Cruise report of
cetacean survey in the Scotia Sea 23 February 2003
Introduction
Cetacean observations were conducted for
the IWC from the British Antarctic Survey vessel
RRS James Clark Ross as part of collaborative data collection . The main aims of the cruise were studies of
krill, zooplankton and oceanography in the
Methods
The survey design
followed a pattern of north-south zig-zag transects conducted from west to east
across the
Observations
were conducted according to the protocol used for single platform observations
during the IWC-CCAMLR survey in 2000 (Reilly et al., 2000). Two
observers searched a 180o sector ahead of the vessel with 7x50
binoculars. Observations were made from the roof of the bridge (
Detailed data on ice conditions were recorded using the ASPeCt (Antarctic Sea Ice Processes and Climate) protocol, whenever the area of sea covered by ice was greater than 5%. If icebergs were present but cover was less than 5% then the number of icebergs in a 180o arc ahead of the vessel were recorded as a comment.
It was not possible to conduct distance and angle experiments using radar on fixed targets. However, the photogrammetric measures of range and bearing allowed comparison between visual estimates and measured values to actual sightings. In addition, some measurements were made to fixed targets to allow comparison with angle and distance experiments conducted on other surveys.
Results
Survey effort
The cetacean survey effort is shown in figures 1-4. Total effort was 220 hours. Most of the survey effort was conducted in deep water with only 7% in depths of less than 200m. Distribution of effort by depth is shown in table 1. Sea surface temperatures ranged from –1.6 to 8.8oC with the distribution of effort by sea surface temperature shown in table 2. A total of 95 n. miles of effort were conducted in estimated ice cover of greater than 5%, this amounted to 4% of the total effort.
Environmental variables that could be related to sighting probability included visual estimates of sea state, overall ‘sightability’ and minke whale visibility. In addition, wind speed and solar radiation were measured by the ship’s instrumentation system. Restricting analysis to effort in sightability ‘moderate to excellent’ and wind speeds of less than 12ms-1 results in 1672nm of effort compared to a total effort of 2237nm. This would include 203 out of 214 sightings and only exclude 2 sightings identified to species level.
Cetacean sightings
Table 3 lists the number of on-effort sightings and total number of individuals by species. The locations of some of these are also shown on figures 1 - 4. In addition, two species, Commerson's dolphin (Cephalorhynchus commersonii) and Gray's beaked whale (Mesoplodon grayi) were also sighted off-effort (table 4).
The locations of all sightings relative to the vessel are shown in figure 5 Some degree of rounding in radial distances is evident corresponding to a division of 0.1 reticles (the Wincruz software rounded all reticle readings to the nearest 0.1 reticles). Analysis of the ranges and bearings measured photogrammetrically provide additional data with a measured level of accuracy, for comparison. A preliminary comparison of estimated distances against measured (figure 6) indicates no substantial bias in distance estimation and moderate variance. Analysis of bearing estimates suggested a root mean square error of around 5o. Further analysis of these data is planned. Distribution of perpendicular distances to species with similar strength and type of visual cue are shown in figures 7-10.
Fin whales were generally observed north of the SACCF (Southern Antarctic Circumpolar Current Front) whereas minke whales were predominantly observed to the south of this and towards the southern ends of the transects. Sei whales were also observed to the north of the SACCF and sometimes associated with right whales, but not in the same areas as fin whales. Of 16 sightings in greater than 5% ice cover, 2 were right whale, 1 was killer whale and 13 were minke whale.
Pinniped sightings
Table 5 lists sightings of pinnipeds with the proportion of sightings of animals hauled out on ice. Fur seals were the most frequently encountered pinniped, often at great distances from ice or land. Almost all the sightings of crabeater and leopard seals were on or close to ice.
Discussion
The generally good weather conditions during the survey allowed a greater amount of survey effort than had been expected. The amount of effort was around 50% greater than that achieved from the James Clark Ross during the CCAMLR synoptic survey in 2000. The area covered by both surveys was broadly similar and the two data sets should prove comparable due to similar survey protocols and the fact that both observers on this study were also involved in the CCAMLR survey.
