Variation in Timing of Conception Between Populations of the Harbor Porpoise

Börjesson, Patrik; Read, Andrew J.

doi:10.1644/bem-016

Cited by 25 publications

(27 citation statements)

References 17 publications

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“…This enables calves to be born when maternal prey is abundant and of high quality (Urian et al 1996, Börjesson & Read 2003. Short-beaked common dolphins in the current study exhibited a seasonal pattern of reproduction that was intermediate between the highly synchronised births of harbour porpoises, where most births occur over a few weeks (Börjesson & Read 2003), and the extended parturition season of tropical odontocetes, e.g.…”

Section: Female Reproductive Parameters In the Ena And Other Delphinumentioning

confidence: 73%

“…Unlike , in which the average length at birth was calculated from tooth sections that either did not have a neonatal line, or where it was just forming, in the current study we estimated size (length and weight) at birth using Börjesson & Read's (2003) overlap method. This method calculates the mean of overlapping foetal and calf sizes by including the value of the largest non-overlapping foetus (85 cm) and the smallest non-overlapping calf (95 cm).…”

Section: Methodsmentioning

confidence: 99%

“…The date of conception was estimated for all foetuses and was based on the age of individual foetuses, as described by Börjesson & Read (2003): (8) where t is the foetal age in days, u is foetal growth rate (cm mo -1 ), Lt is the actual length of the foetus (mm), 30.5 is the average number of days in a month, and t 0 is the nonlinear growth rate. Individual conception dates were calculated by subtracting the estimated foetal age (t in days) from the date found (day of year).…”

Section: Methodsmentioning

confidence: 99%

“…The timing of parturition tends to be highly synchronised in populations of mammals at high latitudes where seasons of high productivity are brief and less synchronised, and more protracted in low-latitude 281 populations (Börjesson & Read 2003). This enables calves to be born when maternal prey is abundant and of high quality (Urian et al 1996, Börjesson & Read 2003.…”

Section: Female Reproductive Parameters In the Ena And Other Delphinumentioning

confidence: 99%

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Importance of biological parameters in assessing the status of Delphinus delphis

Murphy¹,

Winship²,

Dabin³

et al. 2009

Mar. Ecol. Prog. Ser.

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Short-beaked common dolphins Delphinus delphis in the eastern North Atlantic (ENA) are subject to mortality due to entanglement in various types of fishing gear. However, for this region, there is no population-level information available on trends in abundance, (incidental) mortality rates or even the actual distributional range. Working under the assumption that only 1 population exists in ENA waters, the current study presents basic life history data and investigates whether biological information obtained from postmortem data is, in itself, useful for managing this population. Life history parameters were estimated by analysing postmortem data obtained over a 16 yr period by UK, Irish, French, Galician (northwest Spain) and Portuguese stranding and bycatch observer programmes. An annual pregnancy rate of 26%, a calving interval of 3.79 yr, an average age attained at sexual maturity of 8.22 yr and an average length at sexual maturity of 188 cm were determined. With respect to the findings based solely on mortality data, significance testing failed to detect differences that could be construed as evidence of the population exhibiting what might be density-dependent compensatory responses. The low annual pregnancy rate reported throughout the sampling period may suggest either that the level of anthropogenic mortality did not cause a substantial population level decline, or a prey base declining at approximately the same rate as the dolphin population. However, this approach alone does not facilitate an assessment of the current state of the D. delphis population in the ENA. Population abundance estimates, trends in abundance and knowledge of factors that affect the dynamics of the population, such as annual mortality rates in fisheries, temporal variations in prey abundance and effects of contaminants on reproductive activity, are required not only to set management objectives, but also to give context to cross-sectional life history information.

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Section: Female Reproductive Parameters In the Ena And Other Delphinumentioning

confidence: 73%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Female Reproductive Parameters In the Ena And Other Delphinumentioning

confidence: 99%

See 2 more Smart Citations

Importance of biological parameters in assessing the status of Delphinus delphis

Murphy¹,

Winship²,

Dabin³

et al. 2009

Mar. Ecol. Prog. Ser.

