I note that each shipwreck record includes a date of loss. I'd be interested to see a histogram of frequency by year.
awk -vFPAT='([^,]*)|("[^"]+")' -vOFS=, '{if ($1~/^[0-9]+$/){N++; if ($6=="Unknown"){ U++}}} END {print N, U}' Wrecks_April_2018.csv
17972,2137
EDIT: Didn't realise in the above that most wrecks are missing from the map due to unknown coords. Filtering these out we get
3736,1596
https://www.urbanghostsmedia.com/2015/01/rms-lusitania-wreck...