scholarly journals Identifying key habitat and seasonal patterns of a critically endangered population of killer whales

2013 ◽  
Vol 94 (6) ◽  
pp. 1317-1325 ◽  
Author(s):  
Ruth Esteban ◽  
Philippe Verborgh ◽  
Pauline Gauffier ◽  
Joan Giménez ◽  
Isabel Afán ◽  
...  
Keyword(s):  
Generalized Additive Models ◽  
Bluefin Tuna ◽  
Additive Models ◽  
Killer Whales ◽  
Gulf Of Cadiz ◽  
Strait Of Gibraltar ◽  
Cetacean Species ◽  
Atlantic Bluefin Tuna ◽  
Presence Data ◽  
Gulf Of Cádiz

Killer whales have been described in the Gulf of Cadiz, southern Spain, in spring and in the Strait of Gibraltar in summer. A total of 11,276 cetaceans sightings coming from different sources (dedicated research surveys, whale watching companies and opportunistic observations) were used to create two presence–‘pseudo-absence’ predictive generalized additive models (GAM), where presence data were defined as sightings of killer whales and ‘pseudo-absence’ data as sightings of other cetacean species. One model was created using spring data when killer whales’ main prey, Atlantic bluefin tuna, enter the Mediterranean Sea, and the other model used summer data when Atlantic bluefin tuna return to the Atlantic Ocean. Both model predictions show that killer whales are highly associated with a probable distribution of bluefin tuna during their migration throughout the study area, constraining their distribution to the Gulf of Cadiz in spring and the Strait of Gibraltar in spring and summer. Knowledge of the distribution of killer whales in the study area is essential to establish conservation measures for this population.

First record of Norwegian killer whales attacking and feeding on a harbour porpoise

2015 ◽  
Vol 8 ◽  
Author(s):  
A. Mel Cosentino
Keyword(s):  
North Atlantic ◽  
Marine Mammals ◽  
First Record ◽  
Harbour Porpoise ◽  
Sperm Whales ◽  
Killer Whales ◽  
Strait Of Gibraltar ◽  
Cetacean Species ◽  
The North ◽  
Northern Bottlenose Whales

Orcinus orcais a cosmopolitan species and the most widely distributed marine mammal. Its diet includes over 140 species of fish, cephalopods, sea birds and marine mammals. However, many populations are specialised on certain specific prey items. Three genetically distinct populations have been described in the North Atlantic. Population A (that includes the Icelandic and Norwegian sub-populations) is believed to be piscivorous, as is population C, which includes fish-eating killer whales from the Strait of Gibraltar. In contrast, population B feeds on both fish and marine mammals. Norwegian killer whales follow the Norwegian spring spawning herring stock. The only description in the literature of Norwegian killer whales feeding on another cetacean species is a predation event on northern bottlenose whales in 1968. Daily land-based surveys targeting sperm whales were conducted from the Andenes lighthouse using BigEyes®binoculars (25×, 80 mm). The location of animals at sea was approximated through the use of an internal reticule system and a graduated wheel. On 24 June 2012 at 3:12 am, an opportunistic sighting of 11 killer whales was made off Andenes harbour. The whales hunted and fed on a harbour porpoise. Despite these species having overlapping distributions in Norwegian waters, this is the first predatory event reported in the literature.

scholarly journals How deep does sand deposits in the Alentejo basin (Gulf of Cadiz) reach? Evaluating slope stability from bottom-current activities through time

2020 ◽  
Author(s):  
Davide Mencaroni ◽  
Roger Urgeles ◽  
Jonathan Ford ◽  
Jaume Llopart ◽  
Cristina Sànchez Serra ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Sediment Supply ◽  
Excess Pore Pressure ◽  
Bottom Current ◽  
Gulf Of Cadiz ◽  
Strait Of Gibraltar ◽  
Gulf Of Cádiz ◽  
The Stability ◽  
Iberian Margin ◽  
Excess Pore

