Spatial, Temporal, and Dietary Overlap of Leatherback Sea

SPATIAL, TEMPORAL, AND DIETARY OVERLAP OF LEATHERBACK SEA

TURTLES (DERMOCHELYS CORIACEA) AND OCEAN SUNFISHES (FAMILY

MOLIDAE)

By Nicole A. Desjardin

A Thesis Submitted to the Faculty of

The Charles E. Schmidt College of Science

in Partial Fulfillment of the Requirements for the Degree of

Master of Science

Florida Atlantic University

Boca Raton, FL

May 2005

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SPATIAL, TEMPORAL, AND DIETARY OVERLAP OF LEATHERBACK SEA

TURTLES (DERMOCHELYS CORIACEA) AND OCEAN SUNFISHES (FAMILY

MOLIDAE)

Nicole A. Desjardin

This thesis was prepared under the direction of the candidate’s thesis advisor, Dr. Jeanette Wyneken, Department of Biology, and has been approved by the members of her supervisory committee. It was submitted to the faculty of The Charles E. Schmidt College of Science and was accepted in partial fulfillment of the requirements for the degree of Master of Science.

SUPERVISORY COMMITTEE:

______Thesis Advisor

______

______Chairman, Department of Biology

______Dean, The Charles E. Schmidt College of Science

______Vice President for Research and Graduate Studies Date

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ACKNOWLEDGEMENTS

This research project would not have been possible if not for the generous supply of

aerial and longline bycatch data from the NOAA Fisheries Service, Southeast Fisheries Science

Center (Miami and Pascagoula Laboratories) and the Northeast Fisheries Science Center. I thank

D. Abercrombie, A. Bertolino, C. Brown, G. Diaz, S. Epperly, L. Garrison, J. Poffenberger, N.

Thompson, and W. Witzell from the Miami Lab. Other NMFS personnel guided me in my data

analysis including G. Fulling, K. Mullin, W. Hoggard, and D. Palka. Statistical assistance was

provided by D. Gawlik, J. Harlin, T. Monson, and M. Salmon. I could not have completed the

GIS analysis without the help of and B. Anazeski, C. Johnson, M. Villanueva, and S. Wong.

Special thanks also to R. Kenney and the North Atlantic Right Whale Consortium for sharing

their ideas and data.

Gastrointestinal tract samples for this study were collected with the help of S. Barco, L.

Belskis, J. Conrad, P. Davis, C. DeMaye, K. Dodge, K. Durham, M. Godfrey, K. Holloway–

Adkins, T. Norton, G. Novak, L. Otlein, and C. Trapani. Special thanks to M. Conti, E.

DeMaye, D. Lynch, and K. Singel, with the state and federal Fish and Wildlife departments. The

following people provided logistical assistance: J. Garzaniti, A. Pride, Sgt. Mattox, Manalapan

Town Manager Dunham. I also thank M. Gardner, E. King, and C. Johnson for assisting with necropsies and photography. D. Calder, R. Condon, M. Frick, J. Higgins, and R. Mariscal provided valuable help in nematocyst identification. Samples obtained outside of Florida were shipped to Florida Atlantic University under the US FWS Regional endangered species blanket permit # 697823 and Florida Marine Turtle Permit # 073.

I especially thank my advisor, Jeanette Wyneken, and my committee members, Mike

Salmon and Nancy Thompson, for their guidance, and my friends and family who encouraged me through it all.

ABSTRACT

Author: Nicole A. Desjardin

Title: SPATIAL, TEMPORAL, AND DIETARY OVERLAP OF LEATHERBACK SEA TURTLES (DERMOCHELYS CORIACEA) AND OCEAN SUNFISHES (FAMILY MOLIDAE)

Institution: Florida Atlantic University

Thesis Advisor: Dr. Jeanette Wyneken

Degree: Master of Science

Year: 2005

Investigation of the spatio-temporal movements of leatherback sea turtles (Dermochelys coriacea) and ocean sunfishes (family Molidae) as well as analyses of their prey support the hypothesis that they may occupy the same ecological niche. This study examined the spatial and temporal occurrences of sunfishes (Mola mola and Masturus lanceolatus) and leatherbacks in the western Atlantic Ocean and assessed dietary overlap. Analyses of leatherback and sunfish distributions, gleaned from aerial surveys, showed greater spatial and temporal overlap along the

Northeast coast of North America than in the Gulf of Mexico. Both species co-occur more often during warmer months. Pelagic longline fisheries bycatch data revealed varying patterns of occurrence across the year, and do not correlate with coastal distribution patterns. Nematocysts found within GI tract contents of stranded animals indicate that they may feed on similar prey, identified as cnidarians in the classes Hydrozoa, Scyphozoa, Anthozoa, Cubozoa, and Staurozoa.

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TABLE OF CONTENTS

LIST OF TABLES...... viii LIST OF FIGURES ...... ix

Part I...... xi ABSTRACT...... xi INTRODUCTION ...... 1 METHODS ...... 3 RESULTS ...... 7 DISCUSSION...... 13 APPENDIX...... 21 LITERATURE CITED ...... 30

Part II ...... 60 ABSTRACT...... 60 INTRODUCTION ...... 61 METHODS ...... 63 RESULTS ...... 65 DISCUSSION...... 66 LITERATURE CITED ...... 74

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LIST OF TABLES

Part I

Table 1: Aerial surveys used to estimate leatherback and sunfish co-occurrence in the U.S. Atlantic shelf waters...... 44

Table 2: Survey effort and number of animals sighted for the Northeast. Numbers reflect sightings from aerial surveys (TO 95, TO 98, TO 02, MATS 95, and CETAP)...... 46

Table 3: Survey effort and number of animals sighted in the GOM. Numbers reflect sightings from aerial surveys (GoMEX 92, 93, 94 and GulfCet I & II)...... 46

Table 4: Longline fishing effort (# of longlines fished) and numbers of leatherbacks and sunfishes caught in the Northeast (NEC,MAB, NED), taken from POP data set...... 46

Table 5: Longline fishing effort (# of longlines fished) and numbers of leatherbacks and sunfishes caught in the Gulf of Mexico (GOM), taken from POP data set...... 47

Table 6: Longline fishing effort (# of longlines fished) and numbers of leatherbacks and sunfishes caught in the Northeast (NEC,MAB, NED), taken from FLS data set...... 47

Table 7: Longline fishing effort (# of longlines fished) and numbers of leatherbacks and sunfishes caught in the Gulf of Mexico (GOM), taken from FLS data set...... 47

Part II

Table 1: Stranded leatherbacks used in this study, listed in order by stranding date. Stranding ID’s are assigned by the stranding coordinators. CCL = curved carapace length in cm, CCW = curved carapace width in cm...... 81

Table 2: Stranded sunfish used in this study, listed in order by stranding date...... 82

Table 3: Nematocyst types identified in this study and their distribution within five classes of cnidarians. Based upon Mariscal (1974). -, absent; +, present; *, found only in this class ...... 82

Table 4: Distribution of the 6 nematocyst types identified in my study specimens (grouped by season)...... 83

Table 5: Estimated size ranges of the 6 nematocyst types observed. Measurements (in micrometers,...... 83

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LIST OF FIGURES

Part I

Fig. 1. Pelagic longline fisheries reporting areas, used by NMFS to classify fishing effort: (1) Caribbean (CAR), (2) Gulf of Mexico (GOM), (3) Florida East Coast (FEC), (4) South Atlantic Bight (SAB), (5) Mid Atlantic Bight (MAB), (6) Northeast Coastal (NEC), (7) Northeast Distant (NED), (8) Sargasso (SAR), (9) North Central Atlantic (NCA), (10) Tuna North (TUN), (11) Tuna South (TUS). Aerial surveys conducted in the “Northeast” were within the NEC and MAB regions. Aerial surveys conducted in the Gulf of Mexico were within the GOM region. For longline bycatch analyses, data from the “Northeast” were collected in the NED, NEC, and MAB and Gulf of Mexico bycatch data were collected in the GOM...... 48

Fig. 2. Number of survey days per month in the Northeast. Survey effort was greatest in summer...... 49

Fig. 3: a. Map of the continental shelf region off the northeast coast of the U.S. Locations of sunfishes (open circles) and leatherbacks (black circles) are indicated. b. Flight transects and survey boundaries for aerial surveys flown in the Northeast...... 50

