For a few years now, the small marine mammals have regularly entered rivers in northern Germany in the months from early March through late May, as this year’s data collected by GRD shows again. Seemingly not shy at all at times, they can in particular be spotted in the Elbe river up to city of Hamburg and in the Weser river up to the city of Bremen during this period.
Having been absent for almost 100 years, the smart hunters have returned to their former partial habitats. They seem to be following migrating fish schools of stint and twaite shad which enter the rivers from the North Sea to spawn. Hamburg’s citizens were especially lucky this year because they could watch harbor porpoises nearly every day in April while sitting in cafes like the "Strandperle" or from the pontoon in Teufelsbrueck. So long as no major intrusions or changes are made to the waterways the porpoises are likely to return next spring too.
More than 300 detailed reports of harbor porpoise sightings
In the period from late February 2013 until on May 31, we received more than 300 detailed reports of harbor porpoise sightings. A big thank you to all the dedicated observers who contributed to our reporting scheme - this has allowed us to gain valuable insights into the porpoises’ whereabouts and obtain a very good picture of their distribution in the Elbe river, especially in the Hamburg area, and their behavior. The small cetaceans have thus come closer to us than ever before.
A conservative estimate suggests that as many as 50 to 80 harbor porpoises, or even more, were foraging in the Elbe river from the Koehlbrand region to the town of Wedel during this time period. GRD has published the data on its online sighting maps on its website as the reports have come in and has provided a data compilation to many authorities and institutes. We also would like to thank the media for their interest in this protected species and their coverage of the issue in newspapers, radio and TV reports. Thanks to the help of everybody we have already achieved a lot for the harbor porpoises
First results from 2013
At the same time as the smelt entered the river, the first harbor porpoises were spotted in Hamburg on February 27 and March 9. In mid-March the sightings and the number of the individuals sighted started to increase steadily. The small cetaceans chose the lower Elbe river up to the town of Wedel and the port of Hamburg as their hunting grounds in the spring.
Although the sightings of single individuals with around 30 % and of two individuals with about 37 % made up for the major part, we did receive a surprising amount of sightings of larger groups of 4 to 8. From the Koehlbrand region we obtained reports of groups of even up to 10 animals hunting in the afternoon every day over weeks.
A new hunting technique
The smart marine mammals drive schools of small fish into the harbor basins, or into bays like Billwerder Bay, where they can more easily snatch their prey. With the help of the Hamburg Waterways and Shipping Office we set up click detectors (CPODs) at several spots in the Elbe river, which record the porpoises‘ ultrasound clicks as digital data. The devices provided excellent recordings and support the observations. They revealed almost permanent activities off Wedel as of late March––the porpoises were also hunting at night, which they can easily do by using their echolocation. This also explains why we have received several reports about porpoises sleeping at the water surface during the day - everybody needs a rest sometime! This is dangerous though.
Deadly risks from fast boats
Facing deadly risks from fast boats Porpoises traveling into the Elbe river are evidently facing many risks: the Elbe is a high-traffic waterway and certainly no ideal habitat because pollution, noise, and fast vessels pose serious threats to the porpoises. The fact that they put up with these risks shows how vital this feeding ground is to them.
Our 2013 records show a sad total of 20 harbor porpoises found dead in the Elbe river alone, with an accumulation especially over the past two weeks as the pleasure craft season started.
Quite a few of the dead animals displayed signs suggestive of collisions with fast watercraft: porpoises cannot react quickly enough to escape them.
One porpoise was still alive, but very weak when found. It was spitting blood and gasping for air for 15 minutes before it died in agony. Another one was gasping for air when found and then also died.
Some other carcasses had wounds from propeller strikes. Given that the harbor porpoises stay in an area extending from the city to Hamburg down to the town of Wedel, GRD calls for a temporary speed limit in this area during the harbor porpoise season from early March through late May
Dead cetaceans must be examined
Finally, in late May our call for having every porpoise found dead examined by a veterinary was successful. Up to now, the carcasses found in the federal city state of Hamburg have been simply disposed of at carcass disposal sites, forever lost to research, forfeiting chances to investigate the causes of death and perform other examinations. From now on every porpoise found dead in Hamburg will also be necropsied.
Dedicated to the protection of these marine mammals, Dr. Veit Hennig of Hamburg University, who actively supported the data collection on our joint trips with the University’s Zodiak and the cooperation with the media, and the University of Veterinary Medicine Hannover, Foundation (Stiftung Tierärztliche Hochschule Hannover) with Prof. Dr. Ursula Siebert, who examines every harbor porpoise found dead in Schleswig-Holstein, also support our efforts in this respect.
Again, we would like to thank all persons, boaters and walkers alike, the employees of the Hamburg Waterways and Shipping Office, Dr. Hennig and his students from Hamburg University, and the media for their fantastic contributions to the data collection on harbor porpoises.
We will certainly gain many exciting insights from the data analysis that will follow.