A Ranked Inventory of Commercially-important Mollusks of Panay, West Central Philippines as a Guide to Prioritize Research

A first-ever effort to rank commercially-important mollusk species of Panay Island was conducted based on an extensive survey between March and April 2018. Ranking was based on the following criteria, namely: commercial value (40%), catch rates (20%), sources of threats (type of gear, processing plants, and number of fishers) (20%), frequency in the markets and source sites (10%), and literature available (10%), modified to a certain extent. A total of 90 mollusk species categorized into bivalves (49), gastropods (32), and cephalopods (9) were ranked. The comb pen shell Atrina pectinata (Pinnidae), Indian squid Uroteuthis duvaucelii (Loliginidae), and the scallop Mimachlamys sanguinea (formerly Chlamys senatoria) (Pectinidae) formed the top three species in the list strongly attributed to their high commercial value and thus catch rates. Squids, in general, are caught by trawls, whereas most of the other species are harvested primarily by gleaning and diving. The study highlights the high diversity of the malaco-fauna of Panay, as well as the multi-gear character of tropical fisheries. This ranked inventory can be used in prioritizing research on mollusks, by identifying target species for more in-depth studies useful for establishing their present status.


. I N T R O D U C T I O N
P hylum Mollusca, the second-largest phylum of animals after the arthropods, is represented by many commercially-important species, primarily belonging to Class Gastropoda, Bivalvia, and Cephalopoda. The Philippine Statistics Authority (PSA) reported for 15 years (2002-2017) a total municipal squid production of 672T metric tons (MT) for the entire Philippines with a corresponding value of approximately PHP 48.5M (PSA 2018). Western Visayas supposedly contributes to this considerably, where production (89.9T MT) and value (PHP 7M) correspond to 13.4% and 14.4% of the total for the entire Philippines, respectively. Based on initial data, however, the values of Western Visayas are gross underestimates (del Norte- Campos et al. in prep.). These statistics also simply lump species together so that the real picture of the commercial importance (amount harvested) of individual species is not accounted for. This generalized picture makes prioritization of re-search for commercially-important marine mollusks more difficult. An earlier study to mitigate this problem was conducted for the invertebrates in Panay (del Norte- Campos et al. 2000). A set of criteria was used to rank species importance based on their commercial value, catch rate, threats, frequency in markets, and information available. Albeit acknowledged to be incomplete, the study came up with 50 species, 34 (68%) of which are mollusks. Based on this and subsequent studies, mollusks, among other invertebrates, are harvested in Panay using trawls (del Norte-  and by diving (Declarador and del Norte-Campos, 2004). Gleaning, which until recently, remained to be a largely undocumented method of collection, also proves to be a reliably consistent and easily accessible source of income (del Norte- del Norte-Campos et al. 2005) for coastal populations, especially women. Following to a great extent, the methods of del Norte- Campos et al. (2000), an inventory of the commercially-important mollusks of Panay Island was conducted with the similar aim FULL PAPER of ranking the species to serve as a guide in selecting target species for in-depth studies. These studies include population and reproductive biology, as well as fishery monitoring, which altogether are important in establishing the status of the resource.