Fig. 4: Number of leatherbacks and sunfishes sighted in the Northeast, expressed as sightings per unit effort (animals seen per number of survey days in a month). There was no significant difference in the distributions of leatherbacks and sunfishes across the year in this region (Two- sample Kolmogorov-Smirnov Test, p = 0.100)...... 51

Fig. 5. Locations of sunfishes (open circles) and leatherbacks (dark circles) along the southern portion of the U.S. Atlantic coast, taken during the SECAS 95 aerial surveys. Bathymetry contours, in meters, are labeled...... 52

Fig. 6. Number of survey days per month in the Gulf of Mexico. Survey effort was highest in summer and fall...... 53

Fig. 7. Number of leatherbacks and sunfishes sighted in the Gulf of Mexico, expressed as sightings per unit effort (animals seen per number of survey days in a month). There was no significant difference in the distributions of leatherbacks and sunfishes across the year in this region (Two-Sample Kolmogorov-Smirnov Test, p = 0.249)...... 54

Fig. 8: a. Map of the Gulf of Mexico. Locations of sunfishes (open circles) and leatherbacks (black circles) are indicated. b. Flight transects and survey boundaries for aerial surveys flown in the Gulf of Mexico...... 55

Fig. 9. Co-occurrence, expressed as nearest distance, of leatherbacks and sunfishes in the Northeast and Gulf of Mexico. Animals were seen closer together in the Northeast (within ~40km) and farther apart in the Gulf of Mexico (within ~90km)...... 56

Fig. 10. Average nearest distances between leatherbacks and sunfishes in the Northeast. Animals were sighted together from May through October and seen closest together in May and farthest apart in October...... 57

Fig. 11. Average nearest distances between leatherbacks and sunfishes in the Gulf of Mexico. Animals were sighted together in March, May, July, September, and October and were seen closest together in September and farthest apart in October...... 57

Fig. 12. Locations of co-occurrences of leatherbacks and sunfishes in the pelagic environment, determined from longline bycatch data sets (FLS and POP). There were 49 instances where leatherbacks and sunfishes were caught on a single longline haul. Catches were located throughout the NED, NCA, NEC, MAB, SAB, and GOM regions...... 58

Fig. 13. Proportion of longline hauls that caught leatherbacks or sunfishes in the Northeast (NE, a and b) and Gulf of Mexico (GOM, c and d). Months of the year are shown on the horizontal axis and the proportion of longline hauls is shown on the vertical axis. Black bars indicate Observer (POP) bycatch data and white bars indicate Logbook (FLS) bycatch data...... 59

Part II

Fig 1. The 25 types of nematocysts used for identification. Reproduced from Mariscal (1974). 86

Fig. 2. Nematocysts identified in the GI tracts of leatherbacks and sunfish. Photographs are arbitrary and identifications are partly tentative. Scale bar indicates 20 micrometers. a. holotrichous isorhiza (undischarged, discharged), b. atrichous isorhiza (undischarged, discharged), c. homotrichous anisorhiza, d.heterotrichous microbasic eurytele, e. microbasic mastigophore, f. stenotele ...... 87

Part I

ANALYSIS OF SPATIAL AND TEMPORAL OVERLAP OF LEATHERBACK SEA

TURTLES (DERMOCHELYS CORIACEA) AND OCEAN SUNFISHES (FAMILY

MOLIDAE)

ABSTRACT

Leatherback sea turtles (Dermochelys coriacea) and ocean sunfishes (family Molidae) were hypothesized to be competitors because they share an unusual prey type, gelatinous zooplankton. Analyses of aerial survey data indicate that these animals have similar occurrence patterns in U.S. coastal waters. Despite a higher density of sunfishes in the Northeast, the spatio- temporal occurrence patterns of leatherbacks and sunfishes were nearly identical, with peak abundance in summer/fall. In the Gulf of Mexico, sightings were fewer, but leatherbacks and sunfishes were present year-round, although sunfishes were sighted more often in winter/spring.

Distances between leatherbacks and sunfishes were greater in the Gulf of Mexico (90 km) than in the Northeast (40 km). Pelagic longline fisheries bycatch data reveal varying patterns of occurrence across the year and do not correlate with distribution patterns identified through aerial survey data. Leatherbacks and sunfishes were caught together on a single longline haul 49 times.

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INTRODUCTION

Leatherback sea turtles (Dermochelys coriacea Vandelli 1761) and ocean sunfishes

(family Molidae) show remarkable similarities in their distribution and dietary preferences, despite great morphological differences and phylogenetic distance. Both are wide-ranging species, known to occur in temperate and tropical regions. The geographic range of Atlantic leatherbacks extends from approximately 71° N lat to 41° S lat (Mrosovsky 1987). Great migrations are also common for these turtles. Many leatherbacks in the western Atlantic spend the spring and early summer months in the Caribbean or south Florida, using this area for mating or nesting, and they frequent waters off New England, Nova Scotia and Newfoundland during the late summer and fall (Bleakney 1965, James & Herman 2001, NMFS-SEFSC 2001).

Ocean sunfishes, represented by four species (Mola mola Linnaeus 1758, Ranzania laevis

Pennant 1776, Masturus lanceolatus Lienard 1840, and Mola ramsayi Giglioli 1883), also have a worldwide distribution (Fraser-Brunner 1951). In the western Atlantic, their range extends from

47 º N lat to 42º S lat (Threlfall 1967, Anderson & Cupka 1973). Published information on sunfish distribution along the U.S. Atlantic coast is sparse and gathered mostly from incidental sightings or catches.

A study by Kenney (1996) showed that leatherbacks and sunfishes have overlapping spatial occurrence patterns in the northeast Atlantic). Numbers of sunfishes in continental shelf waters between Cape Hatteras and the Gulf of Maine were estimated to reach 18,000 in the summer months and the population size was estimated to be approximately 20 times larger than that of the leatherback in this region. Kenney noted that leatherbacks and sunfishes also showed the same temporal occurrence patterns, with a peak in the northeast during late summer. He hypothesized that there is the potential for competition between these animals. However, testing

1 this hypothesis or conducting a thorough examination of their spatial relationships was beyond the scope of his data and analyses.

Diet studies on leatherbacks consistently show that they are gelatinovores, feeding primarily on scyphomedusae, hydromedusae, siphonophores, and tunicates (Bleakney 1965,

Brongersma 1969, Davenport & Balazs 1991, Frazier et al. 1985, den Hartog & Van Nierop

1984, James & Herman 2001). Sunfishes also consume gelatinous zooplankton including scyphomedusae, hydromedusae, salps, and ctenophores (Fraser-Brunner 1951, Hubbs and

Schultz 1929, MacGintie 1938, Sommer 1989). Stomach contents of specimens caught inshore suggest that they may feed on crustaceans, ophiuroids, mollusks, hydroids, corals and algae

(Fraser-Brunner 1951). A comparative dietary analysis showed that both leatherbacks and sunfishes feed on similar types of prey, including hydrozoans (siphonophores), scyphomedusae, and cubomedusae and that they experience dietary overlap (Desjardin, Part II 2005).

Since leatherbacks and sunfishes are dependent on similar food resources, their distributions may be driven by the abundance of prey items. Jellyfish distributions are largely dictated by currents and wind and by their reproductive and developmental patterns (Johnson et al. 2001); they tend to aggregate at physical discontinuities (currents boundaries, thermal fronts, and upwellings) within the ocean (Graham et al. 2001). During aerial surveys of U.S. southeastern coastal waters, Thompson and Huang (1993) recorded leatherbacks feeding along the edges of major currents and near upwellings. Luschi et al. (2003) described leatherback movements near South Africa as being largely shaped by current flows and eddies. Ocean sunfish (Mola mola) tracked off the coast of southern California showed highly directional migratory movement within specific temperature ranges (Cartamil & Lowe 2004).

Environmental conditions such as temperature and nutrient availability may make jellyfish

2 distributions patchy and unpredictable (Lucas 2001), therefore, leatherbacks and sunfishes may use temperature gradients and oceanographic features as clues to prey availability and may migrate to similar locations to forage.

Here I examine if these species share the same niche space by measuring their co- occurrence patterns. This study was undertaken to further examine the spatial and temporal patterns in this overlap and to test the hypothesis that these species have identical distributions and occurrence patterns. Aerial survey data and longline fisheries bycatch data were used to test this hypothesis and oceanographic factors were identified that might contribute to the spatial and temporal overlap of these species.

