sm82s1151-4793

Discards regulation vs Mediterranean fisheries
sustainability

M. Demestre and F. Maynou (eds)

Deep-sea sharks as by-catch of an experimental fishing survey for black scabbardfishes (Aphanopus spp.) off the Canary Islands (NE Atlantic)

Mafalda Freitas 1,2, Luísa Costa 1, João Delgado 3, Sebastián Jiménez 4, Viriato Timóteo 3,
Joana Vasconcelos 3, José A. González 5

1 OOM - Funchal Marine Biology Station and Marine and Environmental Sciences Centre (MARE), Funchal, Madeira, Portugal.
(MF) (corresponding author) E-mail: mafalda.freitas@cm-funchal.pt. ORCID-iD: https://orcid.org/0000-0002-2758-7177
(LC) E-mail: luisa.costa@cm-funchal.pt. ORCID-iD: https://orcid.org/0000-0001-9107-6200
2 OOM - Funchal Natural History Museum, Rua da Mouraria 31, Funchal, Madeira, Portugal.
3 OOM - Research Service, Regional Directorate of Fisheries, Funchal, Madeira, Portugal.
(JD) E-mail: joao.delgado@madeira.gov.pt. ORCID-iD: https://orcid.org/0000-0003-4268-7202
(VT) E-mail: viriatotimoteo@gmail.com
(JV) E-mail: joana.pr.vasconcelos@madeira.gov.pt. ORCID-iD: https://orcid.org/0000-0003-3880-2554
4 Instituto Español de Oceanografía, Centro Oceanográfico de Canarias, Vía Espaldón PCL8, Dársena Pesquera, 38180 Santa Cruz de Tenerife, Spain.
(SJ) E-mail: sebastian.jimenez@ieo.es. ORCID-iD: https://orcid.org/0000-0002-6534-4096
5 Applied Marine Ecology and Fisheries, i-UNAT, Universidad de Las Palmas de Gran Canaria, Campus Universitario de Tafira, 35017 Las Palmas de Gran Canaria, Spain.
(JAG) E-mail: pepe.solea@ulpgc.es. ORCID-iD: https://orcid.org/0000-0001-8584-6731

Summary: The deep-sea sharks associated as by-catch of the Madeiran midwater drifting longline fishery for scabbardfishes (Aphanopus spp.) were investigated by means of an experimental survey at 800-1200 m depth within the Canary Islands Exclusive Economic Zone, whose fishing grounds have been exploited during the past 15 years. Nine species of chondrichthyans were identified, belonging to five families: Pseudotriakidae, Centrophoridae, Etmopteridae, Somniosidae and Chimaeridae. Data on length, weight and sex ratio for the 436 chondrichthyan individuals caught in the March 2009 survey are given. Several voucher specimens of each species caught were deposited in the collections of the Natural History Museum of Funchal.

Keywords: by-catch; deep-sea Chondrichthyes; midwater drifting longline; NE Atlantic.

Tiburones de profundidad en las capturas accesorias de una campaña de pesca experimental de pez sable negro (Aphanopus spp.) en las islas Canarias (Atlántico nororiental)

Resumen: Se investigaron los tiburones de profundidad en las capturas accesorias de la pesquería de palangre de deriva de media agua que tiene por objetivo el sable negro (Aphanopus spp.) mediante una campaña experimental en la Zona Económica Exclusiva de Canarias a profundidades de 800 a 1200 m, en caladeros que han venido siendo explotados en los últimos 15 años. Se identificaron nueve especies de condrictios pertenecientes a cinco familias: Pseudotriakidae, Centrophoridae, Etmopteridae, Somniosidae y Chimaeridae. Se aportan datos de talla, peso y proporción de sexos para los 436 ejemplares de condrictios capturados en la campaña de marzo de 2009. Los especímenes de referencia capturados fueron depositados en las colecciones del Museo de Historia Natural de Funchal.

Palabras clave: capturas accesorias, condrictios de profundidad, palangre de deriva de media agua, Atlántico nororiental.

