2. Biological Parameters

2.1 Distribution

Temperate waters of continental and insular shelves, very occasionally recorded well offshore in oceanic waters but most commonly seen very close to the coast. They are not recorded from the tropics, and records from the warmest areas are often of dead, stranded or moribund specimens. They may occur in boreal waters during the summer. Although widely distributed, they are generally infrequently recorded except in a few apparently favoured coastal areas, where they are usually seen in relatively large numbers for only part of the year.

Their north Atlantic distribution extends from the transition between Atlantic and Arctic waters (including Newfoundland (Canada), the Gulf of Maine (USA), south and west of Iceland, off the North Cape of Norway and in the western Barents Sea and White Sea), to the Mediterranean (at least as far east as Turkey) and as far south as Senegal (possibly only as dead, stranded specimens) and Florida, USA (including moribund specimens at the southern edge of their range).

In the south Atlantic they are recorded from southern Brazil to Argentina and off the west and south coast of Cape Province, South Africa. In the northwest Pacific, they are recorded from Japan to the Koreas and China, in the northeast Pacific from the Gulf of Alaska, through British Columbia to Gulf of California, and in the southeast Pacific off Ecuador, Peru and Chile. In Australasia, they are only rarely recorded from Australia (New South Wales, Victoria, Tasmania, south and southwestern Australia) but they are more common in cooler New Zealand waters. (Compagno 1984, Last & Stevens 1994).

Major north Atlantic range states include Norway, Sweden, the United Kingdom, Ireland, France, Spain, Portugal, Italy, Greece and Turkey in Europe; the USA and Canada (northwest Atlantic and also Northeast Pacific). Other range states in the North Atlantic include the other Mediterranean countries (possibly excluding the extreme east and southeast), Iceland, Faeroes, Denmark, Russian Federation, and possibly northwest African states.

Elsewhere, major range states include Japan, the Republic of Korea, the Democratic People's Republic of Korea, and China in East Asia; Brazil, Argentina, Uruguay, Ecuador, Chile and Peru in South America; South Africa and New Zealand.

Distribution records are characterised by highly seasonal appearances, and the species may be highly migratory, although no long-distance tracking of individuals has been reported. The majority of basking shark records in UK waters appear to be correlated with a narrow range of water temperatures: 8°-14°C, 14°C in Japan, or 8-12°C in Newfoundland (Lien and Fawcett 1986). Owen (1984), however, reported sightings off the New England northwest Atlantic coast ranging from sea surface temperatures of 11°-24°C, with most sightings at surface temperatures of 16°-24°C, and peak densities at 22°-24°C.

Records in higher latitudes are most common during the spring and summer months, suggesting a seasonal migration occurs. This migration may take place from deep to shallow water (indicated by high levels of squalene in liver oil in spring, followed by increasing levels of vitamin A later in the year) or from lower to higher latitudes as sea temperatures rise, or both. In the North Atlantic, basking sharks appear in the southern part of their range in spring, more northern areas in summer, then apparently almost disappear in autumn and winter. Owen (1984) reports that basking sharks are first sighted by aerial surveys in the spring over very deep water along the southern and eastern margins of Georges Bank, off New England (USA). They move into shallow shelf waters as the season progresses, particularly after the thermocline has developed and zooplankton densities are at their height.

In the eastern North Pacific, basking sharks are recorded in largest numbers in winter (November to March) on the Californian coast, and occur in northern latitudes (Washington and British Columbia) in the spring and summer (Compagno, 1984). In the western North Pacific, the Japanese basking shark fishing season off the Shima Peninsula, Mie Prefecture, was also in spring and early summer (March to May).

There is a pronounced spatial and seasonal population segregation, with groups of animals of similar sizes and the same sex often sighted together. Most basking sharks caught in surface fisheries in Scottish waters were recently mated females (F:M ratio of 18:1, Watkins 1958), and 65-70% of sharks taken in Japan were also female. Conversely, catches in sub-surface gill nets off Newfoundland included twice as many male as female sharks (Lien & Fawcett 1986). Despite the large numbers of mature females taken in fisheries, there is only one known record of a pregnant female (with a litter of six). Newborns and juveniles are also only rarely seen, indicating that their populations occur elsewhere, out of the range of surface fisheries.

Basking shark numbers (or recorded sightings) in some regions appear to vary over an indeterminate time scale. For example, exceptionally large numbers of basking sharks were sighted in Brittany, France and southwest England in 1998 (Speedie 1998), but apparently not in other areas of the UK. Similar ‘invasions' have been reported elsewhere from time to time (Kunzlik 1988, Castro et al. in preparation). However, superimposed on this pattern is one of individual sharks being re-sighted repeatedly at certain locations year after year (Watterson in lit., Compagno in lit.).

