Sheryan P. Epperly

Natal homing in juvenile loggerhead turtles (Caretta caretta)

Juvenile loggerhead turtles (Caretta caretta) from West Atlantic nesting beaches occupy oceanic (pelagic) habitats in the eastern Atlantic and Mediterranean, whereas larger juvenile turtles occupy shallow (neritic) habitats along the continental coastline of North America. Hence the switch from oceanic to neritic stage can involve a trans‐oceanic migration. Several researchers have suggested that at the end of the oceanic phase, juveniles are homing to feeding habitats in the vicinity of their natal rookery. To test the hypothesis of juvenile homing behaviour, we surveyed 10 juvenile feeding zones across the eastern USA with mitochondrial DNA control region sequences (N = 1437) and compared these samples to potential source (nesting) populations in the Atlantic Ocean and Mediterranean Sea (N = 465). The results indicated a shallow, but significant, population structure of neritic juveniles (ΦST = 0.0088, P = 0.016), and haplotype frequency differences were significantly correlated between coastal feeding populations and adjacent nesting populations (Mantel test R2 = 0.52, P = 0.001). Mixed stock analyses (using a Bayesian algorithm) indicated that juveniles occurred at elevated frequency in the vicinity of their natal rookery. Hence, all lines of evidence supported the hypothesis of juvenile homing in loggerhead turtles. While not as precise as the homing of breeding adults, this behaviour nonetheless places juvenile turtles in the vicinity of their natal nesting colonies. Some of the coastal hazards that affect declining nesting populations may also affect the next generation of turtles feeding in nearby habitats.

Survival of Pelagic Juvenile Loggerhead Turtles in the Open Ocean

Abstract We deployed pop-up archival transmitting tags on 15 loggerhead sea turtles (Caretta caretta) that had been lightly hooked in the United States pelagic longline fishery and on 10 loggerheads that we dip-netted off the surface to serve as controls in the North Atlantic Ocean. We received data from tags of 10 lightly hooked turtles and 7 control turtles. We used data transmitted by the tags in a known-fate model to estimate annual survival rates and determine if there were differences in survival between the 2 groups. The best model indicates there is no difference in survival between the lightly hooked and control turtles, and the estimated annual survival rate was 0.814 (95% CI = 0.557–0.939). Our results suggest that when all fishing gear is removed lightly hooked turtles may not suffer any additional mortality relative to control turtles.

Fecundity of Atlantic menhaden, Brevoortia tyrannus

Since the 1950’s the population structure of the Atlantic menhaden,Brevoortia tyrannus, has undergone dramatic changes. High rates of fishery exploitation during the 1960’s resulted in a drastic decline in the breadth of the age structure and numbers of spawning aged fish. The stock recovered under continued exploitation during the 1970’s in spite of these unfavorable conditions. Hence, the length and age at first spawning, the seasons and areas of spawning, and the potential number of ova produced as a function of length were reexamined during the 1978, 1979, and 1981 fishing seasons. No changes were detected in the reproductive biology of Atlantic menhaden. The size at first spawning, areas, and season of spawning were similar to results of previous studies. The minimum fork length of potential spawners was 180 mm. Few age-1 fish were mature but most females were mature at age-2. Analysis of the ovaries collected along the coast indicated some spawning occurred in the spring, a limited amount occurred in the summer, and most spawning occurred during the fall and winter. There was high intra-and interyear variability in the relationship between length and potential number of ova produced, and regression coefficients encompassed values from two previous studies, each based on a single fishing year. Data from this and the previous studies were combined and equally weighted to generate a representative predictive equation for the potential number of ova spawned as a function of length: eggs = 2563e0.0150(FL).

Summer Abundance Estimates of Caretta caretta (Loggerhead Turtles) in Core Sound, NC

Abstract We estimated summer abundance of juvenile Loggerhead Turtles at our study site in Core Sound, NC with a Horvitz-Thompson type estimator, which uses count data and recapture probability to estimate abundance. Abundance ranged from 192 (95% CI = 88–1047) to 633 (95% CI = 219–1047) turtles over the six years of this study. These results provide preliminary estimates of juvenile Loggerhead Turtle abundance during the summer in Core Sound.

Accuracy tests for sonic telemetry studies in an estuarine environment

We evaluated accuracy and precision of a directional sonic telemetry system and 2 positioning systems to study sea turtle (Cheloniidae) use of estuarine habitat in Core Sound, North Carolina. Accuracy and precision of location estimates affect the power of statistical tests for use of habitat studies and define the amount of movement that can be reliably measured. Angle errors associated with the sonic system averaged −2.5° ± 5.67 (SD) for a 95% error arc of ± 11.34° (range −17−12°). We obtained 45 location estimates after correcting 90 bearings for bias. Location errors (E), obtained from stationary positions at 400-1,200 m, ranged from 14.6 to 281.0 m with a median of 75.6 m. The 90 and 95% confidence areas for these data were 11.1 and 21.2 ha, respectively. Location error varied (P < 0.01) WITH GEOMETRIC MEAN DISTANCE (D g ) between receivers and transmitters. Areal measures of confidence obtained at the D g 500-600 m were the smallest (2.1-2.8 ha) among 3 distance intervals within 500-1,200 m. Attained levels of accuracy and precision were adequate to determine turtle movement and distribution in relation to selected fisheries activities, but of limited value for use of habitat studies. Inaccurate position estimates of monitoring platforms (e.g., boats) also affect location estimates. Precision of position estimates of a stationary boat anchored at a known location (i.e., channel marker) were poor, averaging 62 m, when obtained from Long Range Navigation System (LORAN). In contrast, positions obtained from Differential Global Positioning System (DGPS) varied by 3 m. The DGPS did not affect (P = 0.94) location estimation. Average difference between estimates using known location coordinates and those obtained from DGPS was 0.56 with a 95% confidence interval of ± 1.29 m. We recommend that DGPS be used when evaluating sea turtle use of habitat. The DGPS was more accurate than LORAN and was unaffected by geography

Evaluation of a sonic telemetry system in three habitats of an estuarine environment

A directional sonic telemetry system in small embayment, seagrass, and channel habitats in Core Sound, North Carolina was evaluated. We compared point location estimates calculated after correcting for system bias in three different ways: using test station (i.e. known location transmitting–receiving stations) angle errors, and using a within test site and an among test site mean angle error estimate. Estimates are necessary because, when tracking an animal, system bias cannot be corrected for using test station angle errors. In addition, telemetered animals may move beyond test areas or into different habitats. We found no significant difference (P>0.05) among point location estimates, suggesting that a within or an among mean angle error was an acceptable estimate. Choosing the appropriate angle error estimate must be done carefully because both presented limitations. A within test site mean angle error was the more conservative approach, avoiding biases caused by significant (P 97% of the seagrass habitat in Core Sound. Although the majority (80%) of the polygons are small (<10.0 ha), they represent <5% of the total seagrass area. In addition, classifying use of habitat in areas where polygons are ≤6.9 ha is possible because small polygons have a contagious distribution; hence, their areas may be additive. Risks of misclassifying use of habitat can be reduced also by controlling the size of confidence areas (Ae) by adjusting the distance between observers and the tracked animal. The confidence area as a function of distance can be predicted because location error varied linearly and significantly with geometric mean distance (Dg). On the basis of this relationship, Dg must be <326 m for Ae95 to be <10.0 ha.