Two days of trawling in the Eurogully: Did trawler OD7 find a mammoth graveyard?

Dick Mol (The Netherlands)

The first finds of mammoth fossils and other representatives of the ice age megafauna occurred in 1874. It was assumed then that there must have been a mammoth graveyard offshore of the province of Zeeland in The Netherlands. To date, many thousands of megafaunal remains have been collected from the seabed, and not just woolly mammoths.

They include woolly rhinoceroses, steppe bison and wild horses, in most cases as an auxiliary catch during trawling (for instance, see Mol et al., 2008). This is because, when fishing in the North Sea, fishermen tow ‘trawls’ (fishing nets) along the seafloor to catch flatfish like sole and plaice. This process is often referred to as “dragging”. However the nets also stir up a lot of debris from the seabed and, as well as modern garbage, this produces an incredible amount of fossils from the Pleistocene (also known as the ice ages).

Towards the end of 2011, an unexpectedly huge amount of fossil mammoth bones was suddenly uncovered just off the coast of the province Zuid-Holland in The Netherlands. This article is about that find.

For a number of reasons, the awareness of the scientific community of the additional catches of Pleistocene fossils by the North Sea trawling industry has increased tremendously over the last three decades. There are now many palaeontologists coordinating efforts with fishermen in connection with the retrieval of fossil remains. Initially, this targeted fishing for fossils took place mostly near the ‘Brown Bank’, about 50 nautical miles to the west of the coast of the Dutch ‘IJmuiden’, followed by several dedicated fishing expeditions in the Euro-Meuse Gullies, which together make up the navigational route to Rotterdam for large ships with very deep draws (see Mol and Post, 2010) for a complete overview of those expeditions).

In addition to these expeditions, many commercial fishermen routinely retain fossils brought up with their catch, bring them back to port at the end of the week and make them available for paleontological investigation. Depending on the area of operation, many trawlers collect a number of fishing crates full of skeletal remains, which are promptly traded with eager collectors on the dock.

One of the trawlers with a great reputation for fossil collecting from the late Pleistocene is The Adrianus, registered as the OD7 or the Ouddorp 7. This vessel is a so-called ‘eurocutter’, with a length of just over 24m. Only these relatively small vessels are allowed to operate within the 12 mile zone, very close to the shore. This is precisely the area of greatest interest for palaeontologists.

These areas have been dredged intensively to collect sand to fortify beaches such as Hoek van Holland and the ‘Zandmotor’. However, this dredging also exposes fossil remains, which have lain hidden on the seafloor for thousands of years. During the dredging, these end up lying on the sea bottom waiting to be collected by the next trawl. One of the most important areas for fossil bones, is the aforementioned Euro-Meuse Gullies, which is dredged nearly continuously to ensure that large, ocean-going ships can pass through.

Turbulent times

At the moment, the beam trawler fishing business is having a tough time, as a result of all kinds of limitations being imposed by governments. And many ships have been updated or adapted to other fishing techniques that use less fuel than the traditional beam trawls. However, this impacts the previously abundant supply of fossil remains from the late Pleistocene fauna. Fewer trawlers at work mean fewer fossils retrieved from the treasure trove of fossils just offshore. The cutter, Adrianus, has also been affected. This has been used several times for dedicated expeditions fishing for mammoth remains, but the vessel was sold in December 2011 and the new foreign owner is using it for fishing in the waters around Ireland, where it will no longer collect mammoth bones in its nets.

An abundance of mammoths

This article pays tribute to the previous captain – Jaap Klijn – and crew of the Adrianus for their commitment to palaeontology. It is also a testimony to the incredible profusion of mammoth and other remains of the Late Pleistocene megafauna. During the last two weeks of November 2011 – the swan song of its active duty as beam trawler – the OD7 Adrianus operated in the Eurogully for two, 24-hour periods. No – it wasn’t a dedicated expedition for science, just a routine commercial fishing expedition for flatfish.

