Beach-cast small cetaceans bear evidence of continued catches and utilisation in coastal Peru, 2000-2017
Koen Van Waerebeek, Manuel Apaza, Julio C. Reyes, Joanna Alfaro-Shigueto, Luis Santillan, Elena Barreda, Ali Altamirano-Sierra, Jose Astohuaman-Uribe, Clara Ortiz-Alvarez, Jeffrey Mangel
International Whaling Commission
Considering minimal direct monitoring of cetacean takes in most of South America, strandings data may serve as an useful proxy for removal levels, as the majority of beach-cast small cetaceans near fishing towns are thought to be fisheries related. A total of 942 specimens (873 identified) tallied via mostly opportunistic beachcombing efforts along the Peruvian coast in the period 2000-2017 included 8 species (% of ID-only): Phocoena spinipinnis (66.3 %), Lagenorhynchus obscurus (14.9 %), 2 Delphinus spp. (10.1 %), Tursiops truncatus (8.5%), Grampus griseus (0.11 %) Kogia sima (0.11%), Mesoplodon peruvianus (0.11%). Pair-wise comparisons between the northern, central and southern regions revealed significant geographic variation in species prevalences for 10 of 12 sample pairs, but little variation for T. truncatus. The overwhelming prevalence of P. spinipinnis, especially in southern and south-central Peru, was at odds with pre-2000 data of L. obscurus as the predominant species among cetacean takes. On the central coast, L. obscurus prevalence declined significantly from 77.5% (1985-1990) to 52.8% (1991-1993) in large samples (thousands) to a present low of 25.4%. Renewed concern is expressed for its conservation status. Uniquely, along the metropolitan Lima coastline, the boat-shy Burmeister's porpoise was rarely found (6.4%), possibly due to high disturbance from intense boat traffic. The Tacna coast, southern Peru, has sparse human population and limited nearshore boat traffic, but extensive gillnets deployed from shore (redes de corriente) extending up to 1-1.5 km. At Ite, Tacna, P. spinipinnis represented 76.4% of beach cast small cetaceans. At Wakama (Lima), stranding seasonality of L. obscurus (winter highs, summer lows) was consistent with the seasonality from historical catch statistics. A minimum incidence of human interaction (bycatch, intentional take, utilisation) of 58.5 % (n=41) determined at Chilca Playa is an underestimate as decomposition likely erased forensic evidence in a number of specimens. Our results demonstrated the relevance of even small-scale, opportunistic beachcombing efforts, at least until a nation-wide strandings network can be established. Enhanced by standardized protocols, continued dedicated surveying along Peru's coastline is recommended, as to provide improved estimates of human interaction and species/age/sex prevalences, compare stranding densities and collect selected data, samples and voucher specimens for natural history studies. Comprehensive records of base-line cetacean mortality levels may help calibrate future unusual (mass) mortality events. Long-term datasets may contribute to the formulation of conservation and management measures.