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Migration patterns and the location of wintering areas, where reproduction takes place, constitute a major gap in knowledge on the biology of most species of baleen whales (Lockyer and Brown 1981, Berta and Sumich 1999, Mate et al. 2007). This applies in particular to Northern Hemisphere rorquals. They are generally regarded as migratory, spending the summer in productive feeding areas at high latitudes, where they are believed to fulfill most of their annual food requirements during a period of 4–6 mo (Lockyer and Brown 1981, Víkingsson 1995). During the winter breeding season they are believed to inhabit lower latitudes although migration routes and wintering areas in the North Atlantic are poorly known except for humpback whales (Megaptera novaeangliae; Smith et al. 1999).

Common minke whales (Balaenoptera acutorostrata) are the most numerous baleen whale on the Icelandic shelf (Donovan and Gunnlaugsson 1989, Borchers et al. 2009, Pike et al. 2011). Abundance estimates in Icelandic shelf waters during summer, based on data from sightings surveys conducted between 1987 and 2009, varied between 10,000 and 44,000 whales (Borchers et al. 2009, Pike et al. 2011). They belong to the so-called Central North Atlantic stock, distributed in summer from the east coast of Greenland to Iceland and Jan Mayen Island (Donovan 1991). Delineation of the stock boundaries is, however, based on limited data and the actual boundaries must be considered uncertain. While minke whales have been seen in Icelandic waters throughout the year (Marine Research Institute, unpublished data) most of these animals are believed to depart Icelandic waters during the autumn but their whereabouts during the winter breeding season are virtually unknown. Little information exists on the timing of the migration, although data from small-type whaling in the late 20th century indicate the species is present in Icelandic coastal waters at least during March–November, with relatively high densities during April–September and a peak in July (Sigurjónsson and Víkingsson 1997).

Satellite telemetry (Fancy et al. 1988) has greatly increased knowledge on the movements of animals and it has become a valuable tool for addressing important management questions (e.g., Heide-Jørgensen et al. 2006, 2012). Compared to other baleen whales, very few common minke whales have been tracked successfully by satellite telemetry. Heide-Jørgensen et al. (2001) reported on the movements of two common minke whales in Norwegian waters in 1994 and 1999 for 31 and 19 d, respectively. Kishiro and Miyashita (2011) tracked a single common minke whale for 27 d in Japanese waters in 2010.

Attempts to track minke whales in Icelandic waters using satellite telemetry were initiated in 2001 with increased effort from 2003 as part of a multifaceted research program (Marine Research Institute 2003). One element of this program was to obtain information on the routes and destinations of the whales as they move out of Icelandic waters in the autumn. Such information is important, not only for improving the basis for conservation and management of the stock, but also to contribute to filling a major gap in our knowledge of the natural history of the North Atlantic common minke whale.

Three types of satellite transmitters were deployed on minke whales. In 2001 and 2002 an ST-15 (Telonics Inc.), external transmitter unit equipped with two lithium thianyl batteries cast in epoxy in the shape of a cylinder 110 mm in length and 28–35 mm in diameter, was used. The unit was preprogrammed to be on for 24 h and off for 72 h. The antenna extended from one end of the transmitter while the other end of the transmitter was glued to a stainless steel cup mounted on an 8 mm diameter titanium dart equipped with three 60 mm long barbs. The barbs functioned to anchor the dart in the blubber and muscle layers below the skin. The stainless steel cup acted as a flange that stopped the transmitter from penetrating through the skin.

In 2004 a long, flat, box-shaped stainless steel implantable tag (113 × 20 × 10 mm, two M1 lithium cells, Wildlife Computers SPOT4) with a harpoon head tip and two barbs along the body of the transmitter (flat box) was used. It had a stop plate that prevented penetration deeper than 10 cm and was delivered with a release cup that slid backward after it hit the whale. The transmitter had the capacity to make 20,000 transmissions and was duty cycled with “one day on and three days off” and 300 transmissions/day (without carryover). It was set to transmit between 0600 and 2300 local time (GMT). In 2008 and 2010 a cylindrical stainless steel implantable tag (20 × 113 mm, 1 AA cell Wildlife Computers SPOT3) was used. All three transmitter models had transmission repetition periods of 45 s and were equipped with a conductivity switch that prevented transmissions when the tag was underwater. The tags used after 2004 were duty cycled to be on during day light periods (0800–2000 GMT).

