Christopher C. Koenig

Reproductive styles of shallow-water groupers (Pisces: Serranidae) in the eastern Gulf of Mexico and the consequences of fishing spawning aggregations

SynopsisSeasonal and spatial aspects of spawning for three commercially important grouper species in the northeastern Gulf of Mexico are detailed. These species — all of which are protogynous hermaphrodites - spawn in deep water (> 25 m for red grouper,> 40 m for gag and scamp), making it difficult to observe spawning behaviors without ROV or submersible support. They respond to intense fishing pressure in ways that are directly related to their respective reproductive styles. Species that aggregate appear to be more susceptible to such pressures than those that do not, as evidenced by marked skewing of sex ratios in favor of females. Gag, Mycteroperca microlepis, have suffered a drop in the proportion of males from 17% to 1% in the last 20 years; scamp, Mycteroperca phenax, have dropped from 36% to 18%; and red grouper, Epinephelus morio, which do not aggregate, have shown little change in the sex ratio over the past 25–30 years.

Stock Identification of Gag, Mycteroperca microlepis, Along the Southeast Coast of the United States

Abstract: The gag grouper Mycteroperca microlepis is an important component of commercial and recreational fisheries along the South Atlantic coast of the United States and in the Gulf of Mexico. Over the past two decades, this species has experienced significant declines in abundance and an increasing skew in sex ratios. Analysis of microsatellite DNA variation in this species shows mosaic patterns of population subdivision and significant departures from Hardy-Weinberg equilibrium in all sampling locations. Given the length of the pelagic stage (egg and larvae), the prevailing current patterns, and the migratory capabilities of the adults, it is unlikely that these observations are the result of restricted gene flow among genetically differentiated populations. The apparent structure of gag populations most likely reflects inbreeding in size-limited populations. Population declines, skewed sex ratios, and perhaps variance in female fecundity appear to have acted in concert to limited the number of individuals that contribute to a given year class. These data are reinforced by studies of other fish stocks that have experienced precipitous declines over the past two decades.

Models To Compare Management Options For A Protogynous Fish

Populations of gag (Mycteroperca microlepis), a hermaphroditic grouper, have experienced a dramatic shift in sex ratio over the past 25 years due to a decline in older age classes. The highly female-skewed sex ratio can be predicted as a consequence of increased fishing mortality that truncates the age distribution, and raises some concern about the overall fitness of the population. Management efforts may need to be directed toward maintenance of sex ratio as well as stock size, with evaluations of recruitment based on sex ratio or male stock size in addition to the traditional female-based stock-recruitment relationship. We used two stochastic, age-structured models to heuristically compare the effects of reducing fishing mortality on different life history stages and the relative impact of reductions in fertilization rates that may occur with highly skewed sex ratios. Our response variables included population size, sex ratio, lost egg fertility, and female spawning stock biomass. Population growth rates were highest for scenarios that reduced mortality for female gag (nearshore closure), while improved sex ratios were obtained most quickly with spawning reserves. The effect of reduced fertility through sex ratio bias was generally low but depended on the management scenario employed. Our results demonstrate the utility of evaluation of fishery management scenarios through model analysis and simulation, the synergistic interaction of life history and response to changes in mortality rates, and the importance of defining management goals.

Absolute Abundance and Survival of Juvenile Gags in Sea Grass Beds of the Northeastern Gulf of Mexico

Abstract The absolute number of individuals and survival of juvenile gags Mycteroperca microlepis in a 15.4-km2 shallow sea grass meadow in St. George Sound, Florida, were estimated by the Jolly–Seber mark–recapture method. Abundance was estimated within three sampling stations (150 m × 150 m) by means of standard (150 m, 1.8 km/h) tows with a 5-m otter trawl. The average densities (95% confidence limits), based on three stations sampled every 1–2 weeks from June to mid-September 1991, were 496 (251–744), 424 (210–670), and 549 (165–1,773) juveniles/ha. Trawl capture efficiencies and the effects of sea grass habitat conditions and size of juvenile gags were estimated so that absolute numbers could be determined outside the sampling stations. We estimated absolute abundance outside the sampling stations by trawling and dividing gag captures per standard tow by trawl capture efficiency estimates. The estimated absolute abundance of juvenile gags for the entire 15.4-km2 area was 943,615. Survival of juvenile...

A Review of Gulf of Mexico Marine Protected Areas

Abstract Commercial and recreational fishers in the Gulf of Mexico routinely express in public testimony their concern over the number of fishery regulations in general, and the prospect of having closed areas that affect their opportunities to fish. Of the 16 closed areas, or marine protected areas, in the Gulf that restrict shrimp and reef-fish fishing, most have not provided anticipated protection for exploited species. The unintended consequences in several cases affect other fisheries or endangered species by shifting fishing effort and thus increasing the vulnerability of additional populations. Three areas are so new that few data are available to demonstrate their effectiveness, although preliminary data are promising. The main problems hindering the effectiveness of Gulf closed areas are ill-conceived development, lack of performance monitoring, and inadequate enforcement. We suggest that well-designed Gulf closed areas be created to address fishing gear impacts on habitat, provide an area free o...