METHODS

Aerial Survey Data

I used aerial survey data, supplied by the NOAA Fisheries Service (NMFS), to estimate leatherback and sunfish co-occurrence in western Atlantic shelf waters. These aerial surveys were flown in sections along the coast from Nova Scotia to the Gulf of Mexico, during various months of the year, from 1978-2002 (Table 1). Surveys were selected to avoid sampling bias and were included only if the observers were recording both leatherbacks and sunfishes. The data from the Cetacean and Turtle Assessment Program (CETAP) survey were restricted to dedicated aerial survey flights only; no shipboard surveys were included in this analysis. The numbers and positions of each species were parsed from these data sets. The sunfishes sighted during aerial surveys were most likely Mola mola or Masturus lanceolatus, but exact species identification is difficult when determined from an aerial platform; hence sunfish were counted as one category, regardless of species. These two species are closest in size, shape, and

3 coloration (and are noticeably different from Ranzania laevis) and are known to exist in the study area. Mola ramsayi does not occur where the surveys were conducted.

The coastal areas surveyed were defined using the terminology employed by the NMFS to designate areas of fishing effort for the U.S. pelagic longline fleet (Fig. 1). The Northeast and

Mid Atlantic areas (NEC & MAB) were grouped as “Northeast” and the Gulf of Mexico area

(GOM) encompassed the surveys in this region. Data were obtained for all seasons for the

Northeast and Gulf of Mexico. Surveys conducted in the Northeast were CETAP, TO (Twin

Otter Arial Survey) 95, MATS 95 (Mid-Atlantic Tursiops Survey), TO 98, TO 02. The Gulf of

Mexico surveys included GOMEX (Gulf of Mexico) 92, 93, 94, GulfCet (Gulf of Mexico

Cetacean) I, and GulfCet II. For the South Atlantic region (SAB & FEC), only one winter survey was obtained [SECAS (Southeast Cetacean Aerial Survey) 95] These latter data provide a “snapshot” of the spatial and temporal distribution of leatherbacks and sunfishes in the southeast alone during this season.

Seasonal effects and co-occurrence

Spatial and temporal distribution patterns were analyzed for evidence of a seasonal influence. Leatherback and sunfish distributions across the year (corrected for survey effort) within regions were examined independently using one-sample Kolmogorov-Smirnov tests.

Their seasonal distributions within regions were compared to one another using two-sample

Kolmogorov-Smirnov tests. In addition, correlations between the distributions were examined using the Pearson product-moment and Spearman’s rho correlation analyses. Scatterplots were generated to identify outliers in the data. The data were also analyzed to quantify leatherback/sunfish co-occurrence. For the purpose of this study, the spatial and temporal co- occurrence of leatherbacks and sunfishes was defined as both species being sighted on the same

4 day, during a single survey. For each survey, the distance between each leatherback and the nearest sunfish (both sighted on the same day) was measured. Using these nearest distance measures, co-occurrence patterns were identified for the Northeast and Gulf of Mexico. A

Mann-Whitney U test was used to test the assumption that the co-occurrence of leatherbacks and sunfishes was the same across the two areas (Northeast and Gulf of Mexico). Where possible, areas of higher leatherback or sunfish concentration were examined and physical features were identified that may explain the more intensive use of these areas.

Leatherback and sunfish locations were mapped using ArcView GIS Version 3.2 and the flight transects or survey boundaries were obtained for each survey to show the area of search effort. The nearest distance (co-occurrence measure) between leatherbacks and sunfishes sighted on the same day was calculated using the ArcView extension ‘Nearest Features, with Distances and Bearings’ (v. 3.8) (Jenness 2004). The sightings of animals at all locations indicate their presence at or near the surface, but do not indicate their absence in any other areas. The patterns of distribution described here are based only on sightings within designated survey areas. It is important to note that many of these surveys were not specifically designed to estimate sea turtle or sunfish abundance, however, surveys were only included in this analysis if both leatherbacks and sunfishes were recorded, if seen by the aerial observers. Sightability of leatherbacks and sunfishes does not factor into these analyses as no attempt was made to estimate the population density of these species.

Pelagic Longline Data

The pelagic observer program (POP) and the mandatory fishery logbook system (FLS), managed by the NOAA Fisheries Service, Southeast Fisheries Science Center (SEFSC), provided a second source of sightings data. Leatherback and sunfish bycatch from the U.S.

5 pelagic longline fleet is either recorded by fisheries observers or reported independently by the vessel owners and operators. Data on target and non-target catches from roughly 8 % of the longline fishing vessels in the Atlantic and Gulf of Mexico are reported by the observers

(Beerkircher et al. 2002). In this study, leatherback and sunfish bycatch data from these vessels were analyzed according to date and location. Catch data (regardless of whether a sunfish or a leatherback was caught) from the POP were obtained for the years 1992-2002 and the FLS data were obtained for the years 1996-2002. Longline vessels are widely distributed in the Atlantic and their effort is confined to individual sets of longline fishing gear. These data cover a wide area (to approximately 20º W lon and to 5º N lat) and allowed the comparison of spatio-temporal occurrence patterns of leatherbacks and sunfishes in U.S. continental shelf waters and in the offshore environment. Due to this broad distribution, co-occurrence could only be identified as leatherbacks and sunfishes caught as bycatch on the same longline haul (defined as a single length of longline fished at one time). Longlines were about 25 -50 km in length and the number of hooks per longline ranged from 200 to over 1000.

Seasonal effects and co-occurrence

All recorded instances of leatherback or sunfish bycatch in this data set were mapped as above. The point at which the longline fishing gear began to be hauled back was used to mark the location of capture, although the actual catch site was at some point along the length of the line (hence the error in capture locations could be as much as about 50 km). Incidental capture of the two species within a single longline haul was recorded and the location within the NOAA

Fisheries designated reporting zones was identified. The numbers of leatherbacks and sunfishes caught as bycatch in each region (Northeast or Gulf of Mexico) were corrected for effort by dividing by the total number of hauls fished in that area. The resulting proportions were used to

6 examine the distribution of leatherbacks and sunfishes across the year in each offshore region.

Seasonal distributions of leatherbacks and sunfishes across the year within the Northeast region

(including NEC, MAB, NED) and within the Gulf of Mexico (GOM) (Fig. 1), were analyzed

independently using one-sample Kolmogorov-Smirnov tests. The seasonal distributions from the bycatch data were compared to the distributions obtained from aerial surveys using two-sample

Kolmogorov-Smirnov tests. Pearson’s product-moment and Spearman’s rho correlation analyses were also performed and scatterplots were generated to identify any major outliers in the data.

The average length of the hauls where both species were caught was calculated for the Northeast and Gulf of Mexico in order to determine the maximum approximate distance within which both species occurred. This distance represents a measure of offshore co-occurrence. Finally, in order to test for uniformity among longline bycatch data sets, the FLS bycatch data were compared to the POP data using Kolmogorov-Smirnov tests and the Pearson and Spearman correlation analyses.

RESULTS

Aerial surveys - Distribution and co-occurrence patterns

Leatherbacks and sunfishes show similar patterns of distribution, associated with season, in the Northeast. Analyses of the aerial surveys conducted in the Northeast region show roughly the same spatial and temporal use patterns by leatherbacks and sunfishes. The majority of survey days in this region were in June, July, and August (119 survey days; Table 2, Fig 2).

Leatherbacks and sunfishes use the waters extending from Nova Scotia to Cape Hatteras (35 º N lat to 44º N lat) out to the 1000-m isobath (Fig. 3); however, sunfishes were much more abundant and evenly distributed throughout the area. Sunfishes were present in Northeast waters from

February to December, with a peak in June, showing a distribution across the year that was

7 significantly different from a uniform distribution (one-sample Kolmogorov-Smirnov test, D(max)

=,0.441, p = 0.019, Z(2) = 1.529; Table 2, Fig. 4). Leatherbacks also showed a pattern of

distribution across the year that was significantly different from a uniform distribution (one-

sample Kolmogorov-Smirnov test, D(max) = 0.585, p = 0.001, Z(2) = 2.027). They were present

from May through October, with the greatest numbers seen in July and August (Table 2, Fig. 4),

and were concentrated from Long Island to Cape Hatteras. A comparison showed that the

spatio-temporal patterns of distribution for leatherbacks and sunfishes did not differ (two-sample

Kolmogorov-Smirnov test, D(max) = 0.500, p = 0.100, Z(2) = 1.225). Correlation analyses showed a significant relationship between their distributions (Pearson’s r = 0.811, p < 0.01; Spearman’s

= 0.886, p < 0.01). A single outlier in the data was excluded to more closely estimate the correlation (see Appendix). The resulting correlation was significant with Spearman’s = 0.850, p < 0.05, but not significant with Pearson’s r = 0.591, p = 0.055. The SECAS 95 survey flown in

winter (Jan - Mar) along the south Atlantic coast (within the 200 m isobath, where surveys

ended) from Cape Hatteras to Central Florida reported sightings of both leatherbacks and

sunfishes, indicating that these waters are also used by both species in colder months of the year

(Fig. 5).

