dolphins
35 400 Median Median Lower 95% Lower 95% 30 350 Upper 95% Upper 95%
Actual value 300 Actual value 25
250 20 200 15 150
10 Estimated annual by-catch Estimated annual by-catch 100
5 50
0 0 0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 250 300 350 400 450 500 Number of interviews Number of interviews
(e) Sarawak, Northern, gillnets, dugongs (f) Sarawak, Northern, trawls, dolphins
80 20 Median Median Lower 95% Lower 95% 70 Upper 95% Upper 95%
60 Actual value 15 Actual value
50
40 10
30
Estimated annual by-catch 20 Estimated annual by-catch 5
10
0 0 0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 250 300 350 400 450 500 Number of interviews Number of interviews
23 4.5 Sightings
4.5.1 Sabah
Almost all of the fishermen interviewed could readily distinguish between a dugong and a cetacean (Jaaman et al., 2004). Many said that dugongs usually avoid humans and could be seen only when the animals were hunted or incidentally caught during fishing. Nevertheless, a few interviewees reported occasional sightings of dugongs at night, swimming slowly or grazing on seagrass in shallow areas.
Based on the fishermen’s descriptions and their identification from illustrations in the field guides and poster, six species or groups of cetaceans were recorded present. In all regions, most fishermen could differentiate the Irrawaddy dolphin, Indo-Pacific humpbacked dolphin and finless porpoise (Neophocaena phocaenoides) from other cetaceans. The bottlenose, spinner and spotted dolphins were also reported, but their description often overlaps, thus these species were grouped as the open water dolphins. Interviewees also recalled encountering large cetaceans, which could be the short-finned pilot whale, melon-headed whale, false killer whale, or killer whale. These were generally described as groups of dark coloured cetaceans that were relatively larger than dolphins, and were tentatively grouped as small whales. Other sightings, which were often described as extremely large animals that produced a water spout (probably the sperm whales or baleen whales), were categorised as large whales.
Interview results indicated that the most commonly sighted cetaceans in Sabah were the Irrawaddy dolphins and open water dolphins (Figure 7). The Indo-Pacific humpbacked dolphins were also commonly reported in the Northeastern and Eastern regions. All sightings of Irrawaddy dolphins and Indo-Pacific humpbacked dolphins were reported to occur in estuaries, bays or waters close to shore, and fishermen interviewed in the Northeastern and Eastern regions said that the species often followed trawlers during fishing. The open water dolphins were said to come close to shore occasionally, but most sightings were reported to occur offshore or in deeper waters. In all regions, occasional sightings of finless porpoises, small whales and large whales were also reported.
4.5.2 Sarawak
Except in Limbang and Lawas (Northern region) where few fishermen reported occasional sightings of dugongs, many fishermen interviewed in other areas of Sarawak said that they had never seen a dugong. Nevertheless, two interviewees in Sematan (Southern region) claimed that they had seen dugongs in few occasions in waters near to Kalimantan (Indonesia) border.
As in Sabah, fishermen interviewed in Sarawak described and identified similar species or groups of cetaceans to occur in their areas. In all regions, the Irrawaddy dolphins, open water dolphins and Indo-Pacific humpbacked dolphins were commonly reported, although the latter has the least records (Figure 8). All sightings of Irrawaddy and Indo-Pacific humpbacked dolphins were reported to occur in estuaries, bays or waters close to shore. Although the two species and open water dolphins (probably Tursiops) were mentioned to follow trawlers fishing in shallow waters, these sightings were occasional. Most sightings of open water dolphins were reported to occur offshore or in deeper waters. Occasional sightings of finless porpoises, small whales and large whales during fishing were also reported from all regions.
24 Figure 7: Summary of marine mammal sightings reported by fishermen in (a) Western, (b) Northeastern, and (c) Eastern regions, Sabah. The proportions of interview records reporting common, occasional, and no marine mammal sightings.
(a) 100%
90%
80%
70%
60%
50%
40% Percentagerecords of 30%
20%
10%
0% D. dugon O. brevirostris Open water S. chinensis N. Small whale Large whale dolphins phocaenoides Marine mammal species/group
(b) 100%
90%
80%
70%
60%
50%
40% Percentagerecords of 30%
20%
10%
0% D. dugon O. brevirostris Open water S. chinensis N. Small whale Large whale dolphins phocaenoides Marine mammal species/group
(c) 100%
90%
80%
70%
60%
50%
40%
Percentage of records 30%
20%
10%
0% D. dugon O. brevirostris Open water S. chinensis N. Small whale Large whale dolphins phocaenoides Marine mammal species/group Common Occasional No record
25 Figure 8: Summary of marine mammal sightings reported by fishermen in (a) Southern, (b) Central, and (c) Northern regions, Sarawak. The proportions of interview records reporting common, occasional, and no marine mammal sightings.
