The discovery of new non-native marine species in the central Mediterranean is becoming a common event. Most of these newly arrived aliens are either Red Sea species that have entered the Mediterranean through the Suez Canal and established themselves in the eastern Mediterranean, from where they have spread westwards, or else are warm-water Atlantic species that have entered the Mediterranean through the Strait of Gibraltar and are spreading eastwards. In both cases, this phenomenon has been linked to a warming trend in Mediterranean surface waters during the past few decades. However, there are a few cases where the occurrence of a non-native species cannot be accounted for in this way. Recently, researchers from the Department of Biology of the University of Malta and from the Faculty of Sciences of the University of Nice-Sophia Antipolis in France have reported an extreme case from Malta.
On 22 November 2009, angler John Attard who was taking part in an amateur fishing marathon in aid of a charitable institution at the Valletta Waterfront, landed a strange fish which he photographed and then released back to the sea, as required by the competition rules. A month later on Christmas Day, Catherine Gras, a French visitor, was diving on the wreck of HMS ‘Maori’ close to the mouth of Marsamxett Harbour when she spotted a distinctive fish, which she photographed. Since both persons did not recognize the species, they posted a picture of the fish on the ‘Malta Fishing Forum’, a Maltese fishing website, and on the French ‘DORIS’ website, respectively. Independently of each other, Prof. Patrick J. Schembri and postgraduate student Julian Evans in Malta, and Prof Patrice Francour and Dr Pascaline Bodilis in France, identified the species as the Barred Knifejaw, Oplegnathus fasciatus. What is surprising about this is that the native range of this species is the region of Korea, Japan, Taiwan, and Hawaii in the North West and Eastern Central Pacific and it has not been previously recorded from the Mediterranean, or from the Atlantic or from the Red Sea and Indian Ocean – that is, anywhere between Malta and its native area of distribution. Moreover, comparison of the photographs taken by John Attard and by Catherine Gras showed the fish to be different individuals. Therefore it appeared that at least two individuals of the Barred Knifejaw had somehow found their way from the Eastern Central Pacific to Malta, a distance of over 10,000 kilometres.
That the fish made the journey under their own steam is not a realistic possibility and therefore transport due to human activity is the most likely explanation. The two teams of researchers speculated on possible ways in which this could have happened: through aquaculture (the Barred Knifejaw is cultured in Korea), the aquarium trade, or via shipping. Detailed enquiries ruled out both aquaculture and the aquarium trade, which left shipping. Transport of alien species by ships is a well known phenomenon for microscopic or very small organisms, which travel in ballast water, however, the two specimens of Knifejaw photographed in Malta were at least 12 cm long and entry to and exit from ballast tanks requires passage through high powered pumps protected by fine-mesh screens. Considering the size of the fish and their known biology, the researchers concluded that it is most unlikely that the fish travelled in ballast tanks. However, medium to large sized ships do not pump seawater directly from the sea but from a chamber know as a ‘sea chest’ which opens to the outside on the ship’s hull below the waterline, and in large ships sea chests may hold several cubic metres of seawater. In effect sea chests act like seawater aquaria and provide a means of transport for marine species that does not involve passage through a pump. Although sea chests are protected by grids, these have large openings and are often damaged or dislodged in transit. There are therefore quite plausible ways in which fish of the size of the Barred Knifejaw found in Malta could be transported from a source area thousands of kilometres away and be released into the wild in a good state of health.
In the report published by the two research teams in the international journal Acta Ichthyologica et Piscatoria, they suggest that shipping, but not necessarily ballast water, has been the most probable transport agent in the present case and in others involving the long-distance translocation of large fish.
Reports of unusual marine creatures are always welcome. Please contact Professor Patrick J. Schembri at the Department of Biology of the University of Malta (+356 2340 2272). The list of publications and a list of other works by Professor Patrick Schembri are available online.
The specimen of the Barred Knifejaw captured from the Valletta Waterfront, Malta, on 22 November 2009 (© 2009 John Attard)
29 March 2017