In the Gulf of Mexico, these species show slightly different spatial and temporal patterns

of habitat use. Aerial surveys in this region were conducted on the continental shelf, in all

seasons of the year. The majority of survey days occurred in October (39 survey days) and July

(32 survey days) (Table 3, Fig. 6). Leatherbacks were sighted in the Gulf in February and March and from May through December, with the highest number of sightings occurring in October

(Table 3, Fig. 7). Leatherbacks were seen in all seasons of the year, indicating a more uniform

pattern of distribution (one-sample Kolmogorov-Smirnov test, D(max) = 0.286, p = 0.278, Z(2) =

0.992) (Fig. 7). Most leatherback sightings occurred near the Mississippi River delta and in the

Florida panhandle region, out to the 1000 m isobath, beyond which survey effort ceased (Fig.

8a). There was, however, very little survey effort in a 100-200 km stretch along the continental shelf off western Florida (between the coast and the 200 m isobath) (Fig. 8b).

Sunfishes were sighted in February, March and May and from July through November

(Table 3, Fig. 7). The greatest number of sunfishes was seen in March. However, this pattern was significantly different from a uniform distribution (one-sample Kolmogorov-Smirnov test,

D(max) = 0.654, p < 0.0005, Z(2) = 2.267). Sunfish sightings were also the most numerous east of the Mississippi River delta and in the Florida panhandle region, again, inside the 1000 m isobath.

The vast majority of these sightings occurred in winter. When the spatio-temporal distribution patterns of leatherbacks and sunfishes across the year in the Gulf were compared, they were not significantly different (two-sample Kolmogorov-Smirnov test, D(max) = 0.417, p = 0.249, Z(2) =

1.021). However, correlation analyses did not show a significant correlation between their

distributions (Pearson’s r = -0.094, Spearman’s = -0.179)

The trends in leatherback and sunfish co-occurrence (as defined in this study) varied

between the Northeast and Gulf of Mexico. The majority of leatherbacks and sunfishes were

sighted closer to one another in the Northeast (within 40 km) than in the Gulf of Mexico (within

90 km, Fig. 9). Co-occurrence measures between regions were significantly different (Mann-

Whitney U = 875.00, p < 0.0005, Z(2) = -4.101)

Animals co-occurred in the Northeast from May through October (Fig. 10). The average

(±1 std) nearest distance in the Northeast was 26.2 km (±35.4), with co-occurring animals

sighted farthest apart in October. In the Gulf of Mexico, the average nearest distance was 52.0

km (±37.6) and animals co-occurred in March, May, July, September and October, with animals being sighted farthest apart in October (Fig. 11).

Leatherbacks and sunfishes co-occurred in the Northeast along the coast, mainly inside the 200-m isobath, even though survey effort continued out to the 2000 m isobath. There were a

few co-occurrences near Nova Scotia with more from Cape Cod (near Georges Bank) to Cape

Hatteras. The greatest numbers of co-occurrences were in the waters between Long Island and

Cape Hatteras. All leatherback sightings were in areas where sunfishes were also found.

Leatherbacks were not sighted with sunfishes in the Gulf of Maine, although sunfish were present throughout this area. In the GOM, co-occurrences were mainly inside the 200-m isobath in the region between the Mississippi River delta (where surveys extended to the 1000 m isobath) and the Florida panhandle. Animals were also seen together between the 200 and 1000 m isobaths off the west coast of Florida and off the coast of Texas and Louisiana. There were no areas in the GOM where leatherbacks and sunfishes showed a consistently high number of co- occurrences. In the area east of the Mississippi River delta and along the shelf off the west coast of Florida leatherbacks were spotted mostly in July, whereas sunfish were seen in this region mainly in February and March.

Pelagic longline bycatch – Distribution and co-occurrence patterns

Spatio-temporal distribution and co-occurrence patterns of leatherbacks and sunfishes in the pelagic environment also were assessed using longline bycatch data. In total, 24% of all reported or observed longline hauls caught either a leatherback or a sunfish. There were 49 instances of leatherbacks and sunfishes being caught together on one longline haul (Fig. 12).

This represents only 0.55 % of all longline hauls either observed or reported, and 2.26 % of all hauls that caught either leatherbacks or sunfishes. The average length of a haul was 47.6 km in

1 0

the Northeast and 45.5 km in the Gulf of Mexico, suggesting that leatherbacks and sunfishes co- occur within about 47 km of each other in the offshore environment. This value is consistent with co-occurrence patterns in the Northeast, derived from aerial survey data.

The proportion of leatherback bycatch in the Northeast (including NEC, MAB, NED;

Fig. 1) was highest from June to October, while the proportion of sunfish bycatch was highest in

February, March and April in this region (Fig. 13). In the Gulf of Mexico, the proportion of leatherback bycatch differed among bycatch data sets. Leatherbacks were caught more often in

April, May, and July, as reported by the POP, and in July, October, and December, as reported by the FLS. The proportion of sunfish bycatch in the Gulf was high from January to March.

The longline bycatch data were subjected to the same analyses as the aerial data, to examine patterns of distribution across the year (using one-sample Kolmogorov-Smirnov tests), and yielded the following results: the distribution of leatherbacks in the Northeast was not significantly different from uniform (POP, D(max) = 0.269, p = 0.352, Z(2) = 0.931; FLS, D(max) =

0.293, Z(2) = 1.014, p = 0.255), the distribution of sunfishes in the Northeast was significantly

different from uniform (POP, D(max) = 0.617, p < 0.0005, Z(2) = 2.136; FLS, D(max) = 0.417, p <

0.031, Z(2) = 1.443), leatherback distribution in the Gulf of Mexico was not significantly different

from uniform (POP, D(max) = 0.341, p = 0.122, Z(2) = 1.182; FLS, D(max) = 0.367, p = 0.079, Z(2) =

1.271), and the distribution of sunfishes in the Gulf of Mexico was not significantly different

from uniform (POP, D(max) =0.383, p = 0.059, Z(2) = 1.327; FLS, D(max) = 0.284, p = 0.289, Z(2) =

0.983).

Analyses of distribution patterns from bycatch data in the Northeast and Gulf of Mexico

showed some correlations with those obtained from aerial observations. Leatherback bycatch in

the Northeast showed a peak in summer/fall (from May to November), revealing a pattern of

1 1

distribution similar to the one obtained from aerial surveys (aerial vs. POP: two-sample

Kolmogorov-Smirnov test D(max) = 0.417, p = 0.249, Z(2) = 1.021; Pearson’s r = 0.605, p < 0.05,

Spearman’s = 0.808, p < 0.01; aerial vs. FLS: two-sample Kolmogorov-Smirnov test D(max) =

0.417, p = 0.249, Z(2) =1.021, Pearson’s r = 0.755, p < 0.01, Spearman’s = 0.796, p < 0.01).