The use of photogrammetric methods proved an effective way of measuring radial distance and bearing to sightings. In addition, these methods provided the equivalent of distance testing experiments for estimating the variance of distances based on reticle readings and estimated angles. This is especially important for multi-disciplinary cruises where dedicated ship time is not available for distance experiments.
One encounter of
particular interest to the SOWER 2000 objectives was on
The detections
of six individuals in two groups of sperm whales are unlikely to be sufficient
for strip width estimation. This number of sightings is consistent with
previous visual and acoustic surveys in the
Observations of Gray's beaked whale were also of particular interest. The long-held view on the occurrence of Gray’s beaked whale is that it covers a circumglobal distribution in temperate or cold temperate waters of the southern hemisphere between 30º and 45º (e.g. Marcuzzi and Pilleri, 1971; Ross, 1979; Rice, 1998; Pitman, 2002). For a detailed review of documented specimen and sighting localities see Mead (1989).
Goodall and
Galeazzi (1985) first referred to some 53 stranding observations or specimens
of M. grayi recorded from the tips of
the southern continents, the southernmost being Tierra del Fuego at ca. 54ºS.
Mead (1989), repeated by Ohsumi et al.
(1994), discusses a particular specimen in the National Museum of New Zealand
(nmnz 612) which he says was collected from an unknown locality in the
Antarctic; Mead adds ‘it is difficult to attach much importance to this record
because M. grayi has been known to
stray before‘ (referring to the only record from the northern hemisphere, in
The Netherlands). However, the origin of this specimen should be of interest.
Anton van Helden, curator of marine mammals at Te Papa museum (in litt. to KVW,
While Pitman (2002) cites for the distribution of M. grayi ‘circumglobal in temperate waters of the southern hemisphere’, in the same paper an excellent photo by Richard A. Rowlett ‘taken in Antarctic waters’ is printed. Ohsumi et al. (1994) indicate a single sighting of Gray’s beaked whale in the Antarctic based on the IDCR/SOWER survey programme since 1987/88, at about 62º30’S, 150ºE (estimated from map) in the Australian Antarctic basin. So far we are aware, there exist no other similar, published records.
These observations of Gray’s beaked whale sighting from the Scotia Sea, south of the Polar Front widens the possibility that the subantarctic and Antarctic oceans may be part of the normal distribution area for M. grayi like it is now becoming increasingly recognized for M. layardii (e.g. Pitman, 2002). The issue should become clearer still in the future with an increasing percentage of the hitherto lumped ‘ziphiids’ sightings identified to species.
References
Goodall, R.N.P. and Galeazzi, A.R. 1985. A review of the food habits of the small cetaceans of the Antarctic and Sub-antarctic. pp. 566-72. In: W.R. Siegfried, P.R. Condy & R.M. Laws (eds.). Antarctic Nutrient Cycles and Food Web.
Leaper, R., Gillespie, D. and Papastavrou, V. (2000). Results of passive acoustic surveys for odontocetes in the Southern Ocean. J. Cetacean Res. Manage. 2(3): 187-196
Leaper, R. and Gordon, J. (2001). Application of photogrammetric methods for locating and tracking cetacean movements at sea J. Cetacean Res. Manage. 3(2):
Marcuzzi, G. and Pilleri, G. 1971. On the zoogeography of cetacea. Investigations on Cetacea 3(1): 101-170.
Mead, J.G. 1989. Beaked whales of the genus Mesoplodon. pp. 349-430. In: S.H. Ridgway and R. Harrison. Handbook of Marine Mammals.Vol. 4. Academic Press.
Ohsumi, S.,
Pitman, R.L. 2002. Mesoplodont whales (Mesoplodon spp.). pp. 738-742. In: W.F. Perrin, B. Würsig and J.G.M. Thewissen (eds.). Encyclopedia of marine mammals. Academic Press.
Reilly, S., Hedley, S., Hewitt, R., Leaper, R.,
Thiele, D., Pitman, R.L., Naganobu, M., Watkins, J. and
Rice, D.W. 1998. Marine Mammals of the World. Systematics and Distribution. Special Publication No. 4. The Society for Marine Mammalogy. 231pp.
