Abstract
Assessing fishing effects on chondrichthyan populations has predominantly focused on quantifying mortality rates. Consequently, sub-lethal effects of capture stress on the reproductive capacity of chondrichthyans are largely unknown. We investigated the reproductive consequences of capture on pregnant southern fiddler rays (Trygonorrhina dumerilii) collected from Swan Bay, Australia, in response to laboratory-simulated trawl capture (8 h) followed immediately by air exposure (30 min). Immediately prior to, and for up to 28 days post trawling, all females were measured for body mass (BM), sex steroid concentrations (17-β estradiol, progesterone, testosterone) and granulocyte to lymphocyte (G:L) ratio. At parturition, neonates were measured for total length (TL), BM and G:L ratio. Trawling reduced maternal BM and elevated the G:L ratio for up to 28 days. Trawling did not significantly affect any sex steroid concentrations relative to controls. Neonates from trawled mothers were significantly lower in BM and TL than control animals, and had an elevated G:L ratio. Our results show that capture of pregnant T. dumerilii can influence their reproductive potential and affect the fitness of neonates. We suggest other viviparous species are likely to be similarly affected. Sub-lethal effects of capture, particularly on reproduction, require further study to improve fisheries management and conservation of chondrichthyans.
Highlights
Assessing fishing effects on chondrichthyan populations has predominantly focused on quantifying mortality rates
Maternal total length (TL) and body mass (BM) at collection from the wild ranged 880–1030 mm and 4.12–6.2 kg for females allocated to the control group, and 900–988 mm and 4.02–5.9 kg for females allocated to the trawl group
Our results indicate that capture during pregnancy in T. dumerilii caused stress that resulted in significantly reduced maternal post-partum BM and neonatal size (TL and BM) relative to untrawled control animals
Summary
Assessing fishing effects on chondrichthyan populations has predominantly focused on quantifying mortality rates. The effects of capture, handling and release techniques on chondrichthyan are predominantly assessed by measuring the more immediate and short-term (usually a few days) physiological responses to acute stress, which may or may not result in immediate or delayed mortality[4,5,6,7,8,9]. The role of T is less well understood, it is thought to regulate final maturation of the ovarian follicles, mating behaviour[25] and possibly the control of embryonic diapause[23] It is not known how acute or chronic stress influences maternal sex steroid synthesis in chondrichthyans, but alterations to their circulating concentrations may reveal their effect on reproductive investments such as ovulation and follicular development[26,27,28]
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