Coupling ecology and economy: modeling optimal release scenarios for summer flounder (Paralichthys dentatus) stock enhancement

Increasing interest in the use of stock enhancement as a management tool necessitates a better understanding of the relative costs and benefits of alternative release strategies. We present a relatively simple model coupling ecology and economic costs to make inferences about optimal release scenarios for summer flounder (Paralichthys dentatus), a subject of stock enhancement interest in North Carolina. The model, parameterized from mark-recapture experiments, predicts optimal release scenarios from both survival and economic standpoints for varyious dates-of-release, sizes-at-release, and numbers of fish released. Although most stock enhancement efforts involve the release of relatively small fish, the model suggests that optimal results (maximum survival and minimum costs) will be obtained when relatively large fish (75–80 mm total length) are released early in the nursery season (April). We investigated the sensitivity of model predictions to violations of the assumption of density-independent mortality by including density-mortality relationships based on weak and strong type-2 and type-3 predator functional responses (resulting in depensatory mortality at elevated densities). Depending on postrelease density, density-mortality relationships included in the model considerably affect predicted postrelease survival and economic costs associated with enhancement efforts, but do not alter the release scenario (i.e. combination of release variables) that produces optimal results. Predicted (from model output) declines in flounder over time most closely match declines observed in replicate field sites when mortality in the model is density-independent or governed by a weak type-3 functional response. The model provides an example of a relatively easy-to-develop predictive tool with which to make inferences about the ecological and economic potential of stock enhancement of summer flounder and provides a template for model creation for additional species that are subjects of stock enhancement interest, but for which limited empirical data exist

Review of size- and age-dependence in batch spawning : implications for stock assessment of fish species exhibiting indeterminate fecundity

Most assessments of fish stocks use some measure of the reproductive potential of a population, such as spawning biomass. However, the correlation between spawning biomass and reproductive potential is not always strong, and it likely is weakest in the tropics and subtropics, where species tend to exhibit indeterminate fecundity and release eggs in batches over a protracted spawning season. In such cases, computing annual reproductive output requires estimates of batch fecundity and the annual number of batches—the latter subject to spawning frequency and duration of spawning season. Batch fecundity is commonly measured by age (or size), but these other variables are not. Without the relevant data, the annual number of batches is assumed to be invariant across age. We reviewed the literature and found that this default assumption lacks empirical support because both spawning duration and spawning frequency generally increase with age or size. We demonstrate effects of this assumption on measures of reproductive value and spawning potential ratio, a metric commonly used to gauge stock status. Model applications showed substantial sensitivity to age dependence in the annual number of batches. If the annual number of batches increases with age but is incorrectly assumed to be constant, stock assessment models would tend to overestimate the biological reference points used for setting harvest rates. This study underscores the need to better understand the age or size-dependent contrast in the annual number of batches, and we conclude that, for species without evidence to support invariance, the default assumption should be replaced with one that accounts for age- or size-dependence

The State of Coral Reef Ecosystems of Southeast Florida

The northern extension of the Florida reef tract and a complex of limestone ridges run parallel to the subtropical Atlantic coastline of southeast Florida. Spanning 170 km from the northern border of Biscayne National Park (BNP) in Miami-Dade County to the St. Lucie Inlet in Martin County, the reefs and hardbottom areas in this region support a rich and diverse biological community (Figure 5.1). Nearshore reef habitats in southeast Florida include hardbottom areas, patch reefs and worm reefs (Phragmatopoma spp.) exhibiting abundant octocoral, macroalgae, stony coral and sponge assemblages. Offshore, coral reef associated biotic assemblages occur on linear Holocene Acropora palmata mid-shelf and shelf margin reefs that extend from Miami Dade County to Palm Beach County (Lighty, 1977; Figure 5.2). Anastasia Formation limestone ridges and terraces colonized by reef biota characterize the reefs from Palm Beach County to Martin County (Cooke and Mossom, 1929). The coastal region of southeast Florida is highly developed, containing one third of Florida’s population of 16 million people (U.S. Census Bureau, 2006). Many southeast Florida reefs are located just 1.5 km from this urbanized shoreline. Despite their unique position as the highest latitude reefs along the western Atlantic seaboard, the reefs of southeast Florida have only recently received limited scientific and resource management attention. Andrews et al. (2005) discussed the reefs of southeast Florida and the critical need to implement actions that fill resource knowledge gaps and address conservation and threats to reef health. This report further examines and updates the list of stressors imperiling the health of southeast Florida’s reefs, and presents information gained from new research, monitoring and management efforts to determine the extent and condition of reef resources in this distinctive region