Tables
Table 1. Distribution of effort (in nautical miles) by depth of water (metres)
|
0-999m |
1000-1999m |
2000-2999m |
3000-3999m |
4000-4999m |
No depth reading |
Total |
|
484 |
212 |
433 |
845 |
240 |
23 |
2237 |
Table 2. Distribution of effort (in nautical miles) by sea surface temperature (oC)
|
-2 to 0 |
0 to 2 |
2 to 4 |
4 to 6 |
6 to 8 |
8 to 10 |
No temp reading |
Total |
|
239 |
664 |
865 |
276 |
94 |
76 |
23 |
2237 |
Table 3. On-effort cetacean sightings
|
Species |
Number of sightings |
Total individuals |
|
Fin whale (Balaenoptera
physalus) |
15 |
36 |
|
Sei whale (Balaenoptera
borealis) |
4 |
8 |
|
Antarctic minke whale (Balaenoptera bonaerensis) |
10 |
24 |
|
Undetermined minke whale (Balaenoptera bonaerensis/acutorostrata) |
30 |
48 |
|
Sperm whale (Physeter
macrocephalus) |
6 |
6 |
|
Humpback whale (Megaptera
novaeangliae) |
12 |
38 |
|
Right whale (Eubalaena
australis) |
20 |
33 |
|
Southern bottlenose whale (Hyperoodon planifrons) |
15 |
31 |
|
Undetermined beaked whale of genus Mesoplodon (Mesoplodon sp.) |
4 |
13 |
|
Undetermined beaked whale (Ziphiidae) |
9 |
24 |
|
Killer whale (Orcinus
orca) |
4 |
33 |
|
Pilot whale (Globicephala
sp.) |
2 |
85 |
|
Hourglass dolphin (Lagenorhynchus
cruciger) |
9 |
58 |
|
Peale's dolphin (Lagenorhynchus
australis) |
2 |
5 |
Table 4. Observations of Gray's beaked whale
|
Identification |
Date |
Location |
Group size |
Depth SST (ºC) |
Comments long, white rostra sticking out above water surface; no teeth seen. in 1 individual: long rostrum seen before whitish head surfaces; body
grey-brown, no scars seen on 3.5-5m body |
|
M. grayi |
|
61.39º S 031.19º W |
6 (5-7) |
3,956m 1.16 ºC |
|
|
like
– M.grayi |
|
56.85º S 031.60º W |
4 (4-5) |
3,608m 2.64 ºC |
Table 5. Pinniped sightings on effort.
|
Species |
Number of sightings |
Total individuals |
Proportion on ice |
|
Fur seal (Arctocephalus
sp.) |
390 |
1019 |
0.14 |
|
Crabeater seal (Lobodon
carcinophagus) |
15 |
27 |
0.93 |
|
Leopard seal (Hydrurga
leptonyx) |
12 |
13 |
0.83 |
|
Weddell seal (Leptonychotes
weddellii) |
5 |
5 |
1.00 |
|
Unidentified Phocid |
18 |
25 |
0.72 |
Figures
Figure 1. On effort sightings of fin whales (upward pointing triangles), sei whales (downward pointing triangles), and minke whales (open circles)
Figure 2. On effort sightings of humpback whales (open circles)
Figure 3. On effort sightings of right whales (open circles)
Figure 4. On effort sightings of sperm whales, killer whales and southern bottlenose whales
Figure 5. Location of all cetacean sightings relative to the vessel
Figure 6. Comparison of estimated and measured radial distances to sightings
Figure 7. Perpendicular distances to fin and sei whale sightings combined (distances are shown as the mid-point of 250m wide bins).
Figure 8. Perpendicular distances to minke whale sightings (distances are shown as the mid-point of 250m wide bins).
Figure 9. Perpendicular distances to humpback and right whale sightings combined (distances are shown as the mid-point of 250m wide bins).
Figure 10. Perpendicular distances to all baleen whale sightings combined (distances are shown as the mid-point of 250m wide bins).
