Survival and Growth of Cut Vs Hooked Commercial Sponges in the Florida Keys
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Survival and growth of cut vs hooked commercial sponges in the Florida Keys Item Type monograph Authors Stevenly, John; Sweat, Don Publisher Florida Sea Grant College Download date 27/09/2021 22:47:01 Link to Item http://hdl.handle.net/1834/18012 Technical Paper No. 38 Survival and Growth of Cut vs Hooked Commercial Sponges in the Florida Keys by John Stevely and Don Sweat I"U)RIM =A GRANT COLL€G€ StEVIXU AM) GRCWTH OF CUT vs . HOOKED COMMERCIAL SPONGES IN THE FU3RIDA KEYS John Stevely and Don Sweat Florida Sea Grant Extension Program 117 Newins-Ziegler Hall University of Florida Gainemille, FL 32611 Project No. IR-82-15 Grant No. NA8OAA-D-00038 Technical Papers are duplicated in limited quantities for specialized audiences requiring rapid access to infonoation. They are published with limited editing and without formal review by the Florida Sea Grant College Program. Content is the sole responsibility of the author. This paper was developed by the Florida Sea Grant College Program with support frcm NQ7Ul Office of Sea Grant, U.S. Department of Ccmnerce, grant nwlber NA8OAA-D-00038. It was published by the Sea Grant Extension Program which functions as a aanponent of the Florida Cooperative Extension Service, John T. Woeste, Dean, in conducting Cmpxative Extension work in Agriculture, Hme Economics, and marine Sciences, State of Florida, U.S. Department of -ce, and Eoards of Cormty Ccmaissioners, cooperating. Printed and distributed in furtherance of the Acts of Congress of May 8 and June 14, 1914. The Florida Sea Grant College is an Equal Rployment-Affinoative Action employer authorized to provide research, educational infonoation and other services only to individuals and institutions that function without regard to race, color, sex, or national origin. TECHNIC& PAPER NO. 38 September 1985 INTRODUCTION Until the 19401s, the sponge fishery was one of the most valuable fisheries in Florida. However, a combination of the sponge blights of 1939 and 1946 and the introduction of synthetic sponges resulted in reduction of the fishery to a small fraction of its former importance (Stevely, --et a1 ., 1978). In recent years, increasing scarcity of sponges in the sponge beds off of Tarpon Springs has threatened the continued existence of the remaining Tarpon Springs sponge fleet. Although an exploratory sponge fishing survey of state territorial waters off of Monroe County (Florida Keys), Florida, had indicated that commercial quantities of sponges were present (Sweat and Stevely , unpubl ished man- uscript), Florida Statute (F.S. 370.17) prohibits use of "deep sea diving apparatus to harvest sponges in this area." This Statute states, "No person may use diving suits, helmets, or other apparatus used by deep sea divers in taking commercial sponges from any waters within the territorial limits of this state." The purpose of the law was .not to prohibit reasonable methods of harvesting sponges but to protect young sponges. It was enacted to prevent damage to young sponges caused by heavily weighted divers stepping on them. Early sponge diving gear was of the deep sea variety. Scuba and hookah, common gear today, did not become a viable method of extended underwater diving until many years after enactment of the law. Light hookah gear with rubber-soled, canvas athletic shoes has now replaced the heavy helmet and lead boot-clad diver. The Florida Saltwater Fisheries Study and Advisory Committee recommended in 1982 that sponge diving be allowed in the state territorial waters off Monroe County. However, objections were raised concerning the possibility of overfishing due to increased fishing pressure following legalization of sponge diving. Therefore, the present project was undertakeil for the purpose of establishing whether a change in harvesting technique -- cutting rather than tearing the sponge loose -- could insure sponge regeneration and thus reduce the possibility of overfishing. Sponges have remarkable regenerative ability; and if even a small quantity of sponge material is left attached to the substrate, the sponge may survive and grow back to a commercially valuable size. METHODS AND MATERIALS During June, 1982, a commercial sponge fisherman assisted the project by locating a bed of sheepswool sponges (Hi ppiospongi a lachne) off of Vaca Key (Marathon) in the Florida keys (Fig. 1). The site was marked with a buoy, and Loran C coordinates were recorded to insure relocation of the study site. The bottom of the site was marked off by laying out a grid of polyethylene line held in.place. by rebar stakes driven into the substrate. Sponges were located by swimming along the grid lines. Upon locating a sponge, its position was