(a) 100%
90%
80%
70%
60%
50%
40% Percentage of records of Percentage 30%
20%
10%
0% D. dugon O. brevirostris Open water S. chinensis N. Small whale Large whale dolphins phocaenoides Marine mammal species/group
(b) 100%
90%
80%
70%
60%
50%
40% Percentage of records Percentage 30%
20%
10%
0% D. dugon O. brevirostris Open water S. chinensis N. Small whale Large whale dolphins phocaenoides Marine mammal species/group
(c) 100%
90%
80%
70%
60%
50%
40%
Percentage of records 30%
20%
10%
0% D. dugon O. brevirostris Open water S. chinensis N. Small whale Large whale dolphins phocaenoides Marine mammal species/group Common Occasional No record
26 4.6 Species caught/utilisation
4.6.1 Sabah
In all regions, both dugongs and cetaceans were reported caught incidentally in fishing gears (Table 1). Interview results indicated that Irrawaddy dolphins and open water dolphins were the most reported cetacean species caught by boats employing gillnets (Figure 9). Several gillnet boats with cetacean by-catch also reported catching Indo-Pacific humpbacked dolphins and finless porpoises. All trawlers with cetacean by-catches reported catching Irrawaddy dolphins, although some also reported catching open water dolphins and Indo-Pacific humpbacked dolphins. The finless porpoises and open water dolphins were caught by boats employing fish stake and purse seines, respectively. There was no report of by-catch of small or large whales in fishing gears.
Fishermen who reported by-catches said they released/discarded or took caught marine mammals. The majority of them who reported by-catches of dugongs, open water dolphins and finless porpoises said they took the caught animals (Figure 10). All and most of the fishermen who reported by-catches of Indo-Pacific humpbacked dolphins and Irrawaddy dolphins, respectively, said they released/discarded the caught animals.
Interview results also indicated that all fishermen who took incidentally caught dugongs, open water dolphins or finless porpoises used the meat for family consumption and shared it among neighbours (Figure 11). In the case of Irrawaddy dolphin by-catch, all fishermen who took the caught animals reported to share the meat among neighbours and used it as shark bait, while a few said they consumed it with family members. There were also some fishermen who said they traded dugong or open water dolphin meat and used it as shark bait.
Dugong and open water dolphin meat is often regarded as a delicacy by coastal communities, particularly among the Bajau ethnic groups, in Sabah (Jaaman et al., 2004). The selling of directed or incidentally caught dugongs has been recorded from Labuan, Weston and Malawali Island in the Western region; Kudat, Sandakan and the islands of Banggi, Malawali, Jambongan and Tambisan in the Northeastern region; and from Semporna and Timbun Mata Island in the Eastern region (Jaaman et al., 2004). A whole dugong was reported to fetch a price of up to RM400 (US$105.25) and a three- to five-inch piece or a kilogram of dugong meat was reported to cost between RM2 – RM15 (US$0.50-4.00). There was in one occasion in December 2000, when officers from the Department of Fisheries Sabah confiscated a hunted dugong that was about to be traded in Kudat fish market. The open water dolphins, however, were reported sold in Semporna where a one- to two-inch piece of dolphin meat was reported to cost about RM2 (US$0.50) and a whole animal could fetch a price of between RM50 and RM100 (US$13.15-26.30).
4.6.2 Sarawak
Although cetaceans were reported caught incidentally in fishing gears from all regions, dugong by-catches were reported only from the Northern region (Table 2). Interview results indicated that Irrawaddy dolphins were the most reported cetacean species caught by boats employing gillnets (Figure 12). About half of the gillnet boats with cetacean by-catches reported catching open water dolphins and few reported catching Indo-Pacific humpbacked dolphins and finless porpoises. The majority of trawlers with cetacean by-catches reported catching Irrawaddy dolphins and open water dolphins, although some also reported catching
27 Indo-Pacific humpbacked dolphins. The open water dolphins were the only cetacean group reported caught by purse seiners. There was no report of by-catch of small or large whales in fishing gears.
As in Sabah, all of the fishermen who reported by-catches of dugongs and finless porpoises said they took the caught animals (Figure 13). All fishermen who reported by-catches of Indo-Pacific humpbacked dolphins said they released/discarded the caught animals. Most of the fishermen who reported by-catches of Irrawaddy dolphins and open water dolphins also said they released/discarded the caught animals.