The deployment system used for attaching the tags to whales was the Air Rocket Transmitter System (ARTS), a device now widely used internationally for tagging baleen whales (Heide-Jørgensen et al. 2001, Mate et al. 2007, Silva et al. 2013, Kennedy et al. 2014). The ARTS consists of an air gun with adjustable air pressure delivered by a scuba tank. It has a barrel large enough to carry a plastic tube that acts as both a carrying rocket for the tag as well as a floatation device in case the tag misses the whale. The tag is attached to the carrying rocket with a nylon wire and when the tag is implanted the carrying rocket releases from the tag. The “rocket” in this study consisted of the tag in combination with a finned tailpiece. The tailpiece provided stabilization during flight as well as flotation, ensuring retrieval of the tag in case of a missed attempt/shot. The pressure and distance to the minke whales when the rocket was launched was 10–17 bars and 10–18 m respectively.

In 2001, 2002, 2008, and 2011 the tagging was conducted in coastal, northern Icelandic waters (Skjálfandi Bay and Eyjafjörður) from the 10 m research boat Einar í Nesi (9 tons, Cummins engine, 254 hp). In 2004 and 2010 tagging was conducted in Faxaflói Bay, Southwest Iceland, in 2004 from the 18 m small-type fishing/whaling vessel Njörður (33 tons, Caterpillar engine, 408 hp) during August and September and in May 2010 from a 12 m tourist boat Ingólfur ÍS (14 tons, Volvo penta engine, 520 hp). The maximum speed of the boats used was around 15–20 km/h, except for Ingólfur (69 km/h). The whales were spotted as they broke the surface, usually within 500 m of the vessel. Whales were approached as gently as possible at slow speed (<9 km/h), sometimes turning off the engine during the whales' deep dives. Depending on the whales' behavior, the speed of pursuing might then be increased after around one hour of the slow speed approach. The length of the whale was visually estimated to the nearest 0.5 m using the boat length as a reference point.

Determination of positions was facilitated through Argos Data Collection and Location Service (Hays et al. 2001). Location data were obtained from six classes of accuracy: 3, 2, 1, 0, A, and B. Positions of classes 1–3 have estimated accuracies of 1,000, 350, and 150 m (Service Argos, in litt.). Experimental studies, however, indicate that for tracking marine animals, slightly lower accuracy can be expected for all three location classes. Also the accuracy of class A locations may approach that of class 1, whereas the accuracy of 0 and B may be around 10 km and 7 km, respectively (Hays et al. 2001, Vincent et al. 2002, Costa et al. 2010). In the context of migration route and destination all three classes of low-accuracy positions contribute important information to the tracks of whales and the errors seem insignificant relative to the scale of whale movements.

The majority (>91%) of the positions obtained were of low quality (0, A, and B; Table 1), so an average daily position was calculated for each 24 h day in order to reduce the impact of the low-accuracy location data. Travel distances were calculated on the basis of these average daily positions and thus do not include nondirectional movements within a day. Therefore, they should be considered minimum estimates of daily travel distance.

Table 1. Details of the instrumentation of eight minke whales off Iceland between 2001 and 2010. Departure from the shelf was defined as the midpoint between the last date on the shelf and the first date off the shelf. For the locations, accuracy class 3 indicates positions with a nominal accuracy of 150 m, class 2 positions of <350 m, class 1 positions of <1,000 m and classes 0, A, and B no assigned accuracy. Position of the tag on the whale is given by L=left, R = right, M = mid, F = front, H = high. Tagging positions: N: north Icelandic waters (Skjálfandi Bay and Eyjafjörður); S: southwest Icelandic waters (Faxaflói)
Tag IDTypeDateTagging position (°N/°W)Distance/ pressureWhere on whaleSize of whale (m)Departure from shelfAverage daily travel distance on shelf (SD) km/d Average daily travel distance off shelf (SD) km/dDays between tagging and last location3210ABSumComments
  1. a

    Calculated from average travel speed of that whale during migration.

