From Pelagia to pilot whales, mippits to minkies
Published: 15 October 2015
On October 3rd the RV Cefas Endeavour set sail from Portland to begin surveying pelagic food-webs off the southwest coast of the UK. Fifteen scientists, covering a wide diversity of specialisms joined the research survey which was funded under Defra project POSEIDON with further support from MERP. This is the fifth year of pelagic surveying in this region (known as the ‘PELTIC’ surveys) and the primary aims were to carry out a combined fisheries acoustic and trawl survey to determine the distribution and abundance of small pelagic fish species; to collect plankton samples and ichtyoplankton; to record hydrographic data (temperature, salinity, chlorophyll, pCO2, O2) and to quantify the abundance of jellyfish in the region. In addition, locations, species numbers and activities of seabirds and marine mammals were systematically recorded during daylight hours by three Marinelife observers on the ship’s bridge. High resolution ESAS observations were collected on critically endangered Balearic shearwaters as well as cetaceans as part of a new initiative between the Centre for Environment, Fisheries & Aquaculture Science (Cefas), Natural England and Marinelife.
Large catches of pilchard (sardine), mackerel, horse-mackerel, sprat and anchovy were obtained using a specially-designed pelagic trawl net. Zooplankton samples revealed the area to be highly productive and many jellyfish (in particular the ‘mauve stinger’ Pelagia noctiluca and the barrel jellyfish Rhisostoma pulmo) were also caught in large numbers. Through much of the surveying campaign the ship was accompanied by common dolphins and harbour porpoise, but also rarer cetaceans including minke whales, white beaked dolphins and long-finned pilot whales. The ornithologists on board were particularly delighted to be visited by several rare bird species, most notably a Richard’s pippit, alpine swift and a merlin, as well as the usual gannets, shearwaters, storm petrels, gulls, meadow pippits (‘mippits’) and an influx of migrating gold-crests.
A particularly delightful encounter happened on the 11th October when a small pod of common dolphins were spotted fishing for leaping garfish off Lands’ End. The fish had been attracted by the ship’s lights during a night plankton station, and the dolphins were clearly making the most of the situation.
Pelagic food-webs are an under-studied, but vitally important component of marine ecosystems. The research cruise involved close working between government (Cefas), and NERC scientists as well as the crew and volunteer observers. Fundamental new knowledge was obtained as well as thousands of samples. The new information on pelagic fish included a possible shift in the timing of spawning for pilchard over the past 50 years, from predominantly in the spring, to mainly in the autumn. This may have been associated with changes in food availability or long-term changes in climate. Several of the fish species (most notably anchovy and sardine) are warm-water species that are known to have increased in abundance in recent years, whereas comparatively few cold-water pelagic fish species such as herring were observed in the trawl catches this year.
The pelagic fieldwork campaign was timed to coincide with the autumn plankton bloom (with satellite images downloaded each day), and this year concurrent demersal and benthic sampling was carried out aboard the ‘RV Prince Madog’ as part of MERP. It is hoped that the resulting datasets from these two complimentary research cruises can be used to characterise the whole ecosystem from phytoplankton and micro-benthos, all the way up to baleen whales and seabirds.