Interview results also indicated that all fishermen who took incidentally caught dugongs or finless porpoises used the meat for family consumption and over half of them reported to share the meat among neighbours or trade it (Figure 14). In the case of Irrawaddy dolphin by-catch, all fishermen who took the caught animals reported to use the meat as shark bait, more than half said they shared it among neighbours and a few said they consumed it with family members. In the case of open water dolphin by-catch, all fishermen who took the caught animals reported to use the meat as shark bait and shared it among neighbours, while a few said they consumed it with family members and trade it.
Many fishermen who consumed incidentally caught marine mammals claimed the meat as tasty and delicious. Although the selling of dugong meat was reported only from Limbang and Lawas, incidentally caught open water dolphins and finless porpoises were sometimes traded in all regions of Sarawak. The meat was reported to cost between RM2 – RM6 (US$0.50-1.60) per kilogram. Recently in October 2001, officers from the National Parks and Wildlife Division of Sarawak Forest Department confiscated finless porpoise meat that was being sold in Pendam fish market near Kuching
28 Figure 9: The proportion of cetacean by-catch records for fishing activities in Sabah.
O. brevirostris Open water dolphins S. chinensis N. phocaenoides
100%
90%
80%
70%
60%
50%
40%
30%
20% Proportion of dolphin by-catch records by-catch of dolphin Proportion
10%
0% Gillnet Fish stake Trawl net Purse seine Fishing gear
Figure 10: The percentage of marine mammal by-catch records reporting the release/discard or take of animals in Sabah.
Release Take (often) Take (sometimes)
100%
90%
80%
70%
60%
50%
40% Percentage of records of Percentage 30%
20%
10%
0% D. dugon O. brevirostris Open water dolphins S. chinensis N. phocaenoides Marine mammal species/group
29 Figure 11: The proportion of marine mammal take records reporting uses of animals/meat in Sabah.
Family consumption Share among neighbours Trade the meat/animals Use as shark bait
100%
90%
80%
70%
60%
50%
40%
30%
20% Proportion of marine mammal take records mammal of marine Proportion 10%
0% D. dugon O. brevirostris Open water dolphins S. chinensis N. phocaenoides Marine mammal species/group
Figure 12: The proportion of cetacean by-catch records for fishing activities in Sarawak.
O. brevirostris Open water dolphins S. chinensis N. phocaenoides
100%
90%
80%
70%
60%
50%
40%
30%
20% Proportion of dolphin by-catch records by-catch dolphin of Proportion
10%
0% Gillnet Trawl net Purse seine Fishing gear
30 Figure 13: The percentage of marine mammal by-catch records reporting the release/discard or take of animals in Sarawak.
Release Take (often) Take (sometimes)
100%
90%
80%
70%
60%
50%
40% Percentage of records of Percentage 30%
20%
10%
0% D. dugon (Northern) O. brevirostris Open water dolphins S. chinensis N. phocaenoides Marine mammal species/group
Figure 14: The proportion of marine mammal take records reporting uses of animals/meat in Sarawak.
Family consumption Share among neighbours Trade the meat/animals Use as shark bait
100%
90%
80%
70%
60%
50%
40%
30%
20% Proportion of mammal marine take records 10%
0% D. dugon (Northern) O. brevirostris Open water dolphins S. chinensis N. phocaenoides Marine mammal species/group
31 5. DISCUSSION
One source of mortalities of marine mammals (and other taxa) associated with fisheries involves catch and entanglement in gear, and this by-catch may be extensive (Perrin et al. 1994; Northridge and Hofman, 1999). To date, concern has been directed mainly at fisheries, particularly those using commercial gears, operating well offshore (Tregenza et al., 1997; Morizur et al., 1999; Silvani et al., 1999; Lopez et al., 2003; Tudela et al., 2005). Although there have been few studies involving more localised, inshore fisheries of the Southeast Asia, and their effects on cetaceans (e.g. Reeves et al., 2003; Perrin et al., In press), such investigations have not been systematically conducted anywhere in Malaysian waters. This is the first attempt to determine the nature and magnitude of by-catches of marine mammals and estimate the associated level of mortality in fisheries in East Malaysia.