13280ST1512 August 2001N (66°05′/17°36′)NA/11LMH6NA10 (10)NA18   171321 
13282ST1515 August 2001N (66°07′/17°37′)NA/11LFH6NA16 (12)NA65 23 174971Partially implanted
3960ST1520 August 2002N (66°16′/17°54′)13/13 62 November 20016 (7)164 (23)8116111150101180 
50683Flatbox14 September 2004S (64°08′/22°27′)10/10LFH829 September 200428 (30)176 (101)25 351255286 
50686Flatbox27 August 2004S (64°09′/22°11′)10/10RFH56 November 2004aNA110 (77)101  1 236Tag implanted too deeply
50685Flatbox23 September 2004S (64°11′/22°17′)10/17LFH8.5NA7 (5)NA14    5914 
21802Cylinder7 November 2008N (65°47′/18°08′)18/22  NA NA2     33 
37278Cylinder6 May 2010S (64°14′/22°22′)18/20RMH6NA NA64    336 

Between 2001 and 2011, 17 minke whales were instrumented with satellite tags in Iceland. Of these, eight provided position data (Table 1), however one of them did so for only two days. Of the nine tags that did not provide any data, two were probably positioned too low on the side of the whales. The reason for failure of the other seven is unknown.

A minke whale tagged in Skjálfandi Bay, North Iceland, on 12 August 2001 (#13280) was tracked until 29 August by which time it had traveled a minimum of 153 km along the northern coast of Iceland (Fig. 1). Another whale tagged in Skjálfandi Bay on 15 August 2001 (#13282) was tracked until 18 October. During this period the whale moved at least 958 km, with an average daily travel distance of 16 km (range 2–38 km/d). This whale's movements consisted mainly of visits to fjords in northeastern Iceland with no apparent travel offshore (Fig. 1). During the period 27 August to 23 September 2004 seven minke whales were tagged in Faxaflói Bay, southwest Iceland. Useful data were received from three of these animals (Table 1). One of them only transmitted data for 2 wk during which it stayed in the bay close to the tagging site. Tagging attempts in Faxaflói Bay during the spring yielded limited results with only one minke whale providing useful, albeit very limited, data. This individual was tagged in Faxaflói Bay on 6 May 2010 and the first signals were received 45 d later close to the tagging site. Six positions were received between 20 June and 8 July, all in Faxaflói Bay.

image

Figure 1. Tracks of two common minke whales (#13280 and #13282) satellite-tagged in August 2001 in northeastern Iceland. Sites of tagging (large open circles) and last positions (large closed circles) are indicated on the map. Data points are average positions for each day, and the dotted lines between them extrapolations (the shortest distance between average daily positions). Depth contours represent 100 m and 200 m.

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A minke whale tagged in Skjálfandi Bay on 20 August 2002 was tracked for 88 d, (#3960, Fig. 2). Like #13282 tracked in 2001, this individual remained in coastal northern Icelandic waters past mid-October. By 31 October it had moved northeast of Iceland, and four days later signals were received more than 350 km further south. The last signals were received on 8 November when the animal was at 56°N, 27°W, indicating continuous fast movement southward.

image

Figure 2. Tracks of two common minke whales (#50683 and #50686) satellite-tagged in Faxaflói Bay, southwest Iceland, in August and September 2004 and of one common minke whale (#3960) tagged in Skjálfandi Bay, northeast Iceland in 2002. All dates of transmissions are indicated for #50686 as well as the dates of last positions for #50683 and #3960. As no positions were available for the first 89 d after tagging for whale 50686 a dotted line is drawn between the first two points for this whale. The box indicates the position of a large group of minke whales reported by Slijper 1964.