However, the bycatch data for the Northeast did not reveal patterns of distribution for sunfishes that were similar to the aerial data. Sunfishes were encountered in all months, with larger numbers caught in March and September; there was no obvious increase in numbers of sunfishes caught in summer (aerial vs. POP: two-sample Kolmogorov-Smirnov test D(max) = 0.667, p =

0.010, Z(2) = 1.633, Pearson’s r = -0.198, Spearman’s = 0.270; aerial vs. FLS: two-sample

Kolmogorov-Smirnov test D(max) = 0.833, p < 0.0005, Z(2) = 2.041, Pearson’s r = 0.014,

Spearman’s = 0.341). For sunfishes in the Gulf of Mexico, the seasonal distribution pattern obtained from the POP data set was not significantly different from the pattern of distribution from the aerial data set, which revealed a peak in winter; however there was no significant correlation between them (aerial vs. POP: two-sample Kolmogorov-Smirnov test D(max) = 0.500, p = 0.100, Z(2) = 1.225, Pearson’s r = 0.449, Spearman’s = 0.092). The FLS bycatch data set

did not correlate with the aerial data (aerial vs. FLS: two-sample Kolmogorov-Smirnov test

D(max) = 0.583, p = 0.034, Z(2) = 1.429, Pearson’s r = 0.591, Spearman’s = 0.244). In the Gulf

of Mexico, the two leatherback bycatch data sets did not correlate with the aerial data. The aerial

data showed a year-round presence of leatherbacks and did not agree with the patterns derived

from the bycatch data (aerial vs. POP: two-sample Kolmogorov-Smirnov test D(max) = 0.750, p =

0.002, Z(2) = 1.837, Pearson’s r = -0.037, Spearman’s = 0.091; aerial vs. FLS: two-sample

Kolmogorov-Smirnov test D(max) = 0.667, p = 0.010, Z(2) = 1.633, Pearson’s r = -0.011,

Spearman’s = 0.045).

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In most cases, the POP and FLS data sets did not show agreement in distribution patterns

of leatherbacks and sunfishes in either the Northeast or Gulf of Mexico (POP vs. FLS:

leatherbacks in Gulf of Mexico, two-sample Kolmogorov-Smirnov test D(max) = 0.667, p =

0.010, Z(2) = 1.633, Pearson’s r = -0.021, Spearman’s = -0.231; sunfishes in the Northeast, two- sample Kolmogorov-Smirnov test D(max) = 0.583, p = 0.034, Z(2) = 1.429, Pearson’s r = 0.025,

Spearman’s = 0.406). For sunfishes in the Gulf of Mexico, the two-sample Kolmogorov-

Smirnov test indicated that the two distributions were significantly different (D(max) = 0.917, p <

0.0005, Z(2) = 2.245), however they did correlate (Pearson’s r = 0.677, p < 0.05, Spearman’s =

0.755, p < 0.01). The two data sets did correlate for leatherbacks in the Northeast (two-sample

Kolmogorov-Smirnov test D(max) = 0.500, p = 0.100, Z(2) = 1.225, Pearson’s r = 0.737, p < 0.01,

Spearman’s = 0.571). An even stronger correlation emerged when an outlying data point was excluded for these data sets (Pearson’s r = 0.954, p < 0.01, Spearman’s =0.883, p < 0.01, see

Appendix).

DISCUSSION

Distribution and co-occurrence patterns from aerial surveys

Leatherbacks and sunfishes have very similar spatio-temporal distributions in Northeast waters. However, there were seasonal differences in distribution and abundance of the two taxa in the Gulf of Mexico. The overall patterns found suggest that these animals undergo migrations associated with season. The information that was derived from the aerial data set is sufficient to

describe patterns of distribution and movement in shelf waters of the western north Atlantic and

in the Gulf of Mexico, but the seasonal and geographic limits of the aerial surveys do not allow for a complete characterization of the spatial and temporal movements of these animals

1 3

Leatherbacks and sunfishes were both sighted during aerial surveys in Northeast waters from May through October. Evidence for a seasonal migration into and out of this region comes from the drastic increase and decrease in numbers of animals spotted during consecutive months.

(such as sunfish sightings from April to May or between August and September, or leatherback sightings from June to July or between August and September). Despite some variability in effort, the remarkable changes in the numbers of sightings indicate a large-scale movement of animals into or out of the survey area. It is unlikely that weather conditions contributed to this effect, by affecting sightability, as conditions between months, such as from August to

September, do not vary greatly.

Leatherbacks were sighted in northern waters from May through October, while sunfishes were sighted in all months except January. The lack of sightings in winter is not an artifact of reduced survey effort. There were 25 survey days during the month of January, which is comparable to the effort in May and June, where 240 and 362 sunfishes were spotted, respectively. In addition, there were six survey days in February and 17 in March, and only seven sunfishes were sighted during this period. So, this suggests that fewer sunfish are seen in winter, due either to decreased sightability or to the migration of a large number of animals southward or offshore. Leatherbacks were not sighted between November and April despite 95 days of surveying; this time period is greater than that when sunfishes were not seen, suggesting that leatherbacks tend to leave the northeast sooner and return later than sunfish.

The overlap of leatherbacks and sunfishes in Northeast waters during spring and summer corresponds with seasonal environmental changes. Elevated water temperatures and changes in primary productivity and zooplankton abundance in shelf waters increase food availability for these animals (Cura 1987). From May through September, productivity is high, spurred by a

1 4 bloom in phytoplankton in spring, which leads to an increase in zooplankton (Davis 1987).

Gelatinous zooplankton, such as hydromedusae, scyphomedusae (Cyanea capillata), siphonophores, and ctenophores, are important predators of zooplankton (Davis 1987); the increase in abundance of these jellies makes nearshore waters rich foraging grounds for gelatinovores. Bleakney (1965) reports that fishermen in Nova Scotia refer to the months of

June through October as “turtle season.” Leatherbacks arrive in eastern Canadian waters during the period of time when C. capillata are seasonally abundant, and fishermen frequently observed leatherbacks feeding on these jellyfish. Although less is known about sunfishes in northern waters, their abundance (much greater than leatherbacks in this region; Kenny 1996) and persistence, in small numbers, during all months of the year except January, indicates that they may profit from increased prey availability and that they are also capable of withstanding cold water temperatures.

The greatest overlap of leatherbacks and sunfishes in northern waters occurred inside the

200-m isobath from Long Island south to Cape Hatteras, while aerial surveys were conducted out to the 1000-m isobath. This shelf region is one of the most productive in the world (Sherman et al. 1988) and may be one reason why both species used this area intensively. Polar and tropical waters in this area are mixed by oceanic fronts associated with the Gulf Stream and warm core rings that develop from this current (Lozier et al. 1995). Nutrient-rich estuarine waters that drain onto the continental shelf also increase phytoplankton abundance, which tends to be greater closer to shore (O’Reilly et al. 1987). These oceanographic features may enhance productivity and increase food availability by aggregating gelatinous zooplankton that feed on the phytoplankton.

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A bloom of phytoplankton in fall increases nutrients in shelf waters, but does not have the

trophic impact of the spring bloom (Sherman et al. 1988). Later in winter, phytoplankton

abundance is two orders of magnitude less than in summer (Cura 1987). Decreased nutrients,

temperature declines, and altered water circulation patterns contribute to a suite of environmental

changes that may trigger leatherback and sunfish movement out of the Northeast. Although

leatherbacks are capable of maintaining a high internal body temperature compared to the

environment, even in cold, northern waters (James & Mrsovsky 2004, Spotila & Standora 1985),

their migration out of this region during winter suggests that it is energetically more profitable to

move into warmer waters. Sunfishes too may face restricted nutrient resources with declining

water temperature and decreasing plankton biomass, although they do not necessarily follow warm water during cool periods (Lee 1986). Like leatherbacks, they can withstand the water temperatures experienced during extremely deep dives (about 6 º C), but usually must return to a layer of warmer water after prolonged deep dives into colder water (Cartamil & Lowe 2004).

In the Gulf of Mexico, the spatial distributions of leatherbacks and sunfishes were similar, but co-occurrence patterns were different. The temporal difference in their distributions indicates that sunfishes are more abundant in winter, and leatherbacks are more abundant in late summer/ fall. The Gulf of Mexico does not experience such dramatic declines in ocean temperature as does the Northeast. This is most likely the reason for both species being present across all seasons. Planktonic prey in the gulf may concentrate near current boundaries, such as the Loop Current or its enclosed eddies, and in high nutrient areas, like the Mississippi River delta. These areas are likely to provide plentiful food resources, and leatherbacks and sunfishes were observed in these areas. The use of the GOM waters by leatherbacks in the late summer/fall suggests that they migrate to this region after spending the winter/spring months

1 6

elsewhere. Likewise, sunfishes may be entering the GOM in the winter or spring, and moving to different foraging or breeding areas in summer and fall.