The placement of observers on-board fishing boats proved to be the most reliable method for collecting information regarding marine mammal by-catch (Tregenza et al., 1997; Morizur et al., 1999; Silvani et al., 1999; Tudela et al., 2005). In Malaysia, the Wildlife Protection Act 1972 and Fisheries Act 1985 protect all marine mammals from directed or incidental catches in fisheries. However, this is poorly enforced and there is no by-catch reporting or monitoring scheme in place. Even within the European Union, many governments of the Member States have not established routine monitoring of marine mammal catches and kills in fisheries (Morizur et al., 1999; López et al., 2003), despite an obligation to do this under Article 12.4 of the Habitats Directive (92/43/EEC). Furthermore, fishermen frequently refused to accept voluntarily the boarding of observers, especially in boats employing fishing gears that are known to catch cetaceans (Morizur et al., 1999; López et al., 2003; Tudela et al., 2005). Given the nature of the fisheries in East Malaysia, which involved a large number of small artisanal fishing boats, employing a diversity of fishing gears, adequate sampling of fishing trips is simply not feasible using on-board observers alone. In this study, only a small proportion of fishing trips in Sabah were observed and none were followed in Sarawak. No marine mammal by-catch took place during any of the observed fishing trips onboard trawlers and purse seiners, although boats employing gillnets, fish stakes or other traditional gears were not sampled.
Evidently, the estimate of by-catch rate and the number of animals caught annually is derived mainly from interviews and may only have indicated a minimum level of fishing mortalities. Interviews of fishermen to estimate by-catch have been suggested by Lien et al., (1994) as to obviously contain unknown or uncontrolled errors and biases, and may be regarded as providing, at best, a rough guide to the scale of the problem. Nevertheless, in most of the interview sessions during the survey, at least an officer from relevant local authorities was present. However, fishermen mostly did not conceal but readily spoke about the occurrence of marine mammal by-catch and what they do with a caught animal. This probably because it was the first time they were asked such questions and they have no experienced of getting punishment from the authorities for catching cetaceans and/or dugongs, though the majority of them knew that catching marine mammals is illegal (Jaaman et al., 2004). This finding is also consistent with Dolar et al. (1994; 1997), Marsh et al. (1995), Persoon et al., (1996) and Lopez et al. (2003) who reported the willingness of respondents in relaying information regarding marine mammal catches and utilisation during their surveys.
Another potential source of bias in estimating and reporting rates of marine mammal by- catch, particularly in Sabah, is the fisheries statistics used. The Summary of Annual Fisheries Statistics Sabah 2002 (DoFS, 2004) is not up-to-date due to the fact that the number of
32 fishermen, boats and fishing gears published is based on listing made in 1998. The number of full-time fishermen is probably an underestimation; the number of illegal immigrants active in the industry has not been ascertained but could run into thousands (TRPDS, 1998). There are many unlicensed boats and gears of the traditional types and part-time fishermen observed during the survey, but they were not listed (no estimate) in the published summary. These issues need to be addressed, and an up-to-date information on the species’ life history parameters, on site catch monitoring data, and an accurate estimate of the absolute abundance of cetaceans and dugongs in the regions are essential, in order to determine the reliability of the by-catch estimates and the sustainability of the incidental catches in fisheries. Nevertheless, the fisheries statistics used to estimate by-catch rate for Sarawak is indeed based on 2002 data.
5.1 Sightings and By-catches of Marine Mammal Species
The present study suggests that at least four specific (D. dugon, O. brevirostris, S. chinensis and N. phocaenoides), and two other less identifiable (Tursiops spp. and Stenella spp.), marine mammal taxa were non-targeted by-catches in fisheries in East Malaysian waters. Most of the reported by-catch in Sabah was dugong, whereas cetaceans were the main by- catch in Sarawak and dugongs were reported caught only by five boats in the Northern region. The facts that it was not reported caught and many fishermen, except in Limbang and Lawas, in Sarawak had never seen a dugong, may suggest that the animal distribution on the west coast of Borneo is limited down to Limbang and Lawas waters (and probably also down to Brunei waters). The coast of Sarawak is generally characterised by sandy shores against the dominance of mangrove swamp, coral reefs, seagrass beds and coastal islands along the coast of Sabah, which offer habitats that preferred by dugongs. Jaaman and Lah-Anyi (2003) suggested that dugong population in Sabah seems likely to be shared in the north with the Island of Palawan and in the east with the Southern Sulu (Philippines) and Kalimantan (Indonesia).
The Irrawaddy dolphin, open water dolphins and Indo-Pacific humpbacked dolphin were the most reported cetacean species caught incidentally in fishing gears. This is consistent with their sightings, where the Irrawaddy dolphin and Indo-Pacific humpbacked dolphin were commonly reported to occur in estuaries, bays or waters close to shore, while most sightings of open water dolphins were reported to occur offshore or in deeper waters. Also during observed trawl and purse seine fishing trips in Sabah, the Irrawaddy dolphins and Indo- Pacific bottlenose dolphins (T. aduncus) were frequently sighted, either in transit or during fishing. Nevertheless, the Indo-Pacific humpbacked dolphins and spinner dolphins (S. longirostris) were sighted in several occasions during trips observed in the Eastern region.