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One whale tagged on 14 September 2004 (#50683) stayed within the tagging area in Faxaflói Bay until 22 September, when it moved west to the continental slope area and stayed for about a week. On 30 September this whale headed south along the Reykjanes Ridge at a mean daily travel distance of 176 km. The last signal received from this animal was on 8 October when its position was at around 50°N, 34°W (Fig. 2).

On 17 November 2004 the first signals were received from a minke whale that had been tagged in Faxaflói Bay on 27 August (#50686). Video recordings of the tagging event indicated that the failure of this tag to transmit for almost three months after tagging was caused by too deep implanting. Its position at the time of first transmission was over the Mid-Atlantic Ridge, 900 km west of northern Spain (Fig. 2). The next positions for this whale were received on 23 November by which time it had traveled some 700 km to the south and into the vicinity of the Azores. By 5 December when the next usable transmissions were received, the animal had moved farther south in the Canary Current and was 1,000 km northwest of the Cape Verde Islands. This area is approximately 3,700 km from Faxaflói Bay where the tag was deployed on the whale 101 d earlier. Assuming the same daily traveling rates for the first half of the migration, this whale would have left the Icelandic continental shelf in early November (Table 1).

The tagging work reported here represents the largest such effort applied to common minke whales to date, and it also produced the longest tracks of tagged common minke whales to date (Heide-Jørgensen et al. 2001, Kishiro and Miyashita 2011). Compared to tagging of larger baleen whales, minke whale tagging clearly remains a challenge, given that less than half of the tagged whales provided useable position data, techniques require further development. A major difficulty is getting close enough to the whale to deploy the transmitter. The tag needs to be well positioned high on the whale so that the antenna can clear the water and allow transmissions when the whale surfaces. Finally, the tag needs to be anchored in such a way that it will stay on the animal. It is usually impossible to assess the tag attachment because the whale disappears and can rarely be approached for a follow-up inspection of the deployment site. All of these factors add to the considerable challenges of tagging common minke whales and slow down the learning process from the occasional successes. Considerable investment in the development of better methods will be needed before large-scale tagging and long-term tracking of minke whales becomes feasible.

The deployments in 2001 and 2002, although few in number, indicated fairly stationary behavior of minke whales in coastal North Icelandic waters during the late summer and fall prior to the onset of migration. They also cast doubt on the peak of migration being in September, as had previously been assumed from catch data (e.g., Sigurjónsson and Víkingsson 1997). One of these whales (#3960) departed in the beginning of November, while another one (#13282) had not started a migration by 18 October when the last position was received. However, the only whale tagged in Faxaflói Bay in 2004 for which the departure date could be determined (#50683) left Icelandic waters at the end of September. The two “late migrants” tagged north of Iceland (#3960 and #13282) were both estimated as 6 m in length (corresponding to immature or pubertal individuals) while the “early” migrant, tagged in Faxaflói Bay, was estimated as 8 m long and thus likely mature. Spatio-temporal segregation by sex and maturity on the feeding grounds is a well documented phenomena in common minke whales (Horwood 1990) although a potential difference in timing of migration is poorly documented. The observations presented here could indicate later onset of the fall migration for small (immature) minke whales and the indirectly estimated departure of whale #50686 (6 November) is consistent with that view. However, a much larger sample size is needed before firm conclusions can be drawn regarding size-segregated departures. Unfortunately, no biopsies for determination of sex were obtained from the tagged animals.

The total combined tracking period for the eight minke whales was 370 d with signals received on 104 d. All the positions received were within the present IWC boundaries for the Central North Atlantic stock. Although these observations can be interpreted to support the present delineation of this stock, the limited scope of the data must be acknowledged. Most of the tagging was conducted in late summer and autumn and little is known about movements earlier in the year. Recent research has indicated a change in mid-summer distribution of Central North Atlantic common minke whales due to changes in prey availability (Víkingsson et al. 2014). Further satellite tagging during spring might help explain the nature of these changes by linking movements of minke whales with distribution of major prey species.

