Both the conservation status of bottlenose dolphins (Tursiops truncatus) (Habitats Directive 92/43/CEE, Annex II) and the Marine Strategy Framework Directive demand for data on their ecology and ...anthropogenic threats. To evaluate the bottlenose dolphin's toxicological status in continental Portugal, several trace elements (As, Cd, Cu, Hg, Mn, Ni, Pb, Se, Zn) were determined in 25 stranded individuals. The potential effect of sex, body length and stranding location on trace element concentrations was analysed. In the present study, bottlenose dolphins presented high mercury levels, only exceeded by animals from the Mediterranean and Adriatic seas. Only essential elements were influenced by dolphin sex, whereas Cd, Hg and Pb bioaccumulated in larger dolphins, and hepatic Hg and Cd concentrations were higher in the northwest coast of continental Portugal. The location effect may relate to variations in bottlenose diet and trace element availability, according to the proximity to anthropogenic sources in the Atlantic Iberian coast.
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•High levels of mercury in bottlenose dolphins from Portugal.•Mercury only exceeded by levels reported in the Mediterranean and the Adriatic.•Evidence of bioaccumulation of several trace elements.•Essential trace elements were influenced by sex of bottlenose dolphins.•Evidence of stranding location effect on trace element levels.
The striped dolphin, Stenella coeruleoalba, is one of the most abundant cetacean species off the Western Iberian coast, however, studies on the species regarding biology, ecology, threats or ...conservation efforts are lacking. This study investigates stranding patterns (years 1981–2014) and diet (2002–2014) of striped dolphins (Stenella coeruleoalba) off the Portuguese mainland coast. Stranded animals were sampled along the whole coast (n = 252). Most stranded striped dolphins were recorded in the first half of the year and strandings increased over time. Analysis of stomach contents (n = 36) showed that striped dolphins in the area are mostly piscivorous (80% by number and weight of the diet), taking pelagic, meso-pelagic and demersal species. In terms of reconstructed biomass prey, sardine (Sardina pilchardus) and blue whiting (Micromesistius poutassou) were the most important. Prey items revealed that both sexes forage at a range of depths (pelagic and demersal systems) in both neritic and oceanic habitats, although females feed more often in coastal waters. Moreover, diet results also indicate that striped dolphins may co-occur with other neritic cetacean species, such as the common dolphin, Delphinus delphis, thus sharing some preferred prey species. The study revealed that striped dolphins on the Iberian coast interact with coastal fisheries sharing the same target species. Management measures for fisheries will need to be consistent with an ecosystem-based approach.
Pollution is among the most significant threats that endanger sea turtles worldwide. Waters off the Portuguese mainland are acknowledged as important feeding grounds for juvenile loggerheads. ...However, there is no data on trace element concentrations in marine turtles occurring in these waters. We present the first assessment of trace element concentrations in loggerhead turtles (Caretta caretta) occurring off the coast of mainland Portugal. Also, we compare our results with those from other areas and discuss parameters that may affect element concentrations. Trace element concentrations (As, Cd, Cu, Pb, Mn, Hg, Ni, Se, Zn) were determined in kidney, liver and muscle samples from 38 loggerheads stranded between 2011 and 2013. As was the only element with higher concentrations in muscle (14.78 μg g−1 ww) than in liver or kidney. Considering non-essential elements, Cd presented the highest concentrations in kidney (34.67 μg g−1) and liver (5.03 μg g−1). Only a weak positive link was found between renal Cd and turtle size. Inter-elemental correlations were observed in both liver and kidney tissues. Hepatic Hg values (0.30 ± 0.03 μg g−1) were higher than values reported in loggerheads in the Canary Islands but lower than in Mediterranean loggerheads. Cd concentrations in the present study were only exceeded by values found in turtles from the Pacific. Although many endogenous and exogenous parameters related with complex life cycle changes and wide geographic range may influence trace element accumulation, the concentrations of Cd are probably related to the importance of crustaceans in loggerhead diet in the Portuguese coast.
•High levels of cadmium in loggerheads stranded in mainland Portugal.•Evidence of bioaccumulation of renal cadmium.•Cadmium-Zinc correlations were observed in liver and kidney tissues.•The 3 largest loggerheads showed lower Cd concentrations than smaller turtles.
The present study is a detailed analysis of sea turtle strandings over a 36-year period (1978–2013) along the Portuguese mainland coast. Out of the 806 stranded individuals, the loggerhead turtle ...Caretta caretta was the most frequent species (57.1 %) followed by the leatherback turtle Dermochelys coriacea (41.8 %), while green turtles Chelonia mydas and Kemp’s Ridley turtles Lepidochelys kempii were rare (respectively 1.0 and 0.1 %). Relative stranding densities of loggerheads showed an increase through time, whereas two leatherback stranding peaks were detected during the years 1994–1998 and 2009–2013. The highest loggerhead stranding density was observed on the southern coast during spring and summer when they are more susceptible to anthropogenic threats. The highest number of leatherback strandings was observed in the North-Central and Central-South western sectors during autumn and in the southern sector during summer, which may relate to seasonal food availability and water temperature considering those stranded animals that were subject to a post-mortem evaluation interaction with fisheries as the primary cause of stranding. Results show for the first time that waters off the Portuguese mainland coast is an important pathway for loggerheads and leatherbacks in the North Atlantic region. The present study serves as important baseline to the development of future sea turtle conservation efforts in the Portuguese mainland coast.