. M A T E R I A L S A N D M E T H O D
The survey was conducted between March and April 2018 in all four provinces of Panay Island (Fig. 1). The number of sampling sites (towns/cities) by province surveyed were as follows: Iloilo (6), Capiz (6), Aklan (3), and Antique (2), with each sampling site having their respective source sites, i.e., barangays (see Table 1). The different sites were visited, and interviews with fishers were conducted using a survey form (Table 2). Assistance in initial identification and selection of target sites for the interview was provided by local municipal agricultural officers (MAO's), faculty members of local fisheries schools and state colleges, as well as barangay captains. Printed images of known species were shown to interviewees to help validate species identity. Type specimens of unknown species were identified in the laboratory using literature such as FAO (1998 a & b) and Laureta (2008), while the rest were sent to the National Museum for Nature and Science (NMNS), Tokyo, for verification of taxonomic identification.  The data were analyzed using a set of criteria (Table 3) adopted and slightly modified from del Norte- Campos et al. (2000). The criteria are meant to highlight species with high commercial value and thus catch rates. Thus, species which score high in this scheme are those: a) with the highest commercial value, especially export value; b) which are processed with a processing plant, and thus high value added; c) which are fished more (i.e., high fishing intensity: high catch rates and more fishers); d) caught using destructive gear; and e) studied less (in terms of number of published literature). In this study, the last criterion was modified by giving a higher rank to species that have received less attention (i.e., relatively undoc- umented). This conforms more to use the resulting ranked inventory as a basis for selecting target species for more detailed studies, i.e., less studied, more attention needed. Commercial Value (CV), assigned a total weight of 40%, was assessed using actual prices (in PHP) recorded during the interviews. This was further broken down to Local Commercial Value, LCV (15%), and Export Commercial Value, ECV (25%). Estimated Catch Rate, CR (standardized to kg hr-1) (20%), which served as the proxy for Estimated Volume of Catch, was encoded using averaged fishery monitoring data recorded during the 1st to 2nd quarters of the year (January-June). Sources of Threats (20%) were Table 3. Criteria used in ranking mollusk species inventoried in Panay Island in March-April 2018 (adopted/modified from del Norte- Campos et al. 2000).
The Philippine Journal of Fisheries 26(2): 119-136 further broken down into: 1) presence of processing plants, PP (8%); 2) number of traders, herein modified to number of gleaners/fishers, G/F (6%); and 3) destructiveness of gear, G (6%). Species with processing plants were assigned a value of 1 while those without were assigned a value of 0. The number of fishers was further ranked in descending order with a decreasing number of fishers, i.e.,>150 fishers (=3), 100-150 (=2), and <100 (=1). Frequency (10%) was evaluated by assigning the number of days in a week that the species are usually observed in the markets (FPM, 5%) and source sites (FSS, 5%). The degree of the destructiveness of gear (G) was ranked with the highest value of 6 assigned to trawl, deemed as the most destructive gear, down to a value of 2 for passive gears such as traps and lift nets. Lastly, the criterion Information Availability, IA, based on the number of published studies in the Philippines, as mentioned above, deviated totally from del Norte- Campos et al. (2000), i.e., species which had been studied least (0 to 5 studies) were given a higher score (6), highlighting the need for more attention on these lesser-known/documented species. Marketing of collected shells are in most areas conducted on the same day, and this is true in both cases where there are designated buyers, or when the fishers themselves have to sell in local markets.
For each criterion, the mean of individual en-tries for each species for all areas was computed. These means were divided by the total value of entries for that criterion and weighted by multiplying each with the corresponding percentage value assigned for the said criterion. Individual weighted scores for each species for each criterion were summed to get the final score. The species were then ranked from highest to lowest based on their final scores. To make the procedure for computation clearer, Table 4 illustrates the computation for all species. From here, we can see the input values used for each criterion, the sum of inputs across all species with input values for the specific criterion, and the respective % weight for each criterion. Weighted score for each species is then computed as follows: Weighted score = (actual input value/total value) x % weight Thus, for example, the local commercial value (LCV) used for the comb shell Atrina pectinata was PHP 105.00 kg -1 , which was divided by the total LCV for all species recorded during the survey (PHP 5,427.1) = 0.019 x % weight for LCV 15% = 0.003. The same was done for all criteria, and the sum of all weighted scores taken (= 0.176), which is the final score for this species.  Table 4. Illustration of how ranking score is arrived at for all species using Atrina pectinata as an example. (LCV= local commercial value in PHP kg -1 ; ECV = export commercial value in PHP kg -1 ; CR = catch rate in kg hr -1 ; PP = processing plant; G/F = score assigned for number of gleaners/fishers; G = score assigned based on degree of destructiveness of fishing gear/method; FPM = frequency in markets; FPS = frequency in source sites; IA = score assigned based on number of information available). See also Table 3 for scoring scheme.

