Distribution and Apparent Abundance of the Basking Shark, Cetorhinus maximus, off the Central and Southern California Coast, 1962-85

JAMES L. SQUIRE, Jr.

Background soup, the liver for squalene, the hide for In February 1955, the author recorded leather, and the carcasses for fish meal their occurrence in Monterey Bay during Basking sharks, Cetorhinus maximus, (Compagno, 1984). an aerial survey for pelagic fish (Anony­ are frequently observed along the central Observations on the occurrence of mous, 1955). Seventy-four basking and northwestern southern California these sharks offcentral California, based sharks werecounted in the northeast por­ coast during the winter and spring on records ofEdward Durden, an aerial tion of Monterey Bay, within 1.5 miles months. These large plankton feeding fish spotter who worked with the basking ofshore. They appeared to be feeding in elasmobranchs, second in size only to the shark fishery during the 1948-1950 an area of patchy plankton. whale shark, Rhineodon typus, had been period, were published by Squire (1967). This paper describes the distribution the subjectofa small commercialfishery These records indicate that basking and abundance of basking sharks along offCalifornia in the late 1940'sand early sharks are commonly observed during the central and southern Californiacoast 1950's for their liver oil, rich in vitamin October to May, with commercial con­ (1962-85) as recorded by aerial fish spot­ A, and in lateryearsfor reduction into fish centrations noted offPismo Beach and in ters participating in the NMFS aerial meal and oil (Roedel and Ripley, 1950). Monterey Bay. This occurrence differs monitoring program for coastal pelagic These fisheries were sporadicand did not from that reported in north European resources. Comparison is made of the take basking sharks in large numbers. waters where basking sharks are com­ seasonal occurrence ofphytoplanktonoff Along the west coast ofNorth Ameri­ monly observed during the summer. the central Californiacoastand theabun­ ca, the othersubstantial amount of"fish­ In European waters it is proposed that dance of basking sharks. ing" occurred in the 1950's when an they may shed their gill rakers in early eradication program was conducted in winter, and hibernate near the bottom Methods British Columbia waters by the Canadian during the winter and spring months In 1962, the National Marine Fisher­ Fisheries Department. Basking sharks (Matthews, 1962). Along the California ies Service Southwest Fisheries Center were damaging Pacific salmon, On­ coast, they are frequently observed in (SWFC) startedan aerial monitoring pro­ corhynchus spp., gill nets and a boat areas ofhigh phytoplankton abundance. gram for pelagic fish resources using the equipped with a sharp plow-like device was used to ram and kill basking sharks. About50sharks were reported killeddur­ ing the first month ofoperation (Anony­ mous, 1956). Basking sharks are fished by harpoon in many areas of the world (Norway, Ireland, Scotland, Iceland, China, Japan, Peru and Ecuador). These fisheries are reported to be sporadic due to periodic depletion ofbasking shark stocks (Com­ pagno, 1984). Basking shark meat is used for human consumption, fresh or dried salted. The fins are used for shark-fin

James L. Squire, Jr., is with the Southwest Fisheries Center, National Marine Fisheries Service, NOAA, P.O. Box 271, La Jolla, CA 92038. The basking shark, Cetorhinus maximus.

