Laura May-Collado ^1,2, Tim Gerrodette ³, John Calambokidis ⁴, Kristin Rasmussen ⁴ & Irena Sereg ⁵

1 CIMAR, Ciudad de la Investigación, Universidad de Costa Rica, 2060 San José, Costa Rica.

2 Department of Biological Sciences, Florida International University. 11200 SW 8th St. Miami, Florida 33199; lmayc002@fiu.edu

3 National Marine Fisheries Service, National Marine Fisheries Service, Center 8604 La Jolla Shores Dr. CA 92037.

4 Cascadia Research Collective, Water Street Building, 218 ½ West Fourth Avenue, Olympia, Washington 98501, USA.

5 American University, Department of Environmental Sciences, 4400 Massachusetts Avenue NW, Washington D.C. 20016-8007.

Received 19-III-2004.     Corrected 18-XII-2004.     Accepted 17-I-2005.

Key words: Conservation, Central America, dolphins, marine mammals, whales.

Costa Rican waters support 32 species of marine mammals belonging to the orders Sirenia, Carnivora (Sub-order Pinnipedia) and Cetacea (Rodríguez-Herrera et al. 2002). About 30 cetacean species within the Delphinidae, Ziphiidae, Physeteridae, Kogiidae and Balaenopteridae inhabit or are expected to be found in the Pacific and Caribbean economical waters of Costa Rica (May-Collado in press). According to Gerrodette and Palacios (1996) Delphinus delphis, Stenella coeruleoalba, beaked whales (Ziphiidae), and Tursiops truncatus are the most abundant cetaceans in Costa Rican Pacific waters. Based on reports of distribution patterns (throughout the Eastern Tropical Pacific) in Costa Rica, cetaceans are more likely to inhabit oceanic waters (e.g., Dizon et al. 1994, Kinzey et al. 1999, 2000a, 2001). However, some species may have populations in both, oceanic and neritic waters (e.g., Stenella attenuata) (Rodríguez-Fonseca 2001, MayCollado and Morales 2005).

In Costa Rica, cetacean research has focused primarily on the biology of three resident species, the bottlenose dolphin, Tursiops truncatus, (e.g., Acevedo-Gutierrez and Würsig 1991, Acevedo-Gutierrez 1996, Acevedo- Gutierrez and Burkhart 1998, Cubero-Pardo 1998), the coastal spotted dolphin, Stenella attenuata graffmani (e.g., Cubero-Pardo 1998, May-Collado 2001, May-Collado and Forcada 2001, May-Collado and Morales 2005, Rodríguez Sáenz and Rodríguez-Fonseca 2004), and the humpback whale, Megaptera novaeangliae (e.g., Acevedo and Smultea 1995, Calambokidis et al. 1999, 2000, Rasmussen et al. 2001, 2002). Available information suggests that in the northern Pacific environmental factors such as water transparency and dissolved oxygen concentrations play an important role in the abundance of the local population of coastal spotted dolphins (May-Collado 2001, May-Collado and Forcada 2001). In addition, the feeding activities of this population are associated with the seasonality of the area (MayCollado 2001, May-Collado and Morales 2005). Studies on the bottlenose dolphins indicate that in some areas they have very restricted movement patterns and therefore depend on the local habitat to reproduce and feed (Acevedo- Gutierrez and Burkhart 1998, Cubero-Pardo 1998). Finally, recent studies indicate that humpback whales observed in different seasons of the year, along the Pacific coast of Costa Rica, are migrating primarily from feeding grounds off California (January-April) and Antarctica Peninsula (June to October) to breed and give birth in national waters (Steiger et al.1991, Calambokidis et al. 1999, 2000, Rasmussen et al. 2001, 2002).

Even as the knowledge of cetacean natural history is increasing in Costa Rican waters, relevant information for conservation purposes such as distribution pattern is scarce. The existent information on their distribution is either to the scale of the Eastern Tropical Pacific (ETP) (e.g., Perrin et al. 1985, Au and Perryman 1985, Polacheck 1987, Reilly 1990, Reilly and Fiedler 1994, Reilly et al. 2002, Wade and Gerrodette 1993, Dizon et al. 1994, et al. 1999, 2000a, 2001), or to very localized areas (e.g., Acevedo-Gutierrez and Smultea 1995,Acevedo-Gutierrez and Burkhart 1998). Although Rodríguez-Fonseca (2001) and May- Collado (in press ) summarized published cetacean sightings in Costa Rican waters, detailed maps of cetacean sighting distribution in the EEZ Pacific of Costa Rica are lacking. Because understanding the distribution patterns at different scales is important in the planning of conservation and management plans, our main goal is to provide an up to date species check-list and maps of all cetaceans sightings reported during twenty two years of surveying the Pacific EEZ of Costa Rica.