Citation/Cómo citar este artículo: Freitas M., Costa L., Delgado J., Jiménez S., Timóteo V., Vasconcelos J., González J.A. 2018. Deep-sea sharks as by-catch of an experimental fishing survey for black scabbardfishes (Aphanopus spp.) off the Canary Islands (NE Atlantic). Sci. Mar. 82S1: 151-154. https://doi.org/10.3989/scimar.04793.03A

Editor: F. Maynou.

Received: April 6, 2018. Accepted: July 12, 2018. Published: October 5, 2018.

Copyright: © 2018 CSIC. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License.

Contents

Summary
Resumen
Introduction
Materials and methods
Results
Discussion
Acknowledgements
References

INTRODUCTIONTop

The deep-sea fishery of the bathypelagic black scabbardfishes, Aphanopus carbo and A. intermedius, has a long tradition off the Portuguese mainland and around the Madeira archipelago, representing one of the world’s longest standing exploitations of meso- and bathypelagic fishes (Delgado et al. 2013Delgado J., Reis S., González J.A., et al. 2013. Reproduction and growth of Aphanopus carbo and A. intermedius (Teleostei: Trichiuridae) in the northeastern Atlantic. J. Appl. Ichthyol. 29: 1008-1014., 2018Delgado J., Amorim A., Gouveia L. et al. 2018 (in press). An Atlantic journey: The distribution and fishing pattern of the Madeira deep sea fishery. Reg. Stud. Mar. Sci.). Off Madeira this fishery is performed with midwater drifting longlines set between 800 and 1200 m depth over the continental slope and nearby seamounts. This is one of the oldest known fisheries in the world targeting a deep-water resource (Leite 1988Leite A. 1988. The deep-sea fishery of the black scabbard-fish Aphanopus carbo Lowe, 1839 in Madeira Island waters: 240-243. Proceedings of the World Symposium on Fishing Gear and Fishing Vessel Design. Marine Institute St. John’s, Newfoundland, Canada.).

A preliminary study on the by-catch and incidental catch of a potential black scabbardfish (Aphanopus spp.) fishery off the Canary Islands, based on a few experimental surveys on board research vessels, was published by Pajuelo et al. (2010)Pajuelo J.G., González J.A., Santana J.I. 2010. Bycatch and incidental catch of the black scabbardfish (Aphanopus spp.) fishery off the Canary Islands. Fish. Res. 106: 448-453..

Ten years ago, Portugal and Spain signed an agreement to study the impact of the black scabbardfish fishery off the Canary Islands, using commercial fishery vessels from Madeira in an experimental survey. The main objectives were i) to study deep-sea sharks as a by-catch of this Madeiran fishery off the Canary Islands, and ii) to compare this by-catch with the by-catch off Madeira and the Portuguese mainland with the same fishing system. The results of this survey are now presented on this short paper.

MATERIALS AND METHODSTop

In March 2009 an experimental fishing survey was carried out off the Canary Islands between 800 and 1200 m depth using black scabbardfish midwater drifting longlines of the Madeiran type. This fishing gear has 5000 hooks (type 6) (Martins and Ferreira 1995Martins R., Ferreira C. 1995. Line fishing for black scabbardfish (Aphanopus carbo Lowe, 1839) and other deep water species in the eastern Atlantic to the north of Madeira. In: Hoppe A.G. (ed), Deep Water Fisheries of the North Atlantic Oceanic Slope. Kluwer Academic Publishers, Dordrecht, The Netherlands. pp. 323-325.) and is usually set well above the bottom in the water column between 700 and 1300 m depth, without contacting the seafloor (Delgado et al. 2018Delgado J., Amorim A., Gouveia L. et al. 2018 (in press). An Atlantic journey: The distribution and fishing pattern of the Madeira deep sea fishery. Reg. Stud. Mar. Sci.). Fishing operations were carried out by two Madeiran professional vessels, F/V Pico Dourado and F/V Pico Alto, with scientific observers on board. In accordance with Canary Islands legislation restrictions (no more than 500 hooks per longline are permitted), both vessels used two separate longlines, one much longer than the other: a professional one with around 5000 hooks and an experimental one with around 500 hooks. The neon flying squid Ommastrephes bartramii was used as bait in all longlines. Twenty hauls were carried out off the islands of Tenerife, La Gomera, La Palma, Fuerteventura and El Hierro (Fig. 1). The sampled areas were not randomly selected, but based on the captains’ experience from the fishery grounds, as well as on the target species’ vertical distribution in the area (Pajuelo et al. 2008Pajuelo J.G., González J.A., Santana J.I., et al. 2008. Biological parameters of the bathyal fish black scabbardfish (Aphanopus carbo Lowe, 1839) off the Canary Islands, Central-east Atlantic. Fish. Res. 92: 140-147.).