Areas in the GOM where leatherbacks and sunfishes co-occurred include the waters near the nutrient-rich Mississippi River delta and the shelf off the west coast of Florida. A few animals were seen co-occurring near Florida, but many were observed separately, in different seasons. This indicates that this area provides suitable habitat (for foraging or otherwise) year-

round. Since such a small number of animals were sighted in the GOM overall and there were

no areas in the GOM where co-occurrences were high, resources (food) may not be very

abundant or their visits to the GOM may be influenced by factors other than those driving NE

distributions. The presence of leatherbacks and sunfishes off the west coast of Florida suggests

that this region may be a particularly productive area. The Loop Current, which meanders within the GOM from the area between the Yucatan and Florida peninsulas, forms primarily in spring, but it can occur during any season. It occasionally intrudes farther northward toward the

Mississippi River delta and to the Florida continental shelf (Wiseman & Dinnel 1988). Warm core rings from this current also penetrate westward into the gulf (Elliott 1982). These currents cause upwellings in the gulf and may spur the transport of nutrients from the Mississippi and

Mobile rivers toward the east (Gilbes et al. 1996). Other nutrient sinks off the Florida west coast come from the discharge of local rivers into the ocean. Blooms of phytoplankton that occur in these regions may be the result of this increased nutrient load (Gilbes et al. 1996). This chlorophyll plume, although sporadic, has been documented in winter, spring, and summer months, and may be the reason for heavier use of the shelf area off the west coast of Florida by leatherbacks and sunfishes.

1 7

The co-occurrence measures between regions were significantly different. Co-occurrence

patterns for the GOM show less clustering of leatherbacks and sunfishes than in the Northeast.

This result is likely not an indicator of prey distribution, but rather may reflect the densities of

leatherbacks and sunfishes in each region. Sunfishes were much more abundant across most of

the Northeast, which could account for the small distances between leatherbacks and sunfishes.

Sightings of leatherbacks and sunfishes in the GOM were much fewer, so the larger nearest

distance measures here may reflect the scarcity of sightings in this region.

There are possible biases from the survey designs that may influence the results of the co- occurrence analyses and the reported areas of concentrations. Co-occurrence measures may reflect the size of the survey area, which varied among surveys. For surveys with a smaller area of search effort, the co-occurrence measures may have been biased towards smaller values, and

vice versa for surveys with a larger search area. However, for the purposes of this study, co-

occurrence measures were obtained to estimate the extent of two-dimensional spatial overlap

(not accounting for vertical overlap within the water column) and were interpreted with this bias in mind. Areas where sightings of leatherbacks and sunfishes were concentrated may also reflect survey bias. The GulfCet surveys, for example, were undertaken to estimate cetacean distribution in areas potentially affected by current and planned oil and gas activities. Since the surveys only covered these target areas, sunfishes or leatherbacks in other locations were not encountered.

Distribution and co-occurrence patterns from longline bycatch data

The results from longline bycatch data differ from the aerial data in how they define seasonal distribution and co-occurrence patterns for leatherbacks and sunfishes. Co-occurrences offshore occurred in the middle of the Atlantic Ocean, in the Northeast, along the U.S. east coast

1 8

and in the GOM. There were no areas, or times of year, where simultaneous bycatch of both species was high.

Spatio-temporal distribution patterns from the longline data generally did not correspond with patterns seen in the aerial data. These differences suggest at least three possibilities. First, the aerial survey data may underestimate leatherbacks and/or sunfishes since they are only recording animals at the surface. Second, longline bycatch information may be biased if the species are attracted to the longlines by baits, hence the more powerful swimmers (leatherbacks) could concentrate in an area more rapidly, thus appearing more abundant. Third, leatherbacks and sunfishes are not distributed in the same patterns in the offshore environment as they are in continental shelf waters.

The sampling methodologies are very different, so it is not surprising that these data do not correspond. The longline data include captures of animals that are either hooked in the mouth or foul hooked, as opposed to the aerial data, which records the spatial locations of animals that are freely swimming. Capture by longline also implies that the animal was in the area being fished and was attracted to the baits or some other features that characterize the set location. Longlines are typically set out in productive offshore regions, in areas where the target catch is expected to be high. This may have an effect on the bycatch rates of leatherbacks and sunfishes, which may also be attracted to these areas. The duration and time of day when aerial surveys are conducted differs drastically from when longlines are fished. Aerial surveys are flown in midday and are typically only a few hours long. Longline sets are fished during dayling and at night and are soaked for a longer period of time (~12 hours). Also, longlines are fished at a range of depths (< 10m - > 100m) while aerial surveys record animals at the surface.

1 9

The two longline bycatch data sets are relatively inconsistent with each other, perhaps reflecting the different observers or fishers recording the data. Variations in the data set, such as years of data obtained, slight differences in fishing locations, and the small proportions that resulted from correcting the numbers of animals caught for fishing effort may have affected the statistical outcome as well.

Despite these differences, the positions of leatherbacks and sunfishes in coastal waters, obtained from aerial data, show clear trends in the distribution and seasonal patterns of movements for these animals in the Northeast and GOM. It is apparent that leatherbacks and sunfishes overlap in their spatio-temporal habitat needs in both regions. The foraging dynamics of a poikilotherm and a reptile that behaves as an endotherm (Spotila & Standora 1985) would suggest that leatherbacks might out-consume sunfish, as they are potentially more mobile and would have greater energy requirements. However, the larger number of sunfishes in northern waters could indicate that there is much greater potential for competition between these species in this region simply because of their shear numbers. There were very few instances of leatherbacks and sunfishes identified within close range (< 1 km) of each other. Hence by foraging and migrating over a very large spatial scale, direct competition is likely avoided.

Additional investigations directly addressing the environmental parameters that attract leatherbacks and sunfishes, especially in the pelagic environment, would be valuable in understanding how these gelatinovores use the same waters. In a management context, this same understanding may prove valuable in preventing accidental capture of these species by longline or other fisheries and for managing coastal waters to minimize human impact on these populations.

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APPENDIX Statistical analyses and results

1. Testing for differences in co-occurrence measures between the Northeast and Gulf of Mexico.

Software program: SPSS for Windows (version 13.0) Test Used: Mann-Whitney Rank Sum Test

This test is used with ordinal (rank order) data to test whether two independent samples come from different populations, with different median values. This test tolerates violating the assumption of homogeneity of variance and does not require that the data fit a normal distribution.

Assumptions for this test: 1. Each sample has been randomly selected from the population it represents. 2. The two samples are independent of one another. 3. The original variables observed are continuous random variables. 4. The underlying population distributions from which the samples are obtained are identical in shape (but not necessarily normal).

Ho: The two samples are drawn from a single population Ha: The samples represent two independent populations

( = 0.05 for all tests)

Group N Mean Rank Sum of Ranks NE 172 91.59 15753.00 GOM 22 143.73 3162.00 Total 194 0

U = 875.00, p < 0.0005 (Z(2) = -4.101)

Since p < 0.05, I reject the Ho. There is a significant difference in co-occurrence values between the Northeast and Gulf of Mexico. The average of the ranks for the GOM is greater than the average of the ranks for the NE, so a directional hypothesis is supported, indicating that co- occurrence measures in the GOM are greater than in the NE.

Reference:

Sheskin, D.J. Handbook of parametric and nonparametric statistical procedures. 2nd edition. Boca Raton: Chapman & Hall/CRC, 2000.

2 1

2. Testing the individual distributions across the year of leatherbacks and sunfishes (for aerial and longline data, in both the Northeast and Gulf of Mexico)

Software program: SPSS for Windows (version 13.0) Test Used: One-Sample Kolmogorov Smirnov Test

This is a goodness-of-fit test that is used to examine the agreement between a set of samples and a specified theoretical distribution. This test was used to examine the distributions of leatherbacks (or sunfishes) across the year for aerial and longline data in the Northeast and Gulf of Mexico. All sample distributions were tested against a uniform distribution to identify any seasonal patterns in abundance for leatherbacks and sunfishes. This test was chosen instead of a chi square test because the chi square test is not applicable with small sample sizes and also groups the data, causing a loss of information since individual observations are not treated separately.

Assumption of this test: The distribution of the underlying variable is continuous (appropriate for variables measured on an ordinal scale).

Ho: The distribution of leatherbacks (or sunfishes) across the year is not different from a uniform distribution Ha: The distribution of leatherbacks (or sunfishes) across the year is different from a uniform distribution.

