Roman Klepikovskiy, Nikolay Lukin, Timofey Mishin
Knipovich Polar Research Institute of Marine Fisheries and Oceanography, Murmansk, Russia Abstract
We present data on the distribution of marine mammals (primarily cetaceans), in the waters of the Barents Sea, obtained in the course of PINRO marine research activities in recent years. The article focuses on the results of observations made in the course of trawl-acoustic and ecosystem surveys (TAS and ES respectively ) onboard PINRO research vessels during different seasons of the year. In February-March during Joint Russian-Norwegian multispecies TAS for demersal fish, we carried out research in the southeastern Barents Sea. This time low cetacean numbers were recorded, and although these were higher in the western part of the survey area. Marine mammals were sighted in May-June during the International ES of the northern seas (IES) in the south Barents Sea. This time the number of cetaceans encounters was significantly higher, while their abundance also increased and their distribution was wide. Marine mammals observations were made in August-October during the annual joint Russian-Norwegian Barents Sea ecosystem survey (BESS) in all areas of the Russian zone. This time, the widest cetacean distribution was registered. The next PINRO marine mammals sightings were registered during the multispecies TAS for estimation of juvenile fishes and stock assessment of demersal fishes in the Barents Sea and adjacent waters in October-December, when low numbers of marine mammals were registered. Research covered almost the entire surface of the Barents Sea. On the basis of these studies, we determined that the distribution of the main species of cetaceans was usually closely associated with pelagic fish aggregations obtained from trawl-acoustic data.
Keywords: marine mammals, distribution, encounters, Barents Sea, vessel observations Introduction
The main PINRO research area in the Barents Sea is a region of intensive fishing activity, in which almost all the main fish stocks encountered in high numbers are exploited. For their rational use, it is necessary to take into account all potential influences, including the presence of predatory marine mammals. For this, we need information about the composition of marine mammals species;
seasonal distributions, the time that they remain in given areas, migration routes, numbers, diet specialisation and so on.
Currently, research on the distribution and numbers of marine mammals in the Barents Sea area is performed on board PINRO research vessels and during coastal expeditions. Previously, from 1997 until 2005, aircraft were usually employed for this purpose.
Nowadays, PINRO research cruises in the Barents Sea enable us to collect data on marine mammals throughout the year. At present almost all PINRO marine research cruises are trawl-acoustic based and ecosystem oriented, which enables to determine why marine mammals occupy particular areas of the Barents Sea.
Data on marine mammals distribution, encounters and numbers, besides evaluating their role in the Barents Sea ecosystem and their impact on commercial fish species, can also be used as an indicator of aggregations of fishery target species, including the state of the environment as a whole. Marine
mammals are also a huge potential commercial resource that only Norway is currently developing in the Barents Sea.
Materials and methods
PINRO marine mammals research in the open area of the Barents Sea takes two forms:
1. Marine mammal observations during specialized trawl-acoustic and ecosystem surveys (TAS and ES respectively);
2. Marine mammal data collected during fisheries on board fishing vessels and from other cruises.
PINRO currently performs regular annual specialised studies of marine mammals in the Barents Sea during:
- The Joint Russian-Norwegian multispecies TAS for demersal fish in the Barents Sea in February-March;
- The International ES of the northern seas in May-June;
- The Joint Russian-Norwegian Ecosystem Survey in the Barents Sea (BESS) in August-October;
- Multispecies TAS for estimation of juvenile fishes and stock assessment of demersal fishes in the Barents Sea and adjacent waters in October-December.
Vessel-based naked-eye transect surveys of marine mammals are performed when the vessel is under way, either from the navigation deck or from the ship’s bridge. We use 7x50 binoculars (only to determine the species), a special protractor, ship or portable GPS system, digital camera, portable personal computer for data processing. All the marine mammals observed are identified to species level, and if this is impossible, recorded as “unidentified” (unid.), for example, unid. whale, unid.
dolphin, unid. seal. During the observations, the date, time, position, type, numbers, size of the group, distance from vessel, behaviour and weather conditions are recorded in a working log. The distance to the observed object is measured using a binocular grid or a special measuring ruler.