The average minimum daily traveling speeds were considerably faster off the shelf than in coastal waters (Table 1). This is not unexpected as movement into slope waters is assumed to indicate that the animal has begun to migrate, whereas much feeding activity is known to take place in coastal waters. The average traveling speeds during migration (4.6–7.3 km/h) reported here are similar to those recorded from migrating gray whales (Eschrichtius robustus), and fin whales (Balaenoptera physalus) (Swartz et al. 1987, Mate and Urban-Ramirez 2003, Silva et al. 2013) and somewhat higher than reported for blue (Balaenoptera musculus) and humpback whales (Bailey et al. 2009, Kennedy et al. 2014).

The tracks of the three minke whales that departed from Icelandic waters provide the first documentation of the migration route and indication of winter destination of minke whales summering in Iceland. All three followed an offshore route heading south in the middle of the Atlantic. Contact was lost early with two of the whales but all three were heading in the same direction at the time. The third whale, for which contact was maintained until it had passed the Azores, continued south to a position in the mid Atlantic at about 28°N. This represents the longest tracking record for a common minke whale to date, both in terms of distance traveled (3,700 km) and tracking duration (100 d). There is no previous documentation for the autumn migration route of common minke whales worldwide nor of balaenopterids in the North Atlantic. The indications from the present study of offshore movement pattern close to the Mid-Atlantic Ridge is similar to that described for northwards spring migration of fin, blue, and sei (Balaenoptera borealis) whales migrating past the Azores towards Greenland, Canada, and Iceland (Olsen et al. 2009, Prieto et al. In Press, Silva et al. 2013) and humpback whales migrating from the Caribbean Sea towards Iceland and Norway (Kennedy et al. 2014).

Winter sightings of minke whales are uncommon throughout the North Atlantic (Slijper et al. 1964, Folkow and Blix 1991, Mitchell 1991, Van Waerebeek et al. 1999) and this suggest that these relatively abundant whales occur mainly offshore during the winter. Indeed, most of the few and sporadic sightings have been in offshore areas of the southern North Atlantic. Although the species identifications have been disputed, Slijper et al. (1964) reported large numbers of minke whales in an offshore area between 20°N and 30°N in May possibly representing a northward migrating herd (see Fig. 2). The position where contact was lost with the southernmost tracked whale in this study (#50686) lies at the edge of that area. At about the same latitude but farther east, Van Waerebeek et al. (1999) reported a number of minke whale sightings and strandings around the Canary Islands and along the West African coast. Although most of these observations were made during winter, they included three summer stranding records. All of these animals for which length could be measured or estimated (n = 18) were deemed to be immature whales, like whale #50686. Folkow and Blix (1991) reported two minke whale sightings close to the Cape Verde Islands on 10–12 December 1989. No further minke whale sightings were made in their subsequent crossing of the Atlantic approximately between 18°N and 20°S during 12–24 December.

It will be necessary to track more minke whales, for longer periods, to determine the actual winter migratory destination(s) of whales from Iceland. However, these initial attempts have been informative, adding to the impression from the sparse sighting and stranding evidence that offshore areas of the central and/or eastern part of the southern North Atlantic constitute the winter habitat for the population.

Acknowledgments

  1. Top of page
  2. Acknowledgments
  3. Literature Cited

Lars Kleivane, Tryggvi Sveinsson, and Mikkel V. Jensen were in charge of the minke whale tagging work with assistance from Birgir Stefánsson and Arne Geisler. The study was supported by the Icelandic Centre for Research (RANNIS), the Marine Research Institute, Iceland and the Greenland Institute of Natural Resources. We thank Randall Reeves for comments on an earlier version of the manuscript and Bjarki Th. Elvarsson for generating the figures. The study was conducted in full compliance with Icelandic law and regulations concerning animal welfare issues.

Literature Cited

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