Assessment of Harbour Porpoise Bycatch along the Portuguese and Galician Coast: Insights from Strandings over Two Decades.

The Iberian harbour porpoise population is small and fisheries bycatch has been described as one of its most important threats. Data on harbour porpoise strandings collected by the Portuguese and Galician stranding networks between 2000 and 2020 are indicative of a recent mortality increase in the western Iberian coast (particularly in northern Portugal). Overall, in Portugal and Galicia, individuals stranded due to confirmed fishery interaction represented 46.98% of all analysed porpoises, and individuals stranded due to probable fishery interaction represented another 10.99% of all analysed porpoises. Considering the Portuguese annual abundance estimates available between 2011 and 2015, it was possible to calculate that an annual average of 207 individuals was removed from the population in Portuguese waters alone, which largely surpasses the potential biological removal (PBR) estimates (22 porpoises, CI: 12-43) for the same period. These results are conservative and bycatch values from strandings are likely underestimated. A structured action plan accounting for new activities at sea is needed to limit the Iberian porpoise population decline. Meanwhile, there is an urgent need for a fishing effort reorganization to directly decrease porpoise mortality.

Harbour Porpoise Abundance in Portugal over a 5-Year Period and Estimates of Potential Distribution.

The Iberian porpoise population is small and under potentially unsustainable removal by fisheries bycatch. Recently, a marine Site of Community Importance (SCI) was legally approved in Portugal, but no measures ensued to promote porpoise conservation. Information about porpoise abundance and distribution is fundamental to guide any future conservation measures. Annual aerial surveys conducted between 2011 and 2015 show a low overall porpoise abundance and density (2254 individuals; 0.090 ind/km2, CV = 21.99%) in the Portuguese coast. The highest annual porpoise estimates were registered in 2013 (3207 individuals, 0.128 ind/km2), followed by a sharp decrease in 2014 (1653 individuals, 0.066 ind/km2). The porpoise density and abundance estimated in 2015 remained lower than the 2013 estimates. A potential distribution analysis of the Iberian porpoise population was performed using ensembles of small models (ESMs) with MaxEnt and showed that the overall habitat suitability is particularly high in the Portuguese northern area. The analysis also suggested a different pattern in porpoise potential distribution across the study period. These results emphasize the importance of further porpoise population assessments to fully understand the spatial and temporal porpoise habitat use in the Iberian Peninsula as well as the urgent need for on-site threat mitigation measures.

Floating marine litter and their risks to cetaceans off Portugal.

Floating Dangerous Debris For Cetaceans (DDFC) and cetacean abundances were assessed by shipboard visual surveys off continental Portugal. Plastic litter (other than fishing gear) was the most abundant category, corresponding to 56.53% of the total recorded DDFC. Areas of DDFC and cetacean potential overlap suggest that cetaceans are generally exposed to DDFC at different risk levels within the study area. The highest concentration areas of DDFC and cetaceans did not overlap, whereas lower DDFC concentration areas (70% kernel probability contour) overlapped with 45% of the distribution area obtained for cetaceans. Future marine litter management measures (prevention or mitigation) should be focused on the predicted high DDFC-cetacean interaction risk area in the central region of the study. DDFC are representative of the overall floating litter distribution and future floating litter assessments could be based on DDFC categories alone.

Striped dolphins as trace element biomonitoring tools in oceanic waters: Accounting for health-related variables.

In Europe, monitoring contaminant concentrations and their effects in the marine environment is required under the Marine Strategy Framework Directive (MSFD, 2008/56/EC). The striped dolphin (Stenella coeruleoalba) is the most abundant small cetacean species in Portuguese oceanic waters, representing a potential biomonitoring tool of contaminant levels in offshore waters. Concentrations of nine trace elements were evaluated by ICP-MS in kidney, liver and muscle samples of 31 striped dolphins stranded in the Portuguese continental coast. The mean renal Cd concentration was high (19.3 µg.g-1 wet weight, range 0.1-69.3 µg.g-1 wet weight) comparing to striped dolphins from other locations. Therefore, the present study reports a possibly concerning level of Cd in the oceanic food chain in Portuguese offshore areas. This study also aimed at evaluating potential relationships between trace element concentrations and striped dolphins' biological and health-related variables. Individual length was related with some of the trace element concentrations detected in striped dolphins. Indeed, Cd, Hg and Se bioaccumulated in larger animals, whereas the reverse was observed for Mn and Zn. Striped dolphins with high parasite burdens showed higher levels of Hg, while animals showing gross pathologies presented higher concentrations of Cd and Se. This study reported relationships between trace element concentrations and health-related variables for the first time in striped dolphins and it also provided information on the relative contamination status of Portuguese oceanic waters in comparison to other regions in the world.

Bioaccumulation of trace element concentrations in common dolphins (Delphinus delphis) from Portugal.

The common dolphin (Delphinus delphis) is one of the most abundant species in Atlantic Iberia, representing a potentially important tool to assess the bioaccumulation of trace elements in the Iberian marine ecosystem. Nine elements (As, Cd, Cu, Hg, Mn, Ni, Pb, Se and Zn) were evaluated in 36 dolphins stranded in continental Portugal. Dolphins had increasing Hg concentrations (16.72µg·g-1 ww, liver) compared with previous studies in Atlantic Iberia, whereas Cd concentrations (2.26µg·g-1 ww, kidney) fell within reported ranges. The concentrations of some trace elements (including Cd and Hg) presented positive relationships with dolphin length, presence of parasites and gross pathologies. Common dolphins may help biomonitoring more offshore Atlantic Iberian areas in future studies, which would otherwise be difficult to assess.

Spatial distribution of floating marine debris in offshore continental Portuguese waters.

This study presents data on abundance and density of macro-floating marine debris (FMD), including their composition, spatial distribution and potential sources off continental Portugal. FMD were assessed by shipboard visual surveys covering ±252,833 km(2) until the 220 nm limit. The FMD average density was 2.98 items/km(2) and abundance amounted to 752,740 items. Unidentified plastics constitute the major bulk of FMD (density=0.46 items/km(2); abundance=117,390 items), followed by styrofoam, derelict or lost materials from fisheries, paper/cardboard and wood material. The North sector of the area presents higher FMD diversity and abundances, probably as a result of the high number of navigation corridors and fisheries operating in that sector. Most FMD originate from local sources, namely discharges from vessels and derelict material from fisheries. Considering the identifiable items, cables and fishing lines were the only fishing related items among the top ten FMD items in Portuguese offshore waters.