A CONTRIBCTION TO THE LIFE HISTORIES OF COMMERCIAL SHRIMPS (Penaeidae) TN NORTH CAROLINA1 AUSTIN B. WILLIAMS University of North Carolina Institute of Fisheries Research. Morehead City, North Carolina ABSTRACT This paper reviews the estuarine portion of the life histories of Penaell.l' setiferus, P. duorarlll1l and P. aztecus in North Carolina. After larval migrations from spawning places at sea, the young enter estuaries as benthonic post-larvae. P. setiferus is judged to grow 36 mm, P. duorarlllll 52 mm, and P. azteclls 46 mm per month in brackish nursery areas during the warmer months. Juveniles gradually move toward the sea as they approach mature sizes. P. aztecus recruitment is greatest in May. The earliest recruits reach commercial size by July. No juveniles and few adults overwinter in N.C. P. duorarum recruitment extends from June to October. The earliest recruits reach commercial size in autumn, but the remainder overwinter and attain commercial size in spring. Mature adults occur in the littoral zone prior to the recruitment period. P. setiferlls recruitment occurs chiefly in June. The young attain commercial size by late summer. A sparse population of adults overwinters in the littoral zone. These are sexually mature in spring. A number of ecological factors in the nursery areas are discussed. Thc role of interspecific competition for nursery areas is considered. P. azteclls and P. duorarul1l occupy these areas at different times. P. setiferus may compete with both of these species for nursery ground. INTRODUCTION The purpose of this paper is to outline the portions of the life histories of Penaeus setiferus (Linn.), P. duorarum Burkenroad and P. aztecus Ives which occur in estuaries extending from Onslow Coun- ty to Hyde County, North Carolina (Fig. 1). Two factors make this region an especially favorable place for these life history studies. First. the North Carolina penaeid shrimp fishery is the most northern one on the Atlantic coast of the United States. Although penaeid shrimps range north of North Carolina, occasiomilly to the southern shore of Massachusetts in summer, this fishery is probably near the northern limits of the breeding ranges for the different species. (Penaeid shrimps are present in Chesapeake Bay but trawling in the Bay is prohibited.) If any special adaptations in the life histories of the species are imposed by the northern geographic limits of the breeding IContribution No. 38 from the University of North Carolina Institute of Fisheries Research. Morehead City, North Carolina. 19551 Williams: Commercial Shrimp 117 ranges, they could be expected to be apparent here. Second, because of an unusual coastal geography, North Carolina has the largest sounds on the southeast coast of the United States. These large shallow sounds with their numerous tributaries provide abundant nursery areas for young shrimps. ". n' ,. UNIVERSITY OF NORTH CAROLINA INSTITUTE OF FISHERIES RESEARCH I'AL.I ••• •••••••• ••~•••1!"•• ... .', o c ... FIGURE J. Twenty-one eastern counties of North Carolina with associated coastal features. Shaded area indicates approximate extent of commercial shrimping grounds. White letters in solid circles indicate localities along western shore of Pamlico Sound from which samples of juveniles were taken in 1953 (see also Tab. r). HISTORICAL The past 30 years have been a period of great advancement in knowledge of penaeid life histories throughout the world. The life histories of penaeids which occur in waters adjacent to the south- eastern and southern United States have attracted special interest since the early 1900's, but of the three species which compose the bulk of American Atlantic commercial catches (Penaeus setiferus, P. duo- 118 Bulletin of Marine Science of the Gulf and Caribbean l5(2) rarum and P. aztecus), P. setiferus has received the most attention. Information on life histories of P. duorarum and P. aztecus is in the form of scattered notes and observations, or is listed under the name of P. brasiliensis with which these forms were formerly confused. For the purposes of the study at hand, mention of the recent litera· ture is deemed sufficient. Spaulding (1908) and Viosca (1920, 1923) were among the first to study Penaeus setiferus life history in Louisi- ana. Weymouth et al. (1933) contributed to the life history of P. setiferus in the Gulf of Mexico and along the coast of the southeastern United States. Burkenroad (1934, 1939) made systematic contribu- tions with notes on reproduction and life histories. Pearson (1939) contributed a detailed study on early stages in the life history of P. seti/erus and other species. King (1948) published results of histologic work on the reproductive organs of P. setiferus. Further life history data were supplied in a summary by Anderson et al. (1949) and by Burkenroad (1949). Gunter (1950) reported additional life history data. Broad (1950, 1951a) gave information on adult shrimps in North