Cross-Shelf Exchange Associated With the Gulf Stream in the South Atlantic Bight: Direct Observations Using an Autonomous Underwater Glider

An autonomous underwater glider was deployed in March 2014 to sample the Gulf Stream and its adjacent shelf waters in the South Atlantic Bight, providing a new look at cross-shelf exchange associated with Gulf Stream dynamics. Observations collected over 4 weeks reveal significant cross-shelf exchange (up to 0.5 Sv) at the shoreward edge of the Gulf Stream, which was 2 orders of magnitude larger than estimates from long-term mean hydrographic conditions. Gulf Stream frontal eddies may have contributed to some of the largest fluxes of heat (0.5°C Sv) and salt (0.03 Sv g/kg) onto the shelf. We estimate that the largest upwelling event during the mission could have brought nitrate concentrations over 20 μM to within 125 m of the surface. This study demonstrates clear capabilities of autonomous underwater gliders for sampling in and near fast moving boundary currents to obtain unique and critical in situ observations effectively

Potential Sources of Red Snapper (\u3ci\u3eLutjanus campechanus\u3c/i\u3e) Recruits Estimated With Markov Chain Monte Carlo Analysis of Otolith Chemical Signatures

Otolith chemical signatures were used to estimate the number of likely nursery sources that contributed recruits to a suite of red snapper (Lutjanus campechanus) year-classes sampled in 2012 in US Atlantic Ocean waters from southern Florida (28°N) to North Carolina (34°N). Otoliths from subadult and adult fish (n = 139; ages 2–5 years) were cored and their chemical constituents analysed for δ13C, δ18O, as well as the elemental ratios of Ba : Ca, Mg : Ca, Mn : Ca and Sr : Ca. Results from multiple linear regression analyses indicated that there was significant latitudinal variation for δ13C, Ba : Ca, Mg : Ca and Mn : Ca. Therefore, these variables were used to parameterise Markov Chain Monte Carlo (MCMC) models computed to estimate the most likely number of nursery sources to each age class. Results from MCMC models indicated that between two and seven nursery sources were equally plausible among the four age classes examined, but the likely number of nursery sources declined for fish aged 4 and 5 years because of apparent mixing between more northern and more southern signatures. Overall, there is evidence to reject the null hypothesis that a single nursery source contributed recruits among the age classes examined, but increased sample size from a broader geographic range may be required to refine estimates of the likely number of nursery sources

A Perspective on the Biology of Florida Keys Coral Reefs

South Florida is a unique enclave of the Caribbean thanks to the nexus of geography and environmental factors. Tropical mangrove, sea grass, coral reef epifaunal and infaunal sedimentary communities are common from Stuart on the east coast to Tampa Bay on the west coast. Florida is the only state in the continental United States to have such an ecosystem in its coastal waters. Climate and hydrodynamic features support a variety of plants and animals. The Florida Keys are the most Caribbeanlike region in Florida. These “islands in the sun” have attracted millions of visitors and residents; some of the more famous include: George Meade (Union General in the Civil War ), James Audubon (artist), President Harry Truman (built the Little White House in Key West ), Humphrey Bogart and Lauren Bacall (who made the movie Key Largo in Key Largo), Ted Williams (baseball player and avid fisherman), Tennessee Williams (playwright), Ernest Hemingway (writer), and Jimmy Johnson (football coach). Many respected scientists worked their crafts in the coral reefs of the Florida Keys including Louis and Alexander Agassiz, Louis Pourtalès, Alfred G. Mayer, Thomas W. Vaughan, William Longley, Reginald Daly, Lawrence Cary, Walter Stark, Robert Ginsburg, and Eugene Shinn. A significant portion of the foundation of coral reef science is the result of research conducted in the Florida Keys. The first underwater photographs (some in color) of coral reef fish were taken in the Keys. The first coral reef underwater park (John Pennekamp) and marine protected area (Dry Tortugas ) were created in the Keys