Inter-year variation in pup production of Caspian seals Pusa caspica 2005–2012 determined from aerial surveys

Abstract

Assessing species abundance and reproductive output is crucial for evaluations of population dynamics, conservation status and the development of management objectives. The Caspian seal Pusa caspica is a key predator in the Caspian Sea ecosystem and is listed as Endangered by the IUCN. Here we report on fixed-wing aerial strip transect surveys of the breeding population on the Caspian Sea winter ice field carried out in February, 2005−2012. Potential detection biases were estimated by applying a Petersen mark-recapture estimator to the counts from double photographic observations. We also tested for effects of weather conditions on count results, and for correlations between pup production and ice conditions and net primary productivity (npp). Fluctuations in pup production estimates were observed among years, ranging from 8200 pups (95% CI: 7130−9342) in 2010 to 34 000 (95% CI: 31 275−36 814) in 2005. Total adults on the ice ranged from 14 500 in 2010 to 66 300 in 2012. We did not detect significant associations between pup production and either ice summary data (ice season length and ice area) or npp. The observed inter-year variation may be partly due to underlying biological drivers influencing the fecundity of the population, although measurement errors arising from observation bias, plus variation in survey timing and weather conditions may also have contributed. Identifying the potential drivers of Caspian seal population dynamics will require extending both the survey time series and the quality of supporting data. However, inter-year fluctuations should still cause concern that the population may be vulnerable to environmental variability and ecosystem dynamics.

Individual variation in seasonal movements and foraging strategies of a land-locked, ice-breeding pinniped

“…Caspian seal pupping peaks during early February, and lactation lasts for around 3 to 4 wk (Badamshin 1966). The active movements of seals over the ice season suggests that unless constrained by breeding or ice conditions they do not spend long periods on the ice sheet and may forage in different locations, supporting observations of females regularly leaving pups on ice to go to sea (Krylov & Vorozhtsov 1972) and observations of significant numbers of lone pups during aerial surveys (Dmitrieva et al 2015). This behaviour contrasts with other ice-breeding species such as ringed seals which show higher levels of site fidelity during breeding since they need to maintain breathing holes during the whole ice period (Kelly et al 2010).…”

“…During formation of the ice sheet most animals moved into the centre of the north basin and were located along the ice edge or within the ice field around the 'Saddle' area. Their locations overlapped with areas of high seal density identified from concurrent aerial population surveys in February in 2010 to 2012 (Dmitrieva 2013, Dmitrieva et al 2015.…”

“…The tagging of moulted pups on the ice would contribute to understanding movement and habitat use of juveniles. Overall, the data suggest that Caspian seals are likely to have little population structure since they disperse throughout the whole Caspian from the Komsomolets Bay moulting site, and during the winter animals ranged through the whole breeding distribution in the ice pack identified from aerial surveys (Dmitrieva 2013, Dmitrieva et al 2015. Such long range dispersal, high mobility, and aggregated breeding is comparable with other ice-breeding species with weak population structure, such as ringed seals in the Arctic, where the annual life history is governed by seasonal and spatial separation of breeding substrate and food resources (MartinezBakker et al 2013); hooded seals in the North Atlantic where migration patterns reflect favourable foraging conditions (Coltman et al 2007, Andersen et al 2013; and in Weddell seals (Chambert et al 2015).…”

Disappearing giants: a review of threats to freshwater megafauna

“…Less directly, Lake Trout ( Salvelinus namaycush ) populations in Ontario lakes declined following introductions of Smallmouth Bass ( Micropterus dolomieu ) and Rock Bass ( Ambloplites rupestris ) that led to a decline in their key food source, native littoral prey fishes through competition . Introduced Comb Jellyfish ( Mnemiopsis leidyi ) posed a serious risk to Kilka ( Clupeonella cultriventris ), the main prey of Caspian Seal in the central and the southern Caspian Sea, by depleting Kilka's food base (e.g., zooplankton) and also through predation on their eggs and larvae . In most cases, invasive species affect freshwater megafauna through competition for resources or through induced profound changes to local food webs; however, hybridization with invasive species is also a significant threat.…”

A Nietzschean Take on a Hundred-Dollar Bill: Reading Weber’s “Protestant Ethic” in Connection with a Contemporary Economist’s Comments

“…популяция оценивалась в 104-168 тыс. особей, согласно модели возрастной популяционной структуры Dmitrieva et al 2015]. Несмотря на введение достаточно жёстких санкционных мер со стороны государства в рамках курса на ужесточение регулирования изъятия ценных биоресурсов, анализ количества туш тюленей, поступающих на рынки Дагестана и отчасти Казахстана, показывает постоянное увеличение доли тюленей в уловах осетровых .…”