Ocean-scale footprint of a highly mobile fishing fleet: social-ecological drivers of fleet behaviour and evidence of illegal fishing

Managing the footprint of highly mobile fishing fleets is increasingly
important due to continuing declines of fish populations. However,
social-ecological drivers for fisher behaviour remain poorly understood
for many fleets globally. Using the Sri Lankan fleet as a case study, we
explored the role of social, environmental and policy drivers of effort
distribution and illegal fishing. We used semi-structured interviews and
participatory mapping with 95 fishers, combined with explanatory modelling
(Generalised Linear Models, GLM) and multivariate statistics, including
Principal Component Analysis (PCA). Our findings highlight broad footprint
(~3,800,000 km2) of this fleet, with fishing effort expended in high seas
(53.9%), domestic (40.9%) and, illegally, in foreign waters (5.2%). 26% of
fishers directly admitted to fishing illegally in foreign waters during
interviews, whereas 62% of fishers indicated doing so during participatory
mapping. GLMs explained underlying decisions of where to fish (36% of the
total deviance in effort distribution) as a function of social variables
(14%), notable distance from landing sites (13%), and environmental
variables (11%), notably Sea Surface Temperature (10%). Multivariate
analysis revealed that individual fisher characteristics associated with
illegal fishing, such as a level of reliance on sharks, vary across the
fleet. Analysis of qualitative data suggested that the influence of
interpersonal and community social networks and perceptions of higher
catch value, particularly of sharks, may be important. Our approach
demonstrates the utility of mixed methods research, including the
collection of qualitative data, for creating a detailed understanding of
spatial behaviour, including decisions of whether to fish illegally.
Results highlight the importance of adopting a social-ecological lens to
investigate drivers for human behaviour, and non-compliance with rules. We
advocate for a nuanced approach to monitoring and managing of fleets,
including investigating localised social drivers for illegal fishing and
enhancing regional transparency in fleet monitoring.