Young Scombroids from the Waters Between Cape Hatteras and Bahama Islands

YOUNG SCOMBROIDS FROM THE WATERS BETWEEN CAPE HATTERAS AND BAHAMA ISLANDS

W. L. KLAWE Inter-American Tropical Tuna Commission La Jolla, California

ABSTRACT A collection of young scombroid fishes made by the United States Fish and Wildlife Service in 1953 and 1954 in the waters between Cape Hatteras and the Bahama Islands contained 50 specimens. These fish are either from stomachs of six species of pelagic fishes or from collections made with dip- nets. The following genera and species were represented: (1) Thunnus atlanticus, (2) Katsuwonus pelamis, (3) Euthynnus alletteratus, (4) Auxis thazard, (5) Sarda sarda (6) Thunnus sp. indet., and (7) Scomberomorus sp. indet. It is inferred that the time of spawning of the various species of scornbraids from that area conforms with the time of spawning in the southern portion of the Florida Current and in the Gulf of Mexico.

INTRODUCTION Since 1952 the United States Fish and Wildlife Service has collected a considerable amount of biological, physical and chemical data in the Florida Current from Cape Hatteras to the area of Bahama Islands (Anderson et al., 1956a and 1956b; Anderson and Gehringer, 1957a and 1957b, 1958a and 1958b, 1959a and 1959b, and 1959c). In the course of these activities numerous collections of young fishes resulted. Recently the author has had the opportunity to examine some of the scombroids from these collections. This paper summarizes the results. I wish to thank Mr. William W. Anderson of the Bureau of Com- mercial Fisheries, U. S. Fish and Wildlife Service, for the loan of the young scombroids from collections of the South Atlantic Fishery In- vestigations. Permission to publish my findings was kindly granted by the Director, Bureau of Commercial Fisheries, U. S. Fish and Wildlife Service.

METHODS AND MATERIAL The material originates from collections made by U. S. Fish and Wildlife Service personnel between May 1953 and December 1954 aboard M. V. Theodore N. Gill. The fish come either from stomachs of large pelagic fish caught on a troll or from collections made with a dip-net. The latter method consists of dipnetting small fish which ag- 1961] Klawe: Young Scromboids 151 gregate around sargasso weed or which at night are attracted by an electric light suspended over water from an anchored or drifting vessel. Table I lists the stations at which young scombroids were taken, together with details as to the place and method of capture. The specimens, which had been preserved in formalin, were ex- amined under a binocular miscroscope and were dissected or stained as necessary for identification. The standard method for staining of bony parts has been employed, with alizarine red used for staining and potassium hydroxide and glycerol used for clearing (Clothier, 1950). Gill-raker counts, where possible, were made on the first arch, from the right side of the fish. Some of the material from the stomach contents was so far digested that these counts could not be made. The measurement of total length represents the direct distance from the tip of the snout to the tip of the shortest median ray of the caudal fin. For identification such criteria as general shape, pigmentation and meristic characters were used. For fish digested to a large extent the following characters proved to be most useful: (1) total number of vertebrae, (2) number of thoracic and caudal vertebrae, (3) position on the vertebral column of the vertebra with first closed haemaJ arch, and (4) gill-raker counts. For convenience the nomenclature of Rivas (1951) has been fol- lowed, with the exception of employing Thunnus albacares in place of T. argentivittatus for the Atlantic yellowfin tuna. RESULTS identified scombroids. There is present in this collection a total of fifty young scombroid specimens; including the following genera and species: Thunnus atlanticus, Katsuwonus pelamis, Euthynnus alletteratus, A uxis thazard, and Sarda sarda. In addition; a number of young forms were recognized as Thunnus and Scomberomorus but could not be assigned to species, as will be discussed later. Blackfin tuna, Thunnus atlanticus There are four blackfin tuna ranging in total length from 58 to 99 mm. All individuals originate from stomach contents (Table 1). These fish were caught in June and October. The gill-raker counts for these fish are as follows: Total length Gill rakers 58 mm. 6+1+17 96 mm. 6+1+15; 7+1+16 99 mm. 6+1+16 152 Bulletin of Marine Science of the Gulf and Caribbean [11 (1)

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Oceanic skipjack, Katsuwonus pelamis This species is represented by 20 individuals ranging in total length from 25 mm to 69 mm. All specimens originate from stomach contents of four adult oceanic skipjack, which were captured on 5th December 1954, in the general area 33°00' N, 76°40' W (Figure 1). Some of the fish were digested to such an extent that it was impossible to establish the number of gill rakers for all twenty individuals. The following are the gill-raker counts which were made. It should be pointed out that, due to digestion, many of the total lengths could be only estimated.