Every 60 minutes during the transect, coordinates are recorded, including the transect's starting and finishing coordinates. Any marine mammals opportunistically observed outside the transect are also recorded. Observations are also made when setting and hauling the trawl, when the vessel is actually trawling, or drifting, including under adverse weather conditions (Zyryanov, 2004).
During TAS, when the research vessel is following the planned tacks with its acoustic equipment active, it is possible to view the relationship between marine mammal encounters and distribution with the presence of other marine organisms. Simultaneously with the acoustic survey, control trawls are carried out at predetermined points. When marine mammals are registered, the echo sounder recordings are analysed, as are individuals from any trawl catches . With these results in hand, it is possible to define and characterize with some accuracy the prey of marine mammals in the area (Klepikovskiy, Nosov, 2013).
In addition to its specialised marine research projects, PINRO collects information about marine mammals on board fishing vessels and from other cruises that involve PINRO staff, who collect available data regarding commercial fish species, and wherever possible make marine mammal observations.
Results
This article presents the results of specialized observations of marine mammals during TAS and ES surveys carried out on board PINRO research vessels.
During the Joint Russian-Norwegian multispecies TAS for demersal fishes in the Barents Sea in February-March, observations by PINRO of marine mammals were performed in 2004, 2011, and
every year since 2012. During the survey, PINRO research vessels explored the southeastern part of the Barents Sea (Figure 1).
Figure 1. PINRO research area with research vessel routes and total numbers of cetaceans counted during Russian-Norwegian multispecies TAS for demersal fish in the Barents Sea, February-March.
The main results of the observations made during this period in the PINRO research area show low marine mammals (mostly cetaceans) encounters in the eastern part of survey. Most of the marine mammals encounters take place in the western part of the survey area (Figure 2).
Figure 2. Species composition, distribution and percentage of cetaceans counted during Russian-Norwegian multispecies TAS for demersal fishes in the Barents Sea, February-March.
In the area centred on 71º56´N/29º08´E, mixed concentrations of capelin (Mallotus villosus) and herring (Clupea harengus) and wintering groups of white-beaked dolphin (Lagenorhynchus albirostris) numbering 100-500 individuals were observed, and in the area centred on
close to capelin aggregations in the northern and southern parts of the research areas, small numbers of humpback (Megaptera novaeangliae) and fin (Balaenoptera physalus) whales (mostly individuals) were observed, apparently remaining for the winter in the Barents Sea or having already returned there. Minke whales (Balaenoptera acutorostrata) were not observed.
Marine mammal observations have been performed by PINRO during the International ES of the northern seas in May-June since 2008. Our research covers the southern part of the Barents Sea from east to west (Figure 3).
Figure 3. PINRO research area with research vessel routes and numbers of cetaceans recorded in the Barents Sea during the annual International ES of the northern seas, May-June.
Compared to the previous survey (February-March) there is a significant increase in encounters of marine mammals and a wider distribution within PINRO's research area (Figure 4).
The species found here in largest numbers were white-beaked dolphin, minke whale, fin whale and humpback whale. The white-beaked dolphin was recorded both singly and in groups of from 2-8 to 15-20 individuals in almost all over the research area. These species concentrated on capelin and herring aggregations. Most minke whale were observed singly in the eastern and central parts of the research area, where they were recorded close to herring and cod (Gadidae) aggregations. Fin whales were the most numerous species of the balaenopteridae. During the observations fin whales were recorded singly and in groups of up to five individuals. Most of these animals were observed in the western part of research area between 20ºE and 27ºE close to macroplankton, capelin and herring aggregations. Humpback whales were recorded singly and in groups of up to four individuals, and most were observed west of 27ºE. Humpbacks were sometimes recorded together with white-beaked dolphin, actively feeding on herring and capelin aggregations. Among the toothed whales in some years we also observed harbour porpoises (Phocoena phocoena), killer whales (Orcinus orca), northern bottlenose whales (Hyperoodon ampullatus) and sperm whales (Physeter macrocephalus).