Archeological Evidence of Large Northern Bluefin Tuna

I J Abstract.-This study presents ar cheological evidence for the presence of Archeological evidence of large adult bluefin tuna. Thunnus thynnus, northern bluefin tuna, in waters off the west coast of British Columbia and northern Washington State for the past 5,000 years. Skeletal Thunnus thynnus, in coastal remains oflarge bluefin tuna have been waters of British Columbia and recovered from 13 archeological sites between the southern Queen Charlotte northern Washington Islands, British Columbia. and Cape Flattery, Washington, the majority found on the west coast of Vancouver Susan Janet Crockford Island. Vertebrae from at least 45 fish from 8 Pacific Identifications sites were analyzed. Regression analy 601 J Oldfield Rd .. RR #3. Victoria. British Columbia. Canada vax 3XI sis <based on the measurement and E-mail address:[email protected] analysis ofmodern skeletal specimens) was used to estimate fork lengths ofthe fish when alive; corresponding weight and age estimates were derived from published sources. Results indicate that bluefin tuna between at least 120 and Evidence is presented here for the maining 5 sites could not be exam 240 em total length <TLJ (45-290 kg) occurrence of adult bluefin tuna, ined, owing largely to difficulties in were successfully harvested by aborigi Thunnus thynnus, in waters ofthe retrieving archived specimens but, nal hunters: 83% ofthese were 160 em northeastern Pacific, off the coast in one case, because all skeletal TL or longer. Archeological evidence is of British Columbia and northern material had been discarded by augmented by the oral accounts ofna tive aboriginal elders who have de Washington, for the past 5,000 museum staID. Tentative estimates scribed strategies used until the late years. The physical evidence con ofthe size ofthe archeological speci 19th century for hunting bluefin tuna. sists of archeological remains of mens were made by comparing the Despite this information. there are no large bluefin tuna harvested by ab size ofvertebrae from modern speci 20th-century records of adult bluefin original hunters. Aboriginal North mens ofknown length with the size tuna in the northeastern Pacific. Ar cheological evidence suggests that ei Americans of this area (part of the of vertebrae collected from archeo ther perturbations in the distribution so-called "NorthwestCoast" culture logical deposits. The resulting of Pacific bluefin have occurred rela region) were accomplished seamen length estimates were then used to tively recently or the specific environ and skilled hunters ofmarine mam calculate weight and age estimates mental conditions favoring the move mals (Mitchell and Donald, 1988). by using length-weight algorithms ment of large tuna into northeastern Pacific waters have not occurred in this Coastal archeological sites through derived from recent data. Data are century. out this region often contain abun presented in a manner that should dant skeletal remains of the many facilitate the analysis of any addi fish andmarinemammal species that tional archeological specimens sustained human populations over recovered. thousands of years (Calvert, 1980; In addition to the results of the Huelsbeck, 1983; Mitchell, 1988). analysis of the archeological mate Skeletal remains oflarge bluefin rial, anecdotal evidence is presented tuna have been recovered from 13 from ethnographic accounts oftuna archeological sites. The archeologi fishing methods related by native cal deposits containing tuna date elders of the Mowachaht tribe who from at least 5,000 years ago until live on the west coast of Vancouver the early 20th century. The exist Island. These recent oral accounts ence of bluefin tuna remains from substantiate and augmentthe physi this region have been previously cal evidence: they describe bluefin reported (McMillan, 1979), butnone tuna ethology, pinpoint the time of were systematically analyzed until year that bluefin tuna were present now. and confirm that large bluefin tuna Forthis study, 78 intactvertebrae were being harvested in the north from 8 archeological sites were mea eastern Pacific until the late 19th sured and the data compared with century. The historic evidence for Manuscript accepted 4 September 1996. those from vertebrae of modern bluefin tuna occurrence in this area, Fishery Bulletin 95:11-24 (1997). specimens (specimens from the re- although sparse, is also presented. 12 Fishery Bulletin 95( 1). 