Offshore Earthquakes Do Not Influence Marine Mammal Stranding Risk on the Washington and Oregon Coasts.

Rachel Grant,Will Hoppitt,Anna Savirina

doi:10.3390/ani8020018

Abstract

Simple SummaryMarine mammals stranding on coastal beaches is not unusual. However, there appears to be no single cause for this, with several causes being probable, such as starvation, contact with humans (for example boat strike or entanglement with fishing gear), disease, and parasitism. We evaluated marine mammal stranding off the Washington and Oregon coasts and looked at offshore earthquakes as a possible contributing factor. Our analysis showed that offshore earthquakes did not make marine mammals more likely to strand. We also analysed a subset of data from the north of Washington State and found that non-adult animals made up a large proportion of stranded animals, and for dead animals the commonest cause of death was disease, traumatic injury, or starvation.The causes of marine mammals stranding on coastal beaches are not well understood, but may relate to topography, currents, wind, water temperature, disease, toxic algal blooms, and anthropogenic activity. Offshore earthquakes are a source of intense sound and disturbance and could be a contributing factor to stranding probability. We tested the hypothesis that the probability of marine mammal stranding events on the coasts of Washington and Oregon, USA is increased by the occurrence of offshore earthquakes in the nearby Cascadia subduction zone. The analysis carried out here indicated that earthquakes are at most, a very minor predictor of either single, or large (six or more animals) stranding events, at least for the study period and location. We also tested whether earthquakes inhibit stranding and again, there was no link. Although we did not find a substantial association of earthquakes with strandings in this study, it is likely that there are many factors influencing stranding of marine mammals and a single cause is unlikely to be responsible. Analysis of a subset of data for which detailed descriptions were available showed that most live stranded animals were pups, calves, or juveniles, and in the case of dead stranded mammals, the commonest cause of death was trauma, disease, and emaciation.

Highlights

The causes of marine mammal stranding events are complex, often multi-factorial, and generally not well understood
3).This earthquakes in the vicinity of the Cascadia Subduction Zone, we examined a subset of data from dataset had information on cause of death and whether stranding was alive or dead, which was not the north of Washington State, where 604 records of marine stranding were collected over five years, available in our main dataset
Our analysis suggests it is very unlikely that earthquakes are a major cause of marine mammal mass our analysis suggests it is very unlikely that earthquakes are a major cause of marine mammal mass stranding events, with an estimated 0.35% of mass stranding events (95% C.I. = [0, 0.56]) being caused stranding events, with an estimated 0.35% of mass stranding events (95% C.I. = [0, 0.56]) being caused by earthquakes

Summary

Introduction

The causes of marine mammal stranding events are complex, often multi-factorial, and generally not well understood. Where there was a known cause, half of all marine mammal stranding events off the coast of California from 1991 to 2008 were attributable to toxins that were produced by algal blooms of the planktonic species Pseudo-Nitzschia spp. accumulating through the Animals 2018, 8, 18; doi:10.3390/ani8020018 www.mdpi.com/journal/animals. Brownell et al [6], ruled out toxic algal blooms, as well as other factors such as moon phases, magnetic field shifts, disease, trauma, fisheries causes, and starvation in mass stranding events of pygmy killer whales, Feresa attenuata off the coast of Taiwan, over a 38 year period, and suggested anthropogenic sound as a probable cause. Many other authors have attributed anthropogenic sound, in particular naval activity, as a possible cause of mammal stranding events [7]. The exact location that marine mammals strand may be some distance from the original source of disturbance and/or mortality event and may depend on secondary factors, such as ocean currents, coastal topography, and wind forcing

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