SMM 2011
30:1
Beaked whales in Irish waters: what can long-term strandings records tell us? Hernandez-Milian, G. and Rogan, E. E-mail:
[email protected] School of Biological, Earth & Environmental Sciences, Distillery Fields, University College Cork, Distillery Fields, North Mall, Cork, Ireland
Introduction: Systematic records have been kept continuously since 1913 and have been published on a regular basis, with stranding records dating back to the 1800s (e.g., Berrow & Rogan, 1997; McLeod et al., 2004). In this work, we update the stranded records of beaked whales, correct some strandings records, add some new unpublished information and present some information on diet.
Methodology: The majority of the stranding data compiled has been submitted previously to the Irish Naturalists’ journal and peer-reviewed. Total body length & sex of the animals were recorded. The coastal areas around Ireland were divided into four main areas (Fig. 1) for geographical comparison. Seasonal patterns were examined & “Cause of death” are summarized into three general categories: bycatch, live stranding & stranded dead/unknown.
Results: A total of 132 records of beaked whales have been recorded stranded on Irish coast, where more than 37.9% of the strandings were Northern bottlenose whale Hyperoodon ampullatus (n = 50), 36.4% Cuvier’s beaked whale Ziphius cavirostris (n = 48), while Sowerby’s Mesoplodon bidens & True’s beaked whale M. mirus stranded 10.6% & 8.3% respectively. An unusual Gervais’ beaked whale M.europaeus was also recorded. The sex ratio in most species stranded was not significantly different from parity (Chi-squared test, p=0.018) 30
45
a)
Winter Spring Summer Autumn NA
56.0% 25 20
39.6%
40 35 35.4%
40
b)
Irish Sea South Coast West Coast North Coast
20
44.0% 32.0%
15
15
10
10 5
5
5 NBW
SBW
TBW
CBW
Dead
25
15
0
Bycaught
30
25
10
Alive
35
30
20
c)
24.3% 10.8%
0
0 NBW
SBW
TBW
NBW
CBW
SBW
TBW
Fig 2. Seasonal (a), Geographical (b), and “cause of dead” (c) stranding distribution of the main beaked whale species (NWB, Northern beaked whale; SBW, Sowerby’s beaked whale; TBW, True’s beaked whale; CBW, Cuvier’s beaked whale) stranded.
No patterns on the strandings were found for Sowerby’s and True’s beaked whales.
Conclusions: Fig 1. Stranding pattern of Northern bottlenose whale (top), Cuvier’s beaked whale (middle) and other (True’s, Sowerby’s, Gervais’ and unknown) beaked whales (bottom) from 1829 to 2009
45 40
2001-2009 1951-2000 1900-1950 1829-1899
35 Incidence of strandings (%)
Four stomachs of two Northern bottlenose whale (NBW), one Sowerby’s (SBW) and one True’s beaked whale (TBW) were analysed; one of the NBW contained a total of 1142 cephalopod beaks, where more than 90% comprised 4 Teuthida species; the second only had 2 Teuthida beaks (Santos et al. in prep.). Most of the prey found in the SBW were gadoids (whiting, blue whiting, Trisopterus sp., and three myctophids). Pieces of plastic and twine were found in a True’s beaked whale stomach.
50
30 25 20 15 10 5 0
NBW CBW SBW TBW UNK GBW There appears to be an increase in strandings of beaked Fig 3. Stranding distribution of beaked whales whales along the Irish coast in the last 10 years (Fig. 3) & an from 1829 - 2009 increase in the records of live strandings. Most strandings occurred on the west coast of Ireland, which is a large area with a large continental shelf, but elsewhere the shelf edge is quite close to the landmass, particularly in the northwest, where the shelf slopes off quickly to the deep waters of the Rockall Trough.
The high number of bottlenose whale strandings in August and in the Irish Sea is of note. However, MacLeod et al., 2004 reported a high peak in strandings in September. It may be that the Irish Sea is used as a migration corridor or that bottlenose whales are following prey species into this area. Acknowledgments: This analysis is funded under the Beaufort Ecosystem Approach to Fisheries Management award, as part of the Irish Government’s National Development Plan (NDP), the Beaufort Marine Research Award is grant aided by the Department of Communications, Energy & Natural Resources (DCENR) & the Department of Agriculture, Fisheries & Food (DAFF) under the Strategy for Science Technology & Innovation (SSTI) & the Sea Change Strategy. We are grateful to all those people who report strandings to us and to the Irish Whale and Dolphin Group. We are also extremely grateful to all those people who have helped out in post-mortem examination including Mick Mackey, Sinead Murphy, Irene Gassner, Evelyn Philpott and Trish Clayton, and Dr. Susie Brown for producing the maps. Go raibh míle maith agaibh go léir! References: Berrow, S.D. & Rogan E. 1997. Mammal Review 27(1), 51-76
McLeod et al. 2004. Journal of Cetacean Research Management 6(1): 79-86