However, the nets can’t tell the difference and, this time, the accessory catch of fossil remains was extraordinarily large. Apart from 30 standard fish crates filled with smaller skeletal remains of mammoths, rhinos, reindeer, wild horses, Irish elks, hyenas and other representatives from the bygone mammoth steppe, there was also a plethora of other large remains, like maxillae and mandibles (upper and lower jaws), scapulae, humeri, femurs, pelvises and, in particular, the tusks of woolly mammoths.

A quick inventory tells us that these complete and incomplete tusks belonged to at least 11 different mammoths. Remains of marine mammals have also been recovered from the same sediments, including seals and the beluga, also known as the ‘white whale’ or ‘sea canary’ as a result of its sound. Those remains appear to be of about the same age (see below for an explanation of how whales and mammoths could end up in the same sediments).

This abundant collection is unprecedented – I have never seen such a wealth of fossils in the four decades that I have been active in palaeontology, nor have any of the other specialists with whom I have discussed these finds.

A mammoth graveyard?

No – the OD7 did not pull its nets through a mammoth graveyard. It was just operating in an area that happened to be a natural fan or sink for sediments from the palaeo-rivers, currently known as the Rhine and the Meuse, somewhere between 100,000 and 10,000 years ago. During this period, Europe consisted of a vast, cold, treeless steppe, referred to as the ‘mammoth steppe’. Large herbivores like mammoths and woolly rhinos, along with predators such as lions and hyenas, were attracted by the Rhine-Meuse river delta for their daily drink. Some animals died in this delta area and their remains were buried quickly enough for the hard parts (bones) to be preserved.

The abundance of remains clearly shows that the area was a popular place, inhabited by many animals. Also, several fossils have been found that belonged to the same specimen and this strongly suggests that the animals died there, in situ, since transport of the remains (for instance, by water) would have separated the bones. The many dental remains are giving a good indication of the age of the animals at time of death and it turns out that the animals were of all ages. Therefore, it is our understanding that this area, off the coast of ZuidHolland, was a sort of paradise for the behemoths from the Pleistocene, when a totally different shoreline existed and the sea level was some 122m lower than it is today.

The fossil remains have been transferred to the town of Urk, where they are being cleaned, sorted and dried in a workshop. They will also be carefully examined for evidence of scavenging by predators like hyena and possible modification by humans. After preservation, the remains will be added to several collections, where they will be available for scientific research.

Fossil hunting on the beach

It was beam trawlers that predominantly collected the larger fossils of big animals. However, small mammals – like the hare and arctic fox – also populated the mammoth steppe, but their skeletal remains are too small to be collected by the nets of trawlers. This is also true of the small parts of large animals, such as the phalanges, sesamoid bones and the end tail vertebra. Unfortunately, they just slip through the nets.

However, we can also hunt for faunal remains (both large and small) on the beaches of, for instance, Hoek van Holland, s’Gravenzande and de Zandmotor near the beach of Ter Heijde (Van der Valk et al., 2011), and also on the beach of the Maasvlakte-2, which is an artificial peninsula off the coast of Zuid-Holland. Many people are actively searching these places for just such small remains and they have already collected a large number of teeth, molars and small bones.

These faunal remains from the late Pleistocene continuously wash onshore or are exposed by wind and water, and these little tokens are a welcome supplement to the large fossils, tons of which have been recovered from the seafloor. In this way, collection will continue after the demise of the beam trawling industry, but there is still so much to collect. Unfortunately, those large auxiliary catches from beam trawlers like the Adrianus are now history.

References

Mol D., K. Post (2010): Gericht korren op de Noordzee voor de zoogdierpaleontologie: een historisch overzicht van de uitgevoerde expedities. Cranium 27, 2, 14-28.

Mol, D., J. de Vos, R. Bakker, B. van Geel, J. Glimmerveen, H. van der Plicht & K. Post, 2008. Kleine encyclopedie van het leven in het Pleistoceen: mammoeten, neushoorns en andere dieren van de Noordzeebodem. Veen Magazines, Diemen.

Valk, B. van der, D. Mol & H. Mulder, 2011. Mammoetbotten en schelpen voor het oprapen: verslag van een onderzoeksexcursie naar fossielen op “De Zandmotor” voor de kust tussen Ter Heijde en Kijkduin (Zuid-Holland). Afzettingen WTKG 32, 3, 51-53.