Otolith-fish size relationship in juvenile gag (Mycteroperca microlepis) of the eastern Gulf of Mexico: a comparison of growth rates between laboratory and field populations

Abstract In this study, we conducted experiments on wild-caught juvenile gag Mycteroperca microlepis from the eastern Gulf of Mexico to evaluate the effect of food availability on somatic growth and otolith growth. Juveniles were fed at two different food levels until all fish attained similar sizes. We found that food availability significantly affected growth rates. However, we also found that this manifested itself in differential otolith size. That is, slower-growing gag had larger, heavier otoliths than equal-sized faster-growing gag; an experimental result that has been observed previously among various fish species. We wanted to apply these experimental results to field-caught gag because our initial observations indicated that gag from more southern latitudes along Florida’s west coast were larger than gag from more northern latitudes, at least during the early juvenile period. Applying these relationships to regional field populations, we found that juvenile gag from the more northern latitudes appeared to grow faster than those from southern latitudes, using an otolith–fish size proxy for growth. However, examination of fish length–age relationships revealed that juvenile gag growth rates were not significantly different between regions. These results are contrary to the expectation that larger-sized gag from southern latitudes are growing faster, and suggests that other factors, such as spawning time and habitat quality may explain regional size differences.

Mapping, habitat characterization, and fish surveys of the deep-water Oculina coral reef Marine Protected Area: a review of historical and current research

Deep-water Oculina coral reefs, which are similar in structure and development to deep-water Lophelia reefs, stretch 167 km (90 nm) at depths of 60–100 m along the eastern Florida shelf of the United States. These consist of numerous pinnacles and ridges, 3–35 m in height, that are capped with thickets of living and dead coral, Oculina varicosa. Extensive areas of dead Oculina rubble are due in part to human impacts (e.g., fish and shrimp trawling, scallop dredging, anchoring, bottom longlines, and depth charges) but also may be due in part to natural processes such as bioerosion, disease, or global warming. In the 1970s, the reefs were teeming with fish. By the early 1990s, both commercial and recreational fisheries had taken a toll on the reefs, especially on the coral habitat and populations of grouper and snapper. In 1984, 315 km2 (92 nm2) was designated the Oculina Habitat of Particular Concern (OHAPC), prohibiting trawling, dredging, bottom longlines and anchoring, and establishing the first deep-sea coral marine protected area in the world. In 2000, the Oculina Marine Protected Area (MPA) was expanded to 1029 km2 (300 nm2). Despite these protective measures, manned submersible and ROV observations in the Oculina MPA between 1995 and 2003 suggest that portions of the coral habitat have been reduced to rubble since the 1970s, grouper spawning aggregations may be absent, and illegal trawling continues. This paper is a review of the results of the mapping, habitat characterization, and fish surveys from the early historical studies (1960–1980s) to the more recent surveys (1995–2003).

Benthic Habitat Modification through Excavation by Red Grouper, Epinephelus morio, in the Northeastern Gulf of Mexico

Red grouper (Epinephelus morio) is an economically important species in the reef fish community of the south- eastern United States, and especially the Gulf of Mexico. It is relatively common in karst regions of the Gulf and is asso- ciated with low-relief rocky features devoid of overlying sediments. Working both inshore in Florida Bay, Florida (U.S.A.), and offshore in the Gulf of Mexico shelf-edge fishery reserves, Madison Swanson and Steamboat Lumps, we characterized red-grouper habitat and the associated faunal assemblages and demonstrated through a series of experiments that red grouper expose rocky habitat by excavating with their mouths and fanning with their fins to clear away surficial sediment, thereby providing habitat for themselves as well as other reef-dwelling organisms. They also maintain this habi- tat by periodically clearing away sediment and debris. Such maintenance provides a clean rocky substrate for the attach- ment of sessile invertebrates, thereby modifying habitat features to provide refuge for many other species of fish and mo- tile invertebrates. We demonstrated increased biodiversity and abundance associated with habitat structured by red grou- per, and we speculate here as to its fishery importance as habitat for other economically important species such as spiny lobster (Panulirus argus) and vermilion snapper (Rhomboplites aurorubens).

Groupers on the Edge: Shelf Edge Spawning Habitat in and Around Marine Reserves of the Northeastern Gulf of Mexico

The northeastern Gulf of Mexico contains some of the most diverse and productive marine habitat in the United States. Much of this habitat, located on the shelf edge in depths of 50 to 120 m, supports spawning for many economically important species, including groupers. Here, we couple acoustic surveys with georeferenced videography to describe the primary spatial and geologic features of spawning aggregation sites for four economically important species: gag (Mycteroperca microlepis), scamp (M. phenax), red grouper (Epinephelus morio), and red snapper (Lutjanus campechanus), with notes on fish distribution and abundance and spawning activities. We provide information on movement patterns of reef fish determined using acoustic telemetry. Finally, we discuss the possible coupling of geomorphology with hydrographic features to influence the overall productivity of the region and the importance of spatial fishery management in sustaining that productivity.

Energy allocation in juveniles of a warm-temperate reef fish

During the first year of life, organisms are faced with competing demands for energy between growth and storage. Most research on energy allocation in young fishes has focused on cold-temperate species which are subjected to strong seasonal fluctuations in productivity, while few studies have considered those at lower latitudes where seasonality is less pronounced. Gag (Mycteroperca microlepis) of the northeastern Gulf of Mexico settle in coastal seagrass beds in the spring as juveniles and emigrate to offshore reefs in the fall. Upon settlement, these young fish grow at remarkably fast rates, but their growth slows considerably before emigration. Slowed growth can be explained by one of three hypotheses: (1) size-specific emigration times; (2) reduced feeding efficiency associated with declines in primary and secondary productivity; or (3) energetic shifts in allocation from growth to storage. Gag emigrate essentially as a cohort, so slowed growth does not result from differential emigration patterns based on fish size. They also emigrate before seasonal declines in primary and secondary productivity; thus, food remains abundant and feeding efficiency constant. The more plausible hypothesis is that there is an energetic shift from growth to storage. The liver serves as the primary site of lipid storage and the hepatosomatic index of juvenile gag increases coincident with reduced growth. The overall effect of increased energy stores is presumably for use during offshore migration and/or for overwinter survival.