Interactions between cetaceans and the purse-seine fishery operating along the whole Portuguese continental coast were studied based on on-board observations from 2010 to 2011. Cetacean presence and ...mortality were estimated and characteristics under which interactions were most likely to occur were identified. Observations were made on 163 fishing trips (0.7% of the average annual number of fishing trips) and 302 fishing operations/hauls. Cetaceans were present during 16.9% of fishing events; common dolphins (Delphinus delphis) accounted for 96% of occurrences, mostly overnight in summer and early autumn. Regression models showed that cetacean presence during a fishing set was significantly (p < 0.05) associated with sardine catches, effort, and latitude/longitude. Encirclement and mortality occurred in 2.3 and 1.0% of fishing events, respectively. Encircled species were the common dolphin, bottlenose dolphin (Tursiops truncatus), and harbour porpoise (Phocoena phocoena), but only common dolphin showed mortality (three individuals); raised to fleet level, estimated total mortality rates of common dolphins were 69 (95% CI 37-110) in the north and 91 (95% CI 55-165) in the south for 2010 and 78 (95% CI 47-140) in the south only for 2011. The estimated annual mortality rate due to purse seining is 113 (95% CI 3-264) common dolphins, which is 0.63% of the current most optimistic estimate of population size for the Portuguese fishing area (SCANS II). The wide confidence limits, as well as variation between years, reflect low observer coverage, emphasizing the need for increased monitoring to cover gaps in the spatial and seasonal distribution of observer effort and provide reliable estimates of bycatch.
The Mediterranean subpopulation of common dolphin (Delphinus delphis) is classified as endangered by the IUCN. Still, information about their diet in the Mediterranean is scarce. Stomach contents of ...37 common dolphins stranded in the Alboran Sea and Strait of Gibraltar were analyzed. A total of 13,634 individual prey of 28 different taxa were identified. For fish, Myctophidae was the most important family as indicated by the highest index of relative importance (IRI = 8,470), followed by the family Sparidae (IRI = 609). The most important Myctophidae species was Madeira lantern fish (Ceratoscopelus maderensis) and for Sparids, the bogue (Boops boops). Cephalopods, instead, were found in low quantities only with 31 prey from the Loliginidae, Ommastrephidae, and Sepiolidae families. Overall, our results indicate that common dolphins are mainly piscivorous (99.77%N, 94.59%O, 99.73%W), feeding mostly on mesopelagic prey. Although common dolphins inhabit mainly coastal waters in the study area, the narrow continental shelf seems to facilitate the availability of Myctophids and other members of the mesopelagic assemblage to dolphins when the assemblage migrates to the surface at night. Our results represent the first attempt at quantifying the diet of this predator in the Alboran Sea and Strait of Gibraltar.
Competition with fisheries and incidental capture in fishing gear are the major current threats for seabirds at sea. Fishing is a traditional activity in Portugal and is mainly composed of a great ...number of small vessels. Given the lack of knowledge on effects of the Portuguese fishing fleet on seabird populations, bycatch was assessed in mainland coastal waters for 2010–2012. Interviews and on-board data were divided into 5 strata, according to fishing gear: Bottom trawling, Bottom longline, Purse seine, Beach seine, Polyvalent (≥12 m) and Polyvalent (<12 m). Polyvalent included Setnets, Traps and Demersal longlines. Overall, 68 birds were recorded to be bycaught. The average catch per unit effort (CPUE) was 0.05 birds per fishing event. Polyvalent (<12 m), Polyvalent (≥12 m) and Purse seiners had the biggest seabird bycatch rates, with 0.5 (CPUE=0.1), 0.11 (CPUE=0.05) and 0.2 (CPUE=0.11) birds per trip, respectively. Within Polyvalent gear, Setnets captured the largest diversity of seabird species (CPUE=0.06), while Demersal longline had the highest CPUE (0.86). Northern gannet was the most common bycaught species. Although more observation effort is required, our results suggest that substantial numbers of Balearic shearwater might be bycaught annually, mainly in Purse seine and Setnets.