This study is based on data collected by the National Marine Fisheries Service Southwest, Fisheries Science Center (from 1979 to 2000), the Cascadia Research Collective (from 1996 to 2001) and Proyecto Cetacea-CIMAR (from 1998 to 2001). It should be noted, however, that these three entities vary in their methodologies, sample and season effort, and area studied, thus results from each may not be strictly comparable, limiting the strength of our conclusions.

Materials and methods

Study Site: The Costa Rican Pacific Exclusive Economic Zone (EEZ) is a part of the Eastern Tropical Pacific (ETP), an area that contains some of the most productive oceans of the world (Philbrick et al. 2001). The Pacific EEZ of Costa Rica is part of the so called "Central American Bight" (referring to the coastal waters from Guatemala to Ecuador) an area that contains the most variable waters within the Tropical Surface Water Province, because of the influence of the Inter-tropical Convergent Zone (ITCZ) (Au and Perryman 1985). During the first half of the year, north-eastern winds blow across Central America from the Atlantic, producing coastal upwelling, wind stirring, and complex temperature patterns (Au and Perryman 1985). In the second half of the year the ITCZ migrates north, bringing southerly winds, rain that reduced water salinity, and intensified the Equatorial Countercurrent (Wyrtki 1967, 1974).

Surveys: This paper is based on a matrix constructed with data from three sources:the Southwest Fisheries Service Center (SWFSC), Cascadia Research Collective (CRC)and the Centro de Investigaciones del Mar y Limnología (CIMAR) throughout the entire Costa Rican EEZ at different times of year and using different methodologies. Here we provide a brief description of the goals of each research entity and their respective survey methods.

(1) The SWFSC is a laboratory of the US National Marine Fisheries Service that has conducted research on cetacean populations of the ETP since the mid-1970’s (Kinzey et al. 2000a), focusing on those species believed to be most affected by the purse-seine fishery for yellowfin tuna, Thunnus albacares (Wade and Gerrodette 1992, Wade et al.2002). They have produced abundance estimates of 24 stocks of cetaceans by implementing in the most part of their surveys, stratified analysis with line-transects (see Wade and Gerrodette 1992, 1993, Kinzey et al. 2000b). Surveys have been conducted throughout the entire Eastern Tropical Pacific using two to three ships along pre-determined track lines (which vary in length) (Fig.1) (Kinzey et al. 1999, 2000a, 2001). Observers actively search for marine mammals from 6:00 a.m.to 6:00 p.m. and report the geographical position, bearing, species ID, distance and group size of each sighting, including environmental data (e.g., sea water temperature, salinity, and thermocline depth). We used a total of 1029 sightings of cetaceans reported by the SWFS from 1979 to 2000 in the EEZ of Costa Rica.

(2) The CRC is a non-profit organization that is conducting a long-term study on humpback whales (Megaptera novaeangliae ) and other marine mammals particularly off the south Pacific shore of Costa Rica since 1996 (Calambokidis et al. 1999). Using two small boats (~7m) they have surveyed the coastal waters from north Dominical and Drake Bay to waters offshore Caño’s Island and Golfo Dulce (Fig.1). Survey effort in all years was consistent in all areas, with a total number of 18 to 27 surveys covering from 2229.25 to 3207.9 km per year. No predetermined-transects are used during these surveys, instead photo-ID surveys are used. The direction of the survey is based on information from previous whales sightings (see Rasmussen et al. 2001, 2002). Data recorded includes geographical position, species ID, approximate group size, environmental data (e.g., sea state, swell height, etc.), and photo identification. We include in the matrix a total of 612 sightings documented by CRC from 1997 to 2001 in the south Pacific of Costa Rica.

(3) Proyecto Cetacea is a project developed by the CIMAR, University of Costa Rica to study the abundance trends, habitat use, acoustics and photo-identification of the marine mammals that inhabit the coastal waters of the north Pacific of Costa Rica (Cuajiniquil Bay, Murciélago’s Islands and Papagayo Gulf and surrounding waters). The study focused on the spotted dolphins (Stenella attenuata ) and humpback whales (M. novaeangliae). Using a small boat (~7m), pre-determined strip transects were surveyed monthly from 1998 to 2001 (from 6:00 a.m to 6:00 p.m.) (see May-Collado 2001). For every encounter the following data were recorded: geographical position, group size, and environmental variables (e.g., superficial water temperature, salinity, dissolved oxygen, thermocline depth, and sea state). A total of 130 sightings was included in the matrix.

