Kyne & Simpfendorfer.. - Shark Specialist Group

Table 2.6. Age and growth of etmopterid sharks. von Bertalanffy growth model (VBGM)
parameters: L ∞ (mm TL), k (year -1 ), t 0 (years); t max oldest fish (years), A mat age at maturity
(years). Band count method: Int DS, internal dorsal spine band count; Ext DS, external dorsal
spine band count; Vert, vertebral band count.
Species Location Method
VBGM parameters
L ∞ k t 0
t max A mat Reference
Etmopterus
baxteri
SE Australia Ext DS ♀ 681
♂ 606
0.040
0.082
-4.51
-1.43
57
48
30
20
Irvine et al. (2006a)
SE Australia Int DS ♀ 693
♂ 596
0.116
0.163
-1.56
-2.00
26
22
11.5
10.5
Irvine et al. (2006a)
Etmopterus
spinax
Western Mediterranean Vert -- -- -- 7 -- Gennari et al. (2002)
Western Mediterranean Vert -- -- -- 7 5 Sion et al. (2002)
Family Somniosidae. Sleeper Sharks.
The small squaloid family Somniosidae includes the relatively well-studied Portuguese
dogfish Centroscymnus coelolepis, a group of species (C. owstoni, Centroselachus crepidater
and Proscymnodon plunketi) for which there is reasonable biological information, and some
very poorly-known species, particularly from the genera Scymnodalatias, Scymnodon and
Zameus. The vast majority of information on the biology of the family comes from the
Northeast Atlantic and southeastern Australia. The systematics of Somniosus species has
recently been reviewed (Yano et al. 2004) and there remains only a single undescribed species
in the family, the longnose sleeper shark Somniosus sp. A. However, the only known
specimen of this species, from off Portugal, was destroyed in a fire (Yano et al. 2004,
Compagno in prep. a).
Reproductive and age and growth parameters for somniosid sharks are summarized in Tables
2.7 and 2.8, respectively.
Details of the reproductive biology of the large Somniosus species is sketchy, although they
are known to mature at very large sizes (~4500mm TL in female S. microcephalus, ~4350mm
TL in female S. antarcticus and ~3700mm TL in female S. pacificus) (Ebert et al. 1987, Yano
et al. 2007). Very large numbers of follicles have been reported for Sominosus spp, 372+ for
S. pacificus (Ebert et al. 1987) and up to 2931 in S. microcephalus (Yano et al. 2007). Actual
reported litter sizes are considerably smaller, 8 in S. rostratus (a smaller Somniosus reaching
1140mm TL) (Barrull and Mate 2001) and at least 10 in S. microcephalus (see Yano et al.
2007). Litter sizes in other somniosids range from 1–9 in C. crepidater, 1–29 in C. coelolopis,
5–31 in C. owstoni to moderately high (59) in Scymondalatias albicauda (Table 2.7). Yano
and Tanaka (1988) found that fecundity increased with maternal size in C. coelolepis.
The lack of developing or preovulatory follicles in gravid or post-partum female somniosids
indicates that there is a resting phase after parturition prior to the next pregnancy. This has
been shown in such species as P. plunketi, C. crepidater, C. owstoni and C. coelolepis (Daley
et al. 2002, Irvine 2004). The length of these resting periods remains undetermined as they are
difficult to assess in species with aseasonal reproductive cycles, as is the case with somniosids
(Irvine 2004). However, the length of the gestation period in sleeper sharks is thought to be
long (1–2 years) and the existence of a resting period results in a probable reproductive cycle
of 2–3 years.
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