Tagging programmes using satellite transmitters and other electronic tags are proposed in a number of locations. If successful, these should help to elucidate the migratory routes of these sharks.

Siccardi (1960, 1971) suggested that there are four species of Cetorhinus, two in the North Atlantic and Mediterranean (C. maximus and C. rostratus), one from southern Australia (C. maccoyi), and one from the South Atlantic (C. normani). Compagno (1984) and Springer and Gilbert (1976) consider there is insufficient evidence to separate these species. Tomás and Gomes (1989) describe some morphological dissimilarities between basking sharks caught in gill net fisheries off south-eastern and southern Brazil and those described from the North Atlantic. These observations may indicate that little or no exchange takes place between northern and southern hemisphere populations by migration in deep cold waters below the thermocline. No research has addressed the question of whether genetically distinct sub-populations exist in different oceans or hemispheres. Some tissue sampling is now taking place and the DNA studies planned may eventually help to clarify the status of various populations.

2.2. Habitat availability

Habitat availability is not considered to be a constraint for this species.

Basking sharks are mainly recorded from temperate coastal, inshore and oceanic waters, reported from surface sightings when the sharks are feeding or congregating at or very close to the surface. Surface waters preferred for feeding and possibly mating activity appear to be ocean fronts, or close inshore off headlands and islands and in bays where 'tide lines' are formed in areas of strong tidal flow and zooplankton aggregate (Earll 1990, Sims et al. 1997, Sims and Quayle 1998).

Basking sharks are also taken occasionally in temperate oceanic drift nets and as by-catch in shallow and deep-set nets in coastal areas. Bonfil (1994) uses observer data to extrapolate to a figure of some 50 basking sharks taken annually in the whole of the Pacific oceanic drift net fisheries, suggesting that only small numbers are found away from the coast. The species is thought to over-winter in deep water offshore, but the location of such wintering grounds is generally unknown. Only a few winter records have been reported, including sharks caught in deep water trawls in the Gulf of St Lawrence, Newfoundland, Canada (Lien and Aldrich 1982) and the Firth of Clyde, Scotland (Fairfax 1998). Owen (1984) describes how the first sharks sighted on or near the surface in spring are over deep water on the edge of Georges Bank, off New England, USA.

2.3 Population status

The global status of the basking shark is assessed as Vulnerable (A1a,d, A2d) in the 1996 IUCN Red List of Threatened Animals.

The assessment is based on past records of rapidly declining local populations of basking sharks as a result of short-term fisheries exploitation and very slow population recovery rates recorded (see fisheries accounts in the following pages). It also takes into account the likely potential for similar population declines to occur in the future from directed fisheries, driven at least in part by the demand for fins in international trade, and from continued global by-catch. Several authors describe fisheries for other sharks that have caused serious stock declines (e.g. Ripley 1946, Olsen 1954, Rae 1962, Holden 1968 and 1974, Casey et al 1978, Gauld 1989, Cailliet et al 1993). Compagno (1984) considers the basking shark "to be extremely vulnerable to overfishing, perhaps more so than most sharks ... ascribed to its slow growth rate, lengthy maturation time, long gestation period, probably low fecundity and probable small size of existing populations (belied by the immense size of individuals in their small schools)." The best estimates of age at maturity for basking sharks are 12-16 years for males, up to 20 years for females, with a litter size of six, and gestation period from 12 to 36 months. Longevity is likely to be 50 years. The interval between litters may be two to four years. (Pauly 1978 and in press, Compagno 1984, Fowler in press.) This is not excessive for such a large shark, considering the well-documented gestation periods of 18-24 months recorded for the much smaller spiny dogfish Squalus acanthias, collated by Camhi et al. 1998.

No firm estimates are available for the total global population or regional populations of this species. Owen (1984) suggested that numbers sighted during aerial surveys for cetaceans and turtles in the Northwest Atlantic, which covered about 10% of the shelf area and could only identify sharks swimming at depths of less than 3-4 m, might represent only 1/7th of the total population present. On this basis, he estimated that as many as 4-6,000 sharks might be present in the Gulf of Maine and off the New England coast (USA) during the summer months. He compared this with an estimated population of 2,000 sharks in the Monterey Bay area of the US west coast (Squire 1967). McNally (1976) reports that a fishery removed 12,360 basking sharks over a 29-year period from the west coast of Ireland, the majority during the 1950s. The Norwegian fleet took another 800 in the area from 1973-83, and presumably significant numbers before 1973, when records by ICES (International Council for the Exploration of the Sea) Fishing Area become available (Annex 2b). Recent sightings data (Berrow & Heardman 1994) suggest that this population has not recovered since the main Irish fishery closed in the 1970s, following many years of low catches.

