Squatina occulta

Taxonomy

Assessment Information

Geographic Range

Population

Habitat and Ecology

Threats

Conservation Actions

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Taxonomy [top]

Kingdom	Phylum	Class	Order	Family
ANIMALIA	CHORDATA	CHONDRICHTHYES	SQUATINIFORMES	SQUATINIDAE

Scientific Name:

Squatina occulta

Species Authority:

Vooren & da Silva, 1991

Common Name/s:

English

–

Smoothback Angel Shark

Taxonomic Notes:

There is some controversy concerning the nomenclature of angel sharks in southern Brazil. Vooren and Silva (1991) synonymized S. punctata with S. guggenheim. Soto (2001), in a checklist of sharks of Brazil, states that the reference in Vooren and Silva (1991) to the occurrence in Brazil of Squatina guggenheim Marini, 1936 is in fact a reference to Squatina punctata Marini, 1936, and that the description of Squatina occulta Vooren & Silva, 1991 is a reference to Squatina guggenheim as originally described by Marini (1936), but no evidence is presented to justify these statements. Furtado-Neto and Carr (2002), through the study of mitochondrial DNA, suggested the existence in southern Brazil of three species of the genus Squatina: S. argentina (Marini, 1930), S. guggenheim Marini, 1936 and S. occulta Vooren & Silva, 1991. Compagno (in prep.) follows the nomenclature of Soto (2001).

In acknowledgement of these issues, the IUCN SSC Shark Specialist Group has prepared assessments for all nominal Southwest Atlantic Squatina species: S. argentina, S. punctata, S. occulta and S. guggenheim. In this assessment, S. occulta Vooren & Silva, 1991 is presented, which Soto (2001) and Compagno (in prep.) refer to as S. guggenheim.

Assessment Information [top]

Red List Category & Criteria:

Endangered A2bd ver 3.1

Year Assessed:

2007

Assessor/s

Vooren, C.M. & Chiramonte, G.

Evaluator/s:

Musick, J.A., Kyne, P.M. & Valenti, S.V. (Shark Red List Authority)

Justification:
Preface: In acknowledgment of unresolved and controversial taxonomic and nomenclatural issues, the IUCN SSC Shark Specialist Group has assessed all nominal Southwest Atlantic Squatina species, until such time as agreement is reached on these issues (see taxonomy section for further details). Assessed species are: longfin or Argentine angel shark Squatina argentina (Marini, 1930); spiny angel shark Squatina guggenheim Marini, 1936; shortfin angel shark Squatina occulta Vooren & Silva, 1991; and, angular angel shark Squatina punctata Marini, 1936.

Squatina occulta was assessed as EN A1acd+2d on the 2000 Red List. It is updated here due to better information and further evidence of declines.

Squatina occulta is endemic to the Southwest Atlantic from Rio de Janeiro, Brazil (24°S) through Uruguay to Buenos Aries Province, Argentina (38°S) on the continental shelf and slope at depths of 10 to 350 m. The species' low reproductive potential (litter size of 6 to 8, age at maturity of 10 years and a particularly long female breeding cycle, which may be 4 to 5 years) together with its vulnerability to both trawl and gillnet gear makes it highly susceptible to population depletion. Angel sharks are heavily fished in southern Brazil and significant declines have been documented there. Annual catches of angel shark from the southern Brazil continental shelf peaked at about 2,000 t in 1986 to 1989 and again in 1993, and then decreased to 900 t in 2003. Angel shark CPUE by otter and pair trawl on the continental shelf decreased by about 85% from 1984 to 2002. Research trawl surveys of the outer shelf in the years 1986/87 and 2001/02 confirmed that in southern Brazil the abundance of S. occulta has decreased by 80% and this is attributed to recruitment overfishing. In the trawl and gillnet fishery for the monkfish Lophius gastrophysus at the shelf edge and upper slope, S. occulta and S. argentina have been significant bycatch species, indicating that there has also been considerable pressure at the shelf edge and on the slope for S. occulta. Additionally, an angel shark bottom gillnet fishery on the outer shelf commenced around 1990 and at present large amounts of angel shark is caught this way. The core of the species' occurrence is southern Brazil, and at present there is no evidence for the existence of abundant populations of the species outside Brazil. Due to the presence of trawl and other demersal fisheries throughout the range of the species and the documented reduction of angel shark stocks due to intensive fishing off southern Brazil, an assessment of Endangered is warranted across its Southwest Atlantic distribution. The conservation status of the species will rely heavily upon the success of a recently developed management plan for the southern Brazil gillnet monkfish fishery. In the first instance, the resolution of taxonomic and nomenclatural issues, in order to accurately define the occurrence, distribution and declines of individual species, is paramount to the conservation of Southwest Atlantic angel sharks.