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Full size image

Fig. 1. – Map of the Canary Islands showing set locations off the islands of Tenerife, La Gomera, La Palma, Fuerteventura and El Hierro.

Shark individuals caught were identified following Compagno et al. (2005)Compagno L., Dando M., Fowler S. 2005. Sharks of the world. A field guide. Collins, London, 368 pp. and then counted and weighed by species on board. Catches of chondrichthyans and CPUE values by fishing operation (location) were calculated, as well as an average CPUE per island. CPUE values were expressed in kg (total weight) per 1000 valid hooks. For each species caught, all individuals or well-representative subsamples were selected and preserved on board and then measured (total length TL, in mm), weighed (total weight TW, in g), and sexed at the laboratory.

Several voucher specimens of each species caught were deposited in the collections of the Natural History Museum of Funchal (MMF).

RESULTSTop

A total of 436 individuals of 9 mesopelagic species of Chondrichthyes belonging to 5 families (Pseudotriakidae, Centrophoridae, Etmopteridae, Somniosidae and Chimaeridae) were captured. The leafscale gulper shark (Centrophorus squamosus) (Centrophoridae), represented by 170 individuals, was the most abundant species. The velvet dogfish (Zameus squamulosus) (n=129) and the roughskin dogfish (Centroscymnus owstonii) (n=121) (both Somniosidae) were well-represented in the catches. The capture of the other five chondrichthyans could be considered as incidental (Table 1).

Table 1. – Chondrichthyan species caught, with number of individuals, descriptive statistics for size and weight, and sex ratio (males:females). Size as total length (TL); weight as total weight (TW).

Species Common name Individuals caught Individuals studied Mean TL±sd (mm) TL range (mm) Mean TW±sd (g) TW range
(g)
Sex ratio (M:F)
Centrophorus granulosus Gulper shark 10 8 970±141 850-1520 5100±2687 3200-26000 1:1
Centrophorus squamosus Leafscale gulper shark 170 132 1070±98 820-1370 7120±2487 3200-23000 1:0.08
Etmopterus princeps Great lanternshark 3 3 448±48 400-495 333±115 200-400 1:2
Etmopterus pusillus Smooth lanternshark 1 1 - 470 - 400 -
Centroscymnus owstonii Roughskin dogfish 121 118 681±85 505-835 1174±478 200-2400 1:6.4
Zameus squamulosus Velvet dogfish 129 129 633±100 460-800 1132±638 400-2700 1:1.6
Pseudotriakis microdon False catshark 1 1 - 2100 - 33000 -
Chimaera monstrosa Rabbit fish 1 1 - 462 - 580 -

Apart from the list of chondrichthyan species caught, Table 1 also indicates the number of individuals captured, the descriptive statistics for size and weight, and the sex ratio (males:females) for each species.

Table 2 show catches of chondrichthyans and CPUE values per location. Mean CPUE per island surveyed varied from 0.00 off Lanzarote (no shark was caught) to 182.96 kg/1000 hooks off Fuerteventura, with low CPUE values for the remaining sampled islands.

Table 2. – Catches of chondrichthyans and CPUE values per fishing operation (location), with an average CPUE per island. CPUE expressed in kg (total weight) per 1000 hooks.

