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Yellowfin feed primarily on fishes smaller than themselves, such as flying fish, sauries, and sardines, and on invertebrate animals of the plankton such as copepoda, shrimps, crab larvae, spiny lobster larvae and squid and other mollusks.
Yellowfin range in size up to several hundred pounds, although these largest fish are seldom seen. Those taken in the catch average from 30 to 40 pounds. Little is known of the spawning habits of this tuna. Along our coast none has been found with fully ripe sexual organs. However, specimens have been taken off Central America with ripe ovaries, and very small juveniles were collected in the same area by Fish and Wildlife Service biologists in the early spring months. Observations also indicate that this species spawns in the Marshall Islands.
Although yellowfin are taken by both purse seiners and boats fishing with live bait, the latter bring in the greater part of the catch. The bait boats, or tuna clippers, are the largest registered fishing vessels in California and are equipped to stay at sea for extended periods of time and scout for fish at considerable distances from port. As a result a large percentage of the total landings of yellowfin is taken south of the international boundary, partly in Mexican waters and partly off the Central American coast.
Yellowfin is used almost entirely for canning, and is only occasionally found in the fresh-fish market. The canned product is of excellent quality and is marketed as "light meat tuna."
Since 1926, the yellowfin catch has exceeded that of any other single species of tuna and since 1918, has brought the fishermen from $10 to $20 more a ton than any of the other tunas with the exception of albacore. In 1917, the first year for which records are available, yellowfin brought $50 a ton, while fishermen received only $30 per ton for albacore. Since that time-the price of yellowfin has slowly increased until during the 1947 season, these fish command from $310 to $340 per ton. For the period from 1943 to 1947, yellowfin made up approximately 49 percent of the total catch of the west coast tuna fishery.
BIG-EYED TUNA-Parathunnus sibi
This tuna is very similar in appearance to yellowfin, differing slightly in outline, size of head, length of pectoral, size of eye and internal characteristics. These are occasionally taken at the Galapagos Islands and sometimes at Guadalupe Islands and vicinity. It is difficult to determine what part of the catch in any one year is made up of big-eyed tuna, but it is probably negligible and would be included with the yellowfin in published records.
BLUEFIN TUNA- Thunnus thynnus (also called horse mackerel, tunny, leaping tuna, great tunny)
Bluefin tuna is known along the Pacific coast from the Columbia River south to along the coast of Lower California. It also occurs in the Atlantic and there are related species in other parts of the Pacific.
Like the yellowfin, it preys on all small schooling fishes, even bonitos and on invertebrates.
Nothing is known of the migrations or the locations of the spawning grounds in the Pacific. No ripe females have been taken in the California fishery which may last from June to November. Eggs and larvae are known from the Mediterranean. The smallest Pacific fish on record weigh from 6 to 10 pounds. This species is most abundant in June and July and at this time the commercial catch is at its highest. Usually bluefin makes its appearance in the San Diego area, but at times has bypassed San Diego to be taken first near San Pedro.
Little fishing effort was spent on bluefin tuna until 1918 when the purse seine gear became popular in southern California waters. Until that time, bluefin fishing was unprofitable for the fishermen as they found it difficult to catch enough fish to pay for their trips.
The efficiency of the purse seine method combined with the demand for fish during the First World War, resulted in an over 7,000-ton catch in 1919. Until 1930, fish had been taken only in the region from Santa Cruz Island south to the international boundary, but at that time it was discovered that catches could be made around the Guadalupe Islands and the fishing grounds were extended. Large modern refrigerated purse seiners have made fishing at distances away from port even more practical.
The catches of bluefin tuna in California waters between 1924 and 1930 were analyzed using the average catch per month as the most accurate criterion of fishing success. It was concluded that although no assumption could be made that the entire population had remained the same, the availability to the fishermen had remained relatively constant and no protective legislation was needed at the time.
For the period from 1943 to 1947, bluefin tuna made up 10 percent of the total catch of the west coast tuna fishery.
ALBACORE Thunnus germo (also known as abrego, long-finned tuna)
This is one of the smallest of the tunas in size, rarely exceeding 80 pounds in weight. It is found along the Pacific coast from British Columbia southward to Lower California, generally in the open sea. In some years it may be taken at any time along the California coast, but it usually appears during the warmest months. Although albacore is taken commercially from June through December, the period of maximum abundance is during July and August.
This species is considered to be the most desirable of the tunas by the canners and is packed as "white meat tuna." The catch is almost entirely disposed of to canneries, only an occasional fish appearing in the fresh fish market.
Until 1936, the fishery had been confined to the California coast but in that year the fish appeared off the Oregon coast in abundance; a fishery started there and since has spread north to British Columbia. The landings have fluctuated widely from year to year and, beginning with 1926, were virtually nothing for a 12-year period.
Albacore is usually throught to migrate over great distances, perhaps even across the Pacific, and during the years that it was scarce on our coast, it was plentiful in Hawaii and Japan. Little is known of the spawning and breeding grounds. Although Pacific albacore with ripe eggs had been taken in Hawaii, it has never been found in this condition off either the American or Japanese coasts. The Oregon Fish Commission has found in studies made on the Pacific albacore that the population visiting the west coast of the United States and also Japan is composed entirely of two or three ages of fish and rarely if ever includes any very young or very old fish. This fish, like the yellowfin and bluefin, feeds on small schooling fish, on squid and small animals of the plankton.
