Dependence of recruitment on parent stock of the spiny lobster, Panulirus argus, in Florida

ABSTRACTDespite management practices to achieve sustainabil-ity, commercial landings for Florida spiny lobster(Panulirus argus) have experienced a drastic decline(57%) since 2000. This is cause for concern not onlyfor economic reasons, but for issues of sustainability.An annual index of P. argus post-larval (puerulus)abundance, estimated with a generalized linear modelwith signiﬁcant mean sea-level effects, shows a 36%decrease in annual puerulus supply since 1988. Inaddition, local Florida spawning stock biomass esti-mated from an age-structured sequential populationanalysis decreased 57% since 1988. Puerulus abun-dance follows a highly correlated (R = 0.76) trendwith a 12-month delayed spawning stock abundance,which supports the contention that the Floridaspawning population is a signiﬁcant contributing fac-tor to post-larval recruitment in Florida. Residualsabout the puerulus on spawning stock abundancefunction follow closely an interannual North AtlanticOscillation Index signal. This residual effect is thoughtof as a secondary regional population effect on Floridapuerulus recruitment. The Florida spiny lobster stock isexploited with no ﬁshing mortality controls due to thePan Caribbean recruitment concept adopted in Floridaspiny lobster management. Therefore, the potential ofrecruitment overﬁshing exists if ﬁshing mortalitycontrols to protect local spawning stock abundance,such as catch quotas, are not introduced.Key words: ﬁsheries management, Florida Keys, meansea level, puerulus, recruitment, spiny lobsterINTRODUCTIONThe Caribbean spiny lobster, Panulirus argus, is foundthroughout subtropical areas in the Central WesternAtlantic Ocean from Bermuda to Brazil. It is moreabundant in the Western Caribbean Sea, includingFlorida and The Bahamas, and also in Brazil. Wide-spread distribution of the species is largely attributedto the dispersal of their long-lived pelagic larvae byocean currents. In Florida, spiny lobster commerciallandings have long been identiﬁed with recruitmentvariability (Powers and Bannerot, 1984; Ehrhardt,2005). Of signiﬁcant concern to ﬁshers and managersis the conspicuous decrease in landings (57%) ob-served in the Florida ﬁshery since the early 21st cen-tury. Such drastic decreases have occurred in spite ofstiff conservation measures historically implementedin the ﬁshery (e.g., 50% trap reduction; 76 mm cara-pace length to protect immature individuals; 4-monthclosed season to control mortality during peakspawning).Signiﬁcant recruitment variability is commonamong Palinurids and only a few studies demonstratethe statistical link between oceanic larval abundanceand post-larval recruitment with environmental vari-ables (Pringle, 1986; Pearce and Phillips, 1988; Phil-lips and McWilliam, 1989; Polovina and Mitchum,1992). These variables affect larval transport andsurvival of the early life stages in many (but not fullyexplained) ways. A limited number of statisticalmodels have succeeded in forecasting spiny lobsterlandings using one or more environmental variablesand larval⁄post-larval abundance indices (Cruz et al.,1993, 1995; Phillips et al., 1994). However, none ofthe above studies has linked spawning stock abun-dance and the resulting post-larval abundance; hence,the likely effects of ﬁshery exploitation on recruitmentof spiny lobster stocks are not known.The Florida spiny lobster population is fully func-tional in that intense seasonal local spawning (Ber-telsen, 1999; Bertelsen and Cox, 2001; Bertelsen andMathews, 2001) generates high larval densities (Ber-telsen et al., 2004), and the cycle from post-larval algalstages to mature stock is characterized by well deﬁnedand distinct use of juvenile and adult habitats in