Flatfish (Pleuronectiformes) species richness and depth distribution in the Gulf of Nicoya, Golfo Dulce, and two adjacent areas on the Pacific coast of Costa Rica

Introduction: Information on the number of flatfish species and their depth distributions is scarce for the Eastern Tropical Pacific. Historical data is important to evaluate changes in ecosystems due to local, regional and global stressors. Objective: To provide information on the presence. depth distributions and lengths of flatfish species collected by trawl nets. Methods: Fish studies were conducted by trawling at four sites along the Pacific coast of Costa Rica by the survey vessels Skimmer (1979-1980), Nishin Maru (1987-1988) and Victor Hensen (1993-1994). The published lists of species were consulted, museum specimens were accessed, and an updated list of flatfish species assembled. Results: A total of 36 species were found over a depth range of 8-359 in. The family Paralichthyidae included 13 species followed by the Cynoglossidae with 12 species. Achiridae with six and Bothidae with five. Thirty-five species were collected at depths from 10-235 m in the Gulf of Nicoya and Golfo Duke. Monolene asadeae was collected oll'shore at a depth range of 254-359 m. The Gulf of Nicoya estuary yielded 27 species during the Skimmer expedition over a depth range of 8-60 m, while 31 species were found during the V. Hensen survey at depths from 10-228 m. The V. Hensen survey in Golfo Dulce (20-235 m) collected 19 species, and 17 species in Coronado Bay (21-187 in). Off the Nicoya Peninsula (56-359 in) 13 species were collected by the Nishin Mani shrimp trawler. Atotal of 21 species (58 %) were found at depths greater than 100 m which were probably exposed to low oxygen concentrations. During the V. Hensel) survey Symphurus chabanaudi and S. elongates were collected more frequently in the Gulf of Nicoya, while S. leei was collected more frequently in Golfo Dulce. Cluster analyses based on presence-absence data for the Gulf of Nicoya and Golfo Dulce revealed low station similarity indicating possible habitat partitioning among species. The size (Total length) of 33 species measured from both the Gulf of Nicoya and Golfo Dulce ranged from 8 cm (Syacium cf longidorsale, Trinectes xanthurus) to 50 cm (S. ovale). Only 12 species were found with lengths over 20 cm. Data on flatfish landings by the semi-industrial fishing fleet for the period 2000-2016 indicates that this group represents less than 1 % of the total landings (shrimp and bycatch), with a minimum of 365 kg in 2001 and a maximum of 13 414 kg in 2013. Conclusions: The number of flatfish species of the Pacific coast of Costa Rica appears relatively high but comparable to the numbers found in other tropical regions. A reduced fishing impact on the populations together with this updated list of flatfish provide a good baseline for a new survey of lish populations. Both are important for a future updating of the trophic models available the Gulf of Nicoya and Golfo and their use as tools for better management of the ecosystems.