For the period from 1943 to 1947, albacore accounted for about 19 percent of the total catch of the west coast tuna fishery.
OCEANIC SKIPJACK-Katsuwonus pelamis (also known as oceanic bonito, striped tuna skippy)
This is the smallest of the tunas, rarely exceeding 25 inches in length. On the Pacific coast it is found from British Columbia to the Galapagos Islands and probably to the south. This species is probably more abundant than yellowfin. The greater part of the catch is taken south of California off Mexico and Central America. Skipjack is not found off California every year and it is presumed that it appears only when temperature, food, and other physical conditions are suited to its needs. When it does appear in California waters, it is usually from August to December.
Fish and Wildlife Service biologists have found that this species spawns off Central America and in the Marshall Islands, but otherwise little is known of their spawning habits.
Skipjack, like yellowfish, is taken primarily by the bait boats, but also by purse seiners. These two species have similar habits and distribution and often school together. Skipjack is generally taken only when yellowfin is not available, as yellowfin commands a higher price and also keeps better for long periods of time, when iced in the hold.
For the period from 1943 to 1947, skipjack made up about 19 percent of the total west coast tuna catch.
BLACK SKIPJACK-Euthupnus lineatus (also called cross-bred mackerel)
This species is found off the west coast of Lower California as far as Cape San Larazo at Los Frailes, along both coasts of the Gulf of California and off the coasts of Mexico and Central America to the Cocos Island. Little is known of the life history of this fish, although a spawning region has been found off Central America. The flesh of this species is darker than that of the other tunas and it is not at present utilized commercially. It will probably be at some later date.
BONITOS-Sarda sp. (also called skipjack, striped tuna)
There are three species of bonito on the Pacific coast, the California bonito (Sarda lineolata), Mexican (Sarda velox), and Chilean (Sarda chilensia).
Only the first two are landed in California. These fishes are apparently less migratory than the tunas and seem to be more localized in their distribution. Bonito are not in great demand by the canneries and are considered to be inferior in quality to the tuna. As a result, during the period from 1943 to 1947, only 3 percent of the catch of the west coast tuna fishery was made up of bonito. ably only a small fraction of the resources is being taken.
CALIFORNIA bONITO-Sarda lineolata
This fish attains a weight of about 6 to 8 pounds and has been found at one time or another from Puget Sound to along the coast of Lower California. It is most abundant between Santa Barbara and Magdalena Bay. Investigation has shown that it spawns during late spring and summer from close inshore to as far out as 80 miles. This is a predatory fish and travels in the open sea in schools in pursuit of smaller fishes and invertegrate animals.
MEXICAN BONITO-Sarda velox
This species is about the same size or a little larger than the California bonito and is found from Magdalena Bay southward.
Considerable quantities of small schooling fishes are taken every season by the tuna clippers for use as yellowfin and skipjack live bait. No accurate records are kept of the amount or species taken.
The principal species taken are sardines, Sardinops caerulea, and anchovies, Engraulis mordax and Anchoviella compressa off California; and anchovettas, probably Catengraulis mysticetus and thread herring, Opisthonema libertate, farther south.
These bait fishes are not distributed uniformly along the coast. part of the bait that is taken off the California coast comes from the vicinity of San Diego where small sardines and anchovies are relatively abundant. Small sardines are also taken along Lower California at Ensenada, San Quentin, in Sebastian Viscaino Bay, Turtle Bay, and Magdalena Bay. Almejas Bay, in inlet of Magdalena Bay, is the most northerly region of abundance of the anchovetta.. Guaymas and Kino Bay furnish the right bait grounds off the Gulf of California. From Magdalena Bay southward to the Gulf of Nicoya, only the Gulf of Fonesca supplies bait in at all dependable quantities. The other two highly reliable bait grounds are located in the Gulf of Nicoya and the Gulf of Panama. There are, of course, many other grounds up and down the coast fished less regularly. The Galapagos Islands supply various species of bait in limited amounts, but boats fishing there usually attempt to secure a full load of bait from the mainland.
Since no records are kept of the amount of bait taken, a rough estimation of the quantity has been made. Data from 1926 on are available in published Fish and Wildlife Service records on the amount of skipjack and yellowfin taken by line (mostly bait boats) and these amounts are divided by region of catch (north or south of the international boundary). By using an estimated value of 25 scoops of bait for each ton of fish taken and another estimated value of 10 pounds of fish per scoop of bait, the number of pounds of bait used during a season was calculated. The resulting figures given in table 5 show the amount of bait used north of the international boundary and south of the international boundary.
TABLE 1.-Total Pacific coast commercial tuna landings 1
1 Data from published California Fish and Game records and from Pacific Fisherman.
2 Probably bluefin.
4 Less than 500 pounds.
TABLE 2.-Total Pacific coast commercial tuna landings, showing origin of catch 1
1 Data from published California Fish and Game records, published by United States Fish and Wildlife Service records, and from Pacific Fisherman yearbooks. 2 Caught north of the international boundary.
3 Caught south of the international boundary, probably all off Mexico, with the exception of skipjack and yellowfin.
♦ Probably bluefin.