Demography of the bottlenose dolphin Tursiops truncatus (Mammalia: Delphinidae) in the Eastern Ligurian Sea (NW Mediterranean): quantification of female reproductive parameters

Figures & data

Figure 1. The Eastern Ligurian Sea study area was divided into four sub-areas: A, Capo Arenzano–Punta Chiappa; B, Punta Chiappa–Punta Mesco; C, Punta Mesco–Punta Bianca; D, Punta Bianca–northern Elba Island.

Figure 2. Mother–calf association (Photo credit: Alessia Rossi).

Table I. Column 1 (from left): the surveyed sub-areas; column 2: observed number of sightings of females in association with young; in parentheses the corresponding expected number of sightings under hypothesis H₀ that the encounter rate (ER) is the same throughout the entire study area; column 3: total number of sightings of females alone or in association with young; in parentheses the corresponding expected number of sightings under the same H₀ hypothesis; column 4: sighting effort in km; column 5: ER of adult females in steady association with a young individual per 1000 km of sighting effort; column 6: ER of adult females, per 1000 km of sighting effort.

Sub-area	No. sightings of females with a young individual	No. of sightings of females	Sighting effort (km)	ER Female + cubs	ER All adults
A	1 (11.7, p = 0.00013)	7 (44.3)	4029.24	0.25	1.74
B	51 (28.7, p = 0.00006)	182 (108.7)	9883.91	5.16	18.41
C	25 (17.7, p = 0.0382)	132 (67.0)	6090.72	4.10	21.67
D	32 (50.8, p = 0.032)	91 (192.1)	17,473.28	1.83	5.21
Total	109	412	37,477.2	2.91	10.99

Table II. Female fertility under the four different scenarios described in the text. Per each scenario: (a) the number of births (first row); (b) the exposure time (second row); (c) the resulting fertility rate b (third row) per 1000 adult females yr⁻¹ (computed by dividing the number of births by the exposure time), in parentheses below, the corresponding 95% bootstrap percentile confidence interval (CI); (d) the corresponding predicted interval between births, computed as 1/b (fourth column).

	Scenario 1	Scenario 2	Scenario 3	Scenario 4
Number of births	74	85	61	72
Exposure time (yr)	255.5	255.5	176.8	176.8
Fertility rate b (per 1000 yr^−1)	289.6	332.7	344.9	407.1
	(CI: 259.5–321.3)	(CI: 296.6–372.3)	(CI: 311.9 – 379.6)	(CI: 371.4–443.9)
Births interval (yr)	3.45	3.0	2.90	2.45

Table III. Summary reproduction parameters of genus Tursiops in the literature. ^aThis study; ^bMitchenson (2008); ^cFruet et al. (2015); ^dWells and Scott (1990); ^eTezanos-Pinto et al. (2015); ^fHenderson et al. (2014); ^gKogi et al. (2004); ^hMann et al. (2000); ⁱSteiner and Bossley (2008).

Site	Species	Fertility rate (yr^−1)	Calving interval (yr)	Cub mortality rate
Eastern Ligurian Sea^a	T. truncatus	0.29–0.41	2.45–3.45	0.25
Scotland^b	T. truncatus	0.11	3.18	-
PLE, Brazil^c	T. truncatus	0.11	3	0.16
Sarasota Bay, USA^d	T. truncatus	0.144	4	0.19
Bay of Island, NZ^e	T. truncatus	0.25	4.3	0.34–0.52
Doubtful Sound, NZ^f	T. truncatus	-	5.3	0.33
Mikura Island, Japan^g	T. aduncus	0.24	3.4	0.14
Shark Bay, Australia^h	T. aduncus	-	4.55	0.29
Port River, Australia^i	T. aduncus	-	3.8	0.3

Mitchenson H. 2008. Inter-birth interval estimation for a population of bottlenose dolphins (Tursiops truncatus): accounting for the effects of individual variations and changes over time. Master Thesis. Scotland: University of St. Andrews.

 Google Scholar

Fruet PF, Genoves RC, Möller LM, Botta S, Secchi ER. 2015. Using mark-recapture and stranding data to estimate reproductive traits in female bottlenose dolphins (Tursiops truncatus) of the Southwestern Atlantic Ocean. Marine Biology 162:661–673. DOI:10.1007/s00227-015-2613-0.

 Web of Science ®Google Scholar

Wells RS, Scott MD. 1990. Estimating bottlenose dolphin population parameters from individual identification and capture-release techniques. Reports of the International Whaling Commission Special Issue 12:407–415.

 Google Scholar

Tezanos-Pinto G, Constantine R, Mourão F, Berghan J, Scott Baker C. 2015. High calf mortality in bottlenose dolphins in the Bay of Islands, New Zealand-a local unit in decline. Marine Mammal Science 31:540–559. DOI:10.1111/mms.2015.31.issue-2.

 Web of Science ®Google Scholar

Henderson SD, Dawson SM, Currey RJC, Lusseau D, Schneider K. 2014. Reproduction, birth seasonality, and calf survival of bottlenose dolphins in Doubtful Sound, New Zealand. Marine Mammal Science 30:1067–1080. DOI:10.1111/mms.12109.

 Web of Science ®Google Scholar

Kogi K, Hishii T, Imamura A, Iwatani T, Dudzinski KM. 2004. Demographic parameters of Indo-Pacific bottlenose dolphins (Tursiops aduncus) around Mikura Island, Japan. Marine Mammal Science 20:510–526. DOI:10.1111/mms.2004.20.issue-3.

 Web of Science ®Google Scholar

Mann J, Connor RC, Barre LM, Heithaus MR. 2000. Female reproductive success in bottlenose dolphins (Tursiops sp.): life history, habitat, provisioning and group-size effects. Behavioral Ecology 11:210–219. DOI:10.1093/beheco/11.2.210.

 Web of Science ®Google Scholar

Steiner A, Bossley M. 2008. Some reproductive parameters of an estuarine population of Indo-Pacific bottlenose dolphins (Tursiops aduncus). Aquatic Mammals 34:84–92. DOI:10.1578/AM.34.1.2008.84.

 Google Scholar