CLYMENE DOLPHIN (Stenella clymene): Western North Atlantic Stock

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Clymene

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April 2014

CLYMENE DOLPHIN (Stenella clymene):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The Clymene dolphin is endemic to tropical and sub-tropical waters of the Atlantic (Jefferson and Curry 2003).

Clymene dolphins have been commonly sighted in the Gulf of Mexico since 1990 (Mullin et al. 1994; Fertl et al.

2003), and a Gulf of Mexico stock has been designated since 1995. Four Clymene dolphin groups were sighted

during summer 1998 in the western North Atlantic (Mullin and Fulling 2003), and two groups were sighted in the

same general area during a 1999 bottlenose dolphin survey (NMFS 1999). Two groups of Clymene dolphins were

sighted during summer 2011 in the western

North Atlantic, with one group in the same

general area off North Carolina as the 1998 and

1999 sightings, and the other group off Florida

over the Blake Plateau (NMFS unpublished

data). These sightings and stranding records

(Fertl et al. 2003) indicate that this species

routinely occurs in the western North Atlantic.

The western North Atlantic population is being

considered a separate stock for management

purposes, although there is currently no

information to differentiate this stock from the

northern Gulf of Mexico stock(s). Additional

morphological, genetic and/or behavioral data

are needed to provide further information on

stock delineation.

POPULATION SIZE

The number of Clymene dolphins off the

U.S. Atlantic coast is unknown. Sightings of

this species have not occurred or have been rare

during any given survey, and hence only 1

abundance estimate has ever been made for U.S.

Atlantic waters.

An estimate of abundance was derived

through the application of distance sampling

analysis (Buckland et al. 2001) and the

computer program Distance (Thomas et al.

1998) to sighting data from a 1998 survey along

the U.S. Atlantic coast. Data were collected

using standard line-transect techniques

conducted from NOAA Ship Relentless during

July and August 1998 between Maryland

(38.00°N) and central Florida (28.00°N) from

the 10 m isobath to the seaward boundary of the

U.S. EEZ. Transect lines were placed

perpendicular to bathymetry in a double saw-

tooth pattern. Sightings of Clymene dolphins

were primarily on the continental slope east of Cape Hatteras, North Carolina (Figure 1). The best estimate of

abundance for the Clymene dolphin was 6,086 (CV=0.93) (Mullin and Fulling 2003) and represents the first and

only estimate to date for this species in the U.S. Atlantic EEZ. However, as recommended in the GAMMS

Workshop Report (Wade and Angliss 1997), estimates older than eight years are deemed unreliable, and therefore

should not be used for PBR determinations.

Figure 1. Distribution of Clymene dolphin sightings

from NEFSC and SEFSC vessel summer surveys during

1998, 1999 and 2011. Isobaths are the 100-m, 1,000-m

and 4,000- m depth contours.

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Minimum Population Estimate

Present data are insufficient to calculate a minimum population estimate for the western North Atlantic stock of

Clymene dolphins.

Current Population Trend

There are insufficient data to determine population trends for this stock.

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are unknown for this stock. For purposes of this assessment, the

maximum net productivity rate was assumed to be 0.04. This value is based on theoretical modeling showing that

cetacean populations may not grow at rates much greater than 4% given the constraints of their reproductive history

(Barlow et al. 1995).

POTENTIAL BIOLOGICAL REMOVAL

Potential Biological Removal (PBR) is the product of minimum population size, one half the maximum net

productivity rate, and a recovery factor (MMPA Sec. 3. 16 U.S.C. 1362; Wade and Angliss 1997). The minimum

population size is unknown; therefore, PBR for the western North Atlantic Clymene dolphin stock is undetermined.

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

Total annual estimated fishery-related mortality and serious injury to this stock during 2007-2011 was zero, as

there were no reports of mortalities or serious injury to Clymene dolphins.

New Serious Injury Guidelines

NMFS updated its serious injury designation and reporting process, which uses guidance from previous serious

injury workshops, expert opinion, and analysis of historic injury cases to develop new criteria for distinguishing

serious from non-serious injury (Angliss and DeMaster 1998; Andersen et al. 2008; NOAA 2012). NMFS defines

serious injury as an “injury that is more likely than not to result in mortality”. Injury determinations for stock

assessments revised in 2013 or later incorporate the new serious injury guidelines, based on the most recent 5-year

period for which data are available.

Fishery Information

Detailed fishery information is reported in Appendix III.

