Relative Abundance and Potential of Pelagic Sharks Along Florida's East Coast


Introduction coast. The longline fishery for sary quality (Otwell, 1984) have discour­ in this area, which began in 1975, under­ aged many from retaining Relative abundance and fishery poten­ went a very rapid fleet expansion, and by them. Nonetheless, since the feasibility tial of pelagic sharks were investigated 1980 there were an estimated 200 vessels of harvesting these pelagic sharks is by sampling the shark by-catch aboard engaged in the fishery (Berkeley et aI., largely dependent on the profitability of commercial swordfish, Xiphias gladius, 1981). Landings increased steadily to 3.2 the swordfish fishery, the low ex-vessel longline vessels along Florida's east million pounds in 1980, declining price will not necessarily preclude their slightly to about 3.0 million pounds in exploitation. the early 1980'SI. Fleet size declined to While pelagic sharks may be underuti­ between 50 and 100 boats, although the lized, they are not necessarily underex­ power of these vessels far ex­ ploited. In an analysis of various ABSTRACT-Catch rates, relative ceeded that of the initial fleet (SAFMC, that directly or indirectly catch pelagic abundance, and some biological informa­ 1985a). sharks, Anderson (1985) suggests that tion on various shark species were docu­ Pelagic sharks constitute, by far, the sharks in both the Atlantic and the Gulf of mented during a 2- study of the shark largest component of the incidental catch Mexico may already be overexploited. by-catch ofthe swordfish, Xiphias gladius, in this fishery, generally exceeding the Whether or not this is so, the slow growth fishery off Florida's east coast. A total of 613 sharks composed of 13 species were swordfish catch (Anderson, 1985). Until rates and low reproductive potential of recorded in the study area from September 1981, there was little market for sharks in sharks greatly increase the possibility of 1981 to September 1983. Seasonal trends Florida and, with the exception of the (Holden, 1974), making in the abundance of all sharks combined shortfin mako, lsurus oxyrhincus, nearly careful monitoring of the fishery and the were consistent between with high abundance from September to November all sharks were discarded at . In 1981, resource essential if such problems are to and a secondary peak in February and demand for sharks began increasing and, be avoided. March. Likewise, in both years, night, while the ex-vessel price was still too low Little quantitative information is avail­ signatus; silky, C. fal­ to support a directed fishery ($0.35 ­ able on the distribution, abundance, or cifonnis; and , $0.50/pound dressed weight), it was suf­ of the various species of pelagic Sphyma lewini, sharks dominated the catch, comprising 86 percent of the total ficient to encourage swordfish fishermen sharks found off the southeast U. S. shark catch. to land their by-catch. Since then, de­ coast. Casey and Hoey (1985) present the The annual mean shark CPUE was 4.16 mand has fluctuated considerably, but species composition recorded in the U.S. sharks per 100 hooks set, compared with the ex-vessel price has remained almost recreational fishery in 1978 for the At­ an annual mean swordfish CPUE of 3.67. 1t was estimated that, annually, at least 4.8 constant. In contrast, during the same pe­ lantic south of Virginia. They also sum­ million pounds ofsharks were caught along riod the price of swordfish increased marize the species composition of sharks the east coast of Florida incidental to from an average of $1.75/pound (Cato recorded during an unspecified period on swordfishing during the years ofthe study. and Lawlor, 1981) to perhaps $3.00/ The average annual reported shark land­ pound. This decline in relative value, ings during the same period was only 3.3 The authors were with the Rosenstiel School of percent ofthis estimated catch. Our results combined with the difficulty of landing Marine and Atmospheric , Division of indicated that, for most species, sharks and the careful processing and Biology and Living Resources, University of predominated in the catch and that 89 per­ handling required to maintain the neces- Miami, 4600 Rickenbacker Causeway, Miami, cent ofthese were below their reported size FL 33149. Steven A. Berkeley is presently with at maturity. This, combined with the ob­ the South Atlantic Fishery Management Coun­ cil, 1 Southpark Circle, Suite 306, Charleston, 66 served percent mortality rate of hooked I Unpublished swordfish landings data, corrected SC 29407. The permanent address of Wilfredo sharks, suggests that the development of a and revised at the NMFS Southeast Fisheries L. Campos is P-2 J.C. de Jesus St., Area 17, fishery, directed or otherwise, should pro­ Center Swordfish Stock Assessment Workshop, U.P. Campus, Diliman, Quezon City, Philip­ ceed with caution. Miami, Fla., 16-26 April 1986. pines 3004.