Analysis: We plotted a total of 1771 sightings of 19 species and 3 genera using the software Arc GIS 8.1. The maps show the geographical position of all cetacean sightings made from 1979 to 2001 collected by the three sources combined. We also constructed sighting maps for the subspecies of the dolphin species Stenella attenuata and S. longirostris. Throughout this paper we will describe cetacean sighting distribution based on water depth, by approximately assigning species to neritic and oceanic waters (also referred as pelagic or offshore waters) (Levinton 1995, Wells et al. 1999). Neritic waters are shallower than 200 m and include inshore (e.g., bays, gulfs) and coastal (habitat along the open shoreline) waters (Levinton 1995, Wells et al. 1999). Oceanic waters are deeper than 200m (Levinton 1995, Wells et al. 1999). More specifically, cetaceans with more than 60% of their sightings in shallow waters will be refer as neritic species and those with more than 60% of their sightings in deep waters will be refer as offshore or oceanic species. Taxonomic nomenclature is based on Rice (1998).

Delphinidae was the family most commonly observed (76% of all sightings), followed by Balaenopteridae (13%), Ziphiidae (3%), Physeteridae (2%), and Kogiidae (2%). About 4% of the sightings corresponded to unidentified cetaceans. We observed a total of 12 dolphin species, three rorqual species, two ziphiid species, and one Kogia species. Among delphinids Stenella coeruleoalba and Tursiops truncatus were the most commonly observe. Large average group size was observed on Delphinus delphis, S. attenuata graffmani, S. longirostris orientalis and S. longirostris unid subspecies. Within Balaenopteridae, M. novaeangliae was the most commonly encountered species (Table 1). Overall, cetacean sightings were widely distributed throughout the EEZ Pacific waters, with concentrations of some species sightings (and stocks) in the coastal waters at northern and southern ends of Costa Rica (Fig.2).

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SubOrder Mysticeti Family Balaenopteridae (rorquals)

In addition to Balaenoptera edeni, B. musculus, and Megaptera novaeangliae we mapped sightings of animals categorized as B. borealis / B. edeni, meaning that we were not able to confirm the presence of one or three ridges on the rostrum. However, these sightings most likely correspond to B. edeni that is commonly found in the northern and western of the Costa Rican EEZ. It is unlikely that any include B. borealis since the SWFSC has not been able to confirm the presence of this species during twenty-two years of surveying Costa Rican waters (T. Gerrodette pers. comm. 2003). Additionally, CRC in 1997 reported a possible sighting of B. physalus at 8.408N/-83.558W, the interpretation of this sighting should also be treated carefully, because it was not confirmed.

Humpback whales were seen primarily during two time periods: January to March and August to early October. Unlike sightings of other whales, all sightings of humpback whales were close to shore and within the neritic zone. Sightings were heavily concentrated in the area around Osa Peninsula in southern Costa Rica where dedicated photo-ID surveys conducted by Cascadia Research were based. The other two species sightings were primarily in oceanic waters (Fig.3).

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(Dwarf and Pygmy Sperm Whales)

The dwarf sperm whale, Kogia sima, was the only confirmed Kogiidae species. Although this species has been reported in the central and south Pacific coastal waters, most of our sightings occurred in offshore waters (Fig.4).

Family Physeteridae (Sperm Whale)

Physeter macrocephalus sightings were widely distributed in offshore waters, particularly in the southeastern portion of the EEZ, including Coco Island (Fig.5).

Family Ziphiidae (Beaked-whales)

Two species of beaked whales were confirmed: Mesoplodon densirostris and Ziphius cavirostris. However, other Mesoplodon species and unidentified ziphiids were also commonly observed in the area. Although, Z. cavirostris, Mesoplodon spp. and unidentified ziphiids were occasionally observed in neritic waters, overall, ziphiids sightings showed a wide distribution throughout oceanic waters (Fig.6).

 

Family Delphinidae (Dolphins)

With the exception of Lagenodelphis hosei which was observed only once in oceanic waters (8.408 N/-88.558 W), we constructed distribution maps for all dolphin species. Based on the percentage of sightings in neritic and oceanic waters, dolphin species were grouped into three categories:

(1) Species with sightings primarily in oceanic waters: Orcinus orca, Peponocephala electra, Stenella coeruleoalba, Grampus griseus, Delphinus delphis, S. longirostris (Fig.7,9).

(2) Species with sightings in both offshore and neritic waters: G. macrorhynchus, Steno bredanensis, Tursiops truncatus, Pseudorca crassidens, and S. attenuata offshore stock (Fig.8,9). It is important to notice that none of the data sources regularly surveyed the Gulf of Dulce where there is a resident population of T. truncatus. However, such surveys would probably not change the consideration of T. truncatus as an offshore-neritic species in the Costa Rican EEZ.