On the other hand, finless porpoise sightings and by-catches were only occasionally reported. This suggests that perhaps its population, like dugong, has greatly decline. Previously, the species was reported common in estuaries and coastal waters of Borneo (Banks, 1931; Weber, 1923; Medway, 1977; Payne et al., 1985). Perrin et al. (In press) stated that a factor to consider in present and future assessments is that low by-catch rates in many areas reflect the fact that cetacean and dugong populations have already been severely reduced by direct and incidental removals.
Dugong and cetacean species in East Malaysian waters are particularly susceptible to gillnets. Trawl nets were reported to catch all species, except the finless porpoise, while purse seines were reported to catch open water dolphins occasionally. In Sabah, besides being reported caught in gillnets, dugongs and finless porpoises were also caught in fish
33 stakes. Carcasses of incidentally caught dugong, Indo-Pacific bottlenose dolphin, pantropical spotted dolphin (S. attenuata) and finless porpoise were recovered from a number of fishermen and fish traders during the survey period. A few hunted dugong and spinner dolphin carcasses were also recovered (Jaaman et al., 2004). Although whales were occasionally sighted further offshore, fishermen reported no by-catch of small or large whales in fishing gears. Thus, by virtue of their ecological habits, such as being close to shore, dugongs, Irrawaddy dolphins, Indo-Pacific humpbacked dolphins, finless porpoises and possibly also Indo-Pacific bottlenose dolphins, are more susceptible to human impacts than other species. This is previously suggested by Dolar et al. (1997) and clearly evident in this study.
5.2 Magnitude of the Marine Mammal By-Catches
The magnitude of marine mammal by-catch is apparently greater in Sabah than in Sarawak. The overall results also indicate that gillnets have the most detrimental effects on marine mammal populations, as compared to other fishing gears. This may have been anticipated, since that fishing effort (as illustrated by the number of boats and fishing trips) is particularly greater in Sabah and with boats employing gillnets. No cetacean or dugong by- catch was reported in several strata (e.g. Western-trawl net, Western-purse seine, Northeastern-fish stake, Northeastern-purse seine, Southern-purse seine, Northern-purse seine), but under-recording is strongly suspected due to the nature of fishing practices. Nevertheless, gillnets, which are relatively cheap, easy to operate, effective in catching high- valued fish species and widely used by fishermen in East Malaysia (DoFS, 2004; DoMFS, 2004), have been recognised as the main cause for cetacean and dugong by-catches worldwide (Perrin et al., 1994; Perrin et al., 1996; Marsh et al., 2002).
In the case of marine mammal by-catches in Sabah, boats fishing in the Sulu (Northeastern) and Celebes (Eastern) Seas reported a significantly higher number of incidences involving dugongs than boats fishing in the South China Sea (Western). The magnitude of cetacean by-catch is apparently similar throughout Sabah. The incidence of marine mammal by-catch is significantly higher in gillnets or fish stakes, as compared to trawl nets and purse seines. Since most gillnet or fish stake boats are outboard-powered, the category recorded significantly higher number of incidences than boats in the non-powered or inboard-powered categories. This obviously raised serious concern, as fishermen using gillnets and outboard- powered boats in Sabah also reported a significantly greater magnitude of marine mammal hunting. (Jaaman et al., 2004).
As mentioned earlier, dugongs were reported seen and caught only in the Northern waters of Sarawak South China Sea. Cetacean by-catches, however, were reported throughout the State and with the magnitude significantly greater in the Southern than in Central and Northern regions. However, the magnitude of cetacean by-catch is similar between gillnets, trawl nets and purse seines, and between outboard- and inboard-powered boats.
Although fishing effort was considerably greater in regions with high number of by-catch incidences, the numbers of marine mammals and cetaceans reported caught in Sabah and Sarawak, respectively, were not significantly different between the regions. This indicates that by-catch rates may not reflect cetacean or dugong population density. The facts that numbers of animals caught were also not significantly different between gear-type and boat- type categories, may suggest that if fishing efforts are similar between the categories, the susceptibility of marine mammals to all the categories could possibly be the same.
34
5.3 Sustainability of the Marine Mammal By-catches
The number of cetaceans or dugongs in Malaysian waters has never been ascertained. However, the cetacean population is assumed small in numbers, as suggested for the populations in other countries in the Southeast Asian region (Perrin et al., 1996; In press). For the dugong, substantial populations are known to exist in the coastal waters of tropical Australia, but throughout the remainder of the region, its populations are believed to be fragmented and their numbers low and declining (Perrin et al., In press).
