Table 1. Statistics for short-beaked common dolphin mitochondrial DNA control region sequences.

Genetic Analyses Reveal Multiple PopulationsOf Delphinus delphis in the eastern North Pacific

S. J. Chivers, N. M. Hedrick, and C. A. LeDuc  NMFS, Southwest Fisheries Science Center,8604 La Jolla Shores Dr., La Jolla, CA 92037

Contact author at Susan.Chivers@noaa.gov; Poster can be viewed at http://swfsc.nmfs.noaa.gov/PRD/PROGRAMS/POP-ID/default.htm

Short-beaked common dolphin, Delphinus delphis, are the species most frequently killed in the gillnet fishery operating off the coast of California (CA). However, our ability to accurately assess the impact of this fishery is limited by recognition of a large, geo-politically defined management unit. D. delphis are not unique in having geo-political boundaries recognized for management, because they are the default when our knowledge about a species’ distribution, ecology and natural history is insufficient to identify boundaries that correspond to demographically isolated groups of animals. The geo-political boundaries for the CA/OR/WA stock of D. delphis equate to those of the U.S.A.’s exclusive economic zone off the coasts of CA, Oregon and Washington. Available data on dorsal fin color patterns, contaminant concentrations, reproductive seasonality and genetics suggest there are multiple populations within the CA/OR/WA stock, but each data set was too limited by sample size and temporal/spatial coverage to identify potential population boundaries. In this geographic region, D. delphis are a particularly difficult species to study because they are abundant (i.e., N~446,595), continuously distributed and have high haplotypic diversity (i.e., 98%). We sequenced 400 base pairs of the mitochondrial DNA control region for 312 specimens, which were individually assigned to geographic strata for analyses. Our a priori geographic strata were defined using information about the species’ biology and the oceanography of the region. We detected evidence of genetic distinctness among the strata using both ΦST and 2 (P < 0.05) and concluded that the strata likely represent demographically isolated populations with boundaries corresponding to the region’s primary oceanographic water masses: the Inshore Countercurrent off southern CA, the California Current off central and northern CA, and the Central North Pacific waters ~200nm off central and northern CA.

ABSTRACT

MATERIALS AND METHODS

RESULTS

CONCLUSIONS

● The data set: Standard protocols were used to generate 402 base pair sequences of the mitochondrial DNA control region.● Putative populations: (Figure 1) were identified based on habitat as defined by oceanographic conditions off the coast of CA (Figure 2). Additionally, the central and northern stocks recognized in the eastern tropical Pacific (ETP) were included.● Analytical Methods: 2 ΦST and 2 were used to test Ho of panmixia; α= 0.05 for significance

Table 2. P-values for pairwise comparisons of a priori strata defined as putative populations. Results of statistical comparisons with ΦST are below the diagonal and with 2 are above the diagonal. P-values < 0.05 are printed in bold text, and P-values < 0.1 are printed in italics text. All pairwise comparisons were statistically significant with P<0.05 by one or both statistical measures except for two that had 0.05<P<0.1 for 2 only: the Central ETP versus Northern ETP, and the Central ETP versus N. Pelagic strata comparisons.

● Results suggest that short-beaked common dolphin population boundaries correspond to habitat boundaries. ● Two populations were genetically distinguishable within the currently recognized CA/OR/WA stock: the Southern CA Bight and CA Current populations.● Two populations were genetically distinguishable west of the CA/OR/WA stock and outside the U.S.A.’s 200nm EEZ: the North Pelagic and South Pelagic populations.

Figure 1. The collection locations for samples (n = 312) used in this study. The numbered circles identify the strata defined for the population structure analyses: (1) Central ETP, (2) Northern ETP, (3) Southern CA Bight, (4) CA Current, (5) Northern Pelagic, and (6) Southern Pelagic.

BACKGROUND

● One stock is recognized off the coasts of California, Oregon and Washington: the CA/OR/WA stock.● Analyses of available biological data (e.g. color patterns, reproductive seasonality and contaminant concentrations) suggest there is more than one stock within the CA/OR/WA stock ● D. delphis are the most frequently killed cetacean species in the drift gillnet fishery that operates within the CA/OR/WA stock boundaries. Time/area closures in effect for the fishery have resulted in nearly all the fishing effort taking place off southern California. Thus, evaluating the appropriateness of the existing stock boundaries is relevant to assessing the impact of the incidental kill.● STUDY OBJECTIVE: To evaluate demographic isolation of putative populations of D. delphis in the eastern North Pacific using genetic data.

PutativePopulations

1. Central

ETP(n=25)

2. Northern

ETP(n=20)

3. SouthernCA Bight(n=105)

4.CA

Current(n=113)

5.

N. Pelagic (n=23)

6.

S. Pelagic(n=26)

1. Central ETP * 0.0562 <0.0001 <0.0001 0.0508 0.2062

2. Northern ETP 0.2978 * 0.0062 0.0012 0.0258 0.0578

3. Southern CA Bight 0.0102 0.1091 * 0.0242 <0.0001 0.0006

4. CA Current 0.0010 0.0096 0.0390 * 0.0001 0.0094

5. N. Pelagic 0.1223 0.882 0.2499 0.0102 * 0.4544

6. S. Pelagic 0.0023 0.0380 0.2423 0.7898 0.0268 *

7.66(+/- 3.579)Average pairwise differences

0.0189(+/- 0.0098)

Nucleotide diversity

187# of haplotypes

Eastern North Pacific (n=312)

Sequence characteristics

Figure 3. A short-beaked common dolphin with the ‘anomalous’ (i.e., lacking the buff colored cape) color pattern that has been documented for common dolphins far offshore of CA. Is this color pattern more predominant in the North Pelagic population of short-beaked common dolphin? To date, the available data suggests a correlation.

Figure 2: Schematic diagram of the primary oceanographic currents off the coast of CA.

1

2

3

45

6

35°

15°

25°

5°135° 125° 105°115° 95° 85° 75°

43

Ca

liforn

ia

Cu

rren

t

160°

160°

140°

140°

120°

120°

100°

100°

80°

80°

North Equatorial Current

North Pacific Current

North PacificCentral Gyre

California

Current

North Equatorial Countercurrent

South Equatorial Current

SUBTROPICALSURFACE WATER

EQUATORIALSURFACE WATER

SUBTROPICAL SURFACE WATER

TROPICALSURFACE WATER

Costa Rica Dome

Peru Current

20°20°

10°10°

0°0°

10°10°

20°20°

30°30°

40°40°

50°50°

We thank the NMFS, Southwest Region Fishery Observer Program for collecting samples from incidentally killed dolphins, the NMFS, Southwest Fisheries Science Center (SWFSC) Chief Scientists Lisa Ballance, Jay Barlow and Tim Gerrodette, the crew and officers of the NOAA ships David Starr Jordan and McArthur, and SWFSC scientists Bob Pitman, Doug Kinzey, Paula Olson, Juan Carlos Salinas and Ernesto Vasquez for collecting skin samples from dolphins encountered during research cruises. We also thank Jay Barlow, Jim Carretta, Barb Taylor and members of the Pacific Scientific Review Group for helpful comments on our research.

ACKNOWLEDGEMENTS