**2. How many** *P. vannamei* **have escaped?**

There have been numerous reports of escapes from aquaculture production facilities into non-native waters. The presence of *P. vannamei* has been reported in Texas, South Carolina, and Hawaii, USA [23–28]; Thailand [29, 30]; Venezuela [31]; Brazil [32]; Puerto Rico [33]; Vietnam [34]; and Southern Gulf of Mexico coast [35]. In the Philippines, Briggs et al. [29] reported that a population of *P. vannamei* already exists in the wild through intentional release and escapes. The implementation to ban the importation of all live shrimp and prawn species of all stages except for scientific or educational purposes by the Bureau of Fisheries and Aquatic Resources (BFAR) in 1993 led to illegal importation in 1997 by private sector due to disease problems with the culture of *P. monodon*, and the regulations are known to have resulted in the dumping of PL *P. vannamei* into the wild in attempts to escape detection. Also, typhoons have also resulted in the liberation of *P. vannamei* from culture ponds into the surrounding sea. On average, 20 typhoons hit the Philippines every year, and some of the most destructive and deadliest typhoons include Yolanda (2013), Pablo (2012), Sendong (2011), Ondoy (2009), Frank (2008), Milenyo (2006), and Reming (2006) (http://bagong.pagasa.dost.gov.ph/). Based on the main author personal experience, *P. vannamei* has been sometimes a part of catch by local fisherman in Buguey Lagoon, Cagayan. Its presence in the lagoon is possibly due to the escape from the Dataj Aquafarm which is actively engaging in the grow-out of *P. vannamei* in four different locations in the municipality of Buguey and Camalaniugan with a total area 77.91 hectares. The lagoon serves as the main water source of the farms. More frequent flood incidence in the area is taking place especially during typhoons or heavy rains due to black sand mining that started in 2009 until 2013 that widens the mouth of the lagoon.

Through the years, the culture of *P. vannamei* in the Philippines is continuously growing even during the implementation of the shrimp importation ban from 1993

*Spatial Variability in Environmental Science - Patterns, Processes, and Analyses*

species are regarded as IAS.

*Aristichthys nobilis* [10].

any new pathogens [18].

(i.e., outside the range it occupies naturally or could not occupy without direct or indirect introduction or care by humans), which includes any part, gametes, or propagule of such species that might survive and subsequently reproduce. On the other hand, Invasive alien species (IAS) are species whose introduction and/ or spread outside their natural past or present distribution threatens biological diversity which occurs in all taxonomic groups, including animals, plants, fungi, and microorganisms, and can affect all types of ecosystems [3]. Generally, exotic

IAS is one of the five most important direct drivers of biodiversity loss and change in ecosystem services [4]. According to the Invasive Special Specialist Group, [5], IAS can interact with migratory species in several ways resulting in cumulative negative impacts, for example, as a threat on their breeding sites, on their stopover and wintering grounds, and during migrations. These impacts may result in local extinction or decline in population numbers as well as changes to migration patterns. IAS impacts native species (including migratory species) and their habitats through several mechanisms, including predation, habitat degradation (grazing, herbivory, browsing, rooting/digging and trampling), competition, hybridization, disease transmission, parasitism, poisoning/toxicity, biofouling, etc. IAS has resulted in major impacts on biodiversity at a global scale, where at least 39% of the species extinctions during the past 400 years are due to IAS [6]. The importation of alien or exotic aquatic species from other countries is continuing in the Philippines. Most of the importation is for aquaculture and the aquarium trade. Exotic species are either purposely or accidentally introduced in rivers and lakes which are inhabited by endemic and indigenous fish species. Most of these introductions have contributed negative impacts on freshwater/wetland ecosystems and have caused biodiversity loss [7, 8], while some introduced species have contributed a significant proportion to aquaculture in the Philippines [9]. In terms of such contributions, the Nile tilapia *Oreochromis niloticus* is next to milkfish *Chanos chanos* among the aquaculture species, followed by the big head carp

There are 181 organisms (28 families) introduced of exotic aquatic species since the 1900s; however, 40 organisms have unknown records of introductions in the Philippines [11]. In 2018, the IUCN Invasive Species Specialist Group [12]'s Global Invasive Species Database (GISD) lists 84 alien species, 12 with bio status unspecified and 54 that are native to the Philippines. The Pacific whiteleg shrimp *P. vannamei* is not included in the list; however, published studies reported the risk of culturing the shrimp outside its natural geographic range. For intensively farmed *P. vannamei* in Indonesia, the final numerical score is 3.39 out of 10, where the presence of three red criteria (Habitat, Chemicals, Disease) results in an overall red "Avoid" recommendation. Red mark means that these items are overfished or caught or farmed in ways that harm other marine life or the environment [13].