Atrina pectinata
*input value for PP is the mean value for 2 sites

Species Occurrence
A total of 95 mollusk species were encountered in the survey, of which 90 species belonging to three classes: Bivalvia (49), Gastropoda (32), and Cephalopoda (9) were ranked (Table 5). Figure 2 shows the relative distribution of the three mollusk classes by province. It can be seen here that bivalves predominate in Iloilo and Capiz, while there are more gastropods in Antique and Aklan. Cephalopod's occurrence in Iloilo, Capiz, and Antique is comparable, whereas Aklan's cephalopod resources are poor. Twenty-seven of the 90 species recorded in this survey were also reported in the study conducted by del Norte- Campos et al. (2000), while 62 species are new in the inventory for mollusks of Panay. These differences are likely due to the broader area covered in the present study, as well as the likelihood of some species having been omitted in the past study as they have only gained more considerable attention in the recent years. For example, several scallops (Pectinidae) species, namely Mimachlamys sanguinea (formerly Chlamys senatoria), Bractechlamys vexillum, Decatopecten amiculum, Annachlamys striatula are now included in the list due to the addition of Isla Gigantes Norte and Sur (previously excluded) in the present areas surveyed. These four species also ranked 3rd to 6th place, which validates their commercial importance. A few species have gained more attention, such as the granular ark Tegillarca granosa (also known as Anadara granosa) over which a stronger interest has increased due to the possibility of foreign markets (Korea). As such, the already high harvest rates (1.68 kg hr -1 ) in the Batan Bay area are exceeded by even higher catch rates (6.16 kg hr-1) in Capiz. The cephalopods, comprised of nine species, figure prominently in the list and confirm their reported commercial importance in Philippine fisheries. The list now includes oceanic species, such as the purpleback flying squid Sthenoteuthis oualanensis which is caught in deeper waters (9.1-18.3 m) in Antique by lighted jiggers, spear, and hook and line. While the flying squid has been previously reported to occur in the northwestern Philippines (Siriraksophon et al. 2000;Basir 2000), as well as in Ayungon and Bindoy, Ne-gros Oriental (Campos et al. 2016), it has never been recorded in Panay waters. The once-named Uroteuthis bartschi by del Norte- Campos et al. (2000), is now verified actually to be the swordtip squid Uroteuthis edulis. The confusion was likely caused by the similar elongate body shape of both species. The list also includes the day octopus Octopus cyanea, as well as O. nocturnus, which is only encountered in Antique (Table 6).

No.
Species Gari elongata x gleaning Some species formerly reported to be abundant have now suffered a decline. These include, for instance, the angelwing Pholas orientalis, which is now caught in much smaller quantities and on a very erratic basis. While biological data are available and intense restocking efforts (Marasigan and Laureta 2001;Laureta et al. 2014), it is apparent that the lack of parallel management efforts has caused its decline. The hammerhead oyster Malleus malleus, reported to be the number one species (mean monthly catch = 483 kg) in the diving fishery of Bancal bay, northern Panay (Declarador and del Norte-Campos 2004) only ranks 14 th in the present survey. The same goes for the Asian moon scallop Amusium pleuronectes, which was once caught in huge quantities in the Visayan Sea (Gabral-Llana 1983) and landed in Estancia, northeastern Panay. Currently, this scallop is now only landed in much lesser quantities in Concepcion, Iloilo and Roxas Capiz (del Norte- Campos et al. in prep.).
Aside from the occurrence of species by province, Table 6 also shows the gears/methods of fishing for each. Included herein is the glistening abalone Haliotis glabra, a species of abalone not previously reported in Panay. This species is regularly gleaned in Nabas, Aklan. Restocking efforts in various areas in the western Visayas by SEAFDEC (Buen-Ursua and Ludevese 2011;Lebata-Ramos et al. 2013) pertain to another abalone species, the Donkey's ear abalone Haliotis asinina, reportedly introduced in Panay. Table 5 shows the list of species ranked ac-cording to the given set of criteria. The number 1 species in the list, the comb pen shell Atrina pectinata, ranked higher than the Indian squid, which has greater local and export commercial value (see below). This is primarily because the comb pen shell is the only mollusk species with processing plants in the area (scored in the criteria PP = processing plant) dedicated to extracting the species' adductor muscles for export to Taiwan. It is thus logically conceivable that a more targeted, severely wasteful, level of harvesting (Burgos et al. in prep.), is being conducted for this species given that only its adductor muscle has a high commercial value.

