Highest Catch of the Vulnerable Broadnose Sevengill Shark Notorynchus Cepedianus in the South-West Atlantic

Journal of Fish Biology (2018) 92, 543–548 doi:10.1111/jfb.13532, available online at wileyonlinelibrary.com

Highest catch of the vulnerable broadnose sevengill shark Notorynchus cepedianus in the south-west Atlantic

A. M. De Wysiecki*, A. C. Milessi†‡§, R. Wiff‖ and A. J. Jaureguizar†‡

*Av Colón 2685, Mar del Plata, 7600, Argentina, †Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CIC), Argentina, ‡Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), Paseo Victoria Ocampo 1, 7600, Mar del Plata, Argentina and ‖Center of Applied Ecology and Sustainability (CAPES), Pontificia Universidad Católica de Chile, Santiago, Chile

(Received 25 September 2017, Accepted 6 December 2017)

An exceptional catch of 97 broadnose sevengill sharks Notorynchus cepedianus in Samborombón Bay, Argentina, in 2013 is described from a single overnight gillnet fishing operation. Sixty-five female and 32 male N. cepedianus, ranging in size between 105–201 and 112–190 cm LT, respectively, were recorded in this catch. Fishers’ observations and published information suggest that this species aggre- gates in the area seasonally for feeding. © 2018 The Fisheries Society of the British Isles

Key words: Argentina; conservation; fishers’ knowledge; incidental catch; small-scale fishery.

The broadnose sevengill shark Notorynchus cepedianus (Péron 1807) has been reported in temperate coastal and continental shelf environments worldwide (Com- pagno, 2005). In the south-west Atlantic Ocean (SWA) it has a wide latitudinal distribution, from southern Brazil (25∘ S; Sadowsky, 1970) to the Magellan Strait in Argentina (52∘ S; Guzmán & Campodónico, 1976). Probably as a result of its low commercial importance, landing information is fragmentary in the SWA. For example, historical official landing reports for the entire coast of Argentina recorda mean annual catch of only 1·23 t between 2008 and 2016, whereas total shark landings for the same period were 92 544·2 t (Secretary of Fisheries, www.agroindustria.gob .ar). A fragmentary and scarce occurrence of this species is also found in regional scientific studies. As examples, Van Der Molen et al. (1998) reported only seven N. cepedianus in a total of 454 commercial fishing trawls between 1993 and 1996 in coastal waters off Patagonia (42–51∘ S); Lucifora et al. (2005) sampled 136 N. cepedianus from a recreational fishery between 1998 and 2001 in Anegada Bay (40∘ S); Cedrola et al. (2009) recorded 111 individuals from tournaments and recreational fisheries between 2004 and 2007 in nearshore central Patagonia∘ (48–49 S); Massa (2013) indicated low relative abundance and low frequency of occurrence of

§Author to whom correspondence should be addressed. Tel.: +54 223 420 9156; email: [email protected] 543

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Fig. 1. Southern Samborombón Bay area where the Notorynchus cepedianus catch occurred. Contours indicate depth intervals. the species in 10 research cruises between 1993 and 2005 in coastal shelf waters of Argentina (34–41∘ S); and Irigoyen et al. (2015) tagged 13 individuals as part of a fishery-independent programme between 2011 and 2012 in Nuevo ·Gulf (42 5∘ S). According to historical records from grey literature, the highest ever recorded catch of N. cepedianus in Argentina was 68 individuals captured during the 1982 recreational fishing tournament in Rio Deseado, Patagonia∘ (48 S; Caille & Cedrola, 2007). On 23 September 2013, 97 N. cepedianus individuals (c. 2 t total mass) were inci- dentally caught in the southern part of Samborombón Bay (Fig. 1) by one artisanal fisherman. This catch constitutes the highest single capture ever recorded todate for this species in the SWA waters. The fisherman used a 500 m long bottom-fixed gillnet (25 cm stretched mesh size) that soaked overnight c. 2 m deep. Total length (LT, nearest cm) and sex were recorded for each specimen; 65 females ranged between 105 and 201 cm LT, whereas 32 males ranged between 112 and 190 cm LT. The modal peak was in the 140–144 cm LT size class (Fig. 2). With the exception of two males (181 and 190 cm LT), all specimens recorded were smaller than the LT at 50% maturity reported for the species in Anegada Bay (170 cm for males and 224 cm for females; Lucifora et al., 2005). Is important to note however, that the observed size distribution could be biased as a result of gear selectivity. A photograph of the landed catch is shown in Fig. 3. During sampling, several individuals regurgitated stomach contents. The majority of the identifiable food items were chunks of Brazilian menhaden Brevoortia aurea (Spix & Agassiz 1829), South American fur seal Arctocephalus australis, South American sea lion Otaria flavescens and franciscana dolphin Pontoporia blainvillei. These observations are consistent with previous diet analyses of the species, indicating that teleosts and marine mammals are common prey items for individuals larger than 100 cm LT in the region (Lucifora et al., 2005). Chunk remains were also expected as the feeding