As pointed out by Compagno (1984), it should be noted that basking shark populations are probably very small compared with most other sharks. Most recorded fisheries have taken only hundreds or about one thousand individuals annually for a few years before collapsing. The maximum annual recorded catch throughout the northeast Atlantic only occasionally exceeded 3,000 individuals, at the peak of the Norwegian fishery, when more than 30 Norwegian vessels participated for the whole or part of the season (ICES1995). Where observations of basking sharks have been recorded, the total annual number of records is usually in the tens, hundreds, or at most low thousands, including repeat sightings. The Marine Conservation Society obtained 2,610 records with information on 9,064 sharks (doubtless including many repeat sightings) from UK waters from 1986 to 1988. The total number removed from the whole of the Northeast Atlantic during the past 50 years is probably between 80,000 and 100,000 animals (Annex 2a).

2.4 Population trends

A few well documented declines in catches by directed fisheries for the basking shark suggest that stock reductions of at least 50% to over 80% have occurred in some areas over a very short period (usually ten years or less, Fowler in press; Annex 1). These declines have resulted in long-term (lasting several decades) reductions in local populations, with apparently little or no migration into the area from other sources. Examples from Ireland, Japan and British Columbia are given below. However, most other fisheries described in literature (also summarised below) lack accurate recorded data on landings, market conditions and catch per unit effort. It is therefore not always possible to determine whether a short-term fishery ends for market reasons, or because the local population has declined to a point where difficulty in finding the target animals damages the viability of the fishery. Calculations of natural and fisheries mortality derived from north-west European landings (see following paragraph), however, strongly suggest this species is unable to withstand targeted exploitation for long, and confirm that stock depletion is likely to be a major factor affecting fisheries yields.

Pauly (1978 and in press) re-analysed previously published length-frequency data for north-west European basking sharks, mainly obtained from juvenile strandings and adults taken by a Scottish fishery. He modelled growth using the von Bertalanffy growth formula, and estimated total mortality (Z) as 0.33/yr for juveniles (considered too high to represent natural mortality) and 0.16/yr for adults. Adult natural mortality (M) calculated from Pauly (1980) produced an estimate of M = 0.068/yr for adults. Fishing mortality (F) was considered to be 0.094/year in adults, with the ratio of F/Z = 0.6. Pauly (in press) states that this is 'an exploitation rate that no fish - especially not a long-lived, low-fecundity fish such as the basking shark - can withstand for long (Beddington and Cooke 1983)'.

An additional explanation for the rapid collapse of localised fisheries for a widely distributed and apparently seasonally migratory species, is that basking sharks are site-faithful and tend to return to the same coastal summer 'basking' and feeding locations. Despite their wide-ranging nature, they are effectively part of local stocks that are particularly vulnerable to depletion by fisheries activity (Fowler 1996 and in press). Individuals of several other species of large migratory sharks have been found to return seasonally to the same general location to feed, mate, or give birth. Walker (1996) describes examples of localised stock depletion in wide-ranging shark populations. Hueter (1998) suggests that this pattern of ‘philopatry' may occur in many species of shark and lead to localised stock depletion. In effect, there are likely to be sub-populations of basking sharks present in many (if not all) coastal areas, but the degree of exchange between these is unknown. Watterson (in lit.) has seen over 35 individuals returning to the Isle of Man (a UK Crown Dependency), some over a four or five year period. Individual sharks have been recorded as remaining in the area for up to 27 days. One South African basking shark has been re-sighted off Robben Island, Cape Town, on more than one occasion (Compagno, pers. comm.). Sharks marked in the Isle of Man have, however, also been re-sighted in other locations; one each on the west coast of Scotland, southern England, and south-west Ireland, possibly during other stages of their seasonal migrations (Watterson pers. comm.).

There is only very limited information available on wider population trends; data indicating changes in catch per unit effort or annual variation in numbers of sightings are only obtainable on a local, or at most regional, scale. Standardised sightings per hour data from the Isle of Man, where the species has been protected since 1990, suggest a decline in shark numbers from the end of the 1980s, with particularly poor sightings in the mid 1990s (Table 1 and Figure 1). Sightings data corrected for effort from a coastal cetacean-watching site in Cornwall for the period 1995-1998 show no significant trend (Speedie in lit.). Other sightings schemes (Scottish Wildlife Trust and Marine Conservation Society) do not correlate sightings with observation effort and so do not enable trends to be assessed reliably. MCS data (Table 2 and Figure 1) still appear to show a decline in reported sightings between the two periods when the public sightings scheme was actively promoted in 1988-91 and 1995-96.