Sector/island (location) Number of hooks (valid) Catches of chondrichthyans (kg) CPUE
(kg/1000 hooks)
Average CPUE per island
SW El Hierro 400 0.00 0.00 El Hierro: 31.46
SW El Hierro 1800 0.00 0.00
SW El Hierro 400 0.00 0.00
SW El Hierro 3200 0.00 0.00
NE El Hierro 400 70.11 175.28
NE El Hierro 5200 70.11 13.48
SW Fuerteventura 400 85.69 214.23 Fuerteventura: 182.96
SW Fuerteventura 3800 576.46 151.70
E La Palma 1033 23.37 22.62 La Palma: 28.35
NE La Palma 3878 31.16 8.04
NW La Palma 5669 249.28 43.97
NW La Palma 402 15.58 38.76
S Lanzarote 3800 0.00 0.00 Lanzarote: 0.00
S Lanzarote 400 0.00 0.00
NE Tenerife 415 7.79 18.77 Tenerife: 23.22
NE Tenerife 4939 109.06 22.08
SE La Gomera - SW Tenerife 1027 7.79 7.59
SE La Gomera - SW Tenerife 411 0.00 0.00
S Tenerife 400 31.16 77.90
S Tenerife 4800 62.32 12.98

DISCUSSIONTop

With regard to the European Red List of Marine Fishes (Nieto et al. 2015Nieto A., Ralph G.M., Comeros-Raynal M.T., et al. 2015. European Red List of marine fishes. Publications Office of the European Union, Luxembourg.), it is important to highlight that the leafscale gulper shark (Centrophorus squamosus), the most captured species in the survey, has been classified as an endangered species. Previously, this shark species was considered as highly vulnerable to depletion and consequently assessed as endangered in the northeast Atlantic (White 2003White W.T. 2003. Centrophorus squamosus. In: 2008 IUCN Red List of Threatened Species. ). Also, this species was included in the OSPAR List of threatened and/or declining species and habitats (Gibson et al. 2008Gibson C., Valenti S.V., Fordham S.V., et al. 2008. The conservation of northeast Atlantic chondrichthyans. Report of the IUCN Shark Specialist Group Northeast Atlantic Red List Workshop, 76 pp.). Moreover, the gulper shark (Centrophorus granulosus) has been recently catalogued as a critically endangered species (Nieto et al. 2015Nieto A., Ralph G.M., Comeros-Raynal M.T., et al. 2015. European Red List of marine fishes. Publications Office of the European Union, Luxembourg.).

When compared with that of the by-catch identified from the black scabbardfish fishery off Madeira (Bordalo-Machado et al. 2009Bordalo-Machado P., Fernandes A.C., Figueiredo I., et al. 2009. The black scabbardfish (Aphanopus carbo Lowe, 1839) fisheries from the Portuguese mainland and Madeira Island. Sci. Mar. 73: 63-76.), chondrichthyan species composition was quite similar to the present results for the Canary Islands waters, except for the absence of the Portuguese dogfish Centroscymnus coelolepis (Somniosidae) and the birdbeak dogfish Deania calcea (Centrophoridae) off the Canaries. However, given that the present survey was carried out only in March, any type of seasonal distribution pattern in those species would have been missed.

In the eastern Atlantic, landings of the leafscale gulper shark, C. squamosus, the most captured species within the by-catch, over the past decade peaked in 2003 (3042 t) and declined to 243 t in 2009 (Ebert and Stehmann 2013Ebert D.A., Stehmann M. 2013. Sharks, batoids and chimaeras of the North Atlantic. FAO. Rome, 523 pp.). Based on FAO catch data, in Portugal average landings of this species were 893 t per year from 2000 to 2009. In contrast, short time series of CPUE available for the western coast of Portugal seem to indicate that these landings remain stable (Gibson et al. 2008Gibson C., Valenti S.V., Fordham S.V., et al. 2008. The conservation of northeast Atlantic chondrichthyans. Report of the IUCN Shark Specialist Group Northeast Atlantic Red List Workshop, 76 pp.).