History:

2000

–

Endangered

Geographic Range [top]

Range Description:	Squatina occulta is an endemic species of the Southwest Atlantic occurring from 24°S (Rio de Janeiro, southern Brazil) through Uruguay to 38°S (Buenos Aires Province, Argentina).
Countries:	Native: Argentina; Brazil; Uruguay
FAO Marine Fishing Areas:	Native: Atlantic – southwest

Population [top]

Population:	This species does not appear to make seasonal migrations to different depths (Vooren and Klippel 2005). There is apparently a nursery area located off Rio Grande do Sul at depths of 60 to 80 m (Vooren and Klippel 2005).
Population Trend:	Decreasing

Habitat and Ecology [top]

Habitat and Ecology:	Squatina occulta is a bottom-dwelling shark of smooth sandy and muddy grounds on the shelf and upper slope at depths of 10 to 350 m and at bottom temperatures of 14 to 19°C (Vooren and Silva 1991, Vooren 1997, Vooren and Klippel 2005). Maximum size ~130 cm TL; size at maturity ~110 cm TL; size at birth ~33 cm TL. Aplacental yolksac viviparous with a single functional ovary. Number of embryos per litter is 6 to 8 (Vooren and Silva 1991). Gestation period ~11 months, and young are born in spring. The breeding cycle of the female may take four or five years, with variation between individuals (Vooren and Klippel 2005). Vieira (1996) established the following Von Bertalanffy parameters: K=0.129, L_∞=137.9 cm TL and t₀= 1.937. The age at sexual maturity was calculated as 10 years and longevity ~21 years. Chiaramonte (unpublished data) calculated K= 0.147 using the indirect methods of Holden (1974).
Systems:	Marine

Habitat and Ecology:

Squatina occulta is a bottom-dwelling shark of smooth sandy and muddy grounds on the shelf and upper slope at depths of 10 to 350 m and at bottom temperatures of 14 to 19°C (Vooren and Silva 1991, Vooren 1997, Vooren and Klippel 2005).

Maximum size ~130 cm TL; size at maturity ~110 cm TL; size at birth ~33 cm TL. Aplacental yolksac viviparous with a single functional ovary. Number of embryos per litter is 6 to 8 (Vooren and Silva 1991). Gestation period ~11 months, and young are born in spring. The breeding cycle of the female may take four or five years, with variation between individuals (Vooren and Klippel 2005). Vieira (1996) established the following Von Bertalanffy parameters: K=0.129, L_∞=137.9 cm TL and t₀= 1.937. The age at sexual maturity was calculated as 10 years and longevity ~21 years. Chiaramonte (unpublished data) calculated K= 0.147 using the indirect methods of Holden (1974).

Systems:

Marine

Threats [top]

Major Threat(s):	The nocturnal habits of angel sharks render them vulnerable to bottom gillnets, and increases in captures during the 1990s are attributed to the introduction of this gear on the shelf and slope off southern Brazil at that time. Gillnets were reported as six times more effective at catching angel sharks than trawling alone (Vooren and Klippel 2005). Gravid females of the species have been observed to abort embryos easily upon capture, further reducing the reproductive capacity (Vooren and Klippel 2005). A low rate of dispersal between angel shark populations makes them especially prone to local depletion and means that recolonisation will be extremely low. Fishery landing statistics of “angel shark” in southern Brazil refer to S. guggenheim, S. occulta and S. argentina combined. The term “angel shark” in the present assessment refers to this assemblage of species. These three species occur on the continental shelf with S. argentina and S. occulta also occurring on the upper slope. Annual catches of angel shark from the continental shelf peaked at about 2,000 t in 1986 to 1989 and again in 1993, and then decreased to 900 t in 2003. Angel shark CPUE by otter trawl and pair trawl on the continental shelf decreased by about 85% from 1984 to 2002 (Miranda and Vooren 2003, CEPERG 2003, GEP/CTTMar 2003). In the trawl and gillnet fishery for monkfish Lophius gastrophysus at the shelf edge and upper slope, S. occulta and S. argentina have been significant bycatch species, indicating that there is also considerable pressure on the outer shelf and slope for S. occulta. Additionally, an angel shark bottom gillnet fishery on the outer shelf commenced around 1990 and at present large amounts of angel shark are caught this way (Miranda and Vooren 2003). Research trawl surveys of the outer shelf in the years 1986/87 and 2001/02 confirmed that in southern Brazil the abundance of S. occulta has decreased to 20% of its original level and this is attributed to recruitment overfishing primarily due to the bottom gillnet fishery (Vooren and Lamónaca 2002, Vooren and Klippel 2005). At present there is no evidence of the existence of abundant populations of the species outside southern Brazil. In Uruguay and Argentina the species is uncommon in commercial landings but its distribution and abundance have not been studied. In Argentina, angel shark landings have shown a negative trend since a peak in 1998 (Massa et al. 2004), but landings apparently consist almost entirely of S. guggenheim. In Uruguay there is little direct fishing for angel sharks, but they are taken as bycatch in industrial and artisanal fisheries. The estimated capture has been 300 to 400 MT per year since 1997. There are no statistics by species, but the largest captures probably correspond to S. guggenheim and S. argentina (A. Domingo pers. comm). While most information is available from Brazil, trawl and other demersal fisheries operate over the species' area of occurrence, exerting fishing pressure across both the latitudinal and bathymetrical range of the species.