The results obviously show that dugongs in Sabah were more highly susceptible to fishing gears than cetaceans. With the exception of trawl nets and purse seines, the annual total number of dugongs reported caught and the estimated numbers of dugongs caught by boats employing gillnets and fish stakes, and in all regions are higher than for cetaceans. These may have been influenced by several factors. Gillnets and fish stakes are usually set in shallow areas with large tidal fluctuations and often on seagrass beds to catch fish species, such as rabbit fish (Siganus spp.) and threadfin bream (Nemipterus spp.). When fishermen and dugongs used the same area at the same time, this may have increased the chances for the animals to be caught, especially at night or in high turbidity waters. Furthermore, many fishermen said that cetaceans are much cleverer than dugongs in detecting and avoiding fishing nets, but sometimes become entangled when the animals are actively chasing their prey. They also mentioned that cetaceans, like sharks, are strong “fishes” and when caught in nets, the animals usually struggled violently and did better to free themselves, as compared to dugongs, which are often found dead. Lah-Anyi and Jaaman (2002) who found dugongs as more common to strand than cetaceans between 1996 and 2001, also reported that some animals may have died due to entanglement in fishing gears.
Nevertheless, besides cetaceans, dugongs were also reported caught by trawlers in the Northeastern region of Sabah and Lawas and Limbang in Sarawak. In these areas, the international (EEZ) boundaries are obviously close to shore, which make the area for fishing relatively small. This may have forced trawling to be operated in shallow waters and increased the chances for the dugongs and inshore cetaceans to be caught. It was evident during the survey that trawlers in the Sandakan, Darvel and Cowie Bays and Kinabatangan in Sabah were sometimes seen operating in estuaries or waters close to shore.
The estimated annual numbers of cetacean and dugong by-catches in the regions and gear types, particularly in gillnets, is high and may be unsustainable. The only available estimate of cetacean population is in the Philippines waters, adjacent to the Northeastern region of Sabah. Dolar et al. (1997) estimated a population size of 3,979 (CV=0.59) spinner dolphins, 3,455 (CV=0.32) pantropical spotted dolphins and 415 (CV=0.96) bottlenose dolphins in the southern Sulu Sea. Based on ASCOBANS (1997), an anthropogenic removal of more than 2% of the best available cetacean population estimate is considered as “unacceptable interaction”. Assuming that dolphin by-catches reported in the Northeastern region are from the same population and the 2% of anthropogenic removal is exclusively from by-catches in fisheries, there will be an upper limit of 80 spinner dolphins, 69 pantropical spotted dolphins, and 8 bottlenose dolphins, or a total of 157 dolphins caught annually. The estimated annual number of 188 (95% CI = 112 – 282) dolphins caught incidentally in fisheries in the Northeastern region clearly exceeds this figure. It should also be noted that dolphin, particularly the open water dolphins, populations subject to mortality by fisheries in Sabah are also subject to hunting (Jaaman et al., 2004), and directed and incidental catches in the neighbouring Philippines waters (Dolar, 1994; Dolar et al., 1994; 1997).
35
Population simulations indicate that even with the most optimistic combination of life-history parameters (e.g. low natural mortality and no human induced mortality) a dugong population is unlikely to increase more than 5% annually or 27.6% over five years (Marsh, 1995; Boyd et al., 1999). In the case of anthropogenic removal from directed or incidental catches in fisheries, Marsh (1995) and Boyd et al. (1999) suggested that the sustainable level of exploitation may be as low as 2% of females per year. Given the lowest estimated number of dugong by-catches in East Malaysian waters, which is in the Northern region of Sarawak (14, 95% CI = 2 – 30), and if half of this figure (7) are females, at least 350 female dugongs would be needed in the region for the population to be maintained, which is considered to be extremely unlikely. Furthermore, dugongs were also reported as the main marine mammal species hunted in Sabah waters (Jaaman et al., 2004).
5.4 Uses of Marine Mammals
Almost all fishermen who reported catching dugongs and/or finless porpoises in nets utilise their catches, mainly for family consumption and share the meat among neighbours. Incidentally caught open water dolphins are also utilised, mostly by fishermen in Sabah. This is consistent with reports on hunting of dolphins and dugongs, where the Bajau Pelauh and Bajau Laut people are known to regard the animals as a source of red meat and an important element in their tradition and culture for generations (Jaaman et al., 2004). Although finless porpoise is not hunted or commonly caught during fishing, fishermen who reported finless porpoise by-catches claimed that the meat is tastier than dolphin meat and most delicious when grilled, which is why caught animals are unlikely to be released/discarded.