Table 1. Number of basking sharks sighted per hour effort around the Isle of Man (Watterson in lit.)

Table 2. Sightings reported to the Marine Conservation Society, 1986 to 1998.

(* years during which the sightings scheme was promoted.)

Figure 1. Number of sharks seen/hour around the Isle of Man, and reported to the UK Marine Conservation Society, 1985-1998

Some evidence exists for unpredictable cycles in the numbers of basking sharks entering coastal waters. Certain years (including 1998) have seen very large influxes of sharks to some UK areas, while in others the numbers recorded are low (Kunzlik 1988, Speedie 1998, Fairfax 1998). Landings throughout the Northeast Atlantic have also fluctuated strongly. This annual variation in sightings and catch records may, however, be strongly influenced by weather conditions, since basking sharks are generally most commonly sighted on the surface in calm conditions, when they are also most vulnerable to surface harpoon fisheries. Water temperature may also have a significant effect on numbers seen; unusually warm or cold years may result in fewer sightings, possibly a reflection of food availability or distribution through the water column. Finally, basking shark sightings are often associated with the presence of coastal or oceanic fronts, where zooplankton may congregate. Such fronts may be more persistent and sharks more abundant in years when weather conditions are particularly favourable or if incursions of oceanic water into coastal areas occur. The latter may take place as part of a long-term cycle (e.g. the Russell cycle in the English Channel, Russell 1936, Southward 1980), but shorter cycles of six and three to four years are also reported by Robinson and Hunt (1986). In these circumstances migrating sharks may spend longer feeding on high densities of plankton and delay their onward migration to other preferred summer locations.

Some of the fluctuations in north-east Atlantic catches (Figure 4 and Annex 2) may be the result of cyclical fluctuations in zooplankton abundance linked to broad-scale oceanic changes controlled by factors such as summer stratification, the North Atlantic Oscillation or climate (Reid & Planque, in press). Associated changing patterns of basking shark activity may make populations more, or less, vulnerable to fisheries in some years than in others An alternative explanation may be that the wide-ranging Norwegian fleet identified and fished out several local stocks sequentially, resulting in a series of peaks and troughs as each stock was targeted. Neither hypothesis can be tested due to the absence of location data for the majority of catches. The life history of the basking shark, with late maturity and low birth rate probably means, however, that any short-term fluctuations in sightings or catches are not reflections of natural fluctuations in total abundance, but of variations in distribution and / or vulnerability to surface harpoon fisheries.

Irish fisheries
The collapse of two historical fisheries off the Irish coast are well documented: the 18th to 19th Century Sunfish Bank fishery, and the mid-20th Century Achill Island fishery (McNally 1976, Parker & Stott 1965).

The Sunfish Bank is located 30-40 km off the coast of Galway and Mayo, parallel to the coast between Slyne Head and Erris Head (including Achill Island) and not far from the edge of the Continental shelf. McNally notes that it was described in 1836 as being 'remarkable for the break of tide on it, with ebb and flood' (the conditions within which large aggregations of basking sharks are frequently reported elsewhere today). The Sunfish Bank and Achill Island were two of the main areas where large numbers of basking sharks were taken by small boats and relatively primitive equipment at the end of the 18th and first quarter of the 19th Century. Records from this period suggest that this fishery was active for several decades, between 1770 and 1830. The season only lasted for a few weeks in April and May, but at least 1,000 fish (probably more) seem likely to have been taken each year at the height of the fishery. In the early 1830s, sharks became very scarce. Despite continued high prices for 'sunfish' (basking shark) oil, the fishery collapsed in the second half of the 19th Century. A few years' shortage of sharks may be due to adverse weather conditions, but this lack of sharks lasted for several decades. There is no evidence that the collapse of the fishery was due to market factors. The decline in the fishery started 20 years before paraffin became widely available, shark oil was still more valuable in Ireland than paraffin in 1855, and profits to be made from basking shark catches were recorded as being extremely high in 1875, to the extent that 'lives were risked to secure a fish' (McNally 1976).