50(1), 1988 9 83· 82· 81· 80· 79· 78· 77° , ,, , Cape Canaveral 310 longline sets in the same area. Ham­ \ ) ,, merhead, spp. was the most , 2 \ 28· commonly captured shark in both ­ \, eries, followed, in the longline fishery, \ FLORIDA by blue, Prionace glauca; sandbar, Car­ charhinus plumbeus; dusky, C. obscu­ ,, 27· 27· rus; blacktip, C. limbatus; and tiger, Ga­ , leocerdo cuvieri. Burgess (1984) ,, , documented species frequently caught in , the inshore and offshore areas off Flor­ ida. Nurse, cirratum; 26· 26· bull, C. leucas, sandbar, and hammer­ sharks were common inshore spe­ cies, while , Alopias su­ perciliosus; mako, spp.; bignose, 25· 25· C. altimus; silky, C. falciformis; night, C. signatus; and oceanic whitetip, C. longimanus, sharks were common off­ shore. Scalloped hammerhead, S. lewini; dusky, and tiger sharks were frequently 24· caught in both areas. Spatio-temporal distribution patterns are more complex than this because most sharks make sea­ /-- --:;OOlm.;. "" .. sonal migrations, both north-south and o a--.,. 23· inshore-offshore, largely related to tem­ <>~---~--,.~~ " perature and reproductive cycles (Ronsi­ CUBA valli, 1978; Burgess, 1984). In addition, such behavior is modified by the age 81· 80· 79· 77" structure of the population. Younger Figure I.-Location of sarnping area (shaded), including designated (smaller) sharks of some species exhibit "inshore" and "offshore" areas. behavioral separation in space and time from older (larger) members of the popu­ lation (Lineaweaver and Backus, 1970; Casey, 1976). The same has been noted tween lat. 24°30' and 28°00' N (Fig. 1). long. Effort was expressed as total num­ between males and females of some spe­ Standard Florida-style swordfish long­ ber of hooks set. Number of hooks bitten cies (Ronsivalli, 1978; MAFMC, 1980). line gear and methods were used, as de­ off, species composition of the catch, Due to these behavioral characteristics, scribed in Berkeley et al. (1981). Most number of swordfish, number of sharks the wide and incompletely understood sets were made from the Doc's Out /II , a and their location on the line, the condi­ distribution of many species, and the lim­ small commercial swordfish longliner, tion of the fish (dead or alive), and the ited amount of quantititative sampling which fished 9 miles of mainline and 90­ geographical coordinates of the longline that has been conducted, there is a 120 hooks per set. Other vessels in the were also recorded at sea. paucity of data critical for assessing the fleet set up to 25 miles of mainline and Generally, all sharks were retained ex­ state of shark populations. over 300 hooks. Sets were begun around cept hammerheads, whose meat had no In this paper, which is based on the sunset and the gear was allowed to soak market value and which were cut free if results of a 2-year study, we present until shortly before sunrise, when alive. All sharks retained were kept baseline information on catch rates and haulback began. was generally whole until returning to port, where they relative abundance, and some notes on used as bait, although white , were identified, weighed to the nearest the biology of common species within the Mugil curema, was used occasionally. A pound, measured (snout-fork length in context of examining the fishery poten­ chemical light stick (Cyalume2) was at­ cm), and sexed. Stomach contents were tial of the shark resource along Florida's tached to the leader 3-5 feet above each recorded and preserved, females were east coast. hook. Leaders were single strand, 250­ examined for reproductive activity (pres­ pound test monofilament, 80-120 feet ence of embryos), and vertebrae were Methods taken for future ageing studies. Live Between September 1981 and Septem­ hammerheads were identified, sexed, 2Mention of trade names or cornmerical fmns ber 1983, a total of III longline sets were does not imply endorsement by the National their lengths estimated, and cut free. mad~ off the east coast of Florida be­ Marine Fisheries Service, NOAA. Aboard vessels other than the Doc's Out