Other Mortality

There were 2 reported strandings of Clymene dolphins in the U.S. Atlantic Ocean during 2007-2011 (NOAA

National Marine Mammal Health and Stranding Response Database unpublished data, accessed 13 September 2012

(SER) and 9 November 2012 (NER)). Two animals mass stranded off Maryland during October 2011. It could not

be determined if there were signs of human interactions.

There may be some uncertainty in the identification of this species due to similarities with other Stenella

species. Stranding data probably underestimate the extent of human-related mortality and serious injury because all

of the marine mammals that die or are seriously injured may not wash ashore, nor will all of those that do wash

ashore necessarily show signs of entanglement or other human interactions. Finally, the level of technical expertise

among stranding network personnel varies widely as does the ability to recognize signs of human interactions.

STATUS OF STOCK

Clymene dolphins are not listed as threatened or endangered under the Endangered Species Act, and the

Western North Atlantic stock is not considered strategic under the Marine Mammal Protection Act. No fishery-

related mortality or serious injury has been observed; therefore, total fishery-related mortality and serious injury can

be considered insignificant and approaching the zero mortality and serious injury rate. The status of Clymene

dolphins in the U.S. EEZ relative to OSP is unknown. There are insufficient data to determine population trends for

this stock.

REFERENCES CITED

Andersen, M.S., K.A. Forney, T.V.N. Cole, T. Eagle, R. Angliss, K. Long, L. Barre, L. Van Atta, D. Borggaard, T.

Rowles, B. Norberg, J. Whaley and L. Engleby. 2008. Differentiating serious and non-serious injury of

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marine mammals: report of the serious injury technical workshop, 10-13 September 2007, Seattle, WA.

NOAA Tech. Memo. NMFS-OPR-39. 94 pp.

Angliss, R.P. and D.P. DeMaster. 1998. Differentiating serious and non-serious injury of marine mammals taken

incidental to commercial fishing operations: Report of the serious injury workshop, 1-2 April 1997, Silver

Spring, MD. NOAA Tech. Memo. NMFS-OPR-13. 48 pp.

Barlow, J., S.L. Swartz, T.C. Eagle and P.R. Wade. 1995. U.S. marine mammal stock assessment: guidelines for

preparation, background, and a summary of the 1995 assessments. NOAA Tech. Memo. NMFS-OPR-6,

National Marine Fisheries Service, Seattle, WA, 73 pp. Available from: NOAA National Marine Fisheries

Service, 7600 Sand Point Way NE, Seattle, WA 98115-0070.

Buckland, S.T., D.R. Anderson, K.P. Burnham, J.L. Laake, D.L. Borchers and L. Thomas. 2001. Introduction to

distance sampling: estimating abundance of biological populations. Oxford University Press, New York.

432 pp.

Fertl, D., T.A. Jefferson, I.B. Moreno, A.N. Zerbini and K.D. Mullin. 2003. Distribution of the Clymene dolphin

Stenella clymene. Mammal Review 33(3):253-271.

Jefferson, T.A. and B.E. Curry. 2003. Stenella clymene. Mammalian Species 726:1-5.

Mullin, K.D. and G.L. Fulling. 2003. Abundance of cetaceans in the southern U.S. North Atlantic Ocean during

summer 1998. Fish. Bull. 101:603-613.

Mullin, K.D., T.A. Jefferson and L.J. Hansen. 1994. Sightings of the clymene dolphin (Stenella clymene) in the

Gulf of Mexico. Mar. Mamm. Sci. 10:464-470.

NMFS. 1999. Cruise results: Summer Atlantic Ocean marine mammal survey, NOAA Ship Oregon II Cruise OT 99-

05 (236). Available from: NMFS, Southeast Fisheries Science Center, P.O. Drawer 1207, Pascagoula, MS

39568.

NOAA. 2012. Federal Register 77:3233. National policy for distinguishing serious from non-serious injuries of

marine mammals. Available from:

http://www.nmfs.noaa.gov/op/pds/documents/02/238/02-238-01.pdf

Thomas, L., J.L. Laake, J.F. Derry, S.T. Buckland, D.L. Borchers, D.R. Anderson, K.P. Burnham, S. Strindberg,

S.L. Hedley, F.F.C. Marques, J.H. Pollard and R.M. Fewster. 1998. Distance 3.5. Research Unit for

Wildlife Population Assessment, University of St. Andrews, St. Andrews, UK.

Wade, P.R. and R.P. Angliss. 1997. Guidelines for assessing marine mammal stocks: Report of the GAMMS

workshop April 3-5, 1996, Seattle, Washington. NOAA Tech. Memo. NMFS-OPR-12, National Marine

Fisheries Service, Seattle, WA, 93pp.

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