FEMAR

Population Dynamics:

FEMAR uses the information compiled by the RVC surveys, fishery-dependent surveys, and numerous other sources in order to generate population dynamic information for species-of-interest. The majority of FEMAR's work is conducted from a fisheries-management perspective. FEMAR research has provided scientific evidence for declines in exploited marine fish stocks in the Florida / Florida Keys Ecosystem. In addition to dimishing species abundance, fishing also creates a regime of size-selective mortality that can be seen in the decreasing sizes of uncaughtfish. Scientists have suggested that marine protected areas (i.e. areas where fish can find refuge from fishing) may help bolster declining stocks.

There are two theories for how MPAs will boost fishery yields. The biomass-overflow hypothesis suggests that relaxation of fishing pressure within an MPA results in a higher density and average size of targeted species, and this buildup produces density-dependent emigration of adult fish across reserve boundaries; and the larval-export hypothesis suggests that larval production will be amplified by the population within the reserve due to its high spawning stock biomass, and these eggs and larvae will be transported to habitat outside the reserves (Crowder et al. 2000).

FKNMS regulations went into effect in 1997, Dry Tortugas Ecological Reserve regulations went into effect in 2001. In both cases, FEMAR played an important role in the collection and analysis of data to assist management decisions. FEMAR is currently monitoring the effectsof the SPAs (Special Protected Areas) and ERs (Ecological Reserves). Recent RVC data suggests that exploited species such as yellowtail snapper and black grouper may be found at higher densities within reserves as compared to unprotected areas and historical trends. This data also suggests that the stock as a whole may be benefiting from reserve establishment, but it may be too soon to tell. RVC data also suggests that some unexploited species such as the stoplight parrotfish may be impacted by reserves (either positively through protection of habitat or negatively through increased predator densities).

Using the relationship between animal density and habitat variables (e.g. depth, bottom type, salinity, etc.) to partition or 'stratify' the environment into geographical units of high, moderate, and low density levels can substantially improve sampling efficiency (Smith & Ault 1993, Ault et al. 1999a). A major component of FEMAR survey design involves combiningpopulation dynamic density estimates with GIS mapping of the sampling environment in order to better characterize reef fish habitat and generate continual refinements on the stratified random sampling scheme. This feedback process has allowed FEMAR to reduce sampling error over time, leading to higher confidence that trends in our data such as changes in stock abundance or recruitment represent actual dynamics.

Analysis of the RVC data has revealed many interesting trends. There appears to be a direct relationship between size-selective fishing mortality and proximity to human population centers (such as Miami, Key Largo, and Key West) for exploited species such as red grouper. Examination of trends in abundance for unexploited species may be indicators of stock stressors unrelated to fishing, such as environmental variability, habitat damage, pollution, etc. In addition, changes in abundance of unexploited species may also represent shifts in community dynamics due to changes in predator densities (down due to increased fishing effort, up due to protection within reserves). The long-term data series of the RVC also provides a useful way to track cohorts through time, because the smallest age classes (not present in fishery-dependent data) are also 'collected' by the RVC.

Some stocks appear to have been chronically overfished since the late 1970s. There are similarities in key relations within various taxa that separate out into somewhat discrete clusters when maximum size vs. maximum age is plotted. This pattern of species clusters suggests that species within the various taxa groupings will likely respond to exploitation in a similar manner. This sensitivity to exploitation is highest for groupers, followed by snappers, and then grunts. By plotting our most conservative estimates of the ratio of nominal biomass taken by the multispecies reef fishery vs. the biomass that would be taken at a level of maximum sustainable yield against the ratio of nominal fishing mortalityin the multispecies reef fishery vs. the fishing mortality that would be generated at maximum sustainable yield, we arrive at the grim conclusion that many of the Florida Keys reef fish stocks are overfished according to definitions for U.S. fisheries.

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