(3) Species with sightings primarily in neritic waters: S. attenuata graffmani (Fig.9).

S. attenuata graffmani sightings were widely distributed in neritic waters, particularly concentrated in north Pacific (Papagayo Gulf and Cuajiniquil Bay) and in the south Pacific (Dominical, Drake Bay, and Osa Peninsula). This may be artifact of concentrated survey effort in these two areas.

Twenty years of surveys in the Pacific Exclusive Economic Zone of Costa Rica reveal a cetacean community that encompasses 19 species. Mysticetes were represented only by three species members of the family Balaenopteridae that with the exception of Megaptera novaeangliae may inhabit primarily oceanic waters. Rodriguez-Fonseca (2001) indicated that both Balaenoptera edeni and B. musculus are common in the EEZ of Costa Rica. However, our study does not support this conclusion and careful considerations should be taken when treating these species. In fact long term studies by SWFSC in the Eastern Tropical Pacific have indicated that B. edeni is more commonly found at 150º W between 20º N and 10º S and B. musculus appears to be more frequently along of Baja California, Mexico (Kinzey et al. 1999, 2000a, 2001).

Humpback whales from both the northern and southern hemispheres utilize the waters of Costa Rica as a wintering area (Steiger et al. 1993, Calambokidis et al. 1999, 2000, Rasmussen et al. 2001, 2002, Acevedo and Smultea 1995). The humpback whale sightings we report are from January to March and August to October, which correspond with the northern and southern Hemisphere humpback whale wintering seasons, respectively. Photographic identification has shown that whales seen during the Northern hemisphere wintering season are primarily migrating from feeding grounds off California, and whales seen during the southern hemisphere season are migrating from Antarctic. In addition to the concentration of sightings we report in the Gulf of Papagayo and the Osa Peninsula, sightings of humpback whales have also been reported in the Golfo Dulce during the southern hemisphere wintering season and off Cocos Island during the northern hemisphere season (Acevedo and Smultea 1995, Photographer Marco Tulio Saborío pers. comm. 2004).

Delphinidae had the highest number of species. Some were widely distributed in oceanic waters (e.g., S. coeruleoalba), others in both oceanic and neritic waters (e.g., Tursiops truncatus ), and some primarily in neritic waters (S. attenuata graffmani ). For Peponocephala electra, Orcinus orca, and Lagenodelphis hosei similar distribution patterns have been described in other parts of the Eastern Tropical Pacific, where sightings are occasional and occur primarily in oceanic waters (Au and Perryman 1985, Reilly and Fiedler 1994, Wade and Gerrodette 1996, Kinzey et al. 1999, 2000a, 2001). It is important to notice that Orcinus orca and Globicephala macrorhynchus have been informally reported by local artisanal fisherman, sport fishing and diving tours in Montezuma, Cabo Blanco, Isla Catalina (in Golfo de Papagayo), Islas Murciélagos and Isla del Caño and along Osa Peninsula (Biol. Frank Garita, Biol. José Martínez, fisherman Minor Lara, and a number of local captains comm. pers. 1998-2004) and Steno bredanensis was observed once inside Bahía Culebra actively interacting with S. attenuata graffmani (Laura May-Collado and Alvaro Morales pers. observ. 2001).

Our distribution maps provide further support to previous studies in which the Gulf of Papagayo (including the Mucielago’s Islands) and Osa Península (particularly Caño Island) have been described as important breeding grounds for the northern and southern hemisphere M . novaeangliae whales (Calambokidis et al. 1999, 2001, Rasmussen et al. 2001, 2002), and the local population of Stenella attenuata graffmani (e.g., May-Collado 2001, May- Collado and Morales 2005). Similarly, Gulf of Dulce and Cocos Island have been proposed as year-round reproductive and foraging areas for Tursiops truncatus (Acevedo-Gutierrez 1996, Acevedo-Gutierrez and Burkhart 1998, Cubero-Pardo 1998). Although our study does not show patterns to support Cocos Island as important site for Pseudorca crassidens (Acevedo-Gutierrez 1997) and Ziphius cavirostris (Acevedo-Gutierrez 1996) it is important to consider these sites as potential habitats for these two species, until future studies of abundance and habitat use are available.