Total length Gill rakers Total length Gill rakers 25 mm 4+1+20 44 mm 7+1+31; 8+1+33; 9+1+35 29 mm 4+1+25 48 mm 7+1+33 35 mm 5+1+27 49 mm 8+1+31 38 mm 4+1+29 50 mm 8+1+35; 9+1+35; 9+1+3b 42 mm 5+1+33 54 mm 9+1+33 69 mm 10+ 1+36 From the foregoing, it appears that the full gill-raker complement is attained in Katsuwonus pelamis at a larger size than in closely re- lated Euthynnus aLLetteratusor Auxis thazard (Klawe and Shimada, 1959).

Little tunny, Euthynnus aLletteratus Two individuals of Euthynnus aLletteratus, 25 and 35 mm long, are in this collection. Both originate from the stomach of an adult of the same species which was captured in July (Table 1). 154 Bulletin of Marine Science of the Gulf and Caribbean [11 (I)

75-· 70" 65· .•

30·

* KATSUWONlS PELAMIS tr THUNNUS SP.

Y THUNNUS ATLANTICUS •• EUTHYNMJS ALLETTERATUS • AUXIS THAZARD o SARDA SARDA o SCOMBEROMORUS SP. • UNIDENTIFIED SCOMBROID

25· 75° 70· 65" FIGURE 1. Localities of capture of young scombroids from M.V. Theodore N. Gill collection.

Frigate mackerel, Auxis thazard Two small Auxis thazard, of total lengths 11 and 13 mm, were captured under a night light in May (Table 1) at Station 71, offshore between Charleston, S. C., and Cape Hatteras (Figure 1).

Bonito, Sarda sarda A single 34 mm long individual of Sarda sarda was captured in February under a night light. The gill-raker count for this fish is 3+1+11. Scomberomorus sp. indet. Four fish of total lengths ranging from 20 to 30 mm are present in this collection. All originate from stomachs of two Euthynnus caught in September (Table 1). These fish, although fairly well digested, are not beyond reliable generic identification. Specific identification could not be attempted, as the gill rakers could not be located on the first gill arch and the fish were decalcified to such an extent that no counts of fin rays could be made. 1961] Klawe: Young Scromboids 155 These juveniles could be young of any of the following three species: S. cavalla, S. maculatus, and S. regalis, all of which occur in the area of this investigation.

Spawning habits of scombroid fishes in the Florida Current The importance of young tunas as indicators serving for delineation of areas and seasons of spawning has been discussed by Schaefer (1956), Klawe and Shimada (1959), and Klawe (1960). The last paper is especially applicable, since it deals with the southern portion of the Florida Current. In this case, however, we are dealing with an area where, on the whole, the surface currents are of considerable magnitude (Hela, 1954) and passive transportation of these young fish from some distant place into the area of capture is possible. Rivas (1954) and Klawe (1960) have shown that the southern portion of the Florida Current is a spawning area for some tunas. Whether the same applied to the rest of the Current is difficult to answer. Additional evidence is to be sought in collections of early larvae and eggs of various tunas from plankton tows made in the northern portion of the Florida Current. It is doubtful that the fish in the stomachs of pred- ators could have been brought into the area of capture by ingestion and the subsequent migration of the predator. Although adult tuna and other large pelagic fishes are capable of moving considenlble distances. the rate of digestion of rather soft and small items of food, such as young scombroids, is doubtless quite rapid. Concerning the season of spawning of tunas here, it appears to be similar to that in the southern portion of the Florida Current inferred from studies of the larval material (Rivas, 1954; Klawe, 1960), i.e. spring, summer and fall. From the capture of asingle 34 mm Sarda sarda in February it appears that this species spawns in winter. This is not surprising, as oft Dakar, on the eastern side of the Atlantic, Frade and Postel (1955) indicate that February and March are the times of spawning for that species. In the Gulf of Mexico juveniles of S. sarda have been collected in March (Klawe and Shimada, 1959).