<p>Contourite deposits are generated by the interplay between deepwater bottom-currents, sediment supply and seafloor topography. The Gulf of Cadiz, in the Southwest Iberian margin, is a famous example of extensive contourite deposition driven by the Mediterranean Outflow Water (MOW), which exits the Strait of Gibraltar, flows northward following the coastline and distributes the sediments coming from the Guadalquivir and Guadiana rivers. The MOW and related contourite deposits affect the stability of the SW Iberian margin in several ways: on one hand it increases the sedimentation rate, favoring the development of excess pore pressure, while on the other hand, by depositing sand it allows pore water pressure to dissipate, potentially increasing the stability of the slope.</p><p>In the Gulf of Cadiz, grain size distribution of contourite deposits is influenced by the seafloor morphology, which splits the MOW in different branches, and by the alternation of glacial and interglacial periods that affected the MOW hydrodynamic regimes. Fine clay packages alternates with clean sand formations according to the capacity of transport of the bottom-current in a specific area. Generally speaking, coarser deposits are found in the areas of higher MOW flow energy, such as in the shallower part of the slope or in the area closer to the Strait of Gibraltar, while at higher water depths the sedimentation shifts to progressively finer grain sizes as the MOW gets weaker. Previous works show that at present-day the MOW flows at a maximum depth of 1400 m, while during glacial periods the bottom-current could have reached higher depths.</p><p>In this study we derived the different maximum depths at which the MOW flowed by analyzing the distribution of sands at different depths along the Alentejo basin slope, in the Northern sector of the Gulf of Cadiz.</p><p>Here we show how changes in sand distribution along slope, within the stratigraphic units deposited between the Neogene and the present day, are driven by glacial – interglacial period alternation that influenced the hydrodynamic regime of the MOW.</p><p>By deriving the depositional history of sand in the Alentejo basin, we are able to correlate directly the influence that climatic cycles had on the MOW activity. Furthermore, by interpreting new multi-channel seismic profiles we have been able to derive a detailed facies characterization of the uppermost part of the Gulf of Cadiz.</p><p>An accurate definition of sand distribution along slope plays an important role in evaluating the stability of the slope itself, e.g. to understand if the sediments may be subjected to excess pore pressure generation. As sand distribution is a direct function of the bottom-current transport capacity, the ultimate goal of this study is to understand how climate variations can affect the stability of submarine slope by depositing contourite-related sand.</p>

Diet and consumption rate of Atlantic bluefin tuna ( Thunnus thynnus ) in the Strait of Gibraltar

2017 ◽  
Vol 188 ◽  
pp. 112-120 ◽  
Author(s):  
Joan Miquel Sorell ◽  
José Luis Varela ◽  
Nicolas Goñi ◽  
David Macías ◽  
Haritz Arrizabalaga ◽  
...  
Keyword(s):  
Consumption Rate ◽  
Bluefin Tuna ◽  
Thunnus Thynnus ◽  
Strait Of Gibraltar ◽  
Atlantic Bluefin Tuna

scholarly journals Inferring deglacial ventilation ages in Western Mediterranean waters using cold-water corals

2020 ◽  
Author(s):  
Maria de la Fuente ◽  
Luke Skinner ◽  
Gemma Ercilla ◽  
Elia d'Acremont ◽  
Luis Somoza ◽  
...  
Keyword(s):  
Trace Element ◽  
Cold Water ◽  
Western Mediterranean ◽  
Intermediate Water ◽  
Gulf Of Cadiz ◽  
Strait Of Gibraltar ◽  
Gulf Of Cádiz ◽  
The Mediterranean ◽  
Spatio Temporal ◽  
Reservoir Age