1997 The archeological evidence and ethnohistoric ac probably do not return to the western Pacific every counts are significant because ofthe absence ofmod year but rather spend variable lengths oftime in the em records for adult bluefin tuna in the northeast eastern Pacific (Bayliff, 1994). ern Pacific. Consequently, the distribution ofnorth Most harvested adult bluefin tuna are caught in ern bluefin tuna ofall age classes in the Pacific and the western Pacific, where they are known to range all modem records for adults in the eastern Pacific as far north as the Sea of Okhotsk at about 500N are reviewed. The addition ofhistorical information (Bayliff, 1980). Catch records of large bluefin tuna presented here to our present state of knowledge of are noted at feeding areas offnortheastern Honshu, modem bluefin tuna distributions has important Japan (ca. 400N), off eastern Taiwan (about 25°N), implications for our understanding of changing en and in the central Pacific near the Emperor Sea vironmental conditions over time and perhaps also mount (400N, 175°E) (Nakamura, 1969), for determining the impact of20th-century fisheries Adultbluefin tuna are considered rare everywhere on Pacific bluefin tuna populations. in the eastern Pacific; sporadic records have come from southern California and northern Mexico only. Although small bluefin tuna (less than 120 cm total Distribution of Pacific bluetin tuna iength [TL] and 5-45 kg) are caught regularly off California and Mexico and somewhat larger fish The distribution ofnorthern bluefin tuna in the Pa (120-160 cm TL and 45-80 kg) occasionally, adults cific is somewhat enigmatic, especially that of the over 160 cm TL (80 kg) are seldom encountered (Fore adult portion of the population (Foreman and man and Ishizuka, 1990; Bayliff, 1994). Ishizuka, 1990; Bayliff, 1994; Smith et aI., 1994). In the northern portion ofthe eastern Pacific. few Sexual maturity in Pacific northern bluefin is modem records exist for bluefin tuna. Neave (1959) reached at about 5 years, and most spawning is re mentioned three occurrences in British Columbia ported between April and July in waters off Japan waters duringAugust 1957 and 1958, but no sizes or and the Philippine Islands, and inAugust in the Sea numbers were given. These reports came from an of Japan lBayliff, 1994). Northern bluefin tuna are area approximately 200-400 miles offthe west coast transoceanic migrators in both the Atlantic and Pa ofVancouverlsland(49°N, 134°24'W;48°N, 131°06'W; cific; the movements ofthese fish are largely deduced 51°N, 130oWl. A 7.5-kg bluefin tuna was caught in a by tagging experiments and catches of various age salmon seine in July 1958, near Kodiak, Alaska, and classes at specific times and locations (Nakamura, on 1 October 1957, bluefin tuna were sighted 8D 1969; Rivas, 1978; Bayliff, 1994). 100 miles off Cape Flattery, Washington (Radovich, Some ofthe population ofPacific bluefin tuna mi 1961 I. Sea-surface temperatures off the British Co grate from the western to the eastern Pacific Ocean lumbia coast were reported as being warmer than during their first or second year. The proportion of usual during both years. the population that undertakes this migration ap I presume (because no sizes are mentioned in the pears to vary from year to year (Bayliffet aI., 1991). reports) that these recent northern records are for These migratingfish spend a period ofone to sixyears relatively small fish of 5-45 kg because this size in the eastern Pacific, a sojourn which mayor may range is the most common in the eastern Pacific. not be interrupted by visits to the central or western Bluefin tuna larger than 45 kg in the eastern Pacific Pacific before the survivors return to spawn in the are rare enough that they are noteworthy when en west (Bayliff, 1994). Adult fish in the Pacific appear countered. Although the earliest modern record of a to follow a general pattern of being distributed far very large bluefin tuna in southern California ap ther to the west during the spring (when spawning pears to be that of 1899 (Holder. 19131, sporadic oc occurs) and farther to the east in the fall (Bayliff, currences of bluefin tuna over 50 kg have been re 1993). ported since then <Dotson and Graves. 1984; Fore It is not known if all fish return to spawn every man and Ishizuka, 1990). year after sexual maturity is reached. Tagging ex The largest reported catch ofgiant bluefin tuna in periments indicate that although the journey from the eastern Pacific was made in 1988 (Foreman and west to east may take 7 months or less, the journey Ishizuka, 1990). Seiners caught an estimated 987 from east to westtakes nearly 2 years; therefore there adult bluefin tuna between November and early does not appear to be enough time for mature adult January offsouthern California, including many over fish migrating from the eastern Pacific to spawn in 100 kg and some more than 250 kg, including one the west every year. In addition, because a few adult that broke California records at 458 kg and 271.2 fish have been captured in the eastern Pacific either cm TL. Seiner operators involved in this fishery re justbefore orafter the spawning season, some adults ported that large bluefin tuna travelled in small Crockford: Archeological evidence of Thunnus thynnus off British Columbia and northern Washington 13 schools of less than 10 similar-size in _J't3l!"'\, ,( 20 131.0 130~, .... 1290 1280 1270 1260 ,.1 ",::j2~,o 1230 122° dividuals, often less than 5 for very large ", .", .\.':::c-.-f=C:''':'-' 5SO.

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