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Fig. 2. Total length (LT)-frequency distribution of Notorynchus cepedianus (n = 97). , males; , females; , both sexes combined. behaviour is based on actively pursuing or ambushing prey, biting several times during the hunting process (Ebert, 1991; Crespi-Abril et al., 2003). Even though catches of N. cepedianus are rather rare events in the SWA, seasonal variations in its occurrence have been observed. In a recent study of gillnet fisheries across adjacent waters of Samborombón Bay, Jaureguizar et al. (2015) reported that these sharks were more frequently encountered during austral spring compared with the rest of the year. Seasonal fluctuations in its abundance were also observed in Ane- gada Bay (40∘ S) and Rio Deseado (48∘ S), probably because N. cepedianus use these areas for breeding purposes (Lucifora et al., 2005; Cedrola et al., 2009). Local fishers’ historical knowledge also provides insight into the seasonal abundance of the species. For example, expert fishermen in Samborombón Bay perceive that high abundances of N. cepedianus in nearshore areas occur at the start of the austral spring, when exotic aromo trees Acacia longifolia are in blossom (M. Marchi and R. Ubieta, pers. comm.). Despite there being no empirical association between the two phenomena, it is important to consider this non-scientific source of information as a complementary approach to understanding the historical temporal distribution pattern of these sharks (Lima et al., 2017). Brevoortia aurea and whitemouth croaker Micropogonias furnieri (Desmarest 1823) use these coastal embayments as juvenile nursery habitats (Acha et al., 1999; Acha & Macchi, 2000; Jaureguizar et al., 2003) and it is hypothesized that the seasonal variations in N. cepedianus abundance could be related to its feeding behaviour as demonstrated elsewhere (Barnett et al., 2010; Williams et al., 2012). Fur- ther work is needed to investigate whether N. cepedianus repeatedly uses the area for feeding or if its appearance only constitutes a rare event. Notorynchus cepedianus has been categorized as a data deficient species by the International Union for Conservation of Nature (Compagno, 2005) because insuffi- cient information has been gathered to assess its vulnerability. Nearly two decades ago however, a study revealed that N. cepedianus were highly sensitive to fishing

Fig. 3. View of the landed catch of Notorynchus cepedianus on a jetty in San Clemente port. exploitation based on their life-history traits (Smith et al., 1999). In Argentina, the main threats to the conservation of this species relate to by-catch in trawls (Van Der Molen et al., 1998) and gillnet fisheries (Chiaramonte, 1998), as well as targeted recreational fisheries (Lucifora et al., 2005; Cedrola et al., 2009). In fact, two recent studies that investigated temporal changes in the abundances of large-sized sharks in waters of Argentina reported decreasing trends for N. cepedianus (Barbini et al., 2015; Irigoyen & Trobbiani, 2016). Although management actions that restrict landings of large shark species have been implemented for commercial fishing in Argentina (NPOA–Sharks, 2009), small-scale operations and recreational fisheries remain largely unmanaged (Venerus & Cedrola, 2017). The present work highlights the need for a data collection protocol for N. cepedianus in the SWA, in order to assess fishery-related mortality rates and conservation status in future investigations. It also highlights the need for more comprehensive management actions and enforcement to ensure sustainability of this vulnerable apex predator in the region.

We appreciate fishers permission to let us sample the specimens reported in this work.We are grateful to local fishers R. Ubieta and M. Marchi who shared valuable knowledge. Wealso thank C. Silva, I. Bruno and P. Casagrande who helped during the sampling. R. Wiff was funded by CAPES project CONICYT FB 0002. This is an INIDEP contribution No. 2097.

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