*P. vannamei* [14] is native to the Eastern Pacific coast from the Gulf of California, Mexico to Tumbes, North of Peru [15]. In the Philippines, *P. vannamei* was imported from Panama in the 1970s and from Hawaii in 1990 [16, 17]. However, there was no documentation of these introductions because government regulations were not followed in most cases, and it was not known whether the exotic species introduced

Risk can be defined as the likelihood of harm occurring as a result of an action or inaction [19]. Harm refers to the undesirable consequences to humans or components of a valued ecosystem [20]. However, Senanan et al. [21] argued that there is a challenge in analyzing the ecological risk of alien species because of difficulty in predicting the harm, estimating the likelihood of harm occurring and the severity of the harm. These parameters are species and ecosystem specific and are

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to 2006. In fact, about 700 hectares of *P. vannamei* illegal farms in Luzon have been reported in 2003 [36]. The ban was lifted in 2007 after experimental trials and a series of public consultation and hearings [37]. In 2008, there were 38 grow-out farms engaged in *P. vannamei* farming, and it increased to 53 farms in 2013 [38]. Additionally, based on the [39] master list of shrimp farms as of December 2013, the shrimp has been polycultures with fish (17 farms, 642.7 ha) and *P. monodon* (4 farms, 33.0 ha). In 2014, there were 27 accredited hatcheries that continually support the demand of seedling requirements of the shrimp [40]. As of August 31, 2019, however, there were already 40 accredited hatcheries and 545 grow-out farms of the shrimp with a total productive area of 7382.08 hectares [41–43]. The boom and rapid expansion of the shrimp aquaculture are expected because of its demand for both the local and global markets. With this continuous expansion of *P. vannamei* farming, it is possible that shrimp can be found in the different estuary or brackish water rivers in the Philippines wherein the hatcheries and grow-out farm's operations are found due to escapes. The probability of escapes is higher because out of the total farms in 2019, 331 farms with an area of 4144.19 hectares were operating extensive grow-out practices wherein old and not properly designed ponds are usually utilized. A small percentage of escapes per operation cycle could translate to significant numbers of individuals entering the ecosystem. According to Panutrakul et al. [44], the shrimp can enter estuary at various life stages including post-larvae (produced from hatcheries), juveniles, and subadults (cultured in ponds). As of 2019, however, no studies have been conducted in the Philippines to verify the presence of the shrimp in the wild.

In Thailand, floods in Surat Thani and Pranburi in 2003, for example, led to several million *P. vannamei* escaping to the coastal environment. Not surprisingly, the shrimp, therefore, has been reported in fisherfolk's catches on Andaman and Gulf of Thailand coasts. No detailed information on catches is available, but numbers have not been reported as large [29]. Similarly, an incident of escape was reported from farms to the Bangpakong River in Thailand [30, 45]. The study showed that the numbers of the shrimp sampled in the river positively correlated with the location and area of shrimp ponds. Manthachitra et al. [45] used remote sensing and a geographic information system (GIS) to estimate the location and total area of shrimp ponds (active, inactive, and abandoned ponds) in the Bangpakong River watershed and found that most ponds were located within 5 km of the river. The presence of the shrimp was confirmed based on the survey of marine shrimp populations in the Bangpakong River during the same period conducted by Senanan et al. [30]. The mean proportion of *P. vannamei* relative to all penaeid shrimp per net per year (all stations combined) ranged from 0.005 (June 2005) to 0.16 (January 2006), with the highest abundance detected in 2006. The presence of the shrimp in the river may be a consequence of pond water releases during the intense farming activities of 2005. In the Southern Gulf of Mexico coast, there is a first report of the presence of *P. vannamei* [35]. During a shrimp monitoring program survey conducted in this area, seven specimens were collected in the Carmen-Pajonal-Machona lagoons near La Azucena and Sanchez Magallanes in Tabasco, Mexico.
