Following the report by the Cetacean Stranding Investigation Programme (CSIP) published before Christmas several people have contacted the museum via twitter/facebook asking if the fall in the number of recorded strandings is due to decline in the number of cetaceans in UK waters? and whether man is responsible for the fall in numbers?
For those who have not read the report, one of the main points was there has been a 22% fall in the numbers of animals stranded between 2005 and 2010 compared with the number recorded 2000- 2005. Unfortunately we are only able to record dead animals and are not able to relate this number to the actual number of live animals around the UK coast. The number of stranded animals in 2011 looks to have increased over the 2010 numbers, does this mean a recovery for UK animals? - No. One years data or even 5 years are not enough to show trends.
Now that whale and dolphin watching has now become a tourist activity, with places such as Cornwall and the Scottish Isles having commercial boats taking people to look at cetaceans, more people are aware of the sealife around the UK coast and there are websites to record sightings eg Seawatch. Please do record any sightings, as no one knows how many animals there are swimming around our shores. There are several groups trying to identify individual whale and dolphins by photograhing their dorsal fins and tail flukes. For example the Seawatch Foundation run a Photo a Fin campaign to gather information. http://www.seawatchfoundation.org.uk/events.php?uid=254
However it is difficult to correlate the number of strandings with the number of live sightings. Many factors influence if information is gathered about dead animals, the main one being if someone actually reports that an animal has stranded to us. Most people assume that 'someone else' will do something about a dead cetacean, there are only a few occasions that a stranded animal is reported to us by more than one member of the public, so we believe many more go unreported. There is now a freephone to call (0800 6520333) to report any cetacean stranded in the UK
The reason for CSIP is to gather information about strandings (which the Natural History Museum started in 1913). With more data we can look for longer term patterns in the number of strandings and causes of death for animals which are taken for post mortem. We can then hope to influence the decisions made by goverments in London, Edinburgh and Cardiff about the marine life around the UK
The question of whether man activities causes the death of some cetaceans is not in doubt. There is evidence that manmade underwater noise causes cetaceans to panic and die due to embolisms - similar to the bends in human divers. One of the CSIP investigators co-authored a paper on the mass stranding of beaked whales in the Canary Islands in 2002 which was linked to navel sonar activity. It is rare to be able to link any death with one particular sonic activity. However most deaths caused by man are due to bycatch- animals which have died due to fishing eg caught in nets an ddrowned. Between 1991 and 2010 almost 600 animals have been had their cause of death identified at post mortem as bycatch. There is research underway into underwater 'pingers' to deter dolphins from going near fishing boats. CSIP are currently investigating the levels of toxic chemicals eg PCBs in dolphins. These manmade chemicals are known to accumulate in the top predators eg Dolphin and Killer whales and while may not cause death directly will impact on the general health of an animal. Man's activities also affect the other animals that CSIP investigate - seals, marine turtles and basking sharks.