Laboratory experiments were conducted to study the effects of different prey types and concentrations on the feeding behaviour of the Iberian sardine Sardina pilchardus. Known concentrations of ...different prey types (both single prey type and a mixture of prey types) were provided to a shoal of sardines acclimated to laboratory conditions and their feeding behaviour was observed. Data on feeding mode choice, feeding selectivity and filtration efficiency were collected, and clearance rates for different prey types and sizes were estimated. Sardines use 2 feeding modes and switch between them depending on prey size. Filter-feeding was used to capture prey <724 mu m and particulate feeding to capture prey greater than or equal to 780 mu m; therefore the feeding mode switch occurs within these limits. Sardines are able to feed on nanoplankton and can retain prey items as small as 4 mu m, and filtration efficiency increases from 20% at this prey size to close to maximum for prey >200 mu m. Sardines show selective feeding, preferentially ingesting fish eggs compared to other prey types (even larger fish larvae) when fed cultured, mixed prey assemblages and selecting copepods and decapods over other zooplankton prey when fed wild- collected, mixed prey assemblages. Clearance rates were generally low compared to other clupeids, arising from the smaller mouth gape and lower swimming speed of this species. Results obtained from this study suggest that filter-feeding is the dominant feeding mode of S. pilchardus and that it is able to efficiently utilize microplankton prey, and corroborate previous dietary studies indicating that small zooplankton and chain-forming diatoms dominated stomach contents.
Common dolphins (Delphinus delphis) are top predators, feeding on a wide variety of prey species, several of which are also targeted by fisheries. The last remaining healthy group of the endangered ...Mediterranean common dolphin subpopulation is located in the Alboran Sea. Their feeding grounds overlap with the fishing grounds of trawlers targeting European hake (Merluccius merluccius) and blue whiting (Micromessistius poutassou) as well as purse seiners targeting small pelagic species such as European sardine (Sardina pilchardus), European anchovy (Engraulis encrasicolus), horse mackerel (Trachurus spp.) and mackerel (Scomber spp.). In the present study, we estimated that individual common dolphins in the Alboran Sea have a food consumption of 3.35 ± 0.67 kg/day, based on scaling equations applied to stranded animals. This figure is similar to the ones reported for other European populations. Although common dolphins mainly feed on mesopelagic species of none or little commercial interest, they also feed on commercial species, which could lead to a potential conflict with fisheries in the area. We estimated common dolphins in the Alboran Sea could consume more than 16,000 tonnes of fish annually, including ca 7365 (95% CI: 3838–11,639) tonnes of Madeira lanternfish (Ceratoscopelus maderensis), 2,888 (1123–5223) tonnes of bogue (Boops boops), 2770 (879–5270) tonnes of European sardine, 1,850 (170–4116) tonnes of gobies (Gobiidae), and 1497 (65–3352) tonnes of European hake (reference period 2006-2011). Estimated sardine, anchovy and blue whiting consumption was low when compared to the landings in the area, however estimated hake consumption was above the reported hake landings in recent years (393.4 ± 146 tonnes landed annually between 2006 and 2011). Additionally, direct interactions between common dolphins and main fisheries were evaluated in a total of 111 observed fishing trips (70 in trawlers and 41 in purse seiners) in the area. Although no bycatch of common dolphin was recorded, non-lethal interactions between dolphins and the fishing activity were detected from observations of this on-board observer program. These interactions, together with the high prevalence of stranding with signs of fishing interactions from the study area, may imply an additional threat to this endangered cetacean subpopulation.
In Portugal mainland, the purse seine fishery is one of the most important fisheries, accounting for about 50% by weight of landings. At present, these fleets mainly target sardine (Sardina ...pilchardus) and chub mackerel (Scomber colias). This work aimed to study the Portuguese purse seine fleet activity (vessel length>16m) and catch composition using onboard observations from 2009 to 2013. Data were collected during 179 trips and 229 fishing sets. Short trips (mean 9.38 h) with one to two sets (duration time 1.39 h/set) were observed, where most of the trip was dedicated to searching (43.7% of total trip duration) and fishing (23.5%). Fishing time depended of the number of sets and search time, which increased due to the growing scarcity of fish and distance to and from fishing grounds to the homeport. S. colias was the main species captured followed by S. pilchardus, although there were an inverse trend in the two species landings. Other pelagic species such as horse mackerel (Trachurus trachurus), Atlantic mackerel (S. scombrus), blue jack mackerel (T. picturatus) and anchovy (Engraulis encrasicolus) were also caught but represented small volumes of the catch. The average capture and landings observed were 4.47 (±S.D. 7.64) and 3.19 (±S.D. 4.46) tons per set. Capture and landings were both higher in the North, intermediate in the South and lower in the Centre. Differences between fish captured and fish landed are due to slipping. Slipping was more frequent in the North, mainly because of the implementation of daily limit quotas. In the South, usually was the result of the mixture of S. pilchardus with non-commercial species that would decrease its landing price. Throughout the study period, S. pilchardus landings peaked of 64 000 ton in 2008, decreased 20% until 2011 and dropped sharply after 2012. Landing patterns of S. colias, the second most important species, have been inverse, increasing continuously since 2009. On the overall, the decline of S. pilchardus landings has been compensated by increasing capture and landings of S. colias along the country.
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