Deep-diving beaked whales dive together but forage apart.

Echolocating animals that forage in social groups can potentially benefit from eavesdropping on other group members, cooperative foraging or social defence, but may also face problems of acoustic interference and intra-group competition for prey. Here, we investigate these potential trade-offs of sociality for extreme deep-diving Blainville's and Cuvier's beaked whales. These species perform highly synchronous group dives as a presumed predator-avoidance behaviour, but the benefits and costs of this on foraging have not been investigated. We show that group members could hear their companions for a median of at least 91% of the vocal foraging phase of their dives. This enables whales to coordinate their mean travel direction despite differing individual headings as they pursue prey on a minute-by-minute basis. While beaked whales coordinate their echolocation-based foraging periods tightly, individual click and buzz rates are both independent of the number of whales in the group. Thus, their foraging performance is not affected by intra-group competition or interference from group members, and they do not seem to capitalize directly on eavesdropping on the echoes produced by the echolocation clicks of their companions. We conclude that the close diving and vocal synchronization of beaked whale groups that quantitatively reduces predation risk has little impact on foraging performance.

Use of survival rates of the barnacle Chthamalus stellatus as a bioindicator of pollution.

Concentrations of heavy metals and trace elements in marine environments have increasingly become a problem for several ocean ecosystems, due to increments in pollution. Habitats daily exposed to extreme conditions, such as the intertidal rocky platforms and pools, are more vulnerable to pollution effects. In the coast of Punta del Hidalgo (Tenerife, Spain), we have located a water-treatment plant that could be pouring periodically pollutants to the near shore. We studied coverage and survival rates of the cirriped Chthamalus stellatus inhabiting the intertidal near the sewage pipe of the water plant of ​Punta del Hidalgo and in a control area in a proximate location. Concurrently, water samples from intertidal pools were obtained from both affected and control areas in order to corroborate the presence of pollutants, analyzing the concentrations of metals and trace elements. The results obtained clarified that the area near the underwater outfall presented higher percentage of coverage and mortality of C. stellatus than the control zone. The analysis of metal content in water samples also showed higher concentrations of metals for the affected area compared to the control one. We therefore propose the use of survival rates of populations of C. stellatus in the intertidal as bioindicators of metal pollution.

Metal content in stranded pelagic vs deep-diving cetaceans in the Canary Islands.

The Canary Islands are home to many cetacean species, many of which are resident species. The present work aims to analyze, for the first time to the best of the authors' knowledge, the macronutrients, micronutrients and trace elements and toxic heavy metals in muscle and liver tissue of six species of stranded cetaceans in the Canary Islands. The study species were: Tursiops truncatus, Stenella frontalis, Delphinus delphis, Grampus griseus, Globicephala macrorynchus and Physeter macrocephalus. Statistical analysis studied the significant differences between the concentrations in muscle and liver tissues, with the differences in element content depending on the type of diving and length of the species. The results indicate that there are differences between muscle and liver for Ca, Cd, Co, Cu, K, Mg, Mn, Mo, Ni, Pb, Sr, V and Zn. Deep-diving animals differ in their concentrations of Cr, Cu, Mg, Mn, Mo, and Zn with respect to shallow-diving animals in muscle and in liver in Al, B, Cr, K, Mn and Mo. As for the differences between sex, the males present differences in their concentrations of B, Cd, K and Mg in muscle tissue with respect to the females, while differences in the liver were only detected in the Fe content. The study of the correlations shows that as the size of the animal increases, the concentration of Cd increases while the concentrations of Al, Cu and Zn decrease. The specimens foraging in shallower waters had the highest concentration of the macronutrient.