Abstract
A total of 1,268 harbour porpoises were obtained from fishing nets in Icelandic coastal waters from September to June in the years 1991 to 1997. Foetal sex ratio was 1.2:1 (male:female). The bias towards males increased further among older animals in the present collection. The modal year classes were 0 and 1 years but the oldest porpoise was a female estimated at 20 years of age. Length at birth was estimated as approximately 75 cm, and females grew faster and attained larger sizes than males. Asymptotic length was 149.6 cm for males and 160.1 cm for females. Estimated age and length at sexual maturity was 1.9 to 2.9 years and 135 cm for males and 2.1 to 4.4 years and 138 to 147 cm for females. Immature individuals were significantly shorter than pubertal and mature animals in both sexes in age classes 1 to 3. Testes weight increased only slightly with body size in immature males but increased rapidly around maturity. Pronounced seasonality was alsoobserved in testes weight, indicating a peak in testes activity in summer. Lack of data from the summer makes the exact timing of parturition and mating unknown. Births do, however, most likely peak in June and July and lactation lasts at least 7 to 8 months. Ovulation and pregnancy rates were 0.98.
Highlights
Interactions of harbour porpoise (Phocoena phocoena) with commercial fisheries (IWC 1994) and their susceptibility to pollution in coastal areas (Reijnders et al 1999) have evoked increased concern in recent years
The main emphasis was put on studies of feeding ecology (Víkingsson et al 2003), while studies were conducted on reproductive biology (Halldórsson and Víkingsson 2003), morphology, genetics (Tolley et al 2001), energetics and toxicology
Sample composition Teeth and/or reproductive organs were sampled from 1,268 harbour porpoises obtained from September to June in the years 1991 to 1997 (Fig. 2)
Summary
Interactions of harbour porpoise (Phocoena phocoena) with commercial fisheries (IWC 1994) and their susceptibility to pollution in coastal areas (Reijnders et al 1999) have evoked increased concern in recent years. Most studies have put emphasis on investigating population size and structure and life history parameters that may reveal status of populations and their potential vulnerability to human interactions (Bjørge and Donovan 1995). Harbour porpoises are common in Icelandic waters and an offshore population estimate of 27,000 obtained from a shipboard survey in 1987 is most likely downward biased Sæmundsson (1939) discussed seasonal migrations of harbour porpoises into shallow waters in Iceland during summer but systematic studies on Icelandic harbour porpoises have not been conducted in any research field to date. In order to attain basic biological information on the species in Icelandic waters, a wide ranging research project was initiated in 1991. In this paper biological parameters associated with growth and reproduction will be discussed
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