<p>Mediterranean Outflow Water (MOW) acts as a net source of salt and heat into North Atlantic intermediate depths that ultimately contributes to the Atlantic Meridional Overturning Circulation. On this basis, it has been hypothesised that MOW variability might influence global climate. Although several studies have documented major glacial-interglacial changes in deep- and intermediate Mediterranean circulation patterns, little is known about associated impacts on MOW properties, in particular its residence time and geochemical signature. Using a set of cold-water coral samples from along the ‘pre-MOW’ and MOW path, i.e. from the Alboran Sea to the northern Galician Bank including the Strait of Gibraltar and the Gulf of Cadiz, we aim to identify changes in both the ventilation state of the water masses flowing out of the Mediterranean and the distribution of coral growth.With this purpose, paired Uranium-series and AMS radiocarbon ages have been obtained in the same coral samples allowing any potential change in the reservoir age to be inferred accurately, as well as allowing a spatio-temporal ‘coral map’ to be created. Furthermore, these results have been complemented by trace element measurements in benthic foraminifera from the Alboran coral mound sediment core.</p><p>Our results show a particular spatio-temporal coral distribution with glacial presence only at the deepest sites of the Gulf of Cadiz (~1000m), followed by ~300m Western Mediterranean (WMed) coral appearance across the deglaciation/mid Holocene (14-4 kyr), to end with a proliferation at the Strait of Gibraltar and Galicia Bank from ~6 kyr towards the present. We hypothesise 1) that ~300m WMed area might have been bathed in Atlantic waters inflow during the glacial due to sea-level drop, returning to LIW (Levantine Intermediate Water) influence over the deglaciation, and 2) that MOW reached deeper areas outside of the Mediterranean Sea in the Gulf of Cadiz during the glacial period. Regarding the reservoir age, little change at the WMed is observed at 150-450m across the deglaciation as compared to the large ventilation excursion detected in the Iberian Margin at ~1000m. However, a ventilation age gradient of ~300 yr related to water depth is observed within WMed corals when appearing at the Bølling-Allerød, in synchrony with significant changes in hydrographical parameters inferred from foraminiferal trace element from the same area. Overall, our results suggest a water mass reorganization at the surface-intermediate layer of the WMed during the deglaciation and early Holocene, but the ultimate nature of these changes needs yet to be explored by further analysis of Nd isotopes as well as of trace elements beyond the deglaciation.</p>

Using Bayesian stable isotope mixing models and generalized additive models to resolve diet changes for fish-eating killer whales Orcinus orca

2020 ◽  
Vol 649 ◽  
pp. 189-200
Author(s):  
AJ Warlick ◽  
GM Ylitalo ◽  
SM O’Neill ◽  
MB Hanson ◽  
C Emmons ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Diet Composition ◽  
Killer Whale ◽  
Generalized Additive Models ◽  
Additive Models ◽  
Data Sources ◽  
Orcinus Orca ◽  
Mixing Models ◽  
Killer Whales ◽  
Isotope Mixing Models

Understanding diet composition is fundamental to making conservation and management decisions about depleted species, particularly when nutritional stress is a potential threat hindering recovery. Diet in free-ranging marine mammals is challenging to study, but stable isotope mixing models are a powerful means of estimating the contribution of prey species to diet and can improve precision by leveraging information from multiple data sources. We evaluated diet composition of a fish-eating killer whale population (Southern Resident killer whales, Orcinus orca) using 2 approaches. First, we fit generalized additive models to evaluate seasonal and interannual patterns in isotopic values across age, sex, and pod, which revealed seasonal carbon enrichment for certain pods and a recent increased nitrogen enrichment that could suggest increased Chinook salmon consumption, changing isotopic values of prey, or nutritional stress. Second, we developed a Bayesian stable isotope mixing model that accounts for the different integration times represented by bulk stable isotopes and fecal samples. Results showed that estimated prey contributions are similar between prey data sources, though the precision of estimates from periods with smaller sample sizes was improved by using an informative prior to account for the different consumption windows of the data. This study illustrates the importance of improving our understanding of how killer whale diets vary over time (both seasonally and across years) and uses a novel approach to resolve 2 sources of diet information (stable isotope, fecal samples) with different consumption windows.

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