LITERATURE CITED ANDERSON, WILLIAM W., JACK W. GEHRINGER AND EDWARD COHEN 1956a. Physical oceanographic, biological, and chemical data, South Atlantic Coast of the United States, M/V Theodore N. Gill Cruise 1. U.S. Fish and Wildlife Service, Special Scientific Report-Fisheries No. 178, 160 pp. 156 Bulletin of Marine Science of the Gulf and Caribbean [11 (1) 1956b. Physical oceanographic, biological, and chemical data, South Atlant.ic Coast of the United States, M/V Theodore N. Gill Cruise 2. U.S. Fish and Wildlife Service, Special Scientific Report-Fisheries No. 198, 270 pp.

ANDERSON, WILLIAM W. AND JACK W. GEHRINGER 1957a. Physical oceanographic, biological, and chemical data, South Atlantic Coast of the United States, M/V Theodore N. Gill Cruise 3. U.S. Fish and Wildlife Service, Special Scientific Report-Fisheries No. 210. 208 pp. 1957b. Physical oceanographic, biological, and chemical data, South Atlantic Coast of the United States, M/V Theodore N. Gill Cruise 4. U.S. Fish and Wildlife Service, Special Scientific Report-Fisheries No. 234, 192 pp. 1958a. Physical oceanographic, biological, and chemical data, South Atlantic Coast of the United States, M/V Theodore N. Gill Cruise 5. U.S. Fish and Wildlife Service, Special Scientific Report-Fisheries No. 248. 220 pp. 1958b. Physical oceanographic, biological, and chemical data, South Atlanti:; Coast of the United States, M/V Theodore N. Gill Cruise 6. U.S. Fish and Wildlife Service, Special Scientific Report-Fisheries No. 265, 99 pp. 1959a. Physical oceanographic, biological, and chemical data, South Atlanti:: Coast of the United States, M/V Theodore N. Gill Cruise 7. U.S. FiSh and Wildlife Service, Special Scientific Report-Fisheries No. 278, 277 pp. 1959b. Physical oceanographic, biological, and chemical data, South Atlantic Coast of the United States, M/V Theodore N. Gill Cruise 8. U.S. Fish and Wildlife Service, Special Scientific Report-Fisheries No. 303, 227 pp. 1959c. Physical oceanographic, biological, and chemical data, South Atlantic Coast of the United States, M/V Theodore N. Gill Cruise 9. U.S. Fish and Wildlife Service, Special Scientific Report-Fisheries No. 313, 226 pp.

CLOTffiER, CHARLES R. 1950. A key to some southern California fishes based on vertebral char .. acters. Fish Bull., Sacramento, 79: 1-83.

HELA,ILMO 1954. The surface current field in the western part of the North Atlantic. Bull. Mar. Sci. Gulf and Caribbean, 3 (4): 241-272. KLAWE, W. L. 1960. Larval tunas from the Florida Current. Bull. Mar. Sci. Gulf & Carib .. 10 (2): 227-233. KLAWE, WITOLD L., AND BELL M. SHIMADA 1959. Young scombroid fishes from the Gulf of Mexico. Bull. Mar. Sci. Gulf & Carib., 9 (1): 100-115. POSTEL, E. 1955. Contribution a l'Etude des Thonides de l'Atlantique Tropical. Rapp. et Proc.-Verb. Cons. lnt. Explor. Mer, Vol. 137, p. 31-32. 1961] Klawe: Young Scromboids 157

RIVAS. LUIS RENE 1951 A preliminary review of the western North Atlantic fishes of the family Scombridae. Bull. Mar. Sci. Gulf & Carib., 1 (3): 209-230. 1954. A preliminary report of the spawning of the Western North Atlantic bluefin tuna (Thunnus thynnus) in the Straits of Florida. Bull. Mar. Sci. Gulf & Carib., 4 (4): 302-322.

SCHAEFER, MILNER B. 1956. Scientific investigations of the tropical tuna resources of the Eastern Pacific. Papers presented at the International Conference on the Conservation of the Living Resources of the Sea (Rome, 18 April to 10 May, 1955), United Nations, New York, pp. 194-221.