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MARE - Marine and Environmental Sciences Centre

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Temperature and food-mediated variability of European Atlantic sardine recruitment
Publication . Garrido, Susana; Silva, Alexandra; Marques, Vitor; Figueiredo, Ivone; Bryere, Philippe; Mangin, Antoine; Santos, A. Miguel P.
The influence of the environmental conditions during larval development on the resulting recruitment strength was investigated for European sardine (Sardina pilchardus) at Atlanto-Iberian waters. Satellite-derived Sea Surface Temperature (SST) and Chlorophyll-a concentration (Chla) data from the previous spawning seasons (January to March/April and October to December of the previous year) were related to recruitment success data in the main recruitment hotspots. Recruitment data was taken from yearly acoustic scientific cruises and from the ICES recruitment index estimated by an age-structured model for the entire stock. A linear discriminant analysis model using SST, Chla, and the abundance of spawners during the spawning season identified years of high and low recruitment for all the recruitment hotspots with an accuracy of >= 79%. In general, high recruitment years were associated with high Chla and low SST, although the most important variables to discriminate between the groups were area-specific. High recruitment years were mostly related to high food availability (Chla), particularly during the last quarter of the previous year. In Western Iberia and in the Gulf of Cadiz, high recruitment years were also associated to lower SST, whereas in the Bay of Biscay, where SST during the winter was generally below the optimal range approximate to 11-12 degrees C for sardine larval development, higher recruitment was associated with high SST. For ICES data of the southern European sardine stock, lower SST and higher Chla during the last quarter of the previous year were associated with high recruitment years and SST alone was able to discriminate between the two recruitment groups with 73% accuracy. Although the time-series of available data are still small, these significant relationships are consistent with field and laboratory studies relating larval growth and mortality with main environmental drivers. These relationships should be further investigated in the following years to evaluate if they can be used to construct reliable indicators to predict the level of recruitment and abundance with sufficient advance to help in the management of this important fishing resource.
Size-based differences in isotopic niche width (delta C-13 and delta N-15) of green turtles (Chelonia mydas) nesting on Principe Island, Gulf of Guinea
Publication . Ferreira, Rogério L.; Ceia, Filipe R.; Borges, Teresa C.; Ramos, Jaime A.; Bolten, Alan B.
Within the same population, nesting green turtles (Chelonia mydas) might exploit different niches by exhibiting polymorphic foraging strategies and/or inhabiting geographically distinct foraging areas. This is crucial information for the conservation of this species. Here, we used stable carbon and nitrogen isotope ratios (delta C-13 and delta N-15) to test for differences in a population of green turtles nesting on Principe Island (1 degrees 37 ' N; 7 degrees 24'E), Central Africa. A total of 60 nesting females were sampled on the two main nesting beaches of the island in December 2012. Minimum curved carapace length (CCL) was recorded, and delta C-13 and delta N-15 values were measured in the epidermis of each individual. Overall, CCL varied from 87.0 to 108.0 cm (mean +/- SD =100.0 +/- 5.1), delta C-13 values from -19.4 to -8.6 parts per thousand (-17.3 +/- 1.8) and delta N-15 values from 7.9 to 17.3 parts per thousand (13.6 +/- 1.5). Despite the large variation in both isotopic ratios, their distributions were unimodal, showing an absence of polymorphic foraging strategies and isotopically distinct foraging areas. However, smaller females (< median, 100.8 cm) occupied a much larger isotopic niche (i.e., four times greater) than larger females. These results suggest that nesting green turtles may forage opportunistically on the resources available in each of their foraging home ranges, with smaller females venturing to more isotopic-diversified areas and/or exhibiting broader foraging strategies than larger females. In addition, and in accordance with other studies, findings suggest that the foraging grounds used by the Principe green turtle nesting females are distributed mainly throughout the Gulf of Guinea.
Intra- and interspecific associations in two predatory reef fishes at a shallow seamount
Publication . Gandra, Miguel; Afonso, Pedro; Fontes, Jorge
the spatial dynamics of marine populations are shaped by habitat availability, environmental variability and individual interactions, particularly when multiple species share limited habitat such as patchy offshore reefs. the yellowmouth barracuda Sphyraena viridensis and the almaco jack Seriola rivoliana are the 2 most abundant bentho-pelagic reef predators in the Azores archipelago (central North Atlantic). They aggregate at shallow offshore seamounts, and largely share diet preferences, but very little is known about how habitat and resources are shared by these predators intra- and inter-specifically. Here we use long-term (over 3 yr) passive acoustic telemetry to investigate the patterns of activity, space use and associative behaviour at an isolated, small shallow seamount. By quantifying fine-scale spatiotemporal overlaps and performing null model randomization tests, we found evidence of non-random associations, mostly between conspecifics of both species, as well as shifts in diel and seasonal patterns of space occupancy. Both species were detected more often during spring, and appear to be more active during daytime, suggesting the absence of fine-scale temporal habitat partitioning. Additionally, we found evidence of size-dependent spatial behaviour in almaco jack, with similarly sized individuals co-occurring more often and larger specimens being more infrequently detected. This study quantitatively assesses individual associations using solely presence-absence data collected through passive acoustic telemetry, showing the potential of this approach in a broader application to a significant number of past and ongoing studies, even if many were not originally designed to study this important aspect of fish ecology.
Portuguese purse seine fishery spatial and resource overlap with top predators
Publication . Wise, Laura; Galego, Catarina; Katara, Isidora; Marçalo, Ana; Meirinho, Ana; Monteiro, Silvia S.; Oliveira, Nuno; Santos, Jorge; Rodrigues, Pedro; Araujo, Helder; Vingada, Jose; Silva, Alexandra
The Portuguese purse seine fishery, with average annual catches of 70 000 tonnes, operates mainly in coastal areas and targets small pelagic fish (SPF). Potential competition for resources may occur between the fishery and some species of marine mammals and seabirds, as suggested by observed incidental catches. For those species directly affected by the fishery, the spatial distribution of marine taxa and the fishing fleet are key pieces of information for spatial planning and management. We analysed the spatial and resource overlap between the fishery's distribution and effort, and the distribution and abundance of 6 species of top predators -seabirds (n = 4) and marine mammals (n = 2) between 2010 and 2014. Estimates of annual consumption by top predators and the fishery catch within the distributional range of one of their main prey species (sardine Sardina pilchardus) were also determined. Spatial overlap between all considered species and the fishery was low (<0.221), and only 2 species (common dolphins Delphinus delphis and Cory's shearwaters Calonectris borealis) showed high resource overlap with the fishery (>0.7). Overall, values of consumption of SPF by the top predators were of the same order of magnitude as mean annual purse seine landings for the studied area. Our results can be used for marine spatial planning, including designation of Marine Protected Areas and the development of an ecosystem-based model for the effective management of the Portuguese purse seine fishery that takes into account the consumption of natural predators.

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Funding agency

Fundação para a Ciência e a Tecnologia

Funding programme

6817 - DCRRNI ID

Funding Award Number

UID/MAR/04292/2013

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