Figure 2. Landings in the Achill Island basking shark fishery

Basking sharks were next recorded in abundance around Achill Island in 1941 (McNally 1976), although numbers had presumably been increasing for some time. This was some 50 years after the previous fishery in the area had ceased, and more than 100 years since large numbers of shark had been taken off this coast A new fishery based on entangling sharks in nets in Keem Bay on the Island started in 1947. Between 1,000 and 1,800 sharks were taken each year from 1951 to 1955 (an average of 1,475/year), but a significant decline in catch records occurred from 1956 onwards. Average annual catches were 489 in 1956-1960, 107 in 1961-65, and then about 50-60 per annum for the remaining years of the fishery (Figure 2).

There is no evidence that this steady decline in catches was the result of a significant decline in fishing effort, which is considered to have been fairly constant at this shore-based fishing station. It is more likely to reflect the falling numbers of sharks entering Keem Bay, as a result of a steeply declining regional shark population. Fishing effort actually increased in the early 1970s as a result of increasing oil prices and re-investment, and catches rose elsewhere (see below). Harpoon guns were installed on three Achill Island boats in 1973, enabling the fishermen to move out of the Bay to the coast of Galway. Regardless, the fishery was unable to increase landings and closed in 1975 (Kunzlik 1988). A total of 12,360 fish had been taken in 29 years at this one site, with 10,676 of these caught from 1949 to 1958 (see Figure 2 and Annexes).

Another Irish basking shark fishery started in county Waterford (southeast Ireland) in 1974, taking an estimated 180 sharks that year and 350 in 1975 (McNally 1976), and confirming the value of basking shark products at this time.

The collapse of the Achill Island fishery was likely accelerated by the activity of Norwegian basking shark fishermen in west Irish waters, including the Sunfish Bank and other areas offshore from Achill Island (S. Myklevoll pers. comm., quoted in Kunzlik 1988). The numbers of sharks taken by this fleet in Irish or any other EC waters were not reported before 1973, so the proportion of earlier Norwegian catches taken in Irish waters is unknown. ICES Fishing Area landings records from 1973 indicate that a few hundred sharks were taken off the west coast of Ireland by the Norwegian fleet in 1973-74 (Area VIb-c), but Norwegian catchers were active off west Scotland in 1975 (Figure 3 and Annex 2b). However, total Norwegian landings for the whole northeast Atlantic (including Norwegian and Scottish coastal waters) were still relatively low during the initial period of decline at Achill Island (Figure 4). It seems likely that, as in later years, the majority of their catches were being taken off the Norwegian coast at this time.

Fowler (1996 and in press) suggests that the percentage decline in the regional population of basking sharks which occurred off the west coast of Ireland during these fisheries, as indicated by the steep and long-lasting decline in catches, was certainly greater than 50%. Indeed, considering Irish landings alone, the most recent Achill Island fishery appears to have caused a local population decline of over 80% in less than ten years. Average catches during the final 15 years of the fishery were less than 10% of the yields in the early 1950s. When the Norwegian catches from this area of the Irish coast are taken into consideration (so far as is possible in view of the lack of catch data by ICES Area for the 1950s and 1960s), then the regional population decline may have been even greater.

Despite incomplete data for Norwegian fleet catches in the area, the Achill Island catch data are considered to broadly reflect a general decline in the regional population of basking sharks on the west coast of Ireland as a result of this fishery. Evidence outlined above for localised stock depletion as a result of fisheries for other species of shark (Walker 1996) supports this theory. While such declines in landings may, in the short term, be due to weather conditions, Berrow & Heardman (1994) note that there were still very few observations by fishermen of basking sharks recorded along this whole west and north-west coast of Ireland in 1993, compared with other previously un-fished coastal areas. Another reason suggested for the decline in the Achill Island fishery is that there was a decline in zooplankton abundance over the same period, which may have affected the number of sharks available to harpoons at the surface (Anon., in press; Reid & Planque, in press). If so, this decline has lasted for forty years.

Scottish fisheries
Fairfax (1998) summarises the limited information available on the earlier 18^th and 19^th century fisheries in Scotland. These appear, like the Irish fishery, to have ceased by the mid 1830s, with large numbers of sharks not being reported again until the 1930s. Fairfax (1998) and Kunzlik (1984) present data on landings from the 20^th century Scottish basking shark fisheries, which concentrated on the Firth of Clyde and West coast (see Annex I). Several such fisheries started up in the 1940s, some targeted full time at the basking shark during the summer season, while others were more opportunistic. Regardless, all appear to have ceased after only a few years of good catches (Figure 4, Annex 2a). It is unclear whether this fishery was short-lived because of stock depletion (by the Scottish fishermen themselves, or Norwegian shark catchers operating close to the west coast of Scotland), or because of falling oil prices in the 1950s.

