Lamna nasus (Northeast Atlantic subpopulation)http://dx.doi.org/10.2305/IUCN.UK.2006.RLTS.T39343A10210612.en
|Scientific Name:||Lamna nasus (Northeast Atlantic subpopulation)|
|Species Authority:||(Bonnaterre, 1788)|
See Lamna nasus
|Red List Category & Criteria:||Critically Endangered A2bcd+3d+4bd ver 3.1|
|Assessor(s):||Stevens, J., Fowler, S.L., Soldo, A., McCord, M., Baum, J., Acuña, E. & Domingo, A.|
|Reviewer(s):||Cavanagh, R.D., Heupel, M. & Simpfendorfer, C. (Shark Red List Authority)|
The porbeagle is a wide-ranging, coastal and oceanic shark, but with apparently little exchange between adjacent populations. Low reproductive capacity and high commercial value (in target and incidental fisheries) of mature and immature age classes makes this species highly vulnerable to over-exploitation and population depletion. This depletion, despite variations in availability of data and degree of depletion between the northern and southern hemispheres, is considered to meet Vulnerable criteria globally. The eastern and western North Atlantic populations have both been seriously over-exploited by directed longline fisheries. Collapse of the Northeast Atlantic population led to intensive target fishing in the well-documented Northwest Atlantic fishery in the 1960s, with most of the virgin biomass removed in just six years. Renewed target fishing in the 1990s led to a further population decline to ~11–17% of virgin biomass within the three generation period for this species. Recently improved management in the Northwest Atlantic should now help stocks to recover, however the Northeast Atlantic population has been subject to unrestricted fishing pressure ever since its earlier crash. Data are lacking, but stock depletion is considered to be much greater than in the Northwest Atlantic. Longline tuna and swordfish fleets in the southern hemisphere take a significant partially-utilised bycatch. Only limited trend data are available, including over 90% declines in landings by the Uruguayan longline fleet in the southwest Atlantic.
|Previously published Red List assessments:||
|Range Description:||The porbeagle shark is a wide-ranging coastal and oceanic species found in temperate and cold-temperate waters worldwide (1 to 18°C, 0 to 370 m), more common on continental shelves. Coastal and oceanic, amphitemperate, with centres of distribution in the North Atlantic and in a circumglobal band of temperate water of the southern Atlantic, southern Indian Ocean, southern Pacific and Antarctic Ocean (Compagno 2001). In the Southwest Atlantic Ocean it is found below 26°S (A. Domingo, pers.comm.), in the Southeastern Pacific, between 23 and 37°S (E. Acuña, pers. comm). Tagging studies in the Northwest Atlantic have shown mainly short to moderate distances of up to 1,500 km along continental shelves (Francis et al. in press). Distances travelled by 143 porbeagle tagged in a US study ranged 4 to 1,005 nautical miles (nm), with a mean distance of 234 nm, with over 90% moving less than 500 nm from their original tagging location (Kohler et al. 2002). Porbeagles tagged off southern England have been recaptured off Spain, Denmark and Norway (2,370 km away), and a porbeagle tagged in Ireland travelled 4,260 km Kohler and Turner 2001), suggesting mixing throughout their range in the Northeast Atlantic (Stevens 1976, 1990). According to the Canadian Department of Fisheries and Oceans (DFO 2001a), mature porbeagle sharks are rarely seen in winter and spring, with monthly catches exhibiting a seasonal and sex-specific migration of mature sharks towards the southern Newfoundland mating grounds in spring. The birthing grounds for the porbeagle shark in the Northwest Atlantic remain unknown (DFO 2001a). There is little known about the porbeagle shark in subequatorial Africa. No information on mating or nursery grounds is available. Porbeagles in the Northwest Atlantic make annual migrations along the coast between the Gulf of Maine and Newfoundland (Campana et al. 1999, Campana and Joyce 2004).|
Native:Denmark; France; Gibraltar; Iceland; Ireland; Norway; Portugal (Azores, Madeira); Russian Federation; Spain; Sweden; United Kingdom
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – northeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||North Atlantic tagging studies (DFO 1999, Kohler et al. 2002, Stevens 1990) indicate only one trans-Atlantic movement (Kohler and Turner 2001), implying that the two north Atlantic populations are distinct. There is no evidence of genetic exchange between the North Atlantic and the Southern Hemisphere population(s), which are separated by warm water. The number of sub-populations in the southern oceans is unknown.
Biomass of the Northwest Atlantic porbeagle population was estimated at 4,409 t (11% of virgin biomass) and female spawners estimated at 6,075 (10% of the virgin abundance) (Campana et al. 2001).
Populations studied in the North Atlantic and Mediterranean segregate by size and sex. Although adults are very rare in the Mediterranean, it appears to be a nursery ground.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||This section is taken mainly from Stevens (in press) species assessment for Lamna nasus (in Fowler et al. in press).
The porbeagle reaches a maximum reported size of 355 cm TL (Francis et al. in press). Males mature at about 165 cm TL in the South Pacific and 195 cm TL in the North Atlantic. Females mature at about 195 cm TL in the South Pacific and 245 cm TL in the North Atlantic (Jensen et al. 2002, Francis and Duffy 2005, Francis et al. in press).
Reproduction is oophagous with litters of 1 to 5 pups (average four) produced, which are 68 to 78 cm TL at birth (Compagno 1984a, Gauld 1989, DFO 2001a, Francis and Stevens 2000, Francis et al. in press). Aasen (1963) estimated that the gestation period was about eight months in the North Atlantic and that individual females breed each year. However, Shann (1923) found two distinct size groups of embryos present in the December–February period and suggested that gestation may last 18 to 24 months. Gauld (1989) noted that a resting period may be present between parturition and fertilisation. Francis and Stevens (2000), Jensen et al. (2002) and Francis et al. (in press) estimate an 8 to 9 month gestation period. Birth occurs in spring off Europe, spring-summer off North America and winter in Australasia (Aasen 1963, Francis and Stevens 2000, Jensen et al. 2002) and the Eastern Pacific off Chile (Acuña et al. unpublished data).