Figure 11. Perpendicular distances to all small whale sightings combined (distances are shown as the mid-point of 250m wide bins).
Appendix – Definitions of data categories entered into Wincruz software
1. Viewing
conditions
1.1 Swell code
When entering swell codes, swell was defined to be waves generated by wind elsewhere. Thus any waves generated by the wind that was currently being experienced were not considered as swell.
1.2
Sightability
Sightability category was a subjective judgement of overall conditions related to detecting a blow from a large baleen whale. This was a combination of sea conditions and meteorological visibility with more emphasis on meteorological visibility than for the minke whale visibility distance. If it was not possible to discern the horizon at all then sightability was classed as ‘Poor=2’ or ‘Too poor to survey=1” if visibility was less than 1 n.mile. If the horizon was visible and allowed reticle readings but had poor contrast for detecting blows then sightability was classed as ‘Moderate=3’. ‘Good=4’ sightability required a clear horizon with enough contrast to allow a blow to be detected at the horizon. ‘Excellent=5’ was limited to near perfect conditions.
1.3 Beaufort
The Beaufort scale was designed as a way of estimating wind speed from the appearance of the sea. In this context however, Beaufort is used as a proxy for sea state. Sea state was categorised as Beaufort N if it was judged to affect viewing conditions similarly to the sea conditions generated by a wind of Beaufort force N blowing across the open sea for some hours. Thus for example, the sea state from an increasing wind which had not yet had time to build up the waves or areas sheltered by ice, would be given lower Beaufort categories than the corresponding wind speed.
2. Weather
Conditions
2.1 Visibility
Visibility is defined in Wincruz as an estimate of the maximum distance (in nautical miles) that a blow from a minke whale could be detected. Most of the minke whales encountered during the survey did not produce a strong blow but visibility was defined assuming a strong blow. In conditions that were judged to be optimum, visibility was recorded as 2.5 n.mile.
2.2 Ice cover was rounded to the nearest 10% by the software. If total cover was less than 5%, which was frequently the case in areas of scattered ice bergs, then the number of bergs in sight in a 180o arc ahead of the vessel was entered as a comment. When ice cover was greater than 5%, detailed ice records were made using the Aspect (Antarctic Sea Ice Processes and Climate) recording procedures.
3. Sighting
data
3.1 Species codes
The species codes and definitions of ‘like’ sightings were the same as for the CCAMLR survey.
3.2 Group size
For sightings surveys where a variety of species from small odontocetes to large mysticetes are likely to be encountered, it is not possible to have a single, consistent, biologically meaningful definition of ‘group’. Instead, group needs to be defined in relation to the sighting process and spatial resolution of the data that can be collected. For line transect surveys, based on perpendicular distances, the main considerations are the way in which groups of animals affect their probability of detection and assigning an appropriate perpendicular distance to clusters of animals when these are considered as a single group. For the purposes of this survey we classified clusters of whales as a group if
(i) The whales were close enough to each other and with some degree of behavioural synchronisation such that the presence of more than one whale increased the probability of detection of an individual. In this case, the recorded sighting location was that of the first sighting location of the group.
(ii) Whales were not necessarily showing any degree of behavioural synchronisation but aggregations were sufficiently dense that it was not possible to distinguish sightings of new individuals from resightings of whales that had already been seen. In this case, the recorded sighting location in Wincruz was to the first animal to be detected, but video scans were performed to allow an estimate of the location of the ‘centre’ of the group.
Appendix II
Structure of database
Cetacean Sightings (on effort)
Cetacean Sightings (off effort - these were sightings made while Wincruz was running but not on effort)
Non-Wincruz off effort cetaceans (these were off-effort sightings which were not entered into Wincruz)
Pinniped sightings (on effort)
All visual data (every entry in Wincruz with corresponding ship data)
Ice Photos
Data fields from Excel file
Observer codes
RL - Russell Leaper
KVW - Koen Van Waerebeek
DS - Debbie Salmon
AS - Ana Sirovic
OBS - any of ship’s crew or other scientists
Pinniped sightings
Species code 25 was added as ‘Unidentified phocid seal’
Effort code
This is MI for
normal observations from the