Oil prices rose again in the mid 1970s, Norwegian catchers took several hundred sharks in 1975, some Clyde basking shark by-catch was processed in the late 1970s, and a small target harpoon fishery started again in the Clyde in 1982. Initial yields from this fishery were good, but these were extremely short-lived and the fishery ceased at the end of 1994 after several poor years of catches (Fairfax 1998, Annex 2a).

Northeast Atlantic Norwegian fishery
A very wide-ranging Norwegian fleet, whose geographical and temporal distribution changes markedly from year to year (Stott 1982), has undertaken the major basking shark fishery in the Northeast Atlantic. Landings have been made from local fisheries from the Barents Sea to the Kattegat, across the North Sea to the south and west of Ireland, west coast of Scotland, Iceland and Faeroe (Pawson and Vince 1998), and have fluctuated widely (see Figures 3 and 4 and Annex 2).

Figure 3. Norwegian landings by ICES Area, 1973-1996

Catches were at their highest (>1,000 and up to >4,000 in some years) between 1959 and 1980, when over 30 vessels were active for all or part of the season (ICES 1995, Figure 4). Shark oil prices were particularly high from the mid-1970s to the early 1980s, and fishing effort is therefore thought to have remained fairly constant over this period.

Figure 4. Targeted Northeast Atlantic basking shark catches, 1946-1996

The subsequent decline in this fishery has been attributed (ICES 1995) to the ageing inshore whaling fleet that targeted basking sharks and a decline in value of basking shark liver oil in the late 1980s. (The latter was the result of the competition from the gulper shark Centrophorus granulosus and kitefin shark Dalatias licha fisheries.) This trend would, however, appear to have been offset by the greatly increased value of the fins in international trade in the 1990s. Regardless, at the present time only a few vessels now continue to fish for this species. A future increase in the activity of the Norwegian inshore whaling fleet may lead to increased opportunistic targeting of basking sharks.

Since the precise locations from which the Norwegian fleet fished for basking sharks are uncertain for the first 27 years of the fishery, it is difficult to detect and evaluate trends in catches, effort, and hence population. Figure 5 presents all landings data combined from the Northeast Atlantic since fisheries restarted in the 1940s, with running means added to smooth the fluctuations that may (as discussed above) be the result of climatic or oceanographic factors. This clearly shows a persistent decline in average landings from the early 1970s to the early 1990s. This period of decline includes a period of peak demand and high value for basking shark oil from the mid 1970s to mid 1980s, which encouraged the establishment of new fisheries in southern Ireland and the Firth of Clyde, Scotland. According to ICES (1995), the Norwegian fleet only declined significantly after 1980, and effort has largely been concentrated off the Norwegian coast since 1984.

Figure 5. Total and mean Northeat Atlantic basking shark landings.

Although no effort data are available, it may be concluded that the declining catches from 1970 to 1980 represent falling yields from declining stocks (possibly despite increased fishing effort), rather than declining fishing effort. This pattern of steeply declining catches is certainly a familiar pattern in other fisheries for large sharks, where much better records, including catch per unit effort data, are available.

Landings increased slightly in the early 1990s (Figures 4 and 5), when the fishery was being sustained by the high value of the fins (ICES 1995, quoting Dr S Myklevoll). The main market for Norwegian fins appears to be Japan, and exports to this market were also increasing steadily in the early 1990s (Directorate for Nature Management, 1995, quoted in Castro et al. in preparation). Norwegian catches have since declined to a new low, despite the continued high value of these products and demand in international markets.

Newfoundland, Canada
Lien and Fawcett (1986) report on an incidental fishery for basking sharks by salmon and cod fishers in Newfoundland. Basking sharks have been incidentally entangled in set nets and occasionally sold for their liver oil for a long time in the area, but written records of these catches are scanty. An estimated 410 sharks were taken from 1980 to 1983 when a survey was carried out of collisions by cetaceans and basking sharks with fishing gear. Incidental shark catches increased in 1981 when a market developed for the fins and liver. When there is no market for the sharks' fins and livers, salmon fishermen generally remove their gear from the water to prevent damage when basking sharks are known to be in the area. If there is a market, the incidental catch becomes a target catch: fishing gear is left in the water and any fish caught is killed and landed, rather than released.

