Massed Strandings of Whales and Dolphins – Effects of Wind, Waves and Tides.

We examined125 mass-stranding events of cetaceans (>=10 individuals) on New Zealand shores over the past 40 years. The wind, waves, wave refraction, shore slopes and tides at the dates and locations of these events were considered. The mass-strandings involved 10 different species, but by far the most common involved the Long-finned Pilot Whale, Globicephala melas. Our hypothesis is that mass-stranding is a three-stage process. The first stage is when an animal becomes ill, its body may become bloated and float on the surface, and the wind and waves may drive it ashore. We assume the second stage is that the dying or dead body may be accompanied by pod members as a result of strong social bonds. The third stage involves the tides and the beach slope. If these are of sufficient amplitude, the nearby attendees will quickly become stranded in the intertidal of a gently sloping beach as the water level falls. We have evaluated evidence for the first and third stages. In the overwhelming majority (91%) of the mass-strandings (omitting events inside estuaries), the available data showed that wind and waves would drive floating objects (bodies) toward the stranding site. Examination of the nearshore slopes and the tide ranges showed that the vast majority of the stranding sites were slowly shelving beaches where the tides would retreat rapidly over 10s of metres. These 2 results are even more pronounced if only Pilot Whale mass strandings are considered.

Long-term patterns of mass stranding of the colonial cnidarian Velella velella: influence of environmental forcing

Velella velella is a pleustonic cnidarian noted worldwide for mass stranding of the colonial phase. Utilizing a 20 yr dataset (2000-2019; 23265 surveys) collected by the COASST citizen science program, we examined the spatio-temporal occurrence of mass strandings of V. velella along the Pacific Northwest coast from Washington to northern California, USA. V. velella mass strandings were documented in 14 years, with expansive events in 2003-2006 and 2014-2019. Events predominantly occurred in spring and were synchronous (April) among years, concurrent with shifts to prevailing onshore winds. Autumn mass stranding events occurred infrequently, with no consistent phenology (2005: November; 2014: August). In stranding years, reports of V. velella were mostly synchronous throughout the surveyed area, and events consistently spanned >400 km of coastline, with highest reporting rates in the vicinity of the Columbia River plume, collectively suggesting extensive V. velella blooms throughout the northern California Current system in some years. Annual metrics of spring V. velella reporting rate (proportion of beaches; January-June) were modeled as a function of indices representing sea surface temperature anomaly (SSTa), easterly (onshore) wind speed, and regional upwelling. The best models (based on Akaike’s information criterion corrected for small sample size) indicated that SSTa averaged over the preceding winter (December-February) was positively correlated with spring reporting rate, suggesting that mass strandings of V. velella may be more prevalent in warmer years. As planetary warming continues, and V. velella strandings are easily recorded by citizen science programs globally, we suggest that stranding prevalence may be one relatively easy measure providing evidence for epipelagic ecosystem response.

Morphometric regressions for the endangered Knysna seahorse, Hippocampus capensis, in the Swartvlei Estuary from mass stranding events

No abstract available.

Echolocation and Navigational Distortion Hypothesis of the Short Finned Pilot Whale Beaching in Southern Coast of Tamil Nadu

Cetacean strandings have been a common occurrence in the past and has been recorded in various places. There have been attempts to explain the phenomenon of mass beaching with various theories. Here in this article we propose a hypothesis on the recent mass stranding of Short-finned pilot whales Globicephala macrorhynchus in the southern coast of Tamil Nadu, India. We propose that navigation disturbance and signal distortion due to ocean topography could be a possible reason for this mass stranding.

An empirical relationship between sea surface temperature and massive stranding of the loggerhead turtle (Caretta caretta) in the Gulf of Ulloa, Mexico

Two mass stranding events of loggerhead sea turtles (Caretta caretta) in the vicinity of the Gulf of Ulloa, Baja California Sur, Mexico, were analyzed during 2003-2006 and 2012-2014. Stranding events were related to the accumulation of consecutive days with lower sea surface temperature (SST) series for the corresponding periods using Pearson correlations. Our results showed that in both periods, a significant cross-correlation was observed between mass stranding and accumulation of consecutive days with temperatures below 18, 17, and 16°C, with a time lag of three to five months. Numerical evidence supports the hypothesis that although the loggerhead turtle mortality is caused by multiple factors under extreme cold events, the environment turns markedly unfavorable for these organisms. Side-effects on health and swimming behavior of the species C. caretta, compromise their ability to avoid obstacles or flee from predators, thus increasing their vulnerability to sickness or lethargy, and possibly leading to the massive stranding of weakened individuals or dead bodies to the beaches of the Gulf of Ulloa. Hence, while SST may not be the direct cause of turtle mortality, it can be a determining factor for the survival of this species.