Influence of artisanal fisheries on the behaviour and social structure ofTursiops truncatusin the South-western Gulf of Mexico

Abstract

Behavioural plasticity in animals is tested whenever competitive interactions for space and/or food resources occur between wildlife and human activities. This study uses the concepts of operational and non-operational interactions between bottlenose dolphins (Tursiops truncatus) and artisanal fisheries in Alvarado, to search for differences in behaviour, age structure and group size. We conducted 20 surveys between 2015 and 2016, and recorded 64 groups by means of scan sampling from either a research boat or a fixed vantage point. Average dolphin group size was small (${\bar{\rm x}}$ = 3.2, SD = 2.2 individuals) and fewer individuals were commonly present when interaction with fisheries occurred. Operational interactions were defined within the first 30 m and occurred mainly with lone individuals (54% recorded from the lighthouse and 82% during surveys); this benchmark also accounted for higher frequencies in locomotion and feeding (χ2 = 83.10; df = 7; P < 0.001). We found a higher rate of new behavioural events for dolphin groups furthest from human activities, as well as a decrease in behaviours that imply greater body exposure as dolphins approach the fishing spots. Age structure and dolphin group size were not different during and in the absence of interaction with fisheries, but most interactions involved male dolphins. Behavioural variations in the dolphins' repertoire are likely a strategy to reduce the risk of injuries or death when interacting with human activities; these dolphins seem to have habituated to or at least tolerate fishing activities within the study area, possibly constituting a sex-biased pressure.

Population Dynamics Reveal a Core Community of the Common Bottlenose Dolphin (Tursiops truncatus) in Open Waters of the South-Western Gulf of Mexico

“…Higher survival rates for resident individuals were indirectly assumed by Morteo et al (2012b), who showed that these animals interact less frequently with fisheries, when compared to non-residents, thus facing lower exposure to entanglements in fishing gear and retaliation measures by fishers. Therefore, although much lower survival estimates for the visitor fraction is largely based on a high proportion of dolphins permanently leaving the study area shortly after the sampling, it is likely that higher mortality for non-residents is also due to a greater risk of predation by sharks and higher risk of entanglement in fishing gear (Morteo et al, 2012b(Morteo et al, , 2014(Morteo et al, , 2017Rechimont et al, 2018;Morales-Rincón et al, 2019). The latter is supported by reports from recently stranded animals -recorded between 2002 and 2019 (decomposition code 1-3, according to Geraci and Lounsbury, 1993) -showing that fisheries-related injuries only occurred in individuals that had not been previously photographed in the study area (Fuentes Del Muro and Morteo, unpublished data, LabMMar-UV).…”

“…The bottlenose dolphin has been widely documented in some localities in the southern GoM (Ortega Ortiz, 2002;Ortega Ortiz et al, 2004;Ramírez-León et al, 2020), including waters off the Tamiahua Lagoon System (Galindo et al, 2009;Martínez-Serrano et al, 2011;Valdés-Arellanes et al, 2011); Nautla (Morteo et al, 2019); and the Alvarado Lagoon System (ALS) in Veracruz state (Morteo, 2011;Morteo et al, 2012bMorteo et al, , 2014Morteo et al, , 2017Morteo et al, , 2019Morales-Rincón et al, 2019), and some coastal areas in the states of Tabasco, Campeche and Yucatán (Delgado-Estrella, 2015).…”

Seasonal population parameters reveal sex‐related dynamics of common bottlenose dolphins in open waters of the southwestern Gulf of Mexico

“…Temporal patterns and social dynamics of these dolphins show different habitat use and associations between sexes, and the recurrent presence of groups of a single sex within the study area indicate a sexually segregated population, where putative females are more abundant than putative males (Morteo et al, 2014). Documented threats to the species off ALS involve vessel harassment (Morales-Rincon et al, 2019), bycatch, or intentional captures (Morteo et al, 2017) to use dolphin meat as bait for shark fisheries (Ortega-Argueta et al, 2005) and, until the year 2000, live captures for display in oceanaria (Alaniz Pasini & Rojas Ortega, 2007). Interactions between dolphins and local fishers are antagonistic due to routine depredation of catches directly from fishing gear, which causes economic loss to the local, artisanal fishery (Rechimont et al, 2018).…”

“…Documented threats to the species off ALS involve vessel harassment (Morales‐Rincon et al, 2019), bycatch, or intentional captures (Morteo et al, 2017) to use dolphin meat as bait for shark fisheries (Ortega‐Argueta et al, 2005) and, until the year 2000, live captures for display in oceanaria (Alaniz Pasini & Rojas Ortega, 2007). Interactions between dolphins and local fishers are antagonistic due to routine depredation of catches directly from fishing gear, which causes economic loss to the local, artisanal fishery (Rechimont et al, 2018).…”

“…Bottlenose dolphins inhabiting these coastal waters have been studied intermittently since 1993 (García Loredo, 1995;Medellín Ortiz, 2012;Morales-Rincon et al, 2019;Morteo, 2011;Morteo et al, 2014Morteo et al, , 2017Rechimont et al, 2018), mostly based on short-term data sets (≤2 years). These studies found that some dolphins can travel up to 300 km towards the Veracruz System National Park and Nautla, to the northwest (Morteo et al, 2017(Morteo et al, , 2019; however, about 30% of the dolphins show high site fidelity and long-term residency (Morteo et al, 2017).…”