marked by attaching a piece of brightly colored surveyor's flagging tape to the line. The position was also recorded on a plastic chart of the grid pattern. Large calipers (S & S standard radiological ) were used to take two measurements of the sponge's diameter and one measurement of the sponge's hei ght. After being measured, alternate sponges were either cut loose using a large, sharp knife or torn loose with a sponge hook on the end of a three- foot handle. Sponges were cut as close to the substrate as possible while attempting to leave a complete sponge base. In practice, this left 1/2 to 1 inch of sponge tissue. The sponge hook was of the type used by commercial sponge divers. When the sponge was removed, the type of harvesting method used was recorded and measurements taken of the remaining sponge base (if there was any left). The exact location of each sponge was marked by driving a rebar stake into the substrate. A numbered, plastic bird band was wrapped around these stakes for identification. Also, in those cases where sponge base was left behind, the sponge base was marked by "sewing" a piece of monofilament line through it and then attaching a plastic bird band. Ten sponges were staked and tagged to serve as a control group. Growth and survival data for experimental and control sponges were collected 12 months (May '83) and 28 months (Nov. '84) after the study was begun. RESULTS Survival of Cut and Hooked Sponges A total of 69 sponges were either cut (N=35) or hooked (N=34). Approximately one-thi rd of a1 1 the study sponges (control, cut, hooked) were not found by the end of the experiment for a variety of reasons which are discussed (Fig. 2). The percentages of found sponges for each group of sponges were not significantly different (G-test; Sokal and Rohl f, 1969). Twelve months after the study began, 70% of the found cut sponges were alive and 39% of the found hooked sponges were alive (Fig.3). The percentage of surviving cut sponges compared to that of surviving hooked sponges was significantly different (G-test; P<.05). Twenty-eight months after the study began, 71% of the found cut sponges were alive and 41% of the found hooked sponges were alive (Fig. 3). Again, the proportion of surviving sponges between the treatments was significantly different (G-test; Pc.05). The slightly higher percentage of surviving cut and hooked sponges found at 28 months compared to 12 months was not significantly different and can be attributed to sampling error. Since fewer sponge sites were found at 28 months (Fig. 2.), the sample size used to calculate percentages of surviving sponges was smaller (number of found cut and hooked sponge sites was 55 at 12 months and 47 at 28 months). On both sampling dates, 100% of the found control sponges were a1 ive. The percentage of surviving found control sponges was significantly different from the percentage of surviving found cut and hooked sponges (G-test; P<.05). Growth of Experimental and Control Sponges Average increase of the maximum diameter of the cut sponge bas was 2.3 cm. (range: -1.5 to 5.0 cm.) after 28 months. Average increase of the maximum diameter of the hooked sponge base was 2.1 cm. (range 0.0 to 4.00). Only a small number of surviving cut sponges (7, or 39%) and hooked sponges (3, or 33%) were judged to have regrown to a commercial size. Whether sponges had or had not grown to a commercially harvestable size was a qual- itative judgement. Although most of the surviving sponge bases had grown to the point of exceeding 12.7 cm. (to be legal size a sponge must have, when wet, a maximum diameter of at least 12.7 cm), they had not yet grown in height sufficiently enough to be judged as a truly commercially valuable product by the authors. Therefore, only sponges which could be crudely estimated to have attained a height of at least 7.6 cm. were considered as commercial-sized sponges. However, there is no legal requirement for a minimum sponge height. The average natural growth rate of control sponges monitored during the study (7 of the 10 original controls were found at the end of the study) was 1.7 cm./year. DISCUSSION Survival of Cut and Hooked Sponges This study shows that both cut and hooked sponges can successfully regrow to a commercially harvestable size. However, cut sponges have a substantially higher chance for survival and consequently have a higher chance for regrowth to a commercial size than do hooked sponges. The higher survival rate of cut sponges can be attributed to the fact that cutting insures that some sponge tissue is left attached to the substrate. Sponge tissue is sometimes left behind when hooking the sponge; but often when the sponge is torn free, very little tissue is left. If sufficient sponge tissue is not left, sediment can easily smother the remaining sponge tissue.