( = 0.05 for all tests)

Example: data from aerial surveys in the Northeast

Leatherbacks n = 12

D(max) =0.585, p = 0.001 (Z(2) = 2.027)

There is a significant difference between the observed leatherback distribution in the Northeast and a uniform distribution.

Sunfishes n = 12

(max) = 0.441, p = 0.019 (Z(2) = 1.529)

There is a significant difference between the observed sunfish distribution in the Northeast and a uniform distribution.

Reference:

Seigel, S. Nonparametric statistics for the behavioral sciences. New York: McGraw-Hill Book Company, Inc., 1956.

2 2

3. Comparing leatherback and sunfish distributions across the year (for aerial and longline data, in both the Northeast and Gulf of Mexico)

Software program: SPSS for Windows (version 13.0) Test Used: Two-sample Kolmogorov-Smirnov Test

This test is used to determine whether two independent samples represent two different populations. It compares the cumulative frequency distributions of two independent samples (and is sensitive to distributional differences such as location/central tendency, dispersion/variability, skewness). This test was selected because it directly tests distributions. The t-test was excluded due to the non-normal nature of the data and because it tests means and the Mann-Whitney U test was excluded because it tests medians. It is possible for two distributions to have identical means and medians but to have different distributions.

Assumptions for this test: 1. All observations in the two samples are randomly selected and independent of one another. 2. Measurements are on an ordinal scale (the categories have a logical or ordered relationship to each other, and are grouped or ranked by whether they have more or less or a characteristic).

Ho: The samples are derived from the same population. Ha: The samples are most likely derived from different populations.

( = 0.05 for all tests)

Example: data from aerial surveys in the Northeast

D(max) = 0.500, p = 0.100, (Z(2) = 1.225)

There is no significant difference in the distributions of leatherbacks and sunfishes across the year in the Northeast.

References:

Seigel, S. Nonparametric statistics for the behavioral sciences. New York: McGraw-Hill Book Company, Inc., 1956.

Sheskin, D.J. Handbook of parametric and nonparametric statistical procedures. 2nd edition. Boca Raton: Chapman & Hall/CRC, 2000.

2 3

4. Testing correlations between the distributions of leatherbacks and sunfishes

Software Program: SPSS for Windows, version 13.0 Tests used: Pearson’s product-moment, Spearman’s rho

These tests evaluate the relationship between two variables and the correlation coefficient measures the intensity of this association. The Pearson test is a parametric test (assuming normally distributed data), while the Spearman test is nonparametric (and does not require normally distributed data). I chose to use both tests to analyze the data in order to show the robust (parametric) and conservative (nonparametric) interpretations of these data. Scatterplots were generated to identify outliers in the data. I excluded outlying data points in cases where there was a significant or nearly significant relationship, to more accurately estimate the correlation. Since there was no aerial survey effort in January (and hence no sightings of leatherbacks or sunfishes) in the Gulf of Mexico, these data were excluded from the correlation analyses so as not to bias the results by including zeroes.

Logbook = Fisheries Logbook System (FLS) longline data Observer = Pelagic Observer Program (POP) longline data Aerial = aerial survey data NE = Northeast GOM = Gulf of Mexico

2 4

Example: Outlier is excluded

(1a) Aerial NE leatherback vs. Aerial NE sunfish r = 0.811, p < 0.01, = 0.886, p < 0.01

2.0000

k c

a 1.5000

e h t :

a :

e l

1.0000

r e

A 0.5000 : :

: 0.0000 ::::

0.0000 5.0000 10.0000 15.0000 20.0000 Aerial NE sunfish

Fig. 1a. Scatterplot of the correlation between leatherback and sunfish distributions in the Northeast (from aerial survey data). Both the Pearson and Spearman correlations are statistically significant at p < 0.01.

2 5

(1b) The data point at 20.45, 2.18 was excluded r = 0.591, n.s. (p = 0.055); = 0.850, p < 0.01

1.0000

b r

e 0.7500

E 0.5000

l a

i : r e

A : 0.2500

: 0.0000 ::: ::

0.0000 5.0000 10.0000 15.0000

Aerial NE sunfish

Fig 1b. Scatterplot of the correlation between leatherback and sunfish distributions in the Northeast (from aerial survey data), with outliers excluded. The Pearson correlation is nearly significant and the Spearman correlation is statistically significant at p < 0.01.

2 6

Example: Initial analyses showed correlation with one test but not the other

(2a) Logbook NE leatherback vs. Observer NE leatherback r = 0.737, p < 0.01, = 0.571, n.s.

0.8000 :

: k

c 0.6000 :

a :

e l

0.4000

k :

o b

g 0.2000

o :

L : : :

0.0000 : :

0.0000 0.0500 0.1000 0.1500 Observer NE leatherback

Fig. 2a. Scatterplot of the correlation between leatherback distributions in the Northeast (from logbook and observer longline bycatch data). The correlation is statistically significant at p < 0.01 (Pearson’s).

2 7

(2b) The outlying data point at 0.1887, 0.0870 was excluded. r = 0.954, p < 0.01, = 0.883, p < 0.01.

0.8000 :

: k

c 0.6000 :

a :

e l

0.4000

k :

o b

g 0.2000

o :

L : :

0.0000 : :

0.0000 0.0500 0.1000 0.1500 Observer NE leatherback

Fig. 2b. Scatterplot of the correlation between leatherback distributions in the Northeast (from logbook and observer longline bycatch data) with outliers excluded. The correlation is highly significant at p < 0.01 (Pearson’s) and = 0.883 (Spearman’s).

2 8

Example: No correlation between variables

(3) Aerial GOM leatherback vs. Aerial GOM sunfish r = -0.094, n.s., = -0.179, n.s.

c a

b 1.0000 :

h t

a :

e :

l 0.5000 :

a : i

r :

e A

: :

0.0000 :

0.0000 0.5000 1.0000 1.5000 Aerial GOM sunfish

Fig. 3. Scatterplot of the data points for leatherback and sunfish distributions in the Gulf of Mexico (from aerial survey data). There is no correlation between these variables.

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LITERATURE CITED

Anderson, W. D. Jr., & D. M. Cupka. 1973. Records of the ocean sunfish, Mola mola,

from the beaches of South Carolina and adjacent waters. Chesapeake Science 14: 295-

298.

Beerkircher, L.R., C.J. Brown, & D.W. Lee. 2002. SEFSC pelagic observer program

data summary for 1992-2000. NOAA Technical Memorandum NMFS-SEFSC-

486: 26p.

Bleakney, J.S. 1965. Reports of marine turtles from New England and eastern Canada. The Canadian Field Naturalist 79 (2): 120-128.

Brongersma, L. D. 1969. Miscellaneous notes on turtles, IIA, IIB. Proceedings. Koninklijke Nederlandse Akademie van Wetenschappen (ser. C). 72: 76-102.

Cooper, T., D. McGrath & B. O’Connor. 1982. Species associated with a sunfish Mola

mola (L.) from the west coast of Ireland. Irish Naturalist Journal 20 (9): 382-383.

Cura, J. 1987. Phytoplankton. In: Georges Bank. MIT Press. (R.H. Backus and D.W. Bourne, eds.)

Davenport J. & G.H. Balazs. 1991. “Fiery bodies” - are pyrosomas important items in the diet of leatherback turtles? British Herpetological Society Bulletin 37: 33-38.

Davis, C.S. 1987. Zooplankton life cycles. In: Georges Bank. MIT Press. (R.H. Backus and D.W. Bourne, eds.)

Elliott, B.A. 1982. Anticyclonic rings in the Gulf of Mexico. Journal of Physical

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Oceanography 12: 1292-1309.

Fraser-Brunner, A. 1951. The ocean sunfishes (family Molidae). Bulletin of the British Museum (Natural History) Zoology 1 (6): 87-121.

Frazier, J., M., D. Meneghel, & F. Achaval. 1985. A clarification on the feeding habits of Dermochelys coriacea. Journal of Herpetology 19 (1): 159-160.

Frick, M. G., C. A. Quinn, & C. K. Slay. 1999. Dermochelys coriacea (leatherback sea

turtle), Lepidochelys kempi (Kemp's ridley sea turtle), and Caretta caretta

(loggerhead sea turtle). Pelagic feeding. Herpetological Review 30:165.