Furthermore, our data provides evidence that dolphin habitats largely overlap with important fishing areas,a situation that must be taken into account for conservation and management purposes. In fact, incidental kills by artisanal fisheries and pursue-seine tuna fishery is suggested to be important in Costa Rican waters (Vidal et al. 1994, Palacios and Gerrodette 1996, Wade et al. 2002). The SWFSC has been estimating annual mortality rates due to artisanal fisheries for most of the EEZ of Central American countries. In Costa Rican waters annual mortality is about 9.5% of the population size for all small cetaceans combined (Palacios and Gerrodette 1996, Wade et al. 2002). According to IWC (1996) anthropogenic mortality rates should not exceed 1-2% of population size, based on the low reproductive rate of cetaceans (Perrin et al. 1994, IWC 1996).

These numbers are particularly important for the subpopulations (or stocks) of S. longirostris and S. attenuata, which in the past have been dramatically reduced by the tuna fishery industry (Perrin et al. 2002a,b). Tuna industry is particularly significant in the Eastern Tropical Pacific because it supports one the world ’s largest fisheries ground of yellowfin tuna (Thunnus albacares). Yellowfin tuna tends to associate with mixed schools of S. longirostris and S. attenuata; this aggregation is follow by several seabird species which make it very conspicuous to fishermen (Au and Pitman 1986). This tuna detection technique is so successful that it has resulted in large tuna catch, but simultaneously has caused dolphin populations to decline (Ballance et al. 2002). For instance, Stenella longirostris orientalis, populations have decreased 70% of their original size (Wade et al.2002). In addition to these two type of fisheries, whale watching activities also appear to have a negative impact, particularly on coastal dolphin populations due to lack of proper training of the operators (Cubero-Pardo 2001).

Although most of the dolphin species listed in this paper are not considered in endangered or vulnerable by CITES II (Convention on International Trade in Endangered Species of Wild Fauna and Flora), it states that trade must be controlled (http://www.cities.org). Several of these species are also listed in the IUCN Red list (The World Conservation Union, http://www.redlist.org). We believe that the level of localism of cetacean species in Costa Rica and in the rest of Central American countries should be considered for their protection. Work done by Escorza-Treviño et al. (2002) on the genetics of S. attenuata graffmani populations along Central America suggests that these coincide with jurisdictional waters of each country. They indicate the existence of six distinct coastal populations, which should be treated as independent units for management purposes. Additionally, the Central America Bight is the most important area of overlap for S. longirostris, S. attenuata, S. coeruleoalba and Delphinus delphis, and protection of these species in Costa Rican waters will reverberate in other Central America countries. The family Balaenopteridae is also listed by the IUCN red list, but it is Megaptera novaengliae the one consider a vulnerable species. Therefore, we believe that future conservation and management efforts should initiate on whales and dolphin species that occupy neritic waters where human activities are most intense and more likely to affect their populations.

In conclusion, here we reported 19 cetacean species and constructed distribution maps for 17 species. However, more information needs to be generated to have a better understanding of the influence of abiotic and biotic factors, seasonality, and human activities that may influence the distribution patterns of these animals. Cetaceans are animals that have a very low population growth rate. Therefore they are very susceptible to any kind of exploitation that affect their behavior (e.g., whale watching, anthropogenic noise, etc.) and immediate population size (e.g., tuna and artisanal fisheries, pollution, etc.). In the immediate future, the protection of these animals and their habitats should be a top priority in Costa Rican marine conservation. These first maps of sighting distribution may provide base-line information to initiate the protection for these animals and their habitat.

We thank MINAE for research permits, CIMAR and the Area de Conservación Guanacaste for logistic and institutional support. Special thanks to Jorge Cortes,Alvaro Morales, Carmen Durán, Roger Blanco, Frank Joyce, Federico Chinchilla and Geovanni Bassey. Thanks to The Nature Conservancy and the Society for Marine Mammalogy (Emily Shane for providing funding to study dolphins in the Gulf of Papagayo and the Oceanic Society Expeditions for supporting humpback whale field work. Numerous people assisted in the data gathering: Gretchen Steiger, Frank Garita, Isidoro Szczepaniak, Heather Harding, Oceanic Society Expeditions participants from Elderhostel, Minor Lara, Frank Lara father and son, Guicha, Samba, Freddy, Andrea Montero, Marian Portillo, Marco Tulio Saborio, Monica Gamboa, Marco Quesada, Alvaro Morales, Frank Garita, Augusta Anderson, SWFSC crew members and marine mammal observ-EAP and Escuela de Biologia students, OTS Biocursos participants. Special thanks to Federico Chinchilla for inspiring this paper and to Ingi Agnarsson and anonymous reviewers for valuable comments and corrections to the manuscript.

Palabras clave: conservación, América Central, delfines, mamíferos marinos, ballenas.

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