Major Threat(s):

The nocturnal habits of angel sharks render them vulnerable to bottom gillnets, and increases in captures during the 1990s are attributed to the introduction of this gear on the shelf and slope off southern Brazil at that time. Gillnets were reported as six times more effective at catching angel sharks than trawling alone (Vooren and Klippel 2005). Gravid females of the species have been observed to abort embryos easily upon capture, further reducing the reproductive capacity (Vooren and Klippel 2005). A low rate of dispersal between angel shark populations makes them especially prone to local depletion and means that recolonisation will be extremely low.

Fishery landing statistics of “angel shark” in southern Brazil refer to S. guggenheim, S. occulta and S. argentina combined. The term “angel shark” in the present assessment refers to this assemblage of species. These three species occur on the continental shelf with S. argentina and S. occulta also occurring on the upper slope. Annual catches of angel shark from the continental shelf peaked at about 2,000 t in 1986 to 1989 and again in 1993, and then decreased to 900 t in 2003. Angel shark CPUE by otter trawl and pair trawl on the continental shelf decreased by about 85% from 1984 to 2002 (Miranda and Vooren 2003, CEPERG 2003, GEP/CTTMar 2003). In the trawl and gillnet fishery for monkfish Lophius gastrophysus at the shelf edge and upper slope, S. occulta and S. argentina have been significant bycatch species, indicating that there is also considerable pressure on the outer shelf and slope for S. occulta. Additionally, an angel shark bottom gillnet fishery on the outer shelf commenced around 1990 and at present large amounts of angel shark are caught this way (Miranda and Vooren 2003). Research trawl surveys of the outer shelf in the years 1986/87 and 2001/02 confirmed that in southern Brazil the abundance of S. occulta has decreased to 20% of its original level and this is attributed to recruitment overfishing primarily due to the bottom gillnet fishery (Vooren and Lamónaca 2002, Vooren and Klippel 2005).

At present there is no evidence of the existence of abundant populations of the species outside southern Brazil. In Uruguay and Argentina the species is uncommon in commercial landings but its distribution and abundance have not been studied. In Argentina, angel shark landings have shown a negative trend since a peak in 1998 (Massa et al. 2004), but landings apparently consist almost entirely of S. guggenheim. In Uruguay there is little direct fishing for angel sharks, but they are taken as bycatch in industrial and artisanal fisheries. The estimated capture has been 300 to 400 MT per year since 1997. There are no statistics by species, but the largest captures probably correspond to S. guggenheim and S. argentina (A. Domingo pers. comm). While most information is available from Brazil, trawl and other demersal fisheries operate over the species' area of occurrence, exerting fishing pressure across both the latitudinal and bathymetrical range of the species.

Conservation Actions [top]

Conservation Actions:	Since 1992 there is a Maximum Permitted Catch (MPC) for angel sharks in Argentina which was 6,000 MT in the years 1995 to 1999 and thereafter was reduced to 4,000 MT (Massa et al. 2003). In Brazil there is no control of the shelf angel shark fishery, and although trawling in inshore waters is prohibited, enforcement of this regulation is difficult. A management plan was developed for the gillnet monkfish fishery in 2002 and approved in June 2005. Foreign chartered fishing vessels were unauthorized to operate after October 2002 and an annual TAC of 1,500 t and an effort limitation of nine vessels implemented for the domestic fleet. Further management arrangements included a permanent VMS tracking system, 100% observer coverage, logbooks and a ban on fishing shallower than 250 m. Furthermore, two no-take zones were implemented, one in the southern and the other in the northern sections of the fishing area (Perez et al. 2002, Perez pers. comm). The conservation status of this species will rely heavily upon the success of these management arrangements. Full observer coverage onboard domestic vessels should provide accurate monitoring of trends in the future.

Conservation Actions:

Since 1992 there is a Maximum Permitted Catch (MPC) for angel sharks in Argentina which was 6,000 MT in the years 1995 to 1999 and thereafter was reduced to 4,000 MT (Massa et al. 2003).

In Brazil there is no control of the shelf angel shark fishery, and although trawling in inshore waters is prohibited, enforcement of this regulation is difficult. A management plan was developed for the gillnet monkfish fishery in 2002 and approved in June 2005. Foreign chartered fishing vessels were unauthorized to operate after October 2002 and an annual TAC of 1,500 t and an effort limitation of nine vessels implemented for the domestic fleet. Further management arrangements included a permanent VMS tracking system, 100% observer coverage, logbooks and a ban on fishing shallower than 250 m. Furthermore, two no-take zones were implemented, one in the southern and the other in the northern sections of the fishing area (Perez et al. 2002, Perez pers. comm). The conservation status of this species will rely heavily upon the success of these management arrangements. Full observer coverage onboard domestic vessels should provide accurate monitoring of trends in the future.

Citation:	Vooren, C.M. & Chiramonte, G. 2007. Squatina occulta. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on 09 February 2010.
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