Carolina, and Heegaard (1953) discussed larval stages of P. setiferus. Various penaeid life histories, or portions of life histories, have been treated by Hudinaga (1942) in Japan, Dakin (1938, 1940, 1946) in Australia, Heldt (1938) in North Africa, Gurney (1944) in Bermuda, Menon (1952) along the southwest coast of India, and Morris and Bennett (1952) in Australia. MATERIAl.S AND METHODS The life histories of organisms such as these which pass through stages characterized by great changes in appearance, size, habit and residence, must of necessity be studied by various means. The work in North Carolina has been carried on in two phases. First, during the years 1948-1951, study was concentrated on the adult shrimp popu- lation and its relation to the commercial fishery. Second, as the in- vestigation progressed, its scope was broadened to include other phases of the life histories, and recently study has been concentrated on the juveniles. The entire investigation has consisted, in large part, of length-frequency studies with accompanying observations on the ecol- ogy of the species. Adults. Broad (1951 b) stated that from 1948 to 1951 the collected materials consisted chiefly of adult shrimps taken from commercial catches as they were landed at fish houses along the coast. Localities 1955] Williams: Commercial Shrimp 119 from which the catches came were established as closely as possible by questioning the skippers of the trawlers. In addition to samples from fish houses, other collections were made with standard commer- cial shrimping gear in various localities at irregular intervals with the lise of the Institute research vessel. All shrimps taken in these manners came from two generalized areas (Fig. 1): (1) the inside waters, sounds, bays and rivers inside the long chain of barrier islands, and (2) from the outside waters, that is, from the ocean outside the barrier islands. Most of the samples were taken during the shrimping season in spring, summer and fall from both inside and outside waters with commercial shrimp trawls which had a mesh size of "VB to 114 in. bar mesh. The relatively few winter samples were taken chiefly by fishing trawlers working offshore in deeper waters with trawls which had a mesh size of 1 to 2 in. bar mesh. The commercial catches were sampled by taking double handfuls of unheaded shrimps from several different locations on the heading tables when the shrimp boats unloaded at the fish houses (Broad 195Ib). All individuals in small catches made with the Institute boat, and all individuals taken by fish trawlers in winter were measured. The total length of the shrimps from tip of rostrum to tip of telson was used as a measurement of size and an index to age, and these lengths were recorded to the nearest millimeter according to species and sex. Juveniles. From November, 1951 through 1953, the samples con- sisted almost entirely of juvenile and young adult shrimps taken from the shallow portions of tidal creeks, bays and sounds. The collections of juvenile shrimps were made with a beam trawl. This trawl was equipped with an oak beam 1'VB in. by 2:Y§ in. by 4]/2 ft., and with runners made of ]/2 in. by 2 in. strap iron approximately 1 ft. high. The bag and cod end were made of 14 in. bar mesh. A tickler chain was fastened between the lower sides of the runners. The trawl was towed from a skiff powered with either a 7 Y2 or a 10 horsepower outboard motor. Nearly all of the materials taken in this trawl were washed through a set of three graduated nesting screens. This combi- nation of fine net and screens was quite efficient in straining out small organisms. All of the shrimps caught were measured in the same manner as the adults. The greater part of this material was taken from fixed localities. Fixed localities were deemed necessary because they formed a basis ]20 Bulletin of Marine Science of the Gulf and Caribbean 15(2) for making comparisons among collections through the seasons, and through any successive years that the study might continue. The pri- mary objectives of this phase of the work were to determine: (1) the location of the nursery areas; (2) which species used the nursery areas; (3) when the different species occupied the nursery areas; (4) where the various growth stages were spent; (5) species preferences in habitat; (6) the growth rates of the species. To collect this informa- tion as rapidly as possible, the survey had to cover a broad choice of ecological situations within a limited area. Fortunately, Carteret and Onslow Counties offered a broad selection of habitats at localities within a few miles of the laboratory. To accelerate the program, the sampling gear was hauled in a trailer to the severaL localities, and all work accomplished from rented skiffs. The localities were further defined by establishing fixed stations in a variety of physical situations within the general locality, and by the institution of a standard tow of 200 yds.