8 Marine Fisheries Review services of aerial fish spotter pilots that 615) had the greatest number ofbasking Point Conception by year, is also given work with the California commercial shark sightings. Block area 607 had the in Figure 3. The number of flights con­ purse seinefleet. Thespotterpilots search largest sighting record, 6,389 basking ducted north of Point Conception in the the offshore areas from offBaja Califor­ sharks, with an averageof96.8sharks per areas ofhigher basking shark abundance nia' Mexico, to the MontereyBay areafor sighting. South of Point Conception the was much greaterbefore 1970than after. concentrations of such target species as greatest numbersighted in any blockarea Aerial fish spotters were actively search­ the northern anchovy, Engraulis mor­ was the area southwest ofVentura (block ing for Pacific (chub) and jack mackerel dax; Pacific or chub mackerel, Scomber 665) with an average of 6. 7 individuals and Pacific sardine north of Point Con­ japonicus; jack mackerel, Trachurus persighting. Inthis area, blockareas664 ception in the 1960's, but after the decline symmetricus; Pacific bonito, Sarda chili­ and 683 had higher sighting rates, but of both the mackerel and sardine re­ ensis; Pacific sardine, Sardinops sagax; few sightings (two for block 664 and one sources to very low levels, little aerial and bluefin tuna, Thunnus thynnus. For for block 683). spotting effort was conducted north of the resource monitoring program the The monthly distribution of basking Point Conception. Edward Durden (per­ spotter pilots maintain a flight log indi­ shark sightings for the coastal area from sonal commun.) reported that from his cating areas searched, species observed, the Santa Barbara Channel to Monterey experience it appeared that theabundance and amount of fish observed (estimated Bay as developed by the aerial monitor­ of basking sharks was much reduced in in short tons) for the area, or numbers of ing program (1962-85) is compared with all areas in the 1970's. schools and size (tonnage) ofthe schools. the monthly sightings in the Monterey A total of399 sightings totaling 8,709 Aerial spotters under contract were also Bay area as recorded by Edward Durden basking sharks were recorded for the asked to make note ofany basking sharks (Squire, 1967) in 1948-50 (Fig. 2). Both coastal area from Port Hueneme to Santa observed. sets of observation data show the peak Cruz, Calif. This was an average of21. 8 Aerial fish spotting records (1962-85) apparent abundance to be October with basking sharks per sighting. The average in the SWFC data base were searched for a lesser occurrence in February or number was 51.9 basking sharks per basking shark sightings. Data on num­ March. sighting for the area north ofPoint Con­ bers sighted are recorded by "block The Monterey Bay and central Califor­ ception; for south ofPointConceptionthe area, " a 10" longitude by 10" latitude area nia coast is a major upwelling area and the average number of basking sharks per (about 8 X 10n.mi. atthe latitude ofCali­ highest phytoplankton concentrations are sighting was 2.9. South ofPointConcep­ fornia). This "blockarea" coding system noted during the summer months. Figure tion the sighting level was 0.009 basking is the same as that used by the California 2 also shows the monthly distribution of sharksperBAF (74,143 BAF). North of DepartmentofFish and Game for record­ phytoplankton volumes in the Monterey Point Conception the sighting level was ing data from the marine waters offCali­ Bay area as recorded by Bolinand Abbott 1.19 basking sharks per BAF (6,695 fornia. When a pilot enters a block area (1963). Zooplankton organisms, being BAF). it is recorded as a block area flight (BAF). grazers on phytoplankton, tend to coexist It would appear that some increase in During 1962-85, aerial spotters recorded with phytoplankton, and the months of population levels ofbasking sharks south a total of6,695 BAF's for the area north high phytoplankton should result in ofPoint Conception may have occurred ofPoint Conception (Zones A and B) and higher levels ofzooplankton, the major since 1975 with apeak in 1981 (Fig. 3). 74, 142 BAF's for the area south ofPoint food source for filter-feeding basking Severe El Nino perturbations occurred Conception (Zones C and D). During sharks. During the months of high phy­ in 1982 and 1983 (Quinn et aI., 1987). 1962-85, 8,713 basking shark sightings toplankton volumes the occurrence of These abnormally warm years, including were recorded, distributed along the basking sharks is low. This may indicate 1984 which was warmer off southern coast from immediately south of Santa that the basking sharks observed in California than during the El Nino peri­ Cruz, California to off Port Hueneme, greater numbers during the fall and od, may have reduced again the avail­ California, and along the Santa Barbara winter are not necessarily in the coastal ability of basking sharks south of Point Channel Islands. Four basking sharks areas for feeding, but these concentra­ Conception. were recorded off northwest Baja Cali­ tions in the inshore area could be related Historical experience in other areas of fornia, Mexico. to mating as described by Compagno the world indicates that basking sharks (1984) for the European population. cannot sustain a prolonged intensivefish­ Results ery (FAD, 1984). Basking sharks, like Figure 1 presents the geographical Abundance Trends many other elasmobranchs, have a slow distribution ofsightings, the total number Greater abundance levels were ob­ growth rate and low fecundity (Holden, of basking sharks sighted and average served prior to 1970. This is reflected 1973). Fisheries in other parts of the number sightedper sightingby blockarea in the number ofbasking sharks sighted world tend to sporadically fish the elas­ during 1962-85. The area north ofPoint per block area (for block areas having mobranch resource, as their abundance Conception, Monterey Bay (block areas sightings) as shown in Figure 3. The dis­ evidently declines rapidly during fishing 508, 516, 517) and the area off Point tribution of sighting effort (number of (Compagno, 1984). Abundance surveys Buchon and Morro Bay (block areas 607 , BAF's) conducted north and south of ofthe California basking shark resource

52(2),1990 9 CRUZ 0 \. 0 37 ~10 MONTEREY BAY 1~': 1\ 801 19 Ir31027 42.1 25.6 517 516 Irv 30 ~3d.o 526

