Towards an ecosystem approach for non-target reef fishes: Habitat uses and population dynamics of South Florida parrotfishes (Perciformes: Scaridae)

of a dissertation at the University of Miami. Dissertation supervised by Professor Jerald S. Ault. No. of pages in text. (299) In the context of the precautionary approach to the sustainable use of coastal marine resources in tropical reefs, it is necessary to identify those species vulnerable to exploitation before their populations are seriously affected. The goal of this research was to develop statistically robust ecosystem-based approaches, while optimizing data acquisition on relatively unexploited fish species in South Florida reefs, i.e., parrotfishes, Family Scaridae, in Biscayne Bay (an onshore coastal bay surveyed by seasonal roller frame beam trawl surveys, 1996-2000) and Florida Keys (a coral reef tract sampled with annual Reef Fish Visual Censuses, RVC, 1997-2001), by following these steps: (I) analysis of information gaps for the stocks (or taxon) under consideration, including systematics, biogeography, population dynamics, reproductive ecology, trophodynamics, habitat use, and fisheries landings and fleet dynamics of Western Atlantic parrotfishes (Chapter 1); (II) determination of four primary research objectives from prioritization of information gap analyses of Step I: essential fish habitat, population dynamics parameter estimations, effects of exploitation, habitat protection and fisheries management on South Florida scarids, and fisheries ecology contributions to sampling and management of reef fishes with commercial potential; (III) determination of essential fish habitats, including ontogenetic shifts, migrations, and connections between reefs and adjacent habitats subject to fisheries (Chapter 2), from integration of stratified sampling design for fisheries-independent surveys, habitat selection theory-based analyses, and length-based analyses; (IV) estimation of population dynamics and fisheries-specific parameters encompassing life history demographics from empirical data or comparisons to theoretical expectations adapted to local conditions (Chapter 3); (V) simulation modeling of a realistic range of fishing scenarios and demographic characteristics using Reef Ecosystem Exploited Fisheries Simulator (REEFS) and size-based mortality estimation (LBAR) algorithms to evaluate the efficacy of potential traditional fisheries and spatial management strategies (Chapter 4); and (VI) application of sampling optimization procedures and fisheries ecology approaches. Nicholsina usta, Sparisoma chrysopterum, and Sparisoma radians were the top three most abundant and frequent parrotfishes in the Biscayne Bay collections. Scarus iseri, Sparisoma aurofrenatum, Sp. viride, and Sp. chrysopterum were the top four scarids in the Florida Keys RVC dataset, with an estimated combined abundance of ~36.8 x 10 individuals in this domain alone. Connectivity among seagrass beds, coral reefs and deep waters had three major patterns: (1) seagrass dwellers, using near shore substrates in the bay, absent in the reef, with a plausible deep-water connection (N. usta); (2) reef dwellers, with inshore-to-offshore ontogenetic patterns in the Florida Keys, ranging from well defined (e.g., Sc. iseri and Sp. aurofrenatum) to weak (Sp. viride) cross-shelf shifts; and (3) a seagrass-reef connection, using Biscayne Bay as an important recruitment ground (Sp. chrysopterum), in which a portion of its population may migrate through Safety Valve onto adjacent reefs, soon after the caudal fin becomes concave (≥12 cm TL, ~ six months of age). Marine protected areas of the Florida Keys National Marine Sanctuary did not show effects on abundance, size composition or spatial distribution of any parrotfish studied. Simulated von Bertalanffy growth curves and observed life stage characteristics indicated that parrotfishes generally exhibit isometric growth, with extensive size overlaps among color phases and no ontogenetic changes in weight-tolength relationships. Two fisheries-oriented algorithms, REEFS and LBAR, suggested relatively short longevities (5 ≤ tλ ≤ 10 years), moderate body growth curvature (0.3 ≤ K ≤ 0.7 y); high instantaneous natural mortality rates (0.3 ≤ M ≤ 0.6 y), and low annual survival rates (54% ≤ A ≤ 27%). Simulated estimates of fishing mortalities (F) ranged from 0.3 (Sp. viride) to 0.6 y (Sp. chrysopterum), indicating low levels of exploitation, but low Spawning Potential Ratios (SPR = 23.5-26%). Proposed potential exploitation based on a legal minimum size equal to their size at first maturity and fishing rates equal or below to their natural mortality should secure SPR values at 45-48%.