/0 Marine Fisheries Review Table 1.-Results of t-testa comparing mean CPUE of Table 3.-Number of seta, hooks, hooks lost, and mean large fish may break a worn leader occa­ swordfish and sharks ~n Inshore and offshore CPUE of swordfish and sharks by month, September areas from February through April 1982. 1981 to September 1983. sionally, most missing hooks are be­ Mean Mean Mean CPUE Mean no. lieved to have been bitten off. Based on Number Number CPUE for CPUE for Year No. No. of hooks the composition of species retained by Area of sets of hooks1 swordfishz sharksz and of of Iost/100 month sets hooks Swordfish Sharks hooks set the gear, there are few fish other than Inshore 8 990 2.61 6.31 Year 1 sharks which would appear capable of Offshore 6 681 2.46 3.77 Sept. '81 3 365 7.94 5.66 3.18 routinely severing 250-pound test Oct. 7 836 5.48 7.80 7.44 Is = 0.14 Is ~ 0.93 Nov. 4 404 5.36 2.63 5.04 monofilament. Thus, we recorded the Dec. 6 709 2.38 3.83 4.58 number of missing hooks because we be­ df = 12 df~ 12 Jan. '82 5 593 2.63 3.32 4.96 Feb. 3 387 1.04 6.96 7.75 lieve that this reflects primarily escaped P>0.40 0.25> P>0.1 0 Mar. 4 512 2.16 5.38 4.43 sharks. Apr. 7 887 3.21 4.37 6.05 10nly those hooks on monofilament leaders May 5 625 3.84 3.83 8.61 ZStandardized catches on monofilament leaders. (Arcsine June} 6 700 2.53 2.37 4.36 Results transformation did not change results). July Data unavailable Aug. Catch Rates Subtotal 50 6,018 3.66 4.70 5.75 Both inshore and offshore areas were Year 2 Sept. 7 758 12.38 6.94 12.00 fished from February through April Oct. 8 1,321 3.28 5.61 3.98 Table 2.-Results Of t-teats comparing mean CPUE of 1982. The mean CPUE of sharks was 2.4 Nov. 4 786 6.41 5.93 7.11 swordfish and sharks between stainless steel and Dec. 3 490 4.84 2.02 2.03 times higher in the inshore area, but the monofilament leaders used In sets from september Jan. '83 3 547 1.76 2.56 2.02 1981 to March 1982 (tests performed on arcslne-trans­ difference was not statistically significant Feb. 5 849 2.73 3.55 3.10 formed data). Mar. 3 443 0.71 3.84 1.78 (t-test, 0.25 > P > 0.10) (Table 1). Number of Mean Mean Apr. 14 2,068 3.10 2.74 3.92 Swordfish catch rates were almost identi­ Type of leaders CPUE for CPUE for May 6 799 0.96 1.36 5.80 leader in 13 sets swordfish sharks June 2 202 0.86 2.28 1.14 cal between the two areas (t-test, July Data unavailable Steel 338 2.40 4.66 P > 0.40). In both inshore and offshore Subtotal 55 8,263 3.54 3.52 4.19 Aug. '83 2 196 4.04 6.21 2.95 sets, more sharks than swordfish were Monofilament 1.2661 5.55 5.44 Sept. 4 404 5.59 4.72 5.77 caught. Is 2.50 Is ~ 0.99 = Grand total 111 14,881 3.67 4.16 4.93 Stainless steel leaders were not effec­ df = 24 df ~ 24 tive in increasing the shark catch (Table