Natanson et al. (2002) and Campana et al. (2002) examined age and growth in the North West Atlantic population and reported a maximum age of 26 years. However they estimated longevity might be as high as 46 years in an unfished population. Ages at 50% maturity for North Atlantic males and females are 8 and 13 years respectively (Jensen et al. 2002).
Porbeagles feed mostly on teleost fish, both pelagic and demersal species, and on cephalopods (Compagno 1984a). In the North West Atlantic, pelagic fish and squid are the main diet in deep water, and pelagic and demersal fish are important in their diet in shallow water (Joyce et al. 2002).
Like other mackerel sharks, the porbeagle is endothermic, maintaining its muscle and visceral temperatures above that of the surrounding seawater. It prefers temperatures below 18°C and has been caught in water temperatures as low as 2°C on the bottom (3°C on the surface) at high latitudes (Svetlov 1978). The preferred temperature range in the Northwest Atlantic is 5 to 10°C (Campana and Joyce 2004).
Porbeagle has been fished in this region by many European countries, principally Denmark, France, Norway and Spain. There has never been any restriction on fishing effort on this stock. The Northeast Atlantic fishery began when Norway started targeting porbeagle in the 1930s using longlines. Norwegian landings first reached a peak of 3,884 t in 1933. About 6,000 t were taken by the Norwegian fleet in 1947, when the fishery reopened after the Second World War, followed by a progressive drop in landings to between 1,200–1,900 t from 1953–1960. The collapse of this fishery led to the redirection of fishing effort by Norwegian and Danish longline shark fishing vessels into the Northwest Atlantic. Norwegian landings from the Northeast Atlantic subsequently decreased from 160 to 300 t/annum in the early 1970s to only 10 to 40 t/year in the late 1980s/early 1990s, while average Danish landings fell from over 1,500 t in the early 1950s to less than 100 t throughout the 1990s (DFO 2001a, Gauld 1989).
French and Spanish longliners have operated directed fisheries for porbeagle since the 1970s. Reported landings from the main French fishing grounds in the Celtic Sea and Bay of Biscay decreased from over 1,092 t in 1979 to 300 to 400 t in the late 1990s. Spanish vessels appear to have taken porbeagle opportunistically both in the early and late 1970s and since 1998. Landings off Spain tend to be greater during the spring and autumn, with a drop in the summer (Mejuto 1985, Lallemand-Lemoine 1991). It is unclear, however, whether the very variable early landings data from the Spanish fleet (from nil to nearly 4,000 t/year) represents huge variations in catches, possibly the result of ‘boom and bust’ fisheries removing different segments of the stock, or differences in catch reporting. Bonfil (1994) estimated that 50t of porbeagle were taken as a supplementary catch in the Spanish longline swordfish fishery in the Mediterranean and Atlantic during 1989. The long line fishery in the Bay of Biscay (ICES Area VIII), directed at the more abundant blue shark, also landed about 30 t of mainly porbeagle and some shortfin mako Isurus oxyrinchus during 1998–2000. ICES data (Heessen 2003) indicate that annual landings from Area IXa into mainland Portugal peaked at almost 3,000 t in 1987 to 1988 and have since declined (these records do not appear in the FAO statistics).
Reported landings from the historically most important fisheries, around the UK and in the North Sea and adjacent inshore waters have decreased to very low levels during the past 30 to 40 years, while catches from the offshore ICES sub-regions west of Portugal, west of the Bay of Biscay and around the Azores have increased since 1989. This is attributed to a decline in heavily fished and depleted inshore populations and redirection of effort to previously lightly exploited offshore stocks.
Norway is allocated a quota of 200 t of porbeagle in European Community (EC) waters, reduced in 1985 from the 500 t established in 1982 (Gauld 1989). Since 1985, the Faeroe Islands can also take 125 t from EC waters (originally 300 t in 1982, 150 t in 1984a). These quotas currently exceed total landings from shelf areas in the region and yield no management benefit.
Annex V of the Convention on the Protection and Conservation of the Ecosystems and Biological Diversity of the Maritime Area [also called OSPAR (Oslo-Paris) Convention] requires OSPAR to develop a list of threatened and/or declining species and habitats in need of protection or conservation in the OSPAR maritime area (Northeast Atlantic). OSPAR member states were invited in 2001 to submit proposals for inclusion on this list. In response, Portugal – on behalf of the Azores, proposed to list porbeagle Lamna nasus in the wider Atlantic because of its biological sensitivity, keystone importance and the severe decline in its population. This proposal has not yet been adopted.
The status of the largely unmanaged, unmonitored Northeast Atlantic stock is likely worse than the seriously depleted Northwest stock, with stringent conservation and management action (fisheries closure and stock assessment) needed urgently to enable stocks to rebuild to levels where sustainable commercial and recreational fisheries are possible.
|Citation:||Stevens, J., Fowler, S.L., Soldo, A., McCord, M., Baum, J., Acuña, E. & Domingo, A. 2006. Lamna nasus (Northeast Atlantic subpopulation). The IUCN Red List of Threatened Species 2006: e.T39343A10210612. http://dx.doi.org/10.2305/IUCN.UK.2006.RLTS.T39343A10210612.en . Downloaded on 13 October 2015.|