Distribution, reproduction and population structure of three gulper sharks (Centrophorus, Centrophoridae) in south-east Australian waters

Abstract

Abstract. Gulper sharks (Centrophorus spp.) are commercially fished in all oceans but the taxonomy and biology of many species are not clearly defined, and stocks are extremely vulnerable to over-exploitation. We present distributional, size-frequency and reproductive data for three species (Centrophorus harrissoni, C. moluccensis and C. zeehaani) that fishing has largely extirpated from the south-east Australian upper continental slope. Trawl-survey catches in 1976-77 from lightly exploited stocks comprised mostly mature males with few mature females or juveniles; a 2009 long-line survey caught higher proportions of mature females and, for C. harrissoni, more juveniles. Females of the three species grew larger and reached maturity at a greater size than males and, for both sexes, maturity sizes were more than 80% of their maximum observed lengths. Reproduction was continuous but data were insufficient to determine seasonality. Ovarian and uterine fecundity were singular for C. zeehaani whereas C. harrissoni and C. moluccensis developed two oocytes and produced one or two embryos; evidence suggests that the left-side uterus is less functional than the right-side. In response to these species' inherent low productivity and continuing reduced numbers, managers have introduced landing restrictions and area closures to enhance Centrophorus stocks in southern Australian waters.

Trophic structure and biomagnification of mercury in an assemblage of deepwater chondrichthyans from southeastern Australia

“…Ebert et al 1992, Cortés 1999, Bulman et al 2002 and stable isotopes (Davenport & Bax 2002, Domi et al 2005 (Pethybridge et al 2011). In contrast, higher TP values were observed in squaliform species, which are well within the range of those previously reported (3.9 to 4.5; Cortés 1999, Bulman et al 2002 and reflect a diet of mainly higher-order fish and squid (Graham & Daley 2011, Pethybridge et al 2011. Using stomach content data and analysed by BrayCurtis dissimilarity indices, Bulman et al (2002) explored the trophic guild structure of the mid-slope and seamount community off southern Tasmania (overlapping with our study area).…”

Comparison of baited longlines and baited underwater cameras for assessing the composition of continental slope deepwater fish assemblages off southeast Australia

“…Combined (cumulative, across-sector) effort on the upper slope ($ 200-700 m depths) increased from virtually nothing in the early 1970s to near-complete spatial coverage by the mid-2000s; for example, demersal trawling alone covered some 70% of the upper slope in 2005 (Smith et al, 2011). One system-level effect of demersal fishing has been a decline in abundance and distribution of vulnerable species, including groups such as deep-water sharks with low biological productivity (Graham and Daley, 2011;Irvine et al, 2012). Broad-scale depletion of two gulper shark species (C. harrissoni and C. zeehaani) off Southeastern Australia lead to their listing as Conservation Dependent under Australia's EPBC Act in 2013.…”

“…Length and sex data were also collected for many species, particularly for commercial teleosts and sharks, but are not reported here. All specimens of Centrophorus harrissoni, Centrophorus zeehaani and Centrophorus moluccensis were sexed and measured (see Graham and Daley, 2011), and many were tagged with dorsal fin tags and released as part of a broader study investigating movement and home-range.…”

First description of deep-water elasmobranch assemblages in the Exuma Sound, The Bahamas

“…Estimates of species productivity and intrinsic rebound potential only exist for 2.2% of deep-ocean chondrichthyans (Kyne and Simpfendorfer, 2010), and those that have been assessed have among the lowest values documented for any species of fish to date (Simpfendorfer and Kyne, 2009). In areas where deep-water sharks have been actively targeted by fisheries, dramatic population declines have been triggered (Anderson and Ahmed, 1993;Barbier et al, 2014;Daley et al, 2002;Graham et al, 2001;Graham and Daley, 2011;Jones et al, 2005;Koslow et al, 2000;Morato et al, 2006;White and Kyne, 2010), and it is likely that bycatch of elasmobranchs in deep-water trawl and longline fisheries is having similar negative effects (Graham et al, 2001). Given the slow rate of scientific advancement in the deep-ocean, it has been suggested that many fisheries may become commercially extinct before scientific study can begin (Haedrich et al, 2001).…”