Canadian Pacific
Basking sharks are common in the traditional knowledge of the Hesquiat and Ahousat people along the central west coast of Vancouver Island. In the 1940s, salmon fishermen complained about the problems with these fish being caught in their nets in Barkley Sound, Vancouver Island. The Department of Fisheries and Oceans therefore ran a shark eradication programme in the 1950s. A large blade was placed on the bow of Fisheries vessels and the sharks were rammed and killed. Information on the numbers of fish killed in this manner varies. Newspaper articles report a maximum of 31 being killed in one day and 50 in the first month of operation in 1956, and a total of 59 sharks killed in 1955 and 51-56 in 1956. Clemens and Wilby (1961) state that 'several hundred' were killed in Barkley Sound up to 1959. Presumably the programme ceased when numbers had been depleted to the extent where basking sharks were no longer posing a significant problem to the salmon fishermen. Darling and Keogh (1994) state 'Basking sharks are rarely sighted in Barkley Sound today, suggesting that the majority of the population in that area were killed.' It seems that a single vessel managed to deplete significantly the Barkley Sound stock of basking sharks over a period of just a few years. This occurred between 35 and 40 years ago, but the population has not recovered.

California, USA
Basking sharks were only taken occasionally during the winter in Californian waters before a directed fishery commenced. Harpooning was initially only for sport, with carcasses incidentally being processed for oil and fish meal. However, the value of these products increased until the fishery became profitable and was operated from two centres: Monterey Bay and the San Luis Obispo Bay to Morro Bay area, 100 miles to the south. These two small areas are the two most important locations for winter concentrations of basking sharks along the central and northwestern southern Californian coast (Squire 1990). An average of 25 sharks per annum was landed during each season (September to May) from 1924 and 1938, with a maximum of about 100 in a single year. The fishery was inactive for several years, possibly due to wartime operations, then was revived in autumn 1946 to develop new uses for the valuable liver oil. It was also intended to process the carcasses for their very thick leather and for animal feed meal, and dry the fins for export to China. Three hundred basking sharks were taken in the first season, with 12 vessels operating in Monterey Bay and about six in the San Luis Obispo Bay area. Some vessels were directed to basking sharks on or near the surface by a spotter plane (Phillips 1947). This fishery continued until the early 1950s with about 200 sharks taken annually (Roedel and Ripley 1950). Squire (1967) reports that the fishery was suspended in California in 1950, because of the low prices paid for the oil and the low availability of basking sharks. Lea (pers. comm.) reports that basking shark sightings off central California over the past 20 years are not as numerous in the past. It has been suggested that the early 1940s and 1950s fisheries reduced the populations substantially, and that the species has never fully recovered. However, basking sharks are still taken incidentally in the area. Finned, but otherwise intact, carcasses have been reported washed up at intervals over the past few years (Sean van Sommeran pers. comm.).

Japan
The main targeted Japanese basking shark fishery used to take place off Nakiri, on the Shima Peninsula, Mie Prefecture. Basking shark hunting is recorded as a traditional activity here since the Edo era (1772). However, basking sharks were also taken as by-catch in the 1960s in set nets in the Nakiri area and elsewhere (including Onahama on the Pacific coast of Middle Japan, and near Tokyo). The fishing season was during the main basking shark migration through the area from March to May. Sharks were most abundant in March when the water temperature was about 14° C. About 65-70% of all sharks caught in the fishery was female, and males caught were found to be holding sperm in their claspers, indicating that mating activity was likely underway during this part of the year.

The basking shark fishery became more intensive in 1967 when oil prices rose, and Nakiri fishermen began harpooning larger numbers of sharks. The fishery used vessels of under 3 tons with a crew of two (one harpooner and one skipper). The fishing boats usually worked in pairs, one acting as the catcher and the other towing the sharks. The main use for the sharks during this period was the valuable squalene-rich liver oils. Shark fin was also important and considered a middle ranked shark fin in Taiwan. Shark meat was sold for human consumption, or processed into fishmeal for animal feed.

During the 12-year period from 1967 to 1978, more than 1,200 individual basking sharks were harpooned (an average of about 100 per year). During the last few years of the fishery, from 1975 to 1978, catches gradually decreased, from about 150 sharks in 1975, to about 20 in 1976, nine in 1977, and six in 1978. The fishery ceased completely in the early 1980s as a result of falling oil prices and the declining numbers of sharks sighted. In the 1990s, only 0-2 basking sharks have been sighted each year off Nakiri during the migration season. This compares with a peak year in 1972, when more than 60 basking sharks were processed for sale in Nakiri market. (This information was compiled from Yano 1976 and 1979, and Uchida 1995.)

China
Parry-Jones (1996a in Phipps 1996) reports that basking sharks used to be landed by a harpoon fishery in Fujian Province and Guangxi Zhuang Autonomous Region up to the 1970s. The species was commonly caught in the 1960s, but is seldom landed now. The report concludes that catches and landings of this species had decreased over the last 40 years, and recommended prohibition of catches of this species (and whale sharks Rhincodon typus) in near-shore waters as a precautionary measure until their status is ascertained.

