First European record of the invasive barnacle <i>Balanus glandula</i> Darwin, 1854

During recent surveys of hard substrata biofouling communities in Belgian marine waters we discovered specimens of the invasive barnacle Balanus glandula. This species is new to the European marine fauna. The species was first encountered in July 2015 in a biofouling community on RV Belgica. In October 2016, the species proved to be common on navigational buoys in Belgian coastal waters and after a dedicated search we discovered the species on many groynes all along the Belgian coast and in the harbour of Zeebrugge. We identified the species both morphologically and genetically. We found two generations indicating that B. glandula had settled in 2015 (possibly the first year of its presence) and also in 2016. We provide identification characters to distinguish B. glandula from other, similar looking, Western European intertidal barnacles. The distribution of B. glandula was originally limited to the Pacific coast of North America. In the past half century B. glandula successfully invaded subsequently the coasts of Argentina, Japan and South Africa. Given its invasion history elsewhere, we forecast that B. glandula is on the brink of invading other European shores

The harbour porpoise <i>Phocoena phocoena</i> in the Belgian part of the North Sea: trends in abundance and distribution

The harbour porpoise Phocoena phocoena is currently common in the Belgian part of the North Sea (BPNS), after decades of virtual absence. This article describes the results of aerial surveys to assess its distribution and density in Belgian waters, in concert with the first results of tests with passive acoustic monitoring devices (Porpoise Detectors - PoDs), and a basic analysis of strandings. The strandings data over four decades clearly demonstrate an increase of harbour porpoises in the BPNS, with only few stranded animals between 1970 and 1997 (0 to 6 per year), increasing numbers between 1998 and 2004 (8 to 40 per year), and even higher numbers between 2005 and 2009 (62 to 94 per year). The combined results of aerial surveys, strandings monitoring and tests with passive acoustic monitoring reveal a seasonal pattern, with harbour porpoises being abundant from February to April, and more scarce from May to January. Average densities in 2008 and 2009, as estimated by aerial monitoring covering most of the BPNS (with the exclusion of the nearshore 5 km strip), ranged from 0.05 animals per km2, or in total less than 200 animals in an area equivalent to the BPNS in August 2009, to 1.01 animals per km2, or in total almost 3,700 animals in an area equivalent to the BPNS during April 2008. In the first quarter of the year porpoises occur throughout the BPNS, including territorial waters (12 mile zone), whereas they are restricted to more offshore and northerly waters later in the year. Erratic invasions in the BPNS however blur general seasonal spatio temporal patterns, which complicates our understanding of spatial distribution and migration

The diet of harbour porpoises bycaught or washed ashore in Belgium, and relationship with relevant data from the strandings database

The harbour porpoise Phocoena phocoena is currently the most abundant marine mammal in Belgian waters. Large-scale changes in the distribution of this top predator in the North Sea have occurred during the last decades, possibly caused by changes in food availability. An analysis of the strandings database 1970-2011, containing data on 737 harbour porpoises, revealed that throughout the year two peaks in strandings occurred: one in spring, for an important part caused by the strandings of animals incidentally bycaught in fishing gear, and a second one during summer. Most of the stranded animals were juveniles, with a higher percentage of males than females. As could be expected, bycaught animals were on average heavier than equally sized naturally died animals, and they had a thicker blubber layer. In naturally died animals the blubber layer was thicker in winter than in summer, illustrating the insulating function of the blubber layer besides its function as an energy storage.We investigated the stomach content of 64 harbour porpoises washed ashore or bycaught in Belgium between 1997 and 2011. Ten of the stomachs were empty. Fish contributed to most of the prey remains. In total we found the remains of 19 fish species belonging to 10 families. The numerically most important prey items in juveniles were gobies (Gobiidae). Reconstructing the original weight of the prey items revealed that gobies constituted the most important prey by weight, but that larger sandeels (Ammodytidae) and to a lesser extent gadoids (Gadidae) were also important. In adults the majority of prey items were gobies and sandeels, but the reconstructed weight of the stomach content revealed that sandeels and gadoids constituted by far the most important prey. Surprisingly, clupeids (Clupeidae) did not contribute much to the diet, although the return of the harbour porpoise is often linked to an increase in herring Clupea harengu stocks in the southern North Sea. Also no twaite shad Alosa fallax were found, although this diadromic fish is common again in the area. A small number of smelt Osmerus eperlanus was found in some of the recently stranded harbour porpoises. Smelt is a diadromic fish of which densities are increasing from very low levels. The fact that juvenile harbour porpoises had apparently fed on large quantities of small bottom fish may help to explain why they were more prone to bycatch than adults. The analysis revealed that a gradual shift occurs in the feeding habits of harbour porpoises while becoming adults: from small benthic fish towards larger fish taken from the water column