Besides in East Malaysia, dugongs caught as by-catch in several other countries of the Southeast Asia are also unlikely to be released alive due to the high value of their body parts (Perrin et al., In press). For a comparison, the average monthly income of a gillnet or traditional fisherman using outboard–powered boat in Sabah is between RM200-300, which is about the wholesale value of a dugong. Furthermore, the tusks, teeth, sternum bones and tear of dugongs were also traded, usually to medicine men (locally known as “pawang”), for use in traditional medicine and/or as aphrodisiac or amulet (Jaaman et al., 2004). The value of these products is not ascertained, but interviewed medicine men claimed they were often sought by local residents. Perrin et al. (In press) concluded that the high value of dugong products reduces the range of mitigating factors appropriate to solving the dugong by-catch problem in Southeast Asia.
The results also suggest that incidentally caught Indo-Pacific humpbacked dolphins are released/discarded and not utilised. Many fishermen who reported by-catches of Irrawaddy dolphins also said they released/discarded the caught animals. There seems to be a general belief among fishermen that disturbing or harming the species will bring bad luck or omen, either to them or their family members. Nevertheless, a few fishermen reported taking incidentally caught Irrawaddy dolphins and used the meat as bait to catch sharks, besides sharing it with neighbours. Incidentally caught open water dolphins were also sometimes used as shark bait, especially in Sarawak. Many fishermen interviewed in the Philippines (Dolar et al. 1994; 1997) and as well as during this survey reported dolphin meat as the preferred bait to catch sharks. Nevertheless, dolphin meat used as shark bait in Sabah is taken mostly from hunted animals (Jaaman et al., 2004).
36 6. CONCLUSION AND CONSERVATION RECOMMENDATIONS
The interview survey and on-board observation represents a first attempt to determine the nature and magnitude of by-catches of marine mammals and estimate the associated level of mortality in fisheries in East Malaysia. However, with results potentially biased and a total lack of abundance estimates for all marine mammal species in the study area, it may under- represent to an unknown degree of the by-catch issue.
Of 753 boats sampled in Sabah, 310 (41%) indicated the occurrence of incidental catches of marine mammals. In Sarawak, a total of 358 boats was sampled and 99 (28%) reported by- catches. Both cetaceans and dugong were reported caught. A total of 306 (95% CI = 250 – 369) cetaceans and 479 (95% CI = 434 – 528) dugongs were estimated caught annually by fishing fleet in Sabah. The Sarawak fishing fleet is estimated to incidentally catch 221 (95% CI = 189 – 258) cetaceans and 14 (95% CI = 2 – 30) dugongs per year. The estimated figures, however, may have provided, at best, a rough guide to the magnitude of marine mammal by-catch involving fleets of about 15,104 boats scattered along an approximately 2,607 km coastline.
The most reported cetacean species caught as by-catch were the Irrawaddy dolphin, open water dolphin (presumably Tursiops spp. and Stenella spp.) and Indo-Pacific humpbacked dolphin. The finless porpoises were also caught occasionally. The magnitude of marine mammal by-catch is apparently greater in Sabah than in Sarawak. The overall results also indicate that gillnets have the most detrimental effects to marine mammal populations, as compared to other fishing gears. This obviously raised serious concern, as fishermen using gillnets and outboard-powered boats in Sabah also reported a significantly greater magnitude of marine mammal hunting. Boats fishing in the Sulu Sea and Celebes Sea reported a significantly higher number of incidences involving dugongs than boats fishing in the South China Sea. The magnitude of cetacean by-catch is apparently similar throughout Sabah. In Sarawak, cetacean by-catches were reported from all regions, with the magnitude significantly greater in the Southern region than in Central and Northern regions. Dugongs were reported caught only in Limbang and Lawas of the Northern region.
The estimated number of marine mammal by-catches in the region and gear-type categories, especially in gillnets, is high and may be unsustainable. In strata with no by- catch reported, under-recording is strongly suspected due to the nature of fishing practices or this may reflect the fact that the populations have already been severely reduced. Being a coastal species that depends on seagrass, which is generally scarce, coupled with a low population increment rate (< 5%), any directed or incidental catches of dugongs in East Malaysia are considered unsustainable. The estimated number of dolphins caught in the Northeastern region of Sabah may have exceeded the maximum recommended anthropogenic removal rate of 2%, thus also considered unsustainable. Although not hunted, the threats of fisheries by-catch on resident populations of Irrawaddy dolphin and Indo-Pacific humpbacked dolphin need to be eliminated to maintain their present numbers.