2.5 Geographic trends

The species is widely distributed in temperate waters, but large numbers tend to be concentrated in only a few favoured coastal areas where feeding and possibly breeding activity takes place at or near the surface. As noted above, basking sharks are most vulnerable to target fisheries where they occur in such surface aggregations, and greatly reduced population numbers have persisted for decades in formerly favoured locales that were fished heavily. In addition, cyclical variations in patterns of sightings or catches of this species have been reported. For example, the Norwegian fishery demonstrated widely fluctuating landings during its peak 20 years of operation, and short term variations in local abundance of basking sharks sighted are also recorded from time to time (Kunzlik 1988, Speedie 1998). These may be linked to alterations in oceanic currents, water temperature and zooplankton aggregations. Long and short-term cycles in plankton abundance have been reported in the Northeast Atlantic and North Sea, with different patterns of abundance being recorded in different areas (Reid et al. 1998 a and b). For example, the abundance of Calanus finmarchius, a significant component of zooplankton, has declined in the north-east Atlantic, in some areas by as much as 50% since 1970 (UK BAP in press). This may also have some influence on basking shark distribution and abundance or availability to the fishing fleet.

2.6 Role of the species in its ecosystem

The role of the basking shark in its ecosystem is unknown, but as a large (up to 10m long) plankton feeder this will presumably be similar to that of the smaller baleen whales.

2.7 Threats

The main threat to basking shark populations is from fishing operations — both targeted on basking sharks and incidental or by-catch in other fisheries. However, because these fish congregate in bays and shallow water, they are also at risk from collisions with vessels and may be harassed by shark watchers. Collisions appear to be a fairly frequent occurrence — large areas of scarring are often observed on the head and dorsal surfaces.

Directed fisheries
Targeted basking shark fisheries use nets to deliberately entangle the fish or harpoon guns to take basking sharks swimming or feeding on the surface. Targeted fisheries have been recorded from Norway, Ireland, Scotland, Iceland, California, China, Japan, Peru, Ecuador (Compagno 1984) and Northern Spain (Evaristo Alfaya pers. comm.). Some of these are described in detail above. The main product of these fisheries has traditionally been the liver oil, although the meat, skin and cartilage are also used, and fins are now a very important product of modern fisheries because of their high value in international trade.

Incidental fisheries
Incidental fisheries take is mainly recorded in set nets and trawls, and is most common in coastal waters. It naturally occurs over a much larger area than targeted fisheries. There is evidence from Newfoundland (Lien and Fawcett 1986) that some incidental fisheries may become targeted fisheries as markets for the products develop. There are reports of finned basking sharks being washed up dead in areas where no directed fisheries are known to exist (e.g. Monterey Bay, van Sommeran pers. comm.). Berrow (1994) extrapolated from very limited observer data to suggest that 77-120 sharks may be taken annually in the bottom set gill net fishery in the Celtic Sea (south of Ireland), though the reliability of this estimate has been questioned (P. Kunzlik in litt.). Berrow and Heardman (1994) received 28 records from fishermen of sharks entangled in fishing gear (mostly surface gill-nets) around the Irish coast during 1993, representing nearly 20% of all records of the species that year. At least 22% of basking shark by-catch in fishing nets died. By-catch in Isle of Man herring fishery has amounted to 10-15 sharks annually, and a further by-catch source here is entanglement in pot fishermens' ropes, amounting to some 4-5 fish annually (Watterson in litt.). Lien and Fawcett (1986) record that at least 410 basking sharks were caught between 1980 and 1983 in salmon gill nets and cod-traps in the coastal waters of Newfoundland. Some basking sharks were also taken in deepwater trawls nearby during the winter months. Fairfax (1998) also reports that basking sharks are sometimes brought up from deep water trawls near the Scottish coast during winter — either in a torpid or lively state. In contrast to these relatively large coastal by-catches, extrapolation of observer data from oceanic gill net fleets suggests that only about 50 basking sharks were among the several million sharks taken annually offshore in the Pacific Ocean (Bonfil 1994).

Basking sharks caught incidentally during fishing operations for other species are sufficiently resilient to be released, apparently unharmed in many cases, possibly even after up to three hours on the deck of a fishing boat (Lien pers. comm. and Watterson in lit.). The survival of sharks returned in this way is not monitored. However, the high value of their fins (and to a lesser extent liver oil, flesh and cartilage), is a strong incentive for fishermen to kill and utilise rather than release this species.