According to the present results and concerns, further studies should be conducted in order to evaluate the real impact of this fishery on the northeastern Atlantic population(s) of the leafscale gulper shark, and should also address technological developments related to the fishing gear tending to minimize its catches.

In order to fully understand the trends of all species caught as by-catch in this fishery, it is important to monitor continuously to obtain representative time series.

ACKNOWLEDGEMENTSTop

The authors are indebted to the masters and crews of the F/V Pico Dourado and F/V Pico Alto for all their work done at sea. Thanks are also due to the technicians of the Estação de Biologia Marinha do Funchal, Direcção de Serviços de Investigação das Pescas, Instituto Español de Oceanografía and Instituto Canario de Ciencias Marinas, who collaborated at sea and in the laboratory. Many thanks to the reviewers for their comments, which greatly improved our manuscript.

REFERENCESTop

Bordalo-Machado P., Fernandes A.C., Figueiredo I., et al. 2009. The black scabbardfish (Aphanopus carbo Lowe, 1839) fisheries from the Portuguese mainland and Madeira Island. Sci. Mar. 73: 63-76.
https://doi.org/10.3989/scimar.2009.73s2063

Compagno L., Dando M., Fowler S. 2005. Sharks of the world. A field guide. Collins, London, 368 pp.

Delgado J., Reis S., González J.A., et al. 2013. Reproduction and growth of Aphanopus carbo and A. intermedius (Teleostei: Trichiuridae) in the northeastern Atlantic. J. Appl. Ichthyol. 29: 1008-1014.
https://doi.org/10.1111/jai.12230

Delgado J., Amorim A., Gouveia L. et al. 2018. An Atlantic journey: The distribution and fishing pattern of the Madeira deep sea fishery. Reg. Stud. Mar. Sci. 23: 107-111.
https://doi.org/10.1016/j.rsma.2018.05.001

Ebert D.A., Stehmann M. 2013. Sharks, batoids and chimaeras of the North Atlantic. FAO. Rome, 523 pp.

Gibson C., Valenti S.V., Fordham S.V., et al. 2008. The conservation of northeast Atlantic chondrichthyans. Report of the IUCN Shark Specialist Group Northeast Atlantic Red List Workshop, 76 pp.

Leite A. 1988. The deep-sea fishery of the black scabbard-fish Aphanopus carbo Lowe, 1839 in Madeira Island waters. Proceedings of the World Symposium on Fishing Gear and Fishing Vessel Design. Marine Institute St. John’s, Newfoundland, Canada, pp. 240-243.

Martins R., Ferreira C. 1995. Line fishing for black scabbardfish (Aphanopus carbo Lowe, 1839) and other deep water species in the eastern Atlantic to the north of Madeira. In: Hoppe A.G. (ed), Deep Water Fisheries of the North Atlantic Oceanic Slope. Kluwer Academic Publishers, Dordrecht, The Netherlands. pp. 323-325.

Nieto A., Ralph G.M., Comeros-Raynal M.T., et al. 2015. European Red List of marine fishes. Publications Office of the European Union, Luxembourg.

Pajuelo J.G., González J.A., Santana J.I., et al. 2008. Biological parameters of the bathyal fish black scabbardfish (Aphanopus carbo Lowe, 1839) off the Canary Islands, Central-east Atlantic. Fish. Res. 92: 140-147.
https://doi.org/10.1016/j.fishres.2007.12.022

Pajuelo J.G., González J.A., Santana J.I. 2010. Bycatch and incidental catch of the black scabbardfish (Aphanopus spp.) fishery off the Canary Islands. Fish. Res. 106: 448-453.
https://doi.org/10.1016/j.fishres.2010.09.019

White W.T. 2003. Centrophorus squamosus. In: The IUCN Red List of Threatened Species 2003. Accessed on April, 2018.
http://www.iucnredlist.org



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