Spatial analysis of marine litter and resident cetaceans of the archipelago of Madeira.
Supervisor: Luis Freitas (Madeira Whale Museum)
Nowadays, important pressures are applied on the marine environment mainly because of humanactivities. An interest about those threats and their impact on marine life arose in the past few years andnew studies emerge every year with the aim of creating a better management of those threats. Thearchipelago of Madeira, small islands of the Central North East Atlantic, is not spared by those pressuresand one of the biggest worries is the impact of those pressures on resident cetaceans. One of the pressureswhich is especially concerning nowadays is marine litter, it is present all around the world and evidenceof its impact is growing rapidly. Systematic surveys were made around the Madeira archipelago fordifferent periods. A total of 4 175 km, 8 742 km and 4 062 km of effort were done in 2001-2002, 2007-2012 and 2017-2018, respectively. Sightings of marine litter together with sightings of cetaceans werecollected throughout those periods and were analyzed using distance sampling and spatial modelling.Over 1 751 sightings of marine litter were recorded during those three periods and the abundance anddistribution of seven types of debris was estimated for 2001-2002 and 2007-2012 (e.g. plastic bags,wood, other items, other plastics, buoy, glass bottles and fishing gear) and eight types for 2017-2018(i.e. adding plastic bottles) and their distribution was modelled with respect to environmental covariates.Here we show that there were significant differences of abundance between the periods, and the fittingof GAMs (generalized additive models) allowed us to estimate the distribution of abundance of certaintypes of debris in Madeira archipelago coastal waters. Moreover, GAMs were also used to unveilpotential relationships between the distribution of two resident species of cetaceans in Madeira coastalwaters and the distribution of marine litter types, using the latter as covariates. Although no direct andclear relationships were found, there were still evidence of some overlap between the main areas ofdistribution of these species and areas of higher predicted abundance of marine debris, thus withincreased risk of interactions. This type of study can help understand the evolution and dynamics ofmarine litter in Madeira archipelago and insular environments, raise awareness about the threat that litterrepresents to marine life and trigger extra effort to monitor and promote management actions in thearchipelago to reduce the input of litter to the marine environment and as a consequence the risks tomarine life, including, cetaceans.