P<0.01 0.25>P>0.10 2). Despite the fact that many sharks es­ caped by biting through the monofila­ 1Mean proportion of steal leaders in 13 sets ~ 21.1 percent. ment leaders, as suggested by the number of missing hooks (Table 3), the steel leaders caught fewer sharks, although the difference was not significant (0.25 > P > 0.10) (Table 2). In addi­ Ill, only species, sex, and estimated 200-fathom contour on the eastern side of tion, there was no apparent difference in length could be recorded as most sharks the Florida Straits (Fig. I). Catch rates the size or species composition of sharks were cut off at the boat. between these two areas were compared. caught on steel leaders compared with To standardize effort, catches were ex­ The fishery presently uses monofila­ monofilament. However, the catch rate pressed as number of sharks per 100 ment leaders, which allow most large for swordfish on steel leaders was signif­ hooks (CPUE). Most set records in­ sharks to escape by biting through them. icantly less than for monofilament cluded information on whole weights We hypothesized that those sharks that (P < 0.01). Steel leaders were only 43 and, when possible, dressed weight escaped would be larger and of different percent as effective in catching swordfish (headed, eviscerated, and removed) species composition than those retained. and 86 percent as effective in catching of individual specimens. If not, weights In an attempt to test this hypothesis and sharks as were monofilament leaders. were approximated using available determine if we could retain a higher per­ Because of this, steel leaders were no length-weight conversions (MAFMC, centage of sharks, 20-25 percent of the longer used after March 1982. 1980) or using the monthly mean weight leaders were replaced with stainless A total of 613 sharks and 523 sword­ of the particular species if lengths had not steel, multi-stranded cable (500-pound fish weighing 70,677 and 35,547 been recorded. test). Statistical comparisons were per­ pounds, respectively, were recorded in During the initial phase of the study, formed on catch rates between the two III longline sets fished off the southeast sets were made in both "inshore" and leader types. Florida coast during the study. Complete "offshore" areas. The inshore area is de­ Monofilament leaders are used in the hook information was recorded for 102 fined as the area from the 100-fathom longline fishery because they increase the sets. Total number of hooks in the 102 contour off the Florida mainland out 15 swordfish catch (Berkeley et aI., 1981). sets was 13,799. The monthly mean miles, while the offshore area extends However, hooks are often missing when shark CPUE ranged from 1.36 (May eastward from there to approximately the the longline is retrieved. Although any 1983) to 7.80 (October 1981), compared

50(I), 1988 II Table 4.-Number of individuals of each shark species recorded In each month from September 1981 to September 1983. Year 1 Year 2 Percent 1981 1982 1983 of Species grand Species S 0 N 0 J F M A M J J A S 0 N 0 J F M A M J J A S total tolal Bigeye thresher 2 1 1 1 2 10 1.6 Bignose 4 2 2 5 2 1 1 17 2.8 Silky 7 10 8 12 12 4 4 8 3 4 22 11 5 2 1 10 7 15 4 9 9 167 27.2 Bull 1 1 2 0.3 Oceanic whilelip 1 2 2 3 2 13 2.1 Dusky 3 1 1 7 1.1 Sandbar 1 1 0.2 Nighl 10 40 5 4 7 3 21 6 17 23 2 3 3 6 3 2 5 160 26.1 Tiger 1 1 1 3 1 1 1 9 1.5 Longfin mako 1 2 0.3 Blue 3 3 3 9 1.5 8ca1. hammerhead 2 5 2 10 18 9 16 11 16 36 5 6 11 5 34 3 199 32.5 Greal hammerhead 2 1 4 0.7 Unident. sharks 2 3 3 13 2.1 Monlhlyand grand lotal 21 65 11 24 20 26 28 36 24 26 50 56 47 10 14 32 13 62 11 8 12 17 613 100.0