Gilbes, F., C. Tomas, J. Walsh & F. Muller-Karger. 1996. An episodic chlorophyll plume on the

west Florida shelf. Continental Shelf Research 6 (9): 1201-1224

Graham, W.M., F. Pages, & W.M. Hammer. 2001. A physical context for gelatinous zooplankton aggregations: a review. Hydrobiologia 451: 199-212.

den Hartog, J.C. & Van Nierop, M.M. 1984. A study on the gut contents of six leathery turtles Dermochelys coriacea (Linnaeus) (Reptilia: Testudines: Dermochelyidae) from British waters and from the Netherlands. Zoologische Verhandelingen. (Leiden) 209:1-36.

Hubbs, C.L. & L.P. Schultz, 1929. The northward occurrence of southern forms of marine life along the Pacific coast in 1926. California Fish and Game 15 (3): 234- 241.

3 1

James, M.C. & N. Mrosovsky. 2004. Body temperatures of leatherback turtles (Dermochelys coriacea) in temperate waters off Nova Scotia, Canada. Canadian Journal of Zoology 82 (8): 1302-1306.

James, M.C. & T.B. Herman. 2001. Feeding of Dermochelys coriacea on medusae in the Northwest Atlantic. Chelonian Conservation and Biology 4 (1): 202-205.

Jenness, J. 2004. Nearest features (nearfeat.avx) extension for ArcView 3.x, v. 3.8a.

Jenness Enterprises. 3 December 2004.

(20 August 2004).

Johnson, D.R., H.M. Perry & W. D. Burke. 2001. Developing jellyfish strategy hypotheses using circulation models. Hydrobiologia 451: 213-221.

Kenney, R.D. 1996. Preliminary assessment of competition for prey between

Leatherback turtles and ocean sunfish in northeast shelf waters. Found in:

Keinath, J.A., D.E. Bernard, J.A. Musick, & B.A. Bell compilers, Proceedings of the

Fifteenth Annual Symposium on Sea Turtle Biology and Conservation. NOAA

Technical Memorandum NMFS-SEFSC-387, 355pp: 1996, p 144-147.

Kenney, R.D. & H.E. Winn. 1986. Marine Mammal Data Transfer and Documentation,

Final Report to: Northeast Fisheries Center, NMFS-NOAA U.S. Dept. of

Commerce, Woods Hole, MA, 12543.

Lee, D.S. 1986. Seasonal, thermal, and zonal distribution of ocean sunfish, Mola mola, off the North Carolina coast. Brimleyana 12: 75-83.

3 2

Lozier, M.S., W. Brechner Owens, & R.G. Curry. 1995. The climatology of the North Atlantic.

Progress in Oceanography 36 (1): 1-44.

Lucas, C.H. 2001. Reproduction and life history strategies of the common jellyfish,

Aurelia aurita, in relation to its ambient environment. Hydrobiologia 451: 229-

246.

MacGintie, G.E. 1938. Notes on the natural history of some marine animals. The American Midland Naturalist 19 (1): 207-219.

Mrosovsky, N. 1987. Leatherback turtle off scale. Nature 327: 286

Nanami, A. & M. Nishihira. 2003. Population Dynamics and Spatial Distribution of

Coral Reef Fishes: Comparison between continuous and isolated habitats.

Environmental Biology of Fishes 68 (2): 101-112.

National Marine Fisheries Service Southeast Fisheries Science Center (NMFS,

SEFSC). 2001. Stock assessments of loggerhead and leatherback sea

turtles and an assessment of the impact of the pelagic longline fishery on

the loggerhead and leatherback sea turtles of the western north Atlantic.

US Department of Commerce NOAA Technical Memorandum NMFS-

SEFSC-455, 343pp.

3 3

O’Reilly, J.E, C. Evans-Zetlin, & D. A. Busch. 1987. Primary production. In: Georges Bank.

MIT Press. (R.H. Backus and D.W. Bourne, eds.)

Rivero, L.H. 1936. Six Records of the Pointed-Tailed Ocean Sunfish near Havana, Cuba. The

American Naturalist 70 (726): 92-95.

Seigel, S. Nonparametric statistics for the behavioral sciences. New York: McGraw-Hill Book

Company, Inc., 1956.

Sheskin, D.J. Handbook of parametric and nonparametric statistical procedures. 2nd

edition. Boca Raton: Chapman & Hall/CRC, 2000.

Sherman, K., M. Grosslein, D. Mountain, D. Busch, J. O’Reilly, & R. Theroux. 1988. The

continental shelf ecosystem off the northeast coast of the United States. In: Ecosystems of

the World: Contintental Shelves. Elsevier, New York. (H. Postma and J.J. Zijlstra, eds.)

Sommer, F., J. Christiansen, P. Ferrante, R. Gary, B. Gray, C. Farwell, & D. Powell. 1989. Husbandry of the Ocean Sunfish Mola mola. American Association of Zoological Parks and Aquariums Regional Conference Proceedings. pgs 410-417.

Spotila, J.R. & E.A. Standora. 1985. Environmental constraints on the thermal energetics of sea

turtles. Copeia 1985: 694-702.

SPSS for Windows, Rel. 13.0 2004. Chicago: SPSS Inc.

3 4

Thompson, N.B. & H. Huang. 1993. Leatherback turtles in southeast U.S. waters.

NOAA Tech. Mem. NMFS-SEFSC-318. 11p.

Threlfall, W. 1967. Some parasites recovered from the ocean sunfish, Mola mola, (L.), in

Newfoundland. The Canadian Field Naturalist 81: 168-172.

Van Bruggen, A.C. 1983. Occurrence of sunfish, Mola mola, in the Skagarak. Fauna och

Flora 78: 285-286.

Wiseman, W.J., Jr., & S.P. Dinnel. 1988. Shelf current near the mouth of the Mississippi

River. Journal of Physical Oceanography 18 (9): 1287-1291.

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Table 1: Aerial surveys used to estimate leatherback and sunfish co-occurrence in the U.S. Atlantic shelf waters.

Survey Dates Year(s) Region surveyed Purpose Name TO 95 Aug 5- Sept 17 1995 Nova Scotia to New Jersey A component of the NEFSC Offshore Marine (inside 1000-m isobath) Mammal Survey TO 98 July 18-Aug 21 1998 Nova Scotia to New Jersey A component of the NEFSC Offshore Marine (inside 1000-m isobath) Mammal Survey

n o

i TO 02 July 19-Aug 16 2002 Gulf of Maine, Georges Bank, Circle-back Method Experimental Abundance g

e east to Long Island (inside Survey (marine mammals and turtles) R

t 1000-m isobath) s a

e CETAP Nov 1, 1978 – 1978-1982 Waters overlying the Characterize marine mammals and turtles in the h t

r Jan 28, 1982 U.S. Outer Continental Shelf Mid- and North Atlantic regions of the U.S. o

N between Cape Hatteras, North Outer Continental Shelf, for use in decision- Carolina, and Nova Scotia, making relative to oil and gas exploration and Canada. development in these regions

MATS July 13-Aug 13 1995 Long Island to Cape Hatteras Estimate bottlenose dolphin abundance in Mid-

(inside 100-m isobath) Atlantic region

h SECAS Jan 27-Mar 6 1995 Cape Hatteras to Central Florida Southeast Cetacean Abundance Survey t t n u

a coast (inside 1000-m isobath) l o t S A GoMEX Sept 13- Oct 24 ‘92 1992-1994 East gulf (92), Central Gulf Estimate cetacean abundance and distribution in

o Sept 17 - Oct19 ‘93 (93), Western Gulf (94) the coastal and continental shelf waters of the c i

x Sept 28 - Nov 9 ‘94 (inside 200-m isobath) Gulf of Mexico e M

o GulfCet I Oct 1- July 15 1991-1995 Between the Florida-Alabama Assess the potential effects of deepwater oil and

f l border, the Texas-Mexico gas exploration and production on marine u

G border, and the 100-m and mammals in the Gulf of Mexico 2,000-m isobaths

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GulfCet II (winter) 1996-1997 Entire continental slope of the Determine the seasonal and geographic Feb - Mar northern Gulf of Mexico (e.g., distribution of cetaceans in the northern Gulf of the continental slope north of 26 Mexico and characterize their habitat in areas (summer) 1997-1998 degrees N latitude) between the potentially affected by oil and gas activities July-Aug 100- and 2,000-m isobaths

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Table 2: Survey effort and number of animals sighted for the Northeast. Numbers reflect sightings from aerial surveys (TO 95, TO 98, TO 02, MATS 95, and CETAP).