\ PT. SUR 2 22>:::; 6 1 4 3 .-J.- TOTAL NUMBER OF ANIMALS 2.0 55 '>c- 2 . 0 540 539 ,,538 22 ~I 1 \ 2: 4 NUMBER OF SIGHTINGS 1 ~6.0 1.0 I 548 5.5 -.0...... AVERAGE 36 0 " 547 4 30 539 I 1 4 4.0 7.5 ~ BLOCK NUMBER 555 554 \. 5 630)1\ 0 A 561 5 4 ...... [\ 4 ; 0 ;Gl.2 602 '\ 601 6,389 9~68 129 r---. 9.5 ~ 607 MORRO BAY 608 187 ! 9 ~1.1 61~.PISMO BEACH \ BUCH~ AREA PT. 193 1 SHOWN B IJ2~ ~ 350 J2t 1/ 1\ \

AONCEPTION 2 67 159 ~~ 2 1 2 6 17 33 64 37 2 1 ~ 5 161S 2.0 2.5 10 T'---J~ x"3.7 1.0 1.0 1.0 1.2 1.1 3.5 651 C 659 658 657 656 655 654 653 652 VENTURA 6 5 30 175 19 4 21 26 1)..-9~5 1.2 1.2 1.4 6.7 ~'1 668 667 666 665 664 2 2 33 6 25 6 1 4 '1 ~ 2 0 1~o--"-3~6 1.~",",\ 6.2 16.0 ~ ,f"""' c: ~ 6~' 684 683 ..... 34 0 6JUl Jt 685t" \ 1 1--Y 1", 1 1 D \.1.0 1.0 3.0 711 710 709 SAN ABA BARP CHA NEL I LANDS

122 0 121 0 1200 119 0

Figure I.-Distribution ofsightings, total number ofbasking sharks sighted, and average number sighted per sighting by block area (1962-85).

10 Marine Fisheries Review 100 100 shouldbe conducted to establish a''base I I- 90 " 90 level" of apparent abundance prior to Z ," , -s any commercial fishing, and compared a ' , '" I :2 80 C '' ,, ::: 40 80 l- with thehistorical abundancelevels pre­ >- •••..../' ' , z eD ' , I a 70 , , ('j 70 sented here. Continuing the survey pro­ CJ ' , :2 z ' , > >­ 60 ' , « 30 60 CD gram to monitor changes in apparent f= A ' ...J I ,: 0 l- abundance from fishing would then pro­ CJ , > I en 50 z 50 CJ vide·necessary information for resource u. 0 :J 40 B,,/ !;< 20 40 u. a , z management. « ,, « en w , ...J 30 CD a: 30 0­ « Av. 0 a Literature Cited 20 !;: 10 20 ~ 'I ..- Anonymous. 1955. Aircraft spotting flight 55-2. --' eD '0­ Calif. Dep. Fish Game, Memo. Rep., 4 p. 10 10 ...... ­ ____ . 1956. Ship spears shark. Pop. Mech. 0 0 1956(11): 172-173. Bolin, R. L., D. P. Abbott. 1963. Studies on the 2 3 4 5 6 7 8 9 10 11 12 marineclimate and phytoplankton ofthe central MONTH coastareaofCalifomia, 1954-1960. Calif. Coop. Oceanic Invest. Rep. 9:23-45. Compagno, L. J. V. 1984. Sharks of the world. Figure 2.-A = average number of basking sharks sighted per block area, by FAOFish. Synop. 125, FAO Species Cat. 4, pt. month, by the aerial monitoring program (1961-85), B = number ofbasking sharks 1,249 p. Food Agric. Organ. U.N., Rome. observed perflight in the Monterey Bay area, by month (1948-50), and C = average Holden, M. J. 1973. Are long-term sustainable phytoplankton volumes recorded for Monterey Bay, by month (1954-60). fisheries for elasmobranchs possible? Rapp. P.-V. Reun. Cons. Int. Explor. Mer. 164: 360-367. Matthews, L. H. 1962. The shark that hibemates. New Sci. 13:756-759. Quinn, W. H., V. T. Neal, andS. E.Antunezde Mayol0.1987. EINiiiooccurrencesoverthepast 140 four and a half centuries. J. Geophys. Res. 92(C13): 14,449-14,461. Roedel. P. M., and W. Ripley. 1950. California 120 sharks and rays. Calif. Dep. Fish Game, Fish. Bull. 75, 88 p. Squire, J. L., Jr. 1967. Observations of basking 100 sharks and great white sharks in Monterey Bay, 1948-50. Copeia 1967(1):247-250.

80

60

40

20

o .~ M o 7 6 5 4 3 2 1

1962636465666768697071727374757677 7879808182838485

Figure 3.-Numberofsharks perblock area, for block areas where observed, and number ofblock area flights (BAF's) north and south ofPoint Conception, Calif.

52(2),1990 11