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“…As female harbour porpoises are thought to be 'income breeders' (Sibly & Calow 1986, Read 2001 and reproductive costs are significant (Lockyer 2007), it is concluded that they must be able to continually locate areas where prey species with high energy content are abundant. The harbour porpoise exhibits strong seasonality in its reproductive cycle (Börjesson & Read 2003), and the majority of births in our study area occur from June 6 to July 16 (Hasselmeier et al 2004 previous year, may therefore be essential in order to meet mating partners and to find enough food for the high energy demand of birth, mating and the first months of lactation (Lockyer et al 2003). …”

mentioning

confidence: 88%

Seasonal distribution of harbour porpoises and possible interference of offshore wind farms in the German North Sea

Gilles

Scheidat²,

Siebert³

2009

Mar. Ecol. Prog. Ser.

100

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The seasonal distribution of harbour porpoises in the German North Sea was investigated, hot spot areas were identified and the proportion of porpoises potentially affected by the imminent construction of offshore wind farms was estimated. Data were collected during dedicated aerial surveys conducted year-round between 2002 and 2006 following line transect methodology. Survey effort amounted to 44 739 km during which a total of 5121 harbour porpoises was detected, including 258 calves. Our data suggest that porpoises move to distinct areas on a seasonal basis as their biological requirements change. They move into German waters in early spring, reach high numbers in early summer and move out of the area in autumn. The abundance estimates for the German exclusive economic zone and 12 n mile zone were highest in spring (55 048 animals; 95% CI: 32 395 to 101 671) and summer (49 687 animals; 95% CI: 29 009 to 96 385) and lowest in autumn with 15 394 animals (95% CI: 8906 to 29 470). Important aggregation zones were detected in offshore waters: in spring, 2 hot spots, Borkum Reef Ground and Sylt Outer Reef (SOR), were identified as key foraging areas. In summer, only the large hot spot SOR persisted, causing a strong north-south density gradient. In autumn, porpoises were more evenly distributed. Most mother-calf pairs were observed during spring and summer in the SOR, underlining its importance as a foraging area when reproductive costs are high. Spatial overlap exists between important areas for porpoises and areas where offshore wind farms are currently licensed or planned. The proportion of the national stock possibly exposed to the construction noise of 18 licensed wind farms was estimated applying different scenarios. Within a 20 km zone of responsiveness -as worst case scenario -39% of the harbour porpoise stock in the German EEZ could be affected during construction.KEY WORDS: Phocoena phocoena · Harbour porpoise · North Sea · Aerial survey · Distribution · Foraging · Reproduction area · Offshore wind farm · Generalised additive model Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 383: [295][296][297][298][299][300][301][302][303][304][305][306][307] 2009 Union ( Fig. 1), and it is therefore imperative to obtain baseline data on marine mammal distributions in order to assess the risk of, and mitigate for, the impact of construction.The southeastern North Sea is an area with a wide range of human activities (Ducrotoy et al. 2000, OSPAR Commission 2000, Halpern et al. 2008. The harbour porpoise Phocoena phocoena (Linnaeus, 1758) is the most common cetacean in the North Sea (Hammond et al. 2002) and the only cetacean species found regularly in German waters (Scheidat et al. 2004, Siebert et al. 2006. There is evidence that harbour porpoise abundance in the southeastern North Sea has declined since the 1940s (Smeenk 1987, Reijnders 1992, Camphuysen & Leopold 1993. Various pressures have been identified, such as bycatch (Kock & Benke 1996, Vinther & L...

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Evaluating the distribution and density of harbour porpoises (Phocoena phocoena) in selected areas in German waters

Scheidat

Gilles

Siebert

2006

Progress in Marine Conservation in Europe

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Variation in Timing of Conception Between Populations of the Harbor Porpoise

Cited by 25 publications

References 17 publications

Importance of biological parameters in assessing the status of Delphinus delphis

Importance of biological parameters in assessing the status of Delphinus delphis

Seasonal distribution of harbour porpoises and possible interference of offshore wind farms in the German North Sea

Evaluating the distribution and density of harbour porpoises (Phocoena phocoena) in selected areas in German waters

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