Species Importance: Commercial Value and Catch Rates
The number two species in the list, the Indian squid Uroteuthis duvaucelii ranked high due to its local and export commercial value (LCV = PHP 275 kg -1 and ECV = 400.00 kg -1 ) and high catch rates. Catch rates for trawl during the summer months (March-April) were comparable for the two areas in Pilar Bay (1.97 kg hr -1 ) and Concepcion Bay (3.7 kg hr -1 ). Higher catch rate values in the latter are due to fishing in the fringes of the highly productive Visayan Sea. Lift nets, on the other hand, despite using attractants (lights), have lower catch rates (1.86 kg hr -1 ) for U. duvaucelii, as they operate more towards nearshore areas.
It is also noteworthy that 4 (Mimachlamys senatoria, Bractechlamys vexillum, Decatopecten amiculum, and Annachlamys striatula) out of the top 10 species are scallops (Pectinidae). Aside from the works of Soliman and Dioneda (2004) and Morillo-Manalo (2017) on C. senatoria, the other three scallop species have been unstudied in the country. They are those occurring in more coralline substrates of the Gigantes Islands where diving fisheries are conducted. The more studied species the Asian moon scallop Amusium pleuronectes (Gabral-Llana and Aprieto 1980;Gabral-Llana 1983;del Norte 1988;del Norte et al. 1988;Belda and del Norte 1988), on the other hand, occurs in soft bottoms and is a trawl by-catch.
While ranking relatively low in the past study, the Chambered nautilus Nautilus pompilius has risen to become one of the top 10 species in the present study, and this is attributed first to the change in its use in the market. Whereas it was formerly harvested only for its shell (del Norte-Campos 2005), its meat is now likewise sold. In addition, change in the species' fishing seasonality was observed, which factored in the rankings, i.e., traps to catch the chambered nautilus are now deployed even outside the rainy season, unlike before.
Five species that were excluded in Table 5 (ranked) are included in Table 6 (not ranked). These are the species which likewise occur in Panay Island but have no direct commercial value as they are only for fisher household consumption. From here, it appears species are divided into two categories, i.e., those caught by single fishing gears/methods (86%), and those caught by a combination of gears (13%). For the species caught by single gears/methods, gleaning is the most important (79.8%) fishing method, followed by diving (14.3%). Exploiting species using a combination of methods, attest to fisher ingenuity and resourcefulness.

Sources of Threats
Of the gears/methods used to catch mollusks in Panay, the trawl remains to be the most destructive gear causing a considerable extent of damage to the bottom (Stiles et al. 2010). Uroteuthis duvaucelii, the number two ranked species (Table 5), also scores high in this criterion as it is caught by trawl and landed primarily in Iloilo and Capiz. At the same time, however, the extent of damage caused by diving and gleaning in terms of the upturning of the bottom substrate cannot be underrated. The existence of processing plants where shucked pen shell adductor muscles (Atrina pectinata) are sold, causes grave threats, together with the means of harvesting this species (digging up the substrate to unearth pen shells). These processing plants which purchase shucked adductor muscles of pen shells for export to Taiwan represent an easily accessible source of income for the fishers, which then will further encourage unabated harvesting at the expense of the stock.

Information Available
Ranking higher less-studied species highlighted those that need more attention, foremost of which is the pen shell Atrina pectinata. While the species has been studied in other areas, e.g., China (Qiu et al. 2014), no known studies on the species exist in the country. While squids have traditionally been included in trawl survey lists (Hernando and Flores 1981), there has been little effort to identify the species correctly and even worse, just referring to all of them as Loligo spp. (e.g., Armada et al. 1983). More specific studies on squids have also been recently conducted, such as that of the age and growth of the bigfin reef squid Sepioteuthis lessoniana (Balgos 1990) and reproductive biology of Uroteuthis duvaucelii (Tajolosa 2011), all species whose names have been updated in FAO (1998b) from the original (Voss 1963). There is also an obvious need for studies on Octopus cyanea, which is caught in all provinces of Panay ( Table 6).
The newly-reported invasive species, the Charru mussel Mytella charruana (Vallejo et al. 2017) in Manila Bay, has fortunately not yet been observed in Panay waters.

. C O N C L U S I O N S A N D R E C O M M E N D A T I O N S
This inventory provides the only known list and importance ranking of the commercially-important mollusk species in Panay Island, albeit short-term and limited. Although the data do not fully integrate the effects of seasonality, the list is considered nonetheless realistic as ranking was based on recorded catch rates (fisher's records) rather than solely based on recall interviews. This ranked inventory does not only highlight the multi-species and multi-gear character typical of many tropical species but also emphasizes the importance of Panay as a center of mollusk biodiversity. There is no area in the Philippines now known for such a high malacofauna record. Although the list is acknowledged to be incomplete and remains to be updated, it provides a picture of species importance and serves as a guide on where future more indepth malacological studies should be focused. Assessment studies on the heavily exploited species can be initiated based on this inventory. Further studies on the species' biology can be investigated, so guidelines may be formulated for their proper resource utilization and to avoid possible stock collapse.