Incidentally caught cetaceans, except the Indo-Pacific humpbacked dolphin, and dugongs are sometimes utilised for human consumption, traded and used as shark bait, particularly in Sabah. Nevertheless, the Bajau Pelauh and Bajau Laut peoples who are common in the Eastern and Northeastern regions may take all catches, as they are known to regard marine mammals as a source of red meat and an important element in their tradition and culture for generations. Almost all fishermen interviewed in this survey claimed that the number of coastal cetaceans and dugongs has dropped significantly in the past few decades. The
37 sighting of dugongs is reported rare nowadays, however, fishermen denied the possibility that the species had become extinct.
There are two acts (i.e. Wildlife Protection Act 1972 and Fisheries Act 1985) currently in place in Malaysia to manage fisheries and protect marine mammals from directed or incidental catches. Generally, fishermen interviewed acknowledge these regulations, but many ignore the ban on taking marine mammals, especially in Sabah. Several factors are evident, but the main ones are poor enforcement and a lack of by-catch reporting or monitoring scheme. There is apparently a shortage of manpower, funding, proper equipments and the commitment of personnel to carry out marine conservation and management activities in East Malaysia. In addition, the law often shows leniency to fisheries related crimes, e.g. in several cases where fishermen were caught trawling close to shore or when marine mammals or the meat/parts were confiscated in fish markets, often the culprits were released with warnings.
Therefore, it is suggested that the management and enforcement authorities, fisheries organisations and community leaders should act promptly to establish a collaborative and dedicated program to report or monitor marine mammal by-catch. This program should focus on minimising the threats through education with the backup of heavy penalties for contravention of regulations. However, enforcing law to inhabitants within a large area often difficult and costly, it is essential to educate coastal communities towards compliance with fishing regulations and conserving their environment, rather than enforcement.
There is currently no mitigation measure or area closure that is specifically established to reduce marine mammal by-catch. Since fishing is the main activity that provides food and generates income to the coastal communities, measures that significantly restrict it are unlikely to be successfully implemented. Nevertheless, several Marine Parks are established, with the primary objective to conserve coral reefs, but allow some traditional fishing and recreational activities to take place. These parks indirectly protect coastal marine mammal species and its habitats, such as dugong and seagrass bed. Thus, the establishment of more marine protected areas (MPAs) with community involvement and integrated coastal zone management (ICZM) approach, at least in areas where marine mammals or its habitats are in serious conflict with humans, need to be given serious consideration.
In addition, live marine mammals can be more valuable than some small-scale or traditional fisheries. Resident species, such as the Irrawaddy dolphin and Indo-Pacific humpbacked dolphin, can be promoted as a product in ecotourism industry. This perhaps will develop an alternative source of income to the fishermen, which in term reduce their numbers and minimise threats to marine mammals.
38 ACKNOWLEDGEMENT
Surveys in Sabah and Sarawak are funded by the Ministry of Science, Technology and Environment Malaysia IRPA Grant No. 08-02-10-0010 “An integrated study of marine mammals and whale shark in the Malaysian Exclusive Economic Zone”, Universiti Malaysia Sabah and University of Aberdeen, UK. We extend our gratitude to the Department of Wildlife Sabah (especially to Edward Tangon, Francis Masangkim and Tawasil Butiting), Department of Fisheries Sabah (Abdul Hamid Mohamad, Abdul Rahman Othman, Albert Golud, Alip Mono, Chin Tet Foh, Haripudin Boro, Irman Isnain, Jalil Karim, Masrani Madun, Matusin Ali and Raden Kitchi), Sabah Parks (Fazrullah Rizally, Salimin and Selamat), Department of Fisheries F. T. Labuan (Adaha Hamdan), Department of Marine Fisheries Sarawak, Sarawak Forest Department (James Bali, Jeloo Sigit – deceased, Oswald B. Tisen, Rahas Bilang, Roslan Wahed), the Royal Malaysian Police, Royal Malaysian Navy, District Offices Sabah and Resident Offices Sarawak. A number of assistants (Ardiyante Ayadali, Cornel J. Miji, Ismail Tajul, Jennifer E. Sumpong, Josephine M. Regip, Mohamad Kasyfullah Zaini, Mukti Murad and Syuhaime A. Ali) who helped with this work, we are grateful to them. Special thanks are due to many fishermen, village headmen and coastal villagers who have relayed to us precious information on cetaceans and dugong by-catches and exploitation. Particular thanks are due to reviewers for comments on the manuscript.
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