Early physical maturation of female common bottlenose dolphin Tursiops truncatus in the eastern Levantine Basin

Abstract

Regional resource limitation in the eastern Levantine Basin was predicted to protract the growth of members of the Israeli sub-population of the common bottlenose dolphin (CBD), compared to CBD sub-populations of similar adult size. Growth curves were fitted to length-at-age data available for 24 male and 26 female CBD stranded or incidentally caught along the Israeli coastline between 2000 and 2009. The obtained model growth constants were compared to those of other CBD subpopulations from the southeastern coast of the United States and a correlation to regional seawater primary productivity was sought. As in other sub-populations, local CBD females initially grow faster than males for approximately 3-4 years and remain longer until around eight years old, after which males surpass them in length. Yet the steep early growth of females as well as its high rate of decay was found to be extreme compared to other CBD sub-populations, with 99% of the asymptotic length being reached at the age of six years. A positive correlation between seawater primary productivity and early growth rate as well as growth decay constants could be demonstrated for CBD males from Texas, Florida and Israeli coasts. Females of the same sub-population presented a non-monotonic relationship to primary productivity. Early female attainment of physical maturity in an ultra-oligotrophic region was unpredicted and is not readily explained. It may accompany early reproductive maturation, selected for as partial compensation for lower lifelong reproductive success.

Small dolphins in a small sea: age, growth and life‑history aspects of the Black Sea common bottlenose dolphin Tursiops truncatus

“…7), and it is also distinct in rapid early growth and maturation. Thus, growth rates for both sexes, as indicated by k values in the Gompertz equation, are extremely high in comparison with other populations (Kerem et al 2013). Given a small adult body size, such a growth curve is a manifestation of an extremely re production-oriented life history of a marine mammal.…”

“…7): rapid early growth and fast attainment of the relatively small asymptotic size. However, the environmental conditions in the eastern Mediterranean, which were suggested as possible causes of such an early maturation of females (Kerem et al 2013), are substantially different from the Black Sea: the Levantine basin is warmer, less productive and more saline. Meanwhile, the male growth curve is closer to that of the dolphins from the Mississippi region of the Gulf of Mexico (data by Mattson et al 2006) (Fig.…”

“…However, the mean and median lengths of adult animals in their samples were far smaller ( This difference in data can be explained if there are 2 morphs inhabiting the Black Sea, a large and a small one. Sympatric distribution of a coastal (smallsized) and an offshore (large-sized) population is usual for many delphinids (Perrin 1984): such ecotypes of common bottlenose dolphins exist in the western North Atlantic (Hersh & Duffield 1990, Torres et al 2003 and possibly in the Mediterranean (Kerem et al 2013). In fact, stable coastal groups of bottlenose dolphins inhabit the northern Black Sea (Bel'kovich 1978, Gladilina et al 2013, whereas large aggregations are also recorded in the offshore waters (Mikhalev 2005).…”

“…Adult dolphins from the Levantine waters of Israel are on average 15 cm longer than Black Sea dolphins (Kerem et al 2013), and other Mediter ranean dolphins are even larger (Sharir et al 2011), as are common bottlenose dolphins from the North Atlantic, South Atlantic and Indo-Pacific (Cockcroft & Ross 1990, Hale et al 2000, Siciliano et al 2007). However, note that the historical large morph (BarabashNikiforov 1940) is similar in size to the dolphins from the geographically close Mediterranean regions, namely the Le vantine basin (Kerem et al 2013) and the Adriatic Sea (Pribani et al 2000; see also the review by Sharir et al 2011). Furthermore, dolphins from the coastal waters of the Gulf of Mexico and Florida are similar in size to present-day Black Sea animals (Fernandez & Hohn 1998, Stolen et al 2002, Mattson et al 2006: the smallest adult common bottlenose dolphins, ca.…”

Factors influencing heterogeneity in female reproductive success in a Critically Endangered population of bottlenose dolphins

“…Not all bottlenose dolphins reach maximum size at the same age (Read et al 1993), and thus it is possible some of the mothers born into the population between 1990 and 2012 would have continued to grow past 8 yr of age. Females often reach asymptotic length before males (Read et al 1993), and Kerem et al (2013) have shown that 99% of growth in female bottlenose dolphin occurs before 6 yr. Additionally, growth rates slow dramatically as dolphins approach asymptotic length (Read et al 1993, Chong & Schneider 2001. Hence, any increases in mother size over the study are likely to be negligible.…”