Marine mammals can play important ecological roles in aquatic ecosystems, and their presence can be key to community structure and function. Consequently, marine mammals are often considered indicators of ecosystem health and flagship species. Yet, historical population declines caused by exploitation, and additional current threats, such as climate change, fisheries bycatch, pollution and maritime development, continue to impact many marine mammal species, and at least 25% are classified as threatened (Critically Endangered, Endangered or Vulnerable) on the IUCN Red List. Conversely, some species have experienced population increases/recoveries in recent decades, reflecting management interventions, and are heralded as conservation successes. To continue these successes and reverse the downward trajectories of at-risk species, it is necessary to evaluate the threats faced by marine mammals and the conservation mechanisms available to address them. Additionally, there is a need to identify evidence-based priorities of both research and conservation needs across a range of settings and taxa. To that effect we: (1) outline the key threats to marine mammals and their impacts, identify the associated knowledge gaps and recommend actions needed; (2) discuss the merits and downfalls of established and emerging conservation mechanisms; (3) outline the application of research and monitoring techniques; and (4) highlight particular taxa/populations that are in urgent need of focus.
High efficiency lunate-tail swimming with high-aspect-ratio lifting surfaces has evolved in many vertebrate lineages, from fish to cetaceans. Baleen whales (Mysticeti) are the largest swimming animals that exhibit this locomotor strategy and present an ideal study system to examine how morphology and the kinematics of swimming scale to the largest body sizes. We used data from whale-borne inertial sensors coupled with morphometric measurements from aerial drones to calculate the hydrodynamic performance of oscillatory swimming in six baleen whale species ranging in body length from 5-25m (fin whale, Balaenoptera physalus; Bryde's whale, Balaenoptera edeni; sei whale, Balaenoptera borealis; Antarctic minke whales, Balaenoptera bonaerensis; humpback whales, Megaptera novaeangliae; and blue whales, Balaenoptera musculus). We find that mass-specific thrust increases with both swimming speed and body size. Froude efficiency, defined as the ratio of useful power output to the rate of energy input (Sloop, 1978), generally increased with swimming speed but decreased on average with increasing body size. This finding is contrary to previous results in smaller animals where Froude efficiency increased with body size. Although our empirically-parameterized estimates for swimming baleen whale drag was higher than that of a simple gliding model, oscillatory locomotion at this scale exhibits generally high Froude efficiency as in other adept swimmers. Our results quantify the fine-scale kinematics and estimate the hydrodynamics of routine and energetically expensive swimming modes at the largest scale.
The cue rate (CR: blows per whale per hour), surfacing characteristics and swim speeds of sei whales (Balaenoptera borealis) were quantified fromfocal follows carried out at Berkeley Sound (East Falkland) between January and May 2017 and off the west coast of West Falkland betweenFebruary and April 2018. In Berkeley Sound, focal follows were conducted from Cape Pembroke lighthouse and from a small boat. In West Falklandall focal follows were conducted from a yacht. Thirty-seven focal follows of sei whale individuals or groups (2–5 individuals) were analysed toproduce CRs ranging from 21.99 to 46.73, with a mean of 31.46 (SD = 5.12). There was no significant difference in the CRs observed from shorevs. boat platforms or between the two study areas. Maximum submergence times exceeding 13min were recorded from both individuals and groups.The durations of 51 whale surfacing events had a mean of 6.4s (SD = 1.7). The average swim speed during boat-based sei whale focal follows was5.7kmh−1. The inter-breath intervals (IBIs) recorded from 13 solitary individuals ranged from 77.2 to 180.1s, with an overall mean of 118.6s (SD= 137.6). A combined approach incorporating IBI parameters and sequence pattern was used to classify 270 IBIs into surface dives (mean = 37.2s),intermediate dives (mean = 113.7s) and true dives (mean = 332.6s). Individuals showed marked variation in dive pattern, with some exhibitingclear cycles of true dives interspersed with surface bouts while others routinely took intermediate-duration dives interspersed by single surfacings.Sei whales in Berkeley Sound exhibited a higher proportion of surface dives than whales in West Falkland, and those surface dives were of lowermean and median IBI. Individual sei whales had surface bouts comprising a mean of 3.8 blows and a mean IBI of 33.4s. These are the firstquantifiable data on surfacing-dive patterns and CRs for sei whales in the Falkland Islands and across the wider range of the species. The data haveconservation and management relevance, including addressing availability bias for line transect and cue count abundance estimates, incorporationinto vessel strike modelling, and understanding foraging behaviour.
Knowledge of the whale shark, Rhincodon typus, in the south-east Atlantic off the coast of West Africa is limited to several bycatch and stranding records. Ten at-sea sightings of whale sharks from Angola (N ¼ 9) and Nigeria (N ¼ 1) are presented, consisting of nine sightings from offshore platforms and a single record from a helicopter. Eight of the records were from oceanic waters exceeding 1000 m, while single records originated from shelf-edge and continental shelf waters. The records support a year-round occurrence of whale sharks in offshore West African waters, although the majority (N ¼ 8) of sightings occurred during the spring and summer months between September and January. Most sightings (N ¼ 8) were of whale sharks estimated to be in the 5 -7 m length-range. These records represent the first verified at-sea sightings in the West Africa region providing novel information on behaviour and distribution, and also confirm Nigeria as a range state for the whale shark.
The Atlantic humpback dolphin (Sousa teuszii) is a critically endangered cetacean species endemic to coastal Atlantic waters of Africa. Its preference for shallow coastal habitat renders it vulnerable to incidental capture (bycatch) in non-selective fishing gears as well as to habitat degradation from all forms of coastal development. Although past and ongoing research has shed light on the distribution and conservation status of the species in a few locations, it is still poorly understood throughout most of the 19 countries in its 7000 km long range. From 2020 onward, international and regional collaboration to increase awareness and promote conservation action has intensified. These efforts, while in the early stages, exemplify the IUCN Species Survival Commission’s Assess-Plan-Act Conservation Cycle. While concrete conservation gains have not yet been achieved, efforts are being made to fill knowledge gaps and to broaden and motivate the network of international, regional, national, and local stakeholders that are actively engaged in marine and coastal conservation actions at multiple levels. The authors assess the strengths and weaknesses of the current approaches and identify elements that may be useful for other species with ranges spanning multiple countries where resources and capacity for conservation action are limited.
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