13 ing the same trend, CPUE increased in August and September 1983. Although 11 mean CPUE for the first year (4.70) was higher than for the second year (3.52), 9 the differences were not significant (t­ w test, 0.20> P > 0.10). Likewise, ~ 7 , CPUE for swordfish was not statistically U different between years (P > 0.40), al­ 5 ~ though a slight decrease was seen, from 3.66 in year I to 3.54 in year 2. Seasonal 3 trends in swordfish CPUE were also con­ sistent for both years with highest values (in numbers) in the late summer and fall months. While catches of both sharks and SON D J F M A M J J A SON D J F M A M J J A S swordfish declined the second year, their 82 83 '------year 1 year 2 ----' relative proportions remained fairly con­ stant. Shark catch rates represented 56 Figure 2.-Monthly mean number of sharks (dots) and swordfish (circles) and 50 percent of the overall yearly mean caught per 100 hooks from September 1981 to September 1983. total catch rate in the first and second years, respectively (Table 3). Species Composition and Relative Abundance with a range for swordfish of 0.86 (June not significantly different among months 1983) to 12.38 (September 1982) (Table (ANOYA, P > 0.50), the same patterns Of the 13 species of shark recorded 3). Sharks constituted 53 percent by were seen in both years. Data for July and during the study, night, silky, and scal­ number of the recorded total catch (ex­ August 1982 and July 1983 were unavail­ loped hammerhead sharks collectively cluding other incidental ) and had able and therefore do not necessarily rep­ represented 86 percent of the total shark an overall mean CPUE of 4.16. Sixty-six resent low abundances or low effort. catch in numbers (Table 4). Although the percent (n=592) of the sharks brought Year 1 (September 1981 through June catch of both scalloped hammerhead and alongside were dead. 1982) showed high CPUE's in Septem­ silky sharks exceeded the catch of night Sharks were most abundant during late ber and October 1981 and February and sharks (Table 4), night sharks had the summer and fall (September-November), March 1982, while year 2 (September highest overall mean CPUE, 1.21 (Table with a secondary peak during late winter 1982 through June 1983) showed high 5). This species represented >50 percent and early spring (February and March) CPUE's in September to November 1982 of the monthly CPUE in October and (Fig. 2). Although mean CPUE's were and February and March 1983. Follow­ April of the first year and in May of the

12 Marine Fisheries Review Table 5.-Monthly mean CPUE for the six most abundant species of shark and their percent of the monthly CPUE (In parantheses) for all sharks from September 1981 to September 1983.

1981 1982 Year Species Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June 1

Bigeye thresher 0.25 0.23 0.26 0.07 (4.4) (3.0) (3.7) (1.5) Bignose 0.64 0.61 0.11 (16.7) (25.7) (2.3) Silky 1.86 1.19 1.92 1.03 1.96 1.04 0.76 1.02 0.48 0.33 1.16 (32.9) (15.3) (73.0) (26.9) (59.0) (14.9) (14.1) (23.3) (12.5) (13.9) (24.7) Oceanic whitetip 0.13 0.30 0.20 0.61 0.11 (1.7) (7.8) (3.7) (25.7) (2.3) Night 2.77 4.83 0.87 0.68 1.80 0.58 2.33 0.96 1.69 (48.9) (61.9) (22.7) (20.5) (25.9) (10.8) (53.3) (25.1) (36.0) Seal. hammerhead 0.49 0.59 0.35 0.17 2.83 3.66 0.69 1.44 0.33 0.95 (8.7) (7.6) (9.1) (5.1) (40.7) (68.0) (15.8) (37.6) (13.9) (20.2) All sharl

Table 5.-Contlnued.

1982 1983 1983 Year Species Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May Jun. 2 Aug. Sep. Overall

Bigeye thresher 0.09 0.07 0.57 0.05 0.06 (1.6) (2.6) (25.0