Annex 3

Relevant Biological, Ecological and Fisheries/Trade Data for Basking sharks Cetorhinus maximus Gunnerus 1765

1. Life History Parameters

Size: Mature individuals range from 5–14 metres, 1,500+ kg weight.

Age of maturity: Unknown: estimates range from 6–20 years.

Maximum lifespan: ~50 years.

Fecundity: Likely to be ovoviviparous. May produce 5–20 young per female, with a gestation period of 12–36 months (AC 1996). New-born young are large (1.7 m) and fully developed. Pregnant females are almost entirely unknown, and may be spatially or bathymetrically separated from those members of the population regularly seen basking on the surface (FAO fact sheet).

Survival rates: High, but largely unknown.

Food sources: Plankton and small fish.

Habitat: Coastal and offshore waters, especially around the continental and insular shelves.

Distribution and abundance: Wide ranging in temperate and boreal waters, pelagic and coastal. No quantitative estimates of regional or global population sizes exist, and insufficient monitoring occurs to enable population trends to be determined reliably (C. maximus proposal). Long-term monitoring of plankton abundance (1950–1995) have shown local increases and decreases over time; C. maximus population fluctuations are likely to be strongly linked to fluctuations in their food supply. Most caught off the UK are subadult or non-pregnant females in the summer, and males in the winter (FAO fact sheet).

Movement patterns: Highly migratory, and noteworthy for their seasonal appearance and subsequent disappearance (FAO fact sheet). The unpredictable occurrence seems to be driven chiefly by oceanographic processes (Sims & Quayle 1998).

Other: Often seen moving slowly at the surface in singles, pairs, or up to 100 individuals (FAO fact sheet). They make unique biological 'plankton recorders' (Sims & Quayle 1998).

Products in trade: Fins, meat, oil

Use of products: The massive liver was once prized for its oil, but demand has waned. Present EU regulations allow the taking of only 100 t of liver (~200 sharks). However, the shrinking market for oil and the erratic distribution of sharks have meant that this quota has never been fully taken (FAO fact sheet). The Norwegian fishery is now supported by the high prices paid in international fin trade – C. maximus fins are now the most valuable sold in Singapore, at $100-300/kg dried (SSG 1996).

Impact of past fisheries: C. maximus fisheries have formed the basis for cottage industries for several hundred years. Fisheries began in the 18th century in Ireland, where the species was exploited for 60 years, until it became scarce. Stocks gradually re-established, and fishing was renewed in 1940s, but catches quickly declined again to low levels (Walker 1998). Sudden collapses were also recorded in other areas in the North Sea, and California. It has also been the object of harpoon fisheries from Norway, Ireland, Scotland, Iceland, USA, Peru, Ecuador, China and Japan, and is often sporadically fished, due to periodic depletion of stocks (FAO fact sheet). Sharks are scarce in areas once fished, and more abundant at other locations. New-borns and juveniles are only rarely seen, indicating that their populations occur out of the range of surface fisheries (C. maximus proposal).

Locations of current fisheries: Norway operates the only directed fishery currently in operation, but there is also evidence of opportunistic fishing of C. maximus when encountered. From a recorded 450 trawls by Patagonian coastal fisheries, a single C. maximus was caught (Van der Molen et al. 1998).

Other threats: Irish records show evidence of C. maximus entangled in fishing nets, usually surface gill nets.

Protection: Legally protected in the United Kingdom, New Zealand, Israel, USA Atlantic and Gulf States, and proposed for protection in the Mediterranean basin.